Physicochemical investigations of the metal complexes ofl-valine with doubly charged ions of nickel, copper and zinc: a combined experimental and computational approach

Abstract

Molecular electrostatic potentials inl-Val and its metal complexes.

A combined experimental and quantum mechanical investigation on some selected metal complexes of l-serine with first row transition metal cations

“…Indication of metal coordination via the nitrogen atom of L-Ser is also provided by the fact that the m(CAN) stretching value of L-Ser (observed at 1125 cm À1 ) is red-shifted in all of its metal complexes (1100-1112 cm À1 ). Moreover, the appearance of new low intensity bands in the range of 473-480 cm À1 in all the metal complexes of L-Ser [28,29], which can be assigned to asymmetric m(MAN) stretching frequencies [29,44], also confirms that the nitrogen atom of L-Ser is involved in metal coordination. It is worth mentioning that the two coordinating ANH 2 groups are positioned trans to each other in the metal complexes since the symmetric m(MAN) stretching mode of the N-M-N group (M = Ni +2 , Cu +2 and Zn +2 ) which usually appears around F.W = formula weight.…”

“…The experimental infra-red spectral data on the asymmetric and symmetric m(NAH) stretching frequencies of L-Ser and its metal complexes suggest that the m as (NAH) and m s (NAH) frequency values of L-Ser (observed at 3215 and 3096 cm À1 respectively) are blue-shifted in all the three metal complexes (3271-3344 and 3176-3258 cm À1 respectively). This clearly suggests deprotonation of the NH 3 + group of the zwitterionic L-Ser molecule and binding to the metal ions through its nitrogen atom [28,29]. Indication of metal coordination via the nitrogen atom of L-Ser is also provided by the fact that the m(CAN) stretching value of L-Ser (observed at 1125 cm À1 ) is red-shifted in all of its metal complexes (1100-1112 cm À1 ).…”

“…The zwitterionic form of a given amino acid, which is the thermodynamically preferred structural motif for most of the genetically encoded amino acids in solid and aqueous phases, is known to get converted into the non-ionic form as a result of metal coordination [28,42]. In order to study the molecular interactions of L-Ser with Ni(II), Cu(II) and Zn(II) ions, the complexes were analyzed using infrared spectroscopy.…”

“…On the other hand, m as (COO À ) stretching mode of L-Ser that appears at 1601 cm À1 shifts to higher side of the frequency scale (up to 1623 cm À1 ) in the metal complexes while the m s (COO À ) stretching frequency of L-Ser (observed at 1411 cm À1 ) shifts to lower side of the frequency scale in its metal complexes (1354-1398 cm À1 ). These observations indicate that L-Ser binds to the metal ions via its carboxylate group [28,29]. Table 2 also presents the separations (Dd values) between the m as (COO À ) and m s (COO À ) stretching modes of L-Ser and its three metal complexes which are indicative of the MAO bond strengths and provide evidence that the carboxylate groups bind to the metal ions in monodentate fashion [45].…”

“…It has now been widely accepted that computational techniques are indispensable in elucidating atomic level structural information about biologically active molecules owing to certain limitations of experimental techniques as pointed out in the literature [26,27]. Experimental investigations carried out in close conjunction with theoretical calculations constitute a more efficient way of assembling atomic level information about the physicochemical properties of bio-molecular systems [26,28,29].…”