Enhanced stereocomplex formation of poly(L-lactic acid) and poly(D-lactic acid) in the presence of stereoblock poly(lactic acid)

Stereoblock poly(lactic acid) (sb-PLA) is incorporated into a 1:1 polymer blend system of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) that has a high molecular weight to study its addition effect on the stereocomplex (sc) formation of PLLA and PDLA. The ternary polymer blend films are first prepared by casting polymer solutions of sb-PLA, PLLA, and PDLA with different compositions. Upon increasing the content of sb-PLA in the blend films the sc crystallization is driven to a higher degree, while the formation of homo-chiral (hc) crystals is decreased. Lowering the molecular weight of the incorporated sb-PLA effectively increases the sc formation. Consequently, it is revealed that sb-PLA can work as a compatibilizer to improve the poor sc formation in the polymer blend of PLLA and PDLA.     

Transient fluctuation of the prosperity of firms in a network economy

The transient fluctuation of the prosperity of firms in a network economy is investigated with an abstract stochastic model. The model describes the profit which firms make when they sell materials to a firm which produces a product and the fixed cost expense to the firms to produce those materials and product. The formulas for this model are parallel to those for population dynamics. The swinging changes in the fluctuation in the transient state from the initial growth to the final steady state are the consequence of a topology-dependent time trial competition between the profitable interactions and expense. The firm in a sparse random network economy is more likely to go bankrupt than expected from the value of the limit of the fluctuation in the steady state, and there is a risk of failing to reach by far the less fluctuating steady state.     

Optimal conflict-avoiding codes of length <Emphasis Type="Italic">n</Emphasis> ≡ 0 (mod 16) and weight 3

A conflict-avoiding code of length n and weight k is defined as a set of binary vectors, called codewords, all of Hamming weight k such that the distance of arbitrary cyclic shifts of two distinct codewords in C is at least 2k−2. In this paper, we obtain direct constructions for optimal conflict-avoiding codes of length n = 16m and weight 3 for any m by utilizing Skolem type sequences. We also show that for the case n = 16m + 8 Skolem type sequences can give more concise constructions than the ones obtained earlier by Jimbo et al.      

A New Method of Low Temperature Methanol Synthesis

Low temperature methanol synthesis is a promising technique for the practical methanol industry. New developments of a new kind of low temperature methanol synthesis were reviewed, including the effects of feed gas, reaction solvent, supercritical media and catalyst modification. The reaction mechanism and kinetics were also summarized primarily. Carbon dioxide played an important role in this new kind of low temperature methanol synthesis. It reacted with hydrogen adsorbed on catalyst surface to form HCOOM, an important reaction intermediate. Alcohol solvent in the low temperature methanol synthesis performed not only a media, but also a homogeneous catalyst. The reaction of the adsorbed formate species with alcohol on Cu/ZnO catalyst surface proceeded according to the Rideal mechanism rather than Langmuir–Hinshelwood mechanism to form alkyl formate. The formation of alkyl formate from alcohol solvent and hydrogenation of such an alkyl formate were the key steps in low temperature methanol synthesis reaction. These results provided new insights into low temperature methanol synthesis.     

Cloning of poly(aspartic acid) (PAA) hydrolase-1 gene from Pedobacter sp. KP-2 and hydrolysis of thermally synthesized PAA by its gene product

Pedobacter sp. KP-2 can degrade and metabolize thermally synthesized alpha,beta-poly(D,L-aspartic acid) (tPAA), which contains 70% of unnatural beta-amide units, with high-molecular-weight. In this study, gene cloning and molecular characterization of PAA hydrolase-1 from KP-2 was carried out. Gene analysis reveals that deduced amino acid sequence of the enzyme shows a similarity to only that of PAA hydrolase-1 from Sphingomonas sp. KT-1. GPC and NMR analyses of the hydrolyzed products of tPAA by PAA hydrolase-1 of KP-2 indicate that this enzyme cleaves the beta-beta amide linkage via endo-mode to yield oligo(aspartic acid) from tPAA. Taking the composition of tPAA and the substrate specificity of PAA hydrolase-1 into consideration, the enzyme possibly plays a crucial role in tPAA biodegradation by KP-2.     

About the structure of cellulose: debating the Lindman hypothesis

The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the solubility or insolubility characteristics of cellulose are significantly based upon amphiphilic and hydrophobic molecular interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochemical principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.     

Facile synthesis of H-type zeolite shell on a silica substrate for tandem catalysis

A new class of silica-based zeolite capsule catalyst was readily prepared employing a dual-layer method under close-to-neutral conditions. In a tandem catalysis process, the precisely controlled synthesis of dimethyl ether was realized. This new concept of H-type zeolite shell preparation and application represents a powerful approach for preparing high-performance, multifunctional catalysts.     

Carbazolyl Benzo[1,2‐b:4,5‐b′]difuran: An Ambipolar Host Material for Full‐Color Organic Light‐Emitting Diodes

We have designed an ambipolar material, 3,7‐bis[4‐(N‐carbazolyl)‐phenyl]‐2,6‐diphenylbenzo[1,2‐b:4,5‐b′]difuran (CZBDF), and synthesized it by zinc‐mediated double cyclization. Its physical properties clarified that CZBDF possesses a wide‐gap character, well‐balanced and high hole and electron mobilities of larger than 10^?3 cm² V^?1 s^?1, and a high thermal stability. Using CZBDF as a host material for heterojunction OLED devices, a full range of visible emission was obtained. Notably, CZBDF also enabled us to fabricate RGB‐emitting homojunction OLEDs, with performances comparable or superior to the heterojunction devices composed of several materials.