Conformational analysis of N- and C-terminally protected tripeptide model glycyl-isoleucine-glycyl: An ab initio and DFT study
نویسندگان
1 Department of Chemistry, Hakim Sabzevari University, Sabzevar 96179-76487, Iran.
2 Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
3 Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
doi
10.22036/pcr.2014.3858چکیده
An ab initio and density functional theory (DFT) study about conformational analysis of tripeptide model HCO−GLY−L−ILE−GLY−NH2 is presented. The tripeptide was scanned about initial, central, and final residues, separately while for every scanning procedure the two other residues had been kept in the β conformation and side chain (SC) dihedral angles were maintained on the gauche− (g‾) state (χ1, χ2 = ‒60). Conformers (L, L, D, D, D), (L, L, D), and (L, L, D, L) were found through scanning of the tripeptide about initial, central, and the last amino acids, respectively. At first, geometries of all conformers were optimized at the HF/6-31G (d) and B3LYP/6-31G (d) levels of theory. In the followings, their thermodynamic properties were obtained with performing of the frequency calculations at the same levels used for optimization. Finally, comparison of the calculated thermodynamic results of the found conformers to the tripeptide minima on Ramachandran map as the standard criteria proposed LLL as the most stable one.
