A mass spectrometry and DFT study of pyrithione complexes with transition metals in the gas phase

Abstract

2-Mercaptopyridine N-oxide (pyrithione, PTOH) along with several transition metal ions forms coordination compounds displaying notable biological activities. Gas-phase complexes formed between pyrithione and manganese (II), cobalt (II), nickel (II), copper (II), and zinc (II) were investigated by infusion in the electrospray source of a quadrupole-time of flight mass spectrometer. Remarkably, positive ion mode spectra displayed the singly charged metal adduct ion [C H MN O S ] ([M(PTO) ] or [M(DPTO)] ), where DPTO is dipyrithione, 2,2'-dithiobis(pyridine N-oxide), among the most abundant peaks, implying a change in the oxidation state of whether the metal ion or the ligands. In addition, doubly charged ions were recognized as metal adduct ions containing DPTO ligands, [M(DPTO) ] . Generation of [M(PTO) ] / [M(DPTO)] could be traced by CID of [M(DPTO) ] , by observation of the sequential losses of a charged (PTO ) and a radical (PTO ) deprotonated pyrithione ligand. The fragmentation pathways of [M(PTO) ] / [M(DPTO)] were compared among the different metal ions, and some common features were noticed. Density functional theory (DFT) calculations were employed to study the structures of the observed adduct ions, and especially, to decide in the adduct ion [M(PTO) ] / [M(DPTO)] whether the ligands are 2 deprotonated pyrithiones or a single dipyrithione as well as the oxidation state of the metal ion in the complex. Characterization of gas-phase pyrithione metal ion complexes becomes important, especially taking into account the presence of a redox-active ligand in the complexes, because redox state changes that produce new species can have a marked effect on the overall toxicological/biological response elicited by the metal system.

Synergy Effects in Heavy Metal Ion Chelation with Aryl- and Aroyl-Substituted Thiourea Derivatives

“…Quantum chemistry emerges as a reliable tool to predict ionophore properties of organic compounds. Indeed, the investigation of interactions between metallic cations and organic compounds has attracted huge interest in the last few decades, where an important activity has been developed by means of computational chemistry. − In many studies, the theory has been combined with experiments, typically carried out with mass spectrometry techniques. − The nature of the metal ion–molecule interaction, the reactivity of the new compounds, and the change in structural and spectroscopic properties of the organic molecules upon ion complexation are among the most important aspects investigated in these studies.…”