Gas-phase NO ⁺  affinities

Abstract

A scale of relative gas-phase NO ؉ binding energies (BEs) ؉ BE of thymine, the only one accessible to direct measurement, amounts to 35.6 ؎ 2 kcal⅐mol ؊1 , which underlines the predictive value of the correlation. This study reports the second successful extension of the kinetic method to the evaluation of the absolute BEs of polyatomic cations, following our recent application to the strictly related NO 2 ؉ ion.The chemistry of the nitryl ion, NO ϩ , is the focus of active interest, recently heightened by the extraordinary multiplicity of roles currently attributed to NO. Nitryl ion, its salts and carriers, are long known as effective reagents in electrophilic nitrosation, whose study is the subject of continuing interest (refs. 1-4 and references cited in ref.2), in particular as concerns the formation of nitrosoamines (5, 6). Passing to atmospheric chemistry, the low ionization potential of NO makes NO ϩ an effective ''charge sink'' in ionized air, and the promoter of a reaction chain eventually leading to hydratedproton clusters (7,8). As the consequence, complexation of NO ϩ by H 2 O and other atmospheric species (N 2 , CO 2 , O 2 ) has a direct bearing on the chemistry of the ionospheric D region (9-11) and of the middle atmosphere (12). The biological and physiological significance of NO ϩ and of its complexes has received much attention, in connection with the recognized impact on human health of a variety of compounds important for dietary or environmental reasons, including nitrites, Nnitrosoamines, NO x oxides, etc. (13-15). For example, it has been suggested that NO ϩ , or some NO ϩ sources present in biological systems, can be involved in the neurotoxic and neuroprotective actions of NO (16,17) as well as in the nitrous acid-promoted crosslinking of DNA, a problem of considerable current interest (18,19). Finally, the use of NO ϩ as a reagent has a considerable potential for trace gas analysis (20).A quantitative knowledge of the interactions of NO ϩ with neutral ligands is central to the understanding and modelling of important problems in many research fields. This strongly suggests a systematic study of the binding energies (BEs) of the nitryl cation to representative ligands, to be carried preferably in the gas phase, to obtain results of general validity, unaffected by specific ion-solvent interactions and hence more directly comparable to those from theoretical approaches and more widely useful for modelling purposes. The interest of the problem was perceived as early as in 1980 by Reents and Freiser (21), who measured the NO ϩ BE to 28 ligands by ion cyclotron resonance (ICR) mass spectrometry. In view of the current upsurge of interest in the NO ϩ complexes, we have undertaken a systematic study aimed at the revision of the NO ϩ BE scale, taking into account the changes undergone in the meantime by certain reference standards used in the early study and the availability of new experimental tools. However, the principal motivation of this work is to be found in the attempt to exten...

Nitrosation of thiols and thioethers in the gas phase: A combined theoretical and experimental study

“…It is important to emphasize that, at the G2(MP2) level of theory, the NOA(H 2 O) is calculated to be lower than the NOA(H 2 S). This ordering is in keeping with the experimental study of Cacace et al [17], but at variance with the theoretical values obtained by Torday et al [20], and to a less extent, by Nguyen et al [19], see Table 1.…”

The kinetic method of making thermochemical determinations

“…Note that the major approximation in deriving the *(*H) form of Eqn (1) is that entropic e †ects cancel. In practice, neither the *(*H) nor the *(*G) approximation is completely valid ; some authors prefer the *(*G) formulation19 while others implicitly consider the *(*H) form to be the more fundamental20 (H. N. Lee The popularity of the kinetic method is the result of several favorable factors : a high degree of sensitivity to di †erences in thermochemical quantities, including subtle di †erences due to isotopic substitution,24 generally excellent agreement with values obtained by other methods (for example, the NO`affinities measured by Cacace et al 25 show a mean discrepancy of^0.2 kcal mol~1 and a maximum discrepancy of^0.5 kcal mol~1 (1 kcal \ 4.184 kJ)), the speed with which measurements can be made and the fact that they can be performed using any instrument capable of tandem mass spectrometry experiments. In addition, the method shares the common advantage of all tandem mass spectrometric experiments that it is not necessary to work with pure samples.…”

Measurement of alkyl and multifunctional organic nitrates by proton-transfer-reaction mass spectrometry

“…Previous studies interrelated the PA of water to the NO + chemical ionization binding energies (BEs), creating an absolute NO + affinity scale (Cacace et al, 1997). The study used the H 2 O-NO + BE as a reference anchor between the two conjugated parameters and concerned various classes of ligands (alkyl halides, alkyl nitrates, alcohols, nitro-alkanes, nitriles, aldehydes, ketones, aromatic and heterocyclic compounds).…”