The physical and chemical properties of silver nanoparticles that are responsible for their antimicrobial activities have been studied with spherical silver nanoparticles (average diameter approximately 9 nm) synthesized by the borohydride reduction of Ag+ ions, in relation to their sensitivity to oxidation, activities towards silver-resistant bacteria, size-dependent activities, and dispersal in electrolytic solutions. Partially (surface) oxidized silver nanoparticles have antibacterial activities, but zero-valent nanoparticles do not. The levels of chemisorbed Ag+ that form on the particle's surface, as revealed by changes in the surface plasmon resonance absorption during oxidation and reduction, correlate well with the observed antibacterial activities. Silver nanoparticles, like Ag+ in the form of AgNO3 solution, are tolerated by the bacteria strains resistant to Ag+. The antibacterial activities of silver nanoparticles are related to their size, with the smaller particles having higher activities on the basis of equivalent silver mass content. The silver nanoparticles aggregate in media with a high electrolyte content, resulting in a loss of antibacterial activities. However, complexation with albumin can stabilize the silver nanoparticles against aggregation, leading to a retention of the antibacterial activities. Taken together, the results show that the antibacterial activities of silver nanoparticles are dependent on chemisorbed Ag+, which is readily formed owing to extreme sensitivity to oxygen. The antibacterial activities of silver nanoparticles are dependent on optimally displayed oxidized surfaces, which are present in well-dispersed suspensions.

Wound healing is a complex process and has been the subject of intense research for a long time. The recent emergence of nanotechnology has provided a new therapeutic modality in silver nanoparticles for use in burn wounds. Nonetheless, the beneficial effects of silver nanoparticles on wound healing remain unknown. We investigated the wound-healing properties of silver nanoparticles in an animal model and found that rapid healing and improved cosmetic appearance occur in a dose-dependent manner. Furthermore, through quantitative PCR, immunohistochemistry, and proteomic studies, we showed that silver nanoparticles exert positive effects through their antimicrobial properties, reduction in wound inflammation, and modulation of fibrogenic cytokines. These results have given insight into the actions of silver and have provided a novel therapeutic direction for wound treatment in clinical practice.

An efficient method has been developed for the chemoselective cysteine modification of unprotected peptides and proteins in aqueous media through the formation of a vinyl sulfide linkage by using electron-deficient alkynes, including alkynoic amides, esters and alkynones. The terminal alkynone-modified peptides could be converted back into the unmodified peptides (81% isolated yield) by adding thiols under mild conditions. The usefulness of this thiol-assisted cleavage of the vinyl sulfide linkage in peptides has been exemplified by the enrichment of a cysteine-containing peptide (71% recovery) from a mixture of cysteine-containing and non-cysteine-containing peptides.

Impregnation of hydroxyapatite with colloidal ruthenium results in the formation of a catalyst that effects cis‐dihydroxylation and oxidative cleavage of alkenes to their respective cis‐1,2‐diols and carbonyl products in good to excellent yields (see scheme). The supported ruthenium catalyst can be easily recycled and reused for consecutive reaction runs without significant deterioration of the catalytic activities. R1, R2=H, alkyl, aryl.

No abstract

Benzylic and allylic halides were conveniently oxidized to aldehydes and ketones by pyridine Noxide in the presence of silver oxide under mild conditions. Aldehydes and ketones, especially aromatic and α,β-unsaturated carbonyl compounds, are important classes of chemicals. Methods for direct conversion of halides to carbonyl compounds have been reviewed. 1,2 Dimethyl sulfoxide (DMSO) is often employed as the oxygen donor. 3,4 However, high temperature is usually required. 3,4 Oxidations involving amine oxides have also been reported. [5][6][7] In our attempt to modify carbohydrates with benzylic halides, we have found that pyridine N-oxide can effectively and conveniently oxidize benzylic and allylic halides to aromatic and α,β-unsaturated carbonyl compounds, respectively, in the presence of silver oxide (Ag 2 O) under mild conditions. 8,9The reactions were carried out in acetonitrile (toluene and tetrahydrofuran gave much lower yield). The reaction mechanism should be identical to that proposed for the reaction with DMSO and base, as shown in Scheme 1. 1,8 Half equivalent of silver oxide was utilized to facilitate the reaction. Silver oxide assists the heterolysis of the carbon-halogen bond in the substitution reaction with pyridine N-oxide. The resulting hydroxide ion from the reaction between silver oxide and halogen then functions as the base in the elimination reaction to produce the carbonyl group. When DMSO was employed instead of pyridine N-oxide as the source of oxygen, the reaction did not go to completion while giving a mixture of products.For most bromides, the reactions were conveniently carried out at room temperature. The reaction was complete in a few hours but was stirred overnight for convenience. For chlorides and some benzyl bromides with very strong electron-withdrawing substituents, slightly elevated temperature (50 °C) was required (Entries 4-7 and 12-15 in Table 1). For some chlorides, only partial conversion was observed (Entries 13 and 14). The substituent effects indicate a S N 1-like mechanism for the first step in the reaction pathway.The reaction workup was very simple. Upon completion of the reaction, sodium sulfate or magnesium sulfate was added and the resulting mixture was filtered through a thin layer of Celite. Concentration of the filtrate gave essentially pure product in quantitative yield. 10

The bis(azido)ruthenium (III) complexes, trans-[Ru(L)

Aldehydes Q 0320 Convenient Oxidation of Benzylic and Allylic Halides to Aldehydes and Ketones. -A reagent combination of pyridine N-oxide and silver oxide allows the convenient oxidation of the substrates to the corresponding carbonyl compounds. -(CHEN, D. X.; HO, C. M.; WU, Q. Y. R.; WU, P. R.; WONG, F. M.; WU*, W.; Tetrahedron Lett. 49 (2008) 26, 4147-4148; Dep. Chem. Biochem., San Francisco State Univ., San Francisco, CA 94132, USA; Eng.) -Mais 40-078