Characterization and control of the aggregation behavior of cyclodextrins

Photon correlation spectroscopy has been employed for the purpose of characterizing the aggregation behavior of cyclodextrin molecules in aqueous solutions. This optical method is generally intended to study particle size distribution of colloidal particles, associates and macromolecules. Herein we report on some general methodological issues of photon correlation spectroscopy aiming to illustrate aggregated and non-aggregated state of parent cyclodextrins and cyclodextrin derivatives, such as (2-hydroxy)propyl-β-cyclodextrin and tetraamino rhodaminyl (2-hydroxypropyl)-β-cyclodextrin in different aqueous media. Based on particle size analysis data we have demonstrated that the tendency of cyclodextrin molecules to form aggregates may be controlled by temperature and by various additives, e.g. urea, citric acid and polyvinylpyrrolidone. In the case of (2-hydroxypropyl)-β-cyclodextrin the effect of degree of substitution was also studied.