Characterization of the conformational probability of N-acetyl-phenylalanyl-NH2 by RHF, DFT, and MP2 computation and AIM analyses, confirmed by jet-cooled infrared data.

摘要: Computational and experimental determinations were carried out in parallel on the conformational probability of N-Acetyl-Phenylalanine-NH2 (NAPA). Ab initio computations completed at BLYP/6-311G(df,p), B3LYP/6-31G(d), B3LYP/6-31G(d,p), B3LYP/6-31+G(d) levels theory, labeled L/61fp, B/6, B/6p, B/6+, respectively. Three experimentally identified conformers compared with theoretical data, confirming their identities as βLanti, γLgauche+, γLgauche- (BACKBONESIDECHAIN) conformers. Evidence comes from matching data for all three constituent N−H stretches NAPA, a ΔExperimental-Theoretical = ∼1−3 cm-1, ∼0−5 ∼1−6 L/61fp B/6+ levels, Corrected-ZPE relative energies computed to be 0.14, 0.00, 0.26 0.67, 0.57 (kcal*mol-1) conformers, respectively, The MP2/6-31+G(d) level theory was subsequently found gi...