Experimental and Computational Thermochemical Study of Sulfur-Containing Amino Acids: L-Cysteine, L-Cystine, and L-Cysteine-Derived Radicals. S-S, S-H, and C-S Bond Dissociation Enthalpies

• Tipo: Artigo em Revista Científica Internacional
• Data: 2010

Autores

Maria Victoria Roux (Autor) Outra; Concepcion Foces Foces (Autor) Outra; Rafael Notario (Autor) Outra; Manuel A V R Ribeiro da Silva (Autor) FCUP; Maria das Dores C Ribeiro da Silva (Autor) FCUP; Ana Filipa L O M Santos (Autor) FCUP; Eusebio Juaristi (Autor) Outra

Revista

Título: Journal of Physical Chemistry B

Vol. 114 Nº 1

Páginas: 10530-10540

ISSN: 1520-6106

Editora: American Chemical Society

Indexação

ISI Web of Knowledge - 45 Citações

Scopus - 48 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

CORDIS: Ciências Físicas > Química > Química física

Outras Informações

ID Authenticus: P-003-3YJ

DOI: 10.1021/jp1025637

Abstract (EN): This paper reports an experimental and theoretical study of the standard (p degrees = 0.1 MPa) molar enthalpies of formation at T = 298.15 K of the sulfur-containing amino acids L-cysteine [CAS 52-90-4] and L-cystine [CAS 56-89-3]. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of crystalline L-cysteine and L-cystine were calculated from the standard molar energies of combustion, in oxygen, to yield CO(2)(g) and H(2)SO(4)center dot 115H(2)O, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of L-cysteine were measured as function of temperature by the Knudsen effusion mass-loss technique. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the Clausius-Clapeyron equation. The experimental values were used to calculate the standard (p degrees = 0.1 MPa) enthalpy of formation of L-cysteine in the gaseous phase, Delta(f)H(m)degrees(g) = -382.6 +/- 1.8 kJ.mol(-1). Due to the low vapor pressures of L-cystine and since this compound decomposes at the temperature range required for a possible sublimation, it was not possible to determine its enthalpy of sublimation. Standard ab initio molecular orbital calculations at the G3(MP2)//B3LYP and/or G3 levels were performed. Enthalpies of formation, using atomization and isodesmic reactions, were calculated and compared with experimental data. A value of -755 +/- 10 kJ.mol(-1) was estimated for the enthalpy of formation of cystine. Detailed inspections of the molecular and electronic structures of the compounds studied were carried out. Finally, bond dissociation enthalpies (BDE) of S-H, S-S, and C-S bonds, and enthalpies of formation of L-cysteine-derived radicals, were also computed.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 11