Radical scavenging abilities of L-tyrosine and L-DOPA Schiff bases and their fluorescence binding studies and molecular docking interactions with bovine serum albumin

Abstract

Phenolic compounds are known for their abilities to scavenge and eliminate reactive oxygen species (ROS) which may lead to oxidative stress. Bearing in mind that Schiff bases are biologically active compounds, a series of Schiff bases derived from the monophenolic l-tyrosine and diphenolic l-DOPA were synthesized and characterized by spectral and elemental analysis. The structure of the l-DOPA naphthyl Schiff base was confirmed and characterized by X-ray. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical assays were used in assessing the effectiveness of these compounds as radical scavengers. l-DOPA derivatives were better radical scavengers with lower IC50 compared to l-tyrosine derivatives. To understand the distribution of these compounds in the blood plasma, their interactions with bovine serum albumin (BSA) were monitored using fluorescent emission spectroscopy where they were found to quench the BSA intrinsic fluorescence by combined static and dynamic mechanism. The fluorescence and FT-IR data showed that conformational changes occurred in BSA after interaction with the Schiff bases. The binding constant of tyrosine and DOPA Schiff bases were in the order of 104 to 108 M−1 suggesting a moderate to good binding ability with BSA. Higher binding affinity and better radical scavenging ability was observed for compounds bearing the naphthyl moiety.The radical scavenging ability of the l-DOPA naphthyl Schiff base was found to increase with decrease in IC50 values from 17 to 15 µM when bound to BSA. Fluorescence measurement and molecular docking studies demonstrated that hydrophobic interactions and hydrogen bonds dominated the interaction between BSA and tyrosine or l-DOPA derivatives. These results gave valuable information for pharmacological mechanism for l-tyrosine and l-DOPA Schiff bases in vivo conditions which can have a vital role in the development of drugs.