The interaction between bovine hemoglobin (BHb) and Ag nanoparticles (Ag NP) has been investigated by ultraviolet-visible, fluorescence, synchronous fluorescence, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopies. The decrease and red shift of 415-nm surface plamon band of Ag NP indicate that the BHb can be adsorbed on the surface of Ag NP. The Soret band was decreased gradually with the increased amount of Ag NP, suggesting the detachment of some heme chromophores from their matrixes in BHb. The fluorescence intensity of BHb was quenched by Ag NP, and the analysis of Stern-Volmer equation reveals that the mechanism may be a static quenching procedure. The binding constant K was obtained with calculation of the spectral data, and the order of magnitude of K was found to be 10⁹～10¹⁰. The blue shift of synchronous fluorescence spectra reveals that the microenvironments around tryptophan and tyrosine residues were disturbed by Ag NP, to make the residues buried inside the hydrophobic cavities. The calculation of far-UV CD data showed that the secondary structure of BHb had slight changes, and the α-helical content was decreased. In addition, the FTIR spectra could provide the evidence that the sulphur atoms of cysteine residues, carboxyl oxygen, and nitrogen atoms of peptide or residues probably have the direct chemical bonds to surface of Ag NP.

Key words: hemoglobin, Ag nanoparticle, conformational change, microenvironment, bond to surface