Theoretical Calculations on Small Amino Acids
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The smallest amino acid, glycine, was among the first amino acids to be investigated by theoretical methods. Its small size makes it particularly suitable for ab initio treatment, even with large basis sets. The results of the ab initio geometry optimization of glycine (1) first suggested the existence of a state undiscovered by microwave spectroscopic studies. This state is the S (extended) state of glycine. Since only the C state (Figure 2.1) had been observed experimentally, it was concluded that the theoretical results were at fault (2). Accordingly, Sellers et al. (3) and Schafer et al. (4) used the gradient method of Pulay (5), with the 4-21G basis set at Hartree-Fock level and found indeed the S structure to be more stable than the C. This theoretical result was confirmed experimentally by the microwave study of Suenram and Lovas (6).
KeywordsPolarization Function COOH Group Correlation Energy Molecular Orbital Calculation Small Amino Acid
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