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A statistically based re-evaluation of the evidence for a racemic abundance of quartz enantiomers suggests that, while this hypothesis is valid at the global scale, local deviations occur such that at any given location either l- or d-quartz may predominate. Thus, the hypothesis that the homochirality of life may have come about through interactions with a dominant quartz enantiomer at a particular location cannot be discounted. Keywords: Enantiomorphic, quartz, homochirality, statistics DOI: 10.2138/am.2009.3089

Boromycin is a macrodiolide that exists as a hydrophobic Boeseken complex formed from boric acid and a chiral polyhydroxy macrocyclic ligand. It was covalently bonded to silica gel through a urea linkage to an attached D-valine ester. When evaluated as a chiral stationary phase, it shows pronounced enantioselecfivity toward primary amine-containing racemates, separating 98% of those tested. The selectivity is most pronounced in the presence of organic solvents and supercritical C[O.sub.2] + methanol. The enantioselective binding site and mechanistic factors are examined. Analytes can be complexed as either the free base or their protonated analogues, with the free base being more strongly associated with the chiral selector.

A combination of anisotropic shielding effect and temperature dependence of NMR chemical shifts makes it possible to develop a supramolecular method for determination of absolute configuration of chiral compounds. The concept, theoretical derivatization, and first demonstration of this daedal noncovalent method using a host-guest system is described. This noncovalent method requires only three substrate solutions and can in principle be applied to any host-guest systems that follow the van't Hoff relation and have a clear anisotropic shielding effect based on a well-defined complex structure regardless of the extent of enantiomer selectivity.

Polarization-altering properties of a unique photoinduced chiral material, which consists of a photoresponsive azobenzene (PCDY50), are investigated in detail under an ellipsometric analysis based on a circular basis. The validity of the processes is confirmed by comparing experimental results and calculations. Furthermore, various kinds of optical functions, such as an optical rotator and ellipticity modificator, are demonstrated by applying invariant ellipticity (or azimuth) state condition to the PCDY50 thin film that is less than 1 [micro]m thick. OCIS codes: 230.5440, 310.6860.

In this work, a new chiral micellar electrokinetic chromatography with laser-induced fluorescence detection (chiral-MEKC-LIF) method is proposed to identify and quantify D- and L-amino acids in three lines of transgenic maize and their corresponding nontransgenic parental lines grown under identical conditions. The optimized procedure includes amino acids extraction, derivatization with FITC and chiral-MEKC-LIF separation in a background electrolyte composed of 100 mM sodium tetraborate, 80 mM SDS, and 20 mM [beta]-CD at pH 10.0. The D-and L-forms of Arg, Ser, Ala, Glu, and Asp, corresponding to the majority amino acids usually found in maize, are separated in less than 25 min with efficiencies up to 890 000 plates/m and high sensitivity (i.e., LODs as low as 160 nM were obtained for D-Arg for a signal-to-noise ratio of three), allowing the detection of 1% D-Arg in the presence of 99% of its opposite enantiomer. Using this method, different D-amino acids are detected in all investigated maize samples providing the reproducible quantification of the o-enantiomeric excess (% D-aa) for each amino acid calculated as % D-aa = 100D-aa/(D-aa + L-aa). Thus, significant differences were observed among the % D-aa values for the different conventional varieties (Aristis, Tietar, and PR33P66 maize) as could be expected from their natural variability. More interestingly, comparing each conventional maize with its corresponding transgenic line, very similar % D-aa values were obtained for one of the studied maize couples (Tietar vs Tietar-Bt) what could be presented as a new proof of their substantial equivalence. However, significant differences in the % D-aa values were observed for the other lines of maize studied. It is concluded that enantioselective procedures can open new perspectives in the study of transgenic organisms in order to corroborate (or not) the equivalence with their conventional counterparts.

A vancomycin-chiral stationary phase (CSP) was fully evaluated in capillary electrochromatography (CEC) in reversed-phase and polar organic modes for a number of racemic pharmaceutical compounds. High efficiency and resolution values were obtained for a number of compound classes including thalidomide in both the polar organic mode (190 000 plates meter(super -1) and Rs = 13.8) and reversed-phase mode (125 000 plates meter(super -1) and Rs = 13.0). Experimental parameters, including organic modifier, organic solvent ratio, ionic strength, pH, temperature, and voltage, were examined in both the aqueous and nonaqueous modes to deduce their effect on the resultant EOF, retention times, resolution, and efficiency of chiral separations. All results were consistent with and found to be a combination of what is known from existing literature on CEC theory and experience obtained with macrocyclic antibiotic CSPs in LC. Column stability was excellent, and each column packed was found to offer repeatable separations even when switching from the aqueous to the nonaqueous mode.

A mass spectrometry method based on ion/molecule reactions for determining enantiomeric excess in mixtures of amino acids is illustrated. Protonated complexes of amino acids with (beta)-cyclodextrin are produced in the gas phase using electrospray ionization. Under a backgound pressure of N-propylamine, the amino acid is replaced by the alkylamine. The rates of the guest exchange reaction vary with the chirality of the amino acid. A calibration curve employing varying mixtures of D- and L-amino acids is produced and the fractions of the D isomer in the test mixtures are determined. The quality of the curve is compared to the chiral selectivity of the reaction. In general, the best calibration curves are obtained in systems with the greatest selectivity.

A study was conducted to identify chiral stationary phases in open tubular column chromatography and to understand the mechanism of their enantioselectivity, in attempts to develop quality cyclodextrin phases for capillary supercritical fluid chromatophapy and gas chromatography. Heptakis (2,3-di-O-methyl)-6-O-tosyl-beta-cyclodextrin was obtained in a 31% yield from heptakis(2,3-di-O-methyl)-beta-cyclodextrin.

Rational protein design can be enhanced with quantitative estimates of the Gibbs free-energy change for refolding one beta-turn conformation into another. This helped in investigating the beta-turn models, a chirally representative group of nine peptides of the form CH3CO-L1-L2-NHCH3, where loop residues L1(i+1) and L2(i+2) are achiral Gly(G), L-Ala(A) or D-Ala(A). Free-energy stimulations employing explicit water molecules were used to calculate the stabilities of their common (type 1) and inverse-common (type I') beta-turn conformers.

An efficient method is described for preparing the four stereoisomers of 6-amino-3-azabicyclo[3.2.1]octane-6-carboxylates by using (R)-1-phenylethylamine as the chiral-inducing moiety. A series of N-3-alkyl compounds are prepared by using a one-pot deprotection-alkylation method starting from these compounds.