3,5-dimethyl-4-amino-1,2,4-triazole (Dat) as a tridentate ligand in the polymeric cations of [Ag-3(Dat)(2)](NO3)(3)

Colourless single crystals of [Ag-3(Dat)(2)](NO3)(3) were obtained from a reaction of silver(l) nitrate and 3,5-dimethyl-4-amino-1,2,4-triazole (Dat). In the crystal structure (orthorhombic, Fdd2, Z = 8, a = 1100.1(2), b = 3500.3(2), c = 1015.4(3) pm, R, = 0.0434) there are two crystallographically non-equivalent silver sites in a one (Ag1) to two ratio (Ag2). Both resemble linear N-Ag-N coordination although angles are 163 degrees and 144 degrees, respectively Each Dat ligand coordinates with the two ring nitrogen atoms at 216 to 219 pm and with one amino-nitrogen atom at 229 pro. According to the composition [Ag-3(Dat)(2)](3+) = [(Dat)Ag-3/2](3+), a polymeric structure is built with all Ag+ ions bridging.

Structure of Adenine on Metal Nanoparticles: pH Equilibria and Formation of Ag+ Complexes Detected by Surface-Enhanced Raman Spectroscopy

The SERS spectra of adenine recorded under a broad range of pH values and concentrations using both silver and gold colloids provided evidence for the existence of several distinct species. At high concentration (0.5-10 ppm), the spectra recorded between pH 1 and 11 showed only two distinct spectra, rather than the three forms that would be expected for a compound with two pK(a) values of 4.2 and 9.8. The spectra at neutral and alkaline pH were identical and assigned to the deprotonated form of adenine on the basis of DFT calculations, isotope shifts, and comparison with the normal Raman spectra of neutral and deprotonated adenine. The spectra at acidic pH were different, consistent with adenine protonation. Neutral adenine was not detected at any pH studied. At low adenine concentration (

Characterization of novel Ag on TiO2 films for surface-enhanced Raman scattering

Novel Ag on TiO₂ films are generated by semiconductor photocatalysis and characterized by ultraviolet-visible (UV/Vis) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM), as well as assessed for surface-enhanced Raman scattering (SERS) activity. The nature and thickness of the photodeposited Ag, and thus the degree of SERS activity, is controlled by the time of exposure of the TiO₂ film to UV light. All such films exhibit the optical characteristics (λ_max ≅ 390 nm) of small (<20 nm) Ag particles, although this feature becomes less prominent as the film becomes thicker. The films comprise quite large (>40 nm) Ag islands that grow and merge with increasing levels of Ag photodeposition. Tested with a benzotriazole dye probe, the films are SERS active, exhibiting activity similar to that of 6-nm-thick vapordeposited films. The Ag/TiO₂ films exhibit a lower residual standard deviation (∼25%) compared with Ag vapor-deposited films (∼45%), which is, however, still unacceptable for quantitative work. The sample-to-sample variance could be reduced significantly (<7%) by spinning the film during the SERS measurement. The Ag/TiO₂ films are mechanically robust and resistant to removal and damage by scratching, unlike the Ag vapor-deposited films. The Ag/TiO₂ films also exhibit no obvious loss of SERS activity when stored in the dark under otherwise ambient conditions. The possible extension of this simple, effective method of producing Ag films for SERS, to metals other than Ag and to semiconductors other than TiO₂, is briefly discussed. 

Controlling the Sulfur Poisoning of Ag/Al2O3 Catalysts for the Hydrocarbon SCR Reaction by Using a Regenerable SOx Trap

The deactivation of a silver-based hydrocarbon selective catalytic reduction catalyst by SOx and the subsequent regeneration under various operating conditions has been investigated. Using a sulfur trap based on a silica-supported catalyst it was found that, for a Ag/SiO2 + Ag/Al2O3 combination, the negative effect of SO2 on the n-octane-SCR reaction can be eliminated under normal operating conditions. The trap can be regenerated by hydrogen at low temperatures or at higher temperatures using a hydrocarbon reductant.

The effect of photo-oxidation on the sticking and reactivity of Ag on amorphous GeS2

Photo-oxidation of amorphous GeS2 films illuminated by band-gap radiation drastically alters the growth mode and reactivity of subsequently deposited Ag. In the former case (monolayer/simultaneous multilayer growth) the Ag reacts with both Ge and S sites. In the latter case (Stranski-Krastanov growth) Ge sites are selectively oxidized and film growth proceeds by Ag nucleation at the unoxidized S sites. The behaviour is very different from that reported earlier for Zn deposition on GeS2, where photo-oxidation results in very large changes in metal sticking probability. XPS, XAES and EXAFS data provide the basis for understanding both this phenomenon and the very different photodiffusion behaviour of Zn and Ag in GeS2.

A PCR-based method to characterise and identify benzimidazole resistance in Helminthosporium solani

Control of Helminthosporium solani, the cause of silver scurf in potato tubers, has been impaired by selection of benzimidazole-resistant strains as a result of repeated use of the fungicide thiabendazole. Identification of thiabendazole-resistant strains of H. solani by conventional techniques takes several weeks. Primers designed from conserved regions of the fungal beta-tubulin gene were used to PCR amplify and sequence a portion of the gene. A point mutation was detected at codon 198 in thiabendazole-resistant isolates causing a change in the amino acid sequence from glutamic acid to alanine or glutamine. Species-specific PCR primers designed to amplify this region were used in conjunction with a restriction endonuclease to cause cleavage in sensitive isolates only and thus provide a rapid diagnostic test to differentiate field isolates.

Preaggregated Ag Nanoparticles in Dry Swellable Gel Films for Off-the-Shelf Surface-Enhanced Raman Spectroscopy

Large, thin (50 mu m) dry polymer sheets containing numerous surface-enhanced Raman spectroscopy (SERS) active Ag nanopartide aggregates have been prepared by drying aqueous mixtures of hydroxyethylcelloulose (HEC) and preaggregated Ag colloid in 10 x 10 cm molds. In these dry films, the particle aggregates are protected from the environment during storage and are easy to handle; for example, they can be cut to size with scissors. When in use, the highly swellable HEC polymer allowed the films to rapidly absorb aqueous analyte solutions while simultaneously releasing the Ag nanoparticle aggregates to interact with the analyte and generate large SERS signals. Either the films could be immersed in the analyte solution or 5 mu L droplets were applied to the surface; in the latter method, the local swelling caused the active area to dome upward, but the swollen film remained physically robust and could be handled as required. Importantly, encapsulation and release did not significantly compromise the SERS performance of the colloid; the signals given by the swollen films were similar to the very high signals obtained from the parent citrate-reduced colloid and were an order of magnitude larger than a commercially available nanoparticle substrate. These "Poly-SERS" films retained 70% of their SERS activity after being stored for 1 year in air. The films were sufficiently homogeneous to give a standard deviation of 3.2% in the absolute signal levels obtained from a test analyte, primarily due to the films' ability to suppress "coffee ring" drying marks, which meant that quantitative analysis without an internal standard was possible. The majority of the work used aqueous thiophenol as the test analyte; however, preliminary studies showed that the Poly-SERS films could also be used with nonaqueous solvents and for a range of other analytes including theophylline, a therapeutic drug, at a concentration as low as 1.0 x 10(-5) mol dm(-3) (1.8 mg/dm(3)), well below the sensitivity required for theophylline monitoring where the target range is 10-20 mg/dm(3).