RESUMO
Stereocomplexes between poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA) have been extensively studied, including, in recent years, several reports on the stereocomplexation of PDLA with small molecules such as peptides. Here, the possible complexation between PDLA and luteinizing hormone releasing hormone (LHRH), a l-configured decapeptide, is considered for which several observations were made: (1) in calorimetry an additional endothermic peak appears at a lower temperature than the melting temperature of pure PDLA; (2) in Raman analyses a band splitting of the C=O stretching mode (not present in pure PDLA) shows up; (3) in X-ray diffraction, however, no change is observed after mixing the two species, indicating no crystal structure modification (and the absence of any stereocomplex crystal structure). The calorimetric double melting peak is merely explained by the presence of two distinct morphological forms of PDLA, whereas the spectroscopic band splitting can be due to simple differences of crystallinity. From these observations it is concluded that the LHRH modifies the crystallization of PDLA without, however, the formation of a stereocomplex.
Assuntos
Materiais Biocompatíveis/química , Hormônio Liberador de Gonadotropina/química , Leuprolida/química , Substâncias Macromoleculares/química , Poliésteres/química , Biopolímeros/química , Calorimetria , Varredura Diferencial de Calorimetria , Carbono/química , Cromatografia , Cromatografia em Gel , Cristalografia por Raios X , Portadores de Fármacos/química , Temperatura Alta , Espectroscopia de Ressonância Magnética , Modelos Químicos , Oxigênio/química , Peptídeos/química , Polímeros/química , Pós , Ligação Proteica , Conformação Proteica , Espectrofotometria , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Temperatura , Termodinâmica , Água/química , Difração de Raios XRESUMO
Eleven bis-ureas have been synthesized, and some of their properties are reported. Several of these compounds form supramolecular polymers in organic solvents. The self-association is shown by FTIR spectroscopy to display cooperativity at two levels. The first level of cooperativity is due to the synergistic association of the two urea functions of a single molecule. The second level of cooperativity is revealed by the fact that the formation of dimers is less favored than that of long oligomers.
