NMR, multi-spectroscopic and molecular modeling approach to investigate the complexes between C.I. Acid Orange 7 and human serum albumin in vitro

In this study, the interaction between C.I. Acid Orange 7 (AO7) and human serum albumin (HSA) was firstly investigated using nuclear magnetic resonance (NMR) spectroscopy in combination with fluorescence quenching spectroscopy, three-dimensional fluorescence spectroscopy, UV–vis absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling method in vitro. The results of NMR data confirmed that AO7 indeed interacted with HSA, and the hydrophobic portion of AO7 should be embedded to the hydrophobic pocket of HSA. The fluorescence quenching analysis revealed that AO7 can bind to HSA. The conformational change of HSA in the presence of AO7 was confirmed by synchronous fluorescence, three-dimensional fluorescence, UV–vis absorption, FT-IR and CD spectra. The binding distance between AO7 and tryptophan residue of HSA was calculated by the efficiency of fluorescence resonance energy transfer. Molecular modeling showed that hydrophobic force and hydrogen bonds were the major interaction between AO7 and HSA.

Graphical abstractThe interaction mechanism of C.I. Acid Orange 7 (AO7) with human serum albumin (HSA) was firstly investigated by NMR spectroscopy, multi-spectroscopic and molecular modeling method under simulative physiological conditions. Molecular modeling study suggested that the binding site was located in the hydrophobic pocket of HSA, and AO7 can bind HSA through the hydrophobic force and hydrogen bonds.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The binding of AO7 to HSA was studied by NMR, fluorescence, FT-IR, UV–vis and CD. ► The fluorescence data and molecular modeling revealed that AO7 can bind to HSA. ► The addition of AO7 can induce the conformational changes of HSA. ► Both hydrophobic force and hydrogen bonds play a major role in the interaction.