An Experimental and Theoretical Investigation of Gas-Phase Reactions of Ca2+ with Glycine

• Published in: Chemistry : a European journal 2006-09, Vol.12 (26), p.6787-6796
• Main Authors: Corral, Inés, Mó, Otilia, Yáñez, Manuel, Salpin, Jean-Yves, Tortajada, Jeanine, Moran, Damian, Radom, Leo
• Format: Article
• Language: English
• Subjects: ab initio calculations; amino acids; calcium; Calcium - chemistry; Cations, Divalent - chemistry; Chemical Physics; Coulomb explosion; gas-phase reactions; Gases; Glycine - chemistry; mass spectrometry; Models, Molecular; Molecular Conformation; Physics; Spectrometry, Mass, Electrospray Ionization; Thermodynamics; Urea - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200600127

The gas‐phase reactions between Ca2+ and glycine ([Ca(gly)]2+) have been investigated through the use of mass spectrometry techniques and B3‐LYP/cc‐pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)]2+ correspond to the formation of the [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca2+ with urea ([Ca(urea)]2+), minimal unimolecular losses of neutral fragments are observed for the gas‐phase fragmentation processes of [Ca(gly)]2+, which is readily explained in terms of the topological differences between their respective PESs. Coulomb explosions that originate from complexes of Ca2+ with the zwitterionic form of the amino acid represent the most favorable fragmentation processes in the gas‐phase reactions of Ca2+ with glycine, leading to [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions (see picture). Carbon monoxide, produced by the unimolecular decomposition of some of these primary ions, is a secondary product.