FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDIES OF CROSS-LINKED HUMAN SERUM-ALBUMIN MICROCAPSULES .3. INFLUENCE OF TEREPHTHALOYL CHLORIDE CONCENTRATION ON SPECTRA AND CORRELATION WITH MICROCAPSULE MORPHOLOGY AND SIZE

Microcapsules were prepared from human serum albumin (HSA) by interfac ial cross-linking with terephthaloyl chloride (TG). TC concentrations were increased from 0.5 to 5% w/v, while pH (9.8) and reaction time (3 0 min) were kept constant. Fourier transform infrared (FT-IR) spectra of lyophilized microcapsules were compared. Correlations were establis hed with microcapsule morphology and size. The results were compared w ith those of previous studies exploring pH or reaction time and with t hose of parallel determinations of microcapsule free amino groups. Wit h 0.5% TC, decreases of the ester-assigned 1724-cm(-1) band area and o f the carboxylate-assigned 1394-cm(-1) band area were observed compare d with pure HSA. This phenomenon was attributed to a removal of contam inating lipids of HSA. Increasing TG concentration resulted in a progr essive increase of the band areas at 1724 cm(-1) (esters) and 1795 cm( -1) (anhydrides), in a further decrease of the 1394-cm(-1) band area ( carboxylates), and in marked alterations of the 1340-1080-cm(-1) regio n. These changes, which revealed the progressive acylation of hydroxy and carboxylate groups of HSA, were accompanied by an increase of the 1624-cm(-1) band area (beta-sheet), reflecting interchain H-bonding du e to cross-linking. As observed in the previous studies of pH and reac tion time, important spectral changes corresponded to low values of -N H2 content, to a decrease in microcapsule mean size (from >30 to <15 m u m), and to modifications of the membrane surface (made rough).