Molecular energetics of cytosine revisited: A joint computational and experimental study

• Tipo: Artigo em Revista Científica Internacional
• Data: 2007

Autores

Jose R B Gomes (Autor) Outra; Maria Ribeiro M C R da Silva (Autor) FCUP; Vera L S Freitas (Autor) Outra; Manuel Ribeiro V R da Silva (Autor) FCUP

Revista

Título: Journal of Physical Chemistry A

Vol. 111

Páginas: 7237-7242

ISSN: 1089-5639

Editora: American Chemical Society

Indexação

ISI Web of Knowledge - 18 Citações

Scopus - 19 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-004-88E

DOI: 10.1021/jp0729009

Abstract (EN): A static bomb calorimeter has been used to measure the standard molar energy of combustion, in oxygen, at T = 298.15 K, of a commercial sample of cytosine. From this energy, the standard (p degrees = 0.1 MPa) molar enthalpy of formation in the crystalline state was derived as -(221.9 +/- 1.7) kJ center dot mol(-1). This value confirms one experimental value already published in the literature but differs from another literature value by 13.5 kJ center dot mol(-1). Using the present standard molar enthalpy of formation in the condensed phase and the enthalpy of sublimation due to Burkinshaw and Mortimer [J. Chem. Soc., Dalton Trans. 1984, 75], (155.0 +/- 3.0) kJ center dot mol(-1), results in a value for the gas-phase standard molar enthalpy of formation for cytosine of -66.9 kJ center dot mol(-1). A similar value, -65.1 kJ center dot mol(-1), has been estimated after G3MP2B3 calculations combined with the reaction of atomization on three different tautomers of cytosine. In agreement with experimental evidence, the hydroxy-amino tautomer is the most stable form of cytosine in the gas phase. The enthalpies of formation of the other two tautomers were also estimated as -60.7 kJ center dot mol(-1) and -57.2 kJ center dot mol(-1) for the oxo-amino and oxo-imino tautomers, respectively. The same composite approach was also used to compute other thermochemical data, which is difficult to be measured experimentally, such as C-H, N-H, and O-H bond dissociation enthalpies, gas-phase acidities, and ionization enthalpies.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 6