Bibliografías temáticas / Racemic Mixture

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Literatura académica sobre el tema "Racemic Mixture"

Autor: Grafiati
Publicado: 8 de septiembre de 2021
Última modificación: 12 de febrero de 2022

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Artículos de revistas sobre el tema "Racemic Mixture"

1

Baregama, Chetna. "STEREOCHEMISTRY - RACEMIC MODIFICATION, RESOLUTION, AND ITS IMPORTANCE WITH RECENTLY USED OPTICALLY ACTIVE DRUGS." Asian Journal of Pharmaceutical and Clinical Research 11, n.º 1 (1 de enero de 2018): 3. http://dx.doi.org/10.22159/ajpcr.2017.v11i1.23090.

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Stereochemistry involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. An important branch of stereochemistry is the study of chiral molecules. Optical activity is the ability of a chiral molecule to rotate the plane of plane-polarized light, measured using a polarimeter. Racemic modification and resolution, both processes are very important in stereochemistry. A mixture of equal parts of enantiomers is called a racemic modification. The process of separating a racemate into pure enantiomers is known as resolution. Recently, various optically active drugs are used for the treatment for various diseases. In these drugs, some are used as mixture of enantiomers and some used as single enantiomer. For preparation of optically active drugs, racemic modification and resolution processes are generally used. Hence, this is very important to know about various steps and types of processes used for the same. Racemic modification is advantageous where racemates have more therapeutic advantages than single isomers. Resolution is advantageous where single entiomer is used for treatment because single enantiomers have less complex and more selective pharmacodynamic profile as compared to racemic mixture so have lesser adverse drug reactions, improved therapeutic profile, less chances of drug interactions than racemic mixtures. Recently used optically active drugs are amlodipine, atenolol, cetirizine, ketamine, metoprolol, omeprazole, pantoprazole, salbutamol, propranolol, clopidogrel, rabeprazole, citalopram, ibuprofen, ketoprofen, zopiclone, etodolac, salbutamol, and nateglinide.
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2

Baregama, Chetna. "STEREOCHEMISTRY - RACEMIC MODIFICATION, RESOLUTION, AND ITS IMPORTANCE WITH RECENTLY USED OPTICALLY ACTIVE DRUGS." Asian Journal of Pharmaceutical and Clinical Research 11, n.º 1 (1 de enero de 2018): 3. http://dx.doi.org/10.22159/ajpcr.2018.v11i1.23090.

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Stereochemistry involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. An important branch of stereochemistry is the study of chiral molecules. Optical activity is the ability of a chiral molecule to rotate the plane of plane-polarized light, measured using a polarimeter. Racemic modification and resolution, both processes are very important in stereochemistry. A mixture of equal parts of enantiomers is called a racemic modification. The process of separating a racemate into pure enantiomers is known as resolution. Recently, various optically active drugs are used for the treatment for various diseases. In these drugs, some are used as mixture of enantiomers and some used as single enantiomer. For preparation of optically active drugs, racemic modification and resolution processes are generally used. Hence, this is very important to know about various steps and types of processes used for the same. Racemic modification is advantageous where racemates have more therapeutic advantages than single isomers. Resolution is advantageous where single entiomer is used for treatment because single enantiomers have less complex and more selective pharmacodynamic profile as compared to racemic mixture so have lesser adverse drug reactions, improved therapeutic profile, less chances of drug interactions than racemic mixtures. Recently used optically active drugs are amlodipine, atenolol, cetirizine, ketamine, metoprolol, omeprazole, pantoprazole, salbutamol, propranolol, clopidogrel, rabeprazole, citalopram, ibuprofen, ketoprofen, zopiclone, etodolac, salbutamol, and nateglinide.
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3

Xu, Zhongwei, Benguo Liu, Zhengxiang Ning y Yan Zhang. "Racemic dihydromyricetin dihydrate". Acta Crystallographica Section E Structure Reports Online 63, n.º 11 (24 de octubre de 2007): o4384. http://dx.doi.org/10.1107/s1600536807050416.

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The title compound, C15H12O8·2H2O, crystallizes with two organic molecules and four water molecules in the asymmetric unit. Crystal symmetry generates a racemic mixture of the chiral organic molecules. An extensive network of intramolecular and intermolecular O—H...O hydrogen bonds helps to establish the structure.
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4

Baggott, Joseph E., Tsunenobu Tamura y Herman Baker. "Re-evaluation of the metabolism of oral doses of racemic carbon-6 isomers of formyltetrahydrofolate in human subjects". British Journal of Nutrition 85, n.º 6 (junio de 2001): 653–57. http://dx.doi.org/10.1079/bjn2001323.

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The racemic mixture, [6RS]-5-formyltetrahydrofolate, is widely used clinically. In human subjects, orally-administered pure unnatural C-6 isomers, [6R]-5-formyltetrahydrofolate and [6S]-5,10-methenyltetrahydrofolate, were recently shown to be metabolized to the natural isomer, [6S]-5-methyltetrahydrofolate. We re-analysed the data from human studies published during the past four decades in which oral doses (≤10 mg) of racemic mixtures of these folates were used. We re-evaluated the data to determine whether these racemic mixtures are only 50 % bioactive or, as we now predict, more than 50 % bioactive. Our analyses indicate that, in human subjects, oral doses of the racemic mixture of the two formyltetrahydrofolates are 20–84 % more bioactive than would be predicted. These data are consistent with the following pathway: chemical conversion of these folates to 10-formyltetrahydrofolate; oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate; subsequent enzymic conversion of 10-formyldihydrofolate to dihydrofolate by 5-amino-4-imidazolecarboxamide ribotide transformylase; and finally the well-established metabolism of dihydrofolate to [6S]-5-methyltetrahydrofolate. An additional review of the literature supports thein vivooxidation of 10-formyltetrahydrofolate occurring to a certain extent, as 10-formyl-folic acid is rapidly formed after the administration of folic acid (pteroylglutamic acid) or 5-formyltetrahydrofolate in human subjects. The dogma that an oral dose of the unnatural C-6 isomer of 5-formyltetrahydrofolate is not bioactive in human subjects does not withstand scrutiny, most probably due to the previously unrecognizedin vivooxidation of 10-formyltetrahydrofolate. This discovery unveils new folate metabolism in human subjects.
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5

Polívka, Zdeněk, Jiří Holubek, Emil Svátek, Jan Metyš y Miroslav Protiva. "Synthesis of the semi-rigid analogues of prothiadene and dithiadene as potential antidepressant and antihistamine agents: 11-[2-(Dimethylaminomethyl)cyclohexylidene]-6,11-dihydrodibenzo[b,e]thiepins and 4-[2-(dimethylaminomethyl)cyclohexylidene]-4,9-dihydrothieno-[2,3-c]-2-benzothiepins". Collection of Czechoslovak Chemical Communications 50, n.º 5 (1985): 1078–88. http://dx.doi.org/10.1135/cccc19851078.

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Reaction of dibenzo[b,e]thiepin-11(6H)-one with 2-(dimethylaminomethyl)cyclohexylmagnesium chloride gave a mixture of stereoisomeric amino alcohols IX from which four homogeneous bases (IXa to IXd) were separated by chromatography. Dehydration of these compounds with boiling dilute hydrochloric acid afforded mixtures of racemic geometric isomers of the title compound VII, which were separated by crystallization. To the prevailing less polar base VIIa (E)-configuration was assigned on the basis of the IR spectrum. Using a similar procedure, thieno[2,3-c]-2-benzothiepin-4(9H)-one gave mixture of amino alcohols X from which three homogeneous stereoisomers X-A to X-C were isolated. Their dehydration resulted in both expected racemic geometric isomers VIII-A and VIII-B. Pharmacological testing proved the character of an antidepressant for the semi-rigid analogue of dithiadene VIII.
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6

Zhang, Jingqun, Qiang Zhou, Chris D. Smith, Haiyan Chen, Zhen Tan, Biyi Chen, Alma Nani et al. "Non-β-blocking R-carvedilol enantiomer suppresses Ca2+ waves and stress-induced ventricular tachyarrhythmia without lowering heart rate or blood pressure". Biochemical Journal 470, n.º 2 (20 de agosto de 2015): 233–42. http://dx.doi.org/10.1042/bj20150548.

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Carvedilol is a racemic mixture of R- and S-carvedilol. R-carvedilol, a non-β-blocking enantiomer, modifies the gating of the cardiac ryanodine receptor (RyR2) and suppresses Ca2+ waves and ventricular tachyarrhythmia (VT) without bradycardia and hypotension that are often associated with racemic carvedilol.
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7

Dachwitz, E. y M. Stockhausen. "On the Occurance of Stereoisomeric Effects in the Dielectric Relaxation Behaviour of Pure Liquid". Zeitschrift für Naturforschung A 43, n.º 5 (1 de mayo de 1988): 476–80. http://dx.doi.org/10.1515/zna-1988-0512.

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In order to find out whether liquids consisting of pure enantiomers of a chiral molecule differ in their dielectric relaxation behaviour from that of corresponding racemic mixtures, the complex permittivity of the following pure substances was measured over a broad frequency range (3 MHz to 72 GHz) at 20° CC: Phenylethylisocyanate, carvone, fenchone, 2-octanol, 2-amino-l-butanol, diethyltartrate and diisopropyltartrate. With the achieved experimental resolution, no stereoisomers effect could be observed with the exception of the tartrates, where there are clear differences in the low frequency features of the enantiomers as compared to the racemic mixture, which very probably are an association effect.
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8

Lee, Hannae, Dongchan Kim, Sooin Kim y Hyun Soo Lee. "Conversion of Racemic Unnatural Amino Acids to Optically Pure Forms by a Coupled Enzymatic Reaction". Molecules 26, n.º 5 (26 de febrero de 2021): 1274. http://dx.doi.org/10.3390/molecules26051274.

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Genetic code expansion (GCE) technology is a useful tool for the site-specific modification of proteins. An unnatural amino acid (UAA) is one of the essential components of this technique, typically required at high concentration (1 mM or higher) in growth medium. The supply of UAAs is an important limitation to the application of GCE technology, as many UAAs are either expansive or commercially unavailable. In this study, two UAAs in a racemic mixture were converted into optically pure forms using two enzymes, the d-amino acid oxidase (RgDAAO) from Rhodotorula gracilis and the aminotransferase (TtAT) from Thermus thermophilus. In the coupled enzyme system, RgDAAO oxidizes the d-form of UAAs in a stereospecific manner and produces the corresponding α-keto acids, which are then converted into the l-form of UAAs by TtAT, resulting in the quantitative and stereospecific conversion of racemic UAAs to optically pure forms. The genetic incorporation of the optically pure UAAs into a target protein produced a better protein yield than the same experiments using the racemic mixtures of the UAAs. This method could not only be used for the preparation of optically pure UAAs from racemic mixtures, but also the broad substrate specificity of both enzymes would allow for its expansion to structurally diverse UAAs.
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9

Bosits, Miklós Hunor, Emese Pálovics, János Madarász y Elemér Fogassy. "New Discoveries in Enantiomeric Separation of Racemic Tofisopam". Journal of Chemistry 2019 (7 de abril de 2019): 1–10. http://dx.doi.org/10.1155/2019/4980792.

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Resolution process of tofisopam has been re-evaluated now based on our new investigations. Originally, it was carried out in the water-chloroform system, where the intermediate salt of high diastereomeric excess was described as (R)-TOF·(R,R)-DBTA·(H2O)3. Opposed to previous assumptions, we have actually found that a different solvate composition, (R)-TOF‐(R,R)-DBTA-CHCl3, forms with chloroform, in which molecules of CHCl3 are captured and held with different strengths. Moreover, resolution of TOF with (R,R)-DBTA is possible (and favourable) in water-free solvent and solvent mixture. However, presence of chloroform is essential, and thus, chloroform is also a suitable solvent alone. Among the tested solvents, toluene-chloroform mixture results in the highest resolution efficiency, while the highest enantiomeric purity was achieved when acetonitrile was in the system too. Resolution efficiency can be also increased by using the quasi-racemic resolving agent and thermodynamic control. Purification of enantiomeric mixtures was examined, and recrystallization of the diastereomeric salt was found to be the most efficient solution. Instructive behaviour of the complex enantiomer-conformer system of tofisopam is emphasized.
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10

Perkowski, P., K. Ogrodnik, M. Żurowska, W. Piecek, R. Dąbrowski, Z. Raszewski y L. Jaroszewicz. "Antiferroelectric and ferroelectric SmC* phases in racemic mixture". Phase Transitions 86, n.º 2-3 (febrero de 2013): 138–46. http://dx.doi.org/10.1080/01411594.2012.715304.

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Tesis sobre el tema "Racemic Mixture"

1

Lekuni, Olivia. "Cost-Effectiveness of selecting an Enantiopure formulation over a racemic mixture". University of the Western Cape, 2017. http://hdl.handle.net/11394/6437.

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Magister Scientiae - MSc (Pharmacy Administration and Policy Regulation)
The aim of this study is to provide more information in terms of the cost-effectiveness of selecting an enantiopure formulation over a racemic mixture in the context of promoting rational use of medicines. This was done by comparing costs and efficacy of escitalopram versus citalopram and esomeprazole versus omeprazole since they are the most commonly used medicines with both racemate and enantiopure products registered.
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2

Castro, João Tiago Duarte Ferreira de. "Benefícios dos estereoisómeros na terapêutica medicamentosa". Master's thesis, [s.n.], 2014. http://hdl.handle.net/10284/4514.

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Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Ciências Farmacêuticas
A maioria dos fármacos comercializados atualmente são estereoisómeros, podendo estes apresentar-se na forma de enantiómeros ou diastereómeros. Desde que ocorreu o desastre da talidomida nos anos 60, a indústria química e farmacêutica apercebeu-se da importância do estudo da quiralidade dos fármacos e das suas propriedades estereoquímicas. A análise da correlação entre a quiralidade e as propriedades toxicológicas e farmacológicas dos compostos levou não só à eliminação de efeitos adversos, como também a diversos benefícios terapêuticos. Tem surgido uma tendência para a comercialização de novos fármacos sob a forma de enantiómeros, suplantando os fármacos antigos que eram comercializados na forma de misturas racémicas. Este trabalho expõe alguns benefícios associados aos estereoisómeros presentes em diferentes grupos terapêuticos, através da análise de diferentes misturas racémicas e dos seus enantiómeros ou diastereómeros. The majority of currently marketed drugs are stereoisomers, which can be enantiomers os diastereomers. Since thalidomide’s disaster occurred in the 60’s, the chemical and pharmaceutical industry realized the importance of studying the chirality of drugs and their stereochemical properties. The analysis of the correlation between chirality and the toxicologal and pharmacological properties has let not only to the elimination of adverse effects, but also to different therapeutic benefits. There has been a tendency towards the marketing of new drugs in the form of enantiomers, supplanting the old drugs which were marketed as racemic mixtures. This work exposes some benefits associated with stereoisomers present in different therapeutic groups, through the analysis of different racemic mixtures and their enantiomers or diastereomers.
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3

Campbell, Matthew 1980. "Resolution of racemic glutamic acid mixtures". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83854.

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Optical isomers (enantiomers) are chiral molecules, which are commonly used in the drug and food industry. The major difference between the two D and L enantiomers is the spatial arrangement of atoms around a central carbon. During normal chemical synthesis a mixture of L and D enantiomers are formed in equally proportion (racemic mixture). Currently, the most common technique for resolution of a racemic mixture is chromatography using chiral specific columns. However, this method is limited in scale and is rather costly. This work studies the possibility for the resolution of racemic glutamic acid by crystallization. Since the solubility of the two enantiomers in water is the same, the separation is based only on the rate of crystallization by using appropriate seed crystals. Experiments are performed with a range of initial supersaturation ratios and seed concentrations. The results show that an appreciable resolution of racemic glutamic acid can be attained with the presence of L seeds in solution. At the highest seed concentration (10 g/L of L glutamic acid), the initial supersaturation of 3.60, 2.50 and 1.60 yields 24.0%, 42.1% and 55.5% pure L glutamic acid crystals, respectively. Therefore as the initial supersaturation is lowered the percent yield of pure L glutamic acid increases.
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4

Piamtongkam, Rungtiwa. "Expression and evolution of lipases from Candida rugosa and Yarrowia lipolytica to modify their activities and specificities". Thesis, Toulouse, INSA, 2010. http://www.theses.fr/2010ISAT0015/document.

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Les lipases, protéines ubiquitaires, sont les enzymes les plus étudiées et les plus utilisées dans l’industrie. Elles catalysent un très grand nombre de réactions, d’hydrolyse et de synthèse, conduisant à une grande diversité de molécules, acides, esters, amides…. Les domaines d’applications sont nombreux : les bio-énergies, les arômes, bio-lubrifiants, bio-plastifiants, émulsifiants, produits phytosanitaires et détergents, cosmétiques, synthons pour la chimie fine, produits pharmaceutiques… Aujourd’hui, grâce aux outils génétiques, il est possible de modifier leur activité, spécificité et thermostabilité pour les adapter idéalement aux contraintes industrielles. Dans ce travail de doctorat, nous nous sommes intéressés à quatre lipases d’intérêt industriel. Les 3 premières appartiennent à la famille des lipases de Candida rugosa (Lip1, Lip3 et Lip4). Bien que très homologues, leurs spécificités sont très différentes. Elles se distinguent de toutes les autres lipases par un site actif composé d’un long tunnel avec la triade catalytique à l’entrée de celui-ci. Cela en fait une enzyme particulièrement intéressante pour la conversion et la purification d’acides gras à longue chaîne. La quatrième est une nouvelle lipase identifiée chez la levure oléagineuse, Yarrowia lipolytica. Elle est très active sur les acides gras à longue chaîne, active à pH acide et présentant une grande énantiosélectivité sur des molécules d’intérêt pharmaceutique, les esters d’acide 2- halogéno-aryl acide acétique. Dans un premier temps, un nouveau système d’expression, une souche spécifique de Yarrowia lipolytica, a été étudié pour l’expression de variants construits par mutagenèse dirigée. Cette souche JMY1212 permet une intégration ciblée dans le génome de Y. lipoytica. Nous avons démontré qu’il s’agissait du premier système d’expression permettant de comparer statistiquement l’activité de variants directement à partir du surnageant de culture. Trois des lipases de Candida rugosa ont été clonées avec succès dans cette souche et leurs activités et spécificités vis-à-vis de la longueur de chaines des acides gras ont été étudiées. Lip1 et Lip3 présentent une spécificité pour les acides gras à longueur de chaine moyenne (C8-C10) alors que Lip4 préfère les C18:1. De, plus, pour la première fois, la purification, à partir d’un mélange d’esters éthyliques issu d’huile de poissons, d’acides gras poly-insaturés (PUFAs); acides cis-5, 8, 11, 14, 17-eicosapentaenoic (EPA) et cis-4, 7, 10, 13, 16, 19-docosahexaenoic (DHA), molécules bonnes pour la santé, a été réalisée avec les trois lipases séparées de C. rugosa. Quelle que soit l’enzyme, le rendement de récupération du DHA est supérieur à 93 % (97, 100 et 93 % pour Lip1, Lip3 et Lip4 respectivement. Une pureté maximale en DHA de ~60 % a été obtenue avec Lip3 et Lip4, à partir d’un mélange initial d’esters éthyliques contenant 25% de DHA. Une différence remarquable entre ces trois enzymes est que Lip4 est capable de mieux hydrolyser l’ester d’EPA (60% contre 14 et 16% pour Lip1 et Lip3). Lip4 est même capable d’hydrolyser le DHA (7% contre 3 et 0 % pour Lip1 et Lip3). La deuxième partie de ce travail a été consacrée à l’amélioration de l’énantiosélectivité des deux enzymes étudiées vis-à-vis de synthons d’intérêt dans l’industrie pharmaceutique, les esters de 2-bromo aryl acide acétique. La construction raisonnée d’un double variant de la lipase Lip2 de Y. lipolytica, D97AV232F, a permis d’obtenir une enzyme totalement énantiosélective (E >200). Celle-ci reconnaît l’énantiomère R alors que la lipase sauvage avait une faible préférence pour l’énantiomère S (E=5). Par ailleurs, cette exceptionnelle augmentation de l’énantiosélectivité s’accompagne d’une amélioration de l’activité de l’enzyme qui est ainsi multipliée par 4,5. Sur ce même mélange d’énantiomères, les 3 lipases de C. rugosa se sont avérées remarquables. Malgré leur grande homologie, leur spécificité est différente. Lip1 et Lip3 sont totalement S spécifiques (E>200), alors que Lip4 est R spécifique (E=15). Le docking moléculaire des énantiomères S et R dans le site actif des lipases Lip1 et Lip4 a permis de mieux comprendre ces différences de spécificité et de proposer des cibles de mutagenèse dirigée. L’encombrement et la nature de l’acide aminé présent en position 296 sont cruciaux pour la discrimination de l’enzyme
Lipases, ubiquitous proteins, are the most studied enzymes and the most used in industry. They catalyse a great number of reactions, hydrolysis and synthesis, leading to a great diversity of molecules, acids, esters, amides. There are numerous fields of applications: bio-energies, flavours, bio-lubricants, bio-plasticizers, emulsifiers, detergents, cosmetics, synthons for fine chemistry, and pharmaceutical products. Nowadays, thanks to genetic tools, it is possible to modify their activity, specificity and thermostability to ideally adapt enzymes for the industrial constraints. In this work, we were interested in four lipases of industrial interest. The third ones belong to the lipase family of Candida rugosa (Lip1, Lip3 and Lip4). Although they present high homology, their specificities are very different. They are distinct from the other lipases by the active site composed of a long tunnel with the catalytic triad at the entry of the tunnel. It leads to enzymes particularly interesting for the conversion and the purification of long chain fatty-acids. The fourth one is a new lipase identified from oleaginous yeast, Yarrowia lipolytica. It is one of the most active lipase on long chain fatty-acids; it is very active and stable at acid pH and presents a high enantioselectivity on molecules of pharmaceutical interest, the esters of 2- halogeno-aryl acetic acid. In this work, we first tested a new expression system, a specific strain of Y. lipolytica, for expression of variants obtained by site-directed mutagenesis. This strain JMY1212 enables integration to be targeted to a special locus of the Y. lipoytica genome. We demonstrated that it is the first expression system in which it is possible to compare statistically variant activities directly from the supernatant of the culture. Secondly, three lipases of C. rugosa were cloned successfully in this strain and their activities and specificities with respect to fatty acid chain lengths were studied. Lip1 and Lip3 have specificity for the fattyacids of medium chain (C8-C10) whereas Lip4 prefers C18: 1. Moreover, for the first time, purification, from a mixture of ethyl esters issued from fish oil, polyunsaturated fatty acids (PUFAs); cis-5, 8, 11, 14, 17- eicosapentaenoic acid (EPA) and cis-4, 7, 10, 13, 16, 19-docosahexaenoic acid (DHA), molecules with health benefits, was realised with the three C. rugosa lipases, separately. Whatever the enzyme the recovery of DHA is superior to 90 % (97, 100 and 93 % for Lip1, Lip3 and Lip4 respectively. The maximal DHA purity ~60 % was obtained with Lip3 and Lip4, with an initial ethyl ester mixture containing 25% DHA. A remarkable difference between these enzymes lies in the fact that Lip4 is able to better hydrolyse the EPA esters (60% against 13% and 16% respectively for Lip1 and Lip3). Lip4 is also able to hydrolyse DHA (7% against 3 and 0 % for Lip1 and Lip3 respectively). The third part of this work was devoted to the improvement of the enantioselectivity of the two enzymes studied with respect to the resolution of a racemic mixture of pharmaceutical industry, the R, S esters of 2-bromo aryl acetic acid. The rational construction of a double variant of Lip2 lipase from Y. lipolytica, D97A V232F was realized to obtain a total enantioselective enzyme (E > 200). This variant recognizes the enantiomer R whereas wild-type lipase had a weak preference for the enantiomer S (E=5). In addition, this exceptional increase in the enantioselectivity is accompanied by a 4.5 fold improvement of the activity. With the same mixture of enantiomers, the 3 lipases of C. rugosa proved to be remarkable from the point of view of enantioselectivity. In spite of their high homology, their specificity is different. Lip1 and Lip3 are completely specific for the S enantiomer, whereas Lip4 is R specific (E=15). The molecular docking of the S and R enantiomers in the active site of Lip1 and Lip4 lipases enables the observed differences in specificity to be better understood and targets for site-directed mutagenesis to be proposed. We demonstrated that the nature of the amino acid present in position 296 is crucial for the discrimination of these enzymes
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5

Lee, Yi y 李易. "Crystallization Behavior of the Racemic Polylactide Mixture in Spin-cast Films". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/66893433765381618245.

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碩士
國立清華大學
化學工程學系
104
The crystallization behavior of racemic polylactide (equimolar PLLA/PDLA) blend spin-cast on thin film was investigated using FTIR and in-situ GISAXS/GIWAXS. The film thicknesses were controlled by coating with different solution concentration, which gives the film thicknesses equal to 630, 200, 65, and 16 nm. There is no crystalline found right after spin-coating, but crystalline peak would emerge during heating (from 40 °C to 250 °C at 3 °C/min) of thin films, which is same as cold crystallization process. It is discovered that racemic PLA blend will form into α and βc phase in 630 and 200 nm thick films, yet only form into βc phase in the films of 65 and 16 nm during cold-crystallization process. By practicing designed experiment, two possibilities are excluded to be responsible for the suppression in 65 and 16 nm thin film. For one hand, α phase is proved be able to form with only optically pure polylactide in 83 and 24 nm thin film. On the other hand, the spin-coating effect which may produce βc phase nuclei near substrate was erased by melt-quench process, but the same suppression of α phase in 65 and 16 nm result are still observed. From the observation of coherence length of α crystals that emerges in large size from the beginning of the GIWAXS peak becoming discernible, which may suggest that α phase have larger nuclei than βc phase. Moreover, when examine GIWAXS characteristic peaks carefully, the reflections of βc phase will emerge earlier than α phase, implying that formation of βc phase is earlier than α phase. The nanograin size of βc phase is ca. 10 nm initially, which is comparatively large in films under 100 nm. Therefore, earlier formation of βc phase will make formation of α phase is restricted by confined free space. The larger space which α phase required to form and the earlier formation of βc phase may be responsible for the suppression of α phase formation in 65 and 16 nm films. Besides, quantitative analysis for GIWAXS reveals that coherence length of crystalline reduced with decreasing film thickness. While the coherence length can be up to ca. 30 nm in the 630 nm thin film before melting, the coherence length in 16 nm thin film was only ca. 16 nm. Moreover, the orientation analysis from GIWAXS points out that the orientation in 630 nm film is worse than others, while 200, 65 and 16 nm thin film give apparent edge-on packing by thickness confinement. The orientation analysis also gives the idea that βc crystals may form in trigonal unit cell, and has its chain backbones lying on substrate. With model fitting analysis in GISAXS, the nanograins of βc phase can be well described with arrayed disks model. According to the fitting results, the radius of disk-like nanograins in 16 nm thin film is 2 times smaller than the one in 630 nm thin film, while the correlation between disks is two times better in 16 nm film than in 630 nm. Finally, by combining the GISAXS/GIWAXS results, a comparison crystal model for βc phase between 630 and 16 nm thin film was proposed.
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Wu, Zong-Ye y 吳宗燁. "The effect of functional groups of racemic rodlike Schiff base mesogens on the stabilization of blue phase in binary mixture system". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/41890230015479625079.

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碩士
大同大學
化學工程學系(所)
104
Four series of rodlike racemic Schiff base mesogens possessing different alkyl chains and two types of linkage, ester and alkynyl groups were synthesized and applied to induce cubic blue phases (BPs) in simple binary mixture systems. The mesophases of these Schiff base mesogens were confirmed by variable-temperature XRD and the characteristic texture of POM. In general, when chiral additive S811 with the ratio of 20-40 wt% is added into the rodlike racemic Schiff base mesogens possessing hydroxyl group, the temperature range of cubic BPs could be induced more than 20 K. The widest temperature range of cubic BP (35 K) presents in the blending mixture composed of rodlike racemic salicylaldimine-based mesogen OH-TIn possessing alkynyl linkage and 35-40 wt% S811. However, Schiff base mesogens with alkynyl linkage and no hydroxyl group show direct isotropic to chiral nematic transition when equal chiral dopants is added. Interestingly, wide BPs (>30 K) also can be induced by adding chiral additive ISO(6OBA)2 with high HTP into the racemic Schiff base mesogen with ester linkage. Cubic BPI and BPII can be confirmed by reflectance spectra and polarized optical microscopy (POM). The results of reflectance spectra indicate that Schiff base mesogens possessing alkoxy chain exhibit wider BPII range than Schiff base mesogens possessing alkyl chain due to larger super-cooling effect in the binary mixture system containing chiral dopant S811. However, only BPII can be induced in the blending mixture system composed of Schiff base mesogen and ISO(6OBA)2 both on heating and cooling processes. On the basis of our experimental results and molecular modeling, the appearance and temperature range of BPs are affected by the values of biaxiality, the polarizability and dipole moment of geometry.
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Magalhães, Joana Cristina Anacleto. "Importância da quiralidade e da estereoquímica na terapia antimicrobiana". Master's thesis, 2016. http://hdl.handle.net/10284/5805.

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A análise dos fármacos quirais justifica-se pelas diferenças a nível da toxicidade e da atividade biológica de dois enantiómeros, embora ambos apresentem características idênticas, como o mesmo ponto de ebulição, a densidade e a reatividade. Enquanto um enantiómero pode possuir uma atividade biológica benéfica, o outro pode ser inativo ou exercer outra atividade, capaz de resultar em efeitos adversos. A escolha entre estereoisómeros individuais ou misturas de estereoisómeros vai depender assim das vantagens terapêuticas associadas, dos possíveis efeitos adversos e dos custos de desenvolvimento. Verifica-se assim uma necessidade de avaliação contínua tanto dos novos fármacos quirais, como também dos já existentes no mercado. Este trabalho expõe a influência da isomeria em vários compostos utilizados na terapia antimicrobiana, nomeadamente os antibióticos, através da análise de diferentes misturas racémicas e dos seus enantiómeros.
The analysis of chiral drugs is justified by differences in the toxicity and biological activity of two enantiomers, while both exhibit the same characteristics, as the same boiling point, density and reactivity. While one enantiomer may have a beneficial biological activity, the other may be inactive or engage in any other activity, can result in adverse effects. The choice between individual stereoisomers or mixtures of stereoisomers will depend thus the therapeutic advantages associated, possible adverse effects and development costs. It appears thus a need for continual assessment of both new chiral drugs, as well as existing on the market. This paper presents the effect of isomerism on various compounds used in the antimicrobial therapy, including antibiotics, through analysis of various racemic mixtures and enantiomers thereof.
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Libros sobre el tema "Racemic Mixture"

1

Capogna, Giorgio. Labour analgesia: choice of local anaesthetics. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198713333.003.0016.

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In this chapter, the rationale for the choice of commonly used local anaesthetics—racemic bupivacaine, ropivacaine, and levobupivacaine—is reviewed, particularly with respect to their potency and differential block. Epidural and spinal dosing for labour analgesia and the role of ‘up–down’ studies to determine the minimum local anaesthetic concentration (MLAC) for labour analgesia is explained. Applying the MLAC model has enabled clinical comparisons at equipotent concentrations and doses. It has also quantified what contribution opioids have on the overall effectiveness of the analgesic mixture, provided a means of optimizing combinations of local anaesthetic–opioid solutions, examined the effect of inter-individual and obstetric variables on local anaesthetic potency, and provided a pharmacological-based rationale for analgesia solutions used for labour analgesia.
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(Editor), James Eames y Matthew Todd (Editor), eds. Separation of Racemic Mixtures: New Methods and Applications. John Wiley & Sons, 2006.

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Capítulos de libros sobre el tema "Racemic Mixture"

1

Bada, Jeffrey. "Racemic (Mixture)". En Encyclopedia of Astrobiology, 1399. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-11274-4_1329.

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Bada, Jeffrey. "Racemic Mixture". En Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27833-4_1329-3.

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Bada, Jeffrey. "Racemic Mixture". En Encyclopedia of Astrobiology, 2105. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-44185-5_1329.

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Russell, Trisha A. y Edwin Vedejs. "Enantiodivergent Reactions: Divergent Reactions on a Racemic Mixture and Parallel Kinetic Resolution". En Separation of Enantiomers, 217–66. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2014. http://dx.doi.org/10.1002/9783527650880.ch6.

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Sun, Fang-Ming, James L. Smith, B. M. Vittimberga y R. W. Traxler. "Effect of Food Processing on Bioactive Compounds in Foods: A New Method for Separation and Identification ofcis-Cinnamic Acid from Its Racemic Mixture". En ACS Symposium Series, 228–40. Washington, DC: American Chemical Society, 2002. http://dx.doi.org/10.1021/bk-2002-0816.ch017.

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Matsuoka, M. "Purity Drop in Optical Resolution of Racemic Mixtures". En Separation and Purification by Crystallization, 59–72. Washington, DC: American Chemical Society, 1997. http://dx.doi.org/10.1021/bk-1997-0667.ch006.

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"Racemic Mixture". En Encyclopedia of Psychopharmacology, 1419. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-642-36172-2_200407.

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Van Thi Nguyen, Ngoc, Kim Ngan Huynh Nguyen, Kien Trung Nguyen, Kyeong Ho Kim y Hassan Y. Aboul-Enein. "Chiral Alkaloid Analysis". En Current Topics in Chirality - From Chemistry to Biology. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96009.

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Alkaloids are distributed in plant kingdom and play important role in protection, germination as well as plant growth stimulants. Most of them are chiral compounds and are clinically administered as the racemic mixture, even though its enantiomers have been known to exert different pharmacological activity. Liquid chromatography using chiral stationary phases (CSP) proved to be an essential tool with a wide range of applications, including analysis of the stereochemistry of natural compounds. This review gives an overview of chiral separation alkaloids that were used in theoretical studies and/or applications in recent years. It shows the possibilities of polysaccharide CSPs have now also been established as the first-choice of chiral phases for enantiomer separation.
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García Ruano, J. L., M. B. Cid, A. M. Martín-Castro y J. Alemán. "Resolution of Racemic Mixtures". En Sulfur, Selenium, and Tellurium, 1. Georg Thieme Verlag KG, 2008. http://dx.doi.org/10.1055/sos-sd-039-00397.

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García-Ruano, J. L., M. B. Cid, A. M. Martín-Castro y J. Alemán. "Resolution of Racemic Mixtures". En Sulfur, Selenium, and Tellurium, 1. Georg Thieme Verlag KG, 2008. http://dx.doi.org/10.1055/sos-sd-039-00996.

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Actas de conferencias sobre el tema "Racemic Mixture"

1

Bychkov, Stanislav S., Boris A. Grishanin y Victor N. Zadkov. "Laser distillation of enantiomers from an isotropic racemic mixture". En International Seminar on Novel Trends in Nonlinear Laser Spectroscopy and High-Precision Measurements in Optics, editado por Sergei N. Bagaev, Victor N. Zadkov y Sergei M. Arakelian. SPIE, 2001. http://dx.doi.org/10.1117/12.428338.

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Lemercier, Gilles, Magali Alexandre, Chantal Andraud, Laurent Guerin, David Chapron, Aleksandra Apostoluk y Jean-Michel Nunzi. "All-optical induction of enantiomer resolution in a racemic mixture". En Optical Science and Technology, SPIE's 48th Annual Meeting, editado por Mark G. Kuzyk, Manfred Eich y Robert A. Norwood. SPIE, 2003. http://dx.doi.org/10.1117/12.507994.

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JEON, S. J. y W. H. HONG. "SEPARATION OF ETHYL (R) 4-CHLORO-3-HYDROXYBUTYRATE FROM RACEMIC MIXTURE BY USING BULK LIQUID MEMBRANE". En Proceedings of the 4th International Conference. WORLD SCIENTIFIC, 2004. http://dx.doi.org/10.1142/9789812702623_0109.

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Bhushan, Indu. "Efficient media for high production of microbial lipase from Bacillus subtilis (BSK-L) using response surface methodology for enantiopure synthesis of drug molecules". En 2nd International Scientific Conference "Plants and Microbes: the Future of Biotechnology". PLAMIC2020 Organizing committee, 2020. http://dx.doi.org/10.28983/plamic2020.044.

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Lipases are a multipurpose enzyme that holds a significant position in industrial applications due to its ability to catalyse a large number of reactions such as hydrolysis, esterification, interesterification, transesterification which makes it a potential candidate. It is also used for the separation of chiral drugs from the racemic mixture and this property of lipase is considered very important in pharmaceutical industries for the synthesis of enantiopure bioactive molecules. Assuming the tremendous importance of lipases, as stereoselective biocatalysts, in pharmaceuticals and various other commercial applications, industrial enzymologists have been forced to search for those microorganisms which are able to produce novel biocatalysts at reasonably high yield. In the present study microbial lipase was isolated from the water sample of pond at Katra, Jammu and Kashmir (India). This enzyme has shown wide specificity and higher enantioselectivity, which make it pharmaceutical important enzyme. To make it economical for industrial application, it was produced on cheap nutrient media using Response Surface Methodology and got maximum production. It was used for resolution of chiral drugs and the significant results obtained during the course of work shall have potential towards pharmaceutical industries.
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Rincón, D. A., M. C. Daza y M. Doerr. "Application of the quantum theory of atoms in molecules (QTAIM) to the study of the enzymatic kinetic resolution of propranolol, an amino alcohol with pharmaceutical applications". En VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020135.

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Propranolol, ((R,S)-1-iso-propylamino-3-(1-naphthoxy)-2-propanol), is a β-adrenergic antagonist and is commercially available as a racemic mixture. Only the S-enantiomer has the desired therapeutic effect. Therefore, many researchers have been working on strategies to obtain S-propranolol with high enantiomeric purity. One approach to carry out the acetylation of (R,S)-Propranolol using Candida antarctica lipase B, CalB. This reaction leads to an enantiomeric purity of 96% at a relatively low conversion rate of 30 %. In our research group, we have been studying this reaction. The CalB active site is composed by the triad catalytic (ASP 187, HIS 224 and SER 105) and oxyanion hole (GLN 106 and THR 40). In a previous work, a QM/MM (Quantum Mechanics / Molecular Mechanics) study was carried out, using a QM region consisting only of the catalytic triad of CalB and (R,S)-propranolol [1]. In the present study, we investigate the effect of expanding the quantum region to include the oxyanion hole and to comprehend the effect of intermolecular hydrogen bonds present between the (R,S)-propranolol and the CalB active site. The electronic structure was analyzed using the Quantum Theory of Atoms In Molecules, QTAIM. Our results show that: 1. the studied reactions are more exothermic with the inclusion of the oxyanion hole than with only the catalytic triad. 2. the intermolecular interactions between (R,S)-propranolol and the CalB active site are dominated by hydrogen bonds (HB). Among those HBs, only one between propranolol and HIS 224, and another one between THR 40 and the carbonyl oxygen of acetylated SER 105 play an important role.
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Ginzburg, Valeriy V., Renfan Shao, Noel A. Clark y David M. Walba. "Theory of chiral-racemic mixtures near the Smectic C-Smectic A transition point: dependence of spontaneous polarization and transition temperature on enantiometric excess". En IS&T/SPIE 1994 International Symposium on Electronic Imaging: Science and Technology, editado por Ranganathan Shashidhar. SPIE, 1994. http://dx.doi.org/10.1117/12.172124.

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