Substituent effects on the tautomerization of amino acids

Abstract

The goal of this research is to examine the substituent effects of alkyl groups on the tautomerization of N,N-dimethylamino acids. This study of substituent effects on the tautomeric distribution of zwitterion and neutral unionized tautomer was studied in D2O and CD3CN. The percentage of zwitterion was determined in these solvents for N,Ndimethylglycine, N,N-dimethylalanine, N,N-dimethylvaline, N,Ndimethylleucine, and N,N-dimethylisoleucine. The role of the solvent on the amino acid tautomerization was also investigated.

Computational methods were also applied to this study to examine the substituent effects on amino acid tautomerization. Spartan and Gaussian 92 programs were utilized to perform the molecular modeling task (HF/STO-3G, HF/6-311++G**) for the identification of the potential energy minima for the zwitterion model and the neutral unionized tautomer model. The design for models of the zwitterion and the neutral unionized tautomer were also investigated in this study. The relative energy difference in these minima for the zwitterion and the neutral unionized tautomer provides information on the relative stability of the tautomers.