Evaluation of the protonation thermochemistry obtained by the extended kinetic method

Abstract

An evaluation of the results obtained by the extended kinetic method for a series of representative bases is presented here. Analysis of the original experimental data is conducted using the orthogonal distance regression (ODR) statistical treatment. A comparison with the proton affinities and protonation entropies obtained from variable temperature equilibrium constant measurements demonstrate deviations, which may be ascribed to random and systematic errors. Considerable random errors are associated with the extended kinetic method if the number of reference bases and the range of effective temperatures are too low. It is also confirmed that large systematic errors on proton affinities and protonation entropies are obtained when large protonation entropy is associated with the considered system. It is, however, encouraging to note that the gas phase basicities obtained by the extended kinetic method are generally comparable to that obtained by other methods within a few kJ/mol.

Gas-Phase Lithium Cation Basicity: Revisiting the High Basicity Range by Experiment and Theory

“…The applications and limitations of the kinetic method in its various forms have been discussed [73][74][75][76][77][78]. Gal et al utilized this method to extend the LiCB scale in the range of monofunctional strong ligands, in particular sulfoxides and sulfones [47], sulfuryl [79], and phosphoryl [80] compounds.…”

Gas-phase proton affinities of guanidines with heteroalkyl side chains

“…For CID, the ions of interest were mass-selected using Q1, interacted with xenon as a collision gas in the hexapole H under single-collision conditions (typically 2 × 10 −4 mbar) at variable collision energies (E lab = 0-6 eV), while scanning Q2 to monitor the ionic products. In the context of the kinetic method [40,41], the variation of the collision energy from nominally 0 to 6 eV in steps of 1 eV can be assumed to alter the effective temperatures of the dissociating ions. The resulting ion ratios were used for the determination of the proton affinities of the investigated bases.…”

A density functional theory (DFT) study on gas-phase proton transfer reactions of derivatized and underivatized peptide ions generated by matrix-assisted laser desorption ionization

“…However, the treatment of this phenomenon remains an open problem: to our knowledge, at the moment there are no theoretical models that can reliably address the entropic effects for peptides and MALDI matrices. From the experimental point of view, instead, measurements with temperature changes, like the extended kinetic method, can give access to quantitative estimates of protonation entropy [37].…”