Gas-Phase Hydration and Alcohol Addition Reactions of Complexes Composed of Ag + and a Single Alcohol Molecule Dorothy Hanna,* ,† Manohari Silva, ‡ Jennifer Morrison, ‡ Sammer Tekarli, ‡ Victor Anbalagan, ‡ and Michael Van Stipdonk* ,‡ Department of Chemistry, Kansas Wesleyan UniVersity, Salina, Kansas 67401, and Department of Chemistry, Wichita State UniVersity, Wichita, Kansas 67260-0051 ReceiVed: December 21, 2002; In Final Form: May 12, 2003 The reactivity of mono-alcohol/Ag + complexes (methanol, ethanol, n-propanol, n-butanol, and tert-butyl alcohol) when stored, without collisional activation, in an ion trap mass spectrometer for periods ranging from 1 to 1000 ms was investigated. During the isolation/reaction time, association reactions between the complex ions and adventitious water and alcohol present within a He bath gas occurred to varying degrees. While the free Ag + ion was unreactive, complexes composed of Ag + coordinated by a single alcohol molecule demonstrated reactivity consistent with the following reactions: (1) formation of an adduct by the addition of a single water molecule, (2) formation of a bis-alcohol complex by the addition of a second alcohol molecule, and (3) formation of the bis-alcohol complex via the exchange of a water molecule for alcohol when investigated under similar experimental conditions. The trend in reactivity followed the order n-butanol > n-propanol > ethanol > methanol. To quantify observed trends in hydration reactivity, experimental kinetic plots were modeled stochastically. Reasonable fits to experimental reaction kinetic plots were achieved using a model that included forward and, in some cases, apparently reverse reactions, consistent with the addition of either water or alcohol in nondissociative fashion. Pseudo-first-order reaction rate constants were generated using stochastic kinetic simulations that provide insight into the relative reactivity of the mono-alcohol/Ag + complexes. To rationalize the observed trends in reactivity, the lowest energy conformations and molecular orbital geometries were determined using Hartree-Fock and density functional theory calculations. Our results show that the hydration and alcohol addition reactivity of Ag + may be influenced by the degree to which electron density can be delocalized within a coordinating ligand and to which the electron density within a hybridized orbital on Ag + is decreased by bonding to an alcohol molecule. Introduction The investigation of gas-phase ion/molecule reactions involv- ing metal ions and metal ion/ligand complexes has long been an active area of research in mass spectrometry (MS). For ex- ample, Kebarle and co-workers investigated the ion/molecule chemistry and binding strengths of K + with benzene and water in a pioneering demonstration of cation-π interactions. 1 Metal ions have been used as chemical ionization agents 2 for the char- acterization of unsaturated organic molecules. Investigations of the intrinsic interactions and gas-phase reactions between metal ions and small molecules have contributed significantly to the understanding of the activation of C-H and C-C bonds in catalysis. 3 Collision induced dissociation (CID) and MS have been used to measure the affinity of crown ethers, 4 glymes, 5 cryptands, 6 calixarenes, 7 and amino acids 8 for metal ions, to probe metal ion binding sites on peptides 9 and oligosaccha- rides, 10 and to elucidate the novel dissociation pathways exhi- bited by the latter classes of molecules when metal cationized. Complexes composed of metal ions and organic ligands have been shown to undergo association reactions with a range of small molecules in the gas phase. For example, Callahan, Vachet, and co-workers, 11 and later Vachet and co-workers, 12 have demonstrated that transition metal ions such as Ni(II), Cu- (II), Zn(II), and Co(II), coordinated by a range of organic ligands containing nitrogen or oxygen heteroatoms, will react with species such as water, acetonitrile, and pyridine in the gas-phase environment of an ion trap mass spectrometer. The ion/molecule chemistry demonstrated was found to be sensitive to the intrinsic coordination structure of the complexes. 11 Several years earlier, Wu and Brodbelt demonstrated that Cu(I) and Ag(I) complexes (with ligands such as pyridine, bipyridine, and phenanthroline), when coordinatively unsaturated, will form water adducts in the ion trap. 13 Groenewold and co-workers have used ion trap mass spectrometry to investigate the gas-phase reactions of silicon and aluminum oxyanions with H 2 O and H 2 S 14 and have applied ab initio calculations to determine the most probable structures and stochastic kinetic simulations to derive relative reaction rate constants. We have recently investigated the tendency for Ag + com- plexes with amino acids to form water and methanol adducts when stored in an ion trap mass spectrometer. 15 While Ag + cationized aliphatic amino acids such as alanine, valine, and tert-leucine formed adducts, amino acids with aromatic side groups (phenylalanine, tyrosine, and tryptophan) were found to be unreactive when compared under similar experimental conditions. 15a For the latter group, semiempirical and ab initio calculations suggested that the lowest energy, and therefore most likely, gas-phase conformation included coordination by the aromatic ring of the side group along with the amine nitrogen and carbonyl oxygen atoms. Because the donation of π electron density to the Ag + ion was a likely determining factor in coordination by the side group, and thus the inhibition of complex reactivity, we investigated the influence of para- position substituents to the aromatic ring on the formation of * To whom correspondence should be addressed. † Kansas Wesleyan University. ‡ Wichita State University. 5528 J. Phys. Chem. A 2003, 107, 5528-5537 10.1021/jp027797w CCC: $25.00 © 2003 American Chemical Society Published on Web 06/25/2003