Circular dichroism study of chiral biomolecules conjugated with silver nanoparticles

Abstract

Chiral biomolecules conjugated with silver nanoparticles were investigated by circular dichroism (CD) spectrophotometer. Silver nanoparticles were prepared by citrate reduction method and gamma-irradiation method, and were characterized by Ultraviolet (UV)-visible spectrophotometer, X-ray diffractometer (XRD) and transmission electron microscopy (TEM). Conjugation of thiol group-containing biomolecules, such as cysteine, glutathione, and penicillamine, with silver nanoparticles resulted in the generation of new characteristic CD signals in the region of 240-400 nm, whereas no CD signal changes were found with lysine or glutamine. Association through hydrogen bonding among the biomolecules is considered to be essential for the CD signal generation, which was confirmed by the experiment with cysteine methyl ester. The chiral biomolecules (such as cysteine)-capped silver nanoparticles were also characterized by UV-vis spectrophotometer, XRD and Fourier-Transform Infra-Red (FT-IR). Interestingly, gold nanoparticles were not found to generate CD signals in the wavelength region tested, indicating that this phenomenon is a unique feature of silver nanoparticles, distinguished from gold nanoparticles.