Birch and pine wood specimens were colonized by individual isolates of 12 brown-rot, 26 white-rot, six soft-rot and four blue (sap)-stain fungi. Homogenized wood was subsequently extracted in 75% ethyl acetate and centrifuged. The filtered extracts were analyzed for their iron-reducing capabilities using a ferrozine-based assay. Agar fungal cultures were also examined directly using a spot test for iron reduction. Extracts from wood colonized by brown-rot fungi showed significantly greater iron-reducing capability than extracts from wood colonized by white-rot or non-decay fungi. Results of the spot test ratings were highly variable, but in general the greatest color responses were associated with the brown-rot cultures. The ability of brown-rot fungi to produce compounds and/or modify the wood components that reduce iron is of relevance to the “chelator-mediated Fenton mechanism” that has been advanced as a theory for the non-enzymatic degradation of wood by brown-rot fungi.
Effects of the heating rate on the physical properties of carbonized wood were investigated by comparing the dimensional shrinkage, electrical resistivity, Young's modulus, and the evolution of turbostratic crystallites in maple hardwood samples carbonized at 600°C, 800°C, and 1000°C under heating regimes of 3°C h-1 and 60°C h-1. Important carbonized wood properties that developed at high temperature and high heating rates could also be produced at slow heating rates and lower temperatures. Furthermore, slow heating rates promoted the formation and growth of graphene sheets in turbostratic crystallites, which had a significant influence on the electrical resistivity and Young's modulus of the carbonized wood. The results indicate that the graphene sheets of turbostratic crystallites formed during wood carbonization were arranged parallel to the axial direction of wood cells and at an angle to the circumference of wood cells in the cross-sectional plane. With regard to the production of carbon products, a decrease in the heating rate may be beneficial for char properties and the prevention of crack production during manufacture of large monolithic carbon specimens from wood and wood-based materials.
Modified wood can provide protection against a range of wood deteriorating organisms. Several hypotheses have been put forward regarding the protection mechanisms against wood decaying fungi including fungal enzyme inefficiency due to non-recognition, lower micropore size, and insufficient wood moisture content. The aim of this study was to obtain new insight into the protection manner of furfuryl alcohol (FA) modified Scots pine sapwood (WFA), and to examine biochemical mechanisms and adaptive changes in gene expression utilised by Postia placenta during early colonisation of WFA. Samples were harvested after 2, 4, and 8 weeks of incubation. After 8 weeks, the mass loss (0.1%) and wood moisture content (21.0%) was lower inWFA, than in non-modified Scots pine sapwood samples (W), 26.1% and 46.1%, respectively. Microscopy revealed needle-shaped calcium oxalate crystals, at all harvesting points, most prominently present after 4 and 8 weeks, and only in the WFA samples. Among the findings based on gene profiles were indications of a possible shift toward increased expression, or at least no down regulation, of genes related to oxidative metabolism and concomitant reduction of several genes related to the breakdown of polysaccharides in WFA compared to W.
Pine wood (Pinus sylvestris) veneer strips were incubated in acetate buffer containing hydrogen peroxide and Fe ions (Fenton's reagent) to mimic aspects of brown rot decay and to assess the degradation of cellulose in wood via measurement of tensile properties (measured in a zero-span mode). Varying the type of iron (ferrous or ferric sulfate) mixed with H2O2 did not yield significant differences in the rates of H2O2 concentration and tensile strength reduction. However, increasing the amount of wood material (the number of wood strips) in the reaction mixture elevated Fe(III) reduction in solution, indicating that wood constituents participated in this reaction. Increasing concentrations of Fe(III) in the reaction mixture resulted in a decrease in H2O2 in solution. Despite an increase in iron concentration and H2O2 decomposition under these conditions, a uniform and consistent strength loss of 30% was observed at all Fe(III) concentrations tested. At fixed Fe(III) concentrations, increasing the H2O2 concentration linearly increased the strength loss of the veneers up to approximately 50% within 24 h. The addition of a low molecular weight, metal-binding, phenolic compound (2,3-dihydroxybenzoic acid) and of a non-chelating hydroquinone to the reaction mixtures entailed a more rapid consumption of H2O2; however, the tensile strength loss of the veneers decreased with increasing concentration of the phenolics. Thus, in contrast to previous studies on cellulose degradation, phenolics reduced the degree of wood decay in a Fenton system.
The bond-valence model (BVM) posits an inverse relationship between bond valence (essentially bond order) and bond length, typically described by either exponential or power-law equations. To assess the value of these forms for describing a wider range of bond lengths than found in crystals, we first assume that the bond critical point density (ρb, reported in e-/Å3) is at least roughly proportional to bond valence. We then calculate ρb-distance curves for several diatomic pairs using electronic structure calculations (CCSD/aug-cc-pVQZ) and Atoms-In-Molecules (AIM) analysis. The shapes of these curves cannot be completely described by the standard exponential and power-law forms, but are well described by a threeparameter hybrid of the exponential and power-law forms. The ρb-distance curves for covalent bonds tend to exhibit exponential behavior, while metallic bonds exhibit power-law behavior, and ionic bonds tend to exhibit a combination of the two. We next use a suite of both experimental and calculated (B3LYP/ Def2-TZVP) molecular structures of oxo-molecules, for which we could infer X-O bond valences of ~1 or ~2 v.u., combined with some crystal structure data, to estimate the curvature of the bond valencelength relationship in the high-valence region. Consistent with the results for the ρb-distance curves, the standard forms of the bond valence-length equation become inadequate to describe high-valence bonds as they become more ionic. However, some of these systems demonstrate even higher curvature changes than our three-parameter hybrid form can manage. Therefore, we introduce a four-parameter hybrid form, and discuss possible reasons for the severe curvature. Although the addition of more parameters to the bond valence-length equation comes at a cost in terms of model simplicity and ease of optimization, they will be necessary to make the BVM useful for molecular systems and transition states.
The bond-valence model has recently been expanded to include a directional component, the vectorial bond-valence sum, which is useful for characterizing non-centrosymmetric distortions involving lone-pair and second-order Jahn-Teller effects. Here we show that the bond-valence sum and vectorial bond-valence sum are equivalent to monopole and dipole terms in a multipole expansion of the bond valence incident to an atom. We then extend the multipole expansion to include a quadrupole term, which describes the ellipsoidal deviation from spherical symmetry of the bonding environment, and is useful for characterizing centrosymmetric distortions, such as those caused by first-order Jahn-Teller effects. These distortions follow characteristic patterns in valence space, which depend upon factors that include the d-orbital configuration and size of the transition metal involved. This extended approach, called the Valence Multipole Model, should prove useful for modeling molecular and crystal structures, including those associated with spin transitions.