Bomb calorimetric and NMR studies on crystalline hexaglycine

• Published in: Thermochimica acta 1989-11, Vol.153, p.123-141
• Main Authors: Colbert, Jennifer C., Domalski, Eugene S., Coxon, Bruce, Vanderhart, David L.
• Format: Article
• Language: English
• Subjects: Chemical thermodynamics; Chemistry; Exact sciences and technology; General and physical chemistry
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/0040-6031(89)85428-0

The enthalpy of combustion of crystalline hexaglycine (C 12H 20N 6O 7cr) has been determined by combustion bomb calorimetry. The molar enthalpy of combustion at 298.15 K for the following reaction: C 12H 20N 6O 7(cr) + 13.5O 2(g) = 12CO 2(g) + 10H 2O(1) + 3N 2(g) is Δ c H m o = −(5930.3 ± 11.3) kJ mol −1; the corresponding enthalpy of formation at 298.15 K is Δ f H m o = −(1650.1 ± 11.7) kJ mol −1. Because of the difficulty in establishing the moisture content of the sample, the enthalpy of combustion is based upon the mass of carbon dioxide formed in each calorimetric experiment rather than upon the mass of sample prior to combustion. A variety of NMR measurements have been made, both 1H NMR and CP-MAS 13C, to characterize hexaglycine and several other oligoglycines, and to determine the water content of the hexaglycine. The energy contribution to the enthalpy of formation of crystalline hexaglycine for the repeating unit, -(CH 2-CO-NH)-, is compared to similar values derived from related peptides and amino acids in the solid phase.