Exploring the mechanism of fluorescence quenching in two biologically active boronic acid derivatives using Stern-Volmer kinetics

- Fluorescence quenching of two biologically active boronic acids is studied in different solvents using aniline as quencher.
- A positive deviation is noticed in Stern-Volmer plot.
- The positive deviation is analyzed using Stern-Volmer kinetics and different quenching models.
- The calculations suggest that static and dynamic quenching is active in the studied system.

The fluorescence quenching of 5-chloro-2-methoxyphenylboronic acid (5CMPBA) and 4-fluoro-2-methoxyphenyl boronic acid (4FMPBA) has been studied at room temperature by steady state fluorescence measurements. Aniline is used as quencher. Emission spectra are corrected for inner filter effect. The positive deviation observed in Stern-Volmer (S-V) plot is analyzed using different quenching models. Various quenching parameters like Stern-Volmer constant (KSV), quenching rate parameter (kq), volume constant (V), and kinetic distance (r) are estimated using extended S-V equations. The calculated values of quenching parameters suggest that static quenching mechanism is active in the studied system provided that the reactions are diffusion limited. Finite sink approximation model is invoked in order to check whether reactions are diffusion limited.