Studies on electrospray silver(I) cationization mass spectrometry and its analytical applications

In this study, the Ag+ binding energies (affinities) of three classes of model ligands were determined by electrospray Ag(I) cationization and mass spectrometric kinetic method measurements. The binding modes of the Ag+-ligand complexes were investigated by theoretical ab initio calculations.; Ag+ binding to amides is used to mimic the interaction of Ag+ with the peptide bond. The experimental Ag+ affinities (kJ mol−1) of six amides were: N,N-dimethylacetamide (207.6), N-methylacetamide (198.2), N,N-dimethylformamide (193.1), acetamide (180.7), N-methylformamide (179.1) and formamide (162.3). The binding interaction is mainly electrostatic in nature, with dominant contribution from ion-dipole interaction. The Ag+ binding energies are enhanced by N-methyl and C-methyl substitution via ion-induced dipole and charge-transfer interactions.; Cation-π interaction is recognized as a new type of non-covalent interaction important in molecular recognition of biological systems and the design of novel functional materials. Ag+ binding to monosubstituted benzenes serves as model systems to study the effect of substituents on cation-π interactions. The Ag+ affinities (kJ mol−1) of six monosubstituted benzenes were: aniline (194.3), benzonitrile (185.0), ethoxybenzene (178.3), methoxybenzene (172.3), phenol (157.7) and nitrobenzene (149.7). The relative stability of the cation-π and non-π O/N binding modes were found to depend on the interplay of ion-quadrupole, ion-dipole, ion-induced dipole and covalent interactions in the Ag+-ligand complexes.; On the other hand, Ag+ prefers to bind to the nitrogen atom(s) of pyridine and diazines in planar structure. The Ag+ binding affinities (kJ mol−1) were: 1,2-diazine (211.7), pyridine (208.8), 1,3-diazine (185.6) and 1,4-diazine (180.1). The interaction is mainly governed by ion-dipole interaction, though charge-transfer interaction between Ag+ and the lone pair electrons of the heterocyclic nitrogen is noticeably present.; Under ESI conditions, Ag(I) cationized 1:1 adduct ions of fatty alcohols, acetates, aldehydes, acids and their methyl esters were easily formed and shown to be at least 50 times more intense (sensitive) than lithium cationization. The high-energy (4.7 keV, laboratory frame) collision-induced dissociation of the Ag+ adduct ions yielded four series of charge-remote fragment ions that reveal the location of double bond positions of these monounsaturated compounds. For methylene-interrupted polyunsaturated fatty acids and their methyl esters, two additional series of charge-remote fragment ions arising from bond cleavage between double bonds were observed and used to provide structural information.; Pyridine and isomeric diazines were separated by argentation capillary electrophoresis with Ag+ present in the electrophoretic medium. The migration (elution) order is consistent with the order of their gas phase Ag+ affinities, but solvent effects are clearly present in determining the elution order of pyridine and 1,2-diazine.