Computational and spectroscopic investigations on boronic acid based fluorescent carbohydrate sensor in aqueous solution at physiological pH 7.5

Abstract

In this study, the structural and photophysical properties of 2-ethoxy-4-fluoro phenyl boronic acid (BA1) fluorescent compound was analysed using experimental spectroscopy, single crystal X-ray diffraction techniques and theoretical calculations were implemented using DFT and TD-DFT methods. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The calculated HOMO-LUMO energies shows charge transfer within the molecule and the transitions were predicted to be as п-п∗. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), UV–Vis absorption spectra and Non-linear optical properties were also studied using the same method and basis set. The BA1 compound has been tested for sugar sensing applications by absorption and emission spectroscopic analysis, to understand BA1 with sugars (D-glucose and D-fructose) complexes. The fluorescence measurements of BA1 at physiological pH 7.5, demonstrated a phenomenal quenching response to fructose and glucose molecules by having a decrease in fluorescence intensity with 3.5 fold and 1.3 fold for 0 M–0.5 M concentration of fructose and glucose, respectively, which shows strong sugar binding affinity. The association and dissociation constants were calculated by employing Stern-Volmer equation. The Job's plot and the mass spectroscopic analysis was carried to know the stoichiometry ratio of binding. The counterpoise correction method was implemented to calculate the complexation energy of the BA1-sugar complexes. The fluorescence life time of the molecule was measured in the presence and absence of sugars. The obtained lifetimes were in comparison with the theoretically calculated lifetimeusing PhotochemCAD. All these results showed that, BA1 can readily bind with sugars and could play an important role in carbohydrate sensing applications.