Cross-linked β-cyclodextrin microcapsules:: preparation and properties

Microcapsules were prepared by interfacial cross-linking of beta -cyclodextrins (beta -CD) with terephthaloyl chloride (TC). Batches were prepared from beta -CD solutions in M NaOH, using 5% TC and a 30 min reaction time. Microcapsules were studied with respect to morphology (microscopy), size (laser diffraction technique) and, for selected batches, IR spectroscopy, determination of beta -CD content (polarimetry after alkaline dissolution of microcapsules) and complexing proper ties, evaluated using p-nitrophenol (pNP) as the guest molecule. Well-formed microcapsules were obtained fi om 5, 7.5, and 10% beta -CD solutions. The mean size of all batches was in the 10-35 mum range. The IR spectrum showed bands at 1724, 1280 and 731 cm(-1), reflecting the formation of esters. The beta -CD contents were 46, 56-58 or 60-66% for batches prepared from 5, 7.5 or 10% beta -CD solutions, respectively. The experiments conducted with 1 mM pNP showed a rapid complexation reaching a maximum within 1 h. When incubating 50 mg lyophilized microcapsules in 10 mi pNP solution, the maximal fixation (97.8 mu mol/g microcapsules) was observed for small-sized partially (approximate to 11 mum) prepared from a 7.5% beta -CD solution. The method then appears as a simple and rapid procedure to provide stable microcapsules, having an interesting guest-binding ability. (C) 2000 Elsevier Science B.V. All rights reserved.