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AbstractThe amount of non-cellulosic glucans in Eucalyptus globuluswood (approx. 4.5%) was assessed by extraction of sawdust with a 0.5 M NaOH solution at 90–120°C and the structural features were elucidated in a glucan-enriched polysaccharide fraction isolated by hot water extraction (120°C, 2 h). Isolated soluble glucans were characterized by wet chemistry methods and a set of 1D and 2D NMR techniques. The major proportion of glucans consisted of amylose (20%) and amylopectin (80%), although a small proportion of ?-(1?3)-glucan (<0.2% on wood weight) was also detected. Although glucans are easily removed in the initial phase of kraft pulping, notable amounts were found in unbleached pulp and it was supposed that in the final stage of kraft pulping a fraction of ?-glucan is precipitated onto the fiber surface and contributes to the pulp yield. [ABSTRACT FROM AUTHOR]

A kinetic study of the oxidation of substituted phenols with either vanadium(v) polyoxotungstate, [α-SiVVW11O40]5− (viz. SiW11V), or manganese(iii) polyoxotungstate, [α-SiMnIIIW11(H2O)O39]5− (viz. SiW11Mn), has been carried out. Because the redox potentials of the polyoxometalate SiW11V and SiW11Mn compounds, viz. POMs, are 0.67 and 0.76 V/NHE, respectively, and those of the phenolic substrates are in the range of 0.4–0.9 V/NHE in water, the resulting oxidation reactions are exoergonic or slightly endoergonic. The reactivity of oxidation of substituted phenols by SiW11V, at 50 °C in buffered (pH = 4) water solution, has been found to correlate with the σ parameter of the substituents, yielding an Okamoto–Brown ρ value (i.e., −3.1) consonant with the electronic requirements of a rate-determining electron-transfer route. The negligible value of the solvent kinetic isotope effect (kH/kD = 1.06) obtained for the oxidation of p-MeO-phenol with SiW11V in H2O vs. D2O solution was also in favour of a rate-determining one-electron abstraction from the substrate, followed by fast deprotonation of the intervening radical cation. Additional support to an outer-sphere oxidation with SiW11V was provided by a satisfactory correlation of the reactivity vs. redox potential of the phenols, and by a Marcus analysis of the experimental oxidation data. A sizeable value for the reorganisation energy (λ) was accordingly obtained. The slightly stronger oxidant SiW11Mn resulted to be more reactive than SiW11V by ca. two powers of magnitude. Our scrutiny of the reactive behaviour of the two POMs towards phenols may provide a model of interpretation for the phenoloxidase activity of the laccase enzymes, a class of multicopper oxidases endowed with redox potentials well comparable with those of the two POMs. [ABSTRACT FROM AUTHOR]

A review on the use of polyoxometalates (POMs) and oxygen, for the delignification of lignocellulosic pulps is presented. Two main processes using POMs for the delignification of pulp have been investigated: an anaerobic process in which the POMs have been used, in aqueous solutions, as stoichiometric reagents for the oxidative degradation of residual lignin, with their re-oxidation by oxygen occurring in a subsequently separate stage; and an aerobic process in which the POMs were designed to perform as catalysts in the oxygen delignification. In the aerobic approach, the lignin oxidation and the reactivation of the POM take place in the same stage of the process. The feasibility of the catalytic system was shown by pilot plant experiments. Following the green chemistry goals, these processes are environmentally friendly approaches and may allow a significant decrease of chlorine-based chemical consumption by the pulp-and-paper industry. The use of the POMs together with laccase for the oxygen delignification of lignocellulosic pulps will also be considered. Final comments regarding the practical application of the POMs are pointed out. [ABSTRACT FROM AUTHOR]