title: Protonation thermochemistry of alpha-aminoacids bearing a basic residue.
abstract: The proton affinity, PA, and protonation entropy, Delta(p)S degree, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic acid (Glu), 6, and glutamine (Gln), 7, have been reinvestigated by the extended kinetic method, using the "isothermal point" method and the orthogonal distance regression, ODR, technique. The proton affinity values of a-aminoacids bearing a basic residue (PA = 926.8; 965.2; 996.0; 993.9; 981.8 and 988.1 kJ.mol(-1) for 2-7, respectively) show significant deviation from the tabulated values. As expected from the effect of a strong intramolecular hydrogen bond in the protonated forms of these peculiar aminoacids, negative protonation entropies are detected (Delta(p)S degree = 36; 43; 37; 29; 95 and 55 J mol(-1) K(-1) for for 27 respectively).
authors.affiliation: Laboratoire des Mécanismes Réactionnels, UMR 7651, Ecole Polytechnique, 91128 Palaiseau cedex, France.
authors.forename: Guy
authors.initials: G
authors.lastname: Bouchoux
authors.forename: David-Alexandre
authors.initials: DA
authors.lastname: Buisson
authors.forename: Cyril
authors.initials: C
authors.lastname: Colas
authors.forename: Michel
authors.initials: M
authors.lastname: Sablier
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D019277:Entropy; D005998:Glycine / Q000737:chemistry*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000596:Amino Acids; D011522:Protons; D005998:Glycine