Chemical Synthesis of Native-Type Cellulose and Its Analogues via Enzymatic Polymerization

Abstract

The first successful chemical synthesis of cellulose was achieved by a polycondensation of β-cellobiosyl fluoride monomer catalyzed with cellulase, an extracellular hydrolytic enzyme of cellulose, in a mixed solvent of acetonitrile and acetate buffer. The product, synthetic cellulose, was the crystalline allomorph cellulose II, a thermodynamically more stable form. More detailed examinations of the polymerization conditions led to the formation of the native cellulose I, a metastable allomorph, for the first time. The key to the success was to use partially purified cellulase and an appropriate mixed solvent of acetonitrile/buffer. The formation of the two allomorphs of cellulose implies that the polarity of the glucan chain ordering can be controlled in a test tube. Based on these findings, a new concept “choroselectivity,” meaning spacial control in ordering the macromolecular chain, has been proposed. Cellulose analogues, 6-O-methylated cellulose and xylan, have been synthesized regio- and stereoselectively by using the enzymatic polymerization technique.     

Effects of Bis(aromatic) Pendants on Recognition of Nucleobase Thymine by Zn2+ -1,4,7,10-tetraazacyclododecane (Zn2+ -cyclen)

We have previously shown that the nucleobase thymine binding to Zn²⁺ -cyclen (cyclen=1,4,7,10-tetraazacyclododecane) complex became stronger by appending acridine, naphthalene, or quinoline rings to the cyclen. Amongst these, the pendant bis((1-naphthyl)methyl) or bis((4-quinolyl)methyl) groups yielded the most effective thymine-recognizing Zn²⁺ -cyclen complexes [J. Am. Chem. Soc., 121 (1999) 5426]. The present study was undertaken to find causes of the bis(aromatic) ring effect by X-ray crystal structure analysis and NMR studies. The crystal structure of the Zn²⁺ -bis((1-naphthyl)methyl)-cyclen complex with a deprotonated 1-methylthymine (1-MeT) failed to show the anticipated evidence for the double ~ - ~ stacking interactions between the two naphthalenes and the Zn 2+ -bound 1-MeT m (1-MeT m =N(3')-deprotonated 1-MeT). Crystal data: formula C₃₆ H₄₇ N₇ O₇ Zn, M r =755.19, monoclinic, space group P2₁/ c (No. 14), a =15.438(2) Å, b =14.093(3) Å, c =16.726(2) Å, g =90.53(1) V =3638.7(8) Å 3 Z =4, R =0.035, R _w =0.049. However, the ¹H NMR studies of Zn²⁼ -bis((4-quinolyl)methyl)-cyclen with 1-MeT in varying H₂O/CH₃ CN solution showed increasing upfield shifts of Me(5') and H(6') of the Zn²⁺ -bound 1-MeT in more aqueous media, indicating that the double intercalation with the two quinolines became more significant in more protic environments. We conclude that the double ~ - ~ stacking effect accounts for the enhanced recognition of thymine base by the appended bis((1-naphthyl)methyl) or bis((4-quinolinyl)methyl) groups.     

New Preparation of Cyclic Acyloxyphosphorane by Reaction of Glyoxylic Acid with Phosphorus(III) Compounds

We have recently found that the reaction of α-keto acids (1) with phosphorus (III) compounds (3) yielded cyclic acyloxyphosphoranes(C-AOPs, 4), a new class of pentacovalent phosphorus species having a P-OC(O) group.^{1, 2)} The present paper deals with a new reaction of glyoxylic acid (2) with 3 to give C-AOPs (5) having no substituent at the C-3 position. 1 is an α-keto acid whereas 2 can be taken as an α-formyl acid. Although it is well known in the field of organic chemistry that the formyl group often behaves differently from a keto group, the reaction of 2 with 3 provides an example in which both groups behave in a similar manner.     

Effects of graded porous structure on local strain distribution under compression in silicone rubber

Silicone rubber samples with gradually changing pore sizes within the range of 70–610 μm are produced using an improved spacer method. The samples are scanned using an X‐ray computed tomography to evaluate their graded structure as compared to uniform rubber. A compressive test reveals that graded porous silicone rubber has characteristic stress–strain curves whose slope changes within a specific strain range depending on the porous structure. Analysis results of local strain based on a digital image correlation of the graded porous silicone rubber under compression demonstrate that the characteristic stress–strain properties are caused by shifts in the main deformation region in the graded structure. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1033–1042     

Enzymatic ring-opening polyaddition for chitin synthesis: A cationic mechanism in basic solution?

The in vitro synthesis of chitin via a nonbiosynthetic path has been achieved for the first time by enzymatic ring-opening polyaddition of a chitobiose oxazoline monomer ( C2O ). Chitinase, a hydrolysis enzyme of chitin, recognized and polymerized the monomer regio- and stereoselectively. The structure of artificial chitin was confirmed by comparison with an authentic natural chitin sample with the use of CP/MAS ¹³C NMR and IR spectroscopy. X-ray diffraction as well as NMR analysis showed its crystal structure of α-chitin. Characteristic features of the present polymerization are described.