Combination of an aromatic core and aromatic side chains which constitutes discotic liquid crystal and organogel supramolecular assemblies

This paper reports unique and unusual formations of columnar liquid crystals and organogels by self-assembling discotic molecules, which are composed of an aromatic hexaazatriphenylene (HAT) core and six flexible aromatic side chains. In HAT derivatives 3a, with 4'-(N,N-diphenylamino)biphenyl-4-yl chains, 3b, with 4'-[N-(2-naphthyl)-N-phenylamino]biphenyl-4-yl chains, and 3c, with 4'-phenoxybiphenyl-4-yl chains, the two-dimensional hexagonal packings can be created by their self-assembling in the liquid crystalline phase, which were characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In certain solvents, HAT molecules 3a-c can form the viscoelastic fluid organogels, in which one-dimensional aggregates composed of the HAT molecules are self-assembled and entangled into three-dimensional network structures. The organogel structures were analyzed by scanning electron microscopy observation, (1)H NMR, UV-vis, and circular dichroism spectroscopy. In contrast to 3a-c, none of the liquid crystalline and organogel phases could be formed from 3d and 3e with short aromatic side chains including a phenylene spacer, and 3f (except a few specific solutions) and 3g without terminal diarylamino and phenoxy groups. In 3a-c, the aromatic side chains with terminal flexible groups make up soft regions that cooperatively stabilize the liquid crystalline and organogel supramolecular structures together with the hard regions of the hexaazatriphenylene core.     

A new synthetic approach to the bicyclo[5.3.1]undecane ring system in taxanes

The bicyclo[5.3.1]undecane derivative 19, which was referred to the A,b ring system of taxane diterpenes, was synthesized by a base-induced fragmentation reaction of the tricyclic diol monomesylate 18 derived highly stereoselectively from 5-methyl-1,3-cyclohexadione.     

Oxidation of (7,16-diethyl-5,6,7,8,9,14,15,16,17,18-decahydrodibenzo[b,i][1,4,8,11]tetraazacyclotetradecine)nickel(II) complexes

The oxidation reaction of two isomers of (7,16-diethyl-5,6,7,8,9,14,15,16,17,18-decahydrodibenzo[b,i]-[1,4,8,11]tetraazacyclotetradecine)nickel(II) diperchlorate and/or dichloride (NiL¹X₂ (X = ClO₄, Cl)) in methanol in air under atmospheric pressure leads to the production of (7,16-diethyl-5,6,7,8,9-pentahydrodibenzo-[b,i][1,4,8,11]tetraazacyclotetradecinato)nickel(II) complexes (NiL²X). Proton and ¹³C nmr spectra suggest that NiL²X is formed by partial oxidation from a macrocyclic skeleton of NiL¹X₂. The dehydrogenation of NiL¹X₂ does not occur at symmetric positions such as d- and k-positions of the macrocyclic skeleton but at unsymmetrical positions such as d- and f-positions. Treatment of NiL¹X₂ and/or NiL²X in a methanol solution with an excess of bases in air gives (7,16-diethyldibenzo[b,t][1,4,8,11]tetraazacyclotetradecinato)nickel(II) (NiL³).     

High-efficiency and minimum-waste continuous kinetic resolution of racemic alcohols by using lipase in supercritical carbon dioxide

A novel continuous-flow scCO(2) process for kinetic resolution of racemic alcohols can be performed with an immobilized lipase to lead to a quantitative mixture of the corresponding optically active acetates with up to 99% ee and unreacted alcohols with up to 99% ee, in which the productivity of the optically active compounds was improved by over 400 times compared to the corresponding batch reaction using scCO(2).     

New Combinatorial Bounds for Authentication Codes and Key Predistribution Schemes

This paper provides new combinatorial bounds and characterizations of authentication codes (A-codes) and key predistribution schemes (KPS). We first prove a new lower bound on the number of keys in an A-code without secrecy, which can be thought of as a generalization of the classical Rao bound for orthogonal arrays. We also prove a new lower bound on the number of keys in a general A-code, which is based on the Petrenjuk, Ray-Chaudhuri and Wilson bound for t-designs. We also present new lower bounds on the size of keys and the amount of users' secret information in KPS, the latter of which is accomplished by showing that a certain A-code is hiding inside any KPS.     

Trapping of fatty acid allyl radicals generated in lipoxygenase reactions in biological fluids by nitroxyl radical

Nitroxyl radicals can trap fatty acid allyl radicals on ferric‐lipoxygenases at lower oxygen content, which are an intermediate in the lipoxygenase reaction. In the present study, we examined whether nitroxyl radical‐trapping of fatty acid allyl radicals on the enzyme proceeds in biological fluids with abundant antioxidants. The fatty acid allyl radical–nitroxyl radical adducts were quantified by HPLC with electrochemical detection (HPLC‐ECD); the adducts in eluate degraded into nitroxyl radical by passing through heating coil at 100°C, and then nitroxyl radical was detected by electrochemical detector. Soybean 15‐lipoxygenase and nitroxyl radical (3‐carbamoyl‐2,2,5,5‐tetramethyl‐3‐pyrroline‐N‐oxyl, CmΔP) were mixed with rat serum prepared from fresh venous blood, and the solution was stood at 37°C for 1 h. One volume of the solution was mixed with 5 vols of cold acetonitrile. After centrifugation, the supernatant was subjected to HPLC‐ECD. Arachidonate allyl radical–CmΔP adducts as well as linoleate allyl radical–CmΔP adducts were detected in the solution, and the content of these adducts remarkably increased in the presence of phospholipase A₂. It is proved for the first time that nitroxyl radical traps fatty acid allyl radicals generated in the lipoxygenase reaction in biological fluid without competition from endogenous antioxidants. Copyright © 2010 John Wiley & Sons, Ltd.     

Luminescence of Silica-Pillared Clays and Gels Derived from Aminofunctional Silanes

Silica-pillared clays were prepared by reacting Na-montmorillonite aqueous suspensions with (3-aminopropyl)triethoxysilane (APTEOS). It was indicated that cubic octamers [NH ₃ ⁺ (CH₂)₃SiO_3/2]₈ derived from APTEOS are intercalated with two different conformations of the alkyl chains. Namely, the cubic octamers are intercalated with the alkyl chains parallel to the silicate layers at low concentration of APTEOS, and then intercalated with the alkyl chains normal to the silicate layers with increase in APTEOS. Gels were prepared from the reaction of APTEOS with acetic acid and by the conventional sol-gel process using (3-aminopropyl)trimethoxysilane (APTMOS). The luminescence spectra of the gel prepared by the sol-gel process and the intercalated clays were similar to that of silica gels. The gel from APTEOS with acetic acid showed broad visible luminescence. The luminescence spectra and the structures of these materials were described.     

Individuals, grasses, and forests of single- and multi-walled carbon nanotubes grown by supported Co catalysts of different nominal thicknesses

The relationships among the nominal thickness of Co catalyst, the structure of the catalyst particles, and the structure of carbon nanotubes (CNTs) growing from the catalyst during chemical vapor deposition were investigated. Various morphologies of CNTs such as individuals, random networks parallel to the surface of the substrate (‘grasses’), and vertically aligned forests of single- and multi-walled carbon nanotubes were grown by only varying the nominal thickness of catalyst under the same reaction condition. These different morphologies at the same growth time were due to the different areal density rather than to the length of CNTs. With increasing nominal thickness of catalyst, the catalyst particles changed in diameter while their areal density remained relatively almost constant. The change in diameter possibly affected the number ratio of active catalyst particles to the whole particles, which in turn affected the areal density of CNTs and yielded the various morphologies. Longer growth time increased the CNT length, which caused further change in CNT morphologies from individuals to grasses and grasses to forests.