Investigations on the binding of human hemoglobin with orange I and orange II

The interactions between human hemoglobin and orange I (or orange II) were investigated by UV/vis absorption, circular dichroism, fluorescence spectra techniques, and molecular modeling method. Orange I and orange II effectively quenched the intrinsic fluorescence of human hemoglobin by static quenching. The processes of the binding orange I and orange II on human hemoglobin were spontaneous molecular interaction procedure with hydrogen bonds, van der Waals force, hydrophobic and electrostatic interactions according to van’t Hoff equation and molecular modeling. There is a single class of binding site of orange I (orange II) in human hemoglobin and the molecular modeling study shows that orange I and orange II are dipped into α2 chain. The results of CD, synchronous fluorescence and three-dimensional fluorescence spectra indicated a small loss of α-helical secondary structure of human hemoglobin induced by orange I and orange II.

► The interactions of orange I and orange II with Hb were studied. ► The multi-intermolecular forces played major roles in stabilizing dye–Hb complexes. ► There is a single class of binding site in human hemoglobin. ► There is a small loss of α-helical secondary structure of Hb induced by dye.