Stefan J. Hill

Wide-Angle X-Ray Scattering and Solid-State Nuclear Magnetic Resonance Data Combined to Test Models for Cellulose Microfibrils in Mung Bean Cell Walls

Peak shapes in an x-ray diffractogram of primary cell walls indicated 18-chain microfibrils with mixed cross-sectional shapes and occasional twinning, consistent with a cellulose-synthesizing complex assembled from six CESA trimers. A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-β-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.

Effect of drying and rewetting of wood on cellulose molecular packing.

Abstract Drying and rewetting of Pinus radiata sapwood latewood was studied by synchrotron wide angle X-ray scattering in transmission mode. Scattering from cellulose was interpreted in terms of chains distributed on a monoclinic lattice. Drying wood material to below the fibre saturation point resulted in decreased spacing between adjacent cellulose polymers within the hydrogen-bonded sheets of chains, and also decreased the monoclinic angle. The changes were partly reversed when the dried wood was rewet, but accumulated through multiple cycles of oven-drying and rewetting. No changes were observed in the fibre repeat distance, thus the distortion of the crystal lattice was not attributed to mechanical stresses associated with drying. Instead, the changes were attributed to formation of intrachain hydrogen bonds at dehydrated crystallite surfaces, causing conformational changes within the cellulose chains and increasing the density of packing. The results help account for the hysteresis observed in moisture desorption-adsorption isotherms during wood material drying and rehydration.

Phosphorus dynamics in sediments of a eutrophic lake derived from 31P nuclear magnetic resonance spectroscopy

The determination of organic phosphorus (P) compounds in lake sediments can provide information on the potential for internal P loading. Settling seston and vertical sediment core samples from highly eutrophic Lake Okaro, New Zealand, were collected during a mixed winter and stratified summer period, representing, respectively, when the water column was well oxygenated and when the bottom waters were anoxic. Samples were analysed with 31P nuclear magnetic resonance (31P NMR) spectroscopy, which showed that both bottom sediments and settling seston contained orthophosphate, orthophosphate monoesters and diesters, pyrophosphates, polyphosphates and phosphonates. Phosphorus concentration in settling seston increased ~2.5-fold in winter as a result of seasonally induced changes in phytoplankton biomass, with a marked increase in the concentration of orthophosphate. Several potentially bioavailable P compounds in the bottom sediments were identified that were likely to contribute to recycling of P from the sediment to the water column. An ‘apparent half-life’ was used to quantify the time scales on which these compounds were recycled to the overlying water column. Orthophosphate monoesters that include inositol phosphates were the most persistent P compound. On the basis of half-lives, high internal P loadings may persist for more than 20 years, potentially hindering restoration efforts in Lake Okaro.

NMR Estimation of Extractables from Bark: Analysis Method for Quantifying Tannin Extraction from Bark

Abstract Extraction and recovery of radiata pine bark tannin for use in adhesives should endeavour to be optimal to ensure process viability. A NMR method has been developed to directly gauge the extent of tannin extraction from bark by analyzing processed residues. 13C Solid-state NMR spectra were obtained for a series of bark and residue samples. The respective peak areas and heights of extractable polyphenolic tannins were compared with residual lignocellulosic materials. From the ratio of NMR peak intensities, diminishing polyphenolic content was apparent with increasing degree of extraction. The percentage polyphenolic tannins removed by extraction could be estimated by a simple equation comparing integrated areas of a sample with those of pure bark. A comparison of percentage extraction values determined gravimetrically with NMR peak ratios gave a good relationship from which the extractables removed from a bark residue could be estimated, potentially providing a measurement of extraction efficiency of a bark processing operation.

Detection of wood cell wall porosity using small carbohydrate molecules and confocal fluorescence microscopy

A novel approach to nanoscale detection of cell wall porosity using confocal fluorescence microscopy is described. Infiltration of cell walls with a range of nitrophenyl‐substituted carbohydrates of different molecular weights was assessed by measuring changes in the intensity of lignin fluorescence, in response to the quenching effect of the 4‐nitrophenyl group. The following carbohydrates were used in order of increasing molecular weight; 4‐nitrophenyl β‐D‐glucopyrano‐side (monosaccharide), 4‐nitrophenyl β‐D‐lactopyranoside (disaccharide), 2‐chloro‐4‐nitrophenyl β‐D‐maltotrioside (trisaccharide), and 4‐nitrophenyl α‐D‐maltopentaoside (pentasaccharide). This technique was used to compare cell wall porosity in wood which had been dewatered to 40% moisture content using supercritical CO2, where cell walls remain fully hydrated, with kiln dried wood equilibrated to 12% moisture content. Infiltration of cell walls as measured by fluorescence quenching, was found to decrease with increasing molecular weight, with the pentasaccharide being significantly excluded compared to the monosaccharide. Porosity experiments were performed on blocks and sections to assess differences in cell wall accessibility. Dewatered and kiln dried wood infiltrated as blocks showed similar results, but greater infiltration was achieved by using sections, indicating that not all pores were easily accessible by infiltration from the lumen surface. In wood blocks infiltrated with 4‐nitrophenyl α‐D‐maltopentaoside, quenching of the secondary wall was quite variable, especially in kiln dried wood, indicating limited connectivity of pores accessible from the lumen surface.

Speciation and distribution of organic phosphorus in river sediments: a national survey

PurposeOrganic phosphorus (P) can play a role in in-stream productivity (e.g., periphyton or macrophyte growth), but little is known of the largest likely source of organic P—bed sediment. A survey was conducted of 76 bed sediment samples of rivers within the New Zealand National River Water Quality Network in an effort to determine the concentration and form of organic P species, and variation according to catchment and sediment characteristics or classifications used to characterise anthropogenic P inputs (e.g., as baseline [viz. reference] or impact sites) and therefore likely in-stream productivity.Materials and methodsSediments were analysed for a range of physiochemical properties. NaOH-EDTA extracts were analysed by 31P nuclear magnetic resonance spectroscopy (31P NMR), which isolated orthophosphate from other P species including orthophosphate monoesters, orthophosphate diesters and pyrophosphate.Results and discussionMore P was extracted from sediments at impact compared to baseline sites, while the proportion of organic P increased where microbial processing (as reflected by site elevation) decreased. Analysis by 31P NMR of sediments showed they contained fewer and less-enriched forms of organic P than profiles of typical lake sediments or soils (e.g., no phosphonates or polyphosphates). This was hypothesised to reflect either low P inputs via catchment runoff, or efficient utilisation due to strong P limitation.ConclusionsSome evidence was found of changes in the distribution and form of organic P species in relation to anthropogenic activity and sediment processes. However, organic P concentrations were small and only represented a single sampling. Hence, additional work needs to examine if these changes relate to changes in in-stream productivity over time.

COMMENT ON THE STRUCTURE OF OSMIUM TETROXIDE-CHITOSAN COMPLEX

Reaction of an aqueous solution of osmium tetroxide with the chitosan polymer model, the oligomer tetradeca(β(1→4)2-amino-2-deoxyglucopyranose)-β(2→5)mannitol, afforded a brown solid, the structure of which was proposed to contain osmium imido groups, −N˭Os. The product showed a new, distinct absorption band at 850 cm−1 in the FTIR spectrum, while the 13C CP-MAS NMR spectrum showed a lower signal relative intensity ratio for C2:C3/5 compared with that in the NMR spectrum of the starting oligosaccharide due to a downfield shift of C2 where allylic to the -N˭Os bond. Results from quantum chemical calculations were used to compare computed properties of the previously described “osmium tetroxide-chitosan complex” in which osmium tetroxide was coordinated to chitosan amino ligands with single dative N→Os bonds, and the product prepared in this study, proposed to have covalently-bonded imido bonds between osmium and nitrogen. The consequences of multiple bonding of two chitosan N to the Os atom in the 5d 3 6s hybrid tetrahedral configuration and with the C-N˭Os bond angle greater than 150° required one of the carbohydrate pyranose rings attached to Os to adopt a boat conformation.

Correlations Between the Physiochemical Characteristics of Plant Fibres and Their Mechanical Properties

Lignocellulosic fibres harvested from different plant types exhibit variations in mechanical properties that are associated with their chemical composition and physical features. This diversity indicates that plant fibres could be selected based on their physio-chemical properties for tailored applications such as enhanced vibration damping. In this study, bast, leaf, and mesocarp fibre bundles were investigated to understand correlations between their physiochemical characteristics and their mechanical properties with a particular focus on their vibrational damping ability. Due to the interrelations between the investigated variables such as cellulose content and microfibril angle, a multivariate analysis (principal component analysis) was applied to elucidate trends. The stiffness and strength of the fibre bundles were found to be positively correlated to high cellulose content and low microfibril angle while high toughness was correlated with fibre bundles of high lignin content and high microfibril angle. Conversely, the damping coefficient was found to be positively correlated to fibres containing high level of hemicelluloses, such as those extracted from leafy plants.

Comparison of Micropore Distribution in Cell Walls of Softwood and Hardwood Xylem

Molecular microscopy shows that distribution of porosity across the secondary cell wall in xylem is predominantly related to the degree of lignification in different cell wall layers. The porosity of wood cell walls is of interest for both understanding xylem functionality and from a wood materials perspective. The movement of water in xylem generally occurs through the macroporous networks formed in softwood by bordered pits and in hardwood by the intervessel pits and open conduits created by vessels and perforation plates. In some situations, such as cavitated xylem, water can only move through the micropores that occur in lignified tracheid and fiber cell walls; however, these micropore networks are poorly understood. Here, we used molecular microscopy analysis of radiata pine (Pinus radiata) and red beech (Nothofagus fusca) to determine the distribution of micropores in the secondary walls and middle lamellae of tracheids and fibers in relation to cell wall composition. Using two different types of probe, we identified a greater porosity of secondary cell walls and a reduced porosity of the middle lamella. Areas of reduced porosity were observed in the outer regions of the secondary cell wall of both tracheids and fibers that appear unrelated to lignification or the distribution of cellulose, mannan, and xylan. Hardwood fiber cell walls were less lignified than those of softwood tracheids and showed greater accessibility to porosity probes. Vessel cell walls were comparable to those of fibers in terms of both porosity and lignification. Lignification is probably the primary determinant of cell wall porosity in xylem. The highly lignified middle lamella, and lumen surface, act as a barrier to probe movement and, therefore, water movement in both softwood and hardwood.