Oxidation of Various Kraft Lignins with a Bacterial Laccase Enzyme.

Modification of kraft lignin (KL), traditionally uses harsh and energy-demanding physical and chemical processes. In this study, the potential of the bacterial laccase CotA (spore coating protein A) for oxidation of KL under mild conditions was assessed. Thereby, the efficiency of CotA to oxidize both softwood and hardwood KL of varying purity at alkaline conditions was examined. For the respective type of wood, the highest oxidation activity by CotA was determined for the medium ash content softwood KL (MA_S) and the medium ash content hardwood KL (MA_H), respectively. By an up to 95% decrease in fluorescence and up to 65% in phenol content coupling of the structural lignin units was indicated. These results correlated with an increase in viscosity and molecular weight, which increased nearly 2 and 20-fold for MA_H and about 1.3 and 6.0-fold for MA_S, respectively. Thus, this study confirms that the CotA laccase can oxidize a variety of KL at alkaline conditions, while the origin and purity of KL were found to have a major impact on the efficiency of oxidation. Under the herein tested conditions, it was observed that the MA_H KL showed the highest susceptibility to CotA oxidation when compared to the other hardwood KLs and the softwood KLs. Therefore, this could be a viable method to produce sustainable resins and adhesives.

Enzyme Catalyzed Copolymerization of Lignosulfonates for Hydrophobic Coatings.

Enzymatic polymerization of lignin can generate a variety of value-added products concomitantly replacing fossil-based resources. In line with this approach, a laccase from the thermophilic fungus Myceliophthora thermophila (MtL) was used to couple a hydrophobicity enhancing fluorophenol (FP) molecule, namely 4-[4-(trifluoromethyl)phenoxy]phenol (4,4-F3MPP), as a model substrate onto lignosulfonate (LS). During the coupling reaction changes in fluorescence, phenol content, viscosity and molecular weight (size exclusion chromatography; SEC) were monitored. The effects of enzymatic coupling of FP onto LS on hydrophobicity were investigated by the means of water contact angle (WCA) measurement and determination of swelling capacity. Full polymerization of LS resulting in the production of water-insoluble polymers was achieved at a pH of 7 and 33°C. Incorporation of 2% (w/v) of FP led to an increase in WCA by 59.2% while the swelling capacity showed a decrease by 216.8%. Further, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis indicated successful covalent coupling of the FP molecule onto LS by an emerging peak at 1,320 cm-1 in the FTIR spectrum and the evidence of Fluor in the XPS spectrum. This study shows the ability of laccase to mediate the tailoring of LS properties to produce functional polymers.

Rapid determination of γ-value and xanthate group distribution on viscose by liquid-state (1)H NMR spectroscopy.

A method for the determination of the γ-value and more importantly the distribution of xanthate groups on cellulose xanthate produced during the viscose process is presented. The method is based upon stabilization of xanthate groups attached to the cellulose chain by reaction with 4-methylbenzyl bromide and analysis of the resulting product by liquid-state (1)H NMR. Careful analysis of the proton-spectrum using deconvolution gave a very fast method for the measurement of the γ-value which compared well with the data obtained by IR spectroscopy. In addition it could be shown that the distribution of the xanthate groups on the anhydroglucose monomeric unit (xanthation at position 2, 3 or 6) changes significantly during ripening. The method gave useful results even for viscose with low γ-values of about 25.

Generation of PHB from Spent Sulfite Liquor Using Halophilic Microorganisms.

Halophilic microorganisms thrive at elevated concentrations of sodium chloride up to saturation and are capable of growing on a wide variety of carbon sources like various organic acids, hexose and also pentose sugars. Hence, the biotechnological application of these microorganisms can cover many aspects, such as the treatment of hypersaline waste streams of different origin. Due to the fact that the high osmotic pressure of hypersaline environments reduces the risk of contamination, the capacity for cost-effective non-sterile cultivation can make extreme halophilic microorganisms potentially valuable organisms for biotechnological applications. In this contribution, the stepwise use of screening approaches, employing design of experiment (DoE) on model media and subsequently using industrial waste as substrate have been implemented to investigate the applicability of halophiles to generate PHB from the industrial waste stream spent sulfite liquor (SSL). The production of PHB on model media as well as dilutions of industrial substrate in a complex medium has been screened for by fluorescence microscopy using Nile Blue staining. Screening was used to investigate the ability of halophilic microorganisms to withstand the inhibiting substances of the waste stream without negatively affecting PHB production. It could be shown that neither single inhibiting substances nor a mixture thereof inhibited growth in the investigated range, hence, leaving the question on the inhibiting mechanisms open. However, it could be demonstrated that some haloarchaea and halophilic bacteria are able to produce PHB when cultivated on 3.3% w/w dry matter spent sulfite liquor, whereas H. halophila was even able to thrive on 6.6% w/w dry matter spent sulfite liquor and still produce PHB.

Dialkyl phosphate-related ionic liquids as selective solvents for xylan.

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.