Spectroelectrochemical Investigation of the Interaction of Adenine with Pyridoxine at Physiological pH

Abstract

Spectroelectrochemical techniques were used to probe the interaction of adenine with pyridoxine at pH 7.0. Analysis of UV-visible absorption of the adenine-pyridoxine complex at 260 nm using the Lineweaver–Burk double reciprocal plot produced a linear graph indicating a 1 : 1 mode of interaction between the compounds and a binding constant of 29.1. Change in the background current and broadening of adenine and pyridoxine cyclic voltammetry (CV) oxidation peaks at 1.0 V and 0.8 V, respectively, compared to the CV of the individual compounds is indicative of an interaction. The Raman shift of the coupled –C(11)H2-OH bending and in-plane N(7)-H mode at 1235 cm−1 to 1215 cm−1 of pyridoxine and the shift to the lower wavenumber of the adenine –N(10)H2 rocking band from 942 to 906 cm−1 confirm that the adenine exocyclic amino group and its purine nitrogen atom N(7) interacts with pyridoxine O(12) via the formation of hydrogen bonds. Strong enhancement of surface-enhanced Raman spectroscopy (SERS) bands pertaining to adenine and the bathochromic shift of the normal Raman band due to the adenine ring breathing mode observed at 722 cm−1 in the spectrum of adenine, to 732 cm−1 in the SERS spectrum of aqueous adenine-pyridoxine indicates that the complex adsorbs onto the Ag nanoparticle surface with the adenine portion possessing a perpendicular orientation.