Thermodynamics of solvation of some small peptides in water at T = 298.15 K |
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Institution: | 1. “G. Ciamician” Department of Chemistry, University of Bologna, Via Selmi 2, I-40126 Bologna, Italy;2. “G. Ciamician” Department of Chemistry, Microchemistry and Microscopy Art Diagnostic Laboratory (M2ADL), University of Bologna, Ravenna Campus, Via Guaccimanni 42, I-48100 Ravenna, Italy |
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Abstract: | The enthalpies of solution in water, ΔsolHm, of some small peptides, namely the amides of five N-acetyl substituted amino acids of glycine, l-alanine, l-proline, l-valine, l-leucine and two cyclic anhydrides of glycine and l-sarcosine (diketopiperazines), were measured by isothermal calorimetry at T = (296.84, 306.89, and 316.95) K. The enthalpies of solution at infinite dilution at T = 298.15 K were derived and added to the enthalpies of sublimation, , at the same temperature, to obtain the corresponding solvation enthalpies at infinite dilution, . Moreover, the partial molar heat capacities at infinite dilution at T = 298.15 K, , were calculated by adding molar heat capacities of solid small peptides, Cp,m(cr), to the values obtained from our experimental data. CH2 group contributions, in terms of solvation enthalpy and partial molar heat capacity, were ?3.2 kJ · mol?1 and 89.3 J · K?1 · mol?1, respectively, in good agreement with the literature data. Simple additive methods were used to estimate the average molar enthalpy of solvation and partial molar heat capacity at infinite dilution for the 1/2CONH?CONH functional group in the small peptides. Values obtained were ?46.7 kJ · mol?1 for solvation enthalpy and ?42.4 J · K?1 · mol?1 for partial molar heat capacity, significantly lower than values obtained for the CONH functional group in monofunctional model compounds. |
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