Release of Arabinose from Wheat Insoluble Arabinoxylan by the Action of α-L-Arabinofuranosidase in Synergism with Endo-Xylanases

Wheat arabinoxylan (water-insoluble fraction) contains ~36% arabinose which may include both singly or doubly substitutions at C2/C3 of the Xylp units. α-L-Arabinofuranosidses (ABFs) of two GH families were analyzed for their respective activities on the hydrolysis of Xylp-Araf. BaABF (GH43) produced twice the yield of arabinose residues from the heteroxylan compared to AnABF (GH51) under the same reaction conditions. Two endo-xylanases (of GH10 and 11) also showed differential hydrolytic activities on the Xylp chain, with the GH10 XYN-ATM double the amount of reducing sugar yield (as xylose equivalent) than using the GH11 XYN-M3. When the ABF and XYN were combined in optimial ratios, a synergistic increase of 73.8% in arabinose yield was observed.

Crystal and Molecular Structure of a New Mono—substituted Titanocene C

Cyclopentadienyl)[η￣5- (1-(4-methoxyphenyl)cyclohexyl)-cyclopentadienyl]titanium dichloride has been synthesized through a novel modified reaction route. The molecular structure of the title complex was determined by single-crystal Xray diffraction. Crystallographic data: C_(23)H_(26)Ocl_2Ti· 0. 3C_6H_(14),M_r=462. 44, triclinic, P1, a=11. 704(2) , b= 16. 340(4) , C=6. 824(1), a=90. 51(2) , β= 106. 98(1), γ=69. 82(2)°, V= 1165. 4(4) , Z=2, D_c= 1. 317 g/cm￣3, μ(MoKa) = 6. 2cm￣(-1), F(000) = 486 , and the final R= 0. 059 and R_w= 0. 085 for 2723 observed reflections with I>3σ(I). The cyclopentadienyl ring is symmetrically bonded to Ti(Ti-C distances 2. 361 (5)～2. 386 (5)) but the substituted cyclopentadienyl ring is asymmetrically bonded (Ti C2. 327 (4)～2. 438 (4)). The solvent petroleum-ether is disordered in the crystal.

Cloning of an α-L-Arabinofuranosidase and Characterization of Its Action on Mono- and Di-Substituted Xylopyranosyl Units

An α-L-arabinofuranosidase (ARF) gene of 1503 bp was synthesized, subcloned into pET26b vector, and expressed in Escherichia coli. The enzyme was purified in active form, and consisted of 500 amino acid residues, corresponding to 55 kD based on SDS-PAGE. The affinity-purified protein was characterized using arabinofuranosyl xylooligosaccharides (AXOS) as substrates. The pH effect was investigated showing an optimum at pH 5.5. XaARF catalyzed the cleavage of arabinose at C3 of the xylopyranosyl unit efficiently if the arabinofuranosyl substitution was at the terminal compared to internal xylose units. The enzyme was able to act on di-substituted xylopyranosyl units with the first cleavage at C3 followed by C2 linkages.

Stereochemical control in propylene polymerization with asymmetrically substituted titanocene/methylaluminoxane catalyst

A new mono-substituted titanocene,（η5-cyclopentadienyl）[η5-（1-（4-methoxyphenyl）cyclohexyl）cyclopentadienyl]dichlorotitanium（I）,has been prepared via a novel modified synthesis,and its X-raycrystal structure has been determined.It crystallizes in the orthorhombic space group P212121 with cell constantsa=0.9680（5）nm,b=1.2846（5）nm,c=1.6944（6）nm,Z=4,R=0.066.The I/methylaluminoxane（MAO）catalystsystem produces at different polymerization temperatures either an isotactic or a syndiotactic polypropylene,both of which have the combined influence of enantiomorphic-site control and chain-end control,or an atacticpolypropylene controlled by Bernoallian propagation mechanism.