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

Abstract

The spectral and fluorescent characteristics of bovine serum albumin (BSA) molecules in the soft crown of silver nanoparticles (AgNP) were studied at different pH values. The formation of BSA + AgNP complexes was established. The coupling constants of the complex (K_ass) and the biomolecular rate constants of the BSA fluorescence quenching (K_q) were determined for different pH values. The dependences of K_ass and K_q on pH are nonmonotonic with maxima at pH 6.0. The number of binding sites (Hill coefficient (n)) and the thickness of the BSA soft crown (Dd) are also maximal at pH 6.0. At higher and lower pH values (relative to pH 6.0), these parameters decrease. Variations in the parameters of interaction between BSA and AgNP are due to changes in the conformational modifications of the protein (content of the a-helix) and the microenvironment of Tyr and Trp protein residues in the soft crown (hydrophobicity of the protein).