Effects of cell-wall acetate,xylan backbone,and lignin on enzymatic hydrolysis of aspen wood

Aspen wood substrates with varying degrees of deacetylation, xylan, and lignin removal have been prepared and submitted to enzymatic hydrolysis with a cellulase/hemicellulase preparation for an extended constant period of hydrolysis. Controlled deacetylation has been achieved by treating wood with various alkali metal hydroxide solutions, at various alkali/wood ratios. It has been found that samples with the same extent of deacetylation produce the same sugar yields upon enzymatic hydrolysis. Increased degree of deacetylation increases the yield of sugars obtained from enzymatic hydrolysis, all other compositional parameters held constant. The acetyl group removal is proportional to the stoichiometric relation between added base and wood acetyl content, i.e., the same number of milliequivalents of base/weight of wood remove the same extent of acetyl groups, regardless of the concentration of the base solution. No cation effects are found among Li, Na, and K alkali hydroxide solutions, suggesting that swelling is not as important a parameter as is the removal of the acetyl groups from the xylan backbone in determining the extent of hydrolyzability of the resulting sample.     

Reaction of carbonyl fluoride with fluorine in the presence of various fluorides as catalysts

The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF₂O + F₂→ CF₃OF. The list of catalysts for this process has now been enlarged to include NaF, MgF₂, CaF₂, SrF₂, BaF₂ and LaF₃. Lithium fluoride and thorium fluoride also give CF₃OF but are less active. Perhaps the substances CsF·HF, KAgF₄ and NiF₂ should be included in this list. Silver fluoride, usually as a mixture of AgF₂ with AgF, has been known to catalyze the reaction of CF₂O with F₂ to give both CF₃OF and CF₃OOCF₃. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF₃OOCF₃ is very high. It has now been shown that TIF₃ behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF₃OOCF₃ than of CF₃OF but require higher temperatures than AgF₂ (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed.     

Observation of unusual surface ordering in a uniaxial Sm-A phase formed by a highly biaxial compound

We have studied one banana-shaped compound using null-transmission ellipsometry. By studying free-standing films of various thicknesses we confirm that this compound exhibits the Sm-A phase. This is the first banana-shaped compound with a relatively small bend angle (approximately 140 degrees) in which a uniaxial phase has been observed. At the lower temperature end of the Sm-A phase we observe unusual ordering at the surface of the film.     

Optical characterization of a nanoscale incommensurate pitch in a new liquid-crystal phase

As a remarkable orientationally ordered soft-condensed matter system, the smectic-C*(alpha) phase exhibits an incommensurate nanoscale helical pitch of more than four smectic layers. Recent theoretical advances predict the existence of a new phase showing a helical pitch of less than four smectic layers (<16 nm). By applying a novel optical technique to the study of freestanding films with increments in thickness of one smectic layer, we have measured the size of this pitch using 633 nm HeNe laser light. Our results confirm the existence of the newly predicted phase in one unique compound.