Resolution of enantiomers of DL-amino acids on silica gel plates impregnated with optically pure (-)-quinine.

TLC resolution of enantiomers from racemic amino acids was achieved on silica gel plates impregnated with optically pure (-)-quinine. The successful solvent systems were butanol-chloroform-acetic acid (3:7:5, v/v) for DL-methionine; 6:8:4, v/v for alanine; 10:1:4; v/v for threonine; and ethyl acetate-carbon tetrachloride-propionic acid (10.5:6.5:3.5, v/v) for valine. Minimum detection limits were found to be different for each of the amino acid, ranging between 0.9 and 3.7 microg. The effects of concentration of impregnating reagent, temperature and pH on resolution of enantiomers have been studied in details.     

Separation of some antihistamines on impregnated TLC silica plates

Different metal salts have been tried as impregnating reagents for developing TLC separation schemes for some antihistamines on silica gel 'G' plates, using a new solvent system benzene + dimethyl formamide + acetic acid (30:10:7). Spots were visualized by spraying with a solution of Dragendroff's reagent.     

TLC resolution of enantiomeric mixtures of amino acids

Summary Resolution of enantiomeric mixtures of DL-amino acids (Nine) using silica gel layers impregnated with (-)-bruncine is reported. The solvent system used was Butanol: Acetic acid: Chloroform (3∶1∶4). The diastereomers were formed and hydrolysed, by dilute HCl spray, on the chromatogram only and the amino acids thus resolved were located by ninhydrin spray. The cross resolution possibilities of enantiomers were also calculated.     

Reversed-phase planar chromatography of some enantiomeric amino acids and oxazolidinones

The resolution of two enantiomeric amino acids and four structurally related oxazolidinones was evaluated by reversed-phase planar chromatography using both home-made microcrystalline cellulose triacetate (MCTA) layers and mobile phase additivies, such as beta-cyclodextrins (beta-Cy), modified alpha, beta, gamma cyclodextrins and bovine serum albumin (BSA), on commercially available RP-18W/F254 and SilC18-50/UV254 plates. All the enantiomers were partially or baseline resolved by at least one of the chiral phases tested. Densitograms of optical antipodes and their mixtures were measured on MCTA layers developed with hydroalcoholic solvents.     

Chemically L-prolinamide-modified monolithic silica column for enantiomeric separation of dansyl amino acids and hydroxy acids by capillary electrochromatography and mu-high performance liquid chromatography

A silica-based chiral monolithic column prepared by sol-gel process and chemical modification of chiral selector was used for enantioseparation of dansyl amino acids and hydroxy acids by capillary electrochromatography (CEC) and mu-high-performance liquid chromatography (mu-HPLC). L-Prolinamide was modified as a chiral selector. The chiral stationary phase (CSP), the chiral complex of Cu(II) with L-prolinamide, provides an anodic electroosmotic flow (EOF) in CEC. The EOF was found to be dependent on applied electric field strength, the pH, and the composition of mobile phases. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pore. D-Enantiomers migrated before L-enantiomers except for dansyl-(Dns)-DL-Ser. The separation efficiencies of up to 17600 (D) and 13,200 plates m(-1) (L) were achieved for the separation of DL-indole-3-lactic acid.     

Enantioselective synthesis and enantiomeric amplification of amino acids under prebiotic conditions

A plausible origin of biomolecular homochirality is advanced, where alpha-methyl amino acids found on meteorites transfer their chirality in the synthesis of normal amino acids. This asymmetry can be amplified to nearly homochiral levels, thus providing the necessary prerequisite for life to start on this planet and elsewhere in the universe.     

Resolution of amino acids by a native-cellulose column

Seventeen aliphatic, hydroxyl, sulfur-containing, aromatic, imino, and heterocyclic DL-amino acids were resolved without derivatization using a native-cellulose column. Chirality was assigned by either CD spectra or co-chromatography. Under these conditions, it is known that the hydrophobic interaction of amino acids with the hydroxyl groups on the cellulose played an important role in the separations. The cellulose column chromatographic system for resolution of amino acid enantiomers was combined with an amino acid analyzer. Thus, the DL-amino acids separated by the latter system were successively resolved by the former.     

TLC separation of some biologically important amino acids on pyridinium tungstoarsenate impregnated layers

Summary A satisfactory TLC separation scheme for 15 important amino acids on silica gel layers impregnated with pyridinium tungstoarsenate using isoamyl alcohol-wateracetic acid (605030) as the solvent system has been worked out. It is found that the Martin relationship is obeyed by similarly constituted amino acids. A plot of R_M vs the concentration of pyridinium ion released shows a scatter suggesting that, besides exchange properties, other factors also strongly influence the movement of amino acids.     

Resolution of amino acids on optically active stationary phase by gasChromatography

Summary The various enantiomeric esters of TFA--amino acid may be separated directly by gas chromatography on optically active stationary phase. In this work we investigated the resolution of relatively volatile amino acids (alanine, -amino-n-butyric acid, valine, threonine, allo-isoleucine, isoleucine, norvaline, leucine, proline, norleucine, serine) and less volatile amino acids (cysteine, aspartic acid, methionine, phenylalanine, glutamic acid) on a glass capillary column coated with N-caproyl-L-valyl-L-valine cyclohexyl ester.     

Separation of amino acids, their derivatives and enantiomers by impregnated TLC

The present state of TLC with respect to separation of amino acids, their different derivatives and their enantiomers by the technique of impregnation is discussed. The main approaches to impregnation viz. mixing of a suitable reagent with the adsorbent prior to plate-making, immersion of the untreated plate in the solution of impregnating reagent prior to development, and modification of the adsorbent, have been identified and discussed for each class of these compounds. The role of impregnation in resolving enantiomers or in improving the separation of mixtures of amino acids or their derivatives in terms of ion pairing, complex formation, ligand exchange or other steric interactions has been elaborated in each category.     

A stereodivergent approach to amino acids, amino alcohols, or oxazolidinones of high enantiomeric purity

(-)-Menthone, an inexpensive chiral auxiliary, was used to prepare both enantiomers of alpha-amino acids, amino alcohols, or oxazolidinones. The sequence includes the S(N)2' displacement by a cuprate reagent and a Curtius rearrangement as key steps.     

Periodic arrangement of silica nanospheres assisted by amino acids

Uniform-sized silica nanospheres with a well-ordered arrangement were successfully synthesized by a novel and simple method; hydrolysis and condensation reactions of tetraethyl orthosilicate were conducted in the presence of basic amino acids.     

Recognition of vinification technology through gas chromatographic data on enantiomeric purity of free amino acids

Analysis of D-amino acids in food, a matter of growing interest due to nutritional implications, has been used as a tool for food evaluation, detection of falsifications and as a genuinity parameter. The evolution of free D-amino acids in wines of a portuguese Vitis vinifera variety (Roupeiro white), bottled during the period 1978–1989 is studied by means of chiral high resolution gas chromatography. D-Ala, D-Val, D-Thr, D-Leu, D-Ser, D-Asx, D-Met, D-Phe, and D-Glx are present in most of the analyzed wines. It was not possible to correlate the evolution of the D/L ratio to the age of the wine. However, a clear correlation between enantiomer purity profiles and the vinification technique could be established. The results show that free D-amino acids may be used as markers for the biotechnological process used in vinification.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

The adsorption of amino acids on the surface of highly dispersed silica

The adsorption of arginine, histidine, lysine, and ornithine on the surface of highly dispersed silica from aqueous solutions was studied as a function of pH. The equilibrium constants of the formation of surface complexes were calculated using the Stern model for the electrical double layer. It was shown that the possibility of adsorption of amino acids on the silica surface is determined by the presence of additional basic groups in their molecules.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 733–738.Original Russian Text Copyright © 2004 by Vlasova, Golovkova.