Spectrofluorometric and computational approaches for the interaction studies of aclonifen and bifenox with human serum albumin

• First report on the interactions of aclonifen (ACF) and bifenox (BIF) with human serum albumin (HSA). • Quenching of HSA fluorescence by ACF and BIF were found as dynamic quenching. • The ACF−HSA and BIF−HSA complexes were characterized by the moderate binding affinity. • Participation of hydrophobic interactions and hydrogen bonds in the formation of ACF−HSA and BIF−HSA complexes. • Existence of both ACF and BIF binding locations in the vicinity of Sudlow’s site I of HSA. Interaction of two broadly used herbicides, aclonifen (ACF) and bifenox (BIF) with the major transporter in human circulation, human serum albumin (HSA) were examined using fluorescence and absorption spectral measurements combined with in silico analysis. Assessment of the fluorescence and absorption spectral results affirmed the complexation between ACF/BIF and HSA. Increase in the K SV value with temperature characterized the ACF/BIF-induced quenching of the protein fluorescence as dynamic quenching. The moderate binding affinities ( K f = 1.74×10 4 – 1.95×10 6 M –1 for ACF–HSA complex; K f = 2.00×10 3 – 1.02×10 6 M –1 for BIF–HSA complex) were pointed out between ACF/BIF and HSA, showing a relatively higher binding constant values with increasing temperatures. Quantitative evaluation of thermodynamic data (Δ S = +0.86 kJ mol −1 K −1 and Δ H = +225.43 kJ mol −1 for ACF–HSA complex; Δ S = +1.11 kJ mol −1 K −1 and Δ H = +304.63 kJ mol −1 for BIF–HSA complex) predicted the contribution of hydrophobic interactions in the ACF–HSA and BIF–HSA association processes, which were well supported by our molecular docking results. In silico analyses were made to acquire insight details into the ACF and BIF binding to HSA at the binding sites and suggested the locations of ACF and BIF binding sites as both subdomain IIA (site I) and subdomain IIIA (site II) of HSA, showing more preference toward site I.