Composition and chirality of amino acids in aerosol/dust from laboratory and residential enclosures.

Initial results from the analyses of geological and anthropological samples for amino acids were difficult to accept because of the high enantiomeric purities of the analytes (i.e., predominantly L-amino acids). Consequently, sources of contamination had to be considered. All sources were eliminated except for direct atmospheric contamination. Essentially invisible, microscopic, aerosol/dust was found to rapidly contaminate the surface of samples and sample containers even after brief exposure times in clean laboratories. Contamination increased with exposure time. The aerosol/dust amino acids were contained predominantly in a proteinaceous material. Aerosol/dust from different locations can contain different percentages of proteinoid/amino acid material. However, the relative concentrations of the amino acids were similar for both laboratory and residential samples. The enantiomeric purity of the L-amino acids studied in aerosol/dust appears to be 99% or greater for the samples examined. Thus, even slight contamination of any sample with microscopic dust or aerosol particles can skew the results of trace amino acid analyses and amino acid e.e. determinations.

Rapid CE microbial assays for consumer products that contain active bacteria.

Recent advances in high efficiency separation methods of bacteria allow their rapid identification and quantitation in some cases. A specific capillary electrophoresis (CE) technique is used to identify and quantitate Lactobacillus acidophilus in both pill and syrup health products as well as Bifidobacterium infantis in a powdered formula supplement. Cell viability can be evaluated as well. In some cases, both the living and dead bacterial cells as well as the molecular excipients can be evaluated in a single run.

Evaluation of the macrocyclic glycopeptide A-40,926 as a high-performance liquid chromatographic chiral selector and comparison with teicoplanin chiral stationary phase.

A new macrocyclic antibiotic of the vancomycin family, referred to by its industrial designation as A-40,926, was bonded to 5 microm silica particles and utilised as a chiral stationary phase (CSP). Since A-40,926 is structurally related to teicoplanin, the A-40,926 CSP was compared to a commercially available teicoplanin CSP. A set of 28 chiral compounds, including amino-acids and related compounds, compounds with a ring containing the stereogenic centre, compounds bearing aromatic structures near their stereogenic centres and alcohols, was tested for enantioseparation on the two CSPs. The results are compared and discussed in terms of enantioselective Gibbs energy difference. The A-40,926 CSP was able to resolve one compound that was not resolved by the teicoplanin CSP. However, it could not separate four compounds that the teicoplanin CSP did separate. It is shown that the A-40,926 CSP is complementary to the teicoplanin CSP, thereby enlarging the number of enantiomers that can be separated by the macrocyclic glycopeptide based CSPs.

Role of the carbohydrate moieties in chiral recognition on teicoplanin-based LC stationary phases.

For this study, we used the macrocyclic antibiotic teicoplanin, a molecule consisting of an aglycone peptide "basket" with three attached carbohydrate (sugar) moieties. The sugar units were removed and the aglycone was purified. Two chiral stationary phases (CSPs) were prepared in a similar way, one with the native teicoplanin molecule and the other with the aglycone. Twenty-six compounds were evaluated on the two CSPs with seven RPLC mobile phases and two polar organic mobile phases. The compounds were 13 amino acids or structurally related compounds (including DOPA, folinic acid, etc.) and 13 other compounds (such as carnitine, bromacil, etc.). The chromatographic results are given as the retention, selectivity, and resolution factors along with the peak efficiency and the enantioselective free energy difference corresponding to the separation of the two enantiomers. The polarities of the two CSPs are similar. It is clearly established that the aglycone is responsible for the enantioseparation of amino acids. The difference in enantioselective free energy between the aglycone CSP and the teicoplanin CSP was between 0.3 and 1 kcal/mol for amino acid enantioseparations. This produced resolution factors 2-5 times higher with the aglycone CSP. Four non amino acid compounds were separated only on the teicoplanin CSP. Six and five compounds were better separated on the teicoplanin and aglycone CSPs, respectively. Although the sugar units decrease the resolution of alpha-amino acid enantiomers, they can contribute significantly to the resolution of a number of non amino acid enantiomeric pairs.

Evaluation of the enantiomeric composition of amino acids in tobacco.

Despite the fact that several studies have reported the concentrations of various free amino acids in tobacco, their enantiomeric composition is unknown. Both the absolute and enantiomeric compositions of proline, alanine, asparagine, aspartic acid, valine, methionine, leucine,and phenylalanine were determined for three strains of tobacco leaf, three types of smokeless tobacco, and six different blended filtered and nonfiltered reference cigarettes. Some of the highest levels of D-amino acids ever found in agricultural products were observed. Possible mechanisms for the production of these D-amino acids are considered. The relevance of D-amino acids in tobacco is discussed.

Evaluation of the macrocyclic antibiotic avoparcin as a new chiral selector for HPLC.

Avoparcin is a macrocyclic glycopeptide antibiotic structurally related to vancomycin, teicoplanin, and ristocetin A. When attached to 5-microns spherical silica gel, the avoparcin proved to be an effective chiral stationary phase (CSP) that could be used in the reversed-phase, normal-phase, and polar-organic modes. The avoparcin CSP was complimentary to the other macrocyclic glycopeptide CSPs in that it could resolve some racemates that the others could not, and vice versa. Some important compounds resolved on the avoparcin CSP include verapamil, thyroxine, mephenytoin, and 2-imidazolidone-4-carboxylic acid. The use of this CSP and the optimization of separations on it are discussed. Avoparcin appears to be a useful addition to this family of CSPs.

Practice and mechanism of HPLC oligosaccharide separation with a cyclodextrin bonded phase.

A series of six oligosaccharides: linear arabinosides, cellosides, isomaltosides, mannosides, maltosides and xylosides containing up to 15 sugar units, as well as alpha, beta and gamma-cyclodextrins, were separated without derivatization with acetonitrile-water mobile phases and a beta-cyclodextrin bonded phase column using both UV (195 nm) and refractive index detection. The mobile phases contained more than 60%v/v acetonitrile to separate the oligosaccharides with baseline resolution with practical retention times. The chromatographic mode is intermediate between normal-phase chromatography and hydrophilic interaction chromatography. Sugar retention occurs through partition exchange and polar interactions. The saccharide-stationary phase interaction was studied through retention behavior and peak efficiency. It is shown that partitioning interactions and hydrogen bonding interactions between the hydroxyl groups of the stationary phase and those of the sugars are the two possible mechanisms responsible for sugar retention. The sugar retention times are dramatically reduced when the mobile phase water content is increased. The conformation of the oligosaccharides also affects retention. Excellent and rapid separation of the saccharide components of commercial corn syrup and dextrin are shown. The plots of the log retention factor versus degree of polymerization (DP) were linear. The slope of these plots was related to the solute-stationary phase interaction energy. This energy is directly related to the mobile phase water content. The kinetics of the interaction is slow. At 1 ml min(-1), the peak efficiencies were in the 10 000-15 000 plate m(-1) range (70-100 d(p)). The efficiency maximum was not reached at 50 mul min(-1) indicating slow interactions between large molecules.