The reaction of a variety of sulphur nucleophiles [thiourea, S-ethyl mercaptoethylamine (EMEA), glutathione (GSH), dimethylsulphoxide (DMSO) and methionine] with the platinum(II) complex [Pt(dien)Cl]+ has been studied at 25°C using the nucleophiles in large excess. The measurements confirm that the sulphur nucleophiles react directly with the platinum complex and that the solvolytic pathway makes little contribution to the reaction. The reactions were monitored by a combination of conductometric and spectrophotometric methods. The oxygen and nitrogen nucleophiles water and imidazole respectively have also been studied. Reagents such as thiourea, EMEA, methionine and glutathione are some 101–102 more reactive than the nitrogen nucleophile imidazole and some 102–103 more reactive than oxygen nucleophile. In a direct competition between sulphur (kS) and nitrogen (kN) nucleophiles for the platinum substrate, as will occur under biological conditions, the kS/kN ratio is at least 10 so that little of the nitrogen-substituted product will be formed in the reaction. 相似文献
Waste cleanup efforts underway at the United States Department of Energy’s (DOE) Savannah River Site (SRS) in South Carolina,
as well as other DOE nuclear sites, have created a need to characterize 79Se in radioactive waste inventories. Successful analysis of 79Se in high activity waste matrices is challenging for a variety of reasons. As a result of these unique challenges, the successful
quantification of 79Se in the types of matrices present at SRS requires an extremely efficient and selective separation of 79Se from high levels of interfering radionuclides. A robust 79Se radiochemical separation method has been developed at the Savannah River National Laboratory (SRNL) which is routinely
capable of successfully purifying 79Se from a wide range of interfering radioactive species. In addition to dramatic improvements in the Kd, ease, and reproducibility of the analysis, the laboratory time has been reduced from several days to only 6 h. 相似文献
Custom built : A promising new approach towards more efficient self‐assembled cage receptors through computer‐aided design is demonstrated. The resulting M4L6 tetrahedral cage, internally functionalized with accurately positioned urea hydrogen‐bonding groups (see structure; yellow: predicted, blue: experimental, space‐filling: SO42?), proved to be a remarkably strong sulfate receptor in water.
Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide), the lead bioreductive drug with selective toxicity for hypoxic cells in tumors, is thought to act by forming an active oxidizing radical of high one-electron reduction potential, E(1), when reduced by reductases. It has a dual mechanism of action, both generating DNA radicals, following its one-electron reduction and subsequently oxidizing these DNA radicals to form labile cations or hydrolyzable lactones through transferring an O atom, resulting in DNA strand breaks. These parallel secondary reactions have been proposed to be also initiated by its two-electron reduced metabolite, the 1-oxide. We have used pulse radiolysis to show that the benzotriazinyl radical of a highly soluble analogue of tirapazamine, the 3-(N,N-dimethyl-1,2-ethanediamine) analogue, is able to oxidize tirapazamine itself. We have found that both tirapazamine and the 1-oxides are in equilibrium with their respective benzotriazinyl radicals, with high concentrations of the more soluble 1-oxide maintaining a high concentration of the more reactive oxidizing radical of tirapazamine. The one-electron reduction potentials, E(1), of the 1-oxides and related compounds have been measured and, together with the E(1) values of tirapazamine and the 2-nitroimidazole radiosensitizer, misonidazole, are shown to predict the published percentages of electron transfer. This radical chemistry study gives an insight into the mechanisms of the potentiation of radical damage, reported for DNA, that underlies the hypoxic cytotoxicity of electron affinic compounds. The E(1) values of the benzotriazinyl radicals of the benzotriazine compounds govern the position of the redox equilibria, which determine the amount of initial radical damage. The E(1) values of the 1,4-dioxides and 1-oxide compounds govern the degree of potentiation of the initial radical damage once formed. 相似文献
This paper presents a computational approach to the deliberate design of improved host architectures. De novo molecule building software, HostDesigner, is interfaced with molecular mechanics software, GMMX, providing a tool for generating and screening millions of potential structures. The efficacy of this computer-aided design methodology is illustrated with a search for bisurea podands that are structurally organized for complexation with tetrahedral oxoanions. 相似文献