A pulsed NMR study of hydrogen diffusion in hydrides of group IVa transition metals

Activation energies E_A for hydrogen diffusion in hydrides of Group IVa transition metals have been determined by ¹H nuclear magnetic resonance measurements of spin lattice relaxation in both the laboratory (T₁) and rotating (T_1p) frames. For the HfHx system both activation energies obtained from T₁ data, and the value of T₁ at the minimum appear to be insensitive to hydrogen content x in the range 1.58 ? x ? 1.98. For hydrides of titanium and zirconium of approximately stoichiometric composition MH₂ (where M = metal), there is excellent agreement between activation energies obtained from T₁ and T_1p data. Mean activation energies obtained were 0.51 eV for TiH_1.98 and 0.83 eV for ZrH_1.96, consistent with a single diffusion mechanism in each case over the temperature range 260–600K and 400–800K respectively. In the case of HfH_1.98 the agreement was less good, values of 0.64 and 0.55 eV being obtained from T₁ and T_1p respectively.     

Aircraft interior noise models: Sidewall trim,stiffened structures,and cabin acoustics with floor partition

As part of the continuing development of an aircraft interior noise prediction model, in which a discrete modal representation and power flow analysis are used, theoretical results are considered for inclusion of sidewall trim, stiffened structures, and cabin acoustics with floor partition. For validation purposes, predictions of the noise reductions for three test articles (a bare ring-stringer stiffened cylinder, an unstiffened cylinder with floor and insulation, and a ring-stringer stiffened cylinder with floor and sidewall trim) are compared with measurements.     

Observation of high transverse momentum electrons at the CERN ISR

A search for high transverse momentum electrons directly produced in proton-proton collisions has been performed at the CERN ISR. The apparatus included a magnetic spectrometer with wire spark chambers, a lead-glass counter array, and a threshold gas ?erenkov counter. At a centre-of-mass energy √s = 52.7 GeV, a signal has been observed in the range $\text{1.6<p}{}_{\mathrm{T}}{}^1\text{<4.7}\text{GeV}\text{/c}$. The signal occurs at a level of approximately 10^?4 of the inclusive pion cross-section.     

Quinoxaline sensitised lanthanide ion luminescence: Syntheses,spectroscopy and X-ray crystal structure of Na{1,4,7-tris[(N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane-10-(2-methylquinoxaline)}I3 C7H8

The synthesis of a quinoxaline-appended aza-macrocyclic ligand together with corresponding Ln^III complexes are described. The luminescence properties of the complexes show that the quinoxaline unit sensitises both visible (Eu^III) and near-IR (Nd^III and Yb^III) emitting lanthanide ions. UV–Vis absorption and time-resolved photophysical studies together with X-ray structural data suggest that as well as contributing chromophorically, the quinoxaline moiety generally participates in the first coordination sphere of Ln^III. The luminescent pH response of the Eu^III complex is also reported. The form of the steady state spectrum changes profoundly in the pH range 2–12, implying a change in the coordination environment, which was confirmed with time-resolved lifetime measurements that suggest an increase in europium inner sphere hydration at acidic pH.     

Synthesis, structures and properties of a new series of platinum-diimine-dithiolate complexes

The new square-planar platinum-diimine-dithiolate compounds [Pt(mesBIAN)SS] have been synthesised {mesBIAN = bis(mesityl)biazanaphthenequinone; SS = 1,2-dithiooxalate (dto) , maleonitriledithiolate (mnt) , 1,2-benzenedithiolate (bdt) , 3,4-toluenedithiolate (tdt) and 1,3-dithia-2-thione-4,5-dithiolate (dmit) }, and the X-ray crystal structures of and determined. Cyclic voltammetry reveals that all the compounds form stable anions, and ESR spectroscopy of these anions shows that the SOMO is based upon the mesBIAN ligand; compounds also show a reversible oxidation wave in their CV. Computational studies reveal that charge-transfer processes from orbitals that are combinations of metal and dithiolate ligand to a mesBIAN pi-based LUMO are responsible for the low energy absorptions seen in the UV/visible spectra of these compounds, and that the reverse process is responsible for the observed room-temperature solution luminescence of [Pt(mesBIAN)Cl(2)] and , and . Compounds and , containing aromatic thiolates, were not found to luminesce under the same conditions. Resonance Raman experiments have shown the origin of band-broadening of the lowest-energy absorption band in the absorption spectra of to be due to vibronic structure within one electronic transition.     

Immobilized Sonogashira catalyst systems: new insights by multinuclear HRMAS NMR studies

A new chelate phosphine linker and its Pd and Cu complexes have been synthesized and immobilized. The solvent impact on these immobilized species, their mobility, and coordination preferences have been studied in situ by HRMAS (High-Resolution Magic Angle Spinning) NMR. The catalyst recycling characteristics match the HRMAS results.     

Catalytic contributions of key residues in the adenine glycosylase MutY revealed by pH-dependent kinetics and cellular repair assays

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Highlights? Asp 138 must be deprotonated to stabilize the transition state for maximal activity ? Consequences of altering catalytic amino acids in MutY on cellular mismatch repair ? Correlation of MutY enzymatic parameters with ability to mediate cellular repair ? Importance of high affinity binding of MutY to the OG:A mismatch for high levels of repair     

Noble metals in polyoxometalates

Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.     

Biologically compatible, phosphorescent dimetallic rhenium complexes linked through functionalized alkyl chains: syntheses, spectroscopic properties, and applications in imaging microscopy

A range of luminescent, dimetallic complexes based upon the rhenium fac-tricarbonyl diimine core, linked by aliphatic chains of varying lengths and functionality, have been synthesized and their photophysical properties examined. Each complex displays characteristic (3)M(Re)L(diimine)CT emission in aerated acetonitrile solution, with long lifetimes in the range of 129-248 ns and corresponding quantum yields in the range 3.2-8.0%. In aqueous solution, as opposed to acetonitrile, the complexes generally show a small hypsochromic shift in λ(em) and an extension of the (3)MLCT lifetime, attributed to a hydrophobically driven association of the alkyl chains with the rhenium-bound diimine units. In live cell imaging experiments using MCF7 cells the complexes all show good uptake by non-energy dependent mechanisms without endosomal entrainment, and with varying propensity to localize in organelles. The degrees of uptake and localization properties are discussed in terms of the length and chemical nature of the linkers, and in terms of the likely interactions between these and the various cellular components encountered.     

Proposed mechanisms for the fragmentation of doubly allylic alkenamides (tingle compounds) by low energy collisional activation in a triple quadrupole mass spectrometer

Tingle compounds are a class of alkenamides with organoleptic properties that include a numbing or a pins and needles effect that is generally perceived on the lips and in the mouth when consumed. They occur in nature in a number of botanical species. Spilanthol and Pellitorine are important examples of tingle compounds. A number of homologs and analogs were synthesized to study the effect of chain length, double bond location, and amide moiety on the tingle effect. This also provided the opportunity to study the behavior of these compounds in the collision cell of a triple quadrupole mass spectrometer. The doubly allylic 2E,6Z-alkenamides, which made up the largest class studied, fragmented in a characteristic way to produce a distonic radical cation and a cyclopropene cation. Mechanisms for the formation of these ions are proposed. The mechanisms are supported by energy-resolved mass spectrometric data, the analysis of deuterated analogs and homologs that are not doubly allylic, and exact mass measurements. Exceptions to the proposed mechanisms are also presented. These data represent the first attempt to apply mechanistic principles to the product ions observed in the MS/MS spectra of these compounds. The authors believe the results of this study will facilitate the identification of these and similar compounds and contribute to the fundamental understanding of the behavior of alkenamides in the collision cell of a triple quadrupole mass spectrometer.