Deciphering the interactions of substituted chromones possessing acetylcholinesterase inhibition activity in human serum albumin matrix

A combination of different biophysical techniques is applied in conjunction with molecular docking calculation to explore the binding interaction of two substituted chromone derivatives namely 7-amino-2-methylchromone (AMC) and 3-cyanochromone (CyC), both of which are screened as potential acetylcholinesterase inhibitors, with human serum albumin (HSA). Analysis of intrinsic tryptophan fluorescence quenching reveals the Stern-Volmer constant (K-SV) for CyC (similar to 1.2 x 10(5) M-1) to be one order in magnitude higher than AMC (similar to 3.9 x 10(4) M-1). Analysis of fluorescence lifetime data indicates static quenching mechanism for AMC; while a significant contribution from the dynamic (collisional) quenching also exits for CyC. The difference in binding thermodynamics of the chromones into the protein binding domain is mainly due to the difference in the primary forces responsible for the binding. The fluorescence titration results are in nice agreement with the complementary circular dichroism (CD) experiments as well as with the results from molecular docking calculation. The results indicate that while CyC binds to Domain IIA (Sudlow's site 1) of HSA with a greater binding affinity of -28.84 kJ/mol, AMC binds at an alternate position, site IB with a lower binding affinity (-27.19 kJ/mol). (C) 2019 Elsevier B.V. All rights reserved.