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, For-L-Ser-NH2, is expected to have three minima (g(+), a, g(-)), [GRAPHICS] the side chain conformational potential energy surface (PES)E = E(chi(1), chi(2)) is expected to have, in the ideal case, nine legitimate 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-chain conformational PES using a rigid gamma(L)(C-7(eq)) backbone conformation (gamma(L); phi = -75 degrees, psi = +75 degrees). Six out of the nine expected minima have been located on the ab initio PES generated for the gamma(L) backbone conformation, at the HF/3-21G level of theory. However, three conformations were missing. The relaxed geometries of the remaining six side-chain conformations have been determined by gradient geometry optimization.