Preparation Of Silver Nanoparticles With Optical Activity Induced By Small Chirality Molecules

In this paper, silver nanoparticles were produced by chemical reduction and photochemical reduction method in solution, respectively. The chirality transfer route and the chirality mechanisms of the prepared silver nanoparticles were discussed.Histidine, one of the essential amino acids for human body, was chose as chiral inducer and stabilizer for the preparation of histidine capped Ag nanoparticles by the reduction of AgNO3 with fresh NaBH4. The prepared Ag nanoparticles were characterized by UV-Vis spectrometer, circular dichroism spectrometer(CD) and transmission electron microscopy(TEM). Influences of the molar ratios of histidine to Ag+, pH values of the solution on the sizes and absorption spectra of the prepared Ag nanoparticles were studied. Monodispered spherical Ag nanoparticles(10 nm in diameter) were prepared when the molar ratio of D, L-histidine to Ag+ was 5:1 and the pH value of the solution was 11.5. The circular dichroism spectra of the silver nanoparticles are greatly influenced by the molar ratios of histidine to Ag+. With the increase of molar ratio the chirality signals are enhanced gradually and new Cotton effect peak appeared in the long wavelength region. In order to cause silver nanoparticles to aggregate, different concentrations of sodium chloride solution were added into the aqueous solution. The stability of Ag nanoparticles prepared by this method was studied.By using deoxycholate sodium(Na Dc) as chiral inducer and stabilizer, NaDc-capped silver nanoparticles in aqueous solution were synthesized by the chemical reduction of AgNO3 with fresh NaBH4 when the pH value of the solution was 5.0 and the solution was aged for 24 hours. The obtained silver nanoparticles have a diameter of around 8 nm. Because of the supramolecular interaction, NaDc-capped Ag nanoparticles aggregated and adsorbed onto the surface of the rodlike NaDc aggregations to form a special organic/inorganic composite structure. CD signals in SPR area emerges as split Cotton effect due to the interaction of Ag nanoparticles adsorbed on the surface of NaDc aggregations. The circular dichroism spectra of the silver nanoparticles are greatly influenced by the pH value of the solution. With the decrease of pH value the chirality signals of the Ag nanoparticles are enhanced gradually.By using photochemical reduction method, silver nanoparticles were prepared through the reduction of precursor silver nitrate under the UV light irradiation by using deoxycholate sodium as chiral inducer and stabilizer. The reduced elemental silver were aggregated to form nanoparticles, meanwhile NaDc molecules in the solution were oxidized. The experimental results indicate that with the increase of pH value, the speed of UV light chemical reduction increases markedly. At the same time CD signals enhance gradually with the increase of the reduction time.