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

Abstract

Microcapsuies were prepared from human serum albumin (HSA) through interfacial cross-linking with terephthaloyl chloride (TC). Reaction times were increased from 2 to 60min, 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 2min 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 1624cm-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 5min, 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 <15 jim) and in important modifications of the membrane surface, made rough.