The role of solute polarizability and microenvironment in the spectroscopic behaviour of the local anesthetic drug - bupivacaine

Abstract

The solvent dependent ground- and excited-state photophysical and photochemical properties of the local anesthetic drug – bupivacaine (BUP) – have been studied using a steady-state spectroscopic technique. The Kamlet-Taft solvent scale was used to describe the solvatochromism of BUP in terms of non-specific (dipole-dipole) and specific (hydrogen bonding) solute-solvent interactions. The performed analysis indicates that the major factor responsible for the shift of the absorption and fluorescence bands is solvent polarity, while the solvent acidity and basicity have a less significant effect. Finally, it has also been shown how the solvatochromic equations can be used, in principle, to obtain estimates for the ground- and excited-state (Franck-Condon and relaxed) dipole moments, the difference thereof and the polarizability of BUP from a simple analysis of spectral shift data (solvatochromic methods of Lippert and Mataga, McRae, Bakhshiev and Mataga and Kubota) and multiple linear regression analysis (model of solvatochromism developed by Bayliss, McRae and Ooshika). In addition, an innovative physical treatment was used, consisting of a non-linear fit of the absorption and emission spectral shift data using the theoretical model of solvatochromism developed by Bilot and Kawski and visualisation of the least squares coefficient (χ2) on a 3D map as a function of the solute polarizability and the gas phase absorption or fluorescence energies. Since the solute polarizability can affect both the electronic characteristics and the reactivity of the molecule, our investigations may have significant implications for the development of the pharmaceutical industry (understanding of the influence of the environment on intermolecular processes occurring in the drug-medium system).