title: The peptide-chain size dependence of positive dissociation energy effect in metallized and protonated polydentate oligoglycine peptides.
abstract: The dependence of the positive dissociation energy (PDE) on the size of both protonated and various metal cationized (M+/2+=Na+, K+, Mg2+, and Ca2+) oligoglycines GnHM (G=glycine; n=1-5, and including 6 for GnHK) in the gas phase has been first determined at the B3LYP level with different basis sets. Results show that these PDEs become negative ones when n>or=5 for GnHNa, n>or=6 for GnHK, n>or=2 for GnHMg, and n>or=3 for GnHCa. Moreover, the PDE effect decreases gradually along the increase of oligoglycine size for all these PDE systems. More charge transfer to the ambient ligand and large electrostatic effect of the two divalent cation (Mg2+ and Ca2+) involved systems make them lose the PDE effect more rapidly, and hold more compact and oblate shapes than the monovalent ones. Differently, polydentate GnHK prefers a spherical to oblate shape along with the increase of oligoglycine size.
authors.affiliation: School of Chemistry and Chemical Engineering, Jinan University, Jinan, 250022, People's Republic of China.
authors.forename: Hongqi
authors.initials: H
authors.lastname: Ai
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Bu
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Shihai
authors.initials: S
authors.lastname: Yan
mesh_terms: D002412:Cations / Q000737:chemistry*; D003198:Computer Simulation; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011522:Protons; D013816:Thermodynamics
chemical_list: D002412:Cations; D008670:Metals; D009842:Oligopeptides; D010455:Peptides; D011522:Protons; C011080:polyglycine