Data of fluorescence, UV–vis absorption and FTIR spectra for the study of interaction between two food colourants and BSA

In this data article, the fluorescence, UV–vis absorption and FTIR spectra data of BSA-AR1/AG50 system were presented, which were used for obtaining the binding characterization (such as binding constant, binding distance, binding site, thermodynamics, and structural stability of protein) between BSA and AR1/AG50.


Experimental factors
The solution of BSA was prepared in phosphate-buffer (0.05 M NaH 2 PO 4 -Na 2 HPO 4 , pH¼ 4.8, 5.5, 6. 3  Value of the data The data are intuitionistic for readers to compare the binding affinity of AR1/AG50 with BSA; The data are helpful to readers for understanding further the related parameters calculated; The data may be of great help to study in detail the similar systems.

Data
The interaction data of BSA with AR1/AG50 were determined using Cary Eclipse fluorescence spectrofluorimeter (Varian, USA), UV-3600 spectrophotometer (Shimadzu, Japan) or Nicolet-6700 FTIR spectrometer; and these data were shown as fluorescence quenching spectra, the Stern-Volmer plots in the absence and presence of ethanol/NaCl, RLS spectra, UV-vis absorption spectra, UVmelting profiles, synchronous fluorescence spectra, and FTIR spectra. Corresponding parameters were calculated based on the interaction data.
In addition, to make the figures in the text become clearer, all of the figures were processed by Photoshop 8.1 software. ChemOffice 2008 was used for drawing the structures of acid red 1 and acid green 50 (Fig. 1). from J&K Scientific Ltd. (Beijing, China) and Acros Organics (New Jersey, USA), respectively. And all other chemicals were analytical reagent grade.

Fluorescence quenching of BSA by AR1/AG50
3.0 mL BSA solution (2.0 μM) was titrated by successive additions of AR1/AG50 solution with the concentration of 3.0 Â 10 À 4 mol L À 1 at different conditions (pH ¼ 4.8, 5.5, 6.3 or 7.4, T ¼293, 298, 304 or 310°K, c(NaCl)¼0.0, 0.04, 0.09 or 0.15 M, and/or ethanol content (%)¼0%, 5% or 10%), and the final concentration of AR1/AG50 was kept at 11.54 Â 10 À 6 mol L À 1 . The fluorescence quenching of BSA with the addition of AR1/AG50 was recorded in the range of 300-500 nm by Cary Eclipse fluorescence spectrofluorimeter (Varian, USA). The width of the excitation and emission slit was adjusted at 5 nm, and the excitation wavelength was selected at 280 nm. The temperature of samples was kept by recycle water during the whole experiment. All fluorescence titration experiments were done manually by 50 mL microsyringe.
The figures of fluorescence quenching spectra ( Fig. 2) were made using Origin 7.5.
2.2.7. The effect of ethanol on the quenching plots of BSA-AR1/AG50 system The measured fluorescence quenching data of BSA by AR1/AG50 without or with ethanol content (5% or 10%) at pH¼4.8, 5.5, 6.3 and 7.4 were corrected [1] and fitted by Origin 7.5 based on Eq. (1) (Fig. 8).   FTIR spectra in the 1800-900 cm À 1 region for free BSA (0.2 mM), BSA-AR1 and BSA-AG50 complexes (the molar ratio of BSA to AR1 or AG50 is maintained at 1:1), and their corresponding difference spectra were indicated in the figure. The contribution of AR1 or AG50 is subtracted from the different spectra in this region.  Table 3 The binding constants K, binding sites number n and thermodynamic parameters for the BSA-AR1/AG50 system at different conditions. Systems NaCl (M) UV-3600 spectrophotometer at pH 4.8 and 7.4, respectively; and corresponding absorption spectra were fitted using Origin 7.5 based on Eq. (2) (Fig. 9).

The synchronous fluorescence spectra
Synchronous fluorescence spectra of BSA (2.0 μM) with the increasing AR1/AG50 concentration (0-75.00 μM) at Δλ¼15 and 60 nm were recorded using Cary Eclipse fluorescence spectrofluorimeter in the range of 250-500 nm. Other scanning parameters were the same as those of the fluorescence titration experiments. Besides, corresponding figures (Fig. 13) was made by Origin 7.5. 2.2.13. FTIR spectra FTIR spectra of free BSA (0.2 mM), BSA-AR1 and BSA-AG50 complexes (the molar ratio of BSA to AR1 or AG50 is maintained at 1:1) were recorded on Nicolet-6700 FTIR spectrometer via the attenuated total reflection (ATR) at a resolution of 4 cm À 1 and 64 scans in the range of 400-4000 cm À 1 at room temperature. The corresponding absorbance contributions of buffer and free AR1/AG50 solutions were recorded and digitally subtracted with the same instrumental parameters, and their FTIR spectra (Fig. 14) was done by OMNIC.

The parameters of S-V plot
The parameters of fluorescence quenching for the BSA-AR1/AG50 system at different conditions were calculated using the S-V equation [1].
2.2.15. Effect of pH, NaCl and ethanol on the binding parameters of BSA-AR1/AG50 system The binding parameters of the two systems (Tables 2-4) were calculated using double logarithm regression curves, Debye-Hückel limiting law and Van't Hoff equation based on the data of fluorescence quenching at different conditions, respectively [2,3].   Table 7 The binding rate constants k and corresponding statistical parameters for the BSA-AR1/AG50 system at different conditions.