Spectroscopic investigation on the mechanism of formation of molecular complexes of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes

Soluble microbial products (SMPs), dissolved organic matter excreted by activated sludge, can interact with antibiotics in wastewater and natural water bodies. Interactions between SMPs and antibiotics can influence antibiotic migration, transformation, and toxicity but the mechanisms involved in such interactions are not fully understood. In this study, integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic, trimethoprim (TMP), which has a low biodegradation rate and has been detected in wastewater. The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances (based on the total dissolved organic carbon concentration) so would have contained sites that could interact with TMP. A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed (R²>0.99), indicating that the fluorescence enhancement between SMP and TMP occurred. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl, carbonyl, and hydroxyl groups were the main functional groups involved in the interactions. The electrostatic and π-π interactions were discovered by the UV-vis spectra and ¹H nuclear magnetic resonance spectra. Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory, and the results confirmed the conclusions drawn from the ¹H nuclear magnetic resonance spectra. The results help characterize SMP-TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Spectroscopic and molecular docking studies on the charge transfer complex of bovine serum albumin with quinone in aqueous medium and its influence on the ligand binding property of the protein

The spectral techniques such as UV-Vis, (1)H NMR and fluorescence and electrochemical experiments have been employed to investigate the interaction between 2-methoxy-3,5,6-trichloro-1,4-benzoquinone (MQ; a water soluble quinone) and bovine serum albumin (BSA) in aqueous medium. The fluorescence of BSA was quenched by MQ via formation of a 1:1 BSA-MQ charge transfer adduct with a formation constant of 3.3×10(8) L mol(-1). Based on the Forster's theory the binding distance between them is calculated as 2.65 nm indicating high probability of binding. For the first time, influence of quinone on the binding property of various types of ligands such as aspirin, ascorbic acid, nicotinimide and sodium stearate has also been investigated. The results indicated that the strong and spontaneous binding existing between BSA and MQ, decreased the intensity of binding of these ligands with BSA. Since Tryptophan (Trp) is the basic residue present in BSA, a comparison between binding property of Trp-MQ adduct with that of BSA-MQ with these ligands has also been attempted. 1H NMR titration study indicated that the Trp forms a charge transfer complex with MQ, which reduces the interaction of Trp with the ligands. Molecular docking study supported the fact that the quinone interacts with the Trp212 unit of the BSA and the free energy change of binding (ΔG) for the BSA-MQ complex was found to be -46 kJ mol(-1), which is comparable to our experimental free energy of binding (-49 kJ mol(-1)) obtained from fluorescence study.

Spectroscopic studies and molecular orbital calculations on the charge transfer reaction between DDQ and 2-aminopyridine

Charge transfer complex formation between 2-aminopyridine (donor, 2AP) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (acceptor, DDQ) has been studied spectrophotometrically in acetonitrile (CH3CN). The newly formed CT-complex has reddish brown color and is characterized by the appearance of new absorption bands in the 375-650 nm regions where acceptor and donor do not have any absorption. Maximum and constant absorbance of the complex was obtained after 10 min at 20 °C with 1 mL 5×10(-3) M DDQ in CH3CN. Based on photometric titration method, the stoichiometry of the formed CT-complex was found to be 1:1 [(2AP)(DDQ)]. Minimum-maximum absorbances method has been applied to estimate the formation constant of the complex where it recorded large value confirming its high stability. Molecular orbital calculations utilizing GAMESS computations were carried out in order to record changes in the electronic structure and molecular geometry of the formed CT-complex. In addition, the infrared vibrational frequencies of the complex were computed and compared with experimental results.