Daisuke Ando

Nuclear spin conversion of methane in solid parahydrogen

The nuclear spin conversion of CH(4) and CD(4) isolated in solid parahydrogen was investigated by high resolution Fourier transform infrared spectroscopy. From the analysis of the temporal changes of rovibrational absorption spectra, the nuclear spin conversion rates associated with the rotational relaxation from the J=1 state to the J=0 state for both species were determined at temperatures between 1 and 6 K. The conversion rate of CD(4) was found to be 2-100 times faster than that of CH(4) in this temperature range. The faster conversion in CD(4) is attributed to the quadrupole interaction of D atoms in CD(4), while the conversion in CH(4) takes place mainly through the nuclear spin-nuclear spin interaction. The conversion rates depend on crystal temperature strongly above 3.5 K for CH(4) and above 2 K for CD(4), while the rates were almost constant below these temperatures. The temperature dependence indicates that the one-phonon process is dominant at low temperatures, while two-phonon processes become important at higher temperatures as a cause of the nuclear spin conversion.

A Comparative Study of Matrix‐ and Nano‐assisted Laser Desorption/Ionisation Time‐of‐Flight Mass Spectrometry of Isolated and Synthetic Lignin

INTRODUCTION Lignin is the second most abundant biopolymer next to cellulose. However, because of the complexity of the heterogeneous macromolecules, it is difficult to elucidate the polymeric structures of lignin by conventional analytical methods. OBJECTIVE To obtain the detailed structures of lignin, we comparatively applied nano-assisted laser desorption/ionisation time-of-flight mass spectrometry (NALDI-TOF MS) and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). METHODOLOGY Synthetic lignin from coniferyl alcohol and an isolated lignin from Pinus densiflora were subjected to NALDI- and MALDI-TOF MS. RESULTS We first obtained NALDI-TOF MS of synthetic and isolated lignin. Mass increments of 178 and 196 Da were observed in NALDI- and MALDI-TOF mass spectra of the synthetic and isolated lignin. The mass intervals indicated that radical coupling forming β-O-4 bonds is the major pathway. Peaks in the low molecular mass region between m/z 500 and 800 were observed more extensively using NALDI-TOF MS than MALDI-TOF MS, which enabled detailed analysis of the interunit linkages in lignin. CONCLUSION Owing to the ionisation profile differentiation from MALDI-TOF MS, NALDI-TOF MS is useful for the structural analysis of lignin.

Multi-step degradation method for β-O-4 linkages in lignins: γ-TTSA method. Part 3. Degradation of milled wood lignin (MWL) from Eucalyptus globulus

Abstract Milled wood lignin (MWL) of Eucalyptus globulus has been treated by a selective degradation method for β-O-4 linkages, which lets the lignin carbohydrate complexes (LCC) intact. The method consists of four reaction steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation and (4) mild alkali treatment (γ-TTSA method). Each step was followed by spectroscopies for chemical structural analysis; especially, the HSQC-NMR analysis was in focus. It was demonstrated that β-O-4 linkages were selectively and quantitatively cleaved by the γ-TTSA method while the β-β linkages in the MWL remained intact. The method leads to an enrichment of LCCs.

Multi-steps degradation method for β-O-4 linkage in lignins: γ-TTSA method. Part 1: Reaction of non-phenolic dimeric β-O-4 model compounds

Abstract The so-called γ-TTSA method has been developed for the cleavage of β-O-4 linkages in lignin. It consists of four steps: (1) γ-tosylation, (2) thioetherification (substitution reaction with 1-dodecanethiol to γ-thioether), (3) sulfonylation (oxidation from γ-thioether to γ-sulfone), and (4) mild alkali degradation of γ-sulfone. The method was tested on non-phenolic dimeric β-O-4 lignin model compounds: 1G (4-benzyloxy-3-methoxyphenylglycerol-β-guaiacyl ether), 1S (4-benzyloxy-3,5-dimethoxyphenylglycerol-β-syringyl ether), and 1H (4-benzyloxyphenylglycerol-β-phenyl ether). It is demonstrated that the mild alkali degradation of the γ-sulfone group proceeds efficiently, i.e., the electron-withdrawing sulfone group at γ-position contributes to the cleavage of β-O-4 linkages. The γ-TTSA method may be especially useful for the elucidation of lignin-carbohydrate complex structures containing benzylether bonds.

Elucidation of LCC bonding sites via γ-TTSA lignin degradation: crude milled wood lignin (MWL) from Eucalyptus globulus for enrichment of lignin xylan linkages and their HSQC-NMR characterization

Abstract The selective lignin degradation in a LCC was proceeded with the γ-TTSA method, which is a selective cleavage method for β-O-4 linkages in lignins, in order to obtain more precise information concerning LCC bonding sites. To this purpose, crude MWL from Eucalyptus globulus, containing lignin and xylan, was treated by the γ-TTSA method. This approach consists of four steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation, and (4) mild alkali treatment. The degradation products were extracted consecutively with Et2O, EtOAc, and THF for the lignin removal, and thus the residue was enriched in LCCs. The residue was characterized by HSQC-NMR. Results indicated that the residue contained xylan and β-β substructures, although lignin was degraded. It can be concluded that the β-β substructures play an important role in the bonding sites between lignin and xylan of Eucalyptus globulus.

Multistep degradation method for β-O-4 linkage in lignins: γ-TTSA method. Part 2: reaction of lignin model polymer (DHP)

Abstract A selective cleavage method for β-O-4 linkages (the γ-TTSA method) was introduced in previous works, which consists of four reaction steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation, and (4) mild alkali degradation. This method was applied to the degradation of a lignin polymer model (dehydrogenation polymer, DHP) consisting of guaiacyl units. Each reaction step was followed by Fourier transform infrared (FT-IR) spectroscopy and heteronuclear single quantum coherence nuclear magnetic resonance (HSQC-NMR) spectroscopy. It was demonstrated that only the β-O-4 linkage was selectively cleaved by the γ-TTSA method, although other linkages, such as β-5 and β-β linkages, were also present in the DHP. Consequently, the γ-TTSA method is expected to be also useful for the degradation of native lignins.

threo-2-(2,6-Dimethoxy-phen-oxy)-1-(4-eth-oxy-3-methoxy-phen-yl)propane-1, 3-diol

In the crystal structure of the title compound, C20H26O7, a lignin model compound, the asymmetric unit contains two molecules which adopt almost identical overall conformations with some deviation in the region of the terminal hydroxyl groups. The two molecules are linked by an intermolecular O—H⋯O hydrogen bond. They also develop intramolecular O—H⋯O hydrogen bonds.

Influence of drying process on reactivity of cellulose and xylan in acetylation of willow (Salix schwerinii E. L. Wolf) kraft pulp monitored by HSQC-NMR spectroscopy

The acetylation behavior of xylan and cellulose in kraft pulp (KP) was investigated. Heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) spectroscopy was used to identify the positions at which the hydroxyl groups of polysaccharides were acetylated. X-ray diffraction analysis was used to determine the acetylation of cellulose in the crystal region. It was found that only xylan was obviously acetylated in the initial stages of the reaction. In the next stage of the acetylation, however, both the xylan and surface of the cellulose crystals reacted. Then, acetylation of the inner crystal region of the cellulose started before the completion of the xylan modification. To improve the reactivity of xylan in KP, the effect of drying or the dehydration of never-dried KP prior to acetylation was also investigated. The use of supercritical CO2 (scCO2) drying produced a KP with a higher specific surface area. This caused the xylan to exhibit a higher reactivity than that resulting from freeze drying and vacuum drying after solvent exchange. Furthermore, never-dry dehydration pretreatment produced xylan with the highest reactivity. This suggests that the cellulose–cellulose and/or cellulose–hemicellulose adhesion in the cell wall that arises as a result of drying reduces the reactivity of the xylan.