FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDIES OF CROSS-LINKED HUMAN SERUM-ALBUMIN MICROCAPSULES .2. INFLUENCE OF REACTION-TIME ON SPECTRA AND CORRELATION WITH MICROCAPSULE MORPHOLOGY AND SIZE

Microcapsules were prepared from human serum albumin (HSA) through int erfacial cross-linking with terephthaloyl chloride (TC). Reaction time s were increased from 2 to 60 min, while pH (9.8) and TC concentration (2.5% w/v) were kept constant. Fourier-transform infrared (FT-IR) spe ctra of lyophilized microcapsules were compared. Correlations were est ablished with microcapsule morphology and size, as had been done in a previous study exploring the effect of increasing pH values. Microcaps ules obtained after 2 min had to be considered separately. Minor alter ations were observed in the spectrum as compared with pure HSA. They c onsisted of a decrease of the ester-assigned 1724-cm(-1) band and of t he carboxylate-assigned 1394-cm(-1) band, attributed to a removal of c ontaminating lipids of HSA, and an increase of the 1624-cm(-1) band, a ttributed to interchain H bonding following acylation of the NH2 group s. Prolonging the reaction time resulted in a progressive increase of the bands at 1724 testers), 1795 (anhydrides), and 1624 cm(-1) (beta-s heet), in a further decrease of the 1394-cm(-1) band (carboxylates), a nd in marked alterations of the 1340-1080-cm(-1) region. These importa nt changes, which appeared after 5 min, reflect the progressive acylat ion of the hydroxy and carboxy[ate groups of HSA. As in the previous s eries of pH-based assays, important spectral changes were shown to cor respond to a decrease in microcapsule mean size (from 32 to <15 mu m) and in important modifications of the membrane surface, made rough.