Fluorescence Quenching Studies of the Interaction Between Riboflavin and Norfloxacin and Analytical Application in the Determination of Vitamin B2

Interaction mechanism of biochar dissolved organic matter (BDOM) and tetracycline for environmental remediation

The persistent organic pollutant of water by residual antibiotics, particularly tetracycline, posed serious environmental and health risks. Biochar dissolved organic matter (BDOM) sorbed pollutants and mitigated migration and transformation. This study investigates the binding interaction mechanisms between BDOM and tetracycline under varying pyrolysis temperatures biochars and pH, with fluorescence quenching techniques. The influence of biochar pyrolysis temperature on tetracycline adsorption behavior by BDOM-tetracycline was also researched. The key results revealed that higher pyrolysis temperatures and lower solution pH enhanced the binding affinity of BDOM for tetracycline, which was mainly attributed to increased aromaticity and reduced oxygen-containing functional groups. The hydrophobic forces of biochar dominated the interaction, with positive enthalpy (ΔH) and entropy (ΔS) values confirming an endothermic, entropy-driven process. The BDOM modified the mobility and bioavailability of tetracycline in the process of environmental pollution remediation, which not only enhances plant growth, but also mitigates ecological risks.

Hetero-association models of non-covalent molecular complexation

The present review discusses the current state-of-the-art in building models enabling the description of non-covalent equilibrium complexation of different types of molecules in solution, which results in the formation of supramolecular structures different in length and composition (hetero-association or supramolecular multicomponent co-polymerisation). The description is focused on standard physical and chemical quantities such as experimental observables and equilibrium parameters of interaction (equilibrium constants and concentrations). The major partial cases of the hetero-association models, such as finite and indefinite isodesmic and cooperative complexations, and Benesi-Hildebrand and Langmuir adsorption models are considered. Future challenges in the development of the hetero-association models are provided.

A Fluorescence Quenching Analysis of the Binding of Fluoroquinolones to Humic Acid

Fluorescence quenching was used to investigate the interaction of six fluoroquinolones with humic acid. Static quenching was observed for the binding of ciprofloxacin, enoxacin, fleroxacin, levofloxacin, norfloxacin, and ofloxacin to humic acid. The equilibrium binding constants were found from Stern-Volmer plots of the data. The quenching experiments were repeated over a temperature range of 25-45 ℃ and van't Hoff plots were generated. From these linear plots, thermodynamic values were calculated for Δ H, Δ G, and Δ S for each of the fluoroquinolones. The equilibrium binding constants were found to be <1 for all the antibiotics studied. The calculated ΔH values were all negative and ranged from -9.5 to -27.6 kJ/mol. The high water solubility of the antibiotics and low ΔH of binding suggests that the antibiotics will be transported easily through the environment. Finally, whether the fluoroquinolones are in a protonated, deprotonated, or partially protonated state is found to correlate to the strength of binding to humic acid.