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Chiral separation by simulated moving bed chromatography

Pais, L.S.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
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The general objective of this work is the study of the behaviour of the Simulated Moving Bed (SMB) processes, with applications to chiral separations. Briefly, SMB chromatography allows the continuous injection and separation of binary mixtures. The simulated countercurrent contact between the solid and liquid phases maximizes the mass transfer driving force, leading lo a significant reduction in mobile and stationary phases consumption when cornpared with elution chromatography. The problem of modeling a SMB separation process is analyzed by two different strategies: one, by simulating the system directly, taking into account its intermittent behaviour (the SMB model); other by representing its operation in terms of a true countercurrent system (TMB model). From the comparative study, we conclude that the prediction of the performance of a SMB operation, and so its flow-rate optimization, can be safely done by using the TMB approach. The effect of the model parameters and operating variables on the SMB performance is analyzed in terms of four parameters: purity, recovery, solvent consumption, and adsorbent productivity. This work shows the influence of the switch time interval, recycling flow-rate, and inlet and outlet flow-rates. Also studied is the influence of axial dispersion and mass transfer resistance on the 8MB performance. We conclude that the mass transfer resistance can reduce significantly the possible set of operating conditions that lead to the desired separation. Moreover...

Determinação dos enantiômeros da atropina em soluções oftálmicas empregando a cromatografia líquida de alta eficiência com fase estacionária quiral; Determination of atropine enantiomers in ophthalmic solutions by liquid chromatography using a chiral stationary phase

Soares, Renata
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/11/2007 PT
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Há muitos agentes terapêuticos comercializados sob forma racêmica. Os enantiômeros podem apresentar diferenças significativas nos perfis farmacocinético e farmacodinâmico. O uso do enantiômero puro em formulações farmacêuticas pode resultar em melhor ajuste de dose e menos efeitos adversos. A atropina, um alcalóide natural da Atropa belladonna, é a mistura racêmica de l-hiosciamina e d-hiosciamina. Este fármaco é principalmente utilizado para dilatar a pupila e como um antiespasmódico. Para quantificar estes enantiômeros, foram desenvolvidos métodos analíticos utilizando a cromatografia líquida de alta eficiência (CLAE) com as fases estacionárias quirais Chiralcel-OD® e Chiral-AGP®. Para quantificar estes enantiômeros em soluções oftálmicas, foi realizada a validação com sucesso de um método por CLAE, empregando uma coluna Chiral-AGP®, a 20°C. A fase móvel foi uma solução tampão fosfato (contendo 10 mM de 1-octanosulfonato de sódio e 7,5 mM de trietilamina, ajustada para pH 7,0 com ácido fosfórico) e acetonitrila (99:1 v/v). A vazão foi de 0,6 mL/min, com detecção ultravioleta em 205 nm. No intervalo de concentração de 14,0 µg/mL a 26,0 µg/mL, o método é linear (r > 0,9999)...

Estudos por RMN de 1H das interações de substratos carbonílicos e carboxílicos com agentes de discriminação quiral; 1H NMR investigations of the interactions of carbonyl and carboxyl derivatives with chiral discriminating agents

Claudio, Thais Bezerra
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/06/2010 PT
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Os sais derivados de alcalóides da Cinchona têm sido muito utilizados como catalisadores de transferência de fase, em reações assimétricas. No entanto, sua performance como agentes de discriminação quiral tem sido pouco explorada. Com o objetivo de melhor compreender as bases moleculares que comandam o reconhecimento quiral dos isômeros ópticos de compostos carbonílicos e carboxílicos, quando em mistura com a quinina ou com sais de alcalóides da Cinchona, foi realizada uma série de experimentos, utilizando a técnica da RMN de 1H. A atribuição dos deslocamentos químicos aos solvatos de cada enantiômero foi feita pelo registro do espectro de RMN de 1H de misturas dos agentes de discriminação quiral com amostras enantiopuras ou enantiomericamente enriquecidas dos substratos. A estabilidade relativa dos solvatos foi estimada utilizando-se modelos moleculares, nos quais foi possível identificar a existência de interações do tipo π-π e de ligações de hidrogênio. As conclusões baseadas nos experimentos de RMN de 1H foram concordantes com as resultantes da análise dos modelos moleculares, construídos para cada par substrato/agente de discriminação quiral; Salts of Cinchone alcaloids are common chiral catalysts for asymmetric phase-transfer reactions. However...

Hydrothermal syntheses of ETS-10 like vanadosilicates using chiral organic molecules. Part I

Paula, Alex S.; de Vasconcellos, Adriano; Ellena, Javier A.; Giotto, Marcus; Nery, Jose G.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 30-46
ENG
Relevância na Pesquisa
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 05/54703-6; Processo FAPESP: 08/56973-9; Vanadosilicates with the structures of ETS-10 and AM-6 microporous materials have been hydrothermally synthesized using organic directing structures agent (SDAs) derivatives of decahydroquinoline, 3,5-dimethyl-piperidine, 2,6-dimethyl-piperidine and (S)-Sparteine. Derivatives of these chiral amines have not been explored before in the sot gel chemistry of vanadosilicates. Physicochemical characterization of the obtained vanadosilicate materials with these different chiral templates was carried out by Xray diffraction (XRD), scanning electron microscopy (SEM). Raman and infrared (IR) spectroscopy, solid-state NMR spectroscopy, and differential thermogravimetric analysis (DTA)/thermogravimetric analysis (TGA). The results suggest that the presence of the chiral organic templates have different effects in terms of the final phase of the synthesized materials and their morphology. The products obtained using chiral template derivatives of decahydroquinoline reveal that certain products might be very enriched with chiral polymorph A while others present structures which are similar to other large-porous vanadosilicate such as AM-6 and AM-13. Derivatives of 2...

Adição de nucleofilos a ions N-aciliminios quirais e reações de ciclização promovidas por Pd(0); Nucleophilic addition to chiral N-acyliminium ions and palladium(0)-mediated cyclization reactions

Luis Gustavo Robello
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/12/2006 PT
Relevância na Pesquisa
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A primeira parte do trabalho envolveu a adição de nucleófilos de carbono a íons N-acilimínios quirais derivados da tetraidroisoquinolina. Após demonstrada a viabilidade da metodologia em sua versão racêmica, a eficiência dos auxiliares quirais cicloexílicos derivados do (1R,2S)-(-)-trans-fenilcicloexanol (97) e (1R,2S,5R)-(-)-8-fenilmentol (98) foi estudada. A adição de aliltrimetilsilano (86b) frente aos íons N-acilimínios quirais forneceu as respectivas tetraidroisoquinilinas aliladas 104b e 106b em rendimentos moderados (56-65%) e razões diastereoisoméricas de 1,6:1 e 1,8:1 quando 97 e 98 foram empregados como auxiliares quirais, respectivamente. A reação de Mannich viníloga envolvendo um nucleófilo pró-quiral, triisopropilsililoxifurano (86c), forneceu os correspondentes butenolídeos 104c e 106c em rendimentos de 42-56%. As razões diastereoisoméricas (rd 3:1 e 2:1) só foram determinadas após seqüência reacional que permitiu a obtenção da hidroxilactama 89 e a recuperação dos álcoois quirais 97 e 98. Baixos níveis de diastereosseletividade (rd = 1,2:1-1,4:1) também foram observados na adição de aliltributilestanho (86d) a íons N-aciliminíos do tipo trans-a e b-naftilcicloexílicos, gerados in situ a partir da reação entre cloroformatos quirais (116b...

Tecnicas de RMN de 1H aplicadas a complexos supramoleculares de calixarenos quirais envolvendo reconhecimento quiral e reduções assimetricas; 1H NMR techniques applied to calixarenes supramolecular chiral complexes involved in chiral recognition and asymmetric reduction

Sergio Antonio Fernandes
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/08/2005 PT
Relevância na Pesquisa
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Esta tese teve como objetivo principal estudar interações intermoleculares empregando a espectroscopia de RMN de H como ferramenta principal. O primeiro capítulo visou "construir" um "hospedeiro quiral" através de interações não covalentes que foi aplicado na discriminação quiral e síntese assimétrica, ambos discutidos, no segundo e terceiro capítulo. Este hospedeiro quiral foi obtido via complexação de calixarenos com aminas quirais ((S)-feniletilamina, (S)naftiletilamina e (R)-2-aminobutanol). A topologia dos complexos foi determinada por RMN de H através de incremento de sinal devido ao acoplamento dipolar observado nas coordenadas girantes entre o hospedeiro (calixareno) e o hóspede (amina). Os experimentos de RMN de H a baixa temperatura foram usados para determinar a conformação preferencial e as mudanças na flexibilidade do calixareno livre e nos complexados. O segundo capítulo, descreve a aplicação dos complexos supramoleculares quirais no reconhecimento quiral e na determinação de excessos enantioméricos de sulfóxidos e ácidos. A importância do solvente, temperatura e topologia foram investigados. O terceiro capítulo focalizou a aplicação dos hospedeiros quirais na redução assimétrica de iminas e sais de metil isoquinolina com boroidreto de sódio. Os excessos enantioméricos são altamente dependentes dos substratos e variam de 0-90%. Finalmente o hospedeiro quiral foi obtido e a topologia totalmente descrita sendo o mesmo aplicado em reconhecimento quiral e síntese assimétrica...

Computer-Assisted Design and Synthetic Applications of Chiral Enol Borinates: Novel, Highly Enantioselective Aldol Reagents

Gennari,Cesare; Ceccarelli,Simona; Piarulli,Umberto; Aboutayab,Karim
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/1998 EN
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We have recently described the development of a quantitative transition state model for the prediction of stereoselectivity in the boron-mediated aldol reaction. This model provides qualitative insights into the factors contributing to the stereochemical outcome of a variety of reactions of synthetic importance. The force field model was used to assist the design and preparation of new chiral boron ligands derived from menthone. The chiral boron enolates were employed in various stereoselective processes, including the addition to chiral aldehydes and the reagent-controlled total synthesis of (3S,4S)-statine. The chiral enolates derived from alpha-halo and alpha-oxysubstituted thioacetates were added to aldehydes and imines. Addition to imines leads to the enantioselective synthesis of chiral aziridines, a formal total synthesis of (+)-thiamphenicol, and a new highly efficient synthesis of the paclitaxel (taxol®) C-13 side-chain and taxol semisynthesis from baccatin III. The stereochemical outcome of the addition to imines was rationalised with the aid of computational studies. Enantioselective addition reactions of the chiral boron enolate derived from thioacetate have successfully been applied to solid phase bound aldehydes to give aldol products in comparable yields and enantioselectivities to the usual solution conditions.

Chiral Koszul Duality

Francis, John; Gaitsgory, Dennis
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
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We extend the theory of chiral and factorization algebras, developed for curves by Beilinson and Drinfeld (American Mathematical Society Colloquium Publications, 51. American Mathematical Society, Providence, RI, 2004), to higher-dimensional varieties. This extension entails the development of the homotopy theory of chiral and factorization structures, in a sense analogous to Quillen’s homotopy theory of differential graded Lie algebras. We prove the equivalence of higher-dimensional chiral and factorization algebras by embedding factorization algebras into a larger category of chiral commutative coalgebras, then realizing this interrelation as a chiral form of Koszul duality. We apply these techniques to rederive some fundamental results of Beilinson and Drinfeld (American Mathematical Society Colloquium Publications, 51. American Mathematical Society, Providence, RI, 2004) on chiral enveloping algebras of (star)-Lie algebras.; Mathematics

Chirality of Light and Its Interaction with Chiral Matter

Tang, Yiqiao
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
Relevância na Pesquisa
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This thesis conducts a systematic study on the chirality of light and its interaction with chiral matter. In the theory section, we introduce a measure of local density of chirality, applying to arbitrary electromagnetic fields. This optical chirality suggests the existence of superchiral modes, which are more selective than circularly polarized light (CPL) in preferentially exciting single enantiomers in certain regions of space. Experimentally, we demonstrate an 11-fold enhancement over CPL in discriminating chiral fluorophores of single handedness in a precisely sculpted superchiral field. This result agrees to within 15% with theoretical predictions. Any chiral configuration of point charges is beyond the scope of our theory on optical chirality. To address chiroptical excitations at nanoscale, we develop a model of twisted dipolar oscillators. We design a simple tunable chiral nanostructure and observe localized chiroptical “hot spots” with dramatically enhanced circular differential scattering. Our work on superchiral light and 3D chiral metamaterials establishes optical chirality as a fundamental and tunable property of light, with implications ranging from plasmonic sensors, absolute asymmetric synthesis to new strategies for fabricating three-dimensional chiral metamaterials. This thesis is organized as such: Chapter 1 provides a background on previous studies of chiroptical phenomena...

Chromatography and mass spectrometry in the study of structure and dynamics of chiral molecules

SABIA, ROCCHINA
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN
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Part A Dynamic high performance liquid chromatography on chiral stationary phases is a consolidated technique that allows the investigation of chiral molecules with labile stereogenic elements that interconvert very quickly at room temperature and result in stereoinversion processes occurring on the time scale of the separation process. Kinetic parameters for on-column interconversions can be extracted from exchange-deformed experimental peak profiles by computer simulation. The technique has been used in a wide range of temperatures and is complementary in scope to dynamic nuclear magnetic resonance spectroscopy. Here we report, in the first part, the separation of the enantiomers of benzodiazepines, a class of molecules whose conformational enantiomers interconvert not only through a single bond rotation but also via “ring-flip” inversion. The second part concerns the first HPLC resolution of the conformational enantiomers of tri-O-thymotide (TOT) a macrocyclic trilactone existing in fast-exchanging multiple chiral conformations. Variable chromatography on brush type stationary phases showed dynamic features due to on-column interconversions of TOT. Part B Chiral recognition is a branch of chemistry aimed at understanding the reactivity as well as the size- and shape-specificity of non-covalent interactions between molecular aggregates formed by chiral species. Mass spectrometry (MS) is a powerful tool for investigating chiral recognition in the gas phase in the absence of perturbing environmental phenomena and discriminating and even quantifying chiral species by interaction with chiral reference molecules. A small library of synthetic receptors was prepared by macrocyclization of complementary A and B fragments to yield A2B2 macrocycles...

The Utilization of Chiral Ion Mobility Spectrometry for the Detection of Enantiomeric Mixtures and Thermally Labile Compounds

Holness, Howard K.
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
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This dissertation utilized electrospray ion mobility mass spectrometry (ESI-IMS-MS) to develop methods necessary for the separation of chiral compounds of forensic interest. The compounds separated included ephedrines and pseudoephedrines, that occur as impurities in confiscated amphetamine type substances (ATS) in an effort to determine the origin of these substances. The ESI-IMS-MS technique proved to be faster and more cost effective than traditional chromatographic methods currently used to conduct chiral separations such as gas and liquid chromatography. Both mass spectrometric and computational analysis revealed the separation mechanism of these chiral interactions allowing for further development to separate other chiral compounds by IMS. Successful separation of chiral compounds was achieved utilizing a variety of modifiers injected into the IMS drift tube. It was found that the modifiers themselves did not need to be chiral in nature and that achiral modifiers were sufficient in performing the required separations. The ESI-IMS-MS technique was also used to detect thermally labile compounds which are commonly found in explosive substances. The methods developed provided mass spectrometric identification of the type of ionic species being detected from explosive analytes as well as the appropriate solvent that enhances detection of these analytes in either the negative or positive ion mode. An application of the developed technique was applied to the analysis of a variety of low explosive smokeless powder samples. It was found that the developed ESI-IMS-MS technique not only detected the components of the smokeless powders...

Chiral dynamics of baryons in the perturbative chiral quark model; Chirale Dynamik der Baryonen im perturbativen chiralen Quarkmodell

Pumsa-ard, Kem
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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In this work we develop and apply variants of a perturbative chiral quark model (PCQM) to the study of baryonic properties dominantly in the low-energy region. In the PCQM baryons are considered in leading order as bound states of valence quarks with a nontrivial structure, while the sea-quark excitations are contained in a cloud of pseudoscalar mesons as imposed by chiral symmetry requirements. Since the valence quark structure dominates, pseudoscalar or chiral effects are treated perturbatively. In a first step we consider a noncovariant form of the PCQM, where confinement is modelled by a static, effective potential and chiral corrections are treated to second order, in line with similar chiral quark models. We apply the PCQM to the study of the electromagnetic form factors of the baryon octet. We focus in particular on the low-energy observables such as the magnetic moments, the charge and magnetic radii. In addition, the electromagnetic N-delta transition is also studied in the framework of the PCQM, where meson cloud contributions play a decisive role. In the chiral loop calculations we consider a quark propagator, which is restricted to the quark ground state, or in hadronic language to nucleon and delta intermediate states...

Gaschromatographische Enantiomerentrennung an einfachen und binären chiralen Selektoren sowie Kopplung der Kapillar-Gaschromatographie mit der NMR-Spektroskopie; Gas chromatographic enantioseparation on single and binary chiral selectors as well as coupling of capillary gas chromatography with NMR-spectroscopy

Kreidler, Diana
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Trotz Abwesenheit von funktionellen Gruppen können chirale Alkane und Cycloalkane gaschromatographisch an alkylierten Cyclodextrinen über Van der Waalssche Kräfte in die Enantiomere getrennt werden. Da unterschiedliche chirale Cyclodextrinselektoren für die Enantiomerentrennung von verschiedenen kleinen chiralen Alkanen benötigt werden, wurden in dieser Arbeit gemischte chirale Selektorsysteme entwickelt. Auf einem binären chiralen Selektor aus Chirasil-beta-Dex und Octakis(6-O-methyl-2,3-di-O-pentyl)-gamma-cyclodextrin (Lipodex G) konnte die simultane Enantiomerentrennung von allen C7-C8 chiralen Alkanen, die ein stereogenes Zentrum aufweisen, in einem gaschromatographischen Lauf erreicht werden. Mit einem weiteren binären chiralen Selektorsystem aus Heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin und Octakis(6-O-methyl-2,3-di-O-pentyl)-gamma-cyclodextrin (Lipodex G) in Polysiloxan PS 086 wurde die simultane Enantiomerentrennung von allen kleinen chiralen Alkanen mit einem stereogenen Zentrum und von 17 alpha-Aminosäuren als N-(O,S)-Trifluoracetyl-alkyl-estern in einer einzigen gaschromato-graphischen Messung ermöglicht. Es wurden auf diesem gemischten binären chiralen Selektorsystem auch Enantiomerentrennungen für zahlreiche chirale Moleküle aus unterschiedlichen Substanzklassen...

Second Harmonic Generation of Chiral-Modified Silver Nanoparticles

Tao, Yue
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.590396%
Chiral molecules, which exist under enantiomers with non-mirror-symmetrical structures, have been the subject of intense research for their linear and nonlinear optical activities. Cysteine is such a chiral amino acid found as a building block of proteins throughout human bodies. Second harmonic generation (SHG) has been considered to investigate chiral molecules. SHG from metallic nanoparticles is promising for nanoplasmonics and photonic nanodevice applications. Therefore, it’s desirable to combine and study nonlinear properties due to both chirality and metallic nanoparticles, and help developing an alternatively optical diagnostic of chiral molecules. Our experiments are carried out with the FemtoFiber Scientific FFS laser system. SHG of silver nanoparticles (Ag NPs) modified by either L-Cysteine (L-C) or D-Cysteine (D-C) is observed, where L-Cysteine and D-Cysteine are a pair of enantiomers. Ag NPs are deposited through Vacuum Thermal Evaporation, controlled under different deposition thicknesses. UV-Vis/IR spectra and AFM are used to characterize Ag NPs under different conditions. Transmitted SHG measurements dependent on incidence are recorded with standard lock-in techniques. Deposition thickness of vacuum thermal evaporation plays an important role in forming diverse Ag NPs...

Enantioselective Mechanism of the Whelk-O1 Chiral Stationary Phase: A Molecular Dynamics Study

Zhao, CHUNFENG
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 4780571 bytes; application/pdf
EN; EN
Relevância na Pesquisa
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The Whelk-O1 chiral stationary phase is widely used in liquid and supercritical chromatography for the separation of enantiomers. The enantioselective mechanism of the Whelk-O1 chiral stationary phase is the main focus of this thesis. Semi-flexible models are developed based on ab initio calculations for the Whelk-O1 selector and a series of chiral analytes. Extensive molecular dynamics simulations are then applied to study the solvation, selectivity and in silico optimization of the chiral stationary phase. The solvation of the Whelk-O1 chiral stationary phase has been explored in a normal phase n-hexane/2-propanol solvent, a reversed phase water/methanol solvent, and a supercritical CO2/methanol solvent. We found that, in all three solvents, the Whelk-O1 selectors are open to the bulk, indicating readiness for docking of analyte. Significant solvent partitioning at the interfaces was noticed, which generates a polarity gradient between the stationary phase and the bulk, and may encourage a high analyte concentration at the interface. Hydrogen bonding activities on the amide hydrogen, amide oxygen, and nitro oxygen of the Whelk selector have also been analyzed. The selectivity of the Whelk selector was studied by molecular dynamics simulations of analyte docking on the chiral stationary phase. The elution orders and the separation factors for a series of analytes were predicted successfully. We found that hydrogen bonding and π-π stacking interactions are essential for the enantioselectivity as they are strong and specific...

Insights into the solvation and selectivity of chiral stationary phases using molecular dynamics simulations and chemical force microscopy

Nita, Sorin
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 6410415 bytes; application/pdf
EN; EN
Relevância na Pesquisa
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The mechanism by which chiral selectivity takes place is complicated by the surface morphology, the possible involvement of the solvent, and the characteristics of the chiral molecules at the surface. My goal is to model and understand the factors which lead to significant discrimination in the case of three closely related chiral stationary phases: N-(1-phenylethyl)-N’-[3-(triethoxysilyl)propyl]-urea (PEPU), [(3,5-dinitrobenzoyl)-amino]-N-[3-(triethoxysilyl)propyl]-2-phenylacetamide (DNB-phenyglycine), and [(3,5-dinitrobenzoyl)amino]-N-[3-(triethoxysilyl)propyl]-4-methylpentanamide (DNB-leucine). Ab initio calculations are used to develop molecular models of these chiral selectors. These models are employed in molecular dynamics (MD) simulations, which provide the theoretical framework for modelling chiral interfaces in different solvent mixtures. The MD simulations of PEPU interfaces show that, in alcohol/water mixtures, the alcohols form domains at the interface with the hydrophobic portions of the molecule tending to orient towards the surface. This disrupts the water hydrogen bonding networks at the interface and leads to the exclusion of water from the surface region relative to the bulk. The MD simulations of DNB-phenylglycine and DNB-leucine selectors in hexane/2-propanol mixtures demonstrate that the interfaces are distinct both in terms of the selector orientations at the surface and in the number of hydrogen bonds formed with 2-propanol. This occurs despite the structural similarity between these two selectors. The interfaces are also prepared experimentally by attaching the chiral selectors onto oxidized Si(111) samples and AFM tips. In particular...

Nonlinear dynamics in torsional chiral metamaterials

Liu, Mingkai
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD)
EN
Relevância na Pesquisa
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The advent and rapid development of metamaterials introduced many revolutionary concepts for manipulating electromagnetic waves. As an important class of metamaterials, chiral metamaterials allow us to control the polarization of electromagnetic waves at the subwavelength scale. While much work has been done on using chiral metamaterials to control electromagnetic waves, the accompanying effects, such as the electromagnetic force and torque acting on the structures, as well as nonlinear optomechanical effects, are still largely unexplored. The exploration of these areas could provide useful insight from both fundamental and practical points of view. In this thesis, we study new properties of chiral metamaterials, in particular the optomechanical properties and nonlinear effects that arise from the coupling between electromagnetic and elastic degrees of freedom. An accurate and efficient model based on the free-space Green’s function under the eigenmode approximation is developed for the study. In Chapter 1, we provide a comprehensive introduction to the basic concepts and history of metamaterials, followed by more focused reviews on chiral metamaterials, different paradigms of tunable metamaterials, the nontrivial electromagnetic force and torque...

Chiral analysis of pollutants and their metabolites by capillary electromigration methods

Hernández Borges, Javier; Rodríguez Delgado, Miguel A.; García-Montelongo, Francisco J.; Cifuentes, Alejandro
Fonte: Wiley-VCH Publicador: Wiley-VCH
Tipo: Artículo Formato: 306441 bytes; application/pdf
ENG
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Chiral separation of enantiomers is one of the most challenging tasks for any analytical technique including capillary electrophoresis (CE). Since the first report in 1985 showing the great possibilities of CE for the separation of chiral compounds, the amount of publications concerning this topic has quickly increased. Although chiral electromigration methods have mainly been used for enantioseparation of drugs and pharmaceuticals, they have also been applied to analyze chiral pollutants. This article intends to provide an updated overview, including works published till January 2005, on the principal applications of CE to the chiral analysis of pollutants and their metabolites, with especial emphasis on articles published in the last ten years. The main advantages and drawbacks regarding the use of CE for chiral separation of pollutants are addressed including some discussion on the foreseen trends of electromigration procedures applied to chiral analysis of contaminants.; J. Hernández-Borges wishes to thank the Ministerio de Educación y Ciencia de España for the FPU grant.; Peer reviewed

Spontaneous chiral symmetry breaking in QCD: a finite-size scaling study on the lattice

Giusti, Leonardo; Necco, Silvia
Fonte: International School for Advanced Studies; Institute of Physics Publishing Publicador: International School for Advanced Studies; Institute of Physics Publishing
Tipo: Artículo Formato: 2373 bytes; text/plain
ENG
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25 pages, 8 figures.-- ISI Article Identifier: 000246396400090.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-lat/0702013; Spontaneous chiral symmetry breaking in QCD with massless quarks at infinite volume can be seen in a finite box by studying, for instance, the dependence of the chiral condensate from the volume and the quark mass. We perform a feasibility study of this program by computing the quark condensate on the lattice in the quenched approximation of QCD at small quark masses. We carry out simulations in various topological sectors of the theory at several volumes, quark masses and lattice spacings by employing fermions with an exact chiral symmetry, and we focus on observables which are infrared stable and free from mass-dependent ultraviolet divergences. The numerical calculation is carried out with an exact variance-reduction technique, which is designed to be particularly efficient when spontaneous symmetry breaking is at work in generating a few very small low-lying eigenvalues of the Dirac operator. The finite-size scaling behaviour of the condensate in the topological sectors considered agrees, within our statistical accuracy, with the expectations of the chiral effective theory. Close to the chiral limit we observe a detailed agreement with the first Leutwyler-Smilga sum rule. By comparing the mass...

Spontaneously resolving chiral cis-[dinitrobis(ethylenediamine)cobalt]X complexes (X = Cl, Br) from the Alfred Werner collection of original samples at the University of Zurich - Alfred Werner's missed opportunity to become the 'Louis Pasteur' of coordination compounds

Blacque,Olivier; Berke,Heinz
Fonte: Universidad Nacional Autónoma de México, Facultad de Química Publicador: Universidad Nacional Autónoma de México, Facultad de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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17 original crystals of [Λ-dinitrobis(ethylenediamine)cobalt]X complexes from the Alfred Werner collection of original samples of the University of Zurich were studied by single crystal X-ray diffraction revealing that the complexes with X = Cl, Br can undergo spontaneous chiral resolution upon crystallization. The main focus of this article was the chiral [Λ- and Δ-dinitrobis(ethylenediamine)cobalt]Cl complexes, which crystallize from racemic solution in the space group P 21 mainly as synthetical twins enriched in one enantiomer, but to a small extent also as pure enantiomorphs. The twinning effect was recognized and correctly described by PhD student Richard Hessen of the Alfred Werner group (PhD thesis 1914). Richard Hessen eventually resolved the [Δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complex by the conglomerate salt resolution method. Based on the availability of the pure [Δ- or Λ-dinitrobis(ethylenediamine)cobalt]Cl complex, he carried out seeding experiments, which proved that the [Δ- and Λ-dinitrobis(ethylenediamine)cobalt]Cl complexes can be enriched to a great extent in one enantiomer by spontaneous chiral resolution. Already in the period of time from 1900 to 1904, various PhD students of Alfred Werner's group (Adolf Grün...