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Artículos de revistas sobre el tema "Racemic Mixture"

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

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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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11

Rosini, Elena, Chiara Allegretti, Roberta Melis, Lorenzo Cerioli, Gianluca Conti, Loredano Pollegioni y Paola D'Arrigo. "Cascade enzymatic cleavage of the β-O-4 linkage in a lignin model compound". Catalysis Science & Technology 6, n.º 7 (2016): 2195–205. http://dx.doi.org/10.1039/c5cy01591j.

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12

Scowen, Ian J., Taghrid S. Alomar, Tasnim Munshi y Colin C. Seaton. "Structural similarity in chiral-achiral multi-component crystals". CrystEngComm 22, n.º 43 (2020): 7334–40. http://dx.doi.org/10.1039/d0ce00301h.

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13

Qiu, Guo-Song, Kui Yan, Shan Zhang, Wei Chen, Shao-Hua Huang y Zheng-Wu Bai. "Different molecular weight chitosan derivatives employed for enantiomeric separation". Analytical Methods 9, n.º 46 (2017): 6560–68. http://dx.doi.org/10.1039/c7ay02174g.

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14

Tonoi, Takayuki y Koichi Mikami. "Fluorous “Racemic” Mixture Synthesis: Simultaneous Strategy for Demixing and Enantioseparation of Racemic Fluorous-Tagged Products". European Journal of Organic Chemistry 2007, n.º 11 (abril de 2007): 1730–33. http://dx.doi.org/10.1002/ejoc.200700037.

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15

Boberg, Mikael, Monica Cal, Marcel Kaiser, Rasmus Jansson-Löfmark, Pascal Mäser y Michael Ashton. "Enantiospecific antitrypanosomal in vitro activity of eflornithine". PLOS Neglected Tropical Diseases 15, n.º 7 (12 de julio de 2021): e0009583. http://dx.doi.org/10.1371/journal.pntd.0009583.

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The polyamine synthesis inhibitor eflornithine is a recommended treatment for the neglected tropical disease Gambian human African trypanosomiasis in late stage. This parasitic disease, transmitted by the tsetse fly, is lethal unless treated. Eflornithine is administered by repeated intravenous infusions as a racemic mixture of L-eflornithine and D-eflornithine. The study compared the in vitro antitrypanosomal activity of the two enantiomers with the racemic mixture against three Trypanosoma brucei gambiense strains. Antitrypanosomal in vitro activity at varying drug concentrations was analysed by non-linear mixed effects modelling. For all three strains, L-eflornithine was more potent than D-eflornithine. Estimated 50% inhibitory concentrations of the three strains combined were 9.1 μM (95% confidence interval [8.1; 10]), 5.5 μM [4.5; 6.6], and 50 μM [42; 57] for racemic eflornithine, L-eflornithine and D-eflornithine, respectively. The higher in vitro potency of L-eflornithine warrants further studies to assess its potential for improving the treatment of late-stage Gambian human African trypanosomiasis.
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16

Altamura, Emiliano, Arnaud Comte, Alice D’Onofrio, Charlotte Roussillon, Dimitri Fayolle, René Buchet, Fabio Mavelli, Pasquale Stano, Michele Fiore y Peter Strazewski. "Racemic Phospholipids for Origin of Life Studies". Symmetry 12, n.º 7 (3 de julio de 2020): 1108. http://dx.doi.org/10.3390/sym12071108.

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Although prebiotic condensations of glycerol, phosphate and fatty acids produce phospholipid esters with a racemic backbone, most experimental studies on vesicles intended as protocell models have been carried out by employing commercial enantiopure phospholipids. Current experimental research on realistic protocell models urgently requires racemic phospholipids and efficient synthetic routes for their production. Here we propose three synthetic pathways starting from glycerol or from racemic solketal (α,β-isopropylidene-dl-glycerol) for the gram-scale production (up to 4 g) of racemic phospholipid ester precursors. We describe and compare these synthetic pathways with literature data. Racemic phosphatidylcholines and phosphatidylethanolamines were obtained in good yields and high purity from 1,2-diacylglycerols. Racemic POPC (rac-POPC, (R,S)-1-palmitoyl-2-oleoyl-3-phosphocholine), was used as a model compound for the preparation of giant vesicles (GVs). Confocal laser scanning fluorescence microscopy was used to compare GVs prepared from enantiopure (R)-POPC), racemic POPC (rac-POPC) and a scalemic mixture (scal-POPC) of (R)-POPC enriched with rac-POPC. Vesicle morphology and size distribution were similar among the different (R)-POPC, rac-POPC and scal-POPC, while calcein entrapments in (R)-POPC and in scal-POPC were significantly distinct by about 10%.
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17

Huynh, Huu-Tri, Olivier Jeannin, Emmanuel Aubert, Enrique Espinosa y Marc Fourmigué. "Chalcogen bonding interactions in chelating, chiral bis(selenocyanates)". New Journal of Chemistry 45, n.º 1 (2021): 76–84. http://dx.doi.org/10.1039/d0nj05293k.

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18

Škvára, Jiří, Ivo Nezbeda y Pavel Izák. "Molecular dynamics study of racemic mixtures. II. Temperature dependence of the separation of ibuprofen racemic mixture with β-cyclodextrin in methanol solvent". Journal of Molecular Liquids 302 (marzo de 2020): 112575. http://dx.doi.org/10.1016/j.molliq.2020.112575.

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19

Delarue Bizzini, Lorenzo, Thomas Müntener, Daniel Häussinger, Markus Neuburger y Marcel Mayor. "Synthesis of trinorbornane". Chem. Commun. 53, n.º 83 (2017): 11399–402. http://dx.doi.org/10.1039/c7cc06273g.

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20

Feizi, Froozan, Mojtaba Shamsipur, Mohammad Bagher Gholivand, Avat (Arman) Taherpour, Ali Barati, Hosna Shamsipur, Ezeddin Mohajerani y Peter Budd. "Harnessing the enantiomeric recognition ability of hydrophobic polymers of intrinsic microporosity (PIM-1) toward amino acids by converting them into hydrophilic polymer dots". Journal of Materials Chemistry C 8, n.º 39 (2020): 13827–35. http://dx.doi.org/10.1039/d0tc03138k.

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In this work, we synthesized novel polymer dots (Pdots) from polymers of intrinsic microporosity (PIM-1) containing a racemic mixture of R- and S-chiral centers as the hydrophobic conjugated polymer chains.
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21

Adachi, Hiroki, Hiroaki Imoto, Seiji Watase, Kimihiro Matsukawa y Kensuke Naka. "As-stereogenic C2-symmetric organoarsines: synthesis and enantioselective self-assembly into a dinuclear triple-stranded helicate with copper iodide". Dalton Transactions 44, n.º 35 (2015): 15372–76. http://dx.doi.org/10.1039/c5dt01490e.

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As-stereogenic C2-symmetric organoarsines were safely synthesized from non-volatile precursors. The racemic mixture of the As-stereogenic ligands was enantioselectively self-assembled into a dinuclear triple-stranded helicate.
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22

Wang, Yuanyuan, Longlong Zhang y Junge Zhi. "Chiral Pentaphenylpyrrole Derivatives with Aggregation-Induced Emission Enhancement and Aggregation Induced Circular Dichroism and Their Helical Self-assembly". E3S Web of Conferences 267 (2021): 02012. http://dx.doi.org/10.1051/e3sconf/202126702012.

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A pair of enantiomers (S)-P5PdiAM and (R)-P5PdiAM containing two chiral substituents, and their raceme rac-P5PdiAM were synthesized by introducing (R)-/(S)- or racemic 1-phenylethylamine into 1-biphenyl-2,3,4,5-tetraphenylpyrrole. The target compounds all show weak aggregation-induced emission enhancement (AIEE) characteristics in the DMSO/H2O mixed system, indicating that the introduction of chirality hardly affect the photophysical properties of the compound. In addition, the chiral compounds (S)-P5PdiAM and (R)-P5PdiAM show strong circular dichroism (CD) signals in THF/H2O mixed solution with a water fraction of 70%, that is, they exhibit aggregation-induced circular dichroism characteristics (AICD). Because the aggregates of (S)-P5PdiAM and (R)-P5PdiAM emit weakly, there is no circularly polarized luminescence (CPL) signals upon aggregation. The chiral compounds (S)-P5PdiAM and (R)-P5PdiAM can self-assemble to form helical nanofibers in a THF/H2O mixture with a water fraction of 70%, while the racemic rac-P5PdiAM assembled to form nano-particles, indicating that chiral substituents have a great influence on the self-assembly and the morphologies of the nano-aggregates.
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23

Wang, Yaling, Rosario LoBrutto, Robert W. Wenslow y Ivan Santos. "Eutectic Composition of a Chiral Mixture Containing a Racemic Compound". Organic Process Research & Development 9, n.º 5 (septiembre de 2005): 670–76. http://dx.doi.org/10.1021/op0501038.

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24

Wang, Yaling, Rosario LoBrutto, Robert W. Wenslow y Ivan Santos. "Eutectic Composition of a Chiral Mixture Containing a Racemic Compound". Organic Process Research & Development 11, n.º 2 (marzo de 2007): 293. http://dx.doi.org/10.1021/op700018h.

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25

Hegstrom, Roger A. "Parity violation and chiral symmetry breaking of a racemic mixture". Biosystems 20, n.º 1 (enero de 1987): 49–56. http://dx.doi.org/10.1016/0303-2647(87)90019-0.

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26

Aliev, M. A., N. Yu Kuzminyh y E. A. Ugolkova. "Nematic ordering of model racemic mixture of stiff trimer chains". Journal of Molecular Liquids 340 (octubre de 2021): 116806. http://dx.doi.org/10.1016/j.molliq.2021.116806.

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27

Tomioka, Kiyoshi. "Catalytic asymmetric reactions using environmentally friendly reagents and catalyst: Asymmetric synthesis versus kinetic resolution". Pure and Applied Chemistry 78, n.º 11 (1 de enero de 2006): 2029–34. http://dx.doi.org/10.1351/pac200678112029.

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Kinetic resolution of racemic compounds is a familiar method for the preparation of optically active compounds. However, an inevitable and critical drawback from the point of view of green chemistry is the consequent wastage of half of the starting compound. A catalytic asymmetric synthesis of 5-arylcyclohex-2-enones was developed starting from racemic 5-(trimethylsilyl)cyclohex-2-enone, which overcomes the drawback of kinetic resolution. A chiral amidophosphane- or BINAP-Rh(I)-catalyzed asymmetric conjugate arylation of racemic 5-(trimethylsilyl)cyclohex-2-enone with arylboronic acids in dioxane-water (10:1) afforded trans- and cis-3-aryl-5-(trimethylsilyl)cyclohexanones in reasonably high enantioselectivity. Dehydrosilylation of the product mixture with Cu(II) chloride in dimethylformamide (DMF) gave 5-arylcyclohex-2-enones with up to 93 % ee in high yield. Enantiofacial selectivity with chiral phosphane-Rh(I) overrides the trans-diastereoselectivity that is maintained in the achiral or racemic phosphane-Rh(I)-catalyzed conjugate arylation of 5-(trimethylsilyl)cyclohex-2-enone.
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28

Chand, Satish y Martin G. Banwell. "Biomimetic Preparation of the Racemic Modifications of the Stilbenolignan Aiphanol and Three Congeners". Australian Journal of Chemistry 60, n.º 4 (2007): 243. http://dx.doi.org/10.1071/ch07044.

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A chromatographically separable mixture of the racemic modification, (±)-1, of the stilbenolignan (–)-aiphanol and congeners (±)-2–4 has been generated by a silver(I)-mediated and potentially biomimetic oxidative coupling of piceatannol (5) with sinapic alcohol (6).
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29

Mamaghani, Manouchehr y Alireza Alizadehnia. "Enzyme Catalysed Kinetic Resolution of Racemic Methyl 3-acethylbicyclo [2.2.1] hept-5-ene-2-carboxylate using pig's liver esterase†". Journal of Chemical Research 2002, n.º 8 (agosto de 2002): 386–87. http://dx.doi.org/10.3184/030823402103172400.

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Racemic methyl 3- endo-acetylbicyclo[2.2.1]hept-5-ene-2- exo-carboxylate and methyl 3- exo-acetylbicyclo[2.2.1]hept-5-ene-2- endo-carboxylate were prepared (as a 1:1 mixture in 98% yield) from (E)-methyl 4- oxo-2-pentenoate, using Diels–Alder methodology. The mixture was separated chromatographically and resolved into the enantiomers by pig liver esterase (PLE) with low to high ee's (98%).
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30

Unelius, C. Rikard, Johan Sandell y Christian Orrenius. "Enantioselective Preparation of the Stereoisomersof 4-Methylheptan-3-ol Using Candida antarctica Lipase B". Collection of Czechoslovak Chemical Communications 63, n.º 4 (1998): 525–33. http://dx.doi.org/10.1135/cccc19980525.

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The four stereoisomers of 4-methylheptan-3-ol were prepared through fractional crystallization of a mixture of their racemic 4-methylhept-3-yl 3,5-dinitrobenzoates, followed by hydrolysis of each crystalline racemate and enantioselective, lipase-mediated transesterification of each pair of enantiomeric alcohols liberated, using the Candida antarctica lipase B as catalyst and S-ethyl octanethioate as the acyl donor. An analytical method of determining the enantiomeric composition of mixtures of 4-methyl-heptan-3-ols was developed. The optical purity of the separated isomers was in the range of 29-97%.
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31

Ocak, Hale, Belkız Bilgin Eran, Sevgi Nuray, Aykun Özkonstanyan, Silvio Poppe y Carsten Tschierske. "Extraordinary magnetic field effects on the LC phases of homochiral and racemic 4-cyanoresorcinol-based diamagnetic bent-core mesogens". Journal of Materials Chemistry C 9, n.º 6 (2021): 1895–910. http://dx.doi.org/10.1039/d0tc05355d.

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A huge effect of a magnetic field on the layer spacing of smectic and polar smectic liquid crystalline phases of a diamagnetic bent-core mesogen is reported, which is opposite for the uniformly chiral compound and its racemic mixture.
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32

Hovorka, Rainer, Sophie Hytteballe, Torsten Piehler, Georg Meyer-Eppler, Filip Topić, Kari Rissanen, Marianne Engeser y Arne Lützen. "Self-assembly of metallosupramolecular rhombi from chiral concave 9,9’-spirobifluorene-derived bis(pyridine) ligands". Beilstein Journal of Organic Chemistry 10 (18 de febrero de 2014): 432–41. http://dx.doi.org/10.3762/bjoc.10.40.

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Two new 9,9’-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands act as concave templates and form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp)2M2{(R)-L}2](OTf)4, [(dppp)2M2{(S)-L}2](OTf)4, and [(dppp)2M2{(R)-L}{(S)-L}](OTf)4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies could also be characterised by single crystal X-ray diffraction.
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33

Rigin, Sergei, Beatrice Armijo, Arcadius V. Krivoshein, Marina Fonari y Tatiana Timofeeva. "Crystal structure and Hirshfeld surface analysis of new polymorph of racemic 2-phenylbutyramide". Acta Crystallographica Section E Crystallographic Communications 75, n.º 6 (21 de mayo de 2019): 826–29. http://dx.doi.org/10.1107/s2056989019007011.

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A new polymorph of the title compound, C10H13NO, was obtained by recrystallization of the commercial product from a water/ethanol mixture (1:1 v/v). Crystals of the previously reported racemic and homochiral forms of 2-phenylbutyramide were grown from water–acetonitrile solution in 1:1 volume ratio [Khrustalev et al. (2014). Cryst. Growth Des. 14, 3360–3369]. While the previously reported racemic and enantiopure forms of the title compound adopt very similar supramolecular structures (hydrogen-bonded ribbons), the new racemic polymorph is stabilized by a single N—H...O hydrogen bond that links molecules into chains along the c-axis direction with an antiparallel (centrosymmetric) packing in the crystal. Hirshfeld molecular surface analysis was employed to compare the intermolecular interactions in the polymorphs of the title compound.
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34

Boiocchi, Massimo y Luigi Fabbrizzi. "Double-stranded dimetallic helicates: assembling–disassembling driven by the CuI/CuII redox change and the principle of homochiral recognition". Chem. Soc. Rev. 43, n.º 6 (2014): 1835–47. http://dx.doi.org/10.1039/c3cs60428d.

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Upon reduction of a mononuclear complex of CuII with a tetradentate ligand (a racemic mixture of the S,S and R,R enantiomers) two dicopper(i) double stranded helicates form, each one containing strands of the same chirality.
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35

Petrov, Ravil R., Ruben S. Vardanyan, Gary S. Nichol, Michael D. Carducci, Shou-wu Ma, Josephine Y. Lai y Victor J. Hruby. "4-{N-[2-(1,3-Dioxo-1,3-dihydroisoindol-2-yl)-3-phenylpropionyl]anilino}-1-phenethylpiperidinium chloride methanol disolvate". Acta Crystallographica Section E Structure Reports Online 62, n.º 7 (14 de junio de 2006): o2815—o2816. http://dx.doi.org/10.1107/s1600536806021817.

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The structure of the title compound, a fentanyl derivative with formula C36H36N3O3 +·Cl−·2CH3OH, crystallizes as a racemic mixture. The organic cation has an extended conformation and the structure displays O—H...O, O—H...Cl and N—H...Cl hydrogen bonding.
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36

Webster, Gregory K. y Robert G. Bell. "Gas Chromatographic Analysis of Fosfomycin in Plasma for Pharmacokinetic Analysis". Journal of AOAC INTERNATIONAL 82, n.º 3 (1 de mayo de 1999): 620–24. http://dx.doi.org/10.1093/jaoac/82.3.620.

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Abstract An efficient method for gas chromatographic analysis of fosfomycin in plasma was developed for preliminary investigations of the bioavailability in poultry of 3 commercial complexes of fosfomycin: a levorotatory Ca(−) salt, a racemic Ca(±) salt, and a tromethamine (THAM) salt. The method was used to determine whether the less expensive racemic mixture would provide equivalent levels of fosfomycin in blood as the pure Ca(−) form and the THAM salt. The THAM salt, a more expensive product to market, was thought to have the greatest bioavailability. The assay is selective, sensitive, and applicable to pharmacokinetic analysis.
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37

Nesvadba, Peter, Piotr Rzadek y Günther Rist. "New Cyclodimerization Reaction of (3,5-Di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)acetic Acid". Collection of Czechoslovak Chemical Communications 66, n.º 8 (2001): 1250–56. http://dx.doi.org/10.1135/cccc20011250.

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(3,5-Di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)acetic acid 1a underwent on heating a new cyclodimerization reaction affording a 1 : 1 mixture of the racemic cis- and trans-isomeric lactone-acids 2. The decisive structure elucidation of 2 was carried out after its mild esterification with diazomethane and separation of the racemic isomeric methyl esters 3a and 3b. The attempted esterification of 2 with methanol and sulfuric acid gave only the methyl diarylacetate 4. In contrast to 1a, which contains the carboxylic acid functionality no cyclodimerization was observed with the corresponding methyl ester 1b or nitrile 1c.
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38

Tonoi, Takayuki, Wei Zhang, Dennis P. Curran y Koichi Mikami. "Fluorous “racemic” mixture synthesis: Polysaccharide-based chiral columns for simultaneous demix and enantioseparation of racemic fluorous tagged compounds". Chirality 20, n.º 3-4 (2008): 597–603. http://dx.doi.org/10.1002/chir.20487.

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39

Park, Songsoon y Hyeon-Kyu Lee. "Efficient kinetic resolution in the asymmetric transfer hydrogenation of 3-aryl-indanones: applications to a short synthesis of (+)-indatraline and a formal synthesis of (R)-tolterodine". RSC Advances 11, n.º 37 (2021): 23161–83. http://dx.doi.org/10.1039/d1ra04538e.

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Efficient kinetic resolution occurs in ATH of racemic 3-arylindanones using (R,R)-or (S,S)-Ts-DENEB catalyst and HCO2H/Et3N mixture providing near equal yields of cis-3-arylindanols and unreacted 3-arylindanones with excellent stereoselectivities.
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40

Maharani, Rani, Ace Tatang Hidayat, Dadan Sumiarsa, Achmad Zainuddin y Ika Wiani Hidayat. "RESOLUTION OF A RACEMIC ISOLEUCINE MIXTURE BY USING METHYL L-MANDELATE". Chimica et Natura Acta 4, n.º 3 (12 de diciembre de 2016): 156. http://dx.doi.org/10.24198/cna.v4.n3.10991.

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A methyl ester of L-mandelic acid was found to be an effective resolving agent for resolution of commercial DL-isoleucine. The resolution was based on Steglich esterification between methyl L-mandelate and Boc-DL-isoleucine. The two resolved isomers were easily separated by using a conventional flash-column chromatography, giving quantitatively good yields. Unfortunately, the methyl L-mandelate was found to be ineffective to resolve four stereoisomers of Fmoc- isoleucine.
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41

WANG, J., C. FU, T. LIN, L. YU y S. ZHU. "Preparation of chiral selective membranes for electrodialysis separation of racemic mixture". Journal of Membrane Science 276, n.º 1-2 (1 de mayo de 2006): 193–98. http://dx.doi.org/10.1016/j.memsci.2005.09.049.

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42

Li, Wenjian, Nicholas J. Hill, Adam C. Tomasik, Galina Bikzhanova y Robert West. "A New Monomeric Saturated N-Heterocyclic Silylene as a Racemic Mixture". Organometallics 25, n.º 16 (julio de 2006): 3802–5. http://dx.doi.org/10.1021/om060544v.

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43

Newman, Hugh F. V., Eamonn P. Dunphy, Norman M. Bleehen, Stanley Dische, Michele I. Saunders, Cheryl Des Rochers, Paul Workman, Ian Lenox-Smith y Carey E. Smithen. "A comparative study of Ro 03–8799: racemic mixture and enantiomers". British Journal of Radiology 59, n.º 706 (octubre de 1986): 997–99. http://dx.doi.org/10.1259/0007-1285-59-706-997.

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44

NEGRIMOVSKII, VOLODYA M., MARCEL BOUVET, EVGENI A. LUK'YANETS y JACQUES SIMON. "Towards chiral 1,2-naphthalocyanines: 2. Synthesis of lutetium bismacrocyclic derivatives". Journal of Porphyrins and Phthalocyanines 05, n.º 04 (abril de 2001): 423–27. http://dx.doi.org/10.1002/jpp.345.

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Starting from 1,2-naphthalocyanine lutetium acetate (1,2- NcLuOAc ) the unsymmetrical lutetium phthalo(naphthalo)cyanine (1,2- NcLuPc ) has been synthesized and characterized by optical absorption spectra and fast atom bombardment (FAB) mass spectrometry. 1,2-Naphthalocyanine shows several geometrical isomers, both the mixture (noted Nc ∑) and one of them ( Nc Cs ) have been used for forming the corresponding bismacrocycles. As a result the first racemic mixture of a chiral unsubstituted phthalo(naphthalo)cyanine complex has been synthesized and characterized.
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45

Raval, Hiten B. y Ashutosh V. Bedekar. "One-pot kinetic resolution–Mitsunobu reaction to access optically pure compounds, using silver salts in the substitution protocol". New Journal of Chemistry 44, n.º 48 (2020): 21238–43. http://dx.doi.org/10.1039/d0nj04802j.

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Racemic carbinols were converted to chirally pure acetates by a combination of one-pot, enzyme mediated KR and Mitsunobu reaction with metal acetates. Use of AoNO3 or mixture with NaOAc gave excellent results. The protocol is further extended to introduce azide in place of acetate.
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46

Salvi, S. T. B., S. G. Antonio y C. O. Paiva-Santos. "Atenolol characterization in solid formulations available in Brazilian market". Powder Diffraction 28, S2 (septiembre de 2013): S448—S457. http://dx.doi.org/10.1017/s0885715613000845.

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Atenolol is the most used drug in Brazil to hypertension treatment. Two crystal structures are known for this molecule: a racemic form (R,S)-atenolol and a pure form S-atenolol. The racemic form is found in commercial tablets. X-ray powder diffraction (XRD) is an adequate tool to study crystalline structures including drugs. Using the Rietveld Method with XRD data it is possible to quantify the crystalline structures existing in the raw material. Other methods like Le Bail and Pawley can be used to the profile fit and phases identification. For this work we analyzed three tablets of atenolol, two generics and the reference (materials were purchased from a drugstore at the city of Araraquara). These tablets were analyzed by Rietveld, Le Bail and Pawley methods. All tablets exhibited the racemic mixture API (R,S)-atenolol. Some crystalline excipients could be characterized: magnesium carbonate hydrate, lactose monohydrate and talc. The conclusion is that the three methods can be efficiently used to characterize the three atenolol tablets.
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47

Ni, Xiongwei, Rachel Shepherd, Jennifer Whitehead y Tao Liu. "Chiral symmetry breaking due to impeller size in cooling crystallization of sodium chlorate". CrystEngComm 20, n.º 43 (2018): 6894–99. http://dx.doi.org/10.1039/c8ce01318g.

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We report, for the first time, that the size of impellers is the exception to Denk and Botsaris's work where a stirrer of the smallest surface area led to close to 100% deracemization, while the data from the largest impeller agreed with the results of Denk and Botsaris, displaying a racemic mixture.
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48

Reichardt, Bastian, Olaf R. Ludek y Chris Meier. "New and Efficient Synthesis of Racemic Cyclopent-3-en-1-yl Nucleoside Analogues and Their Derivatives". Collection of Czechoslovak Chemical Communications 71, n.º 7 (2006): 1011–28. http://dx.doi.org/10.1135/cccc20061011.

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A new, efficient synthesis of racemic cyclopent-3-en-1-yl nucleoside analogues has been developed starting from cyclopentadiene. The key step is the regioselective hydroboration of an intermediately formed mixture of two alkylated cyclopentadienes to give one cyclopentenol. The remaining double bond was further functionalized by hydroboration, epoxidation, cis-hydroxylation and cyclopropanation.
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49

Pálovics, Emese, Dorottya Fruzsina Bánhegyi y Elemér Fogassy. "Effect of the Enantiomeric Ratio of Eutectics on the Results and Products of the Reactions Proceeding with the Participation of Enantiomers and Enantiomeric Mixtures". Chemistry 2, n.º 3 (21 de septiembre de 2020): 787–95. http://dx.doi.org/10.3390/chemistry2030051.

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This perspective is focused on the main parameters determining the results of crystallization of enantiomers or enantiomeric mixtures. It was shown that the ratio of supramolecular and helical associations depends on the eutectic composition of the corresponding enantiomeric mixture. The M and P ratios together with the self-disproportionation (SDE) of enantiomers define the reaction of the racemic compound with the resolving agent. Eventually, each chiral molecule reacts with at least two conformers with different degrees of M and P helicity. The combined effect of the configuration, charge distribution, constituent atoms, bonds, flexibility, and asymmetry of the molecules influencing their behavior was also summarized.
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50

Huang, Chiung-Cheng, Chang-Yi Guo, Wei-Cheng Hsieh, Chih-Yi Fang, Jian-Fu Chiou, Ming-Jiun Shyu, Bo-Hao Chen, I.-Jui Hsu y Jey-Jau Lee. "Wide blue phase range observed in simple binary mixture systems containing rodlike racemic biphenyl mesogens with 2-octyloxy tails". RSC Advances 6, n.º 112 (2016): 110898–910. http://dx.doi.org/10.1039/c6ra20799e.

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