title: Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure and properties of L-arginine and zwitterionic L-arginine.
abstract: Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of L-arginine is examined. The effects of metal ions (Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+)) and water on structures of Arg x M(H2O)m , m = 0, 1 complexes have been determined theoretically by employing the density functional theories (DFT) and using extended basis sets. Of the three stable complexes investigated, the relative stability of the gas-phase complexes computed with DFT methods (with the exception of K(+) systems) suggests metallic complexes of the neutral L-arginine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of arginine in the presence of the metal cations Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+) were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to arginine is exhibited by the Cu(2+) cation. The computed Gibbs energies DeltaG(o) are negative, span a rather broad energy interval (from -150 to -1500 kJ/mol), and are appreciably lowered upon hydration.
authors.affiliation: Department of Pharmaceutical Chemistry, Comenius University, Odbojarov 10, SK-832 32 Bratislava, Slovakia. remko@fpharm.uniba.sk
authors.forename: Milan
authors.initials: M
authors.lastname: Remko
authors.forename: Daniel
authors.initials: D
authors.lastname: Fitz
authors.forename: Bernd Michael
authors.initials: BM
authors.lastname: Rode
mesh_terms: D001120:Arginine / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D019277:Entropy; D005740:Gases / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry; D011522:Protons; D014867:Water / Q000737:chemistry*
chemical_list: D002412:Cations; D005740:Gases; D008670:Metals; D011506:Proteins; D011522:Protons; D014867:Water; D001120:Arginine