Search

The new heteroleptic paddlewheel complexes cis-[Rh2(μ-form)2(μ-np)2][BF4]2, where form = p-ditolylformamidinate (DTolF) or p-difluorobenzylformamidinate (Fform) and np = 1,8-napthyridyine, and cis-Rh2(μ-form)2(μ-npCOO)2 (npCOO- = 1,8-naphthyridine-2-carboxylate), were synthesized and characterized. The complexes absorb strongly throughout the ultraviolet (λmax = 300 nm, ε = 20 300 M-1 cm-1) and visible regions (λmax = 640 nm ε = 3500 M-1 cm-1), making them potentially useful new dyes with panchromatic light absorption for solar energy conversion applications. Ultrafast and nanosecond transient absorption and timeresolved infrared spectroscopies were used to characterize the identity and dynamics of the excited states, where singlet and triplet Rh2/form-to-naphthyridine, metal/ligand-to-ligand charge-transfer (ML-LCT) excited states were observed in all four complexes. The npCOO- complexes exhibit red-shifted absorption profiles extending into the near-IR and undergo photoinitiated electron transfer to generate reduced methyl viologen, a species that persists in the presence of a sacrificial donor. The energy of the triplet excited state of each complex was estimated from energy-transfer quenching experiments using a series of organic triplet donors (E(³ππ*) from 1.83 to 0.78 eV). The singlet reduction (+0.6 V vs Ag/AgCl) potentials, and singlet and triplet oxidation potentials (-1.1 and -0.5 V vs Ag/AgCl, respectively) were determined. Based on the excited-state lifetimes and redox properties, these complexes represent a new class of light absorbers with potential application as dyes for charge injection into semiconductor solar cells and in sensitizer-catalyst assemblies for photocatalysis that operate with irradiation from the ultraviolet to ***800 nm. [ABSTRACT FROM AUTHOR]

The results of studies of the reactivity of strained [1],[1]disilamolybdenocenophane toward zerovalent platinum complexes are reported. Whereas [Pt(PEt3)3] underwent clean insertion into both Si-Cispo bonds of the twofold-bridged molybdenocene, the reaction with the tricyclohexylphosphine analogue is considerably more complex. Thus, treatment of the molybdenum compound with 2 equiv of [Pt(PCy3)2] results in a trinuclear cluster. To gain insight into the mechanistic aspects, the reaction was performed in a 1:1 stoichiometry. Multinuclear NMR spectroscopy revealed the presence of different species in solution. Two constitutional isomers were identified by X-ray diffraction analyses, one presumably depicting an intermediate in the formation of the trinuclear cluster. The predominant isomer in solution was identified as the product of C-H oxidative addition to the platinum phosphine fragment. Its solid-state structure displays an unusual coordination mode of platinum, and structural parameters suggest the formulation as the s-complex of a Mo-Si bond. [ABSTRACT FROM AUTHOR]

Cerium incorporated iron oxide catalysts and a pure iron oxide catalytic material were prepared by the complexation technique and their catalytic performances were investigated for selective oxidation of H2S to elemental sulfur in a fixed-bed flow reactor. Ce−Fe mixed oxide catalyst having a Fe/Ce ratio of 1/1 (2Fe−2Ce) showed complete conversion and very high sulfur selectivity in the temperature range of 200−300 °C. Sulfur selectivity and stability of iron oxide catalyst was significantly enhanced by the incorporation of cerium into the catalyst structure. It was concluded that incorporation of ceria into the catalyst structure significantly improved the redox ability of the catalyst. [ABSTRACT FROM AUTHOR]

An important unmet experimental objective is to analyze local RNA structure in a way that is strictly governed by solvent accessibility. Essentially all chemical probes currently used to evaluate RNA (and DNA) structure via formation of stable covalent adducts employ carbon-based electrophiles, which undergo nucleophilic attack from limited spatial orientations and via highly polar transition states. Reaction by these classical electrophiles is therefore gated by both solvent accessibility and additional electrostatic factors. In contrast, silicon electrophiles react via their d-orbitals and consequently can undergo nucleophilic attack from many spatial orientations. In this work, we explore the use of silanes to react indiscriminately with RNA such that the primary factor governing reactivity is solvent accessibility. We show that N,N-(dimethylamino)dimethylchlorosilane (DMAS-Cl) reacts at the guanosine N2 position to yield a near-perfect measure (r ≥ 0.82) of solvent accessibility in an RNA with a complex tertiary structure. This silane-based chemistry represents a direct and quantitative approach for probing solvent accessibility at the base pairing face of guanosine in RNA. [ABSTRACT FROM AUTHOR]

The article reports that the scientists from the Massachusetts Institute of Technology have found a way to boost the amount of energy that nuclear reactors produce by 50 percent in the U.S. The scientist are able to boost the amount of energy by reconfiguring nuclear-fuel pellets into doughnuts. This new design will help lessen the risk of meltdown by cutting down the temperature at which reactors must be operated. Furthermore, the new design renders the spent fuel more proliferation-resistant. Some environmental groups are rethinking the value of the design because it is an energy source free from greenhouse-gas emissions.