Influence of pH on the Spectral-Luminescent Characteristics of the Soft Protein Crown of Silver Nanoparticles

The spectral and fluorescent characteristics of bovine serum albumin (BSA) molecules in the soft crown of silver nanoparticles (Ag-NPs) were studied at various pH values. The formation of BSA + Ag-NP complexes was established. The association constants of the complex (Kas) and the bimolecular rate constants of the BSA fluorescence quenching (Kq) were determined for various pH values. The dependences of Kas and Kq on pH were nonmonotonic with maxima at pH 6.0. The number of binding sites (Hill coefficient n) and the thickness of the BSA soft crown (Δd) were also maximal at pH 6.0. These parameters decreased at higher and lower pH values (relative to pH 6.0). Variations in the interaction parameters of BSA and Ag-NPs were due to changes in the conformational modifications of the protein (content of α-helices) and the microenvironment of Tyr and Trp protein residues in the soft crown (hydrophobicity of the protein).