title: Influence of ionization on the conformational preferences of peptide models. Ramachandran surfaces of N-formyl-glycine amide and N-formyl-alanine amide radical cations.
abstract: Ramachandran maps of neutral and ionized HCO-Gly-NH2 and HCO-Ala-NH2 peptide models have been built at the B3LYP/6-31++G(d,p) level of calculation. Direct optimizations using B3LYP and the recently developed MPWB1K functional have also been carried out, as well as single-point calculations at the CCSD(T) level of theory with the 6-311++G(2df,2p) basis set. Results indicate that for both peptide models ionization can cause drastic changes in the shape of the PES in such a way that highly disallowed regions in neutral PES become low-energy regions in the radical cation surface. The structures localized in such regions, epsilonL+* and epsilonD+* are highly stabilized due to the formation of 2-centre-3-electron interactions between the two carbonyl oxygens. Inclusion of solvent effects by the conductor-like polarizable continuum model (CPCM) shows that the solute-solvent interaction energy plays an important role in determining the stability order.
authors.affiliation: Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
authors.forename: Adrià
authors.initials: A
authors.lastname: Gil
authors.forename: Mariona
authors.initials: M
authors.lastname: Sodupe
authors.forename: Juan
authors.initials: J
authors.lastname: Bertran
mesh_terms: D000409:Alanine / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D003198:Computer Simulation; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry
chemical_list: D002412:Cations; C407066:N-formylglycinamide; D012997:Solvents; D000409:Alanine; D005998:Glycine