Pirkko Karhunen

DIBENZODIOXOCINS : A NOVEL TYPE OF LINKAGE IN SOFTWOOD LIGNINS

Abstract Correlation peaks found in HMQC spectra of softwood lignins have been assigned to a dibenzodioxocin structure with the aid of model compounds. It constitutes a major hitherto unknown structure in softwood lignins.

The formation of dibenzodioxocin structures by oxidative coupling. A model reaction for lignin biosynthesis

Abstract Oxidation of o,o′-dihydroxybiphenyl compounds together with coniferyl alcohol yields substituted 6,7-dihydro-dibenzo-(e,g)(1,4)-dioxocins, that represent a novel type of linkage in softwood lignins. The mechanism of formation of the 8-membered ring involves intramolecular nucleophilic addition to an intermediate quinone methide structure.

Relative and inherent reactivities of imidazolium-based ionic liquids: the implications for lignocellulose processing applications

Novel methods for the fractionation of wood, as a major renewable chemical and material feedstock, are in demand. Ionic liquids, such as 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), are promoted as potential media for these processes. However, the chemical stabilities of such ionic liquids are in question as they may have an effect on process sustainability or efficiency. With anion nucleophilicity and basicity being implicated more in ionic liquid reactivity, a rough scale of the relative reactivities for [emim]-based ionic liquids is demonstrated, based upon their TGA decomposition temperatures. These values are compared to the proton affinities for the anions of those ionic liquids, as a crude measure of nucleophilicity or basicity. The implications for the temperature-dependent chemical stability of imidazolium-based ionic liquids are discussed, in regard to their interactions with wood biopolymers. It is observed that for ionic liquids with less diffuse anions (more nucleophilic or basic), such as [emim][OAc], they unfortunately become more unstable. This is exhibited by a decrease in the thermal stability and an increase in the degree of interaction with the biomass, to the point of better solvation and even covalent interactions with dissolved components. The ab initio proton affinities, dipole moments, van der Waals surface area, and volumes, are presented for an extended series of anions, commonly used in ionic liquids.

Localization of dibenzodioxocin substructures in lignifying Norway spruce xylem by transmission electron microscopy-immunogold labeling

The lignification process in mature Norway spruce [Picea abies (L.) H. Karsten] xylem cell walls was studied using transmission electron microscopy (TEM)–immunogold detection with a polyclonal antibody raised against a specific lignin substructure, dibenzodioxocin. The study reveals for the first time the exact location of this abundant eight-ring structure in the cell wall layers of wood. Spruce wood samples were collected in Southern Finland at the time of active growth and lignification of the xylem cell walls. In very young tracheids where secondary cell wall layers were not yet formed, the presence of the dibenzodioxocin structure could not be shown at all. During secondary cell wall thickening, the dibenzodioxocin structure was more abundant in the secondary cell wall layers than in the middle lamella. The highest number of gold particles revealing dibenzodioxocin was in the S2+S3 layer. Statistically significant differences were found in the frequency of gold particles present in various cell wall layers. For comparison, wood sections were also cut with a cryomicrotome for light and fluorescence microscopy.

Application of OECD Guideline 423 in assessing the acute oral toxicity of moniliformin.

Moniliformin is a Fusarium mycotoxin highly prevalent in grains and grain-based products worldwide. In this study, the acute oral toxicity of moniliformin was assessed in Sprague-Dawley male rats according to OECD Guideline 423 with a single-dose exposure. Clinical observations and histopathological changes were recorded together with the excretion of moniliformin via urine and feces, utilizing a novel liquid chromatography-mass spectrometry method. According to our study, moniliformin is acutely toxic to rats with a rather narrow range of toxicity. Moniliformin can be classified into category 2 (LD(50) cut-off value 25 mg/kg b.w.), according to the Globally Harmonized System for the classification of chemicals. The clinical observations included muscular weakness, respiratory distress and heart muscle damage. Pathological findings confirmed that heart is the main target tissue of acute moniliformin toxicity. A significant proportion (about 38%) of the administered moniliformin was rapidly excreted in urine in less than 6 h. However, the toxicokinetics of the majority of the administered dose still requires clarification, as the total excretion was only close to 42%. Considering the worldwide occurrence of moniliformin together with its high acute toxicity, research into the subchronic toxicity is of vital importance to identify the possible risk in human/animal health.

Synthesis and crystal structure determination of model compounds for the dibenzodioxocine structure occurring in wood lignins

Model compounds for the dibenzodioxocine structure, a new structural unit recently discovered in wood lignins, have been synthesised by two different methods. In one route, the 8-membered ring is formed by ring closure of an arylglycerol β-aryl ether with a 5,5′-biphenyl structure in the aryl ether moiety. The other, which gave better yields, involves a biomimetic oxidative phenol coupling. Crystal structures have been obtained for one β-aryl ether and of two dibenzodioxocine isomers, as well as of a product of acid hydrolysis containing a 7-membered ring structure.

Cellulose fatty acid esters as sustainable film materials – effect of side chain structure on barrier and mechanical properties

Cellulose is mainly utilized by industry for paper and packaging materials. Due to ecological awareness this biopolymer has recently received an increasing amount of attention as a renewable alternative for replacing traditional oil based products. In this work, hydrophobic cellulose based materials were prepared by acylation of cellulose with tall oil fatty acid based saturated, unsaturated and branched fatty acids. Films were prepared by casting, and their oxygen and water vapour permeabilities as well as mechanical and thermal properties were characterized. Unsaturation and branching had a significant effect on the properties of the films. Comparing these materials with already existing commercial products showed that fatty acid modification of cellulose yields films with increased thermal stability, low water vapour transmission rates and enhanced tensile and elastic properties.

Investigation of lignin models of the biphenyl type by X-ray crystallography and NMR spectroscopy

AbstractLignin models of the biphenyl type have been synthesized and crystal structures of two of them have been determined. The tetraacetate of 5,5′-bis(hydroxymethyl)-3,3′-dimethoxy-2,2′-biphenyldiol crystallizes in space group

Oxidative Coupling of Phenols and the Biosynthesis of Lignin

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