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1
Choi, Kwansik. « Molecular interactions in polar solvents ». Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/17851.
2
Pradhan, Rajendra. « Molecular interactions in mixtures of some industrially important solvents : a physico-chemical study ». Thesis, University of North Bengal, 2018. http://ir.nbu.ac.in/handle/123456789/2698.
3
Dirama, Taner E. « DYNAMICS OF PROTEINS IN GLASSY SOLVENTS ». University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1133800339.
4
Parikh, Bhargiv. « Design, Synthesis and Characterization of D-glucosamine Low Molecular Weight Gelators ». ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1110.
Résumé :
Low molecular weight gelators (LMWGs) have gained much attention over the last few decades, because of their ability to form supramolecular architectures as well as their many potential applications in biomedical research and as advanced materials. Most of the gelators were discovered through serendipity, and their structural requirements are somewhat ambiguous. This is due, in part, to the fact that the supramolecular gelation phenomenon is not yet fully understood, though many structural classes have been found to be excellent organogelators. Carbohydrates are abundant natural resources that are useful in preparing advanced materials. We have previously showed that monosaccharide derivatives can form effective low molecular weight gelators for both organic solvents and aqueous mixtures. In this research, we have studied the gelation capability of several glucosamine derivatives. Several series of 4,6-O-acetal protected glucosamine derivatives were synthesized and screened for their gelation properties in several solvents.
5
Gohres, John Linton III. « Spectroscopic and computational investigations of molecular interactions in gas-expanded liquids ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24692.
Résumé :
Thesis (Ph.D.)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Charles A. Eckert; Committee Co-Chair: Charles L. Liotta; Committee Member: J. Carson Meredith; Committee Member: Rigoberto Hernandez; Committee Member: William J. Koros
6
Young, Christi Lynn Patton. « Solute separabilities in solvent gas-rich liquid-liquid-vapor systems topographical and molecular consideration / ». Access abstract and link to full text, 1993. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9313535.
7
Walker, Elaine M. « Modelling the effect of growth envirnoment on the crystallisation of molecular organic compounds ». Thesis, University of Strathclyde, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360150.
8
Saeed, Akhtar. « Static and dynamic light scattering of high molecular weight polystyrene in good solvents ». Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059401322.
9
Struebing, Heiko. « Identifying optimal solvents for reactions using quantum mechanics and computer-aided molecular design ». Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9150.
Résumé :
A new iterative hybrid methodology, incorporating quantum mechanics (QM) calculations and a computationally inexpensive computer-aided molecular design (CAMD) methodology, QM-CAMD, for identification of optimal solvents for reactions is presented. The methodology has been applied to a Menschutkin reaction, where pyridine and phenacyl bromide are the reactants. The QM calculations take on the form of density functional theory calculations with a given solvent treated using continuum solvation models. The accuracy of the solvent QM calculations is assessed by computing free energies of solvation for different solvation models; the IEF-PCM, SM8 and SMD models are studied and SMD is identified as the best model. Rate constants kQM, determined from QM calculations, are calculated based on conventional transition state theory (Eyring 1935, Evans & Polanyi 1935). By using the SMD solvation model and a statistical mechanics derivation of kQM, rate constant predictions within an order of magnitude are achieved. For a small set of solvents investigated by QM, selected solvent properties are predicted using group contribution (GC) methods. 38 structural groups are considered in this approach. The QM-computed rate constants and solvent properties determined by GC are used to obtain a computationally inexpensive reaction model, based on an empirical linear free energy relationship, which is used to predict reaction rate constants. This predictive reaction model is incorporated into an optimisation-based CAMD methodology. With an objective function of maximising the reaction rate constant subject to molecular and reaction condition constraints, optimal solvent candidates are identified. By considering a design space of over 1000 solvent molecules, solvent candidates containing nitro-groups are predicted to be optimal for the Menschutkin reaction. This outcome supports experimental results for a related reaction available in the literature (Lassau & Jungers 1968). For verification purposes, Ganase et al. (2011) have measured (based on 1H NMR data and kinetic analysis) the rate constant for the reaction of interest in a number of solvents and report a significant increase in the rate constant with nitromethane as the solvent.
10
Withersby, Matthew Anthony. « Supramolecular architecture of late transition metal co-ordination polymers ». Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311739.
11
Masia, Marco. « Solvation dynamics and ion transport in conventional solvents and plasticizers ». Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6607.
Résumé :
El argumento fundamental de esta tesis es el estudio de la solvatación iónica por medio de cálculos con ordenador. Tres lineas de investigación han sido seguidas:(i) Solvatación y mobilidad ionica. Las características principales del processo de intercambio entre la primera y la segunda capa de hidratación iónica para Li+ en agua se ha encontrado ser independiente del estado termodinamico en gran medida. Ha sido demostrado que el desplazamiento cuadrático medio de moléculas pertenecientes a complejos inertes está caracterizado por un largo transitorio debido a la lenta relajación rotacional del complejo. El incremento del coeficiente de difusión iónico debido a los intecambios en la capa de solvatación ha sido calculado por primera vez en el caso de Li+ y Na+. Finalmente, se han derivado leyes de probabilidad que ponen en relación la estereoquímica y la velocidad iónica instantanea.
(ii) Plastificantes. Se propone un nuevo procedimiento para el desarrollo de campos de fuerza intramoleculares, que funciona satisfactoriamente en el caso de dos moleculas de interés en las Batterias a Iones de Litio: carbonato de etileno y -butirolactona. Respecto a la solvatación de Li+ en los dos solventes, el ión está coordenado por 4 moleculas a través del oxigeno del carbonilo con pequeñas distorsiones de la geometría molecular. La nueva asignación de los modos vibracionales hecha para las dos moléculas ha permitido calcular los cambios inducidos por el ión litio, explicando varias caracteristicas de los espectros esperimentales.
(iii) Polarización. Se ha estudiado la eficacia de los metodos de polarización más comunes para simulaciones de Dinámica Molecular en dímeros ión-molécula, usando calculos ab initio como referencia. En lugar de centrarnos en la superficie de energía potencial completa (procedimiento típico), se ha considerado solo la parte electrostática. Se han desarrollado nuevos modelos polarizables para agua y tetracloruro de carbono, que reproducen el comportamiento de sistemas carga-molécula. Ha sido encontrado que, en el caso de dímeros ión-molécula, se requiere una corrección de amortiguamento de la polarización a cortas distancias. El método de los dipolos puntuales junto al método de amortiguamento de Thole reproduce satisfactoriamente las características principales para cationes y aniones atómicos.
The underlying topic of this thesis is the study of ion solvation by means of computer calculations. Three lines of investigation have been followed:
(i) Solvation and Ionic Mobility. The main features of the exchange process between first and second ionic hydration shells for Li+ in water have been found to be largely independent of the thermodynamic state. It has been shown that the mean square displacement of molecules belonging to inert complexes is characterized by a long transient due to the slow rotational relaxation of the complex. The increase of the ionic diffusion coefficient due to solvation shell exchanges has been computed for the first time in the case of Li+ and Na+. Finally, probability laws have been derived which relate the stereochemistry and the instantaneous ionic velocity.
(ii) Plasticizers. A new approach for the development of intramolecular force fields is proposed, which performs satisfactorily in the case of two molecules of interest for Lithium Ion Batteries: ethylene carbonate and -butyrolactone. Concerning the solvation of Li+ in both solvents, it is coordinated by 4 molecules through the carbonyl oxygen with slight distorsions of the molecular geometry. The new vibrational mode assignment performed for both molecules has allowed to compute the vibrational shifts induced by the lithium ion, explaining a number of features present in the experimental spectra.
(iii) Polarization. The performance of the most commonly used polarization methods for Molecular Dynamics simulation is studied for ion-molecule dimers, using ab initio calculations as benchmark. Instead of focusing on the full potential energy surface (the standard approach), only the electrostatic part is considered. New polarizable models have been developed for water and carbon tetrachloride, which reproduce the behaviour of charge-molecule systems. In the case of ion-molecule dimers it has been found that a polarization damping correction is required at short distances. The point dipole method in conjunction with the Thole damping scheme reproduces rather satisfactorily the main features both for atomic cations and anions.
12
Eisenhart, Andrew. « Quantum Simulations of Specific Ion Effects in Organic Solvents ». University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1626356392775228.
13
Aguilar, Huacan Boris Abner. « Improving of the accuracy and efficiency of implicit solvent models in Biomolecular Modeling ». Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64409.
Résumé :
Biomolecular Modeling is playing an important role in many practical applications such
as biotechnology and structure-based drug design. One of the essential requirements of
Biomolecular modeling is an accurate description of the solvent (water). The challenge is
to make this description computationally facile that is reasonably fast, simple, robust and
easy to incorporate into existing software packages. The most rigorous procedure to model
the effect of aqueous solvent is to explicitly model every water molecule in the system. For
many practical applications, this approach is computationally too intense, as the number of
required water atoms is on average one order of magnitude larger than the number of atoms
of the molecule of interest.
Implicit solvent models, in which solvent molecules are represented by a continuum function,
have become a popular alternative to explicit solvent methods as they are computationally
more efficient. The Generalized Born (GB) implicit solvent has become quite popular due
to its relative simplicity and computational efficiency. However, recent studies showed serious
deficiencies of many GB variants when applied to Biomolecular Modeling such as an over-
stabilization of alpha helical secondary structures and salt bridges.
In this dissertation we present two new GB models aimed at computing solvation properties
with a reasonable compromise between accuracy and speed. The first GB model, called
NSR6, is based on a numerically surface integration over the standard molecular surface.
When applied to a set of small drug-like molecules, NSR6 produced an accuracy, with respect
to experiments, that is essentially at the same level as that of the expensive explicit solvent
treatment. Furthermore, we developed an analytic GB model, called AR6, based on an
approximation of the volume integral over the standard molecular volume. The accuracy of
the AR6 model is tested relative to the numerically exact NSR6. Overall AR6 produces a
good accuracy and is suitable for Molecular Dynamics simulations which is the main intended
application.Ph. D.
14
Zhuang, Guorong (Vera). « Application of surface analytical techniques to the study of the reactivity of lithium toward nonaqueous solvents ». Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058811391.
15
Austin, Nick Donnelly. « Tools for Computer-Aided Molecular and Mixture Design ». Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/894.
Résumé :
This thesis explores mathematical optimization techniques to address the computeraided molecular and mixture design problems (CAMD/CAMxD). In particular, we leverage the power of mixed-integer linear programs (MILPs) to quickly and efficiently design over the massive chemical search space. These MILPs, when coupled with state-ofthe- art derivative-free optimization (DFO) methods, make for an efficient optimization strategy when designing mixtures of molecules or when considering a single molecule design problem that involves difficult thermodynamics or process models. In the first chapter, we provide a very general overview of the field of CAMD as addressed from the perspective of mathematical optimization. We discuss many relevant quantitative structure-property relationships (QSPRs) and provide constraints typically used in CAMD/CAMxD optimization problems. The second chapter introduces our DFO-based molecular/mixture design algorithm and describes how this approach enables a much greater molecular diversity to be considered in the search space as compared to traditional methods. Additionally, this chapter looks at a few case studies relevant to crystallization solvents and provides a detailed comparison of 27 different DFO algorithms for solving these problems. The third chapter introduces COSMO-RS/-SAC as alternatives to UNIFAC as the method used to capture mixture thermodynamics for a variety of CAMD/CAMxD problems. To fully incorporate COSMO-RS/-SAC into CAMD, we introduce group contribution (GC) methods for estimating a few necessary parameters for COSMO-based methods. We demonstrate the utility of COSMO-RS/-SAC in a few case studies for which UNIFAC-like methods are insufficient. In the fourth chapter, we investigate reaction solvent design using COSMO-based methods. COSMO-RS is particularly suitable for these problems as they allow for modeling of many relevant species in chemical reactions (transition states, charges, etc.) directly at the quantum level. This information can be immediately passed to the CAMD problem. We investigate a number of solvent design problems for a few difficult reactions. We summarize the work and provide a few future directions in the final chapter. Overall, this thesis serves to push the field of CAMD forward by introducing new methods to more efficiently explore the massive chemical search space and to enable a few new classes of problems which were previously untenable.
16
Moreira, Mariana Hoyer. « Modelação e simulação de sistemas envolvendo Deep Eutectic Solvents e água : estruturas, propriedades e extração de poluentes ». Master's thesis, Universidade de Évora, 2019. http://hdl.handle.net/10174/25878.
Résumé :
Com este estudo pretende-se verificar, por simulação, detalhes estruturais e propriedades de sistemas ternários formados por Deep Eutectic Solvents (DES) e água, gerando hidro-géis e prever a extensão de extração de clorofenóis da água, em um sistema bifásico DES/Água. Os DESs estudados são obtidos pela mistura na proporção 1:4 de dodecanoato de sódio com o ácido octanóico, ou ácido nonanóico, ou ácido decanóico, a 40 ºC.
Os resultados obtidos mostraram que ocorre transferência de massa do poluente da fase aquosa para a fase rica em DES, no caso do sistema bifásico, com poluentes localizados próximos à interface. Os outros sistemas mostraram a formação de domínios aquosos entre as redes tridimensionais formadas pelo DES, característica de hidrogel. Uma proposta de organização estrutural do DES e do gel foi feita baseada em análises das funções de distribuição radial (RDF) calculadas. Concluiu-se que DES tem potencial de utilização em extração de poluentes hidrofóbicos; Modeling and simulation of systems involving Deep Eutectic Solvents and water - structure, properties and extraction of pollutants
ABSTRACT:
The present study’s goals are to clarify through molecular dinamics simulation, structural details and properties of ternary systems formed by DES and water, generating hydrogel, and to predict the extraction extension of chlorophenols from water, in a two-phase DES/water system. The DESs are obtained by mixing 1:4 sodium dodecanoate with oc-tanoic acid, or nonanoic acid, or decanoic acid. The temperature was maintained at 40 ° C in all simulations.
The obtained results showed that the mass transfer of the pollutant from the aqueous phase to the DES rich phase, in the two-phase system. The other systems have shown the for-mation of aqueous domains present between the three-dimensional networks formed by DES, characterizing hydrogel. A proposal of DES’s conformation was made based in the RDF analyses. It was concluded that DES has the potential to be used in the extraction of hydrophobic pollutants.
17
Nguyen, Thi Ngoc Ha. « TUNING MOLECULAR ARCHITECTURES AT THE LIQUID- SOLID INTERFACE BY CONTROLLING SOLVENT POLARITY AND CONCENTRATION OF MOLECULES ». Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-156382.
Résumé :
Das grundlegende Verständnis von Selbstorganisationsprozessen auf molekularem Niveau ist von entscheidender Bedeutung für den Fortschritt der Nanotechnologie. In diesem Zusammenhang werden hier Untersuchungen derartiger Prozesse an der Grenzfläche zwischen einer flüssigen Phase (z.B. einer Lösung) und einer kristallinen Festkörperoberfläche durchgeführt. Die Konzentration der Lösung und die Polarität des Lösungsmittels sind von entscheidender Bedeutung für die Kontrolle der durch Selbstorganisation gebildeten Strukturen von Molekülen an den flüssig-fest Grenzflächen zu einem Graphitsubstrat (HOPG). Im Mittelpunkt der vorliegenden Arbeit stehen die Einflüsse dieser beiden Parameter auf die Anordnung der Moleküle. Zunächst wird die Polarität der Lösungsmittel diskutiert. Lösungsmittel mit verschiedenen Polaritäten wie Phenyloctan (unpolar), Fettsäuren (moderat polar) und Fettalkohole (stark polar) wurden verwendet um Trimesinsäure (TMA) zu lösen. TMA bildet keine geordnete Struktur aus wenn es aus Phenyloctan (PO) abgeschieden wird. Ein poröses Muster ("Chicken-wire"-Struktur) entsteht aus der Lösung von TMA in Octansäure, wohingegen aus der Lösung von TMA in Undecanol ein Linienmuster durch Koadsorption von TMA und Undecanol Molekülen gebildet wird. Als nächstes werden die Auswirkungen der Ultraschallbehandlung der Lösungen zur Kontrolle der Konzentration der Lösung und die daraus resultierende unterschiedliche molekulare Packungsdichte und Strukturen beschrieben. Eine selbstassemblierte Struktur aus Zick-Zack-Dimerketten wird bei der TMA-PO Lösung nur beobachtet, wenn die Lösung für 5 Stunden Ultraschall ausgesetzt wurde. Die hoher Packungsdichte in Form der "Flower"-Struktur wird für Lösungen von TMA in Octansäure gefunden, nachdem diese für lange Zeit mit Ultraschall behandelt wurden. Ein weiterer Aspekt der vorliegenden Arbeit ist die entdeckte Veresterungsreaktion an der TMA-undecanol/HOPG Grenzfläche. 1-undecyl Monoester von TMA wurde überraschender Weise an dieser Grenzfläche gefunden, nachdem die TMA-Undecanol Lösungen, für lange Zeit Ultraschall ausgesetzt wurden. Diese Monoestermoleküle bilden sich an der flüssig-fest Grenzfläche allein auf Grund der erhöhten Konzentration von TMA (ohne jegliche externe Katalysatoren). Der physikalische Hintergrund der Prozesse des Lösens und der Ultraschallbehandlung sind der Gegenstand weiterer Untersuchungen. Selbstassemblierte Abscheidung tritt auch bei Verwendung nur der reinen Lösungsmittel (Octansäure beziehungsweise Undecanol) auf, was zu verschiedenen Mustern führt, welche ebenfalls durch Ultraschallbehandlung kontrolliert eingestellt werden können.
18
Nieto, Draghi Carlos Eduardo. « Transport anb Structural Properties of Aqueous Solutions of Organic Solvents ». Doctoral thesis, Universitat Rovira i Virgili, 2003. http://hdl.handle.net/10803/8520.
Résumé :
Molecular Dynamics simulation technique has been used in this work to obtain equilibrium as well as transport properties of different aqueoussolutions. The peculiar behavior observed in pure water and its mixtures with other substances at different thermodynamic conditions, and the knowledge and understanding of the properties of these systems are the motivations of this work. We have made a direct connection between the local tetrahedral structure of water, created by the presence of hydrogen bonds, and the selfdiffusion coefficient at liquid-like densities. We have found some indications of
an order transition in the three dimensional structure of water at certain conditions of temperature (above 345 K) and densities (between 0.9 to 1.3 g/cm3).
The strong hydrogen bond interaction observed in pure water plays a central role in aqueous solutions. We have studied several properties of aqueous mixtures of associating fluids, such as methanol, ethanol, acetone and dimethyl sulfoxide (DMSO). We observe that the presence of each type of solute perturb the local structure of water in a different manner, and this perturbation gives rise to the formation of chain-like structures with long-range correlation of hydrogen-bonded water molecules that is responsible for the
high viscosity of the mixture. We have also computed the thermal conductivity of the different mixtures, obtaining very good agreement between our simulation results and the available experimental data.
One of the properties that we have analyzed for these binary mixtures is the Ludwing-Soret effect, which is a macroscopic cross effect where a diffusion process is caused by the presence of a temperature gradient in a multicomponent system. This effect can be quantified through the thermal diffusion factor, which is usually positive for most solutions. However, in the
case associating fluids, the value of this coefficient may have a change in its sign at some particular composition. Our simulations reproduce even quantitatively the change in the sign of the Soret coefficient experimentally observed, and to the best of our knowledge, this is the first time that such achievement is reached for a mixture of molecular fluid employing molecular dynamic simulations. Additionally, we have devised a simple lattice model to support the hypothesis that the change in the sign of the Soret coefficient will appear in all cases in which the energy of the crossed interaction between
different species is more negative than the interaction energies between pure components.
The final part of this work is devoted to the computation of structural, transport and dielectric properties of benzene in water at supercritical conditions. We have employed a new Anisotropic United Atom (AUA) model of benzene that reproduces the quadrupolar moment of this molecule. We have computed different properties like self-diffusion coefficient and Maxwell-Stefan
coefficients, and shear viscosity for the mixture at supercritical conditions. A strong density and composition dependence of the properties is observed.
Experimental data shows the presence of aggregates between water and benzene molecules. This fact suggests the presence of some degree of
hydrogen bonding between these two molecules. Our simulations reproduce this behavior and we observed the formation of hydrogen bonds between the two species. In addition, we observe that these bonds are longer lived than the corresponding hydrogen bonds between water molecules. Similarly, we obtain an important reduction of the dielectric constant of the mixture with the increment of the amount of benzene molecules, at least at medium and high
densities.
DE LA TESIS
La simulación Dinámica Molecular ha sido la técnica empleada en este trabajo para la obtención de propiedades de transporte y de equilibrio de sistemas reales. El comportamiento peculiar observado por el agua a diferentes condiciones termodinámicas y en presencia de otras substancias, el conocimiento y entendimiento de las propiedades de este tipo de sistemas son una de las principales motivaciones de este trabajo. Adicionalmente, se ha realizado un extenso estudio de las relaciones intrínsecas existentes entre la estructura local del sistema, desde un punto de vista microscópico, y las
propiedades dinámicas de transporte, tanto en el caso del agua pura como en el caso de mezclas acuosas de solventes orgánicos.
En primer lugar, se ha realizado un análisis de la relación existente entre la estructura local de puentes de hidrógeno presente en el agua pura en condiciones sub y supercríticas, para ello se realizó una comparación entre cuatro diferentes modelos comúnmente utilizados en la literatura. Los resultados obtenidos nos han permitido relacionar de una manera directa la estructura tetraédrica local de las moléculas de agua, creada por la presencia de los puentes de hidrógeno, y el valor que alcanza el coeficiente de autodifusión en condiciones de densidad de líquido.
La fuerte interacción debida a los puentes de hidrógeno presente en las moléculas de agua juega un papel central en el comportamiento de soluciones acuosas. En este trabajo se han estudiado mezclas acuosas de fluidos asociantes, como metanol, etanol, acetona y sulfóxido de dimetilo. El análisis de los resultados de simulación muestra que la presencia de
diferentes tipos de soluto perturban de una manera diferente la estructura tetraédrica local del agua. Esta pérdida en la estructura tetraédrica del agua origina un incremento en la rigidez de las moléculas de agua, con respecto a
otras, más simétricas y menos rígidas, presentes en el agua pura. Como consecuencia, se ha observado un incremento del tiempo de vida de los
puentes de hidrógeno presentes en la mezcla, hecho que justifica el aumento observado en la viscosidad de la mezcla. Por otro lado, se han realizado simulaciones para calcular la conductividad térmica de la mezcla obteniendo
resultados que presentan un acuerdo excelente con los datos experimentales.
El efecto Ludwig-Soret es otra de las propiedades calculadas para las mezclas estudiadas. Este efecto cruzado macroscópico consiste en un
proceso difusivo causado por la presencia de un gradiente de temperatura en sistemas multicomponentes. Este efecto es cuantificado por medio del factor de difusión térmica, el cual suele ser siempre positivo en la mayor parte de
las soluciones. Sin embargo, para el caso de fluidos asociantes, el valor de este coeficiente puede cambiar de signo a una concentración particular. Se ha calculado el coeficiente de Soret para soluciones acuosas de los
compuestos orgánicos antes mencionados. Nuestras simulaciones reproducen el cambio de signo observado en estos sistemas obteniendo un
acuerdo cuantitativo excelente con los datos experimentales. Adicionalmente, se ha podido observar que el cambio de signo en de coeficiente aparece siempre que la energía de interacción cruzada, entre las moléculas de diferentes especies, es mas negativa que las energías de interacción entre los componentes puros.
Finalmente, se han estudiado las propiedades estructurales, dieléctricas y de transporte de mezclas acuosas de benceno en condiciones supercríticas. En nuestras simulaciones se ha utilizado un nuevo modelo anisotrópico de
átomo unificado. Entre las propiedades de la mezcla calculadas se encuentran los coeficientes de auto difusión, difusión de Maxwell-Stefan y
coeficiente de viscosidad en condiciones supercríticas. Adicionalmente, datos experimentales recientes han mostrado la presencia de ciertos grupos de moléculas de benceno y agua formando grupos de agregados. Nuestras simulaciones reproducen la formación de puentes de hidrógeno entre las dos especies con tiempos de vida media superiores a los encontrados entre las moléculas de agua.
19
Shukla, Charu L. « Computationally Probing the Cybotactic Region in Gas-Expanded Liquids ». Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14510.
Résumé :
Gas-expanded liquids (GXLs) are novel and environmentally benign solvent systems with applications in reactions, separations, nanotechnology, drug delivery, and microelectronics. GXLs are liquid mixtures consisting of an organic solvent combined with a benign gas, such as CO2, in the nearcritical regime. In this work, molecular dynamics simulations have been combined with experimental techniques to elucidate the cybotactic region or local environment in gas-expanded liquids. Molecular dynamics simulations show clustering of methanol molecules in carbon dioxide-methanol mixtures. This clustering was not observed in carbon dioxide-acetone mixtures. Furthermore, addition of carbon dioxide enhances diffusivity of solutes in gas-expanded media as shown by both simulations and Taylor-Aris dispersion experiments. Finally, local structure and local compositions around pyrene in carbon dioxide-methanol and carbon-dioxide acetone were investigated using simulations and UV-vis spectroscopy.
20
Mohana, Sundaram Hamsa Priya. « Molecular Modeling of Solute/Co-Solvent/Water Preferential Interactions : Toward Understanding the Role of Hydration and Co-solvent in Weak Protein-Protein Interactions ». The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299609836.
21
香里, 藤井, et Kaori Fujii. « Time-resolved spectroscopic study on fundamental chemical reactions in a unique class of solvents ». Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13158494/?lang=0, 2021. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13158494/?lang=0.
Résumé :
多数の溶媒分子に取り囲まれている溶液中において溶質分子の化学反応素過程を考える場合、溶媒分子による反応の平衡論的、動的な効果を考える必要がある。本研究では、ユニークな反応場として水や有機溶媒とは区別される、超臨界流体とイオン液体をとり上げ、溶質分子のプロトン移動反応、光解離反応について、時間分解レーザー分光と分子動力学計算、理論的解析を行い、その現象を明らかにする試みをおこなった。In solution, solvent molecules involve chemical reaction of solute molecules and could alter both reaction yield and kinetics. In this thesis, the author focused on fundamental chemical reactions (intermolecular proton transfer and photodissociate reaction) in a unique class of solvents, supercritical fluids and ionic liquids. By measuring time-resolved fluorescence spectrum and transient absorption spectrum of solutes, the author discusses how the reaction yield and kinetics are described by solvent physicochemical properties.
博士(理学)
Doctor of Philosophy in Science
同志社大学
Doshisha University
22
Smortsova, Yevheniia. « Dye sensitized solar cells efficiency improvement : optimization of the electrolyte using ionic liquids/molecular solvents mixture and study of the photodynamic properties of organic indolinic derivative dyes ». Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1R061/document.
Résumé :
Parmi les énergies renouvelables, l’énergie solaire est la plus puissante. L’élément clé des DSSCs est le photosensibiliseur, par lequel la génération de photocourant est possible. L’autre élément important est l’électrolyte. Les liquides ioniques (Ils) sont utilisés en tant qu’électrolytes dans les DSSCs du fait de leurs propriétés chimiques: pression de vapeur basse, haute résistance thermique et chimique, polarité et phase modulables, etc. L’objectif de cette thèse est de comprendre les processus photophysiques dans les colorants dérivés d’indolines dans les solvants moléculaires (MS) et les mélanges IL/MS. L’influence du solvant sur les propriétés spectroscopiques de D131, D102, D149 and D205 est d’abord étudiée par spectroscopie stationnaire d’absorption et de fluorescence. Ensuite, la spectroscopie résolue en temps est employée pour étudier leur photophysique et sa dépendance au solvant. Ces expériences ont permis de démontrer l’influence des paramètres d'aptitude de donneur de liaison hydrogène et d'accepteur de liaison hydrogène des solvants. Le rôle majeur de la dynamique de solvatation dans la dynamique des états excités de ces colorants a été montré. Ce phénomène a été suivi dans les mélanges IL/MS en utilisant une sonde fluorescente classique, C153, et des techniques de fluorescence résolues en temps et de dynamique moléculaire. Les réponses de solvatation multi-régimes de ces mélanges sont dirigées par le renforcement de la liaison hydrogène entre la sonde et les composants des mélanges. Les résultats de cette these apportent beaucoup à la compréhension des processus photophysiques fondamentaux régissant les sensibiliseurs et les électrolytes dans les DSSCsAmong all the renewable energy sources, solar energy is the most powerful source far ahead wind or geothermal energies. The first key component of DSSCs is the photosensitizer. It is through this component that the most important steps of photocurrent generation are possible. On the other hand, ionic liquids (ILs) have been proposed as electrolyte for DSSCs due to their peculiar properties: low vapor pressure, high thermal and chemical robustness, tunability of polarity and phase behaviour etc. The objective of this thesis was to get an understanding of the photophysics in the indoline derivated dyes in molecular solvents (MS) and in the IL/MS mixtures. Firstly, the solvent dependence of the spectroscopic properties of D131, D102, D149 and D205 was studied by the steady-state UV-Vis absorption and fluorescence spectroscopy. Then, time-resolved spectroscopy was used to elucidate their photophysics and its solvent dependence. These experiments helped to discern the influence of the hydrogen bond donor and acceptor abilities of the solvent. The solvation dynamics was shown to play a major role in the excited state dynamics of these dyes. This process in IL/MS mixtures was elucidated using the classic fluorescent probe C153 by the means of time-resolved spectroscopy and MD simulations. The complex multi-regime solvation response in these systems was shown to be shaped by the strengthening of the hydrogen bonding between the probe and the mixture components. The results of this thesis work contribute to the fundamental understanding of the photodynamics of the sensitizer and the response of the electrolyte used in the DSSCs
23
Smortsova, Yevheniia. « Dye sensitized solar cells efficiency improvement : optimization of the electrolyte using ionic liquids/molecular solvents mixture and study of the photodynamic properties of organic indolinic derivative dyes ». Electronic Thesis or Diss., Université de Lille (2018-2021), 2018. http://www.theses.fr/2018LILUR061.
Résumé :
Parmi les énergies renouvelables, l’énergie solaire est la plus puissante. L’élément clé des DSSCs est le photosensibiliseur, par lequel la génération de photocourant est possible. L’autre élément important est l’électrolyte. Les liquides ioniques (Ils) sont utilisés en tant qu’électrolytes dans les DSSCs du fait de leurs propriétés chimiques: pression de vapeur basse, haute résistance thermique et chimique, polarité et phase modulables, etc. L’objectif de cette thèse est de comprendre les processus photophysiques dans les colorants dérivés d’indolines dans les solvants moléculaires (MS) et les mélanges IL/MS. L’influence du solvant sur les propriétés spectroscopiques de D131, D102, D149 and D205 est d’abord étudiée par spectroscopie stationnaire d’absorption et de fluorescence. Ensuite, la spectroscopie résolue en temps est employée pour étudier leur photophysique et sa dépendance au solvant. Ces expériences ont permis de démontrer l’influence des paramètres d'aptitude de donneur de liaison hydrogène et d'accepteur de liaison hydrogène des solvants. Le rôle majeur de la dynamique de solvatation dans la dynamique des états excités de ces colorants a été montré. Ce phénomène a été suivi dans les mélanges IL/MS en utilisant une sonde fluorescente classique, C153, et des techniques de fluorescence résolues en temps et de dynamique moléculaire. Les réponses de solvatation multi-régimes de ces mélanges sont dirigées par le renforcement de la liaison hydrogène entre la sonde et les composants des mélanges. Les résultats de cette these apportent beaucoup à la compréhension des processus photophysiques fondamentaux régissant les sensibiliseurs et les électrolytes dans les DSSCsAmong all the renewable energy sources, solar energy is the most powerful source far ahead wind or geothermal energies. The first key component of DSSCs is the photosensitizer. It is through this component that the most important steps of photocurrent generation are possible. On the other hand, ionic liquids (ILs) have been proposed as electrolyte for DSSCs due to their peculiar properties: low vapor pressure, high thermal and chemical robustness, tunability of polarity and phase behaviour etc. The objective of this thesis was to get an understanding of the photophysics in the indoline derivated dyes in molecular solvents (MS) and in the IL/MS mixtures. Firstly, the solvent dependence of the spectroscopic properties of D131, D102, D149 and D205 was studied by the steady-state UV-Vis absorption and fluorescence spectroscopy. Then, time-resolved spectroscopy was used to elucidate their photophysics and its solvent dependence. These experiments helped to discern the influence of the hydrogen bond donor and acceptor abilities of the solvent. The solvation dynamics was shown to play a major role in the excited state dynamics of these dyes. This process in IL/MS mixtures was elucidated using the classic fluorescent probe C153 by the means of time-resolved spectroscopy and MD simulations. The complex multi-regime solvation response in these systems was shown to be shaped by the strengthening of the hydrogen bonding between the probe and the mixture components. The results of this thesis work contribute to the fundamental understanding of the photodynamics of the sensitizer and the response of the electrolyte used in the DSSCs
24
Kotdawala, Rasesh R. « Adsorption studies of hazardous air pollutants in microporous adsorbents using statistical mechanical and molecular simulation techniques ». Worcester, Mass. : Worcester Polytechnic Institute, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-050407-112429/.
Résumé :
Dissertation (Ph.D.) -- Worcester Polytechnic Institute.Keywords: Activated carbons; Hydrogen cyanide; Methyl ethyl ketone; Adsorption; Mercury; Monte-Carlo; Solvents; Molecular simulations; Zeolites; Water; Methanol; Nanopores. Includes bibliographical references (leaves 147-150).
25
Bley, Michael. « Simulating Osmotic Equilibria by Molecular Dynamics - From Vapor-Liquid Interfaces to Thermodynamic Properties in Concentrated Solutions ». Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS122.
Résumé :
L’objectif de cette thèse de doctorat est le développement d’une nouvelle méthode théorique basée sur la simulation des équilibres liquide-gaz par simulations de dynamique moléculaire. Cette nouvelle m´méthode prédit les propriétés thermodynamiques telles que l’activité des solvants et les coefficients d’activité des solutés en phases aqueuses et organiques impliquées dans les systèmes d’extraction liquide-liquide. Ces propriétés thermodynamiques sont nécessaires pour les approches de modélisation thermodynamique mésoscopique permettant d’estimer l’efficacité et la s´électivité d’un système d’extraction par solvant jusqu’au une échelle industrielle. Les propriétés thermodynamiques et structurales des solutions électrolytiques aqueuses et des phases organiques, y compris les agrégats résultant des molécules d’extraction des amphiphiles, sont en bon accord avec les données expérimentales et théoriques disponibles. L’approche de dynamique moléculaire de l’équilibre osmotique fournit un nouvel outil puissant permettant d’accéder aux données thermodynamiquesThe aim of this PhD thesis is the development of a new theoretical method based on the simulation of vapor-liquid equilibria by means of molecular dynamics (MD) simulation. This new method predicts thermodynamic properties such as solvent activities and solute activity coefficients of aqueous and organic phases used in liquid-liquid extraction systems. These thermodynamic properties are required for mesoscopic thermodynamic modeling approaches estimating the efficiency and selectivity of a given solvent extraction system up to an industrial scale. Thermodynamic and structural properties of aqueous electrolyte solutions and organic solvent phase including aggregates resulting from amphiphilic extractant molecules are reproduced in very good agreement with previously available experimental and theoretical data. The osmotic equilibrium MD approach provides a new and powerful tool for accessing thermodynamic data
26
Granero-Fernandez, Emanuel. « Fluides supercritiques et solvants biosourcés : propriétés physicochimiques des systèmes expansés par du CO2 ». Thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/23928/1/Granero%20Fernandez_Emanuel.pdf.
Résumé :
Les objectifs environnementaux (COP21) visant à réduire les émissions de gaz à effet de serre et l'impact de l'industrie sur la nature, font face au défi de la demande croissante d'énergie et de produits. Les procédés chimiques sont les premiers en cause lorsqu’ils mettent en œuvre des solvants. L'ingénierie des solvants est une solution innovante qui vise à trouver des milieux alternatifs bénins possédant les propriétés de solvant adaptés pour chaque étape du procédé.Dans cette perspective, nous avons étudié les Liquides expansés par un gaz (LEGs), qui sont desliquides dont le volume augmente sous l’effet d’un gaz dissous sous pression. En particulier, le CO2 peut être utilisé comme agent d'expansion pour obtenir des liquides expansés par du CO2(LECs), combinant les avantages du CO2 et du solvant. La phase expansée peut contenir des concentrations élevées de CO2, jusqu'à 80%, selon le solvant, ce qui conduit à une réduction du besoin du solvant organique, mais aussi à des changements des propriétés physicochimiques et de transport de la nouvelle phase expansée. On peut de plus moduler ces propriétés par la pression et la température, d'une manière réversible, et améliorer la séparation des produits. Dans cette étude, différents solvants biosourcés ont été utilisés pour obtenir des systèmes expansés par du CO2, tels que les acétates d'alkyle, les carbonates organiques, les méthoxybenzènes, etc.La connaissance des équilibres de phase, des propriétés de solvatation et de transport est essentielle pour concevoir des processus qui exploitent le comportement particulier de ces systèmes biphasiques. Deux approches principales ont été utilisées pour caractériser ces systèmes. Dans un premier temps, des mesures ont été effectuées dans une cellule à haute pression et à volume variable pour évaluer la polarité au travers du paramètre Kamlet-Taft (KT) *(dipolarité / polarisabilité) dans les solvants expansés par du CO2 sous des pressions allant jusqu'à 30 MPa. La technique utilisée a été la spectroscopie UV-Vis suivant le déplacement hypsochromique du Rouge de Nile, une sonde solvatochromique déjà utilisée pour obtenir les paramètres KT dans des solvants purs. De plus, des mesures d'équilibre vapeur-liquide (ELV) ont été effectuées pour obtenir la composition de la phase expansée à différentes pressions et températures afin de comprendre la solvatation du CO2 dans les solvants organiques et de fournir des informations manquantes dans la littérature. En deuxième lieu, dans une approche plus théorique, les données ELV ont été utilisées pour calculer numériquement d'autres propriétés telles que la densité et la viscosité. Des équations d'état et des simulations par dynamique moléculaire (DM) ont été utilisées ; ces dernières donnant de meilleurs résultats dans un mode prédictif de la masse volumique et permettant de suivre les positions moléculaires au cours du temps, qui peut être liée à de nombreuses propriétés, y compris la viscosité étudiée ici. Ces calculs ont été effectués en utilisant un champ de force de type Amber adapté. Les résultats obtenus dans l’ensemble complètent les données de la littérature existante et apportent de nouvelles informations sur les propriétés des LEGs. Par exemple, le comportement non linéaire de l'expansion volumétrique, vérifié après les déterminations de masse volumique sur les simulations DM à l'équilibre, est une clé dans la compréhension des interactions soluté-solvant ; ainsi que les valeurs KT * obtenues qui confirment la large gamme de polarité couverte par ces systèmes.Enfin, certains systèmes expansés par du CO2 ont été utilisés pour produire des nanoparticules de TiO2 pour panneaux solaires, améliorant leur surface spécifique et donc leur efficacité en tant que semi-conducteurs ; et d’autres ont été appliqués à un processus d'activation enzymatique entraînant une augmentation significative du taux de conversion
27
Cavallo, Valentina. « Tailoring intermolecular interactions in methacrylate-based copolymers and nanocomposites : Effect on molecular dynamics and thermal properties ». Electronic Thesis or Diss., Lyon, INSA, 2023. http://www.theses.fr/2023ISAL0103.
Résumé :
Une corrélation entre l’intensité et la nature des interactions intermoléculaires et les propriétés physiques, comme la conductivité thermique, a été rapportée pour des polymères amorphes. En particulier, une augmentation de la conductivité thermique a été associée à l’ajout d’interactions plus fortes par rapport aux liaisons de Van der Walls faibles, c’est-à-dire des liaisons hydrogène et ioniques. Dans ce travail, une tentative d'adapter la conductivité thermique dans les polymères amorphes a été réalisée par ingénierie des interactions intermoléculaires. Le poly(méthylméthacrylate) PMMA a été utilisé comme modèle et des copolymères poly(méthylméthacrylate-co-acide méthacrylique) (PMMA-co-MAA) ont été synthétisés par copolymérisation radicalaire afin d'introduire des liaisons H inter-chaînes et, après neutralisation, des liaisons ioniques. Des copolymères ont été obtenus avec succès jusqu'à 30 % en poids de MAA et caractérisés. Différents comonomères ont été utilisés pour évaluer l'influence d'une unité flexible apportant des liaisons H, le 2-hydroxyéthylméthacrylate (HEMA) ou le 2-carboxyéthylacrylate (CEA). La conductivité thermique a légèrement augmenté en augmentant la teneur en MAA et HEMA, tandis que pour les copolymères CEA, la présence de défauts a empêché la mesure. Le copolymère PMMA-co-MAA a été utilisé comme matrice pour les nanocomposites à base de cellulose afin d'adapter la compatibilité des charges, grâce à la présence de liaisons H entre l'unité MAA et la surface de la cellulose. Des nanofibres de cellulose (CNF) jusqu'à 15 % en poids ont été efficacement dispersées par coulée de solvant dans un mélange de deux solvants (THF/MeOH). La conduction thermique n'a montré aucun changement significatif après l'introduction des CNF. L'analyse mécanique dynamique (DMA) et la spectroscopie diélectrique à large bande (BDS) ont été utilisées en combinaison pour caractériser pleinement la dynamique moléculaire du PMMA-co-MAA copolymère suite à l'introduction de liaisons H inter-chaînes et à l'ajout ultérieur de CNF. Une relaxation β’ supplémentaire, caractérisée par une énergie d’activation (Ea) presque quatre fois plus élevé que le Ea(β), a été trouvée pour les nanocomposites et attribuée à l’établissement de liaisons H entre les groupes -COOH de la matrice et les groupes hydroxyles du CNF. Ainsi, une étude plus approfondie de la relaxation α a permis de révéler l’influence du CNF confirmant la présence de liaisons H interfaciales. En effet, malgré les Tgs similaires caractérisant la matrice et les nanocomposites, un décalage de leurs temps de relaxation vers des températures plus élevées a été observé suite à l’ajout de CNF. Les résultats rapportés dans cette thèse ont mis en évidence que les améliorations de la conductivité thermique obtenues par la modification des interactions entre les chaînes dans les matrices amorphes restent un défi extrêmement complexeA correlation between the strength of the intermolecular interactions and physical properties has been reported for amorphous polymers. In particular, an increment of thermal conductivity has been associated to the addition of stronger interactions compared with weak van der Walls, i.e. hydrogen and ionic bonds. In this work, an attempt to tailor thermal conductivity in amorphous polymers has been made by engineering intermolecular interactions. Poly(methylmethacrylate) PMMA was used as standard and poly(methylmethacrylate-co-methacrylic acid) (PMMA-co-MAA) copolymers were synthesised by free radical copolymerization in order to introduce inter-chain hydrogen bonds and, after neutralisation, ionic bonds. Copolymers were successfully obtained up to 30wt% of MAA and characterized. Also, different comonomers were used to evaluate the influence of a flexible unit bringing H-bonds, 2-hydroxyethylmethacrylate (HEMA) or 2-carboxyethylacrylate (CEA). Thermal conductivity slightly increased increasing MAA and HEMA content, while for CEA copolymers the presence of defects prevented the measurement. Later, PMMA-co-MAA was used as a matrix for cellulose-based nanocomposites to tailor filler compatibility, thanks to the presence of H-bonds between MAA unit and cellulose surface. Cellulose nanofibers (CNF) up to 15wt% were efficiently dispersed by solvent casting in a mixture of two solvents (tetrahydrofuran/methanol). Thermal conduction showed no significant changes following the introduction of CNF. Dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS) were used in combination to fully characterize the macromolecular mobility of PMMA-co-MAA following the introduction of inter-chain H-bonds and the subsequent addition of CNF. An additional β’-relaxation, characterized by an activation energy (Ea) nearly four times higher than the Ea(β), was found for the nanocomposites and ascribed to the establishment of H-bonds between the -COOH groups of the matrix and the hydroxyl groups of CNF, as confirmed by the lower values found for the thermal expansion coefficient of the free volume and the fragility of the material. A deeper investigation about the α-relaxation was able to reveal the influence of CNF confirming the presence of interfacial H-bonds. Indeed, despite the similar glass transition temperatures characterising the matrix and the nanocomposites, a shift of their relaxation times to higher temperatures was observed following the addition of CNF. Results reported in this thesis evidenced that the enhancements of thermal conductivity obtainable by the modification of the interchain interactions between chains in amorphous matrices remains an extremely complex challenge
28
Cezar, Henrique Musseli. « Implementação e desenvolvimento de algoritmo eficiente para deformação intramolecular com o método Monte Carlo ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-19102018-165856/.
Résumé :
Com o avanço do poder computacional nas últimas décadas, a modelagem molecular de problemas em diversas áreas se tornou mais acessível, sendo hoje uma ferramenta fundamental para o entendimento de diversos processos. Em especial, simulações moleculares com campos de força clássicos vem sendo importante para a amostragem de propriedades termodinâmicas, para a determinação de estruturas e população de confôrmeros, e seleção de configurações para utilização com métodos que combinam mecânica quântica com mecânica molecular. Os principais métodos de simulação atualmente utilizados são a dinâmica molecular (MD, do inglês molecular dynamics) e o Monte Carlo (MC). Ambos os métodos são a princípio equivalentes quando o objetivo é a amostragem configuracional, tendo a MD a vantagem de permitir a análise da dinâmica e evolução temporal, e o MC a vantagem de poder gerar configurações de forma probabilística, sem a necessidade de seguir um caminho sobre a superfície de energia potencial, o que pode resultar em uma amostragem mais eficiente. Contudo, não há ainda uma metodologia de MC que possa ser considerada eficiente e bem estabelecida para a amostragem dos graus de liberdade internos de moléculas com complexidade arbitrária. Visando avançar no desenvolvimento de métodos que trabalham nesse sentido, neste trabalho o método apresentado por Shah e Maginn [1] foi implementado e aprimorado. No método, a molécula é fragmentada em partes menores, formadas de graus de liberdade rígidos, que não variam drasticamente durante a simulação. Esses fragmentos por sua vez são conectadas por graus de liberdade maleáveis, os diedros e termos não ligados da energia. Durante a simulação a molécula tem fragmentos apagados, e então é reconstruída utilizando um esquema de Configurational Bias Monte Carlo (CBMC). A contribuição deste trabalho para a metodologia consiste em generalizar os tipos de fragmentos possíveis dentro do método, a simplificação do critério de aceitação e extensões com vieses adicionais, como é o caso do viés no potencial eletrostático e no critério de aceitação da amostragem preferencial com o CBMC. A validade da implementação do método foi avaliada através de simulações em dois sistemas simples: o octano e o 1,2-dicloroetano. Comparando a amostragem e os resultados obtidos para as populações de confôrmeros com resultados de MD e experimentais ou obtidos com outros métodos de MC da literatura foi possível verificar que a implementação reproduz os resultados esperados. Além disso, o equilíbrio conformacional da molécula de óxido mesityl (MOx) que possui duas conformações: syn e anti, foi estudado. Graças a barreira de potencial entre as duas conformações de cerca de 10 kcal/mol, a MD não é capaz de realizar uma amostragem ergódica, enquanto o CBMC realiza a amostragem sem problemas. Na simulação CBMC, a inversão da população dominante em fase gasosa e em água foi observada. Simulações do MOx em acetonitrila e metanol mostraram que a população de confôrmeros anti de fato aumenta conforme a polaridade do solvente. Entretanto, devido ao estiramento da ligação C = O do MOx em metanol devido as ligações de hidrogênio, a contribuição conformacional à posição do máximo da banda de absorção não segue a tendência da polaridade, tendo um deslocamento para o azul maior na acetonitrila do que em metanol. O estiramento da ligação C = O só pode ser observado graças a introdução da amostragem de fragmentos com deslocamentos Cartesianos e algoritmo de Metropolis ao método CBMC original. Esse efeito devido ao estiramento é compensado pelo efeito solvente, de modo que a contribuição total à energia de transição segue a polaridade do solvente. De uma maneira geral, concluímos que o desempenho do método CBMC utilizado é excelente para os casos estudados, e é inclusive superior ao da MD em alguns casos. A implementação no software DICE deixa um legado importante para diversos grupos de pesquisa, não somente por introduzir o CBMC, mas também por melhorias gerais como paralelização, lista de vizinhos e modernização do código, que foram introduzidas ao decorrer do projeto.With the increase of computational power in the last decades, the molecular modeling of problems in several areas has become more accessible, being today a fundamental tool used to understand several processes. In particular, molecular simulations with classical force fields have been important for the sampling of thermodynamic properties, for the determination of structures and population of conformers, and for the selection of configurations to be used with methods that combine quantum mechanics with molecular mechanics. The most common simulation methods used nowadays are molecular dynamics (MD) and Monte Carlo (MC). Both methods are in principle equivalent when the goal is configurational sampling, with MD having the advantage of allowing the analysis of the dynamics and temporal evolution, while MC has the advantage of generating the configurations in a probabilistic manner, not necessarily following a path in the potential energy surface, possibly resulting in a more efficient sampling. However, there is no MC methodology that can be considered efficient and established to sample the internal degrees of freedom of molecules with arbitrary complexity. In order to advance in the development of methods that want to achieve this goal, in this work the method presented by Shah e Maginn [1] has been implemented and improved. In the method, the molecule is fragmented into smaller parts, each one composed by the hard degrees of freedom, which do not vary dramatically during the simulation. Those fragments are then connected by soft degrees of freedom, the dihedral and non-bonded terms of the energy. During the simulation the molecule has some of its fragments deleted, and is reconstructed using a Configurational Bias Monte Carlo (CBMC) approach. The contribution of this work to the methodology is generalizing the fragment types within the method, the simplification of the acceptance criteria and some extensions with additional biases, such as electrostatic potential bias and the acceptance criterion of the preferential sampling with the CBMC. The implementation was evaluated through simulations in two simple systems: octane and 1,2-dichloroethane. Comparing the sampling and results obtained for the populations of conformers with MD results, experimental data or values obtained with different MC methods present in the literature, we verified that the implementation reproduces the expected results. Beyond that, the conformational equilibrium of the mesityl oxide (MOx) molecule which has two conformers: syn and anti, was investigated. Due to the potential energy barrier between the two conformers of about 10 kcal/mol, the MD does not perform an ergodic simulation, while the CBMC does the same sampling accordingly. In the CBMC simulation, the inversion of the dominant conformer in gas phase and water was observed. The MOx simulation in acetonitrile and methanol showed that the frequency of the anti conformer indeed increases with the solvent polarity. Nonetheless, due to the stretch of the C = O bond of MOx in methanol, attributed to the hydrogen bonds formed with the solvent, the conformational contribution to the maximum of the absorption band does not follow the polarity tendency, having a larger blue shift in acetonitrile than in methanol. The C = O bond stretch can only be seen because the Cartesian displacement sampling with the Metropolis method was introduced to the original CBMC method. This effect attributed to the stretch is compensated by the solvent, in a way that the total contribution to the transition energy follows the solvent polarity. In general, we conclude that the performance of the developed CBMC method is excellent to the studied cases, being even superior to MD in some cases. The implementation in DICE leaves an important legacy to several research groups, not only for introducing the CBMC method, but also due to general improvements such as parallelization, neighbor list and code modernization, which were introduced during the project.
29
See, Toh Yoong Hsiang. « Molecular separations with organic solvent nanofiltration ». Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/11320.
Résumé :
This thesis firstly describes the application of organic solvent nanofiltration (OSN) in the recycle of asymmetric hydrogenation catalysts through the retention of the (often) larger catalyst whilst allowing the smaller products to penneate. This improves the catalyst tum over number (TON) and the further addition of the ionic liquid (IL) CyPhoslOl markedly improves the enantiomeric excess in the asymmetric hydrogenation of dimethyl itaconate using Ru-BINAP. The high molecular weight of the catalyst and IL allows them to be simultaneously recycled using an OSN membrane. Although this work identifies significant potential to further the application of OSN in homogeneous catalyst recycle, there is a lack of commercially available OSN membranes with good chemical stability across a range of organic solvents and with the ability to separate compounds in the NF range of 200-1000 g morl. The central part of this thesis addresses these issues through the development of various integrally skinned asymmetric polyimide OSN membranes. A consistent method to describe the penneation property of the molecular weight cut off (MWCO) has been developed. This allows the detennination of membrane performance and integrity across a range of different membranes and solvents. The variation of membrane separation perfonnance across the NF range has been achieved through cfanging various membrane fonnation parameters. Crosslinking of these membranes significa~tly enhances the chemical stability allowing stable perfonnances in a range of organic solvents including polar aprotic solvents. Coupling chemical crosslinking with the fonner methodology simultaneously improves the membrane chemical stability and allows membranes to be tailored for specific separations. Finally, this work also examines some initial steps leading to the scale up of OSN membranes to pilot scale through the use of spiral bound elements.
30
Mandumpal, Jestin Baby. « The molecular mechanism of solvent cryoprotection ». Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/496.
Résumé :
The cryopreservation of animal and human cells, tissues and organs as well as germplasm of endangered plant species is a key area in contemporary biotechnology. In this thesis, certain classes of chemicals known as cryoprotective agents (CPA) are investigated in detail. The structural, dynamic and vitrification properties of representative CPAs are studied using the state-of-the art molecular dynamics simulation techniques. The simulations provide a rationale at the molecular level of the cryoprotective properties of aqueous solutions of compounds such as DMSO, methanol and ethanol.This is a brief synopsis of the thesis:CHAPTER 1. This chapter provides a general introduction of various aspects of cryoprotection. A brief overview of the challenges that are encountered in the cryopreservation protocol is given, followed by a list of known cryoprotectants. Next various mechanisms to account for cryopreservation have been explained in detail. This section is followed by one of the important theme of this thesis, vitrification, and finally water and its properties.CHAPTER 2. This chapter discusses the theoretical background of molecular dynamics simulations and various analyses, and a brief overview of water forcefields.CHAPTER 3. Molecular dynamics simulations of DMSO in water elucidating its structural, dynamic and hydrogen bonding properties are described in this chapter. Comparison with its chemical analogue, Acetone, is made in an attempt to rationalise DMSO‟s exceptional properties in a wide range of temperatures.CHAPTER 4. Structural and hydrogen bonding properties of aqueous ethanol and methanol solutions have been described in this chapter.CHAPTER 5. Estimation of glass transition temperatures of aqueous mixtures of DMSO, acetone, ethanol, methanol and water using simulated annealing molecular dynamics techniques has been described in this chapter.CHAPTER 6. Important conclusions arising from this study and scope of the work have been summarised in this chapter.
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Damasceno, Marcus Vinicius Araujo. « Estudos dos efeitos de solventes no espectro de absorção eletrônica da merocianina de Brooker e derivados ». Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-07042015-145330/.
Résumé :
Nesta tese estudamos o espectro de absorção da Merocianina de Brooker (MB) e três derivados em solventes com diferentes polaridades. O interesse no estudo desses sistemas se dá pela presença de algumas propriedades particulares das merocianinas, por exemplo, apresentam um grande deslocamento solvatocrômico devido à mudança na polaridade do meio. Nós apresentamos os resultados teóricos obtidos para o espectro de absorção das moléculas considerando diferentes estruturas para o estado fundamental: formas trans, cis, zwiteriônica (zw), protonada (MBH+) e dímero(MB2). O efeito do solvente foi considerado utilizando diferentes modelos de solvatação: (i) modelo contínuo polarizável (PCM), (ii) através de uma configuração eletrostática média do solvente (ASEC), (iii) incluindo algumas moléculas explícitas do solvente juntamente com um ambiente eletrostático gerado pelas demais moléculas do solvente. Como uma investigação adicional, apresentamos nossos resultados de medidas experimentais para o espectro de absorção da MB em vários solventes variando acidez e concentração. Vimos, através de cálculos quânticos, que as formas cis/trans apresentam a excitação eletrônica na mesma região, e que a deformação estrutural gerada pela forma zw provoca um deslocamento para o vermelho na excitação eletrônica. Os nossos resultados teóricos e experimentais mostram que a forma MBH+ apresenta um solvatocromismo pequeno, com deslocamento de 20 nm provocado pela mudança água-clorofórmio. Realizando medidas experimentais através da titulação espectroscópica nós obtivemos o pKa associado ao processo de desprotonação/protonação da MB em água e metanol. Em água obtivemos um valor de 8.7, em boa concordância com valores da literatura. Apresentamos um valor inédito do pKap da MB em metanol, 9.9. Conseguimos uma boa descrição teórica para a excitação eletrônica da MB em solventes com alta polaridade, na região entre 430-500 nm, utilizando o método quântico TD-DFT com funcionais B3LYP e CAM-B3LYP e conjunto de funções base 6-311+G**, porém a excitação em solventes de baixa polaridade, que ocorre na região entre 550-650 nm, não é corretamente descrita considerando a MB nos solventes. Nós vimos, através de estudos experimentais, que a sonda MB pode agregar em solventes de baixa polaridade. Os cáculos teóricos para dímeros em solução mostraram a existência de uma excitação eletrônica de baixa intensidade nesta região. Adicionalmente, os espectros experimentais em solventes de baixa polaridade mostraram 2 bandas, onde a segunda se assemelha com a banda observada para a forma MBH+. Para explicar essas 2 bandas experimentais para a MB, apresentamos uma proposta teórica onde ocorre uma transferência de prótons (H+) entre os monômeros do dímero formado, gerando uma estrutura desprotonada (MBH-) e uma protonada (MBH+). Cálculos teóricos para a forma MBH- mostram que essa forma apresenta uma excitação eletrônica de intensidade moderada na região entre 550-650 nm. Com essa hipótese nós conseguimos descrever, através de cálculos teóricos, o solvatocromismo anômalo observado experimentalmente para o espectro eletrônico de absorção da MB nas duas regiões de polaridade dos solventes: alta polaridade, sendo descrita pela forma MB, e baixa polaridade, descrita pela forma MBH-.In this thesis we studied the absorption spectrum of merocyanine Brooker (MB) and three derivatives in solvents with different polarities.The interest in this system is given by the presence of some particular properties of this molecule, for example, it presents a large solvatochromic shift due to the change in the polarity of the medium. We present the results for the absorption spectrum of the molecules considering different structures to the ground state: forms trans, cis, zwitterionic (zw), protonated MBH+ and dimer (MB2). The solvent effect was treaty by different ways: (i) continuous model using the PCM polarizable, (ii) by an average electrostatic configuration of solvent, ASEC, (iii) including some explicit solvent molecules with an electrostatic environment generated by other solvent molecules. As an additional investigation, we present results of experimental measurements in the thesis. We have seen, through quantum calculations, that the forms cis/trans have the electronic excitation in the same region and the structural deformation generated in the zw form causes a red shift. Our theoretical and experimental results show that the MBH+ form has a small solvatochromism, with displacement of 20 nm caused by water-chloroform change. Performing spectroscopic titration we got the pKa associated with the process of deprotonation/protonation of MB in water and methanol. In water we obtained a value of 8.7, in good agreement with the values reported in the literature. We present a unpublished pKap for the MB in methanol, 9.9. We got a good theoretical description for electronic excitation of MB in solvents with high polarity, in the region between 430-500 nm, using a method quantum TD-DFT B3LYP and CAM-B3LYP functional whit basic functions set 6-311+G** but the excitation in low polarity solvents, which occurs in the region between 550-650 nm, is not properly described considering the MB form in the solvents. We have seen, through experimental studies that the MB probe can aggregate in low polarity solvents. Theoretical calculations for dimer in solution showed the existence of a low intensity electron excitation in this region. Additionally, the experimental spectra in low polarity solvents showed 2 bands, where in the second band is similar to the observed to MBH+ form. To explain these two experimental bands for MB, we present a theoretical proposal where there is a proton transfer (H+) between the monomers of the dimer, generating a deprotonated structure (MBH-) and a protonated (MBH+). Theoretical calculations for the MBH- show that this form presents an electronic excitation of moderate intensity in the region between 550-650 nm. With this assumption we can describe, through theoretical calculations, the anomalous solvatochromism for the electronic absorption spectrum of MB in the two polarity regions of solvents: high polarity is described by the MB form, and low polarity, described by the MBH- form.
32
Anim-Mensah, Alexander R. « Evaluation of Solvent Resistant Nano-Filtration (SRNF) Membranes for Small-Molecule Purification and Recovery of Polar Aprotic Solvents for Re-Use ». University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1195148766.
33
Muchowska, Kamila Barbara. « Molecular balances ». Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/17880.
Résumé :
Predicting and quantifying solvent effects on non-covalent interactions is often very challenging, as they are influenced and modulated by multiple factors. In this thesis, a series of molecular torsion balances is used as a tool to tackle the complexities of noncovalent interactions in solution. Chapter 1 presents an up-to-date literature review on solvent effects on non-covalent interactions, with a particular focus on solvent effects on conformational equilibria and molecular torsion balances. Chapter 2 demonstrates the use of molecular torsion balances and a simple explicit solvation computational model to show that the electrostatic potential of the substituted aromatic rings is largely dependent on the explicit solvation of the substituent. The contribution of both bond polarisation and through-space field effects is also covered. Chapter 3 provides a literature review on the deuterium isotope effects on non-covalent interactions, presenting a range of contradictory findings. Molecular torsion balances are used here as a probe of H/D isotope effects on the conformational equilibria, solvent isotope effects and the solvophobic effect in aqueous mixtures. The balances are studied from thermodynamic and kinetic viewpoints, through which both intra- and intermolecular interactions are examined. It is shown here that H/D isotope effects on the presented system are either non-existent or negligibly small. Chapter 4 presents the use of molecular torsion balances to investigate carbonylcarbonyl interactions, taking into account steric and solvent effects. This is compared experimentally and computationally against two existing theories rationalising these interactions. In Chapter 5, a background of metal-ligand interactions is outlined, along the most widely utilised theories rationalising them. The electronic effects of Pt complexation by a pyridyl-substituted molecular torsion balance is analysed both experimentally and computationally, and the arising discrepancies are addressed. The applicability limits of the previously presented simple solvation models are determined using systems displaying extreme electronic effects.
34
Huttenhower, Hillary Anne. « Development of new chemistry for a dual use hydrazine thruster, switchable room temperature ionic liquids, a study of silane grafting to polyethylene and its model compounds, synthesis of the novel hydrazine replacement fuel molecules 1,1-dimethyl-2-[2-azidoethyl]hydrazine and 1,1-dimethyl-2-[2-azidoethyl]hydrazone ». Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41055.
Résumé :
This thesis focuses on the development of new compounds or new processes that are more environmentally friendly and economical than those currently in use. The decomposition of hydrazine, a well established liquid rocket fuel for both the aerospace and defense industries, to the product ammonia is studied. Control of this reaction will allow hydrazine to be used as a propellant for both chemical and electric propulsion. From this a dual stage thruster will be developed that will be more efficient than current systems decreasing the amount of propellant needed and allowing for either a larger mission payload or a longer duration of individual missions. Hydrazine, while beneficial and well established, is also highly toxic, so other work in this thesis focuses on the synthesis of the novel molecule 1,1-dimethyl-2-[2-azidoethyl]hydrazine or DMAEH and its hydrazone intermediate 1,1-dimethyl-2-[2-azidoethyl]hydrazone or De-DMAEH as less toxic hydrazine replacements.
Novel "switchable" ionic liquids have been investigated in this research. These are solvents that can change from molecular liquids to ionic liquids and back, simply with the addition or removal of CO₂ from the system. They can be used for a variety of applications, including as solvents for a reaction and separation system. Due to the recyclable nature of these solvents, waste is decreased making their development and implementation both environmentally and economically beneficial. Finally, the grafting reaction of vinyl silanes onto a hydrocarbon backbone is investigated. Fundamental work is being performed to study the graft distribution, selectivity and mechanism by which this reaction occurs. A more thorough understanding of how this reaction proceeds will allow for the development of a more efficient industrial process.
35
Radford, Isolde. « Implicit-solvent molecular dynamics simulations of peptide folding ». Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609804.
36
González, Yoelvis Orozco. « Fotofísica e propriedades dinâmicas de sistemas moleculares ». Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26032013-150724/.
Résumé :
A fotodinâmica de sistemas moleculares representa um dos principais tópicos atuais da físico-química molecular. O conhecimento das propriedades dos estados eletrônicos excitados tem permitido desenvolver áreas de vital importância como das energias renováveis, da fotomedicina, dos sensores fluorescentes, entre outras. O objetivo desta tese está orientado a estudar teoricamente a influência do meio (ou efeito de solvente) na fotofísica e nas propriedades dos estados eletrônicos excitados de sistemas moleculares. Nesta tese, primeiramente foi feito um estudo em fase gasosa da superfície de energia potencial do sistema molecular HSO2 e do efeito da energia rotacional na reação OH+SO. Na superfície de energia potencial foram caracterizadas um grande número de estruturas estacionárias e foi encontrado um estado de transição que liga a região mais energética da superfície com a menos energética. Em relação ao papel da energia rotacional na reação mencionada, foi realizado um estudo de trajetórias quase-clássicas, onde foi observado um decréscimo da reatividade com o aumento da energia rotacional total depositada nos reagentes. Posteriormente, foi estudado o efeito do solvente nas propriedades dos estados eletrônicos excitados e nos mecanismos de decaimento de três sistemas moleculares, acetona, 1-nitronaftaleno e daidzein. Na acetona, foi estudada a influência da polarização eletrônica do estado excitado n* provocada pelo solvente no deslocamento espectral da banda de fluorescência. A banda de emissão obtida em água mostra um deslocamento espectral muito pequeno em relação à fase gasosa, em concordância com as evidencias experimentais. Também foi observada pouca dependência do deslocamento espectral com o grau de polarização eletrônica desse estado excitado. O sistema molecular 1-nitronaftaleno foi estudado a fim de esclarecer a ultrarápida desativação eletrônica não fluorescente observada experimentalmente após a transição de absorção, assim como, caracterizar os espectros de absorção transitória também observados nos experimentos. Foi encontrado um intersystem crossing muito eficiente entre o primeiro estado excitado singleto e o segundo estado tripleto, que explica o decaimento não fluorescente deste sistema molecular. O modelo de decaimento proposto permite descrever corretamente os espectros de absorção transitória nos solventes metanol e etanol, através de transições de absorção dos estados eletrônicos tripletos. Finalmente, o sistema molecular daidzein foi estudado a fim de entender porque em solvente polar prótico, como a água, o sistema é fluorescente, mostrando um valor de Stokes shift consideravelmente grande e na presença de solvente polar aprótico, como a acetonitrila, não é observada fluorescência. Nesse sentido, foi estudada a evolução dos estados eletrônicos excitados, na presença dos solventes água e acetonitrila, após as transição de absorção. A topologia dos estados eletrônicos excitados é diferente para cada um dos solventes, em acetonitrila o sistema tem acesso a um intersystem crossing muito eficiente que permite o decaimento não fluorescente. Em água o panorama é diferente, neste caso, não é possível a ocorrência do intersystem crossing e o sistema decai por fluorescência para o estado fundamental. No estado eletrônico fluorescente é observada uma polarização eletrônica significativa que provoca o grande valor de Stokes shift observado experimentalmente.The photodynamics of molecular systems represents one of the most important topics of the molecular physical chemistry today. The knowledge of the excited electronic states properties has allowed the development of several important areas, such as the renewable energies, the photomedicine, fluorescent sensors, etc. The aim of this thesis is oriented to the theoretical study of the solvent effect on the photophysics and on the excited electronic states properties of molecular systems. In this thesis, it was initially studied the potential energy surface of the HSO2 molecular system in gas phase and the rotational energy effect on the reactivity of the OH+SO reaction. In the potential energy surface a large number of stationary structures were characterized and it was found a transition state which connects the highest energetic region to the lowest one. Regarding the role of rotational energy on the mentioned reaction, a quasi-classical trajectories study was performed, indicating a decrease in the reactivity when the total rotational energy deposited in the reactants is increased. Subsequently, it was studied the solvent effect on the excited electronic states and on the deactivation mechanisms of three molecular systems, acetone, 1-nitronaphthalene and daidzein. In the acetone molecular system, it was studied the influence of the electronic polarization, caused by the solvent, in the fluorescence spectral shift of the n* excited state. The emission band obtained in water shows a small spectral shift compared to the gas phase, in agreement with the experimental evidences. It was also observed a little dependence of the spectral shift with the degree of the excited state polarization. The 1-nitronaphthalene molecular system was studied to clarify the ultrafast non-fluorescent deactivation mechanism experimentally observed after the absorption transitions, as well as to characterize the transient absorption spectra also observed in the experiments. A very efficient intersystem crossing was found between the first singlet excited state and the second triplet state, which explains the nonfluorescent decay of this molecular system. The proposed deactivation model allows properly describing the transient absorption spectra in methanol and ethanol solvents by absorption transitions from the triplet electronic states. Finally, the daidzein molecular system was studied to understand why in polar protic solvent, such as water, the system is fluorescent, showing a very large Stokes shift value and in polar aprotic solvent, such as acetonitrila, the fluorescence is not observed. In that sense, it was studied the evolution of the excited electronic states in water and in acetonitrile after the absorption transition. The topology of the excited electronic states is different for each solvent, in acetonitrile the system is accessible to a very efficient intersystem crossing that enables the non-fluorescent decay. In water the picture is different, the intersystem crossing is not possible to occur and the system decays by fluorescence to the ground electronic state. In the fluorescent state is observed a considerable electronic polarization that causes the so large Stokes shift value experimentally observed.
37
Xu, Zhuang. « PARTITIONING OF SOLVENT MOLECULES SURROUNGDING POLYMER CHIANS IN SOLVENT-SHIFTING PROCESS ». University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555690517286259.
38
Lima, Jennifer Dayana Rozendo de. « Interações do CS2 com solventes moleculares ». Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-18092015-110004/.
Résumé :
Neste trabalho realizou-se um estudo espectroscópico vibracional do dissulfeto de carbono, CS2, puro e em misturas binárias com diferentes solventes moleculares, a fim de investigar as interações soluto/soluto e soluto/solvente. Os solventes utilizados para esse estudo foram diclorometano (CH2Cl2), clorofórmio (CHCl3), clorofórmio deuterado (CDCl3), benzeno (C6H6) e tetracloreto de carbono (CCl4); e as técnicas utilizadas foram as espectroscopias Raman e infravermelho (IV). A análise das bandas Raman do CS2 que formam o dubleto de Fermi (v1-2v2) permite determinar uma série de valores empíricos, chamados de parâmetros de ressonância de Fermi, dentre os quais, o coeficiente de acoplamento de Fermi (W) foi o mais utilizado neste trabalho. Os diferentes valores de W nos diferentes meios são consequência das forças das interações intermoleculares existentes entre CS2/CS2 e CS2/solvente. Os experimentos demonstraram que os valores de W em todas as misturas binárias investigadas aumentam à medida que a fração molar de CS2 diminui. Isto sugere que quando o CS2 é solvatado por diferentes moléculas, há um aumento da anarmonicidade, dependendo do tipo de interação. A análise da banda atribuída ao modo de deformação angular do CS2, v2, realizada a partir dos espectros no infravermelho sugere que em misturas binárias existem dois regimes de solvatação na solução, uma referente às interações CS2/ CS2, onde as moléculas de CS2 estão preferencialmente solvatadas por moléculas de CS2 e outro regime de solvatação referente às interações CS2/solvente, onde CS2 está solvatado por moléculas do solvente em questão.In this work has performed a vibrational spectroscopic investigation of carbon disulphide, CS2, neat and in binary mixtures with different molecular solvents, aiming at understanding the solute/solute and solute/solvent interactions. The solvents considered for this study were dichloromethane (CH2Cl2), chloroform (CHCl3), deuterated chloroform (CDCl3), benzene (C6H6) and carbon tetrachloride (CCl4); and the techniques used were Raman and infrared (IR) spectroscopies. The analysis of the Raman bands that compose the Fermi doublet (v1-2v2) allows the determination of a series of empirical values, including the coefficient of Fermi coupling (W), used along this work. The different values of W within the different solvents are consequence of the intermolecular forces between CS2/CS2 and CS2/solvent. The experimental data showed that the W values in all investigated binary mixtures increase as the CS2 molar fraction decreases. It suggests that when CS2 is solvated by different molecules, there is an increase of the anarmonicity, depending on the type of the interaction. The analysis of the band assigned to the CS2 bending mode, v2, performed from infrared spectra, suggests that in the binary mixtures there are two solvation regimes in solution, one related to the CS2/CS2 interactions, where the CS2 molecule is preferentially solvated by CS2 molecules, and one where the CS2 is solvated by the respective solvent molecules.
39
ĐORĐEVIĆ, LUKA. « Tailoring Organic Matter : from Molecular Design to Functional Supramolecular Species ». Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908098.
Résumé :
Chemistry beyond the molecule, supramolecular chemistry, has become an essential tool in developing complex chemical systems by mastering intermolecular noncovalent forces. Supramolecular chemistry is considered a key step in the evolution of chemistry to an information science. By appropriate manipulation of noncovalent interactions, the information stored at the molecular level can operate through retrieval, transfer and processing at the supramolecular level. The work presented in this thesis aims at the design of programs, or molecular recognition patterns (hydrogen bonding, donor-acceptors and metal-ion coordination), that operate by spontaneous self-assembly into well-defined and complex supramolecular architectures. Appropriate encoding of the single subunits and processing give access to a variety of systems. Specifically, by integrating active components, functional supramolecular devices are easily accessible. Combination of components that operate with photons or electrons yields photoactive or electroactive devices capable of electron or energy exchange/transfer processes that paved the way to supramolecular photonics and electronics. Additionally, being intrinsically dynamic, supramolecular chemistry provides potential properties such as self-healing, error correction and sensitivity to external stimulus. Self-organization has offered a striking new and chemical approach to the bottom-up nanofabrication and top-down miniaturization approaches in nanoscience and technology, avoiding laborious implementation of physical procedures.
40
Ghosh, Nilanjan. « Structural and associational aspects of some dielectropolar liquid molecules in non polar solvents from relaxation phenomena ». Thesis, University of North Bengal, 2002. http://hdl.handle.net/123456789/670.
41
Adamovic, Ivana. « Solvation ! » Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/835373-NLtQXD/webviewable/.
Résumé :
19 Dec 2004.Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2009" Ivana Adamovic. 12/19/2004. Report is also available in paper and microfiche from NTIS.
42
Choi, Jong-Ho Okumura Mitchio Okumura Mitchio. « Infrared spectroscopy of molecular ions and ion-solvent clusters / ». Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-09252007-09111.
43
Cassiano, Marta Maria. « Dinâmica de Biomoléculas em Água : Simulações com Representação Explícita do Solvente ». Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-21022014-174534/.
Résumé :
O programa THOR de dinâmica e mecânica molecular foi aprimorado com a introdução de técnicas que permitem a modelagem de sistemas biomoleculares na presença do solvente representado explicitamente. Essas técnicas incluem o emprego de condições de contorno periódicas, raio de corte, potencial eletrostático modificado e método shake para vínculos de distância. Além disso, a técnica da lista de vizinhos foi implementada devido ao grande aumento no número de átomos do sistema, pela inclusão explícita do solvente. Alguns sistemas foram modelados e a influência do solvente sobre suas propriedades conformacionais foi analisada, respondendo às expectativas baseadas em previsões teóricas e evidências experimentais.The computational package THOR for molecular mechanic and dynamics simulation was improved by the introduction of techniques for modeling of biomolecular systems with explicit representation of solvent molecules. Those techniques include the application of periodic boundary conditions, the use of a cut-off sphere for the potential, with modifications in the electrostatic potential, and the utilization of the method shake to impose distance constraints. Furthermore, a neighbours list was implemented, due to the high number of atoms to be dealt with when the solvent is explicity represented. Simulations were performed on some systems of biological interest, and the influence of the solvent on their conformational properties was analysed. The results are in good agreement with theoretical previsions and experimental data.
44
Požar, Martina. « On the nature of structural fluctuations in complex liquids ». Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS269.
Résumé :
L'analyse de différents types de structuration, présents dans des liquides simples et complexes et leurs mélanges, a été réalisée en utilisant la méthode de la dynamique moléculaire. Les mélanges complexes ont au moins un composant associatif, tel que l'eau, les alcools (mono-ols et diols) et les amines. La structuration supra-moléculaire dans ces mélanges est détectée, décrite, quantifiée et liée aux interactions atome-atome entre les molécules. Ces systèmes ont des fluctuations aux comportements intéressants, comme le montrent les intégrales de Kirkwood-Buff. Leurs fonctions de corrélation se comportent d'une manière complexe, en fonction du composant, de la concentration et de la température. Le pré-pic aux petites valeurs de k dans les facteurs de structure site-site est défini comme une signature de la ségrégation en domaines dans ces mélanges. Une attention particulière est mise sur la structuration à longue portée, ce qui est une nouveauté compte tenu de la majorité des travaux dans le domaine de la physique des liquides. Cette thèse contribue à une meilleure compréhension des structures micro-hétérogènes dans les liquides moléculaires et permet d'établir des liens avec les hétérogénéités structurelles dans la matière molle et de la bio-matièreThe analysis of different types of structuring, present in simple and complex liquids and their mixtures, was done using the method of molecular dynamics. Complex mixtures have at least one associative component, such as water, alcohols (mono-ols and diols) and amines. The supra-molecular structuring in these mixtures is detected, described, quantified and connected with the atom-atom interactions is the molecules. These systems have interesting fluctuation behaviors, as shown through Kirkwood-Buff integrals. Their correlation functions behave in a complex way, depending on the component, concentration and temperature. The pre-peak at small k values in the site-site structure factor is defined as a signature of molecular domains in these mixtures. A special focus is placed on long-range structuring, which is a novelty considering the majority of the work in the field of the physics of liquids. This thesis contributes to a better understanding of micro-heterogeneous structures in molecular liquids, and gives new links to structural heterogeneities in soft and bio-matter
45
Coutinho, Kaline Rabelo. « Modelo discreto de solvente. Solvatocromismo no espectro de absorção molecular ». Universidade de São Paulo, 1997. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-22062012-154558/.
Résumé :
Um procedimento baseado no uso sequencial de simulação Monte Carlo e cálculos de Mecânica Quântica é proposto e usado para o tratamento de efeitos de solvente, com especial atenção parao sovatocromismo no espectro de absorção molecular. A ideia básica é realizar simulações clássicas com o método Monte Carlo para gerar estruturas supermoleculares do sistema em solução e em seguida tratar estas supermoléculas (soluto, solvente e suas interações) com cálculos quânticos. Um modelo totalmente discreto do solvente é utilizado e, portanto, o uso de meios dielétricos contínuos é dispensado. Neste procedimento, as supermoléculas são compostas por uma molécula do soluto rodeada pela primeira camada de solvatação definida através da função distribuição. Os efeitos de solvente são calculados usando médias configuracionais sobre estruturas supermoleculares descorrelacionadas obtidas através de análises estatísticas das simulações. Como aplicação, os deslocamentos espectrais da primeira banda de absorção do benzeno 1B2u(- *), devido a presença de diversos solventes, foram analisados e calculados. Boa concordância com os resultados experimentais foram obtidos.A approach based on the sequential use of Monte Carlo simulation and Quantum Mechanics is proposed and use for the treatment of solvent effects with special attention to solvatochromic shifts. The basic Idea is to perform a classical Monte Carlo simulation to generate supermolecular structures of the system, then to treat these supermolecules (solute, solvent and all its interaction) by quantum mechanics. This is a totally discrete modelo f the solvent that avoids the use of a dielectric continuum. In this approach, the supermolecules are composed by the solute molecule surrounded by the first solvation Shell as determined by the distribution function. The solvent effects are calculated using ensemble average over uncorrelated supermolecular structures obtained by statistical analysis. As na application, the spectral shifts of the 1B2u(- *) trnsition of benzene in different solvents are investigated. Good agreement with the experimental results are obtained.
46
Adam, Catherine. « Molecular balances for measuring non-covalent interactions in solution ». Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/16466.
Résumé :
Non-covalent interactions in solution are subject to modulation by surrounding solvent molecules. This thesis presents two experimental molecular balances that have been used to quantify solvent effects on non-covalent interactions, including electrostatic and dispersion interactions. The first chapter introduces literature where non-covalent interactions have been studied in a range of solvents, particularly those where the effects of aqueous or fluorous solvents have been investigated. These solvents are of particular interest as they both invoke solvophobic effects on organic molecules, but have differing chemical and physical properties. The second chapter describes the adaptation of the Wilcox molecular torsion balance to study interactions between organic and fluorinated carbon chains in a range of solvents. Solvent cohesion was found to be the principle force driving both the alkyl and fluorous chains together in aqueous solvents, where no contribution to the interaction energy arising from dispersion forces could be detected. In fluorous and polar organic solvents evidence was found for weak favourable dispersion interactions between the alkyl chains. In contrast dispersion forces between the chains were found to be disrupted by competitive van der Waals interactions with surrounding solvent molecules in apolar organic solvents. Association of the fluorous chains was found to be solely driven by solvent cohesion. The final chapter describes the design and synthesis of a novel synthetic molecular-balance framework and describes its application to simultaneously measure solvent and substituent effects on the position of conformational equilibria. Despite the simplicity of the model system, surprisingly complicated behaviour emerged from the interplay of conformational, intramolecular and solvent effects. Nonetheless, a large data set of experimental equilibrium constants was analysed using a simple solvent model, which was able to account for both the intuitive and more unusual patterns observed. A means of dissecting electrostatic and solvent effects to reveal pseudo gas-phase behaviour has resulted from the analysis of experimental data obtained in many solvents.
47
Varma, Pritam S. « Solvent induced NMR chemical shifts that arise from molecular encounters ». Thesis, Aston University, 1987. http://publications.aston.ac.uk/9729/.
Résumé :
Recently Homer and Percival have postulated that intermolecular van der Waals dispersion forces can be characterized by three mechanisms. The first arises via the mean square reaction field < R1; 2> due to the transient dipole of a particular solute molecule that is considered situated in a cavity surrounded by solvent molecules; this was characterized by an extended Onsager approach. The second stems from the extra cavity mean square reaction field < R2; 2> of the near neighbour solvent molecules. The third originates from square field electric fields E2BI due to a newly characterized effect in which solute atoms are `buffeted' by the peripheral atoms of adjacent solvent molecules. The present work concerns more detailed studies of the buffeting screening, which is governed by sterically controlled parameter (2T - T)2, where and are geometric structural parameters. The original approach is used to characterise the buffeting shifts induced by large solvent molecules and the approach is found to be inadequate. Consequently, improved methods of calculating and are reported. Using the improved approach it is shown that buffeting is dependent on the nature of the solvent as well as the nature of the solute molecule. Detailed investigation of the buffeting component of the van der Waals chemical shifts of selected solutes in a range of solvents containing either H or Cl as peripheral atoms have enabled the determination of a theoretical acceptable value for the classical screening coefficient B for protons. 1H and 13C resonance studies of tetraethylmethane and 1H, 13C and 29Si resonance studies of TMS have been used to support the original contention that three (< R1; 2> , < R2; 2> and E2BI) components of intermolecular van der Waals dispersion fields are required to characterise vdW chemical shifts.
48
Böes, Elvis Sidnei. « Estudo teórico da solvatação de ânions em solventes orgânicos ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2005. http://hdl.handle.net/10183/7236.
Résumé :
O presente trabalho relata a parametrização do modelo de contínuo IEF-PCM para o estudo da solvatação de ânions monovalentes em acetonitrila e N,N-dimetilformamida. Nós propomos duas metodologias de parametrização do modelo de contínuo polarizável para este estudo teórico. A primeira proposta é baseada unicamente no cálculo do termo eletrostático da energia livre e na equiparação deste termo com a energia livre de solvatação experimental. Na segunda proposta de metodologia, a parametrização do modelo de contínuo polarizável foi realizada com o auxílio das simulações de dinâmica molecular e dentro desta segunda proposta nós calculamos todos os termos que contribuem para a energia livre de solvatação, a energia de cavitação. a energia eletrostática e a energia de van der Waals. Com a aplicação da primeira metodologia, é obtido um erro médio absoluto de 2,1 kcal/mol nas energias de solvatação dos ânions em acetonitrila enquanto que o erro médio absoluto calculado para energias de solvatação dos ânions em N,N-dimetilformamida é 2,8 kcal/mol. A aplicação da segunda metodologia resulta num erro médio absoluto de 1,4 kcal/mol nas energias de solvatação dos ânions em acetonitrila e um erro médio absoluto de 1,2 kcal/mol nas energias de solvatação calculadas para os ânions em N,N-dimetilformamida. Estes resultados indicam que o modelo de contínuo polarizável IEF-PCM é adequado para o estudo dos efeitos termodinâmicos nas soluções de ânions nos solventes acetonitrila e N,N-dimetilformamida.
49
Youngleson, Jonathan Sinclair. « Molecular genetic characterization of two solvent pathway dehydrogenases from Clostridium Acetobutylicum ». Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/23245.
Résumé :
Clostridium acetobutylicum P262 is an endospore-forming Gram-positive anaerobic bacterium, which has been used for the industrial production of acetone and butanol from carbohydrate substrates. This study forms part of a wider research effort into the genetics and molecular biology of C. acetobutylicum, which has as an ultimate goal the commercial improvement, and a fundamental understanding of the ABE fermentation. The aim of this study was to isolate and characterize genes involved in solventogenesis. The cloning, expression and characterization of the terminal solventogenic butanol dehydrogenase gene ( adhl), and the central pathway β-hydroxybutyryl-CoA dehydrogenase gene (hbd), which form part of a but operon are described.
50
Harper, Heather. « Solvent Dependent Molecular Mechanics : A Case Study Using Type I Collagen ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5035.
Résumé :
Being the most abundant protein in the body, by mass, type I collagen provides the building blocks for tissues such as bone, extra-cellular matrix, tendons, cornea, etc[1-3]. The ability of a single protein to create structures with such various mechanical properties is not fully understood. Before one can engineer and assemble a complex tissue, such as cornea, the mechanisms underlying the formation and assembly, mechanical properties, and structure must be investigated and quantified. The work presented herein contains an extensive study of Type I collagen from the molecular to the tissue level.
The engineering of collagenous tissues that mimic the mechanical and optical properties of native human cornea have been performed by a number of groups[4-7]. In all of these studies, the corneal-mimicking tissues have been created using a number of methods including repeated flow casting. To date, the ability to create self-assembled corneal tissue has not been achieved. Understanding the mechanisms of formation of native cornea will not only bring us closer to achieving self-assembled transplantable corneal tissue but will also aid in the engineering of all collagenous tissues and other structures comprised of filamentous units.
Recently, the study of type I collagen has primarily focused on the tissue, fiber, and fibril scale[2, 8-21]. Grant, et al.[20] measured the elastic modulus of collagen fibrils in various solutions and found that by increasing ion concentration, in the solution around the fibril, the elastic modulus increased. The solution dependent behavior of the elastic modulus of collagen fibrils was measured but the cause of the dependence was unknown. Grant et al. state that due to the complex nature of the interactions between collagen fibrils and aqueous solutions, the exact cause of this effect is difficult to determine. Through work presented herein, not only do we show that this behavior is seen at the molecular level but also quantify the relationship between ionic concentration and molecular stiffness for a variety of ionic species.
Studies of collagen mechanics, on the molecular level, are brief[22-26]. The most prominent of these studies in recent years was performed by Sun, et al.[27] wherein a persistence length of 14.5nm, for human type I procollagen, was measured. The persistence length of the molecule, which is a measure of flexibility, is a highly debated topic with quoted values of 14.5nm[27], 57nm[28], 130nm[29], 175nm[30], 308nm[31], and 544nm[32]. The broad range of values indicates that the flexibility of the collagen molecule is a complex question.
It became apparent that the disagreement of the persistence length of molecular collagen in the literature may be due to the use of different ionic solutions. To address this, an initial atomic force microscope, AFM, study of the persistence length of molecular collagen diluted in DI water and two ionic solutions was conducted. This study showed that there is a strong solution dependence to the flexibility of the molecule. The ionic solutions presented molecules with a large persistence length, a straightened configuration, while the DI water dilution resulted in a persistence length that was a factor of 10 smaller.
Because two different complex ionic solutions in the initial study showed different persistence lengths, an evaluation of the effect of each individual salt was performed. To elucidate the effects of individual ionic species on the conformations and persistence length of Type I collagen varying concentration of monovalent and divalent salts with different cations and anions were tested. It was found that increasing ionic concentration for all species types resulted in a higher persistence length but the rate of change in persistence length as a function of concentration is unique to each species.
In 2002 Leikina, et at.[33] suggested that Type I molecular collagen is unstable at body temperature using differential scanning calorimetry. To examine these results, an AFM study was performed that imaged the collagen molecules after being held at body temperature for varying times. The density of molecules deposited onto mica, above a 200nm length cutoff, was calculated and it shows that the number of molecules above 200nm in length decreases with increasing incubation time.
These environmental studies were performed with an aim to understanding the role of environment in creating a corneal mimicking tissue. Currently, the most promising method of collagen membrane fabrication for corneal replacement was developed by Tanaka, et al.[4]. This unique repeated flow casting method allows for the manufacturing of transparent collagen membranes with controllable thickness and fibrillar alignment. Using the repeated flow casting technique, orthogonally oriented collagen membranes were created and their optical properties were measured using the Generalized High Accuracy Universal Polarimeter, G-HAUP. When engineering a tissue for the eye, the optical properties of the tissue are of the utmost importance. Appropriately for corneal tissues, the measurements for linear birefringence and linear dichroism were negligible.
It was clear, from the literature, that a fundamental understanding of molecular type I collagen was not available. In this work, the mechanical properties and environmentally sensitive behavior of bovine dermal type I molecular collagen is studied. The exploration into the unique behavior of these systems begins with documenting the rich ionic species and concentration dependent flexibility of molecular type I collagen and the temperature dependence on the stability of the molecule is tested. The study concludes with the construction of corneal mimicking tissues using the repeated flow casting method and measuring the complex optical properties of these tissues.