Results 141 to 150 of about 33,103 (197)

Enantiomeric Excesses in Meteoritic Amino Acids

Science, 1997
Gas chromatographic-mass spectral analyses of the four stereoisomers of 2-amino-2,3-dimethylpentanoic acid (DL-α-methylisoleucine and DL-α-methylalloisoleucine) obtained from the Murchison meteorite show that the L enantiomer occurs in excess (7.0 and 9.1%, respectively) in both of the enantiomeric pairs.
J R, Cronin, S, Pizzarello
openaire   +2 more sources

Determination of enantiomeric excess by capillary electrophoresis

Electrophoresis, 2000
Capillary electrophoresis (CE) is becoming an established method for the determination of chiral trace impurities. This paper provides an overview of the state of the art of CE for such determinations. Detection limits of 0.1% impurity is widely accepted as a minimum requirement for chiral trace impurity determinations.
L G, Blomberg, H, Wan
openaire   +2 more sources

Enantiomeric Excesses and Electronic Chirality Measure

Journal of the American Chemical Society, 2003
We present an approach to measure the amount of chirality in the electronic wave function and apply it to the study of a set of asymmetric aminohydroxylation reactions. The correlation coefficient between the chirality measure and the enantiomeric excesses is larger than 0.9 and suggests that this phenomenological approach can be a valuable tool to ...
Luca, Bellarosa, Francesco, Zerbetto
openaire   +2 more sources

Measurement of Enantiomeric Excess Using Molecularly Imprinted Polymers

Organic Letters, 2002
[reaction: see text] A new method is presented for the measurement of enantiomeric excess (ee) utilizing molecularly imprinted polymers (MIPs). The method is demonstrated to be accurate and rapid, as the ee values can be calculated from straightforward concentration measurements.
Yizhao, Chen, Ken D, Shimizu
openaire   +2 more sources

Sensing of enantiomeric excess in chiral carboxylic acids

Chemical Communications, 2015
Cinchona-derived fluorescent molecules are used in a cross-reactive sensor array for the sensing of enantiomeric excess (ee) in carboxylate drugs analysis.
Ali, Akdeniz, Lorenzo, Mosca, Tsuyoshi, Minami, Pavel, Anzenbacher   +3 more
openaire   +2 more sources

Frozen Solution-Mediated Asymmetric Synthesis: Control of Enantiomeric Excess

The Journal of Organic Chemistry, 2020
Asymmetric List-Mannich reactions were carried out in the frozen state to afford optically active adducts in moderate-to-good chemical yields and enantiomeric excesses (ee). The frozen solution exerts critical control of ee via entropy changes, in sharp contrast to the enthalpy-driven asymmetric reactions typically observed in homogeneous solvents ...
Koki Iijima, Makoto Harada, Gaku Fukuhara, Tetsuo Okada   +3 more
openaire   +2 more sources

Enantiomeric Excess of Amino Acids in Hydrothermal Environments

Origins of Life and Evolution of Biospheres, 2005
In a simulated hydrothermal environment allowing fluid circulation between hot and cold regions repeatedly, D- and L-alanine molecules were racemized differently depending upon the concentration of alanine, whether D or L, present in the solution. In particular, the relative population of L-alanine was slightly more enhanced compared to that of D ...
Atsushi, Nemoto, Minako, Horie, Ei-Ichi, Imai, Hajime, Honda, Kuniyuki, Hatori, Koichiro, Matsuno   +5 more
openaire   +2 more sources

Determination of enantiomeric excess by chiral liquid chromatography without enantiomerically pure starting standards

Biomedical Chromatography, 2012
ABSTRACTA facile approach for the enantiomeric excess determination of enantiomeric mixtures without the necessity of pure enantiomer standards is presented. Promethazine and trimeprazine commercial nonracemic mixtures were used as cases study to probe the validity of the method.
F G, Sánchez, A, Navas Díaz, E, Sánchez Torreño, A, Aguilar, I, Medina Lama, M, Algarra   +5 more
openaire   +2 more sources