Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity,Recycling and Regeneration

The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica‐supported acetylacetonate and n‐butoxy zirconium(IV) complexes linked to the surface by one or three siloxane bonds, (SiO)Zr(acac)₃ ( 1 ) (SiO)₃Zr(acac) ( 2 ) and (SiO)₃Zr(O‐n‐Bu) ( 3 ), and their soluble polyoligosilsesquioxy analogues (c‐C₅H₉)₇Si₈O₁₂(CH₃)₂Zr(acac)₃ ( 1′ ), (c‐C₅H₉)₇Si₇O₁₂Zr(acac) ( 2′ ), and (c‐C₅H₉)₇Si₇O₁₂Zr(O‐n‐Bu) (3′ ). The reactivity of these complexes were compared to relevant molecular catalysts [zirconium tetraacetylacetonate, Zr(acac)₄ and zirconium tetra‐n‐butoxide, Zr(O‐n‐Bu)₄]. Strong activity relationships between the silica‐supported complexes and their polyoligosilsesquioxane analogues were established. Acetylacetonate complexes were found to be far superior to alkoxide complexes. The monopodal complexes 1 and 1′ were found to be the most active in their respective series. Studies on the recycling of the heterogeneous catalysts showed significant degradation of activity for the acetylacetonate complexes ( 1 and 2 ) but not for the less active tripodal alkoxide catalyst, 3 . Two factors are thought to contribute to the deactivation of catalyst: the lixivation of zirconium by cleavage of surface siloxide bonds and exchange reactions between acetylacetonate ligands and alcohols in the substrate/product solution. It was shown that the addition of acetylacetone to the low activity catalyst Zr(O‐n‐Bu)₄ produced a system that was as active as Zr(acac)₄. The applicability of ligand addition to heterogeneous systems was then studied. The addition of acetylacetone to the low activity solid catalyst 3 produced a highly active catalyst and the addition of a stoichiometric quantity of acetylacetone at each successive batch catalytic run greatly reduced catalyst deactivation for the highly active catalyst 1 .     

Production and characterization of plutonium dioxide particles as a quality control material for safeguards purposes

Plutonium (Pu) dioxide particles were produced from certified reference material (CRM) 136 solution (CRM 136-plutonium isotopic standard, New Brunswick Laboratory, Argonne, IL, U.S.A., 1987) using an atomizer system on December 3, 2009 after chemical separation of americium (Am) on October 27, 2009. The highest density of the size distribution of the particles obtained from 312 particles on a selected impactor stage was in the range of 0.7-0.8 μm. The flattening degree of 312 particles was also estimated. The isotopic composition of Pu and uranium (U) and the amount of Am were estimated by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and α-spectrometry. Within uncertainties the isotopic composition of the produced particles is in agreement with the expected values, which were derived from the decay correction of the Pu isotopes in the CRM 136. The elemental ratio of Am to Pu in the produced particles was determined on the 317th and 674th day after Am separation, and the residual amount of Am in the solution was estimated. The analytical results of single particles by micro-Raman-scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry (EDX) indicate that the produced particles are Pu dioxide. Our initial attempts to measure the density of two single particles gave results with a spread value accompanied by a large uncertainty.     

Cell-free protein synthesis and assembly on a biochip

Biologically active complexes such as ribosomes and bacteriophages are formed through the self-assembly of proteins and nucleic acids. Recapitulating these biological self-assembly processes in a cell-free environment offers a way to develop synthetic biodevices. To visualize and understand the assembly process, a platform is required that enables simultaneous synthesis, assembly and imaging at the nanoscale. Here, we show that a silicon dioxide grid, used to support samples in transmission electron microscopy, can be modified into a biochip to combine in situ protein synthesis, assembly and imaging. Light is used to pattern the biochip surface with genes that encode specific proteins, and antibody traps that bind and assemble the nascent proteins. Using transmission electron microscopy imaging we show that protein nanotubes synthesized on the biochip surface in the presence of antibody traps efficiently assembled on these traps, but pre-assembled nanotubes were not effectively captured. Moreover, synthesis of green fluorescent protein from its immobilized gene generated a gradient of captured proteins decreasing in concentration away from the gene source. This biochip could be used to create spatial patterns of proteins assembled on surfaces.     

Elytra boost lift,but reduce aerodynamic efficiency in flying beetles

Flying insects typically possess two pairs of wings. In beetles, the front pair has evolved into short, hardened structures, the elytra, which protect the second pair of wings and the abdomen. This allows beetles to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with the elytra extended, suggesting that they influence aerodynamic performance, but little is known about their role in flight. Using quantitative measurements of the beetle''s wake, we show that the presence of the elytra increases vertical force production by approximately 40 per cent, indicating that they contribute to weight support. The wing-elytra combination creates a complex wake compared with previously studied animal wakes. At mid-downstroke, multiple vortices are visible behind each wing. These include a wingtip and an elytron vortex with the same sense of rotation, a body vortex and an additional vortex of the opposite sense of rotation. This latter vortex reflects a negative interaction between the wing and the elytron, resulting in a single wing span efficiency of approximately 0.77 at mid downstroke. This is lower than that found in birds and bats, suggesting that the extra weight support of the elytra comes at the price of reduced efficiency.     

Photochemical source of metals for sediments

A mass budget study of major in-lake Al fluxes, palaeolimnological data on a >10,000 year old sediment record, and in situ photochemical experiments performed at Plesné Lake (Czech Republic) suggest that photochemical liberation of organically bound aluminum (Al) and iron (Fe) by solar radiation is a significant natural source of their ionic species for lakes and subsequent oxyhydroxides for sediments. The results show that photochemically induced transformation of dissolved Al and Fe to solid oxyhydroxides deposited to Plesné Lake sediment dominated (91 and 73%, respectively) their sedimentary flux throughout the preindustrial era, since soil formation initiated in the catchment. The following sequence of processes occurs: (i) soil organic acids dissolve and bind metals and export them from terrestrial to aquatic systems. (ii) Photochemical decomposition of organic-metal complexes liberates a significant portion (approximately 50% in Pleseé Lake) of organically bound Al and Fe as inorganic ions. (iii) The liberated ionic Al and Fe hydrolyze, precipitate as oxyhydroxide particles, and settle. We hypothesise that the same Al and Fe transporting process occurs in other lakes and coastal marine areas and is ecologically important because Al and Fe oxyhydroxides can bind trace metals and phosphorus.     

Continuous ice core melter system with discrete sampling for major ion, trace element and stable isotope analyses

We present a novel ice/firn core melter system that uses fraction collectors to collect discrete, high-resolution (<1 cm/sample possible), continuous, coregistered meltwater samples for analysis of eight major ions by ion chromatography (IC), >32 trace elements by inductively coupled plasma sectorfield mass spectrometry (ICP-SMS), and stable oxygen and hydrogen isotopes by isotope ratio mass spectrometry (IRMS). The new continuous melting with discrete sampling (CMDS) system preserves an archive of each sample, reduces the problem of incomplete particle dissolution in ICP-SMS samples, and provides more precise trace element data than previous ice melter models by using longer ICP-SMS scan times and washing the instrument between samples. CMDS detection limits are similar to or lower than those published for ice melter systems coupled directly to analytical instruments and are suitable for analyses of polar and mid-low-latitude ice cores. Analysis of total calcium and sulfur by ICP-SMS and calcium ion, sulfate, and methanesulfonate by IC from the Mt. Logan Prospector-Russell Col ice core confirms data accuracy and coregistration of the split fractions from each sample. The reproducibility of all data acquired by the CMDS system is confirmed by replicate analyses of parallel sections of the GISP2 D ice core.     

Chronicling a century of lead pollution in Mexico: stable lead isotopic composition analyses of dated sediment cores

Analyses of lead isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of dated sediment cores from two coastal estuaries and two inland lakes chronicle the predominance of industrial lead emissions in Mexico over the past century. These isotopic ratios exhibit a shift in composition from the turn of the previous century (1900) that corresponds with measurable increases (from 2- to 10-fold) in lead concentrations in the cores above their baseline values (3-22 microg/g)--both changes are consistent with the development of Mexican lead production for export and the manufacture of tetraethyl lead additives for Mexican gasolines. While subsequent changes in lead concentrations in the cores correspond with calculated emissions from the combustion of leaded gasoline in Mexico, isotopic compositions of the cores remain relatively constant throughout most of the 1900s (e.g., 206Pb/207Pb = 1.200 +/- 0.003; 208Pb/207Pb = 2.463 +/- 0.004). That isotopic constancy is attributed to the widespread pollution from lead production in Mexico and the dispersion of some of that lead used as an additive in Mexican gasolines.     

Novel reduction of mercury (II) by mercury-sensitive dissimilatory metal reducing bacteria

The dissimilatory metal reducing bacterium (DMRB) Shewanella oneidensis MR-1 reduces ionic mercury (Hg[II]) to elemental mercury (Hg[0]) by an activity not related to the MerA mercuric reductase. In S. oneidensis, this activity is constitutive and effective at Hg(II) concentrations too low to induce mer operon functions. Reduction of Hg(II) by MR-1 required the presence of electron donors and electron acceptors. Reduction occurred with oxygen or fumarate, but had the highest rate when ferric oxyhydroxide was used as a terminal electron acceptor. Geobacter sulfurreducens PCA and Geobacter metallireducens GS-15 reduced Hg(II) to Hg(0) with activity comparable to MR-1; however, neither the DMRB Anaeromyxobacter dehalogenans 2CP-C nor the nitrate reducer Pseudomonas stutzeri OX-1 reduced Hg(II) during growth. This discovery of constitutive mercury reduction among anaerobes has implications to the mobilization of mercury and production of methylmercury in anoxic environments.     

Hydrogen tunneling and protein motion in enzyme reactions

Theoretical perspectives on hydrogen transfer reactions in enzymes are presented. The proton-coupled electron transfer reaction catalyzed by soybean lipoxygenase and the hydride transfer reaction catalyzed by dihydrofolate reductase are discussed. The first reaction is nonadiabatic and involves two distinct electronic states, while the second reaction is predominantly adiabatic and occurs on the electronic ground state. Theoretical studies indicate that hydrogen tunneling and protein motion play significant roles in both reactions. In both cases, the proton donor-acceptor distance decreases relative to its equilibrium value to enable efficient hydrogen tunneling. Equilibrium thermal motions of the protein lead to conformational changes that facilitate hydrogen transfer, but the nonequilibrium dynamical aspects of these motions have negligible impact.