Dissociation of gas‐phase dimeric complexes of lactic acid and transition‐metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Abstract

Dimeric complex ions of the type [M(A-H)A]+, where M=metal ion (Co, Ni, Cu, and Zn) and A=ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]+ ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions.

LC–MS/MS and density functional theory study of copper(II) and nickel(II) chelating complexes of elesclomol (a novel anticancer agent)

“…When 13 C-labeled (at two phenyl rings) elesclomol was used, the m/z becomes 124, corroborating that one phenyl ring is remained in this fragment ion. [14], fatty acids [15] and lactic acid [16]. In contrary, the reduction of Ni(II) to Ni(I) does not occur upon CID of [Ni(II)+elesclomol−H] + ( Table 2).…”

Quantifying the Effect of Surface Ligands on Dendron–DNA Interactions: Insights into Multivalency through a Combined Experimental and Theoretical Approach

“…Thus, in the case of only poorly coordinating anions like tetrafluoroborate, the ionization of the Cu(BF 4 ) 2 complexes resulted in both the loss of the counter ions and reduction from Cu II to Cu I . It is known that copper‐containing complexes show redox reactions (Cu 2+ reduction to Cu + ) during both the ESI process and the dissociation in a collision cell; here the ESI process and the nature of the ligands play an important role 60, 61…”

Complexation of diazaperylene and bisisoquinoline with transition metal ions in the gas phase studied by electrospray ionization mass spectrometry

“…The nitrogen heterocycles 1,10‐phenanthroline ( phen ) and 2,2′‐bipyridine ( bpy ) are intensively studied chelate ligands in the coordination chemistry of transition metal ions in solution1–6 and in the gas phase 7–11. For the latter medium, electrospray ionization mass spectrometry (ESI‐MS) is a well‐established method for studying these complexes,12–15 and a number of different complexes with pyridyl related ligands have been studied by this method 16–21. The binding energies of the transition metal complexes can be estimated on the basis of energy‐variable collision‐induced dissociation (CID) measurements 22–24.…”