The Applicability of the Kinetic Method for Measuring Relative Affinities of Macromolecules for Polyatomic Substrates

Abstract

All rights reserved EUROPEAN JOURNAL OF MASS SPECTROMETRY Ion thermochemistry is a fundamental topic in ion chemistry and, as such, has been the topic of continuing interest since the early days of mass spectrometry. 1-3 Thermodynamic properties such as proton affinity, 4,5 metal ion affinity, 6,7 alkyl cation affinity 8,9 and electron affinity 10,11 have been explored by a variety of experimental and theoretical techniques. The most reliable are equilibrium methods, such as high-pressure mass spectrometry, which can directly yield the desired thermodynamic property of a molecule. Kinetics experiments performed under thermal conditions 12 can also produce reliable results, but these must be interpreted with great care. This is because such experiments directly measure the activation energy of a reaction which may, or may not, be the same as a reaction enthalpy due to the presence of a potential reverse energy barrier in the dissociation reaction. However, when these thermal experiments are not feasible, the "kinetic method," 13 as introduced by Cooks and Kruger in 1977 can, with care, produce reliable thermodynamic data. At

Dissociation of Proton Bound Ketone Dimers in Asymmetric Electric Fields with Differential Mobility Spectrometry and in Uniform Electric Fields with Linear Ion Mobility Spectrometry

“…The internal energy of an ion may be readily increased in near-vacuum by several methods, including collision with one or more molecules or with a surface after prior acceleration, by single and multiphoton absorption, and by blackbody radiation. The energy content of the hyperenergetic ion prior to dissociation may be associated with an effective temperature T eff , a value that is problematical both to define and to determine for polyatomic systems. − For example, values of T eff are derived and used, but not without some controversy, in determining the entropy factor in the kinetic method for proton and other ion affinity determinations. − The estimation of T eff for collisionally activated decomposing ions has sometimes been made by assuming that only a few collisions are required for dissociation to proceed statistically from a “Boltzmann-like” distribution of internal energies. − However, the only accurate measure of T eff that can be made for collisionally activated polyatomic ions is the trivial one when T eff is equal to T , the ambient temperature of a bath gas in which a Boltzmann energy distribution holds at all times.…”

On-line chiral analysis using the kinetic method

“…[25][26][27] Reviews of the capabilities and theoretical basis of the kinetic method have appeared. [28][29][30][31][32][33][34][35] The kinetic method can also be used to perform chiral analysis of small molecules by MS. This application typically involves the in situ formation by electrospray ionization (ESI) of a trimeric cluster ion containing a metal in the 2 + oxidation state (M II ), two chiral reference ligands (ref*), and the analyte of interest (A).…”