Molecular spectroscopic studies examining the interactions between phenobarbital and human serum albumin in alcohol consumption

Identification and Quantification of the Main Psychoactive Ingredients of Cannabis in Urine Using Excitation-Eemission Matrix Fluorescence Coupled with Parallel Factor Analysis

Cannabis is the most prevalent abused substance after alcohol, and its consumption severely harms human health and thus adversely impacts society. The identification and quantification of cannabis in urine play important roles in practical forensics. Excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis was developed to identify and quantify the four main ingredients of cannabis in urine samples. The main ingredients of cannabis including Δ-9-tetrahydrocannabinol (THC), cannabidiol, cannabinol, and tetrahydrocannabinolic acid (THC-COOH) exhibited diverse fluorescence characteristics, and the concentrations of these compounds depicted a positive linear relationship with the fluorescence intensity at the ng/mL level. The EEM/PARAFAC method adequately characterized and discriminated the four ingredients in calibration and prediction samples with a low root-mean-square error of prediction (RMSEP; 0.03-0.07 μg/mL) and limit of quantitation (LOQ; 0.26-0.71 μg/mL). The prediction results of the EEM/PARAFAC method well correlated with that of GC-MS with a low RMSEP range (0.01-0.05 μg/mL) and LOQ range (0.07-0.44 μg/mL) in urine samples. The EEM spectroscopic investigation coupled with the PARAFAC algorithm results in an organic, solvent-less, fast, reliable tool to perform accurate and rapid screening of cannabis abusers.

Inhibition of porphyra polysaccharide on xanthine oxidase activity and its inhibition mechanism

Xanthine oxidase (XO) is a purine catabolic enzyme related to hyperuricemia and gout. Porphyra polysaccharide (PP) is a kind of sulfated polysaccharide with potent biological activity. Herein, the interaction mechanism between PP and XO was studied by enzyme kinetics and multi-spectroscopy methods for the first time. Inhibition kinetics assay showed that PP reversibly inhibited XO activity in a mixed competitive manner with an IC₅₀ of 10.53 ± 0.69 mg/ml. Fluorescence titration studies and thermodynamic parameter calculations revealed that PP could spontaneously bind to XO through hydrophobic interactions, with a class of binding site. Circular dichroism analysis demonstrated that PP induced secondary structure rearrangement and conformational change of XO. Molecular docking further revealed that PP inserted into the hydrophobic cavity of XO, occupying the catalytic center, leading to the inhibition of XO activity. This study may provide new insights into the inhibitory mechanism of PP as a promising XO inhibitor.

Combination mode of antimalarial drug mefloquine and human serum albumin: Insights from spectroscopic and docking approaches

The interaction between mefloquine (MEF), the antimalarial drug, and human serum albumin (HSA), the main carrier protein in blood circulation, was explored using fluorescence, absorption, and circular dichroism spectroscopic techniques. Quenching of HSA fluorescence with MEF was characterized as static quenching and thus confirmed the complex formation between MEF and HSA. Association constant values for MEF-HSA interaction were found to fall within the range of 3.79-5.73 × 10⁴  M^-1 at various temperatures (288, 298, and 308 K), which revealed moderate binding affinity. Hydrogen bonds and hydrophobic interactions were predicted to connect MEF and HSA together in the MEF-HSA complex, as deduced from the thermodynamic data (ΔS = +133.52 J mol^-1 K^-1 and ΔH = +13.09 kJ mol^-1 ) of the binding reaction and molecular docking analysis. Three-dimensional fluorescence spectral analysis pointed out alterations in the microenvironment around aromatic amino acid (tryptophan and tyrosine) residues of HSA consequent to the addition of MEF. Circular dichroic spectra of HSA in the wavelength ranges of 200-250 and 250-300 nm hinted smaller changes in the protein's secondary and tertiary structures, respectively, induced by MEF binding. Noncovalent conjugation of MEF to HSA bettered protein thermostability. Site marker competitive drug displacement results suggested HSA Sudlow's site I as the MEF binding site, which was also supported by molecular docking analysis.