Journal of ThermalAnalysis, Vol. 38 (1992)2771-2778 ENTHALPIES AND ENTROPIES OF FUSION OF SOME SUBSTITUTED DIPEPTIDES Comparison with crystal data G. Barone 1, C. Giancola ~, T. H. Lilley 2, C. A. Mattia I and R. Puliti 3 i DEPARTMENTOF CHEMISTRY, UNIVERSITY 'FEDERICO II', VIA MEZZOCANNONE4, 80134 NAPLES, ITALY 2CHEMISTRYDEPARTMENT AND THE KREBS INSTITUTE FOR BIOMOLECULAR RESEARCH, THE UNIVERSITY,$3 7HF, SHEFFIELD, UK 3INSTITUTEFOR THE CHEMISTRYOF MOLECULES OF BIOLOGICAL INTEREST: NATIONALRESEARCH COUNCIL VIA TOIANO 6, 80072 ARCO FELICE-NAPLES,ITALY Enthalpies and temperatures of fusion or transition for four substituted dipeptides (N- acetylamides of glycyl-L-alanine (NAGAA), L-alanyl-L-alanine (NAA~A), L-prolyl-glyeine (NAPGA) and L-leucyl-L-proline monohydrate (NALPA.H20)) were determined by differen- tial scanning calorimetry and the entropies of fusion derived. The results obtained have been compared with those of the corresponding substituted aminoaeids and some of their racemic crystalline mixtures. The enthalpies and entropies of fusion of some substituted aminoacids have been redetermined. The results are discussed in comparison with crystal structural data, which has been reported in the literature or determined recently by some of the authors. Rationalization of the fusion parameters was attempted mainly on the basis of the number of in- tramoleeular hydrogen bonds and the packing densities in the crystals. Keywords: enthalpies and entropies of fusion, peptides Introduction Uncharged derivatives of aminoacids and peptides have been used as model compounds of natural polypeptides and proteins [1-3] in some solution physico- chemical studies. However, thermodynamic and structural properties of the solid phases of these compounds are interesting per se and, given the lack of informa- tion on this class of compounds, we recently have determined a series of crystal structures [4-9], and sublimation enthalpies and entropies [5, 10, 11]. The struc- tures of a few similar compounds have been reported [12-14]. John Wiley & Sons, Limited, Chichester Akaddmiai KiadJ, Budapest