Biological interactions of fluorinated chalcones: Stimulation of tyrosinase activity and binding to bovine serum albumin

Abstract

The evaluation of tyrosinase activity of CH, CH3F, CH4F, CH23F, CH25F, CH35F and CH2356F as well as of the interactions of CH and fluorinated chalcones CH3F, CH4F and CH2356F with bovine serum albumin (BSA) in a PBS buffer solution (pH=7.4), at 288K, 293K and 298K, were investigated by using spectroscopic techniques, zeta potential and computational methods. Tyrosinase enzymatic activity was measured by UV–vis spectrometry of the oxidation of l-DOPA in the presence of the enzyme and chalcones: the unsubstituted chalcone inhibits tyrosinase activity, whereas its fluorinated derivatives showed the opposite effect, whose sample CH2356F showed the highest percentage activation. Studies of quenching of the BSA fluorescence by CH, CH3F, CH4F and CH2356F show a combination of static and dynamic quenching mechanisms. In addition FRET mechanism can occurs with high probability. For CH the binding constant (Ka) is in the range of 105M−1 indicating a moderate association between chalcone and BSA. On the other hand, for the fluorinated derivatives CH3F, CH4F and CH2356F Ka=104M−1, which indicates that the presence of fluorine atoms on the chalcone structure decreases the binding ability. The thermodynamic parameters ΔH° and ΔS° show that the BSA:CH association is enthalpically and entropically driven, whereas for fluorinated derivatives it is only entropically driven. The negative ΔG° values found in all cases are consistent with a spontaneous albumin:chalcone association. Circular dichroism and zeta potential data show that the binding does not affect significantly the albumin structure. The binding site study clearly indicates that the main binding pocket for the samples is the Trp-212-containing binding site. The largest docking score values also suggest the same binding site. Molecular docking results suggested that the presence of fluorine atoms decrease the number of amino acid residues that can stabilize the interaction of the fluorinated chalcones with BSA. For CH3F and CH2356F the type of interaction between the amino acid residues and ligand structure did not change significantly.