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Chirality

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https://www.readbyqxmd.com/read/29450920/polarization-in-france
#1
Bart Kahr
The special relationship between France and the polarization of light from the beginning of the 19th century until the present day is reviewed in the lives and works of Étienne Louis Malus, François Arago, Jean-Baptiste Biot, Augustin Fresnel, Louis Pasteur, Frédéric Wallerant, Aimé Cotton, Francis Perrin, and Alain Aspect. To avoid a redundant presentation of information that can be found with an Internet search engine, the author emphasizes how the aforementioned individuals have influenced the studies of stereochemistry, molecular chirality, and the polarization of light in his research group...
February 16, 2018: Chirality
https://www.readbyqxmd.com/read/29450916/analysis-of-stereoisomers-of-chiral-drug-by-mass-spectrometry
#2
REVIEW
Xiaolei Chen, Yu Kang, Su Zeng
Chiral molecules are of great importance in the life science since individual enantiomers may differ in biological activity, mechanism, and toxicity, making it necessary to explore efficient chiral analysis methods. Chromatography approaches are often used to differentiate enantiomers while mass spectrometry (MS) was thought to be blind in chiral analysis. With the development of MS technique, it began to play a more and more crucial part in chiral observation. In this review, we will give a detailed introduction of the analysis methods related to MS for chiral drugs, including its mechanism, applications, and future development...
February 16, 2018: Chirality
https://www.readbyqxmd.com/read/29443429/electronic-circular-dichroism-for-the-detection-of-microalbuminuria
#3
Lucie Habartová, Hana Logerová, Lukáš Tomaník, Aneta Marešová, Vladimír Setnička
Over the past decades, chiroptical spectroscopy has proved its incomparable ability to elucidate the structure and spatial arrangement of chiral molecules. Systematic analysis of biomolecules in the natural environment of biofluids, however, remains challenging. In this study, we used chiroptical spectroscopy to monitor urinary levels of human serum albumin. Not only severe proteinuria but even just a slightly increased urinary excretion of albumin (microalbuminuria) may indicate serious health complications, especially for diabetic individuals...
February 14, 2018: Chirality
https://www.readbyqxmd.com/read/29443426/comprehensive-investigation-into-the-interconversion-of-c-2-diastereomers-of-naringin
#4
Hongliang Yao, Weiwei Su, Linhuo Lin, Wenjun Pan, Xuan Zeng, Panlin Li
Naringin is a flavanone that widely presents on daily diet and traditional medicinal materials. The ratios of naringin C-2 diastereomers are found different in reported samples, thus suspiciously leading to various functions. In this study, we measured the interconversion of C-2 diastereomers intensively with ultimate high-performance liquid chromatography and circular dichroism spectra. We examined the diastereomeric naringins in fresh citrus fruit, Huajuhong decoction pieces, and naringin tablet; evaluated the impact of tablet production procedures in factory; and monitored the rapid racemization in incubation...
February 14, 2018: Chirality
https://www.readbyqxmd.com/read/29437251/chiral-molecules-adsorbed-on-a-solid-surface-tartaric-acid-diastereomers-and-their-surface-explosion-on-cu-111
#5
Alexandra Rieger, Cédric Sax, Tobias Bauert, Christian Wäckerlin, Karl-Heinz Ernst
The adsorption of diastereoisomers of tartaric acid, namely, meso (R,S)-tartaric acid, (R,R)-tartaric acid, and the racemic mixture of (R,R) and (S,S) tartaric acid on the (111) surface of a copper single crystal has been studied by means of reflection-absorption IR Spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction, and thermal desorption spectroscopy. Two distinct adsorption modes are identified for all three adsorbate systems. All molecules undergo an identical thermally induced autocatalytic decomposition reaction above 510 K...
February 13, 2018: Chirality
https://www.readbyqxmd.com/read/29424942/tetrathiafulvalene-2-2-paracyclophanes-synthesis-crystal-structures-and-chiroptical-properties
#6
Cécile Mézière, Magali Allain, Cristina Oliveras-Gonzalez, Thomas Cauchy, Nicolas Vanthuyne, Laura G Sarbu, Lucian M Birsa, Flavia Pop, Narcis Avarvari
Two racemic tetrathiafulvalene-[2.2]paracyclophane electron donors EDT-TTF-[2.2]paracyclophane 1 and (COOMe)2 -TTF-[2.2]paracyclophane 2 have been synthesized via the phosphite mediated cross coupling strategy. Chiral HPLC allowed the optical resolution of the (RP ) and (SP ) enantiomers for both compounds. Solid-state structures of (RP )-1 and (rac)-2 have been determined by single crystal X-ray analysis. Intermolecular π-π and S•••S interactions are disclosed in the packing. Single crystal X-ray analysis of (RP )-1 combined with experimental and theoretical circular dichroism spectra allowed the assignment of the absolute configuration of the enantiomers of 1 and 2...
February 9, 2018: Chirality
https://www.readbyqxmd.com/read/29424468/structure-determination-of-butylone-as-a-new-psychoactive-substance-using-chiroptical-and-vibrational-spectroscopies
#7
Dita Spálovská, František Králík, Michal Kohout, Bronislav Jurásek, Lucie Habartová, Martin Kuchař, Vladimír Setnička
Recently, there has been a worldwide substantial increase in the consumption of new psychoactive substances (NPS), compounds that mimic the structure of illicit drugs, such as amphetamines or ecstasy. The producers try to avoid the law by a slight modification of illicit structures, thereby developing dozens of temporarily legal NPS every year. The current trends in the detection and monitoring of such substances demand a fast and reliable analysis. Molecular spectroscopy represents a highly effective tool for the identification of NPS and chiroptical methods can provide further information on their 3D structure, which is the key for the determination of their biological activity...
February 9, 2018: Chirality
https://www.readbyqxmd.com/read/29419897/comparison-of-measured-and-predicted-specific-optical-rotation-in-gas-and-solution-phases-a-test-for-the-polarizable-continuum-model-of-solvation
#8
Tal Aharon, Paul Lemler, Patrick H Vaccaro, Marco Caricato
A comparative theoretical and experimental study of dispersive optical activity is presented for a set of small, rigid organic molecules in gas and solution phases. Target species were chosen to facilitate wavelength-resolved measurements of specific rotation in rarefied vapors and in organic solvents having different polarities, while avoiding complications due to conformational flexibility. Calculations were performed with two density functionals (B3LYP and CAM-B3LYP) and with the coupled-cluster singles and doubles (CCSD) ansatz, and solvent effects were included through use of the polarizable continuum model (PCM)...
February 8, 2018: Chirality
https://www.readbyqxmd.com/read/29419887/chiroptical-and-vibrational-spectroscopic-study-of-genuine-and-counterfeit-medicines-containing-tadalafil
#9
František Králík, Patrik Jirmásek, Martin Kuchař, Vladimír Setnička
No abstract text is available yet for this article.
February 8, 2018: Chirality
https://www.readbyqxmd.com/read/29417637/on-the-chiroptical-properties-of-racemic-crystals
#10
Bart Kahr, Alexander T Martin, Karl-Heinz Ernst
In a recent letter on the "Optical activity from racemates", discussed at the 16th International Conference on Chiroptical Spectroscopy in Rennes (June 2017), scientists claimed to have measured the circular dichroism of colored, racemic crystals of two transition metal complexes, observations that "serve to correct a clear deficit in our understanding of the optical properties of racemates." In fact, there is no deficit in our understanding of the optical properties of racemates. Moreover, the measurements presented are unconvincing as evidence of circular dichroism measured in anisotropic crystals and therefore do not inform our understanding of the specific crystals investigated, or racemates generally speaking...
February 8, 2018: Chirality
https://www.readbyqxmd.com/read/29417636/modifying-oligoalanine-conformation-by-replacement-of-amide-to-ester-linkage
#11
Takahiro Hongen, Tohru Taniguchi, Kenji Monde
Oligo(lactic acid) is an ester-analogue of short oligoalanine sequence and adopts a rigid left-handed helical structure. In this study, oligo(lactic acid) was incorporated into oligoalanine sequences and their conformations were studied by vibrational circular dichroism and electronic circular dichroism spectroscopy. The results suggested that oligo(lactic acid) moiety in these sequences maintains a left-handed helix and increases the conformational propensity of the oligoalanine moiety to form a left-handed polyproline type II-like helix...
February 8, 2018: Chirality
https://www.readbyqxmd.com/read/29406603/editors-note-special-issue-honoring-prof-j-gawronski
#12
EDITORIAL
Marcin Kwit, Nina Berova, John Caldwell
No abstract text is available yet for this article.
February 6, 2018: Chirality
https://www.readbyqxmd.com/read/29406589/study-on-the-hplc-based-separation-of-some-ezetimibe-stereoisomers-and-the-underlying-stereorecognition-process
#13
Bolin Zhu, Yaqi Yao, Yu Zhao, Tiemin Sun, Qing Li
Enantioseparation of ezetimibe stereoisomers by high-performance liquid chromatography on different polysaccharide-based chiral columns (Chiralpak AD-H, Chiralcel OD-RH, and Chiralpak IC) was studied with suitable mobile phases compositions. Attempts were made to comprehensively compare the chiral recognition capabilities of immobilized versus coated polysaccharide-based chiral columns, amylose-based versus cellulose-based chiral stationary phases, reversed versus normal phase modes, and standard versus nonstandard mobile phases...
February 6, 2018: Chirality
https://www.readbyqxmd.com/read/29406583/mutual-inversion-of-flurbiprofen-enantiomers-in-various-rat-and-mouse-strains
#14
Natasja de Bruin, Nerea Ferreirós, Mike Schmidt, Martine Hofmann, Carlo Angioni, Gerd Geisslinger, Michael John Parnham
Flurbiprofen (F) is a nonsteroidal anti-inflammatory drug (NSAID) used therapeutically as the racemate of (R)-enantiomer and (S)-enantiomer. The inversion of RF to SF and vice versa was investigated in C57Bl/6 and SJL mice and Dark Agouti and Lewis rats. The enzyme α-methylacyl-CoA racemase (AMACR) is involved in the chiral inversion pathway that converts members of the 2-arylpropionic acid NSAIDs from the R-enantiomer to the S-enantiomer. We studied C57Bl/6 mice deficient in AMACR postulating that they should show reduced inversion of RF to SF...
February 6, 2018: Chirality
https://www.readbyqxmd.com/read/29393985/validation-of-molecular-force-field-parameters-for-peptides-including-isomerized-amino-acids
#15
Akifumi Oda, Tomoki Nakayoshi, Shuichi Fukuyoshi, Eiji Kurimoto, Noriyuki Yamaotsu, Shuichi Hirono, Ohgi Takahashi
Recently, stereoinversions and isomerizations of amino acid residues in the proteins of living beings have been observed. Because isomerized amino acids cause structural changes and denaturation of proteins, isomerizations of amino acid residues are suspected to cause age-related diseases. In this study, AMBER molecular force field parameters were tested by using computationally generated nonapeptides and tripeptides including stereoinverted and/or isomerized amino acid residues. Energy calculations by using density functional theory were also performed for comparison...
February 2, 2018: Chirality
https://www.readbyqxmd.com/read/29384590/conformation-change-of-hornet-silk-proteins-in-the-solid-phase-in-response-to-external-stimulation
#16
Reiko Kuroda, Tsunenori Kameda
Hornet silks adopt a variety of morphology such as fibers, sponge, films, and gels depending on the preparation methods. We have studied the conformation change of hornet silk proteins (Vespa mandarina) as regenerated films, using chiroptical spectrophotometer universal chiroptical spectrophotometer 1, which can measure true circular dichroism spectra without artifact signals that are intrinsic to solid-state samples. The spectra showed that the proteins in films alter the conformation rapidly from the α-helix to the coiled coil and then to a β-sheet structure in response to heat/moisture treatment, but the transformation stopped at the coiled coil state when the sample was soaked in EtOH/water solution...
January 31, 2018: Chirality
https://www.readbyqxmd.com/read/29359818/the-resolution-of-acyclic-p-stereogenic-phosphine-oxides-via-the-formation-of-diastereomeric-complexes-a-case-study-on-ethyl-2-methylphenyl-phenylphosphine-oxide
#17
Péter Bagi, Bence Varga, András Szilágyi, Konstantin Karaghiosoff, Mátyás Czugler, Elemér Fogassy, György Keglevich
As an example of acyclic P-chiral phosphine oxides, the resolution of ethyl-(2-methylphenyl)-phenylphosphine oxide was elaborated with TADDOL derivatives, or with calcium salts of the tartaric acid derivatives. Besides the study on the resolving agents, several purification methods were developed in order to prepare enantiopure ethyl-(2-methylphenyl)-phenylphosphine oxide. It was found that the title phosphine oxide is a racemic crystal-forming compound, and the recrystallization of the enantiomeric mixtures could be used for the preparation of pure enantiomers...
January 23, 2018: Chirality
https://www.readbyqxmd.com/read/29359493/axially-chiral-ni-ii-complexes-of-%C3%AE-amino-acids-separation-of-enantiomers-and-kinetics-of-racemization
#18
Wenzhong Zhang, Romuald Eto Ekomo, Christian Roussel, Hiroki Moriwaki, Hidenori Abe, Jianlin Han, Vadim A Soloshonok
Herein we present design, synthesis, chiral HPLC resolution, and kinetics of racemization of axially chiral Ni(II) complexes of glycine and di-(benzyl)glycine Schiff bases. We found that while the ortho-fluoro derivatives are configurationally unstable, the pure enantiomers of corresponding axially chiral ortho-chloro-containing complexes can be isolated by preparative HPLC and show exceptional configurational stability (t1/2 from 4 to 216 centuries) at ambient conditions. Synthetic implications of this discovery for the development of new generation of axially chiral auxiliaries, useful for general asymmetric synthesis of α-amino acids, are discussed...
January 23, 2018: Chirality
https://www.readbyqxmd.com/read/29334408/effects-of-metalaxyl-enantiomers-stress-on-root-activity-and-leaf-antioxidant-enzyme-activities-in-tobacco-seedlings
#19
Song Fang, Yi Tao, Yizhi Zhang, Fanyu Kong, Yunbai Wang
The objective of this experiment was to study the effects of metalaxyl enantiomers on the activity of roots and antioxidative enzymes in tobacco seedlings. Water culture experiment was conducted to analyze the effects of different concentrations of metalaxyl enantiomers (30 and 10 mg L-1 ) on root activity and leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and malondialdehyde (MDA) content of tobacco seedlings. The results showed that metalaxyl significantly inhibited root activity and significantly improved leaf SOD, POD, and CAT activities and MDA content...
January 15, 2018: Chirality
https://www.readbyqxmd.com/read/29334407/chiral-separation-of-novel-iminonaringenin-derivatives
#20
Meriem Bouanini, Nasser Belboukhari, J Carlos Menéndez, Khaled Sekkoum, Abdelkarim Cheriti, Hassan Y Aboul-Enein
A series of 4-iminonaringenin derivatives 2-6 have been prepared in good overall yields from a condensation reaction between naringenin and primary amines. The structures of all products were confirmed by ultraviolet, infrared, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance spectroscopic techniques. These derivatives were analyzed by high-performance liquid chromatography using polysaccharide-based chiral stationary phases, namely, Chiralpak IB and Chiralcel OD, using various mobile phases...
January 15, 2018: Chirality
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