PEPTIDE MODELS .13. SIDE-CHAIN CONFORMATIONAL ENERGY SURFACE E=E(CHI(1), CHI(2)) OF N-FORMYL-L-SERINAMIDE (FOR-L-SER-NH2) IN ITS GAMMA(L) OR C-7(EQ) BACKBONE CONFORMATION

Since each torsional mode (chi(1) about the C-alpha-C-beta and chi(2) about the C-beta-O bond) of the side-chain of N-formyl-L-serinamide, F or-L-Ser-NH2, is expected to have three minima (g(+), a, g(-)), [GRAPH ICS] the side chain conformational potential energy surface (PES)E = E (chi(1), chi(2)) is expected to have, in the ideal case, nine legitima te minima. [GRAPHICS] Taking 30 degrees intervals along chi(1) and chi (2), a 12 X 12 grid of points has been generated to examine the side-c hain conformational PES using a rigid gamma(L)(C-7(eq)) backbone confo rmation (gamma(L); phi = -75 degrees, psi = +75 degrees). Six out of t he nine expected minima have been located on the ab initio PES generat ed for the gamma(L) backbone conformation, at the HF/3-21G level of th eory. However, three conformations were missing. The relaxed geometrie s of the remaining six side-chain conformations have been determined b y gradient geometry optimization.