Dissertations / Theses on the topic 'Water dimer'

A água, conhecida como solvente universal, participa da maioria das reações químicas e composições biológicas, tem importância vital em nosso planeta, tornando a vida como conhecemos inconcebível sem a sua presença. Tais propriedades advêm da forma como as moléculas interagem entre si, e a principal ligação química existente é a ligação de hidrogênio. Portanto, compreender como ela acontece e ser capaz de manipulá-la pode ser considerada uma importante técnica na busca de novos comportamentos. Esta dissertação visa compreender como o campo elétrico nas suas variantes: direção, sentido e intensidade podem afetar a água. Sendo tal estudo realizado através de cálculos utilizando métodos de química quântica: Teoria do Funcional da Densidade e a Teoria de Perturbação Moller-Plesset de segunda ordem. Como resultado obteve-se que quando o campo elétrico é aplicado em uma direção e sentido fora do plano da ligação de hidrogênio, a estrutura inicial tende a se rearranjar produzindo uma estrutura mais fracamente ligada do que a ordinária. Quando aplicamos o campo no plano da ligação de hidrogênio, temos resultados mais pronunciados, sendo que, se o sentido for : Doador -> Receptor a estrutura resultante estará mais fracamente ligada e se o sentido for Receptor -> Doador a estrutura produzida estará mais fortemente ligada. Os resultados obtidos mostram também que tais mudanças acontecem principalmente devido a alterações eletrostáticas, como mudança na densidade de carga da ligação de hidrogênio. Também confirmou-se um ponto crítico no campo 0,15 V/Å, como sugerido na literatura. Esta singularidade foi atribuída neste trabalho à uma transição estrutural. O campo também modificou a importância das interações secundárias, principalmente entre os átomos de oxigênio, e ao desligá-lo, o sistema tende a voltar ao estado inicial.
The water is know as the universal solvent, part of most chemical reactions and biological compositions, it is vitally important to our planet, making life as we know it inconceivable without its presence. These properties arise from how the molecules interact, and the main existing chemical link is the hydrogen bond. Therefore, to understand how this happens and be able to manipulate it can be considered an important technique in the search for new behaviors. Thus, this paper aims to understand how the electric field in its variants: direction, sense and intensity can affect the water. This study is undertaken through calculations using quantum chemistry methods: Density Functional Theory and Moller-Plesset Perturbation Theory to Second Order. As a result was found that when the electric field is applied in direction and sense out of the plane of the hydrogen bond, the initial structure tends to rearrange itself to produce a more loosely bound than the ordinary. When the electric field is applied in the hydrogen bond plane, the have results obtained are more pronounced. Sense is: Donor -> Receiver initial structure will be more loosely connected and that when the sense is Receiver -> Donor initial structure will be tightly linked. Our results also show that such changes occur mainly due to electrostatic changes, mainly in the change in the charge density of hydrogen bond. It was also confirmed a critical point in the field 0, 15 V / Å, as suggested by Vegiri. This was attributed to a structural transition. The field also changed the importance of secondary interactions, especially between the oxygen atoms. And when the field is shutdown the system tends back to its to initial structure.

We have used ab initio computational simulation techniques to investigate both intra- and intermolecular interactions in a novel family of ionic organophosphonate molecular crystals. We have examined the influence of various numerical approximations on the computed geometry and binding energies of a selection of well-characterised hydrogen bonded systems. It was found that numerical basis sets provided the efficiency required to study the large hydrogen bonded dimer anions present in the organophosphonate system, while also producing accurate geometries and binding energies. We then calculated the relaxed structures and binding energies of phenylphosphonic acid dimer in the two arrangements in which it is present in the bulk crystal. The computed geometries were in excellent agreement with the experimental structures and the binding energies were consistent with those found for other ionic hydrogen bonded systems. Electron density maps were used to gain insight into the nature of the hydrogen bonding interaction between phenylphosphonic acid dimers. We also examined the effect of aromatic ring substituents on the geometry and energetics of the hydrogen bonding interaction. The nitro-substituted dimer was predicted to have a stronger binding energy than its unsubstituted parent while the methyl-substituted dimer was predicted to have a similar binding energy to its unsubstituted parent. An analysis of crystal field effects showed that the structure of the phenylphosphonic acid dimers in the organophosphonates is a complex product of competing intra- and intermolecular forces and crystal field effects. Cooperative effects in the organophosphonate system were also investigated and it was found that the interactions were mostly one-body (local) in nature. We have examined the intramolecular charge-transfer interaction between copper-halogen cations in the organophosphonate materials. The origin of geometric differences between the Cu(I) starting material and Cu(II) product cations was attributed to the electronic configuration of the Cu ion, not crystal field effects. To gain further insight into the difference in electronic structure between the starting material and product, we attempted to simulate the step-by-step dissociation of the [CuI]+ system. Although this investigation was not successful, we were able to expose some of the pitfalls of simulating dissociating odd-electron systems. We also analysed and compared the charge-transfer interaction in the chloro-, bromo- and iodo-forms of the organophosphonate family. The charge-transfer interaction was predicted to increase on going from the chloro- to the iodo-form, consistent with solid-state UV-visible data. Finally, we used the highly accurate Quantum Monte Carlo (QMC) method to investigate the hydrogen bonding interaction in water dimer and to calculate the dissociation energy. The accuracy of the experimental estimate for the dissociation energy has recently been questioned and an alternative value has been put forward. Our results lend support to the validity of the alternative value and are also in excellent agreement with those from other high-level calculations. Our results also indicate that QMC techniques are a promising alternative to traditional wavefunction techniques in situations where both high accuracy and efficiency are important.

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xii, 88 p.; also includes graphics (some col.). Includes bibliographical references (p. 83-88). Available online via OhioLINK's ETD Center

Au cours de ces travaux de thèse, la synthèse de BODIPYs émettant dans le rouge et le proche infrarouge a été réalisée. Un premier travail d'extension de la conjugaison électronique (soit par introduction de groupements aromatiques sur le corps du BODIPY, soit par dimérisation) a permis d'atteindre les basses énergies du spectre électromagnétique. La validation d'une méthode de synthèse de BODIPYs à l'aide d'orthoesters a permis une mise en oeuvre aisée et une nette amélioration de leurs rendements. Parmi les fluorophores obtenus, les dithiényl-BODIPYs émettant dans la fenêtre thérapeutique (650-900 nm) présentent des propriétés optiques et électrochimiques intéressantes. Ils ont été utilisés pour des applications dans le domaine biologique. Après leur solubilisation dans les milieux aqueux par introduction de groupements ammoniums, la détection d'un acide aminé, la cystéine, a pu être réalisée par spectroscopies d'absorption et de fluorescence mettant en évidence un système ratiométrique. De plus, le marquage d'une protéine modèle, le sérum d'albumine bovine, permet d'envisager l'utilisation de ce type de BODIPYs pour l'imagerie biologique grâce à un rendement quantique de fluorescence élevé en milieu physiologique.

Chimie dynamique: reconnaissance de nucléobases par des récepteurs synthétiques et isomérie cis-trans d'hydrazones acylées.Ce travail traite du développement des systèmes moléculaires qui peuvent s'adapter à l'addition de substances qui agissent comme un gabarit. Cette approche permet d'isoler une espèce majeure à partir d'un mélange de composés par le biais de la chimie combinatoire dynamique (CCD). La première partie de ma thèse de doctorat inclus l'utilisation d'un ADN simple brin (ADNsb) comme un gabarit pour le transfert d'information par auto-assemblage de récepteurs sans avoir besoin d'enzyme. De nouveaux récepteurs de l'adénine et de la guanine (pinces A et G) solubles dans l'eau ont été conçues dans ce but. Une approche utilisant la résonance magnétique nucléaire (RMN) a été utilisée pour déterminer l'affinité de liaison comme preuve d'une reconnaissance spécifique et efficace. Une évaluation dans l'eau par dichroïsme circulaire (CD) et mesure de la température de fusion par UV (Tm) a été réalisée. Cela a permis de tester respectivement la capacité d'auto-assemblage entre les pinces et un modèle ADNsb, et la force du processus de coopérativité. La deuxième partie de ce travail est axée sur le tri spontanné de motifs pyridine acylhydrazone et sur les configurations intéressantes qu'ils adoptent. Nous avons étudié la synthèse d'une série de motifs pyridine acylhydrazone: dimère, trimères et pentamères. Des études RMN ont permis d'évaluer les changements dans l'équilibre configurationnel cis / trans de ces systèmes dynamiques. Les études ont montré que l'équilibre attendu est biaise la cis acylhydrazone pyridine isomère a été observée par diffraction des rayons X
Dynamic chemistry: nucleobase recognition by synthetic receptors and cis-trans acylhydrazone isomerism. This work deals with the development of molecular systems which can adapt upon the addition of substances that act as templates. This approach enables one major species to be identified from a mixture of compounds through the use of dynamic combinatorial chemistry (DCC). The first part of my PhD included the use of a single stranded DNA (ssDNA) as a template for information transfer via the self-assembly of receptors without the need for enzymes. New water soluble adenine and guanine receptors (A and G clamps) were designed and synthesised for this purpose. Nuclear magnetic resonance (NMR) titration studies were carried out to calculate the binding affinity and as a proof of specific and efficient recognition. An assessment in water via circular dichroism (CD) and UV temperature melting (Tm) studies was carried out. This tested the ability for self-assembly between the clamps and a ssDNA template and the strength of the cooperative process respectively. The second part of my PhD focused on the self-sorting of acylhydrazone pyridine motifs and the interesting configurations they adopt. The feasibility to synthesise these acylhydrazone pyridine motifs (dimer, trimers and pentamers) was investigated. X-ray and NMR studies showed that the equilibrium was found to be biased in an unusual way, and the cis acylhydrazone pyridine isomer was observed

碩士
國立臺灣大學
物理研究所
101
The reason why many exchange correlation functionals fail to give correct binding energies for the hemibonding structures of the ionized water clusters can be traced back to the dissociation behaviors of the hemibonded systems predicted by the exchange correlation functionals, since nearly most of the exchange-correlation functionals cannot predict that the hemibonded structure of the water dimer radical cation will dissociate into H2O and H2O+. Thus, the definition of the binding energies is unfair somehow: Although the previous suggested functionals such as BH&HLYP and MPW1K can give accurate equilibrium binding energies of the hemibonding structure, they fail to predict the correct dissociation limits. This will result in a potential curve which is too shallow. Thus, the hemibonded structure calculated by those functionals is much easier to dissociate than it actually should be. Therefore we propose three different criteria to reexamine the water dimer radi-cal cation: (i) The binding energies, (ii) the relative energies between the conformers of the ionized water dimer and (iii) the dissociation behaviors predicted by various exchange correlation functionals. We find that the functional which behaves well all over these three criteria is the wB97X-2 functional. Reasons that LC hybrid functionals generally work better than conventional density functionals for hemibonded systems is also explained in this work.

Thesis (M.S.)--University of Notre Dame, 2004.
Thesis directed by Marya Lieberman for the Department of Chemistry and Biochemistry. "April 2004." Includes bibliographical references (leaves 33-34).

碩士
真理大學
休閒遊憩事業學系碩士班
105
Scuba diving is one of the fastest growing activities in the world now, although the diving certificated population grows year by year, but receiving advanced education is less. The purpose of diving education is to hope that divers will continue to carry out diving activities and receive advanced education and dive everywhere after obtaining a license. And the reasons for continuing to engage in activities are to be interest, fun and other intrinsic motivation to support the individual to participate in the driving force behind the activities. The study was conducted in an interview manner to understand the motivations and constraints that divers continued to receive diving education and continued recreational diving activities. The results showed that the incentive for open water divers to learn continually should be fun and interesting in the process. The instructor must be solid in teaching so that the learning divers feel comfortable and skillful. The dive centers and coaches should hold regular courses and activities to provide more choice of open-warter divers and time arrangements to attract them to continue diving and learning. When diving costs are set, the dive center and coach must measure a reasonable price, so that consumers can accept, while with the promotional program to increase learning will. Second, build a community network to contact divers to share different diving experiences and travel information. Teaching in accordance with standards should befollowed, so that the openwater diver learning process will be safe and complete. According to Crawford and Godbey (1987), constraints is divided into individual internal constraint (psychological fear, physical fear), interpersonal comstraint (lack of peers) and structural constraint (work and work factors, traffic away, money worries, distrust coaches and Lack of good learning quality). According to the findings of the study, it is suggested that: 1. The dive center can carry out the renovation project and adding the II innovative and interesting thinking to the diver's learning effect and safety. 2. Future studies can increase the training process and follow-up diving motivations. 3. The dive centers and instructors can pay more attention to the needs of openwater divers, timely provision of related services.

Microwave and far-infrared high-resolution spectroscopies have been used to investigate the vibrational, rotational, and tunneling dynamics of water-containing, hydrogenbonded dimers, towards the goal of converting the recorded spectra into intermolecular potential energy surfaces (IPSs). Such intermolecular interactions are the basis for much of biological structure and function, as well as reaction and solution dynamics, and a comprehensive set of key IPSs can form the basis set for molecular modeling of these complex phenomena. Specifically studied in this work are the following dimers and some of their isotopomers: N_2•••H_2O, OC•••H_2O, H_3N•••H_2O, CH_3OH•••H_2O. These dimers constitute a series of increasing binding energy, dynamical complexity, and chemical and biological importance.

The dimers of water with isoelectronic N_2 and CO are treated jointly because of their similar properties and level of study. The b-type K = 0 → 1 rotational spectra for N_2•••H_2O and OC•••H_2O, as well as isotopomers containing HOD, D_2O, and ^(13)CO, were recorded between 325 and 661 GHz and measurements were also extended for the a-type spectra of the N_2•••H_2O and OC•••H_2O isotopomers. Each rotational transition was split by the effects of large-amplitude tunneling of the hydrogen and nitrogen nuclei, and the number of tunneling components corresponded with that predicted from PI theory. After the effects of tunneling had been removed from the rotational constants, the structures of the two different complexes were fit to the rotational moments of inertia. These structures correspond to a nearly linear hydrogen bond and alignment of heavy atoms. The tunneling selection rules for OC•••H_2O were confirmed to be "top-to-bottom, bottom-to-top," and the tunneling splittings were obtained from the difference in the A_(eff) rotational constants. Using two- and three-term Fourier expansions, the one-dimensional tunneling coordinate was fit to the tunneling splittings for OC•••H_2O and OC•••D_2O. Ab initio surfaces are used both to visualize the tunneling modes and as a basis for normal mode analyses. A reasonable and justified normal mode separation is presented, with the five intermolecular degrees of freedom separated into geared and anti-geared in-plane and out-of-plane motions of the the subunits as well as the intermolecular stretch. Finally, partial VRT spectra for both complexes recorded between 42 and 53 cm^(-1) are presented and preliminarily assigned to the in-plane geared motion.

Microwave and far-infrared spectra of the H_3N•••H_2O dimer were recorded from 36 to 86 GHz and 520 to 800 GHz. The a-type pure rotational microwave data extend the previous m = 0,K = 0 A-symmetry manifold measurements of Herbine and Dyke [J. Chem. Phys. 83, 3768 (1980)] to higher frequency and also provide an additional set of microwave transitions in the mK = +1 E symmetry manifold. Two sets of five b-type rotation-tunneling bands one set shifted from the other by an approximately constant 113 MHz, were observed in the far-infrared. The splitting into two sets arises from water tunneling, while the overall band structure is due to internal rotation of the ammonia top. Non-linear least-squares fits to an internal rotor Hamiltonian provided rotational constants, and an estimation of V_3 = 10.5 ±5.0 cm^(-1) for the barrier height to internal rotation for the NH3 monomer. A non-linear equilibrium hydrogen bond is most consistent with the vibrationally averaged rotational constants; with the angle cos^(-1) [〈λ_z〉] determined from 〈λ_z〉, the projection of the ammonia's angular momentum onto the framework. The water tunneling splitting and observed selection rules place constraints on the barrier height for proton exchange of the water as well as the most feasible water tunneling path along the intermolecular potential energy surface. An estimated barrier of 700 cm^(-1) was derived for the water tunneling motion about its c axis.

Finally, microwave spectra of CH_3OH•••H-2O and CH_3OD•••D_2O were recorded between 20 and 60 GHz, along with data from our collaborators at the National Institute for Science and Technology for CH_3OH•••H_2O, ^(13)CH_3OH•••H_2O, CH_3OH•••DOH, CD_3OH•••H_2O, and CH_3OD•••D_2O between 7 and 24 GHz. Because CH_3OH and H_2O are both capable of accepting and donating hydrogen bonds, there existed some question as to which donor-acceptor pairing of the molecules was the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions from the methyl torsional A state were assigned for the various isotopomers. The fit of the structure to the rotational constants gave unambiguous confirmation that the only conformation observed in the supersonically cooled molecular beams corresponded to a water-donor, methanol-acceptor complex.