Lignin model compound studies

Partial Rate Factors for Protodedeuteration in Perchloric Acid Solution. All lignin model compounds studied contained hydroxyl, methoxyl, and methyl groups as the only substituent groups. Table II summarizes what the authors believe are the most reliable partial rate factors for these substituents in perchloric acid solution. All partial rate factors are based on determinations in 57% perchloric acid solutions. The partial rate factors for ortho and para positions of methyl and methoxyl groups are based on later work by Suzuki (21). The partial rate factors for phenol were calculated from data on 2, 4, 6-trideuterophenol (6) using the value 9.1 X 10-5 hr.-1 for monodeuterobenzene by Suzuki (21) and assuming 1 3.2 ortho to para ratio. 

Jakobsons, J., J. Gravitis, and V. G. Dashevskii. 1981. Theoretical analysis of conformations of lignin model compounds Studies of internal rotation, the relative stability of rotamers and an intramolecular hydrogen bond in vanillin and m-methoxybenzaldehyde molecules. Zh. Strukt. Khim. 22(2) 43-51. 

QY Hu, C Daneault, and S Robert. Use of a nitrogen-centered peroxide activator to increase the chromophore removal potential of peroxide Lignin model compound study. J. Wood. Chem. Technol. 26 165-174, 2006. 

Chemistry ofDelig niiic tion. The chemistry of delignification is complex and, despite the extensive Hterature, not completely understood. A variety of lignin model compounds have been studied and the results compared with the observed behavior of lignin during pulping (1,10—12,16). 

Studies of pathogenic fungi suggested an explanation for the absence of inducer molecules in host root exudate. Quinones such as 2,6-DMBQ have been shown to be released by white rot fungi as terminal oxidation products of lignin model compounds (38). These findings substantiated previous reports (39-41) that laccases, phenol oxidases using 0 as the oxidant, are directly involved in... 

Model studies showed that veratryl alcohol could mediate the oxidation of a polymeric lignin model compound under certain conditions but could not mediate the oxidation of small molecule model compounds. 

Molecular Weight Distribution Studies Using Lignin Model Compounds... 

Figure 1. Structures of lignin model compounds used in this study.

None of the low-molecular-weight lignin model compounds used in this study, derivatized or not, clearly exhibited associative behavior in the presence of higher fractional polarity eluants. This indicates that the self-association constants for these compounds in these media are small, at least for the concentration range studied. 

The most extensive and systematic study of the chemistry of lignin with theoretical methods has been performed by Remko and co-workers. Their work has involved the nature of intramolecular (40-43) and inter-molecular (44-48) hydrogen bonding of lignin model compounds, spectral transitions (49-52), and conformational analysis (53). The methods used have included CNDO/2 and PCILO (Perturbative Configuration Interaction using Localized Orbitals) (54). 

The lignin model compounds selected for this study possess two functional groups, a phenolic hydroxyl group, and an aliphatic hydroxyl group located on the side chain para to the phenolic hydroxyl group. Experiments were performed to determine the effect of blocking each of these two sites relative to the formation of chromophoric structures. 

Fusion with Alkali and Cupric Oxide in Nonaqueous Solvents. Alkali lignin was fused with potassium hydroxide and cupric oxide in methanol under conditions suggested by Tiemann (20) and in n-amyl alcohol as suggested by Klages (4). These procedures were very effective in earlier model compound studies in our laboratories (12). Ether extracts obtained were less than those from corresponding experiments in aqueous solution, and qualitative compositions were essentially the same. In the case of the amyl alcohol experiments, artifacts with the cupric oxide were obtained. Again, experiments were conducted under more dilute conditions in a bomb under superatmospheric conditions, but results were no better. 

In order to prevent the light-induced yellowing processes of TMP (thermal mechanical pulp) paper a better understanding of the photochemistry of lignins is paramount. In recent years this significant objective has stimulated much interest in the fundamental study of the photophysical as well as the photochemical processes of some lignin model compounds, such as the a-guaiacoxylacetoveratrone (GAY). Basically there are three... 

The lignin model compounds and their derivatives used in this study were custom synthesized at Queen s University by Dr. R. Bowers (Colour Your Enzyme). CIDEP and conventional ESR experiments were conducted using either a Varian E-104 spectrometer or a customized Bruker X-band spectrometer, modified similarly as previously described (7). The light source used for in situ irradiation was either a super high pressure 200 W mercury lamp, a Lambda-Physik EMG101-MSC XeCl excimer laser at 308 nm., or a Quanta-Ray GCR-11 Nd YAG solid state laser equipped for all four harmonic generations. 

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