La liaison intramoleculaire dans les ethers Crown Protones, Augmente les affinites protoniques de ces composes。质子化熵计算 les divers ethers Crown et des dicetones
Gas-phase basicity measurements of dipeptides that contain valine
作者:Greg S. Gorman、I. Jonathan Amster
DOI:10.1021/ja00066a044
日期:1993.6
Gas-phasebasicities of 22 dipeptides that contain valine were measured by a double bracketing method in a Fourier transform ion cyclotron resonance spectrometer. Matrix-assisted laser desorption was used to generate protonated peptide ions which were reacted with reference compounds to bracket the gas-phasebasicity. In addition, neutral peptide molecules were formed by substrate-assisted laser desorption
The deprotonation rate constants and kinetic isotope effects of the cation radicals have been determined by combined use of direct electrochemical techniques at micro- and ultramicroelectrodes, redox catalysis, and laser flash photolysis, over a extended series of opposing bases. Significant steric hindrance to deprotonation results from encumbering of the opposing base and of the functional carbon in the cation radical by alkyl groups. Kinetic isotope effects, ranging from 2 to 12 in terms of k(H)/k(D), appear upon substituting H to D at the functional carbon of the cation radical. The modest magnitude of the kinetic isotope effects and the fact that they are insensitive to steric hindrance show that proton (or H-atom) tunneling does not interfere significantly in the deprotonation reaction. All the cation radicals in the methylacridan series are strong acids, with pK(a)'s ranging from 0.8 to 1.7, as determined from thermodynamic cycles involving measured standard potentials and hydride-transfer equilibrium constants.
The ionic hydrogen bond. 4. Intramolecular and multiple bonds. Protonation and complexes of amides and amino acid derivatives
作者:Michael Meot-Ner
DOI:10.1021/ja00314a003
日期:1984.1
Acid−Base Equilibrium between Phenoxyl−Nitronyl Nitroxide Biradical and Closed-Shell Cation. A Magnetic pH Sensor