This article attempts to bring together basic and complex information which has been gathered on cellulose structure, principally that of native cellulose, over the last few decades. Even though advances have been made in the field of crystallography, powder crystallography cannot yield a definitive cellulose structure and single crystal diffraction is not possible due to the lack of suitable crystals. Knowledge obtained on the biosynthesis of native cellulose and on the polymorphy of cellulose and its derivatives help our understanding of ultrastructure. Many inconsistencies between early crystallographic studies of native cellulose have been clarified by the discovery that two polymorphs (α and β) of cellulose I exist. Models of the possible ultrastructural arrangements within native cellulose have been put forward over the decades; with advancement in technology, computer simulations of small and large systems are being created to test the viability of these ultrastructural models. It is hoped that this review will aid in the understanding of the complexity and uncertainties that still exist in this subject

Cellulose: the structure slowly unravels

N-heterocyclic carbene analogues with low-valent group 13 and group 14 elements: syntheses, structures, and reactivities of a new generation of multitalented ligands.

Novel multifunctional polymers from aromatic diamines by oxidative polymerizations.

Polymeric materials, natural and unnatural, are indispensable to the modern society. They are widely used from everyday life usages as commodity materials to industry and technology usages in the fields such as electronics, machinery, communications, transportations, pharmacy, and medicine as highly advanced materials. Today, it is hard to think of the present society without polymeric materials. Developments of various polymeric materials have been owed to epoch-making innovative works as exemplified typically by the discovery of Ziegler-Natta catalyst,1-3 the concept of living polymerization,4 the discovery of conducting polymers,5 and the discovery of metathesis catalyst.6,7 These observations demonstrate that new polymeric materials are often brought about by new production methods including polymerization catalysts. Historically, polymerization catalysts utilized classical catalysts of acids (Brønsted acids, Lewis acids, and various cations), bases (Lewis bases and various anions), and radical generating compounds since the 1920s, the early stage of polymer chemistry. In the following * To whom correspondence should be addressed. Fax/Tel: (+81)-75-7247688. E-mail: kobayash@kit.ac.jp. † Kyoto Institute of Technology and Emeritus Professor of Kyoto University. ‡ Kyoto University. Chem. Rev. 2009, 109, 5288–5353 5288

Enzymatic polymer synthesis: an opportunity for green polymer chemistry.

Interactions of Cyclophilin with the Mitochondrial Inner Membrane and Regulation of the Permeability Transition Pore, a Cyclosporin A-sensitive Channel

One-step conversion of unprotected sugars to β-glycosyl azides using 2-chloroimidazolinium salt in aqueous solution

Strong bases (lithium diisopropylamide (LDA) or BuLi) convert cyclosporin A (CS) to hexalithio derivative containing a Li alkoxide, four Li azaenolate, and one Li enolate units. The Li6 compound is solubilized in tetrahydrofuran (THF) by addition of excess LDA or LiCl. Reactions with electrophiles (alkyl halides, aldehydes, ClCO2R, CO2, (RS)2, D2O) at low temperatures give products containing new side chains in amino-acid residue 3 of the cyclic undecapeptide (see 1–13, Schemes 1, and 2, and Figs. 1 and 2) in moderate to high yields and, with Re- or Si-selectivities, depending upon the conditions of lithiation of up to 7:1, Pure CS derivatives (Scheme 2, Table 1 in the Exper. Part) can be isolated by column chromatography. N-Alkylations or cleavage of the peptide backbone by carbonyl addition occur only at higher temperatures and/or with prolonged reaction times (see 14 and 15 in Scheme 4). Very little or no epimerization of stereogenic centers occurs under the conditions employed. Possible reasons for the feasibility of these surprizing conversions of CS are discussed (Schemes 4 and 5 and Fig. 3). For comparision, [MeAla3]CS (2b) and [D-MeAla3]CS (2a) were also prepared by conventional peptide synthesis in solution (Schemes 6 and 7). Their 1H- and 13C-NMR spectra are compared with those of CS (Table 2 in the Exper. Part).

Modification of Cyclosporin A (CS): Generation of an enolate at the sarcosine residue and reactions with electrophiles

Cellulose microfibrils with an electron diffraction pattern characteristic of crystalline native cellulose I have been assembled abiotically by means of a cellulase-catalyzed polymerization of beta-cellobiosyl fluoride substrate monomer in acetonitrile/acetate buffer. Substantial purification of the Trichoderma viride cellulase enzyme was found to be essential for the formation of the synthetic cellulose I allomorph. Assembly of synthetic cellulose I appears to be a result of a micellar aggregation of the partially purified enzyme and the substrate in an organic/aqueous solvent system favoring the alignment of glucan chains with the same polarity and extended chain conformation, resulting in crystallization to form the metastable cellulose I allomorph.

Assembly of synthetic cellulose I.

Tomonari Tanaka, Takeshi Matsumoto, Masato Noguchi, Atsushi Kobayashi, and Shin-ichiro ShodaDepartment of Biomolecular Engineering, Graduate School of Engineering, Tohoku University,6-6-11-514 Aoba, Sendai 980-8579(Received February 25, 2009; CL-090193; E-mail: shoda@poly.che.tohoku.ac.jp)Aryl 1-thioglycosides have directly been synthesized ingood yields from the corresponding unprotected sugars andthiols without protection of the hydroxy groups by using 2-chloro-1,3-dimethylimidazolinium chloride (DMC) as dehydra-tive condensing agent. The reaction proceeded in a mixed sol-vent of water and acetonitrile under mild reaction conditions,leading to the predominant formation of -anomers.There has beena growing research interest inthioglycosidesincarbohydratechemistry.

Shin-ichiro Shoda

Papers

One-step conversion of unprotected sugars to β-glycosyl azides using 2-chloroimidazolinium salt in aqueous solution

Modification of Cyclosporin A (CS): Generation of an enolate at the sarcosine residue and reactions with electrophiles

Assembly of synthetic cellulose I.

Direct Transformation of Unprotected Sugars to Aryl 1-Thio-β-glycosides in Aqueous Media Using 2-Chloro-1,3-dimethylimidazolinium Chloride

A facile enzymatic synthesis of cellooligosaccharide derivatives using β-lactosyl fluoride