The structure of cellulose microfibrils in wood is not known in detail, despite the abundance of cellulose in woody biomass and its importance for biology, energy, and engineering. The structure of the microfibrils of spruce wood cellulose was investigated using a range of spectroscopic methods coupled to small-angle neutron and wide-angle X-ray scattering. The scattering data were consistent with 24-chain microfibrils and favored a "rectangular" model with both hydrophobic and hydrophilic surfaces exposed. Disorder in chain packing and hydrogen bonding was shown to increase outwards from the microfibril center. The extent of disorder blurred the distinction between the I alpha and I beta allomorphs. Chains at the surface were distinct in conformation, with high levels of conformational disorder at C-6, less intramolecular hydrogen bonding and more outward-directed hydrogen bonding. Axial disorder could be explained in terms of twisting of the microfibrils, with implications for their biosynthesis.crystallinity | infrared | deuterium exchange | nuclear magnetic resonance | spin diffusion

A new class of stable poly(ethylene-co-tetrafluoroethylene)-based alkaline anion-exchange membrane (AAEM) with enhanced tensile strength has been synthesized in response to the poor mechanical properties of previously reported poly(tetrafluoroethylene-co-hexafluoropropylene) radiation-grafted AAEMs; this type of AAEM exhibits significant through-plane conductivities (up to 0.034 ( 0.004 S cm -1 at 50 °C in water: conductivities that match requirements for application in fuel cells). The methanol permeabilities of this new AAEM class were found to be substantially reduced relative to Nafion-115 proton-exchange membranes; this offers the prospect that thin, low-resistance membranes may be used in direct methanol alkaline fuel cells with reduced methanol crossover. The fuel cell power performances obtained in a H 2 /O 2 single fuel cell at 50 °C with this AAEM is now within 1 order of magnitude of state-ofthe-art Nafion-based fuel cells. It is evident that the alkaline ionomers are not the primary performance limiters of alkaline membrane fuel cells; performances are currently limited by the electrode architectures that have been optimized for use in PEM fuel cells but not alkaline fuel cells. The need for electrodes and catalyst structures that have been specifically tailored for use in AAEM-containing fuel cells is highlighted.

In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production.Growth and form in plants are controlled by the precisely oriented expansion of the walls of individual cells. The driving force for cell expansion is osmotic, but the rate and direction of expansion are controlled by the mechanical properties of the cell wall (Szymanski and

Anion-exchange membranes (AEM) containing saturated-heterocyclic benzyl-quaternary ammonium (QA) groups synthesised by radiation-grafting onto poly(ethylene-co-tetrafluoroethylene) (ETFE) films are reported. The relative properties of these AEMs are compared with the benchmark radiation-grafted ETFE-g-poly(vinylbenzyltrimethylammonium) AEM. Two AEMs containing heterocyclic-QA head groups were down-selected with higher relative stabilities in aqueous KOH (1 mol dm-3) at 80°C (compared to the benchmark): these 100 μm thick (fully hydrated) ETFE-g-poly(vinylbenzyl-Nmethylpiperidinium)- and ETFE-g-poly(vinylbenzyl-N-methylpyrrolidinium)-based AEMs had as-synthesised ion-exchange capacities (IEC) of 1.64 and 1.66 mmol g-1, respectively, which reduced to 1.36 mmol dm-3 (ca. 17 – 18% loss of IEC) after alkali ageing (the benchmark AEM showed 30% loss of IEC under the same conditions). These down-selected AEMs exhibited as-synthesised Cl- ion conductivities of 49 and 52 mS cm-1, respectively, at 90°C in a 95% relative humidity atmosphere, while the OH- forms exhibited conductivities of 138 and 159 mS cm-1, respectively, at 80°C in a 95% relative humidity atmosphere. The ETFE-g-poly(vinylbenzyl-N-methylpyrrolidinium)-based AEM produced the highest performances when tested as catalyst coated membranes in H2/O2 alkaline polymer electrolyte fuel cells at 60°C with PtRu/C anodes, Pt/C cathodes, and a polysulfone ionomer: the 100 μm thick variant (synthesised from 50 μm thick ETFE) yielded peak power densities of 800 and 630 mW cm-2 (with and without 0.1 MPa back pressurisation, respectively), while a 52 μm thick variant (synthesised from 25 μm thick ETFE) yielded 980 and 800 mW cm-2 under the same conditions. From these results, we make the recommendation that developers of AEMs, especially pendent benzyl-QA types, should consider the benzyl-Nmethylpyrrolidinium head-group as an improvement to the current de facto benchmark benzyltrimethylammonium headgroup

Transition metal-alkane complexes-termed σ-complexes because the alkane donates electron density to the metal from a σ-symmetry carbon-hydrogen (C-H) orbital-are key intermediates in catalytic C-H activation processes, yet these complexes remain tantalizingly elusive to characterization in the solid state by single-crystal x-ray diffraction techniques. Here, we report an approach to the synthesis and characterization of transition metal-alkane complexes in the solid state by a simple gas-solid reaction to produce an alkane σ-complex directly. This strategy enables the structural determination, by x-ray diffraction, of an alkane (norbornane) σ-bound to a d(8)-rhodium(I) metal center, in which the chelating alkane ligand is coordinated to the pseudosquare planar metal center through two σ-C-H bonds.

In this paper we report the utility of a variety of silica impregnated bi-and trimetallic catalysts for the conversion of ethanol into 1,3-butadiene. The highest selectivity observed was 67%. The catalysts have been characterised via 29 Si solid-state NMR spectroscopy, TEM, XPS, pXRD and nitrogen adsorption studies. Different silica materials have been investigated as supports and there appears to be a relationship between the pore diameter and the selectivity to 1,3-butadiene. When the same metals were impregnated on non-acidic supports the conversion dramatically reduced.

SummaryNative cellulose in higher plants forms crystalline ®brils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a¯at-ribbon 2 1 helical chain conformation with every glucose residue locked to the next by hydrogen bonds from O-3¢ to O-5 and from O-2 to O-6¢. Using solid-state NMR spectroscopy we show that the surface chains have a different C-6 conformation so that O-6 is not in the correct position for the hydrogen bond from O-2. We also present evidence consistent with a model in which alternate glucosyl residues are transiently or permanently twisted away from the¯at-ribbon conformation of the chain, weakening the O-3¢ ± 0-5 hydrogen bond. Previous molecular modelling and the modelling studies reported here indicate that this translational' chain conformation is energetically feasible and does not preclude binding of the surface chains to the interior chains, because the surface chains share the axial repeat distance of the 2 1 helix. Reduced intramolecular hydrogen bonding allows the surface chains to form more hydrogen bonds to external molecules in textiles, wood, paper and the living plant.

Apatite-type silicates have been attracting considerable interest as a new class of oxide ion conductor, whose conduction is mediated by interstitial oxide ions. We report here the first 29 Si solid state NMR studies of these materials with a systematic investigation of thirteen compositions. Our results indicate a correlation between the silicon environment and the observed conductivity. Specifically, samples which show poor conductivity demonstrate a single NMR resonance, whereas fast ion conducting compositions show more complex NMR spectra. For the oxygen excess samples La 9 M(SiO 4 ) 6 O 2.5 (M = Ca, Sr, Ba) two peaks are observed at chemical shifts of #277.5 and 280.5 ppm, with the second peak correlated with a silicate group adjacent to an interstitial oxygen site. On Ti doping to give La 9 M(SiO 4 ) 62x (TiO 4 ) x O 2.5 (x = 1,2) the second peak disappears, which is consistent with the ''trapping'' of interstitial oxygens by Ti and the consequent lowering in oxide ion conductivity. The samples La 9.33 (SiO 4 ) 6 O 2 and La 9.67 (SiO 4 ) 6 O 2.5 show a further third weak peak at a chemical shift (#285.0 ppm) consistent with the presence of some [Si 2 O 7 ] 62 units in these samples, due to condensation of two [SiO 4 ] 42 units. The effect of such condensation of [SiO 4 ] 42 units will be the creation of additional interstitial oxide ion defects, i.e. 2 [SiO 4 ] 42 A [Si 2 O 7 ] 62 + O int 22 . Overall, the results further highlight the importance of the [SiO 4 ] 42 substructure in these materials, and additionally suggest that 29 Si NMR could potentially be used to screen apatite silicate materials for oxide ion conductivity