Investigation of the binding and simultaneous quantifications of propanil and bromoxynil herbicide concentrations in human serum albumin

This study reported the use of UV-visible and fluorescence spectroscopy and partial-least-square (PLS) multivariate regression for accurate and simultaneous quantifications of two widely used herbicides, propanil, 3,4-dichloropropionanilide (PPL) and bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile (BXL) in human serum albumin (HSA) at physiological conditions. The binding affinity and thermodynamic properties of PPL-HSA and BXL-HSA complexes were also investigated. Partial-least-square (PLS) regression was used to collate the variability in the absorption or emission spectra of PPL-HSA and BXL-HSA complexes with PPL and/or BXL concentrations in HSA samples. The binding constants of 7.66x 10(8) M-1 for PPL-HSA and 4.88x 10(6) M-1 for BXL-HSA complexes were calculated at physiological conditions (temperature, 310 K; pH 7.4). Thermodynamic parameter values: enthalpy (H) (13.99kJ mol(-1)), entropy (S) (0.078kJ mol(-1) K-1), and Gibbs free energy (G) (-10.19kJ mol(-1)) were determined for PPL-HSA complexation at physiological conditions. However, differences in thermodynamic property values of: H (-214.3kJ mol(-1)), S (-0.563kJ mol(-1) K-1), and G (-39.70kJ mol(-1)) were observed for BXL-HSA complexes. The binding constants and negative G values indicated strong binding affinity and thermodynamically favorability of PPL-HSA and BXL-HSA complex formation. Results of the PLS regression calibration showed good linearity (R-2 0.998289), high sensitivity, and impressive low limit-of-detections (LODs) of 1.38x 10(-8) M for PPL and 1.68x 10(-8) M for BXL that are comparable and/or lower than many previously reported LODs for herbicide and pesticide analyses. Most importantly, PLS regression is capable of simultaneous quantifications of PPL and BXL concentrations in HSA samples with good accuracy and low errors of 3.66%. UV-visible spectrophotometers and spectrofluorometers are fairly inexpensive, easy to use, and are readily available in almost every laboratory, making this protocol excellent and affordable for routine analysis of weed/pest control chemical residues in humans. The results of this study are significant and remarkable that will provide critical insight into the binding mechanism of herbicide toxicity in humans and non-target organisms, which are of special interest in the area of biomedical study, environmental risk assessment, and ecotoxicology.