Ultraviolet spectroscopic estimation of microenvironments and bitter tastes of oxyphenonium bromide in cyclodextrin solutions

Abstract

The UV absorbance and bitter taste of oxyphenonium bromide (OB), an antiacetylcholine drug, in cyclodextrin (CD) solutions are measured, and the local environment of the binding site and the reduction of the bitter taste intensity are quantitatively estimated from the UV data. The UV spectrum of OB is changed with the addition of α‐, β‐, and γ‐CD, because the phenyl group of OB is included into the CD cavity. The maximum wavelength, λmax, senses environmental changes of OB best among several spectral characteristics. From comparison of λmax between a CD solution and the reference ethanol–water and dioxane–water systems, the dielectric constant of the binding site is evaluated. This value leads us to estimate the microenvironment and structure of the binding site. The suppression of the bitter taste of 4 mM OB by CDs is in the increasing order α‐CD <γ‐CD <β‐CD. The extent of this suppression can be quantitatively predicted from the UV absorbance by assuming that the free OB molecule alone exhibits the bitter taste, regardless of the kind and concentration of CD. Some implications and limitations of the present approach are discussed.