A New Scheme For Quick Determining The Relative Conformational Energies Of Alanine-α-polypeptide

Total 152 conformers of alanine di-, tri-, tetra-and penta-peptide molecules have been completely optimized at B3LYP/6-31G* level. The features of the conformers'structures have been analyzed and a new scheme has been proposed based on the density functional theory to determine the conformer's relative stability of the alanine?α?polypeptide. the Special Hydrogen atom, the parameters of seven non-bonded interactions have been determined from 22 conformers of alanine polypeptides. The 152 relative conformational energies of the alanine polypeptides have been calculated both by the new scheme and by B3LYP/6-31G* method. Through comparing the 152 conformers'relative energies obtained by the new scheme and B3LYP/6-31G* ones, it can be concluded that the new scheme and the interaction parameters are reasonable for the determination of the conformation stability of alanine polypeptides. In this work, we also used the Coulomb Model, K parameters and the atomic charges which were determined by using a 6-31G* basis set to reproduce the relative conformational energies of 152 polypeptides. And the agreement with B3LYP data is good. Furthermore, the atomic average charges of four, five, six and fifteen groups have been determined and we discussed these average charges for simplifying the Coulomb Model. As we can see, the average charges of five groups were better than the other three average charges to simplify the Coulomb Model. And the atomic charges which were determined by using a 6-31G* basis set were the best than the other four atomic average charges for the Coulomb Model to reproduce the relative conformational energies of 152 polypeptides.