Design and Function of Novel Azoprobe Possessing Multipoint Binding Sites for Dopamine Recognition

Abstract

For selective dopamine (DA) recognition in an aqueous solution, a novel azoprobe possessing crown ether and boronic acid {2-[3,4-(18-crown-6)phenylazo]-5-hydroxy-phenylboronic acid} was designed. This probe was water soluble and changed its color from yellow to red to orange with increasing pH. From UV-vis spectra in the presence of DA or analogous compounds, based on 1 : 1 complex formation of the probe with a guest, the highest binding constant of (1.11±0.021)×10² M⁻¹ was noted for DA. At pH 8, the solution color changed from red to orange upon the addition of DA. This color change was ascribed to bronate ester formation followed by hydrolysis or by the B–N interaction between boronate ester and the azo moiety. This peculiar behavior was found to be strongly affected by the cis-diol moiety of guest molecules.