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Colloidal silver has been formed either by irradiation with 253.7 nm light or by chemical reduction of AgClO4 in the presence of protective agents such as poly(vinylpyrrolidone), carboxy methyl cellulose, and gelatin. The particles were characterized by their absorption maximum and transmission electron micrographs. Peptization effect was observed in the presence of photosensitive benzophenone. Surface modification studies of silver particles in the presence of various complexing agents, viz., N-(hydoxyethyl)-ethylenediaminetriacetic acid, iminodiacetic acid, nitrilotriacetic acid, 2-mercaptobenzimidazole, benzotriazole, 5-aminotetrazole, imidazole, and sanazole were carried out and it was shown that the reactivity of silver particles increases in their presence. However, in the presence of stabilizers, due to competitve reactions, partial recovery of the surface plasmon absorption band was observed. The Fermi potential of surface modified silver particles seems to lie in the range of -0.40 ( 0.05 V.

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Highly stable poly(N-vinyl-2-pyrrolidone) (PVP) protected copper nanoparticles were prepared using a simple chemical reduction route in different solvents {N, N-dimethyl formamide (DMF) and formamide (FA)} under aerated condition. The particles were characterized using TEM, SEM, XRD, and UV−visible spectroscopic techniques. Copper nanostructures of varying shapes and sizes were obtained using hydrazine hydrate as the reducing agent in both DMF and FA. However, reducing by ascorbic acid in FA leads to formation of mostly spherical copper nanoparticles with a narrow size distribution. The Cu nanoparticles serve as effective catalyst for 1,3-dipolar cycloaddition reactions between terminal alkynes and azides to synthesize 1,2,3-triazoles in excellent yields under mild reaction conditions. The nanocatalysts can be recycled and reused several times without significant loss of their catalytic activity.

The protective bioactivity of punicalagin, a high molecular weight polyphenol isolated from pomegranate fruit pith and carpellary membrane, against oxidative damages to lipids, amino acids constituting the proteins, and guanosine as a model for DNA has been investigated. The ABTS*-, guanosine, and tryptophan radical generated pulse radiolytically were repaired by punicalagin, k = (0.9-15) x 10(7) dm3 mol-1 s-1. The results are rationalized on the basis of the scavenging activity of punicalagin against various one-electron oxidizing radicals, namely, .OH, N3., and NO2. . The formation of the transient species in these reactions and the rate constants of the scavenging reactions have been probed using a time-resolved kinetic spectrophotometric technique. The antioxidant action of punicalagin is expressed not only through its scavenging reactions but also by its ability to form metal chelates. Binding of punicalagin with bovine serum albumin and metal ions such as iron and copper revealed different binding affinities, whereas its binding with DNA was very weak and nonspecific. In vitro cytotoxic studies against three cell lines, namely, Vero (normal African green monkey kidney cell line), Hep-2 (human larynx epithelial cancer cell line), and A-549 (human small cell lung carcinoma cell line) showed that this polyphenol is toxic only at higher concentration.

Silver nanosized crystallites have been synthesized in aqueous and polyols viz., ethylene glycol and glycerol, using a microwave technique. Dispersions of colloidal silver have been prepared by the reduction of silver nitrate both in the presence and absence of stabilizer poly(vinylpyrolidone) (PVP). It was observed that PVP is capable of complexing and stabilizing Ag nanoparticles formed through the reduction of Ag + ions in water and ethylene glycol. In the case of ethylene glycol, it has been shown that the use of PVP leads to particles with a high degree of stability. The colloids are stable in glycerol for months even in the absence of stabilizer.

Radiolytic reduction of silver ions and the subsequent formation of silver clusters were studied in aqueous gelatin solutions and are compared with the parallel processes in aqueous solutions. The presence of gelatin in the solution affects the early processes, via complexation of&+ ions with the amino acid moieties ofthe gelatin. The ratio of&+ to gelatin chains predetermines the kinetic consequences to the agglomeration processes. This ratio may accelerate or inhibit any of the processes that involve silver ions (reduction as well as growth). The complexation reduces somewhat the rate ofreduction by hydrated electrons. However, when all the ions are complexed to the gelatin, the agglomeration may become very fast; at the extreme the agglomeration rate is determined by the rate of reduction. Some of the small AgQm+ bind to the gelatin stronger than Ag+ ions. Excess silver ions enhance the stability of smaller transient clusters in the presence of gelatin. Three long-lived aggregates of different sizes are stabilized by the gelatin upon complete reduction of the silver ions.

Pt, Pd, Pt-Ag and Pd-Ag bimetallic nanoparticles were synthesized in ethylene glycol and glycerol using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It has been observed that PVP is capable of complexing and stabilizing nanoparticles. Mixed clusters were formed by simultaneous reduction of the metal ions. The clusters were characterized using UV-Vis spectra, XRD and dynamic light scattering. To understand the mechanism of formation of mixed nanoparticles, several experimental parameters such as in situ irradiation of mixed metal salts and mixing of individual sols were attempted.