Thèses : « Achiral and chiral »

1

Saeed, Mansoor. « Novel achiral and chiral derivatising reagents for indirect chiral resolution ». Thesis, University of Sunderland, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260828.

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2

Carlsson, Björn. « From achiral to chiral analysis of citalopram ». Doctoral thesis, Linköpings universitet, Klinisk farmakologi, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5217.

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Within the field of depression the “monoamine hypothesis” has been the leading theory to explain the biological basis of depression. This theory proposes that the biological basis of depression is due to a deficiency in one or more of three key neurotransmitter systems, namely noradrenaline, dopamine and serotonin which are thought to mediate the therapeutic actions of virtually every known antidepressant agent. Citalopram is a selective serotonin-reuptake inhibitor (SSRI) used for the treatment of depression and anxiety disorders. Citalopram is a racemic compound, in other words composed of a 50:50 mixture of two enantiomers (S-(+)-citalopram and R-(-)-citalopram) and with one of the enantiomers (S-(+)-citalopram) accounting for the inhibitory effect. At the time of introduction of citalopram the physician needed a therapeutic drug monitoring service to identify patients with interactions, compliance problems and for handling questions concerning polymorphic enzymes and drug metabolism. An achiral analytical separation method based on solid-phase extraction followed by high-performance liquid chromatography (HPLC) was developed for routine therapeutic drug monitoring (TDM) of citalopram and its two main demethylated metabolites. As the data available on citalopram were from achiral concentration determinations and to be able to further investigate citalopram enantiomers effects and distribution, a chiral method for separation of the enantiomers of citalopram and its demethylated metabolites was established. The advances within chiral separation techniques have made measurement of the concentrations of the individual enantiomers in biological fluids possible. The process behind enantioselective separation is however not fully understood and the mechanism behind the separation can be further scrutinized by the use of multivariate methods. A study of the optimization and characterization of the separation of the enantiomers of citalopram, desmethylcitalopram and didesmethylcitalopram on an acetylated ß-cyclodextrin column, by use of two different chemometric programs - response surface modelling and sequential optimization was performed. Sequential optimization can be a quicker mean of optimizing a chromatographic separation; response surface modelling, in addition to enabling optimization of the chromatographic process, also serves as a tool for learning more about the separation mechanism. Studies of the antidepressant effect and pharmacokinetics of citalopram have been performed in adults, but the effects on children and adolescents have only been studied to a minor extent, despite the increasing use of citalopram in these age groups. A study was initiated to investigate adolescents treated for depression, with respect to the steady-state plasma concentrations of the enantiomers of citalopram and its demethylated metabolites. The ratios between the S- and R-enantiomers of citalopram and didesmethylcitalopram were in agreement with studies involving older patients. The concentrations of the S-(+)- and R-(-) enantiomers of citalopram and desmethylcitalopram were also in agreement with values from earlier studies. The results indicate that the use of oral contraceptives may have some influence on the metabolism of citalopram. This might be because of an interaction of the contraceptive hormones with the polymorphic CYP2C19 enzyme. Even though the SSRIs are considered less toxic compared with older monoamine-active drugs like the tricyclic/tetracyclic antidepressants, the risk of developing serious side effects such as ECG abnormalities and convulsions has been seen for citalopram, when larger doses have been ingested. Furthermore, fatal overdoses have been reported where citalopram alone was the cause of death. Data on the toxicity of each of the enantiomers in humans have not been reported and no data on blood levels of the enantiomers in cases of intoxication have been presented. An investigation was initiated on forensic autopsy cases where citalopram had been found at the routine screening and these cases were further analysed with enantioselective analysis to determine the blood concentrations of the enantiomers of citalopram and metabolites. Furthermore the genotyping regarding the polymorphic enzymes CYP2D6 and CYP2C19 were performed. In 53 autopsy cases, we found increasing S/R ratios with increasing concentrations of citalopram. We found also that high citalopram S/R ratio were associated with high parent drug to metabolite ratio and may be an indicator of recent intake. Only 3.8 % were found to be poor metabolizers regarding CYP2D6 and for CYP2C19 no poor metabolizer was found. Enantioselective analysis of citalopram and its metabolites can provide valuable information about the time that has elapsed between intake and death. Genotyping can be of help in specific cases but the possibility of pharmacokinetic interactions is apparently a far greater problem than genetic enzyme deficiency.
On the day of the public defence the status of article IV was: Submitted.

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3

Carlsson, Björn. « From achiral to chiral analysis of citalopram / ». Linköping : Univ, 2003. http://www.ep.liu.se/diss/med/07/93/index.html.

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4

Gutierrez, Cuevas Karla Guadalupe Gutierrez. « LIQUID CRYSTALLINE NANOCOMPOSITES : FROM ACHIRAL TO CHIRAL SYSTEMS ». Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1500998489695319.

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5

Haldar, Sripada. « Investigation on some achiral and chiral mesogemic systems by different experimental techniques ». Thesis, University of North Bengal, 2013. http://hdl.handle.net/123456789/1481.

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Carter-Finch, Annabelle Suzanne. « The investigation of achiral and chiral separations by capillary electrochromatography ». Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327053.

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7

Horcajada, Roberto. « Radical-anions of chiral and achiral 1,6-diaminophenazine derivatives as electrogenerated bases ». Thesis, Queen Mary, University of London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401860.

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8

Fergusson, Kenneth Matthew. « The synthesis and properties of achiral and chiral bent-core liquid crystals ». Thesis, University of Hull, 2008. http://hydra.hull.ac.uk/resources/hull:5810.

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The area of liquid crystals has received substantial research effort over the last century, particularly when the beneficial applications such as Liquid Crystal Displays (LCDs) were realised and developed. For the majority of this time, it has been considered that a linear molecular shape is required in order to generate a mesomorphic phase. It was therefore of particular interest and excitement when, in 1996, it was shown that a 'banana-shaped' molecular architecture could exhibit a new class of liquid crystalline phase. Additionally it was found that these new mesophases exhibited chiral domains, leading to electrooptical switching properties, despite the constituent molecules being achiral. Unsurprisingly, these observations have led to a vast frontier of research in the area of 'banana-shaped' and 'bentcore' systems over the past decade and many interesting properties relating to such systems have been reported. The work contained within this thesis investigates two areas of bent-core liquid crystals. Firstly, the introduction of fluoro-substituents to the bent-core of an achiral banana-shaped system has been assessed, in terms of both position, and number of substituents. The resultant mesomorphic properties of these compounds have shown that there is a very delicate boundary between banana, and 'conventional' mesomorphism, relating to subtle changes in molecular structure. Appropriately positioned fluoro-substituents upon the bent-core generate a more linear conformation, facilitating the generation of nematic phases. Possible reasoning for this observation has been discussed. Secondly, the effect of introducing a bent-core to a conventional calamitic structure, and the addition of fluoro-substituents, has been examined. Whilst a variation of this nature to the majority of calamitic molecular structures would have a severely detrimental effect upon the resultant mesophase morphology, it has been shown that this is not always the case and indeed the addition of fluoro-substituents is shown to enhance the mesomorphic stability of the smectic A phase.

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Morrison, Calum M. « Chiral and achiral analysis of benzodiazepine and anti-anginal drugs in forensic toxicology ». Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321443.

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10

Kiakos, K. « Molecular and cellular pharmacology of novel chiral and achiral CC-1065/duocarmycin analogues ». Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444902/.

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CC-1065 and the duocarmycins are highly potent anticancer agents, exerting their biological activity through covalently reacting with adenine-N3 in the minor groove of AT-rich sequences. The alkylation properties and cytotoxicity of a series of novel chiral analogues are reported in this thesis. Structural modifications of established pharmacophores resulting in novel alkylating functionalities as well as variations of the DNA binding domain were introduced in the analogues considered, The sequence specificity of these compounds was assessed by a Taq Polymerase stop assay, identifying the sites of covalent modification on plasmid DNA and the purine-N3 adducts probed by a thermally-induced strand cleavage assay. The cytotoxic potency of the analogues was determined against human, chronic myeloid leukemia, K562, cells, using a MTT based growth inhibition assay. The importance of the chiral centre present in the natural products was subsequently investigated with a series of achiral analogues. The studies established that the chiral centre is not absolutely required for DNA interaction and cytotoxicity. This finding offers the possibility of a new platform for the design of novel, active CC-1065/duocarmycin analogues. A key chiral and an achiral analogue were selected for DNA repair studies. The sensitivity of yeast mutants deficient in specific DNA repair pathways was assessed in order to delineate the mechanisms involved in the repair of the relevant adenine-N3 adducts. Nucleotide excision repair (NER) and post replication repair mutants were the most sensitive to the two analogues. Single-strand ligation PCR was employed to follow the induction and repair of the lesions at nucleotide resolution. Adduct elimination of both agents was by transcription-coupled NER, and dependent upon functional Radl8. Finally, the involvement of NER as the predominant excision pathway was further confirmed in mammalian DNA repair mutant cells.

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11

Lin, Haiping. « Simulations of chiral ordering of achiral molecules by Density Functional Theory and Monte Carlo ». Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490915.

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The self-organization of organic molecules on metal surfaces can play a crucial role in various subjects of science such as electrochemistry and heterogeneous catalysis. However, their practical applications have been suffering from lack of atomic scale understanding of the ordering behavior. Theoretically, however, the description of the self-assembly processes has been limited by the inability of microscopic models to account for the interplay of all elementary processes at realistic temperatures and pressures. In this work, we take the succinate molecules and Cu(1IO) surface as a model system to study the nature of the asymmetric self-assembly behavior of the achiral adsorbates on an achiral surface. In the first step, density-functional theory (DFT) is used to accurately characterize the molecule-surface system on the microscopic level. The obtained energetics is then employed to parameterize a lattice gas Hamiltonian, which subsequently allows to address the mesoscopic ordering behavior at finite temperatures by means of ~v1onte Carlo simulations. Two well-defined ordered structures have appeared in the rvlonte Carlo simulations. The (5 0, 3 2) structure has been confirmed to be the ground state configuration by direct DFT calculations. This structure has not been reported before and it can be the ordering configuration observed in some STrvI experiments. By summing up all the calculations, the nature of the self-organization behavior of succinate molecules on Cu(llO) is attributed to the indirect lateral interactions of the adsorbates. This result may provide a new understanding of designing two dimensional periodic architectures on metal surfaces. Supplied by The British Library - 'The world's knowledge'

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12

Ronsin, Gaël. « Acylation d'un alcool achiral et d'un thiol chiral par le méthylphénylcétène : catalyse et sélectivité ». Rouen, 1999. http://www.theses.fr/1999ROUES025.

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Les cétènes prochiraux dérivés des acides 2-arylpropioniques sont des molécules très réactives et peu valorisées en synthèse énantiosélective. Notre étude présente les résultats en addition énantiosélective du méthanol sur le méthylphénylcétène. Différentes possibilités de catalyse asymétrique par des agents chiraux ont été testées, les dérivés d'alcaloïdes du quinquina et principalement les esters de quinine permettant d'induire les meilleures sélectivités. La température et l'ordre d'introduction des réactifs influencent la sélectivité de la réaction. Ainsi, le 2-phénylpropanoate de méthyle est obtenu avec un excès énantiomérique allant jusqu'à 86 %. Une analyse des données suivant le principe d'isoinversion est présentée, la température d'isoinversion du système étudié étant de 214 K. L'étude structure - énantiosélectivité que nous avons menée a permis de mettre en évidence le rôle joué par la stéréochimie du carbone 9 de la quinine et la nature des substituants de l'oxygène porté par ce carbone. Cependant aucune relation entre sélectivité et valeur de la constante de Hammett n'a été montré. D'autre part, l'addition asymétrique d'un thiol chiral dérivé du glucose sur le méthylphénylcétène permet d'accéder, après hydrolyse, au 2-phénylpropanoate de méthyle avec des excès énantiomériques atteignant 95 %. La sélectivité de la réaction dépend fortement de la nature de la base utilisée. Par analogie avec les résultats obtenus lors de l'addition du DAG, un même mécanisme de catalyse basique géneralisée est proposé. Le rôle de l'oxygène porté par le carbone 5 du glucose dans le processus de sélection a pu être mis en évidence.

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13

Sinha, Debashis. « X-Ray, Dielectric, and electro-optic studies on fluorinated achiral and chiral liquid crystals ». Thesis, University of North Bengal, 2015. http://hdl.handle.net/123456789/2742.

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14

Sayad, D., C. Zebiri, Issa T. Elfergani, Jonathan Rodriguez, Raed A. Abd-Alhameed et F. Benabdelaziz. « Analysis of Chiral and Achiral Medium Based Coplanar Waveguide Using Improved Full Generalized Exponential Matrix Technique ». RadioEngineering, 2020. http://hdl.handle.net/10454/18304.

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Yes
In this work, an analytical study of the electromagnetic propagation in a complex medium-based suspended three-layer coplanar waveguide (CPW) is carried out. The study aims at a numerical calculation of the dominant hybrid mode complex propagation constant in the CPW printed on a bianisotropic substrate. The herein considered bianisotropy is characterized by full 3×3 tensors of permittivity, permeability and magnetoelectric parameters. The study is based on the numerical derivation of the Green's functions of such a complex medium in the spectral domain. The study is carried out using the Full Generalized Exponential Matrix Technique based on matrix- shaped compact mathematical formulations. The Spectral Method of Moments (SMoM) and the Galerkin's procedure are used to solve the resulting homogeneous system of equations. The effect of the chiral and achiral bianisotropy on the complex propagation constant is particularly investigated. Goo d agreements with available data for an anisotropic-medium-based suspended CPW structure are achieved. Various cases of chiral and achiral bianisotropy have been investigated, and particularly, the effect on the dispersion characteristics is presented and compared with cases of isotropic and bianisotropic Tellegen media.
FCT/MEC through national funds and when applicable co-financed by the ERDF, under the PT2020 Partnership Agreement under the UID/EEA/50008/2019 project.

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15

Zheng, Jie. « Development of Chiral/Achiral Analysis Methods using Capillary Electrochromatography and Capillary Electrochromatography Coupled to Mass Spectrometry ». Digital Archive @ GSU, 2006. http://digitalarchive.gsu.edu/chemistry_diss/6.

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The research presented in this dissertation involves the development of chiral and achiral analysis using capillary electrochromatography (CEC) and CEC coupled to mass spectrometry (CEC-MS). Chapter 1 briefly reviews CEC fundamentals and latest development on chiral CEC and CEC-MS. The CEC-UV enantioseparations for several acidic compounds are described in Chapter 2. The optimum resolutions for these acidic enantiomers are achieved in ion-suppression mode, i.e. with an acidic mobile phase. One of major drawback in coupling CEC with MS is the bubble formation at the column outlet end, resulting in irreproducible retention time and erratic baseline, or even current breakdown. By introducing internal tapered columns, the aforementioned limitations of CEC-MS are successfully overcome in Chapter 3. The CEC-MS enantioseparation of warfarin and coumachlor is carefully investigated and applied to quantify R- and S-warfarin in human plasma. For individual enantiomers, a concentration of 25 ng/mL is detectable. To further improve the robustness of CEC-MS column, a new procedure of fabricating internal tapered columns is reported in Chapter 4. These internal tapered columns demonstrate excellent ruggedness, low background noise, and good compatibility in reversed-phase and polar organic modes of CEC-MS. In chapter 5, the feasibility of using internal tapered columns packed with vancomycin chiral stationary phase (CSP) is explored for simultaneous enantioseparation of eight â-blockers using CEC-MS. After a careful optimization of the mobile phase composition, sheath liquid and spray chamber parameter, 15 out of 16 enantiomers could be simultaneously resolved with excellent efficiency and detection sensitivity. The synthesis and characterization of sulfated and sulfonated cellulose phenylcarbamate CSPs is described in Chapter 6. The use of these CSPs, especially the sulfonated one, significantly enhances the EOF profile and sample throughput but maintain high enantiomeric resolving power under various modes of CEC and CEC-MS. By combining CEC and atmospheric pressure photo-ionization (APPI) MS, Chapter 7 demonstrates the separation and detection of mono-methylated benzo[a]pyrene (MBAP) isomers with ~100 times enhancement on detection sensitivity than CEC-UV. In Appedix 2, monolithic columns are synthesized through photopolymerized sol-gel approach and utilized for CEC and CEC-APPI-MS of polyaromatic hydrocarbons, and alkyl phenyl ketones.

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16

Reilly, John. « A comparison of electrophoretic and chromatographic separation techniques for the determination of chiral and achiral impurities ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270880.

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17

Cao, Min. « Enantioselective Transformations Promoted by Cooperative Functions of an Achiral Lewis Acid and a Chiral Lewis Acid : ». Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109203.

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Thesis advisor: Masayuki Wasa
Thesis advisor: Amir H. Hoveyda
This dissertation describes the development of cooperative catalyst systems that contain an achiral Lewis acid and a chiral Lewis acid that may have overlapping functions but play their independent roles to promote enantioselective C–C bond formations. Chapter 1 provides a summary of recent advances made in the field of enantioselective cooperative catalysis that served as intellectual foundations for this dissertation research. As it will be discussed in the first chapter, key limitations of cooperative catalysis are: (1) undesirable catalyst deactivation which occurs due to acid/base complexation, (2) requirement for base sensitive pronucleophiles and acid sensitive electrophiles, and (3) poor reaction efficiency. In an effort to overcome these fundamental limitations, we have developed “frustrated” Lewis pair (FLP)-based catalyst systems that consist of potent and sterically encumbered Lewis acids used in pair with bulky N-containing Lewis bases. To demonstrate the potential of the novel FLP catalyst system, we describe our work involving the enantioselective Conia-ene-type cyclization (Chapter 2). In the subsequent chapter (Chapter 3), we discuss the application of the FLP catalysts for enantioselective β-amino C–H functionalization reactions
Thesis (PhD) — Boston College, 2021
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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18

Ichikawa, Yoshitaka. « Synthesis of Optically Active Helical Polyacetylenes through Rhodium/Chiral Diene-Catalyzed Asymmetric Polymerization of Achiral Monomers ». 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/142579.

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19

Barclay, Victoria K. H. « Development of LC-MS/MS Methods for the Analysis of Chiral and Achiral Pharmaceuticals and Metabolites in Aqueous Environmental Matrices ». Doctoral thesis, Uppsala universitet, Avdelningen för analytisk farmaceutisk kemi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-171550.

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This thesis describes the development of liquid chromatography tandem mass spectrometry (LC-MS/MS) methods for the trace analysis of active pharmaceutical ingredients (APIs) and their metabolites in aqueous environmental matrices. The research was focused on the development of chiral LC-MS/MS methods for the analysis of fluoxetine and metoprolol, as well as their chiral metabolites in environmental water samples. A method was also developed for the achiral compounds, diazepam and nordiazepam. The LC-MS/MS methods were validated by the use of the isotope-labeled compounds. As these isotope-labeled compounds were not found in the wastewater samples, the validation could be assessed at trace level concentrations in the actual matrices in which the analytes were detected. The analytes were extracted from the water samples using solid phase extraction methods. Different types of solid phase extraction sorbents were evaluated. Fluoxetine and norfluoxetine were extracted through the use of a mixed mode polymeric based extraction sorbent. A hydrophilic and lipophilic balanced sorbent was employed for the simultaneous extraction of metoprolol and its metabolites, the base α-hydroxymetoprolol and the acidic metabolite deaminated metoprolol. Moreover, silica based C18 extraction discs were applied for the sample preparation of diazepam and nordiazepam. The chromatographic separations were conducted in reversed phase LC with MS compatible mobile phases. The enantiomers of fluoxetine and norfluoxetine were simultaneously separated using the chiral stationary phase (CSP), α1-acid glycoprotein (AGP). The Chiral AGP column was also applied for the separation of the enantiomers of deaminated metoprolol. For the simultaneous separation of the metoprolol enantiomers and the four stereoisomers of α-hydroxymetoprolol, the cellobiohydrolase (CBH) protein based CSP was used. An octadecyl silica based LC column was applied for the separation of diazepam and nordiazepam. The analytes were detected by the use of tandem quadrupole mass spectrometry operating in selective reactive monitoring mode. High resolution MS, employing a quadrupole time-of-flight (QqTOF) mass analyzer, was utilized for the identification of an unknown compound in wastewater samples. The APIs and their metabolites, as well as their respective enantiomers, were quantified in raw and treated wastewater from Uppsala, Sweden along with surface water from the River Fyris in Uppsala.

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Dang, Viet D. « Achiral and chiral analysis of polychlorinated biphenyls (PCBs) in the aquatic and riparian food webs in Twelve Mile Creek, South Carolina ». Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1202410243/.

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21

Chang, Yejin. « Enantioselective Transformations of α- and β-Amino C-H Bonds Promoted by Cooperative Actions of Achiral and Chiral Lewis Acid Catalysts : ». Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109179.

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Thesis advisor: Masayuki Wasa
Thesis advisor: Amir H. Hoveyda
This dissertation describes the development of cooperative catalyst systems for the regio- and enantio-selective α- and β-amino C-H functionalization of N-alkylamines, inspired by the concepts of frustrated Lewis pairs (FLPs). Prior to this dissertation research, the development of effective and broadly applicable catalytic protocol to transform amino C-H bonds with high enantioselectivity remained as a formidable problem. In Chapter 1, the recent advances in the field of amino C-H functionalization through hydride transfer process that served as intellectual foundations for this dissertation research is presented. As highlighted in the first chapter, key challenges of amino C-H functionalization are: (1) unreactive nature of α, β- and/or γ-amino C-H bonds, (2) requirement for the use of precious metal-based catalysts and external oxidants under acidic/basic and harsh conditions, (3) use of directing groups for regioselectivity, and (4) poor functional group tolerance. Inspired by the unique capability of FLPs to activate otherwise unreactive molecules while disfavoring undesirable acid-base complexation, we have developed a protocol for enantioselective α-amino C-H functionalization of N-alkylamines, where chiral and achiral Lewis acid catalysts work cooperatively (Chapter 2). The application of the cooperative catalyst system comprising of B(C6F5)3, a chiral Lewis acid, and a Brønsted base to the enantioselective β-amino C-H functionalization is described in Chapter 3
Thesis (PhD) — Boston College, 2021
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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22

Bagmare, S. « Synthesis and biophysical properties of nucleic acid analogues bearing 5-atom achiral amide and chiral D/L-amino acid- derived linkages ». Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2012. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2149.

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CATANI, Martina. « Mass transfer characteristics and thermodynamic properties of new generation porous particles for ultrafast, high-efficient separations in chiral and achiral liquid chromatography ». Doctoral thesis, Università degli studi di Ferrara, 2018. http://hdl.handle.net/11392/2488045.

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During the last years, there has been a continuous evolution in high performance liquid chromatography (HPLC) aimed at developing high efficient, selective and fast separation methods. One of the main factors affecting the efficiency of a separation is the type of adsorbent used to pack the column since both physico-chemical and geometrical characteristics of packing particles play a key role on column performance. The investigation of kinetic and thermodynamic properties of porous materials used as stationary phases in LC is of fundamental importance for future developments in column design and new applications. It is well known that the efficiency of separation is strongly influenced by kinetic factors while thermodynamics (adsorption equilibria) affects retention and selectivity. Anyhow, these aspects are very often strictly interconnected to each other. Adsorption equilibria can be investigated through several chromatographic techniques (e.g. frontal analysis, perturbation method). However, new approaches (”Inverse Method”) allow to estimate the adsorption isotherm of any analyte on a stationary phase by means of only few experimental overloading measurements. Kinetic factors have been estimated for a long time through the nonlinear fitting of the experimental van Deemter curve. Recently, this approach has been demonstrated to lead to parameters whose physical meaning is debatable. Accordingly, it has been substituted by a more advanced approach which allows to independently estimate each mass transfer contribution. Experimentally, the effective diffusion coefficient of the analyte in the porous medium is calculated by means of stop-flow techniques (peak parking), where analyte molecules are left free to diffuse in the middle of the column when the flow is switched off. The results of peak parking experiments must be then interpreted in the light of a proper model ofdiffusion in porous media. Mass transfer processes in liquid chromatography can be predicted through CFD simulations. These studies accurately mimic the band broadening in specific sections of packed beds. Combined to sophisticated reconstruction of stationary phase structures and the calculation of transport properties in the reconstructed materials, these approaches have permitted to revise some concepts traditionally accepted in the field of diffusion through porous media (such as, for instance, the independence of mass fluxes outside and inside porous particles). In this thesis, kinetic performance and thermodynamic properties of different types of stationary phases have been explored. Mass transfer kinetics has been firstly investigated in recently introduced sub-2μm monodisperse C18 FPPs for reversed-phase separations characterized by a narrow particle size distribution (nPSD). Then, kinetic performance of new chiral stationary phases (CSPs) for ultrafast separations have been studied by comparing columns in-house packed with both SPPs and sub-2μm FPPs functionalized with the same chiral selector. The results reported in this thesis concern two different studies carried out with two different types of chiral selectors (Whelk-O1 and teicoplanin). Sub-second enantioseparations have been obtained with very short columns packed with these CSPs operated at high flow rates, being an extraordinary result in the field of enantioseparations, unimaginable only few years ago. On the other hand, the adsorption properties of benzene derivatives on a perfluorinated adsorbent have been studied by means of nonlinear chromatography measurements in order to investigate the well-known capacity of perfluorinated stationary phases to selectively recognize perfluorinated molecules (”fluorophilicity”), which is usually referred to be active when the molecule contains at least six sp3 perfluorinated carbon atoms. The results of this study, however, showed that even a single CF3 group induce a drastic change in the adsorption properties of molecules.
Durante gli ultimi anni, il campo della cromatografia liquida ad alta prestazione (HPLC) è stato caratterizzato da una continua evoluzione alla ricerca di nuovi metodi di separazione efficienti, selettivi e veloci. L’efficienza di una separazione è influenzata dalle proprietà chimico-fisiche e geometriche delle particelle che compongono il letto impaccato della colonna. Pertanto, lo studio delle proprietà cinetiche e termodinamiche di questi materiali porosi è fondamentale per lo sviluppo di nuove fasi stazionarie e nuove applicazioni. È noto che l’efficienza di una separazione è influenzata da fattori cinetici, mentre la termodinamica (equilibri di adsorbimento) giocano un ruolo fondamentale per la ritenzione e la selettività, anche se molto spesso questi due aspetti sono strettamente collegati fra di loro. Diverse tecniche cromatografiche (analisi frontale o metodo delle perturbazioni) consentono di indagare gli equilibri di adsorbimento. Recentemente, però, è stato introdotto un nuovo approccio (”Metodo Inverso”) che consente di stimare l’isoterma di adsorbimento di un analita su qualunque fase stazionaria mediante poche misure sperimentali, basate sull’acquisizione di alcuni profili in overloading. I fattori cinetici, invece, sono stati a lungo stimati attraverso il fitting nonlineare della curva sperimentale di van Deemter. Tuttavia, questo metodo porta alla stima di parametri molto spesso privi di senso fisico, pertanto oggi si preferiscono approcci più moderni che consentono la stima indipendente di tutti i contributi al trasferimento di massa. Dal punto di vista sperimentale, i coefficienti di diffusione nella fase mobile e nel mezzo effettivo vengono stimati attraverso la tecnica del ”peak parking”, in cui le molecole di analita vengono lasciate libere di diffondere approssimativamente al centro della colonna in assenza di flusso e i risultati vengono, poi, interpretati mediante un modello di diffusione nei mezzi porosi. I processi di trasferimento di massa in cromatografia possono essere, inoltre, predetti attraverso simulazioni CFD, che mimano accuratamente l’allargamento di banda in una sezione del letto impaccato. Grazie alla combinazione dei risultati derivanti da queste tecniche con quelli di ricostruzione della fase stazionaria, recentemente sono stati rivisitati alcuni concetti come, ad esempio, l’indipendenza dei flussi dentro e fuori dalle particelle. Questa tesi è volta allo studio delle performance cinetiche e termodinamiche di diversi tipi di fasi stazionarie. Inizialmente, la cinetica di trasferimento di massa è stata studiata all’interno di colonne per cromatografia a fase inversa composte da particelle C18 sub-2μm caratterizzate da una distribuzione delle particelle molto stretta. In seguito, sono state studiate le performance cinetiche di nuove fasi stazionarie chirali per cromatografia ultrafast, confrontando colonne impaccate in-house con particelle core-shell e sub-2μm totalmente porose, funzionalizzate con lo stesso selettore chirale. I risultati riportati in questa tesi riguardano due diversi studi effettuati con due diversi tipi di selettore chirale (Whelk-O1 e teicoplanina). Grazie all’utilizzo di colonne corte impaccate con queste nuove fasi stazionarie chirali e alte velocità di flusso, sono state ottenute separazioni di enantiomeri in meno di un secondo. Dall’altro lato, sono stati studiati gli equilibri di adsorbimento di alcuni derivati del benzene su una fase stazionaria perfluorurata attraverso misure di cromatografia nonlineare, allo scopo di investigare la ben nota capacità di queste fasi di riconoscere selettivamente altre molecole perfluorurate (”fluorofilicità”) che contengano almeno 6 atomi di carbonio sp3 perfluorurati. I risultati di questa indagine hanno dimostrato, però che anche un singolo gruppo CF3 è in grado di indurre un drastico cambio negli equilibri di adsorbimento delle molecole sulla fase stazionaria.

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Sattar, A. K. « Catalytic transfer hydrogenation of organic functional groups using Ni, Ru complexes and asymmetric induction using racemic chiral and achiral ligands and synthetic applications ». Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2005. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2462.

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25

Serhan, Zeinab. « Rmn du deuterium en abondance naturelle en milieu oriente chiral et achiral : une nouvelle approche analytique pour la détermination du fractionnement isotopique site-spécifique d'acides gras ». Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112357.

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La spectroscopie RMN 2D du deutérium en abondance naturelle (DAN) en utilisant les cristaux liquides chiraux comme solvant de RMN est une méthodologie efficace pour deux raisons: i) l’interaction quadrupolaire (interaction RMN sensible à l’ordre orientationnel des molécules et spécifique aux noyaux de spin I>1/2) n’est plus nulle en moyenne comme dans les liquides; ii) la chiralité du milieu permet de discriminer spectralement des énantiomères (molécule chirale) ou des directions énantiotopes (molécule prochirale). L'objectif principal de ce travail de Thèse était d'explorer le potentiel analytique de cette technique pour analyser le fractionnement isotopique naturel deutérium dans le cas d’ester d’acides gras saturés (AGS) et (poly)insaturés (AGI). Le but ultime de ce travail est de fournir de nouvelles informations (de nature stéréochimique) pour améliorer la compréhension de certains mécanismes enzymatiques impliqués au cours de leur biosynthèse. Dans ce contexte, nous avons montré que l'utilisation de solutions organiques orientées de polypeptides (mésophases chirales) utilisant des co-solvants polaires comme le DMF ou la pyridine (Py) fournissait les meilleurs résultats en termes d’(énantio)discrimination spectrale (nombre de sites et amplitude) sur la base des déplacements chimiques et des éclatements quadrupolaires du deutérium. Ainsi, la mésophase chirale (PBLG/Py) a été utilisée avec succès pour analyser les AGI comme le linoléate de méthyle (C18), pour lequel nous avons pu mesurer l'excès énantio-isotopomèrique (eei) au niveau de chaque site méthylène de la molécule. Pour la première fois, d'importantes informations relatives à la stéréochimie des mécanismes enzymatiques, inaccessibles par la méthode conventionnelle SNIF-NMR®, ont été déterminées. La même méthodologie impliquant la mésophase achirale (PBG/Py) et chirale (PBLG/Py) s’est révélée également être un excellent outil pour l'analyse des SAFA sous leur forme libre (C14 à C18) ou sous leur forme de triglycérides (3*C4 et 3*C14). L'attribution des doublets 2H détectés sur les spectres RMN 2D anisotropes des SAFA a été confirmée par l'élaboration d'un modèle théorique capable de prédire le comportement orientationnel de ces molécules flexibles. Comme exemple illustratif, la méthode a été appliquée pour étudier les mécanismes enzymatiques convertissant le linoléate en vernoléate dans deux plantes différentes. Enfin, pour améliorer la compréhension des interactions «soluté-polypeptide» impliquées dans les mécanismes d'orientation et d’énantio-discrimination, nous avons étudié par RMN 2D DAN, l'évolution des paramètres d'ordre (matrice de Saupe) de deux molécules prochirales, rigides et apolaires dissoutes dans une mésophase chirale préparée en mélangeant deux polypeptides de même stéréochimie (L), mais dont la nature chimique des chaînes latérales est différente, en fonction de leur proportion massique respective
Natural abundance deuterium (NAD) 2D-NMR spectroscopy using (a)chiral liquid crystals as NMR solvent is a powerful method for two reasons: i) the quadrupolar interaction (an order-sensitive NMR interaction specific to spins I > ½) is not averaged to zero anymore as in liquids; ii) the chirality of medium allows enantiomers (chiral molecule) or enantiotopic directions (prochiral molecule) to be spectrally discriminated. The main objective of this Thesis work was to explore the analytical potential of this technique to analyze the natural distribution of deuterium in the case of esters of saturated fatty acids (SAFA) and (poly)unsaturated fatty acids (PUFA). The ultimate goal of this research is to collect new (stereochemical) information to improve the understanding of some enzymatic mechanisms involved during their biosynthesis. In this context, we have shown that the use of oriented solutions of polypeptide (chiral mesophases) using polar co-solvents such as DMF or pyridine (py) provided better results in terms of spectral (enantio)discrimination (number of sites and magnitude) on the the basis of chemical shifts and deuterium quadrupole splittings. Thus, the chiral mesophase (PBLG/py) has been applied successfully to analyse PUFA’s like the methyl linoleate (C18) for which we could measure the enantio-isotopomeric excess (eie) at each methylen site of the molecule. For the first time, important information related to the stereochemistry of enzymatic mechanisms, inaccessible by the conventional method SNIF-NMR®, have been determined. The same methodology using achiral (PBG / py) and chiral (PBG / py) mesophases, revealed also to be an excellent tool for analysing SAFA in their free form (C14 to C18), or in triglyceride forms (3*C4 and 3*C14). The assignment of 2H doublets detected on 2D-NMR spectra of SAFA’s was confirmed by developing a theoretical model predicting the orientational ordering behavior of these flexible molecules. As illustrative exemple, the method was applied for investigating the enzymatic mechanisms converting the linoleate into vernoleate in two different plants. Finally, to improve the understanding of “solute/polypeptide" interactions involved in the orientation and enantiodiscrimination mechanisms, we have investigated by NAD 2D-NMR the evolution of the order parameters (Saupe matrix) of two apolar, rigid prochiral molecules dissolved in a chiral mesophase made by mixing two polypeptides having the same stereochemistry (L) but different type of side chains, versus their respective mass proportion

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Mohammad, Adil. « Achiral and chiral, C2-symmetric bicyclic guanidinates based on 1,5,7-triazabicyclo[4.4.0.]dec-5-ene as ligands in high- and mid-valent early transition metal chemistry ». Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/714.

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The syntheses of achiral and chiral, C2-symmetric bicyclic guanidine derivatives of 1,5,7-triazabicylo[4.4.0]dec-5-ene (hppH) are described. Quantum mechanical MO calculations based on Spartan were performed in order to study the effects (electronic and steric) of substituents on the basicity of hppH derivatives. These calculations showed that substituting only one methyl group on each carbon next to the bridgehead nitrogen of hppH gives high basicity. Based on these calculations, syntheses of achiral (hpp*H, with four methyl groups) and chiral C2-symmetric (hpp'H, with two methyl groups) derivatives of hppH were developed based on cyclization of 1,5,9-triaminononanes with C1 reagents. The synthesis of hpp*H started from commercially available ethyl cyanoacetate and was completed in six steps with 2.5% overall yield. The synthesis of the chiral, C2-symmetric hpp'H was carried out using L-alanine as the chiral precursor. The key step was the diastereoselective coupling of L-alaninol (derived from L-alanine) with commercially available hydroxyacetone via a reductive amination approach. An important step was successful diastereoselective resolution of N-benzyl-protected meso and C2-symmetric aminodinitriles. Chiral hpp'H was synthesized in six steps starting from L-alaninol in 9% overall yield and was isolated as hpp'H2+I-. Both hpp*H and hpp'H2+I were characterized by 1H and 13C NMR spectroscopy and high resolution mass spectrometry. hpp'H2+I was also characterized by single-crystal X-ray diffractometry. The coordination chemistry of non-methylated hpp- with tantalum is described. The new tantalum complexes TaV(hpp)Cl4, TaV(hpp)2Cl3, Cp*TaV(hpp)Cl3 (Cp* = C5Me5) and Cp''TaV(hpp)Cl3 (Cp'' = C5Me4Et) were synthesized. The first mid-valent hpp- complexes of tantalum, Cp*TaIV(hpp)Cl2 and Cp"TaIV(hpp)Cl2, were obtained by reduction of (C5Me4R)Ta(hpp)Cl3 (R =Me, Et) or reaction of (C5Me4R)2Ta2(µ-Cl)4 with (hpp)SiMe3. 1H NMR spectroscopy and comparative single-crystal X-ray diffractometry of these complexes is discussed.

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Riddell, Nicole. « Packed Column Supercritical Fluid Chromatography : Applications in Environmental Chemistry ». Doctoral thesis, Örebro universitet, Institutionen för naturvetenskap och teknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-56826.

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Although gas and liquid chromatography have emerged as dominant separation techniques in environmental analytical chemistry, these methods do not allow for the concurrent analysis of chemically diverse groups of persistent organic pollutants (POPs). There are also a small number of compounds which are not easily amenable to either of these traditional separation techniques. The main objective of this thesis was to address these issues by demonstrating the applicability of packed column supercritical fluid chromatography (pSFC) coupled to mass spectrometry (MS) in various aspects of environmental chemistry. First, pSFC/MS analytical methods were developed for legacy POPs (PCDDs, PCDFs, and PCBs) as well as the emerging environmental contaminant Dechlorane Plus (DP), and issues relating to the ionization of target analytes when pSFC was coupled to MS were explored. Novel APPI and APCI reagents (fluorobenzene and triethylamine) were optimized and real samples (water and soil) were analyzed to demonstrate environmental applicability. The possibility of chiral and preparative scale pSFC separations was then demonstrated through the isolation and characterization of thermally labile hexabromocyclododecane (HBCDD) stereoisomers. The analytical pSFC separation of the α-, β-, and γ-HBCDD enantiomers as well as the δ and ε meso forms was shown to be superior to results obtained using a published LC method. Finally, technical mixtures of phosphorus flame retardants (RBDPP, BPA-BDPP, and DOPO; a group of related compounds which are challenging to analyze concurrently) were examined using multiple analytical techniques and pSFC was found to be the only method which facilitated the accurate determination of the components of all 3 mixtures. This thesis confirms the potential of pSFC/MS as a fast, green, and cost effective means of separating and analyzing environmental contaminants.

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Ehlert, Dennis K. « Chirale und achirale Liganden für die Fluoreszenzspektroskopie ». [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=95764468X.

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Schierwater, Kathrin. « Chirale und achirale Lanthanoidorganyle mit funktionalisierten Alkoxidbrücken ». [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969985533.

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El, Abdioui Khalid. « Synthèse d'aminoacides d'intérêt biologique. Cyclopropanation de déhydroaminoesters par catalyse achirale et chirale ». Montpellier 2, 1994. http://www.theses.fr/1994MON20105.

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Le but de ce travail est la preparation d'alpha-aminoacides cyclopropaniques par addition de carbenoides, formes a partir de diazoacetates d'alkyle et de complexes de cuivre, sur des dehydro aminoesters n-proteges et d'explorer deux voies possibles d'induction asymetrique, soit par un substrat chiral, soit par catalyse chirale. Dans une partie bibliographique, nous presentons les methodes de synthese asymetrique de ces composes et les types de complexes chiraux des metaux de transition utilisables comme catalyseurs. Cette reaction de cyclopropanation realisee avec les catalyseurs que nous avons prepares dont un nouveau, conduit aux composes souhaites avec de bons rendements. Si l'emploi de catalyseurs chiraux n'a pas donne de reaction de cyclopropanation asymetrique, par contre un resultat encourageant a ete obtenu avec la presence dans le substrat d'un inducteur chiral, la 2-hydroxypinan-3-one

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Scholtysek, Peggy [Verfasser], Alfred [Akademischer Betreuer] Blume, Jörg [Akademischer Betreuer] Kreßler et Thomas [Akademischer Betreuer] Wolff. « Chirale und achirale Polymere in Wechselwirkung mit Phospholipid-Monolayern und -Bilayern / Peggy Scholtysek. Betreuer : Alfred Blume ; Jörg Kreßler ; Thomas Wolff ». Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2014. http://d-nb.info/106071745X/34.

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Scowen, I. J., T. S. Alomar, T. Munshi et Colin C. Seaton. « Structural similarity in chiral-achiral multi-component crystals ». 2020. http://hdl.handle.net/10454/17783.

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Yes
The creation of multi-component crystals between chiral and achiral components has gained increased interest in recent years. In many cases the overall crystal structure is similar with the creation of a pseudo-inversion centre in the enantiopure case. This allows for the formation of solid solutions between the two extremes, which may have applications within chiral resolution. Utilising a combination of database mining, computational prediction and experimental screening, the frequency of formation for such materials has been investigated showing that for co-crystals this occurs more frequently than for salts, though there is a limited number of samples to draw structural conclusions. Computational modelling indicates the prediction of such systems can be challenging due to the similarities in energy of many crystal structures, so development of tools to design such systems is required to fully utilise these concepts.
The Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-track Research Funding Program.

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Oliveira, Bárbara Luís de. « New sensors based on chiral and achiral coordination polymers ». Master's thesis, 2018. http://hdl.handle.net/10451/34895.

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Tese de mestrado em Química, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, em 2018
A área dos materiais funcionais tem sido alvo de muita atenção por parte da comunidade científica nos últimos anos. Esta área abrange os campos da física, química supramolecular, química orgânica e inorgânica e química de coordenação. Estes materiais são estruturas (unidimensionais, bidimensionais ou tridimensionais) que têm de reunir mais do que uma propriedade e, como tal, a combinação de todas estas áreas da química, e da ciência em geral, é necessária, se não essencial. O trabalho desenvolvido ao longo deste projeto tem como objetivo primário a síntese de novos materiais funcionais que possam ser aplicados como dispositivos, mais concretamente, como sensores. Uma das características que se procurou para este tipo de material foi a transição de spin. Esta é uma propriedade inerente aos metais de transição com configuração eletrónica entre d4 e d7, sendo estes compostos sensíveis à aplicação de estímulos externos, como temperatura, pressão ou exposição à luz. A transição pode também ser provocada pela interação com outras espécies, no caso de serem estruturas que permitam o enclausuramento de moléculas hospedeiras. No caso de iões metálicos com configuração d6, caso do Fe(II), a transição de spin é muitas vezes acompanhada de uma alteração da cor do composto. Isto deve-se ao facto de o centro metálico passar de um estado de spin-baixo, em que todos os eletrões se encontram emparelhados (diamagnético), para um estado de spin-alto, em que quatro dos eletrões se encontram desemparelhados (paramagnético). O estudo do comportamento magnético é efetuado utilizando um dispositivo supercondutor de interferência quântica (superconducting quantum interference device- SQUID) que consegue medir a resposta do composto quando exposto a um campo magnético. Esta medida pode ser traduzida em suscetibilidade magnética (χM) e é característica para cada distribuição eletrónica dependendo do número de eletrões desemparelhados no estado de spin-alto e de spin-baixo. No caso do Fe(II) (d6) o valor de χMT é de 3 cm3mol-1K para o spin-alto e de 0 cm3mol-1K para o spin-baixo. No caso de Fe(III) (d5) os valores são de 0.37 cm3mol-1K no estado de spin-baixo e de 4.34 cm3mol-1K no estado de spin-alto. A luminescência é também uma propriedade que se pretendeu promover nos polímeros sintetizados. Uma vez que o perfil de emissão de um composto também se pode alterar com a temperatura, a conjugação deste comportamento com a transição de spin e a mudança de cor contribuiria para a obtenção de um material multifuncional com possível aplicação em sensores. Na procura de ligandos que pudessem promover a luminescência do material, foram escolhidos ligandos derivados de unidades naftaleno e perileno. Uma vez que estas unidades são também conhecidas pelas suas capacidades condutoras, a condutividade foi mais uma das propriedades exploradas para um dos ligandos. A primeira estratégia adotada foi a síntese de ligandos baseados em unidades de benzeno substituídos com grupos piridina nas posições para. Por serem lineares e possuírem dois sítios de coordenação, estes ligandos visam a síntese de polímeros de coordenação de Fe(II) tridimensionais, usando para este efeito um segundo ligando quadrangular plano (tetracianometalato). Estas estruturas denominam-se clatratos de Hofmann e, por serem unidades tridimensionais, possuem cavidades que permitem o enclausuramento de moléculas hospedeiras. A inserção destes compostos poderá afetar as propriedades magnéticas das entidades porosas. Muitos compostos intermediários foram obtidos na tentativa de síntese de vários ligandos seguindo esta estratégia. No entanto, apenas um foi possível isolar e caracterizar por espectroscopia de RMN, infravermelho e de luminescência no estado sólido. Através deste composto e de outro, sintetizado por uma colega, foram obtidos dois clatratos de Hofmann e foram avaliados os seus perfis magnéticos bem como as propriedades luminescentes de um deles. Em relação ao perfil magnético, nenhuma das estruturas apresentava transição de spin, em que uma era spin-alto e a outra spin-baixo. Ao contrário do observado para o respetivo ligando, que apresentou um comportamento bastante emissivo, verificou-se que a estrutura tridimensional não era emissiva. Ambos os polímeros 3D foram submetidos a testes de inserção de diversas moléculas hospedeiras por difusão de vapor e conseguiu-se promover uma transição de spin gradual-rápida próxima da temperatura ambiente num dos clatratos com a piridina. Foi também testada a capacidade de inserção de compostos quirais por parte de umas das estruturas polímericas 3D. Deste modo, foi testada a inserção, em solução, de quatro aminoácidos: ʟ- fenilalanina, ᴅ- fenilalanina, ʟ-alanina e ᴅ-alanina. Verificou-se que o perfil magnético foi alterado para todos os sistemas, apesar de em nenhum dos casos ter havido uma promoção da transição de spin. Para os dois primeiros, ʟ- fenilalanina e ᴅ- fenilalanina, o composto manteve um comportamento de spin-alto enquanto que para os dois últimos, ʟ-alanina e ᴅ-alanina, o composto apresentou valores de suscetibilidade magnética característicos para compostos de Fe(III) no estado de spin-alto. Diversas tentativas de obtenção de um cristal único foram também efetuadas, nomeadamente através da síntese das estruturas por difusão lenta em tubos-H com pequenas quantidades de reagente. Dado que a síntese efetuada por este método é extremamente lenta, a obtenção de cristais não é imediata. Paralelamente, uma segunda estratégia sintética foi adotada em que foram sintetizados ligandos visando a formação de polímeros unidimensionais. Os ligandos desta segunda categoria são assimétricos e não lineares e a sua constituição divide-se em três partes essenciais: um grupo triazole (coordenante ao metal), uma diimida aromática como grupo central e uma zona alifática constituída por cadeias carbonadas. Desta forma foram sintetizados e caracterizados, (por espectroscopia de RMN, infravermelho e luminescência), oito novos ligandos que se dividem em dois grupos: quatro deles formando uma unidade de naftaleno-diimida e os restantes formando um fragmento de perileno-diimida. Destes oito ligandos, apenas os quatro primeiros (naftaleno-diimidas) foram usados na síntese de polímeros unidimensionais por precipitação., Para os ligandos baseados em unidades de perileno-diimidas foi realizada a síntese de dímeros ou oligómeros através da difusão lenta em tubos de ensaio devido à sua baixa solubilidade. Para a obtenção destes oligómeros foi usado um sal de NCS (NaNCS) que se coordena ao ferro impedindo o crescimento do polímero e facilitando a obtenção de pequenas unidades representativas da estrutura. Para os polímeros de coordenação 1D obtidos por precipitação foram estudadas as suas propriedades magnéticas, concluindo-se que apenas um deles apresentava transição de spin, ainda que incompleta, caracterizada como gradual abrupta. Os restantes polímeros apresentaram um perfil magnético característico de spin-alto e para um deles os valores de susceptibilidade magnética apresentaram valores característicos de spin-alto para Fe(III). Para o polímero que apresentou transição de spin, foram também estudadas as suas propriedades condutoras e verificou-se que se comporta como um semi-condutor. As suas propriedades de luminescência foram também estudadas e observou-se que o polímero 1D é extremamente emissivo e que o seu perfil de emissão se altera com a temperatura. Estas três características combinadas fazem deste polímero um excelente candidato para ser aplicado como um material funcional. Os restantes quatro ligandos (perileno-diimida) não foram usados na síntese por precipitação devido à sua elevada insolubilidade em solventes orgânicos. No entanto, através da sua solubilização parcial em clorofórmio, estes ligandos mostraram ser extremamente luminescentes em solução quando expostos a luz a 366 nm. Estudos futuros serão necessários para confirmar este comportamento luminescente bem como se esta propriedade se verifica também no estado sólido. Devido à emissão de luminescência, estes ligandos poderão, no futuro, ter aplicação como dispositivos orgânicos de emissão de luz (organic light-emitting devices -OLEDs).
Functional materials have attracted great attention of the scientific community in the last few years. This area of study comprises the fields of physics, supramolecular chemistry and also organic, inorganic and coordination chemistry. These structures have a combination of different properties and the merge of all these areas is necessary, if not essential. The research work here presented aimed to develop new functional materials with different properties, so they could have applications as sensor devices, and, for this, we focused our efforts in combining spin crossover (SCO) with other properties such as luminescence and/or conductivity. SCO compounds respond to external changes, such as temperature, pressure or light. They can also respond to host-guest interactions, especially in three dimensional (3D) structures. The first strategy adopted was to synthesise para-substituted bipyridine ligands in order to obtain 3D Hofmann clathrates. Another approach used was the synthesis of ligands constituted by a triazole unit, a naphthalene diimide intermediate fragment and an aliphatic region for the assembly of 1D coordination polymers. The magnetic behaviour of all synthesised polymers was obtained by SQUID magnetometry. One of the 1D polymers showed a fast-gradual SCO while the rest showed a behaviour characteristic of mainly HS. In the case of the 3D Hofmann clathrates one of them showed the metal centres were mainly in the HS state and the other one showed profile of a LS state compound. For the insertion tests it was observed that one of the 3D polymers altered its magnetic behaviour in the presence of a guest molecule. The conductivity properties of the 1D polymer with SCO and luminescent properties showed a semiconductor behaviour.

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Wang, SHIHAO. « Chirality Transfer from Chiral Solutes and Surfaces to Achiral Solvents : Insights from Molecular Dynamics Studies ». Thesis, 2009. http://hdl.handle.net/1974/5202.

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Chirality can be induced in achiral solvent molecules located near a chiral molecule or surface, but there have been very few systematic studies in this field either experimentally or theoretically. The focus of this thesis is to study the chirality transfer from chiral molecules to achiral solvents. To capture the chirality transfer in solvent molecules, a solvent model that is sensitive to the changes in the environment is needed. We developed new polarizable and flexible models based on an extensive series of ab initio calculations and molecular dynamics simulations. The models include electric field dependence in both the atomic charges and the intramolecular degrees of freedom. Modified equations of motion are required and we have implemented a multiple time step algorithm to solve these equations. Our methodology is general and has been applied to ethanol as a test. For other solvents in our simulations, such as 2-propanol, limited models are used. The chirality transfer from chiral solutes to achiral solvents and its dependence on the solute and solvent characteristics are then explored using the new polarizable models in molecular dynamics simulations. The chirality induced in the solvent is assessed based on a series of related chirality indexes originally proposed by Osipov[Osipov et al., Mol. Phys.84, 1193(1995)]. Two solvents are considered: Ethanol and benzyl alcohol. The solvation of three chiral solutes is examined: Styrene oxide, acenaphthenol, and n-(1-(4-bromophenyl)ethyl)pivalamide (PAMD). All three solutes have the possibility of hydrogen-bonding with the solvent, the last two may also form π-π interactions, and the last has multiple hydrogen bonding sites. The chirality transfer from chiral surfaces to achiral solvents is also explored. Emphasis is placed on the extent of this chirality transfer and its dependence on the surface and solvent characteristics is explored. Three surfaces employed in chiral chromatography are examined: The Whelk-O1 interface; a phenylglycine-derived chiral stationary phase (CSP); and a leucine-derived CSP. The solvents consist of ethanol, a binary n-hexane/ethanol solvent, 2-propanol, and a binary n-hexane/2-propanol solvent. Molecular dynamics simulations of the solvated chiral interfaces form the basis of the analysis and position dependent chirality indexes are analyzed in detail.
Thesis (Ph.D, Chemistry) -- Queen's University, 2009-09-24 00:25:15.174

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Venkatakrishnan, T. S. « Ruthenium Complexes Of Chiral And Achiral Phosphorus Ligands Based On The P-N-P Motif ». Thesis, 2004. https://etd.iisc.ac.in/handle/2005/300.

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In recent years there is an increasing awareness of the importance of chiral phosphorus ligands in transition metal organometallic chemistry because of the utility of such complexes in homogeneous catalytic reactions. This thesis deals with synthetic, spectroscopic and X-ray crystallographic studies on ruthenium complexes of chiral and achiral P-N-P type ligands, known as "diphosphazanes", with emphasis on ruthenium carbonyl clusters. Several ruthenium carbonyl clusters have been synthesized and characterized by elemental analyses, ER and NMR (lH, nC and 3lP) spectroscopic data. In several instances, the molecular structures of the clusters have been confirmed by single crystal X-ray diffraction studies. Chapter 1 provides a brief overview of various types of chiral phosphorus ligands and general synthetic routes to diphosphazanes. A brief review of the transition metal chemistry of diphosphazanes and diphosphazane chalcogenides (published since 1994) is presented A review of the literature on the carbonyl clusters of the group-8 transition metals (Fe, Ru, Os) bearing mono- and diphosphines is also included in this chapter The scope and aim of the present investigation is outlined at the end of this chapter. Chapter 2 provides the results obtained in the present investigation and a detailed discussion of the spectroscopic and crystallographic data. The essential feature of the work is summarized at the end of the chapter. Chapter 3 gives a detailed account of the experimental procedure for the synthesis of the compounds and spectroscopic and analytical measurements. The experimental details of X-ray structure determination are also given in this chapter. To save space, the coordinates of the H-atoms and the calculated and observed structure factor tables are not included. In some cases, reference to CCDC deposition number is included. The references of the literature are compiled at the end of the thesis and are indicated in the text by appropriate numbers appearing as superscripts. The compounds synthesized in the present study are represented by bold Arabic numerals and are listed in Appendix I. The abbreviations employed in the thesis conform to those generally used in Chemical Abstracts.

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36

Venkatakrishnan, T. S. « Ruthenium Complexes Of Chiral And Achiral Phosphorus Ligands Based On The P-N-P Motif ». Thesis, 2004. http://hdl.handle.net/2005/300.

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In recent years there is an increasing awareness of the importance of chiral phosphorus ligands in transition metal organometallic chemistry because of the utility of such complexes in homogeneous catalytic reactions. This thesis deals with synthetic, spectroscopic and X-ray crystallographic studies on ruthenium complexes of chiral and achiral P-N-P type ligands, known as "diphosphazanes", with emphasis on ruthenium carbonyl clusters. Several ruthenium carbonyl clusters have been synthesized and characterized by elemental analyses, ER and NMR (lH, nC and 3lP) spectroscopic data. In several instances, the molecular structures of the clusters have been confirmed by single crystal X-ray diffraction studies. Chapter 1 provides a brief overview of various types of chiral phosphorus ligands and general synthetic routes to diphosphazanes. A brief review of the transition metal chemistry of diphosphazanes and diphosphazane chalcogenides (published since 1994) is presented A review of the literature on the carbonyl clusters of the group-8 transition metals (Fe, Ru, Os) bearing mono- and diphosphines is also included in this chapter The scope and aim of the present investigation is outlined at the end of this chapter. Chapter 2 provides the results obtained in the present investigation and a detailed discussion of the spectroscopic and crystallographic data. The essential feature of the work is summarized at the end of the chapter. Chapter 3 gives a detailed account of the experimental procedure for the synthesis of the compounds and spectroscopic and analytical measurements. The experimental details of X-ray structure determination are also given in this chapter. To save space, the coordinates of the H-atoms and the calculated and observed structure factor tables are not included. In some cases, reference to CCDC deposition number is included. The references of the literature are compiled at the end of the thesis and are indicated in the text by appropriate numbers appearing as superscripts. The compounds synthesized in the present study are represented by bold Arabic numerals and are listed in Appendix I. The abbreviations employed in the thesis conform to those generally used in Chemical Abstracts.

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Díaz, Pérez Yrene Hortencia [Verfasser]. « New Phthalimide-based sensors for chiral and achiral anions and peroxides / vorgelegt von Yrene Hortencia Díaz Pérez ». 2009. http://d-nb.info/1008304972/34.

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Chou, Yi-Lin, et 鄒依凌. « Study on the Mesophases and Electro-optical Properties of New Chiral Liquid Crystals Possessing Achiral Alkenyl Chain and Semi-fluorinated group at Chiral Terminal Tail ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/33156431778260815131.

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碩士
大同大學
化學工程學系(所)
98
There are many factors affect the properties of ferroelectric (SmC*) and antiferroelectric (SmCA*) liquid crystal phase such as chiral terminal group, rigid core, linking group, terminal chain length and optical purity. For these reasons, the purpose of this research work is an attempt to correlate the various core structures and achiral terminal groups to the formation of mesomorphic phases, especially ferroelectric and antiferroelectric phases in chiral liquid crystal materials. Thus, the chiral precursor, (S)-1-methyl-2-(2,2,3,3,4,4,4-heptafluorobutoxy) ethanol, was designed and synthesized by reacting (S)-propylene oxide with semi-fluorinated alcohol under basic condition. Consequently, four homologous series of chiral liquid crystal materials derived from this chiral precursor were prepared for the study. The mesomorphic phases and their corresponding phase transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric and antiferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'. The results show that rod-like compounds, with the exception of compound III-2 that exhibits N* and SmC* phases, possess both ferroelectric SmC* and antiferroelectric SmCA* phases. The compounds with bend-core structure suppress the formation of the antiferroelectric SmCA* phase and exhibit the phase sequence of Iso.-SmA*-SmC*-Cr.. The thermal stability of ferroelectric SmC* phase for the variation of the core structures in the rod-like compounds displays an order of PhPhCOONa > PhCOOPhPh > PhPhCOOPh > PhCOONa, and that for the variation of achiral terminal end group displays an order of hydroxyalkyl > acryloyl > propionyl > alkenyl > alkyl. Whereas, the thermal stability of antiferroelectric SmCA* phase for the variation of the core structures in the rod-like compounds displays an order of PhPhCOONa > PhCOONa > PhPhCOOPh > PhCOOPhPh, and that for the variation of achiral terminal end groups displays an order of alkenyl > alkyl > acryloyl > propionyl (hydroxyalkyl group suppresses the formation of the antiferroelectric SmCA* phase). For the bend-core compounds, the thermal stability of ferroelectric SmC* phase for the variation of achiral terminal end groups displays an order of alkenyl > acryloyl > alkyl > propionyl (hydroxyalkyl group suppresses the formation of the ferroelectric SmC* phase). The electro-optical measurements show that the bend-core compounds have much lower Ps values (15.39-49.59 nC/cm2) as compared to the structurally similar compounds with the rod-like structure of the molecule(83.21-130.00 nC/cm2). And rod-like compounds composed of a naphthalene ring in the core structure of the molecule have the maximum Ps values (76.30-84.76 nC/cm2) lower than that composed of the phenyl or biphenyl ring in the core structure of the molecule. The measured maximum Ps values for the variation of achiral terminal functional groups in the rod-like compounds display an order of hydroxyalkyl > alkenyl > alkyl ≒ acryloyl ≒ propionyl at any temperature below Curie point. This may presumably due to the variation of the palarizability at the end group of achiral chain in the molecules. The maximum optical tilt angles θ for four series of compounds are in the range of 28.6∘-40.0∘, 29.0∘-38.5∘, 37.0∘-41.0∘ and 40.0∘-41.8∘ for the corresponding compounds I(m=1-5), II(m=1-3), III(m=1-3) and IV(m=1-3). These results indicate that the measured optical tilt angles of the compounds in the ferroelectric and/or antiferroelectric phases have no significant correlation to the variations of achiral terminal groups in the molecules. Keywords: Rod-like compound, bend-core compound, ferroelectric liquid crystal, antiferroelectric liquid crystal.

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39

Lu, Yen-jung, et 盧燕蓉. « Establish an Analysis Method of Chiral and Achiral of Amphetamines and Ketamines by Capillary Electrophoresis, and Clinical Application ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/qwmw4w.

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碩士
輔英科技大學
醫事技術系碩士班
96
Amphetamines are kinds of medicine that stimulates central nervous system, whereby ketamine has been assigned emerging abuses in the recent years. These two kinds of medicine were frequently mixed and abused by young ages. The analysis of chiral for the analyze is another critical issue. In this study, a capillary electrophoresis (CE) method with photodiode array detector (DAD) for the detection of amphetamines and ketamines in methanol/water solution, urine, and blood has been investigated including amphetamine (A), methamphetamine (MA), methylenedioxy-amphetamine (MDA), methylenedioxy-methamphetamine (MDMA), methylenedioxy-ethylamphetamine (MDEA), ketamine, and norketamine. Achiral analysis were separated within 15 minutes through an uncoated fused-silica capillary (50.2cm x 50µm) using tris-phosphate buffer (pH=3.5, 100 mM). Correlation coefficient was higher than 0.9960 in each sample. The recoveries in this method were determined to be 100±10%. Beside the addition of β-cyclodextrin (20mM, as a chiral selector) in tirs-phosphate buffer for the separation of chiral analyze, the condition of CE for chiral analyze are the same as that for achiral analyze. Correlation coefficient was remained to be higher than 0.9960 in each samples. The recoveries in this method were determined to be 100±10%. Precision and accuracy for the analytic method were smaller than 10% in three matrixes. Analysis of chiral and achiral isomers of illegal drugs with capillary electrophoresis takes the advantages to high resolution and rapid dectection. Furthermore, the method is complementary to GC/MS for analysis of amphetamines and ketamines in biological samples. Eventually, the results obtained in this study contribute to the analysis of drug abused in forensic sciences and clinical laboratories.

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Yen, Ping-Chung, et 顏鍾. « EFFECT OF THE LENGTH OF ACHIRAL ALKYL CHAIN AND TERMINAL BRANCHED ALKYL CHAIN OF CHIRAL LIQUID CRYSTALS ON THE STABILITY OF TGBA* PHASE ». Thesis, 1997. http://ndltd.ncl.edu.tw/handle/11565941195493741036.

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41

Yeh, Tsung-Lin, et 葉宗林. « THE EFFECT OF THE CORE STRUCTURE AND THE ALKYL LENGTH ON THE FORMAITON OF MESOPHASES OF THE CHIRAL LIQUID CRYSTAL MATERIALS AND ACHIRAL SWALLOW-TAIL MATERIALS ». Thesis, 1999. http://ndltd.ncl.edu.tw/handle/11287310076061278797.

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碩士
大同工學院
化學工程研究所
87
ABSTRACT Chiral material, (R)-2-alkyl-ols, and achiral material, 1-alkyl-alcohols, were used as building blocks for the preparation of liquid crystal materials. The investigation that the effect of molecular structures on the mesophases and mesomorphic properties was divided into three parts. The first part was to synthesize a homologous series of (S)-(-)-6-(1-methylalkyloxy)naphth-2-yl 4-decyloxybenzoates, (S)MnNDB (n=2~6), in order to investigate the effect of extending the chiral peripheral alkyl chain length on the mesomorphic properties. The results of (S)MnNDB reveal two stable frustrated phases, BP and TGBA, in this series. The stability of the TGBA phase decreases with increasing of the length of peripheral alkyl chain, n. The extension of the alkyl chain has an significant effect on the thermal stability of SC* phase. The second part was to synthesize (S)-(-)-6-(1-methylalkyloxy) naphth-2-yl 4'-decyloxybiphenyl-4-carboxylates, (S)MnNDBPC (n=2~6), in order to understand the effect of extending the rigid core structure by biphenyl on the formation of the SC* phases. The investigation of compounds, (S)-(-)-6-(1-methylalkyloxy)naphth-2-yl 4'-decyloxy biphenyl-4-carboxylates, (S)MnNDBPC (n=2~6), shows that, when the rigid core structure is extended by an additional phenyl ring, the thermal stability of the mesophases increases and all mesophases are enantiotropic. When the alkyl chain length is extended at the chiral tail group, the clearing points exists an odd-even effect, the temperature range of SA phase depressed, the thermal stability of SC* phase is gradually increases. The third part was to synthesize a homologous series of 6-(1-alkylalkyloxy)naphth-2-yl 4'-decyloxybiphenyl-4-carboxylates, AnNDBPC (n=2~5), in order to understand achiral swallow-tailed materials with antiferroelectric-like structure and their potential use in antiferroelectric mixtures. The third part is replace the chiral tail group with achiral swallow-tailed group, the thermal stability of the mesophases is depressed. Achiral swallow-tailed liquid crystalline material, A5NDBPC, is known to give alternating-tilt smectic C phases (SCalt) which have structural similarities to the chiral antiferroelecric phases denoted as SCA*. Optical microscopy and differential scanning calorimetry confirm that these materials show SCalt phase. The compounds were investigated as potential hosts which could be doped with a chiral ferroelectric liquid crystal so as to provide a viable antiferroelectric mixture. At last work is to investigate the electro-optical properties of these chiral and mixture materials, such as the switching current behavior, spontaneous polarization (Ps), dielectric constant and optical transmittance. The chiral compounds of (S)MnNDB and (S)MnNDBPC have been demonstrated to exhibit ferroelectricity in SC* phase by a single peak switching current of the switching behavior, observation of schlieren texture in thin defect film and a single hysteresis loop of the transmittance versus applied field curves. The results of Ps values of (S)MnNDBPC(n=2~6) were higher than (S)MnNDB(n=2~6) as the rigid core structure is extended by an additional phenyl ring. This phenomenon was resulted from the molecular polarity. Finally, the mixture material of (S)M5NDBPC (wt%: 75) and A5NDBPC (wt%: 25), m1, have been demonstrated to exhibit SCAF* phase by a two peaks switching current of the switching behavior.

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Cheng, Te-Sheng, et 鄭德勝. « EFFECT OF THE LENGTH OF ACHIRAL ALKYL CHAIN, TERMINAL ALKYL CHAIN AND THE RIGID CORE STRUCTURE OF OXYGEN-CONTAINING CHIRAL LIQUID CRYSTALS ON THE STABILITY OF FRUSTRATED PHASES ». Thesis, 1997. http://ndltd.ncl.edu.tw/handle/44722884029684878540.

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碩士
大同工學院
化學工程學系
85
Chiral (R)- and (S)-3-alkoxy-2-methylpropionic acids were synthesized as building blocks for the preparation of chiral liquid crystalline materials. The investigation about the effect of molecular structures on the mesophases and mesomorphic properties was divided into three parts. The first part was to synthesize a homologous series of (R)-6-(3- ethoxy-2-methylpropionyloxy)-2- naphthyl 4- alkoxybenzoates , (R)EMPNmB (m=6~13) , in order to understand the effect of extending the achiral peripheral alkyl chain length on the mesomorphic properties. The second part was to synthesize (R)-6-(3-ethoxy-2-methylpropionyl- oxy)-2-naphthyl 4?- decyloxybiphenyl -4-carboxylate ,(R)EMPNBC , in order to understand the effect of extending the rigid core structure by an additional phenyl ring on the formation of the TGB phases . The third part was to synthesize a homologues series of (R)-6-(3-alkoxy-2-methylpropionyloxy)-2- naphthyl 4-decyloxybenzoates , (R)nMPNB (n=2~5) , in order to understand the effect of alkyl chain length attached to the chiral tail on the effect of TGB phases. Furthermore, the influence of chiral moiety between oxygen- and sulfur- containing liquid crystallines on the mesomorphic properties was also compared and discussed. The results of the first homologous (R)EMPNmB reveal that stable frustrated phases exhibit in this series . The stability of the TGBA* phase decreases with the increasing peripheral alkyl chain length, m, whereas the temperature range of the TGBc* phase tents to ascend as m increases. The investigation of compound (R)EMPNBC shows that, when the rigid core structure is extended by an additional phenyl ring , the thermal stability of the mesophases increases , the temperature range of BPI phase depresses, the TGBc* phase disappeares, and a relatively wide temperature range of the Sc* phase appears. The third homologous compounds (R)nMPNB , show that all mesophases are enantiotropic. When extending the alkyl chain length at the chiral tail group, the clearing points exist an odd-even effect, the TGBA* phase disappears and a relatively wide temperature range of the TGBc* phase appears . The results demonstrate that the elongation of the alkyl chain length has no significant effect on the thermal stability of BP, N* and TGBc* phases. When the sulfur atom is replaced by oxygen in the chiral tail group , the clearing points for oxygen-containing materials are higher than that for sulfur containing materials . It is suggested that the oxygen contributes more dipole than sulfur. From binary mixture studies,it is found that the handedness of the helical twist sense for oxygen-containing materials, (R)EMPNmB, is opposite to sulfur-containing materials, (R)EMMPNmB. Furthermore, study in the electro-optical properties shows that the spontane- ous polarizations for oxygen-containing materials are approximately 20 nC/cm2. The magnitude of the Ps reduces as the rigid core structure is extended by an additional phenyl ring. In conclusion , the results demonstrate that oxygen- containing materials exhibit wide temperature range of frustrated phases. It is suggested that these materials possess high degree of "chirality". Our systematic studies also reveal that the spatial configuration of the molecules contributes a significant influ- ence on the formation of frustrated phases.

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Zheng, De-Sheng, et 鄭德勝. « EFFECT OF THE LENGTH OF ACHIRAL ALKYL CHAIN, TERMINAL ALKYL CHAIN AND THE RIGID CORE STRUCTURE OF OXYGEN-CONTAINING CHIRAL LIQUID CRYSTALS ON THE STABILITY OF FRUSTRATED PHASES ». Thesis, 1997. http://ndltd.ncl.edu.tw/handle/00558674379637586241.

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44

Chattopadhyay, Jayeeta. « Activity induced phase separation and the emergence of liquid crystal phases in chiral and achiral systems, and development of an efficient method to compute the entropy of various liquid crystal phases ». Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6168.

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The phase behaviour of shape-anisotropic particles is an emerging field of research that gives rise to various liquid crystal phases. In this thesis, we explore various equilibrium and non-equilibrium properties of shape-anisotropic particles by modelling them as soft repulsive spherocylinders (SRSs) and soft helical rods. In the first part, we introduce the two-temperature model to study the phase behaviour of scalar active SRS and soft helical rods. Most realisations of activity are vectorial in nature due to the force of self-propulsion. Recent studies have shown that many physical and biological processes, like phase separation in colloidal systems, chromatin organisation in the nucleus, are operated by the unequal sharing of energy by the constituents of the system. Such systems are classified as scalar active systems. In the simplest case, these systems can be modelled by connecting half the particles with a thermostat of higher temperature (labelled ‘hot’/‘active’) while maintaining temperature of the rest constant (labelled ‘cold’/‘passive’) at a lower value. The relative temperature difference between the two constituents of the system is a measure of activity. This model is known as two-temperature model that has been found to capture many essential properties of scalar activity. Starting from a homogeneous isotropic phase at a definite temperature, we show that this model leads to phase separation into hot and cold regions and induces liquid-crystal ordering of the cold particles while hot particles remain in the isotropic phase. In particular, we find that activity drives the cold particles through a phase transition to a more ordered state and the hot particles to a state of less order compared to the initial equilibrium state. Hence, the phase boundary of the isotropic-nematic transition shifts towards lower densities for cold particles and higher densities for the hot particles with respect to its equilibrium location. Remarkably, we find liquid crystalline phases for the aspect ratios [length(L)/diameter(D)] as low as L/D = 2, 3 which do not satisfy the minimum shape-anisotropy criteria that Onsager’s theory demands in equilibrium. Similar model we have employed in a system of soft helical particles of various intrinsic chiralities and found different liquid crystal ordering in these cases as well. The following nonequilibrium features emerge from our study: an enhancement of the temperature of half of the particles gives rise to LC ordering in the remaining half of the particles at any density. The hot and cold domains should not be viewed as bulk equilibrium phases with non-equilibrium behaviour only at the interfaces. By calculating the stress anisotropy and heat current, we find that the non-equilibrium behaviour is not restricted to the hot-cold interfaces but pervades the system as a whole, driving various ordering transitions in the cold zone. Thus, our study unravels various aspects of non-equilibrium scalar active rods in the framework of the two-temperature model. In the second part, we discuss the Two-phase thermodynamic (2PT) model for computing entropy, free energy, and other thermodynamic properties of various liquid crystal phases in equilibrium. In the 2PT method, the density of state (DoS) of the LC phases is decomposed into vibrational (solid) and diffusive (gas) components. The thermodynamic quantities are then calculated using harmonic oscillator approximations for the solid component, hard sphere approximations for the gas component, and the rigid rotor approximation for the rotational mode. In the 2PT method, the entropy of a definite state point is calculated from a single MD trajectory, which makes it advantageous for systems for which the analytical form of the equation of state is unknown (such as SRS). Our method can be used to calculate entropy and other thermodynamic quantities of different liquid crystal phases formed by the SRS system.
Inspire fellowship

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45

Yung, Ling-ya, et 袁琳雅. « Study on the Mesophases and Electric-optical Properties of Chiral Materials Possessing Various Achial and Chiral Alkyl Chains at Chiral Tail ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/69532520708963214186.

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碩士
大同大學
化學工程學系(所)
97
The purpose of this research work was an attempt to elucidate the extension of chiral alkyl length of liquid crystal materials possessing the lateral methyl substituent affects on the mesomorphic and electro-optical properties. Thus, new chiral precursors, (S)-1-alkyloxy-2-propanols were designed and synthesized by the reaction of (S)-propylene oxide with alkanols under basic condition. Subsequently, four homologous series of chiral liquid materials, (R)-1-alkyloxy-2-propyl 4-[4’-(4”-alkyloxyphenyl)phenyloxy]benzoates , I(m=8-12,n=5), II(m=8-12,n=6), III(m=8-12,n=7) and IV(m=8-12,n=8), were designed and synthesized to investigate the effect of changing aliphatic alkyl chain length (m) and chiral alkyl chain length (n) on the mesomorphic and electro-optical properties. The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric phase were further identified by the measurements of electric switching behavior and dielectric constant ε'. The results show that all chiral liquid materials display enantiotropic SmA* phase and SmC* phase. The results also show that compounds with shorter alkyl chain (m=8-10) exhibit a phase sequence of Iso.-SmA*-SmC*- Cr1-Cr2, while compounds (m=11, 12) with longer chain exhibit a phase sequence of Iso.-SmA*-SmC*-Cr in cooling process. With the increasing achiral terminal chain lengths, m, the clearing point decrease. The temperature range of the SmA* phase decreases by extending the length of achiral aliphatic chains in a series of compounds I-6(m=8-12, n=5). The physical properties such as switching current, spontaneous polarization, tilt angle and dielectric constant in the ferroelectric SmC* phases of the chiral compounds were measured. In general, the magnitudes of spontaneous polarization ascend with decreasing temperature. The maximum magnitudes of the spontaneous polarization for these compounds are approximately in a range of 7.84-12.71 nC/cm2. Comparison of compounds I, II, III, IV(m=8-12, n=5-8) and PPmPPn(m=8-12, n=1-4) clearly show that the maximum Ps value is increased by extending the length (n) of the alkyl chains at chiral tail from n=1, 2, 3 to 4, but that is decreased by extending the length (n) of the alkyl chains at chiral tail from n=5, 6, 7 to 8. The former results are due to, as the alkyl chain is extended, the chiral center and a certain portion of the alkyl chain are supposed to spend more time lying along the long axis of the molecule, such that the chiral center has a fixed spatial arrangement with respect to its local environment, this in tern will fix the orient of the diple at the chiral center. The later results are presumably due to the effect of increasing mass that shield the dipole at the chiral centre and then reduce the Ps. The maximum tilt angles of compounds are approximately in a range of 16.4-32.00. The magnitudes of apparent tilt angle (θ) values are increased by extending achiral terminal alkyl chain length(m), but that has no significant correlation with the chiral terminal alkyl chain length (n). In conclusion, the optically active alcohols, (S)-1-alkyloxy-2-propanols for the use as the building blocks of the chiral liquid crystals were designed and synthesized. Four series of chiral materials derived from these alcohols exhibit enantiotropic SmA* and SmC* phases. The structure-property correlation of these chiral materials in terms of achiral and chiral alkyl chain lengths (m and n) are established, herein.

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Schierwater, Kathrin [Verfasser]. « Chirale und achirale Lanthanoidorganyle mit funktionalisierten Alkoxidbrücken / vorgelegt von Kathrin Schierwater ». 2003. http://d-nb.info/969985533/34.

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Ehlert, Dennis K. [Verfasser]. « Chirale und achirale Liganden für die Fluoreszenzspektroskopie / von Dennis K. Ehlert ». 1999. http://d-nb.info/95764468X/34.

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Thèses sur le sujet « Achiral and chiral »

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