Yukari Numata

Cross-polarization/magic-angle spinning 13C nuclear magnetic resonance study of cellulose I–ethylenediamine complex

Complete assignments of the cross-polarization/magic-angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectrum of the cellulose I-ethylenediamine (EDA) complex, which is the intermediate of the reaction from cellulose I to cellulose III(I), were performed. In this paper, we used the 13C-enriched cellulose that was biosynthesized by Acetobacter xylinum ATCC10245 strain from culture medium containing D-(2-13C), D-(3-13C), or D-(5-13C)glucose as a carbon source. After conversion into cellulose I-EDA complex by sufficient EDA treatment, the CP/MAS 13C NMR spectra of the 13C-enriched cellulose I-EDA complexes were measured. As a result, 13C resonance lines of each carbon of the cellulose moiety in the complex appeared as a singlet, suggesting that all glucose residues of the complex are magnetically equivalent. The difference in chemical shifts for each carbon between cellulose I-EDA and cellulose I(alpha), I(beta), and III(I), respectively, suggests that the conformation of the cellulose chains for cellulose I-EDA differs from that for cellulose I(alpha), I(beta), and III(I). In addition, fitting analysis of the 13C spectrum of Valonia cellulose I-EDA complex revealed that the complex contains one EDA molecule per two glucose residues in the cellulose chain.

Regulation of endoglucanase gene (cmcax) expression in Acetobacter xylinum

Although cellulose is the most abundant biopolymer in nature, the detailed mechanisms of cellulose biosynthesis remain unknown. Acetobacter xylinum is one of the best-studied model organisms for cellulose biosynthesis. Interestingly, the over-expression of the cmcax gene cause enhancement of cellulose production in A. xylinum, while its product (CMCax) has cellulose degradation activity. The addition of CMCax into medium also promotes cellulose production, suggesting that CMCax is involved in cellulose synthetic pathway. In the present study, we reveal the regulation mechanism of cmcax expression in A. xylinum. First, we treated cells with four kinds of beta-glucodisaccharide. Using an enzyme assay and real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), we observed an increase in CMCax activity and an induction of cmcax expression by gentiobiose treatment. Therefore, we concluded that gentiobiose induced cmcax expression. Although gentiobiose does not originally exist in the cultivation medium, we have revealed that membrane and intra-cellular proteins extracted from A. xylinum produce gentiobiose from glucose, which is one of the components in the cultivation medium. Furthermore, we confirmed that cmcax expression in a wild-type strain increased gradually after 5 d cultivation using real-time qRT-PCR. These results have led us to conclude that the increase in cmcax expression after 5 d cultivation is caused by the increase in gentiobiose, which could be synthesized by a condensation reaction in A. xylinum. Since CMCax plays a pivotal role in the cellulose production system, our results will contribute to the elucidation of mechanisms of cellulose biosynthesis.

CPMAS 13C NMR and X-ray studies of cellooligosaccharide acetates as a model for cellulose triacetate

A series of crystalline oligomers from α-D-cellobiose octaacetate through α-D-cellohexaose eicosaacetate were prepared by homogeneous acetylation of the corresponding cellooligosaccharides and characterized by cross-polarization and magic angle sample spinning (CPMAS) carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy and X-ray analysis to obtain the structural models of cellulose triacetate (CTA) in the solid state. Progressing toward the hexamer, the NMR spectral features of the oligomers, in comparison with two allomorphs of CTA I and CTA II, gradually approached those of CTA I. Specifically, chemical shifts of both the hexamer and pentamer were in agreement with those of CTA I. In addition, X-ray diffraction patterns of the oligomers established that the crystalline pentamer and hexamer had a CTA I lattice despite recrystallization from ethylacetate-n-hexane. Therefore, we conclude that the pentamer and hexamer are useful models for the CTA I structure.

Bacterial cellulose gels with high mechanical strength.

A composite structure was formed between polyethylene glycol diacrylate (PEGDA) and bacterial cellulose (BC) gels swollen in polyethylene glycol (PEG) as a solvent (BC/PEG gel) to improve the mechanical strength of the gels. The mechanical strength under compression and the rheostatic properties of the gels were evaluated. The compression test results indicated that the mechanical strength of the gels depended on the weight percent of cross-linked PEGDA in the gel, the chain length between the cross-linking points, and the cross-linking density of PEGDA polymers. The PEGDA polymers around the cellulose fibers were resistant to pressure; thus, the BC/PEG-PEGDA gel was stronger than the BC/PEG gel under compression. The results of transmittance measurements and thermomechanical analysis showed that the rheostatic properties of the gels were retained even after composite structure formation. BC/PEG-PEGDA gels, which are expected to be biocompatible, may be useful for clinical applications as a soft material.

Studies of the series of cellooligosaccharide peracetates as a model for cellulose triacetate by 13C CP/MAS NMR spectroscopy and X-ray analyses

Abstract The series of crystalline oligomers from α-cellobiose octaacetate through α-cellohexaose eicosaacetate, listed as below, was prepared from homogeneous acetylation of the corresponding cellooligosaccharides and characterized by 13 C CP/MAS NMR spectroscopy and X-ray analysis in order to obtain the structural models of cellulose triacetate (CTA) in solid state. Progressing toward the hexamer, the NMR spectral feature of the oligomers, in comparison with two allomorphs of CTA I and CTA II, gradually approached that of CTA I. Specifically, chemical shifts of both the hexamer and the pentamer were in considerable respective agreement with those of CTA I. In addition, X-ray diffraction patterns of the oligomers established that the crystalline pentamer and hexamer have a CTA I lattice in spite of recrystallization from ethylacetate–hexane. We therefore concluded that the pentamer and hexamer would be useful models for the CTA I structure.

Structural and mechanical characterization of bacterial cellulose–polyethylene glycol diacrylate composite gels

This study explores the structural and mechanical properties of bacterial cellulose-polyethylene glycol diacrylate (BC-PEGDA) composite gels. The molecular dynamics results obtained by solid-state 13C nuclear magnetic resonance analyses suggested that BC and PEGDA molecules were incompatible as composite gels, though BC fibers and PEGDA interact with each other. The mechanical strength of the gels depended on the amount of PEGDA, becoming softer and more stretchable when a tensile force was applied, but for a large amount of PEGDA, they became brittle. The BC-3% and 5% PEGDA gels had similar viscoelastic behaviors as a BC gel, and these composite gels could stick to human skin. Since BC-PEGDA composite gels are composed of BC and PEGDA-both of which are biocompatible, it is thought that these composite gels also have excellent biocompatibility. Taken together, we concluded that the BC-3% and 5% PEGDA gels have great potential for use in medical and cosmetic fields.

13C CP/MAS NMR AND X-RAY STUDIES OF CELLOOLIGOSACCHARIDE ACETATES AS A MODEL FOR CELLULOSE TRIACETATE

ABSTRACT The series of crystalline CTA oligomers (DS = 2−6) were prepared and characterized by 13 C CP/MAS NMR spectroscopy and X-ray analyses in order to obtain structural models of cellulose triacetate (CTA) in the solid state. Progressing toward hexamer, the NMR spectra of the oligomers, in comparison with CTA I and CTA II, gradually approached that of CTA I. In addition, X-ray diffractograms of the oligomers determined that the crystalline pentamer and hexamer have the CTA I lattice in spite of recrystallization from ethylacetate- n -hexane. We therefore concluded that the higher oligomers (DS > 4) of CTA would be useful models for CTA I structure.