Thionicotinamide-capped gold nanoparticles undergo fusion as well as fragmentation upon laser pulse excitation (532 nm). The aggregation effect which is induced by thionicotinamide also disappears following laser pulse excitation. The morphological changes induced by thermal and photochemical effects were found to influence the optical properties of these particles.Self-assembled monolayers (SAM) of organic compounds containing thio or amino functional groups provide a unique way to organize molecules and semiconductor nanoclusters on gold surfaces (see, for example, refs 1 and 2). Attempts have been made in recent years to modify gold nanoparticles with thio compounds. 3-8 Although recent efforts address the issues related to bulk SAM-gold surfaces, spectroscopic studies related to thio-capped gold nanoclusters 9-12 are rather limited. Interaction of thio compounds with gold nanoclusters in solution often leads to aggregation effects. Such an aggregation is noted by the appearance of a broad band in the red-infrared region. Recent laser-induced photochemical studies of metal nanoclusters have noted interesting photophysical properties such as transient plasmon bleaching, electron ejection, and photofragmentation. [13][14][15][16][17] We report here visible laser induced transformations of thionicotinamide gold nanoparticles and the spectral properties associated with changes in the morphology of these particles.Gold colloids were prepared by the conventional citric acid reduction of HAuCl 4 in water with sodium citrate at near-boiling temperature. 18 Surface modification of gold colloids was carried out by adding controlled amounts of thionicotinamide (TNA) to the ruby-colored colloidal gold suspension at room temperature. Transmission electron microscopic examination (TEM) was conducted by applying a drop of the colloid sample to a carbon-coated copper grid. Particle sizes were determined from the photographs taken at a magnification of 150 000 using a Hitachi H600 transmission electron microscope. The laser irradiation was carried out in a quartz cuvette (10 mm × 2 mm) with continuous N 2 bubbling. Laser irradiation experiments were performed using a mode-locked, Q-switched Continuum YG-501 DP Nd:YAG laser system (pulse width ∼ 18ps; λ ) 532 nm, output 1.5 mJ pulse). 17 The absorption spectra of gold nanoclusters in aqueous solutions before and after the complexation with thionicotinamide are shown in Figure 1 (spectra a and b, respectively). The native gold colloids exhibit a prominent surface plasmon band at 520 nm. At relatively high thionicotinamide concentrations the colloidal suspension turns blue and an absorption band in the red-infrared region (λ max ∼ 750 nm) appears. Such a broad band is indicative of aggregation and/or changes in the shape of gold nanoclusters. As indicated earlier, 19 the position of this Figure 1. (a) Absorption spectrum of 0.5 mM gold colloids in water.Absorption spectra of TNA-capped gold colloids (0.5 mM gold colloidal suspension containing 3 mM thionicotinamide) were recorded...

A mechanistic investigation on the photocatalytic reduction of CO2 with hexagonal CdS nanocrystallites prepared in N,N-dimethylformamide (DMF) was carried out from the standpoint of surface structures of the nanocrystallites. A remarkable increase of photocatalytic activity could be achieved by addition of excess Cd2+ to the system. Analysis of the emission behavior depending on the amount of excess Cd2+ in the system suggests that the Cd2+ addition results in the formation of sulfur vacancies on the surface of nanocrystallites due to the adsorption of excess Cd2+ to the surface. The formation of the sulfur vacancies on the surface was supported by in situ Cd K-edge EXAFS analysis of the nanocrystallites in solution as changes in the coordination numbers of cadmium−sulfur and cadmium−oxygen. Theoretical MO calculations using a density functional (DF) method supported the preferential bidentate-type absorption of CO2 with the Cd atom in the vicinity of the sulfur vacancy.

The major clearance mechanism of pravastatin, valsartan, and temocapril appears to be similar, and OATP1B1*1b is one of the determinant factors governing the interindividual variability in the pharmacokinetics of pravastatin and, possibly, valsartan and temocapril.