Multivariate analysis of capillary electrophoresis separation conditions for Z-E isomers of clomiphene.

Plackett-Burman (P-B) experimental design has been used to optimize the factors affecting separation of Z and E isomers of clomiphene (zuclomiphene and enclomiphene respectively) using capillary electrophoresis. The P-B design was used to simultaneously investigate the following five factors: buffer ionic strength, buffer pH, heptakis (2,3,6-tri-o-methyl) beta-cyclodextrin (TMCD) concentration, methanol concentration and injection time, each at three levels. In addition to these, a dummy variable was added to estimate the variability of the system.

Normal phase LC-MS determination of retinoic acid degradation products.

The degradation products formed when 13-cis retinoic acid (13-cis RA) and all-trans RA were exposed to fluorescent light and air were investigated. These retinoids are known to undergo Z-E isomerization (due to the existence of four unsaturated double bonds) and oxidation when exposed to light and air. Analysis by LC was carried out on a 25 cm x 4.

Separation of 13-cis and all-trans retinoic acid and their photodegradation products using capillary zone electrophoresis and micellar electrokinetic chromatography (MEC).

Two retinoic acid isomers; 13-cis retinoic acid and all-trans retinoic acid and their photodegradation products were resolved with capillary electrophoresis (CE) (UV detector, 345 nm) using three different mobile phases: method 1--an acetonitrile modified borate buffer (pH 8.5); method 2--borate buffer (pH 8.5) modified with acetonitrile and alpha-cyclodextrin; and method 3--borate buffer (pH 8.

Association of beta-agonists with corresponding beta 2- and beta 1-adrenergic pentapeptide sequences.

Synthesized beta 1- and beta 2-pentapeptide sequences corresponding to published adrenoceptor transmembrane activation site subtypes were investigated in vitro for selectivity in association for drug ligands of known selectivity. Both nuclear magnetic resonance spectroscopy and molecular mechanics demonstrated that structural differences among the corresponding pentapeptide activation-site sequences can explain agonist selectivity. Results suggest the agonists bind across the activation site loop on the second transmembrane alpha-helix by dipole/dipole interactions between a ligand and the peptide.

Nuclear magnetic resonance (NMR) spectroscopic investigation of interaction energies of ephedrine stereoisomers in noncrystalline solids and its correlation with thermodynamic data.

Equations relating the interaction energies of each of the binary mixtures of ephedrine from linear combinations of the energies of the individual isomers are presented. The interaction energies in the noncrystalline solid mixtures measured from NMR chemical shift data using cross-polarization magic angle spinning nuclear magnetic resonance 13C cross-polarization magic angle spinning nuclear magnetic resonance (13CP/MAS NMR) spectroscopy correlate strongly with interaction energy from thermodynamic data. The summation of changes in relative frequencies for structurally equivalent carbons is used as a measure of differences in electron shielding on mixing.