Systematic investigations on the biophysical complexation of hydroxyethyl starch 200/0.5 with human serum albumin

Spectroscopic techniques have been used to improve the understanding of the interactions between hydroxyethyl starch (HES) 200/0.5 and human serum albumin (HSA) in a simulated physiological fluid of pH 7.4. It has been revealed that static fluorescence quenching occurred when HSA interacted with HES 200/0.5. The negative value of ΔH° (− 2.39 × 10⁴ J·mol⁻¹) and positive value of ΔS° (30.1 J·mol⁻¹·K⁻¹) suggested electrostatic interaction was the dominating force of the binding reaction between HES 200/0.5 to HSA, and the binding process was proved as a spontaneous one with negative ΔG° values (− 3.34 × 10⁵ J·mol⁻¹ at body temperature). The distance between HSA and HES 200/0.5 (r = 2.11 nm) proved efficient energy transfer from Trp to the drug. Moreover, the binding site of HES 200/0.5 to HSA was confirmed by site marker competitive experiments as Sudlow’s site I. Finally, it was observed that the conformation of HSA was changed with a loss of α-helical but acquisition of β contents, where a more stabilized secondary structure was formed.