F 7000 fl fluorescence spectrophotometer

The fluorescence intensity of the interaction between compound 6 and α-glucosidase were measure by F-7000 FL fluorescence spectrophotometer (Hitachi scientific Co, Japan) with an excitation wavelength at 280 nm, and fluorescence emission spectrum was recorded at the wavelength from 300 to 500 nm. Briefly, compound 6 at different concentrations (0–8.0 × 10⁻⁵ mol L⁻¹, 10 μL) were added to α-glucosidase solution (1 U mL⁻¹, 2 mL), respectively. The mixture was incubated at 298 K for 30 s before the test. And fluorescence quenching was described by the following Stern–Volmer equation:^{29 (link)} In the eqn (3), F₀ and F represent the fluorescence intensities in the absence and presence of the quencher, respectively. K_q and K_SV are the quenching rate constants of the bimolecular and the Stern–Volmer dynamic quenching constant, respectively. τ₀ is the average life-time of the biomolecule without the quencher (τ₀ = 6.2 ns)^{30 (link)} and [Q] is the concentration of the quencher. In addition, to further illuminate the internal driving force of tannic acid against α-glucosidase, thermodynamic parameters were calculated under different temperatures (273, 298, and 310 K) using the same method as described above.

1-Deoxynojirimycin, 1,5-dibromopentane, 1,8-dibromooctane and 1,11-dibromoundecane were acquired from Energy-Chemical Co., Ltd (Shanghai, China). Chrysin was obtained from Tianjin Heowns Biochem LLC. 4-Nitrophenyl-α-d-glucopyranoside (pNPG), and α-glucosidase (Saccharomyces cerevisiae, EC 3.2.1.20) were purchased from Solarbio. All other reagents were analytically pure unless otherwise specified. The ¹H-NMR and ¹³C-NMR of all intermediates and products were recorded in Bruker spectrometer. The spectrum data were anatomized by the MestReNova software. The Bruker SolanX 70 FT-MS instrument was used to determine the HR-MS of compounds 4–6. The UV and fluorescence data were recorded by Infinite F50 (TECAN UV-Vis spectrophotometer) and F-7000 FL fluorescence spectrophotometer (Hitachi Scientific Co., Japan), respectively.