The Preparation Of Noble Metal Nano-colloidal Solutions And The Study Of CD Spectra

Noble metal nanoparticles exhibit interesting optical properties due to their unique surface plasmon resonance?SPR?. As confirmed by various studies, surface modification by chiral functional molecules can induce the chirality of noble metal nanoparticles in the surface plasmon resonance region. Chiral noble metal nanomaterials have attracted great interest in recent years because of their potential applications in chiral catalysis, chiral discrimination4 and high-sensitive detection.Gold and silver nanoparticles with optical properties were prepared by liquid chemical reduction and photochemical reduction in the presence of chiral small molecules as chiral inducer and stabilizer. The CD spectra of prepared gold and silver nanoparticles were investigated and the origin of optical activities was discussed.Na DC-capped silver NPs were prepared with AgNO₃ as precursor in the presence of sodium deoxycholate as a chiral inducer by the chemical reduction method. Ag NPs prepared at p H 7 were well dispersed without aggregation and displayed a plasmonic band centered at 387 nm in the absorption spectrum. The CD spectrum exhibit a strong positive Cotton Effect at 380 nm which is associated with the surface plasmon resonance?SPR? of the silver NPs. Lowering the p H value of the reaction solution facilitate the aggregation of the obtained silver NPs. Two peaks at 406 nm and 474 nm were observed for silver NPs prepared at the p H below the p Ka value of Na DC. The CD spectrum exhibits complex CD signal with two postive Cotton effects at 390 nm and 543 nm and a negative Cotton effect at 469 nm. The splitting in absorption and CD spectra is due to the plasmonic coupling between the adjacent NPs in the aggregates. The concentrations of AgNO₃ have an influence on the resulted CD signals. The aggregation level of silver NPs is enhanced by the increasing the concentration of AgNO₃. The CD band at the longer wavelength exhibits a red shift because of the strong plasmonic coupling between adjacent Ag NPs in the aggregates.L-Histidine capped silver nanoparticles were synthesized by the liquid-phase chemical reduction method in the presence of L-Histidine as a reducing agent and chiral inducer. The prepared Ag nanoparticles were characterized by UV-vis Spectrometer, Transission Electron Microscopy?TEM? and circular dichroism spectrometer?CD?. The absorption spectra of the as-synthesized yellow silver colloids display an intense peak centered at 402 nm with a full width at half maximum?FWHM? of 64 nm, which is associated with the surface plasmon resonance?SPR? of the silver nanoparticles. The result of TEM shows that the prepared yellow colored Ag nanoparticles are monodispersed with the average diameter of about 9 nm. The results of CD spectra show that the yellow colored Ag nanoparticles exhibit chiral signals with negative Cotton Effects in the region of surface plasmon resonance?SPR?. The CD signal of the aggregated Ag nanoparticles displays different CD feature from that of monodispersed Ag nanoparticles, which shows bisignated CD couplets with two opposite Cotton effects at shorter wavelength and longer wavelength in the region of SPR, respectively. The splitting of CD signal is due to the plasmonic coupling between the aggregated Ag nanoparticles under light irradiation, which results in the splitting of the energy levels of excited states.Using 2-?4-hydroxyphenyl-azo? benzoic acid?AZO? as template molecule, AZO/gold nanoparticle composite structures were prepared. The aggregates of organic small molecule AZO were prepared through precipitation method. The circular dichroism of AZO template prepared was investigated by changing the experiment conditions. Gold nanoparticles were prepared by two methods. By liquid phase chemical reduction method, gold nanoparticles were synthesized with CTAB as a stabilizer and Na BH4 as a reducing agent. Gold nanoparticles were prepared by photochemical reduction of HAu Cl4 under ultraviolet irradiation using Na DC as stabilizer and reducing agent. AZO/gold nanoparticles composite structures were fabricated by mixing gold nanoparticles and azobenzene templates. The circular dichroism of the composite structures was studied.