Use of allene in 1,3-dipolar addition to a carbonyl ylide: syntheses of 3-hydroxy-cis-nemorensic acid and nemorensic acid

1,3-Dipolar addition of allene to the carbonyl ylide derived from 6-diazoheptane-2,5-dione is the key step in syntheses of 3-hydroxy-cis-nemorensic acid and nemorensic acid.     

Iridium luminophore complexes for unimolecular oxygen sensors

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(2)(vacac), 1, Ir(ppy)(2)(vacac), 2, fac-Ir(ppy)(2)(vppy), 3, and mer-Ir(ppy)(2)(vppy), 4, where C6 = Coumarin 6, vacac = allylacetoacetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl)pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D ((1)H, (13)C) and 2-D ((1)H-(1)H, (1)H-(13)C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (tau = 6.0 micros, phi = 0.22 for 1; tau = 0.4 micros, phi = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.     

Absorption kinetics of uranium tri-n-butyl phosphate in the rat: Implications for occupational exposure

The absorption kinetics for uranium into blood after deposition as tri-n-butylphosphate (UTBP) in the rat lung were combined with human data on particle deposition and clearance from the ICRP Publication 66 respiratory tract model and information from the most recent ICRP biokinetic model for uranium to predict the consequences for exposure of workers. These predictions suggest that, (1) the biokinetics of UTBP are similar to those for a Type F compound as defined by ICRP, (2) the dose coefficient is essentially independent of the aerosol size and isotopic composition, (3) the mass of uranium equivalent to the ALI can vary by 13 fold depending upon the isotopic composition, (4) intakes of uranium as UTBP other than chronic intakes as highly enriched forms should be restricted on the basis of the chemical toxicity of uranium, (5) the assessment of intake by urine bioassay measurements should be interpreted with caution unless the exposure conditions are well defined and (6) severe kidney damage is unlikely at intakes corresponding to the ALI or daily limit.     

Biogeological Raman spectroscopic studies of Antarctic lacustrine sediments

Analysis of lacustrine sediments is an accepted method for deciphering the palaeoenvironment of a lake's catchment area, as each strata of the sediment gives information about the rock type it was eroded from and also the state of the lake, i.e. oxic or anoxic. Antarctica has long been accepted as a putative analogue for Mars, so the analysis of Antarctic material may give results that can be compared to sediments on Mars. Raman spectroscopy has been selected as the method of analysis as it does not destroy the sample, can be used in situ and requires very little sample preparation. It is a suitable method for analysing both inorganic and organic matter and a miniature spectrometer is currently being developed for use in the field. The results from the spectrometers can serve as a guide for analysing sediments on Mars. It has been shown that Raman spectroscopy can detect and differentiate between oxic and anoxic sediments. Both 1064 and 785 nm wavelengths are suitable for laser excitation of organic and inorganic matter.     

Abstraction Versus Electrophilic Substitution: Metaphosphate-Mediated Reactions in the Gas Phase

Abstract

Whereas arylmetaphosphates (ArOPO₂) tend to cyclise by intramolecular C-H insertion (phosphorylation) when generated in the gas phase, their alkyl-substituted counterparts exhibit non-electrophilic behaviour and give rise to alkenes by an unusual 1,2-methyl shift induced by a combination of hydrogen abstraction with concomitant elimination of metaphosphoric acid (HOPO₂).     

On key factors for the fabrication of mesoporous tungsten oxide films from tungstic acid

Thermally stable mesoporous tungsten oxide films (TOFs) were prepared by surfactant templated sol–gel method using tungstic acid as tungsten oxide source. Influence of various experimental conditions on the obtained mesostructures was investigated, including the solvent compositions, addition of hydrogen peroxide, substrates, and aging time, heat treatment, etc. It has been found that the addition of hydrogen peroxide has a significant influence on the flexibility of formed meso-frameworks, and just a small amount can regenerate the degraded coating sol. TOFs were also found to crystallize on ITO coating easier than on bare glass, indicating that the different interactions with the substrates influence the crystallinity of obtained meso-structured TOFs. Film thickness can be adjusted by simply changing the solvent compositions while keeping mesostructures intact. This work clarified several key parameters in delivering well-defined mesostructured TOFs from cheap, moisture-insensitive tungstic acid precursor via the process developed.     

Bis(μ-oxo) dicopper(III) species of the simplest peralkylated diamine: enhanced reactivity toward exogenous substrates

N,N,N',N'-tetramethylethylenediamine (TMED), the simplest and most extensively used peralkylated diamine ligand, is conspicuously absent from those known to form a bis(μ-oxo)dicopper(III) (O) species, [(TMED)(2)Cu(III)(2)(μ(2)-O)(2)](2+), upon oxygenation of its Cu(I) complex. Presented here is the characterization of this O species and its reactivity toward exogenous substrates. Its formation is complicated both by the instability of the [(TMED)Cu(I)](1+) precursor and by competitive formation of a presumed mixed-valent trinuclear [(TMED)(3)Cu(III)Cu(II)(2)(μ(3)-O)(2)](3+) (T) species. Under most reaction conditions, the T species dominates, yet, the O species can be formed preferentially (>80%) upon oxygenation of acetone solutions, if the copper concentration is low (<2 mM) and [(TMED)Cu(I)](1+) is prepared immediately before use. The experimental data of this simplest O species provide a benchmark by which to evaluate density functional theory (DFT) computational methods for geometry optimization and spectroscopic predictions. The enhanced thermal stability of [(TMED)(2)Cu(III)(2)(μ(2)-O)(2)](2+) and its limited steric demands compared to other O species allows more efficient oxidation of exogenous substrates, including benzyl alcohol to benzaldehyde (80% yield), highlighting the importance of ligand structure to not only enhance the oxidant stability but also maintain accessibility to the nascent metal/O(2) oxidant.     

Preparation,characterisation and electrochromic property of mesostructured tungsten oxide films via a surfactant templated sol–gel process from tungstic acid

A novel kind of mesoporous tungsten oxide films (TOFs) has been prepared via a non-ionic surfactant templated sol–gel route from cheap and easy handling tungstic acid. Characterisations by means of various techniques, including XRD, TEM, SEM, ATR and DTA, confirm that the obtained mesostructures are composed of fine mesopores (2–3 nm) and thin pore walls. Compared with previously reported surfactant templated mesoporous TOFs, our initial evaluation on the electrochromic properties showed that the derived TOFs show greatly enhanced colouration efficiency of 44 cm² C⁻¹ and faster colouration/bleaching speed of 10/2 s, respectively. Owing to the ordering of mesostructures delivered by our method, the mesostructural changes associated with the electrochemical reaction during the electrochromic cycling of such materials can be directly monitored by low-angle XRD measurements.