Spectroscopic Study of Interaction of Bare, Citrate Capped and BSA Capped Fe3O4 Nanoparticles with Hemoglobin

Background: Fe3o4 nanoparticles have great potential in different biomedical applications. The study of the interaction of bare, and capped Fe3O4 nanoparticles with common blood proteins is a field of interest for understanding the underlying mechanism and biocompatibility. Objective: This work aims at studying the nature of binding of bare, citrate functionalised and bovine serum albumin coated Fe3O4 nanoparticles (Fe3O4NPs, CFe3O4NPs and BFe3O4NPs) with human hemoglobin (Hb), and their instantaneous effect on amino acid group, heme group and secondary structure of Hb. Methods: Nanoparticles were prepared by the chemical route and characterised by TEM, XRD and UV-Visible and FTIR spectroscopy. UV-visible absorbance and fluorescence emission/ excitation spectroscopy and circular dichroism were performed to study the interaction of nanoparticles with Hb. Results: UV-visible absorbance spectroscopy showed no blue or red shift of absorption peaks. Benesi-Hildebrand curves for the amino acid band and soret band of Hb absorbance spectrum were straight lines with positive intercepts; apparent binding constants and Gibbs free energy change were within a moderate level; they were larger for amino acid band in the presence of CFe3O4NPs, and for soret band in the presence of Fe3O4NPs, but noticeably small for both bands in the presence of BFe3O4NPs. Fluorescence emission/excitation spectra showed no noticeable shift of emission/excitation peak position of Hb in the presence of the three nanoparticles. Multiple peak fitting, done for the L-peak of the excitation spectrum of Hb, showed a major increase in the percentage of peak area of Tyr in the presence of CFe3O4NPs. Circular dichroism measurement showed that CFe3O4NPs, Fe3O4NPs and BFe3O4NPs reduced the α-helix content of Hb in decreasing order. Conclusion: Ground state complex formation of human hemoglobin with the studied nanoparticles with 1:1 stoichiometric ratio is suggested. Moreover, it has been observed that CFe3O4NPs may have a stronger interaction with the amino acid group while bare Fe3O4NPs may have a stronger interaction with the heme group of Hb. Hinderance of the energy transfer from tyrosine to tryptophan of Hb in the presence of CFe3O4NPs is also suggested. CFe3O4NPs may also have some effect on the secondary structure of Hb as indicated through reduction of the α-helix content. BFe3O4NPs have shown very weak interaction with Hb in the UV-visible absorbance spectroscopy, fluorescence emission/excitation spectroscopy and circular dichroism experiment.