Enthalpies of combustion of glycylglycine and dl-alanyl- dl-alanine

• Published in: The Journal of chemical thermodynamics 1992-12, Vol.24 (12), p.1311-1318
• Main Authors: Diaz, E.L., Domalski, E.S., Colbert, J.C.
• Format: Article
• Language: English
• Subjects: Chemical thermodynamics; Chemistry; Elements, mineral and organic compounds; Exact sciences and technology; General and physical chemistry; Thermodynamic properties
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/S0021-9614(05)80272-1

The energies of combustion of crystalline glycylglycine and dl-alanyl- dl-alanine were determined using oxygen bomb calorimetry. The molar enthalpies of combastion Δ c H° m at T = 298.15 K were calculated from the experimental results for glycylglycine and dl-alanyl- dl-alanine in the crystalline state and were found to be −(1969.67 ± 1.26) kJ · mol −1 and −(3267.47 ± 1.84) kJ · mol −1, respectively. For both combustion reactions, the enthalpies are based upon the amount of CO 2 produced. The corresponding molar enthalpies of formation Δ f H° m for glycylglycine and dl-alanyl- dl-alanine are −(747.68 ± 1.29) kJ · mol −1 and −(807.32 ± 1.87) kJ · mol −1, respectively. Values were also derived for the contribution to Δ f H° m of the glycine {−CH 2NHCO−} and dl-alanine {−CH(CH 3)NHCO−} repeating units for peptides in the crystalline state at T = 298.15 K.