1.1. Historical Background Hydrogen bonds1,2 are one of the principal intermolecular forces. A special class are ionic hydrogen bonds (IHBs) that form between ions and molecules with bonds strengths of 5-35 kcal/mol, up to a third of the strength of covalent bonds. These strong interactions are critical, for example, in ionic clusters and nucleation, in electrolytes, ion solvation, and acid-base chemistry, in the structures of ionic crystals, surfaces, silicates, and clays, in surface adsorption, and in self-assembly in supramolecular chemistry and molecular crystals.3 IHBs are also important in bioenergetics including protein folding, enzyme active centers, formation of membranes and proton transport, and biomolecular recognition. With such wide-ranging roles, the fundamental properties of IHB interactions need to be understood. The energetics of IHB interactions cannot be isolated and quantified in the condensed phase. However, these interactions can be isolated and studied quantitatively in gas phase. These studies lead to a fundamental understanding of relations between IHB bond strengths and molecular structure, the solvation of ions, especially in the critical inner shells, and acid-based phenomena and bioenergetics. This review will present the basic insights that have been obtained in the past four decades. It will present a comprehensive review of the thermochemistry and its structural implications obtained from ab initio calculations. Relevant recent results from spectroscopy will be also illustrated. The advent of variable temperature high-pressure mass spectrometry (HPMS) introduced by Field and co-workers in the 1960s4 and pulsed high-pressure mass spectrometry (PHPMS) introduced by Kebarle in the late 1960s5 have been particularly significant. These workers realized that at pressures of several torrs and gas densities of 1016-1017 cm-3 in ion sources, ions can undergo 103-106 collisions with neutral molecules during typical residence times of 0.1-10 ms and establish thermal ion populations and * E-mail: m.mautner@solis1.com. 213 Chem. Rev. 2005, 105, 213−284

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The Ionic Hydrogen Bond

Thermochemical determinations by the kinetic method

Publisher Summary This chapter discusses the hydrogen bonding, which has been recognized as the single most important intermolecular interaction, The chapter presents the hypothesis that there are three kinds of hydrogen bond: weak, strong, and very strong. These are determined by the shape of the potential energy well and the respective positions of hydrogen and deuterium within the well, which can be used to provide information about the well that applies in a particular example. The role of hydrogen bonding in catalysis has been discussed, although mainly in terms of the salicylate ion as a leaving group. With its strong intramolecular hydrogen bond playing an essential part in the reaction mechanism, it seems likely that this will herald other systems where the role of a strong hydrogen bond may serve as the key step in a catalytic process.

Hydrogen Bonding and Chemical Reactivity

A review with over 100 references describes the recent applications of ion-molecule reactions to the study of gas-phase protonated peptides and proteins. The topic is focused specifically on the proton transfer and hydrogen-deuterium exchange reactions of amino acids, peptides, and proteins. A brief background is given of the various methods used for assigning proton affinities and gas-phase basicities. The methods used for measuring the kinetics of deuterium incorporation of charged ion in the presence of a background pressure of deuterating reagents are also described. Ion-molecule reactions are used to determine, among other things, the gas-phase basicities and proton affinities of amino acids, peptides, and proteins, the sites of protonation, intra- and intermolecular interactions, and conformational differences and changes in gas-phase ionic species. Singly charged and multiply charged ions are both covered.

Ion-molecule reactions as probes of gas-phase structures of peptides and proteins.

Various aryl sulfides can be synthesized by nickel-catalyzed alkyl- or arylthiolation of aryl iodide with a disulfide compound. This reaction produces Ni(0) from NiBr2−bpy by the reduction with zinc, and this generated complex works as an activating species to convert ArI into ArSR under neutral conditions. Furthermore, this system enables the use of two RS groups in (RS)2.

High M. Webb

Papers

Quantitative evaluation of intramolecular strong hydrogen bonding in the gas phase