Inclusion Complexation of p-Hydroxybenzoic Acid Esters with α- and β-Cyclodextrins : Dissolution Behaviors and Antimicrobial Activities

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Abstract
Complex formations of 12 p-hydroxybenzoic acid esters (alkylparabens) with .alpha.- and .beta.-cyclodextrins (.alpha.-CyD, .beta.-CyD) were studied in water and in solid state by solubility method, IR spectroscopy, thermal analyses and X-ray diffractometry. Solid complexes for alkylparabens with .alpha.- and .beta.-CyD were obtained and their molar ratios were 1:2 (alkylparaben/.alpha.-CyD) and 1:1 (alkylparaben/.beta.-CyD), respectively, except methylparaben-.alpha.-CyD complex (1:1). The dissolution rate of the complex in water was significantly higher than that of alkylparaben itself, depending upon the magnitude of the stability of the complex. Alkylparaben molecule included within CyD cavity appeared to be inactive and antimicrobial activity [Monilia-albicans, Aspergillus-niger, Penicillum-chrysogenium, Saccharomyces-cerevisiae and Bacillus-subtilis] was directly related to the concentration of free alkylparaben in aqueous solution. Upon addition of CyD, a significant increase in inhibitory-zone diameter was observed by cup-plate method, suggesting improved solubility and diffusibility of the preservatives by inclusion complexation.