title: Experimental and computational thermochemical study of N-benzylalanines.
abstract: Calorimetric measurements are expected to provide useful data regarding the relative stability of α- versus β-amino acid isomers, which, in turn, may help us to understand why nature chose α- instead of β-amino acids for the formation of the biomolecules that are essential constituents of life on earth. The present study is a combination of the experimental determination of the enthalpy of formation of N-benzyl-β-alanine, and high-level ab initio calculations of its molecular structure. The experimentally determined standard molar enthalpy of formation of N-benzyl-β-alanine in gaseous phase at T = 298.15 K is -(298.8 ± 4.8) kJ·mol(-1), whereas its G3(MP2)//B3LYP-calculated enthalpy of formation is -303.7 kJ·mol(-1). This value is in very good agreement with the experimental one. Although the combustion experiments of N-benzyl-α-alanine were unsuccessful, its calculated enthalpy of formation is -310.7 kJ·mol(-1); thus, comparison with the corresponding experimental enthalpy of formation of N-benzyl-β-alanine, -(298.8 ± 4.8) kJ/mol, is in line with the concept that the more branched amino acid (α-alanine) is intrinsically more stable than the linear β-amino acid, β-alanine.
authors.affiliation: Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain. rnotario@iqfr.csic.es
authors.forename: Rafael
authors.initials: R
authors.lastname: Notario
authors.forename: Maria Victoria
authors.initials: MV
authors.lastname: Roux
authors.forename: Concepción
authors.initials: C
authors.lastname: Foces-Foces
authors.forename: Manuel A V Ribeiro
authors.initials: MA
authors.lastname: da Silva
authors.forename: Maria das Dores M C Ribeiro
authors.initials: Md
authors.lastname: da Silva
authors.forename: Ana Filipa L O M
authors.initials: AF
authors.lastname: Santos
authors.forename: Ramón
authors.initials: R
authors.lastname: Guzmán-Mejía
authors.forename: Eusebio
authors.initials: E
authors.lastname: Juaristi
mesh_terms: D000613:Aminobutyrates / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D007536:Isomerism; D008956:Models, Chemical; D008968:Molecular Conformation; D013816:Thermodynamics
chemical_list: D000613:Aminobutyrates; C014328:2-amino-4-phenylbutyric acid