Amino acid enantiomers change

A study was made of the effects of derivatization on the 13C analysis of amino acid enantiomers. Conventional isotope ratio MS and GC-isotope ratio MS were used. The latter method requires volatilization of the analytes, which was accomplished by introducing O-isopropyl and A-trifluoroacetyl groups, causing a change in the 13C analysis of the original analytes. It was proposed to use a set of known standards for such analyses, which are applied in geological studies68. 

The last example reflects in a modest way the importance of the study of stereoisomerism. Biological conversions represent a glorious array of diastereomeric reactions and interactions a given chiral amino acid is metabolized but its enantiomer is not a certain complex drug (often a chiral molecule) alleviates pain but its enantiomer is inactive and subdc changes in structure alter a given chiral compound s action completely in the human body. 

The presence of triethylamine in the aqueous portion of the mobile phase was shown to be important for the separation of enantiomers of /-Boc-amino acids, whereasa native amino acids were almost not affected by the addition of TEAA [34]. Lee and Beesley [48] observed that a change in the ionic interactions occurred when changing the acid/base ratio in reversed and polar organic mobile phases or changing the buffer pH in the reversed-phase mode. Consequently, the retention, selectivity, and peak shape is affected. 

As a further test of the etched open tubular approach for the analysis of optical isomers, another column was fabricated based on the selector naphthylethylamine that had been attached to porous silica by the silanization/hydrosilation method for use in HPLC [70]. As in the HPLC experiments, this column was best suited for the resolution of the optical isomers of dinitrobenzoyl methyl esters of amino acids. The best separation (a = 1.14) was obtained for the alanine derivative. In addition, the peak symmetry and efficiency for the naphthylethylamine column was significantly better than that obtained on the cyclodextrin column. However, as shown in HPLC experiments, changes in the amino acid moiety (replacing alanine with valine, etc.) often results in a loss of chiral resolution. In the case of optical isomers, the separation mechanism in HPLC and CEC modes is identical since only interaction between the solute and the bonded phase can result in resolution of the enantiomers. 

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