Gas phase basicities of polyfunctional molecules. Part 3: Amino acids

Abstract

The present article is the third part of a general overview of the gas-phase protonation thermochemistry of polyfunctional molecules (first part: Mass Spectrom. Rev., 2007, 26:775-835, second part: Mass Spectrom. Rev., 2011, in press). This review is devoted to the 20 proteinogenic amino acids and is divided in two parts. In the first one, the experimental data obtained during the last 30 years using the equilibrium, thermokinetic and kinetic methods are presented. A general re-assignment of the values originating from these various experiments has been done on the basis of the commonly accepted Hunter & Lias 1998 gas-phase basicity scale in order to provide an homogeneous set of data. In the second part, theoretical investigations on gaseous neutral and protonated amino acids are reviewed. Conformational landscapes of both types of species were examined in order to provide theoretical protonation thermochemistry based on the truly identified most stable conformers. Proton affinities computed at the presently highest levels of theory (i.e. composite methods such as Gn procedures) are presented. Estimates of thermochemical parameters calculated using a Boltzmann distribution of conformers at 298K are also included. Finally, comparison between experiment and theory is discussed and a set of evaluated proton affinities, gas-phase basicities and protonation entropies is proposed.

Analysis of Native-Like Proteins and Protein Complexes Using Cation to Anion Proton Transfer Reactions (CAPTR)

“…By comparison, the gas-phase basicity of a lysine residue in a neutral peptide is far lower (1008–1018 kJ/mol) and will decrease with increasing charge state [33,50]. The gas-phase basicity of isolated arginine is ~60 kJ/mol greater than that of isolated lysine [51], therefore 1080 kJ/mol should represent a reasonable upper limit to the gas-phase basicity of arginine in a peptide or protein. Thus, the transfer of a proton from the reactant protein cation to [PDCH–F] − should be >200 kJ/mol exothermic for each CAPTR event.…”

Binary twinned-icosahedral [B21H18]− interacts with cyclodextrins as a precedent for its complexation with other organic motifs

“…From these calculations the gasphase basicity 17 (GB) of B21 was computed to be 233.1 kcal mol À1 , a value very close to the experimentally determined GB for histidine (232.9 kcal mol À1 ). 18 The gas-phase acidity of water is reported to be 158.3 kcal mol…”

Proton affinity of several basic non-standard amino acids

“…PA SC was calculated considering the most stable (neutral and protonated) conformer at 298 K while PA AV was calculated considering the ensemble of conformers at 298 K for both neutral and protonated NSAA. The molar fractions of each conformer were calculated assuming a Boltzmann distribution (which should be only considered approximate, due to the use of the harmonic approximation), more details about protocol can be found in references [11,22]. All quantum mechanics data have been obtained by using the GAUSSIAN 03 and 09 suite programs [29].…”

“…Intrinsic structural and thermochemical properties of standard amino acids have been extensively investigated and re-evaluated [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] (recent overview of the gasphase thermochemistry of standard amino acids can be found in Ref. [22]). However, this is not the case with properties of NSAA.…”