Zinc and cadmium complexation of L‐methionine: An infrared multiple photon dissociation spectroscopy and theoretical study

Abstract

Methionine (Met) cationized with Zn 2+ , forming Zn (Met-H) + (ACN) where ACN = acetonitrile, Zn (Met-H) + , and ZnCl + (Met), as well as Cd 2+ , forming CdCl + (Met), were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy using light generated from the FELIX free electron laser. A series of low-energy conformers for each complex was found using quantum-chemical calculations in order to identify the structures formed experimentally. For all four complexes, spectral comparison indicated that the main binding motif observed is a charge solvated, tridentate structure where the metal center binds to the backbone amino group nitrogen, backbone carbonyl oxygen (where the carboxylic acid is deprotonated in two of the Zn 2+ complexes), and side-chain sulfur. For all species, the predicted ground structures reproduce the experimental spectra well, although low-lying conformers characterized by similar binding motifs may also contribute in each system.

IRMPD Spectroscopic and Theoretical Structural Investigations of Zinc and Cadmium Dications Bound to Histidine Dimers

“…To account for the finite laser bandwidth and unresolved rotational structure, a Gaussian line shape (25 cm –1 FWHM) was used to broaden the calculated frequencies for comparison to the IRMPD spectra . Previous work indicates that this combination of theory and scaling factors provides an accurate description of the structural information for systems with a similar size and makeup. − …”

“…This investigation serves as an extension of earlier studies investigating zinc and cadmium cationized amino acids: histidine monomer and dimer (His), 11 cysteine (Cys), and cysteine methyl ester (Cys-OMe), 12 glutamine (Gln), 13 serine (Ser), 14 asparagine (Asn), 15 glutamic acid (Glu), 16 aspartic acid (Asp), 17 arginine (Arg), 18 lysine (Lys), 19 threonine (Thr), 20 and methionine (Met). 21 ■ EXPERIMENTAL AND COMPUTATIONAL SECTION Materials and Syntheses. Precursors to the Zn(His-H)(His) + and Cd(His-H)(His) + complexes were formed using a procedure adapted from the literature, and all materials were used as delivered and without further purification.…”

“…These action spectra were then compared to calculated spectra for low-energy conformers to determine the most populated conformations present and thus the binding character of these complexes. This investigation serves as an extension of earlier studies investigating zinc and cadmium cationized amino acids: histidine monomer and dimer (His), cysteine (Cys), and cysteine methyl ester (Cys-OMe), glutamine (Gln), serine (Ser), asparagine (Asn), glutamic acid (Glu), aspartic acid (Asp), arginine (Arg), lysine (Lys), threonine (Thr), and methionine (Met) …”

Ligation Motifs in Zinc-Bound Sulfonamide Drugs Assayed by IR Ion Spectroscopy

“…In a considerable number of studies, including contributions from these authors, it has been applied to identify binding motifs and preferred geometries of transition metal complexes coordinating biomolecular ligands and targets [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Zinc complexes of biomolecules have also been assayed [ 33 , 34 , 35 , 36 , 37 , 38 ]. In particular, the structural characteristics of Zn 2+ cationized amino acids were evaluated in a series of studies [ 33 ].…”

“…Zinc complexes of biomolecules have also been assayed [ 33 , 34 , 35 , 36 , 37 , 38 ]. In particular, the structural characteristics of Zn 2+ cationized amino acids were evaluated in a series of studies [ 33 ]. A tridentate structure is observed from zinc complexation of L-methionine, whereas an additional chlorido or acetonitrile ligand yields a four-coordinate zinc complex.…”