Peptide model XXVIII: An exploratory ab initio and density functional study on the side-chain? backbone interaction in N-acetyl-L-cysteine- N-methylamide and N-formyl-L-cysteinamide in their L-backbone conformations

M.A.ZAMORA; H.A.BALDONI; A.M RODRIGUEZ; ENRIZ R.D.; C.SOSA; A.PERCZEL; A.KUCSMAN; O.FARKAS; A.DERETEY; J. VANK; I.G. CSIZMADIA

CANADIAN JOURNAL OF CHEMISTRY

NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS

Lugar: Otawa; Año: 2002 vol. 80 p. 832 - 844

0008-4042

A conformational and electronic study on the energetically preferred conformations ( L) of N- and Cprotected L-cysteine (P-CONH-CH(CH2SH)-CONH-Q, where P and Q may be H or Me) was carried out. After restraining the backbone (BB) conformation to its global minimum ( L or C7 eq ), all nine possible side-chain (SC) conformations were subjected to geometry optimization at the HF/3?21G and the B3LYP/6?31G(d,p) levels of theory. Seven of the nine side-chain conformers were located on the potential-energy surface. All conformers were subjected to an AIM (atoms in molecules) analysis. This study indicates that three of the seven optimized conformers exhibited either or both SC BB- or BB SC-type intramolecular hydrogen bonding. Five conformers, however, had distances between a proton and a heteroatom that suggested hydrogen bonding.