title: An insight into the interaction of L-proline with the transition metal cations Fe(2+), Co(2+), Ni(2+): a gas phase theoretical study.
abstract: The interaction of Fe(2+), Co(2+), and Ni(2+) with L-proline has been studied. Three modes of interaction have been considered: salt bridged (SB), involving binding in a bi-dentate manner through the carboxylate group of L-proline, charge solvated 1 (CS1) involving carbonyl and hydroxyl oxygen, and charge solvated 2 (CS2) involving carbonyl oxygen and the lone pair of the nitrogen atom. All calculations including geometry optimization, metal ion affinities (MIAs), and frequency calculations of the binding structures of Fe(2+), Co(2+), and Ni(2+) to L-proline were calculated using the hybrid density functional theory (DFT-B3LYP) method. All three cations were found to bind preferentially in a zwitterionic (SB) coordination pattern with the metal ion affinity in the order Ni(2+) ˃ Co(2+) ˃ Fe(2+) in all binding forms. The nature of the binding interaction between metal cations and L-proline was found to be mainly electrostatic. Comparison of the infrared vibrations of the C=O, the N-H and the O-H groups of free L-proline with L-proline-M(2+) in both CS1 and CS2 complex structures indicated a considerable shift to lower frequency during complexation. In order to gain more insight into the nature of the interaction of L-proline with group VIIIB metal ions, comparison of the interaction of L-proline with other cations such as (Li(+), Na(+), K(+), Be(2+), Mg(2+), and Ca(2+)) was made. Graphical Abstract L-proline with the transition metal cations Fe(2+), Co(2+), Ni(2.)
authors.affiliation: Department of Chemistry, Faculty of Sciences, University of Guilan, P.O. Box 41335-1914, Rasht, Iran. b.khalili@guilan.ac.ir.
authors.forename: Behzad
authors.initials: B
authors.lastname: Khalili
mesh_terms: D005740:Gases / Q000737:chemistry; D008956:Models, Chemical; D011392:Proline / Q000737:chemistry*; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D005740:Gases; D028561:Transition Elements; D011392:Proline
keywords: DFT study; Fe2+, Co2+, and Ni2+ transition metal cations; Gibbs free energy; Infrared frequency; L-proline; Metal ion affinity (MIA); Natural charge