Papers - UTO Takuya
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Structural stability of the molecular chain sheets composing the crystal structures of cellulose allomorphs: A theoretical study Invited
Takuya Uto, Tsutomu Yonekura, Toshifumi Yui
Cellulose Communications 25 ( 1 ) 20 - 23 2018.3
Authorship：Lead author, Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Cellulose Society of Japan
The structural stabilities of the molecular chain sheet models isolated from the crystal structures of the four cellulose allomorphs, Iα, Iβ, II, and III_I, were studied by density functional theory (DFT) optimization. Intermolecular hydrogen bonds connect molecular chains to form a molecular chain sheet. The DFT-optimized (110) and (100) chain sheet models of the cellulose Iα and Iβ allomorphs, respectively, developed a right-handed twist with a similar amount of twisting. The DFT-optimized cellulose II (010) and (020) models oppositely twisted with right- and left-handed chirality, respectively. The cellulose III_I (1−10) model retained the initial flat structure after the DFT-optimization. The structural features of the DFT-optimized chain sheet models reflected those of the parent crystal models observed in solvated molecular dynamics (MD) simulations.
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Cellulose crystal dissolution in imidazolium-based ionic liquids: A theoretical study Reviewed International journal
Takuya Uto, Kazuya Yamamoto, Jun-ichi Kadokawa
The Journal of Physical Chemistry B 122 ( 1 ) 258 - 266 2018.1
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society (ACS)
The highly crystalline nature of cellulose results in poor processability and solubility, necessitating the search for solvents that can efficiently dissolve this material. Thus, ionic liquids (ILs) have recently been shown to be well suited for this purpose, although the corresponding dissolution mechanism has not been studied in detail. Herein, we adopt a molecular dynamics (MD) approach to study the dissolution of model cellulose crystal structures in imidazolium-based ILs and gain deep mechanistic insights, demonstrating that dissolution involves IL penetration-induced cleavage of hydrogen bonds between cellulose molecular chains. Moreover, we reveal that in ILs with high cellulose dissolving power (powerful solvents, such as 1-allyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium chloride), the above molecular chains are peeled from the crystal phase and subsequently dispersed in the solvent, whereas no significant structural changes are observed in poor-dissolving-power solvents. Finally, we utilize MD trajectory analysis to show that the solubility of microcrystalline cellulose is well correlated with the number of intermolecular hydrogen bonds in cellulose crystals. The obtained results allow us to conclude that both anions and cations of high-dissolving-power ILs contribute to the stepwise breakage of hydrogen bonds between cellulose chains, whereas this breakage does not occur to a sufficient extent in poorly solubilizing ILs.
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Theoretical study of the structural stability of molecular chain sheet models of cellulose crystal allomorphs Reviewed International journal
Takuya Uto, Sho Mawatari, Toshifumi Yui
The Journal of Physical Chemistry B 118 ( 31 ) 9313 - 9321 2014.7
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society (ACS)
The structural stabilities of the molecular chain sheets constituting the crystal structures of the cellulose allomorphs Iα, Iβ, II, and III_I were investigated by density functional theory (DFT) optimization of the isolated chain sheet models with finite dimensions. The DFT-optimized chain sheet models of the two native cellulose crystals developed a right-handed twist with a similar amount of twisting. The DFT-optimized cellulose II (010) and (020) models twisted in opposite directions with right- and left-handed chirality, respectively. The cellulose III_I (1-10) model retained the initial flat structure after the DFT-optimization. The structural features of the DFT-optimized chain sheet models were reflected in the structures of the parent crystal models observed in solvated molecular dynamics (MD) simulations. The minor conformations of the hydroxymethyl groups proposed in the real crystal structures were detected in the MD crystal models and the DFT-optimized (010) model of cellulose II. The crystal chain packing and crystal conversions are interpreted in terms of principal chain sheet stacking.
DOI： 10.1021/jp503535d
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Prediction of cellulose nanotube models through density functional theory calculations Reviewed International journal
Takuya Uto, Tatsuhiko Miyata, Toshifumi Yui
Cellulose 21 ( 1 ) 87 - 95 2014.2
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Nature
We report the generation of a nano-scale tubular structure of cellulose molecules (CelNT), through density functional theory (DFT) calculations. When a cellulose III_I (100) chain sheet model is optimized by DFT calculations, the sheet models spontaneously roll into tubes. The oligomers arrange in a right-handed, four-fold helix with one-quarter chain staggering, oriented with parallel polarity similar to the original crystal structure. Based on a one-quarter chain staggering relationship, six large CelNT models, consisting of 16 cellulose chains with DP = 80, are constructed by combinations of two types of chain polarities and three types of symmetry operations to generate a circular arrangement of molecular chains. All six CelNT models are examined by molecular dynamics (MD) calculations in chloroform. While four CelNT models retain a tubular form throughout MD calculations, the remaining two deform. 3D-RISM theory model is used to estimate the solvation free energies of the four CelNT models. The results suggest that the CelNT model with a chain arrangement of parallel polarity and right-handed helical symmetry forms the most stable tube structure.
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Enhancement of ethanol production from Napiergrass (Pennisetum purpureum Schumach) by a low-moisture anhydrous ammonia pretreatment Reviewed International journal
Masahide Yasuda, Keisuke Takeo, Hayato Nagai, Takuya Uto, Toshifumi Yui, Tomoko Matsumoto, Yasuyuki Ishii, Kazuyoshi Ohta
Journal of Sustainable Bioenergy Systems 3 ( 3 ) 179 - 185 2013.9
Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Research Publishing
Napiegrass (Pennisetum purpureum Schumach) was treated with a low-moisture anhydrous ammonia (LMAA) pretreatment by adding an equal weight of water and keeping it under atmospheric ammonia gas at room temperature for four weeks. After the removal of ammonia and washing with water, a simultaneous saccharification and fermentation (SSF) was conducted for the LMAA-pretreated napiergrass (1.33 g) in a buffer solution (8 mL) using a mixture of a cellulase (80 mg) and a xylanase (53 mg) as well as the cell suspension (0.16 mL) of Saccharomyces cerevisiae. Ethanol and xylose resulted in 91.2% and 62.9% yields, respectively. The SSF process was scaled up using LMAA-pretreated napiergrass (100.0 g) to give ethanol (77.2%) and xylose (52.8%). After the removal of ethanol, the pentose fermentation of the SSF solution (40 mL), which contained 1.00 g of xylose, using cell suspension of Escherichia coli KO11 (70 mL) gave 86.3% yield of ethanol. Total ethanol yield reached 68.9% based on xylan (21.4 wt%) and glucan (39.7 wt%) of the LMAA-pretreated napiergrass.
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Partial crystalline transformation of solvated cellulose IIII crystals, reproduced by theoretical calculations Reviewed International journal
Takuya Uto, Takashi Hosoya, Sachio Hayashi, Toshifumi Yui
Cellulose 20 ( 2 ) 605 - 612 2013.4
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Nature
In hot-water molecular dynamics simulation at 370 K, four cellulose III_I crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1-10) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3-O6 to cellulose-I-like O2-O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1-10) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (100) models were more stable than the cellulose III_I (1-10) models. The optimized structure of cellulose III_I (100) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose III_I to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis.