Interaction of Co⁺ and Co²⁺ with Glycine. A Theoretical Study

Abstract

Cobalt cations are open shell systems with several possible electronic states arising from the different occupations of the 3d and 4s orbitals. The influence of these occupations on the relative stability of the coordination modes of the metal cation to glycine has been studied by means of theoretical methods. The structure and vibrational frequencies have been determined using the B3LYP method. Single-point calculations have also been carried out at the CCSD(T) level. The most stable structure of Co(+)-glycine is bidentate, with the Co(+) cation interacting with the amino group and the carbonyl oxygen of neutral glycine, and the ground electronic state being (3)A. For Co(2+)-glycine, the lowest energy structure corresponds to the interaction of the metal cation with the carboxylate group of the zwitterionic glycine, the ground electronic state being (4)A''.

Quantum localization/delocalization of muonium in the glycine–K+ complex

“…It is seen that four structures (EQ 0 , EQ 1 , EQ 2 , EQ 3 ) are more stable than other structures and have comparable relative energies at this B3LYP/6-31+G(d) level without zero-point correction. This result is in good agreement with previous theoretical studies [29][30][31][32][33][34][35][36][37][38][39][40][41][42]. The EQ 2 structure is stabilized by the presence of the five-membered ring and by attractive electrostatic interactions between K + and negative charges on carboxylic oxygen and the amine nitrogen.…”

“…In addition, it should be pointed out that the interaction between potassium cation and protein plays an especially important role in the selective transport phenomenon across cell membrane. Although many structures of the glycine-K + complex have been extensively studied in the past, we have also characterized the potential energy surface profile of this system using the GRRM (Global Reaction Route Mapping) computational algorithm [43][44][45][46] (which will be described below in detail), that can automatically find all possible local minima and transition states on a given multi-dimensional potential energy surface, to confirm the previous results [29][30][31][32][33][34][35][36][37][38][39][40][41][42]. Fig.…”

“…It is also known that metal-cation binding to amino acid molecules significantly affects the relative stability of various amino acid conformers [29][30][31][32][33][34][35][36][37][38][39][40][41][42]. In particular, there have been many theoretical studies on structures and stability of the complexes between metal-cation and glycine [29][30][31][32][33][34][35][36][37][38][39][40][41][42], the simplest amino acid molecule. Among various metal ions, we here focus on the glycine-K + complex since previous electronic structure studies have shown that energy levels of the neutral and zwitterionic forms are comparable (nearly thermoneutral) and that the proton-transfer barrier height is known to be relatively low of a few kcal/mol.…”

Complexation of glycine by manganese (II) in the gas phase: A theoretical study

“…The structure of glycine cationized with singly charged metal cations has been analyzed in previous theoretical works [13,[31][32][33][34][35][36][37][38][39][40][41][42][43][44]. It has been found that the lowest isomer of cationized glycine is a charge solvated structure.…”

“…In contrast, extensive studies on gaseous glycine have shown that zwitterions (salt bridge forms) are not even local minima on the potential energy surface of glycine [31,[45][46][47][48][49][50][51][52]. One of the ways to induce the natural to zwitterion transition in the gas phase is favoring the zwitterion by attaching a charged species such as an atomic metal cation [13,32,[34][35][36][37]43,44,53]. Such studies have established that for complexation of glycine by doubly charged cations the salt bridge structure, in which the metal ion interacts with the carboxylate end of zwitterionic glycine, is preferred in most cases.…”