Fourier-Transform Infrared Spectroscopic Studies of Cross-Linked Human Serum Albumin Microcapsuies. 2. Influence of Reaction Time on Spectra and Correlation with Microcapsule Morphology and Size

Microcapsuies were prepared from human serum albumin (HSA) through interfacial cross-linking with terephthaloyl chloride (TC). Reaction times 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) spectra of lyophilized microcapsuies were compared. Correlations were established with microcapsuie morphology and size, as had been done in a previous study exploring the effect of increasing pH values. Microcapsuies obtained after 2 min had to be considered separately. minor alterations were observed in the spectrum as compared with pure HSA. They consisted of a decrease of the ester- assigned 1724-crrr1 band and of the carboxylate-assigned 1394-cnrr1 band, attributed to a removal of contaminating lipids of HSA, and an increase of the 1624-cnr1 band, attributed to interchain H bonding following acylation of the NH2 groups. Prolonging the reaction time resulted in a progressive increase of the bands at 1724 (esters), 1795 (anhydrides), and 1624 cm-1 (/J-sheet), in a further decrease of the 1394-cnr1 band (carboxylates), and in marked alterations of the 1340- 1080-crrr’ region. These important changes, which appeared after 5 min, reflect the progressive acylation of the hydroxy and carboxylate groups of HSA. As in the previous series of pH-based assays, important spectral changes were shown to correspond to a decrease in microcapsuie mean size (from 32 to