An increase in the resistance of R-phycoerythrin to thermal aggregation by silver nanoparticles synthesized in nanochannels of the pigment

Abstract

R-phycoerithrin, a water soluble photosynthetic pigment of red algae, was used as a matrix and a reducer for the synthesis of Ag⁰ nanoparticles. The diameter of dominating Ag⁰ nanoparticles determined from the electron microscope images was 6.5 ± 0.5 nm. Dynamic light scattering in the regime of heating with a constant rate showed that the hydrodynamic radius of R-phycoerithrin molecules began to increase at a temperature of more than 50°C. The hydrodynamic radius of R-phycoerithrin with Ag⁰ nanoparticles synthesized in the inner cavity remained constant upon heating to 90°C. It was shown by circular dichroism that the temperature at which the portion of the denatured protein reached 50% was 51.7 ± 0.1°C for R-phycoerithrin and 58.0 ± 0.1°C for R-phycoerithrin with synthesized Ag⁰ nanoparticles. This indicated that thermal stability of R-phycoerythrin increased when its cavity was filled with an Ag⁰ nanoparticle. According to the comparative spectral studies of R-phycoerythrin before and after the synthesis of Ag⁰ nanoparticles and the heat treatment, we conclude that an increase in thermal stability of R-phycoerythrin is caused by chemical intramolecular cross-linking of a protein molecule with an Ag⁰ nanoparticle.