The improved inhibition of Mn (II)-EGCG on α-glucosidase: Characteristics and interactions properties

To improve epigallocatechin gallate (EGCG)’s inhibition on α-glucosidase, Mn (II)-EGCG was prepared and characterized by Fourier transform infrared (FT-IR), mass spectrometry (MS), X-ray diffraction (XRD), nuclear magnetic resonance hydrogen (1H-NMR), and thermogravimetric analysis (TGA). The interactions between Mn-EGCG and α-glucosidase were revealed using fluorescence, isothermal titration calorimetry (ITC), circular dichroism (CD) and molecular docking. FT-IR of Mn-EGCG showed OH participated in the coordination with Mn, a m/z 565.4 peak was found in MS, a new spectral band Mn-O coordination bond was revealed by FT-IR (623 cm−1) and 1H-NMR, Mn replaced H of EGCG at 4′, 3′, 5′′, and 4′′-OH, and the molecular of Mn-EGCG was presumed to be C22H14O11Mn2 [E-4H+2Mn (II)], XRD indicated the broadened and shifted 2θ with crystallinity (79.68%), TGA showed the improved thermal stability of Mn-EGCG (30.8%). Inhibition rate of Mn-EGCG could reach 91.6% with IC50 7.5 mg/L, which was higher than EGCG (70.8%, 14 mg/L). Binding constants of Mn-EGCG were higher than EGCG and increased with temperature, resulting in static quenching of α-glucosidase. ITC and molecular docking showed Mn-EGCG bound to α-glucosidase was dominated by hydrophobic interactions, and three interactions (Alkyl, Pi-Anion, and Metal-Acceptor) appeared. In conclusion, a new functional food component and its inhibition mechanism are described.