Structural analysis of lignin by resonance Raman spectroscopy

Resonance Raman (RR) spectroscopy, combined with Kerr gated fluorescence rejection in the time domain, has recently elucidated lignin structure with unique sensitivity and selectivity. This promises structural studies of fluorescent natural macromolecules, such as lignin, which were previously not possible. Such studies rely on an improved understanding of the RR spectral behavior of lignin, which is today scarcely understood. We explain for the first time this behavior by a semi-empirical theory, and observe its pertinent features for lignin in vascular plants. We have used well-defined oxidative treatments as means of probing lignin structural elements, and show that RR sensitivity and selectivity depend crucially on excitation wavelength. Through the theory we relate these results to basic structural aspects of lignin. Spectra obtained by blue light laser excitation (400 nm) are dominated by low redox potential syringyl lignin groups, whereas lower photon energy (500 nm) decreases the selectivity markedly. RR bands depend on molecular structure but also on molecular environment. Thus charge transfer donor-acceptor interactions within lignin reduce the intensity of bands associated with electron rich moieties. New possibilities for basic and selective structural information on fluorescent natural materials, such as lignin, have thus appeared.     

Kinetics of gas-liquid ozonization of veratrole and its derivatives

The kinetics was studied for the reactions of ozone with model lignin compounds, viz., phenol, veratrole, veratric aldehyde, and veratric alcohol. Using the mass transfer model for a chemical reaction based on the film theory, the reaction rate constants were calculated. The reaction rate constants determined by both the ozone absorption rate and changes in the substrate concentration coincide satisfactorily, indicating adequacy of the kinetic model chosen. A relationship between the structure of the compounds under study and their reactivity was found. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1941–1946, October, 2007.     

Peroxidase-catalyzed synthesis of lignin–phenol copolymers

Horseradish peroxidase catalyzes the copolymerization of phenols with kraft lignin in aqueous-organic solvent mixtures. Nearly all of the lignin and over one-third of the phenol (either p-cresol or p-phenylphenol) is incorporated into the copolymer which is highly insoluble in dimethylformamide (DMF), presumably because of crosslinking of lignin molecules via polyphenol bridges. The copolymer consists of 80% lignin, by weight. In the absence of a phenol, lignin is polymerized into a noncrosslinked, DMF-soluble material. Thermal analysis shows that the copolymerization of phenols with lignin results in a material with markedly lower glass transition temperatures and higher (and more uniform) curing exotherms. The materials appear to act as thermosets and may have application as replacements of conventional phenolic resins. © 1993 John Wiley & Sons, Inc.     

Analysis of lignin degradation products by capillary electrophoresis

Summary A method for the quantitative analysis of phenolic lignin degradation products by capillary electrophoresis (CE) with on-column UV detection has been developed. The liquid biomass solutions contain low molecular hemicellulosic sugars and phenolic lignin degradation products with various degrees of polymerization. Special attention has been paid to the monomeric phenolic components of lignin degradation fragments, e.g. derivatives of phenolic acids, aldehydes, and alcohols. Uncoated fused silica capillaries and borate-phosphate buffer systems at moderate pH conditions were used in order to separate the compounds of interest. To provide validation of the method, the same samples were analyzed independently by HPLC using gradient elution on a RP-C18 column. As sugar degradation fragment, furan-2-carboxylic acid was detected.     

Colloidal chemistry as a guide to design intended dispersions of carbon nanomaterials

In this review, some established concepts from Colloidal Science and their application to graphene and carbon nanotubes dispersions in organic or aqueous media are highlighted to rationalize alternatives for some issues in terms of colloidal properties. Recent applications for carbon-based dispersions are presented, as well as van der Waals interactions in carbon materials and strategies to overcome these interactions, such as increasing electrostatic repulsion between dispersed particles, surface functionalization, or adsorption of passivation agents such as macromolecules, which are the basis of many dispersion and exfoliation procedures. The demonstration of how knowledge and fine control of colloidal interactions have been used to overcome several limitations, such as the preparation of stable and concentrated dispersions of carbon materials and keeping appreciable electrical conductivity, is presented. It is also showed that the same knowledge can help the development of more environmentally friendly carbon-based colloids as well as the improvement of similar systems as dispersions of two-dimensional materials.     

Pretreatment of softwood by acid-catalyzed steam explosion followed by alkali extraction

A process for converting lignocellulosic biomass to ethanol hydrolyzes the hemicellulosic fraction to soluble sugars (i.e., pretreatment), followed by acid- or enzyme-catalyzed hydrolysis of the cellulosic fraction. Enzymatic hydrolysis may be improved by using an alkali to extract a fraction of the lignin from the pretreated material. The removal of the lignin may increase the accessibility of the cellulose to enzymatic attack, and thus improve overall economics of the process, if the alkali-treated material can still be effectively converted to ethanol. Pretreated Douglas fir produced by a sulfuric-acid-catalyzed steam explosion was treated with NaOH, NH₄OH, and lime to extract some of the lignin. The treated material, along with an untreated control sample, was tested by an enzymatic-digestion procedure, and converted to ethanol by simultaneous saccharification and fermentation using a glucose-fermenting yeast. NaOH was most effective at removing lignin (removed 29%), followed by NH4OH and lime. However, the susceptibility of the treated material to enzymatic digestion was lower than the control and decreased with increasing lignin removal. Ethanol production was similar for the control and NaOH-treated material, and lower for NH₄OH- and lime-treated material.     

Variation of S/G ratio and lignin content in a Populus family influences the release of xylose by dilute acid hydrolysis

Wood samples from second generation Populus cross were shown to have different lignin contents and S/G ratios (S: syringyl-like lignin structures; G: guaiacyl-like lignin structures). The lignin contents varied from 22.7% to 25.8% and the S/G ratio from 1.8 to 2.3. Selected samples spanning these ranges were hydrolyzed with dilute (1%) sulfuric acid to release fermentable sugars. The conditions were chosen for partial hydrolysis of the hemicellulosic fraction to maximize the expression of variation among samples. The results indicated that both lignin contents and S/G ratio significantly affected the yield of xylose. For example, the xylose yield of the 25.8% lignin and 2.3 S/G (hihg lignin, high S/G) sample produced 30% of the theoretical yield, whereas the xylose yield of the 22.7% lignin and 1.8 S/G (low lignin, low S/G) was 55% of the theoretical value. These results indicate that lignin content and composition among genetic variants within a single species can influence the hydrolyzability of the biomass.     

Edge Plane Pyrolytic Graphite Electrodes for Halide Detection in Aqueous Solutions

The behavior of chloride, bromide and iodide at edge plane pyrolytic graphite electrodes has been explored in aqueous acid solutions. The voltammetric response in each case has been compared with that of basal plane pyrolytic graphite, glassy carbon and boron‐doped diamond. The electrochemical oxidation of chloride is found to only occur on boron‐doped diamond while the electrochemical reversibility for the oxidation of bromide on edge plane pyrolytic graphite is similar to that seen at glassy carbon whilst being superior to basal plane pyrolytic graphite and boron‐doped diamond. In the case of iodide oxidation, edge plane and basal plane pyrolytic graphite and glassy carbon display similar electrode kinetics but are all superior to boron‐doped diamond. The analytical possibilities were examined using the edge plane pyrolytic graphite electrode for both iodide and bromine where is was found that, based on cyclic voltammetry, detection limits in the order of 10^?6 M are possible.     

Octyl glucoside inhibits [14C]DHP mineralization whereas peroxidase activity is stimulated inPhanerochaete Chrysosporium

Octyl glucoside stimulated peroxidase formation inPhanerochaete chrysosporium ME-446 cultivated in cellulose-based media. Addition of 0.1% of the nonionic surfactant resulted in a ninefold (143 U/L) and sixfold (119 U/L) increase in LiP formation under conditions of N limitation and N excess, respectively. Octyl glucoside also stimulated MnP formation, but to a lesser extent than observed with LiP. The cellobiose-oxidizing enzymes (cellobiose dehydrogenase and cellobiose:quinone oxidoreductase) were stimulated by octyl glucoside when used at a concentration of up to 0.05%, but higher concentrations gave values similar to those for the controls. Little proteolytic activity was detected in the presence of the surfactant. In general, activities of the enzymes studied were of the same order as those seen using Tween-80. In contrast with Tween-80, octyl glucoside markedly inhibited [¹⁴C]DHP mineralization. Attempts to account for the observed inhibition of synthetic lignin degradation by P.chrysosporium in the presence of octyl glucoside are discussed.