Synthesis,Chiroptical, and Redox Properties of Ferrocene‐Containing Optically Active Polymers

The Sonogashira–Hagihara coupling polymerization of ferrocene‐containing l ‐phenylalanine‐derived optically active o‐, m‐, p‐substituted bis(iodophenylene) monomers 1o , 1m , 1p with 1,4‐diethynylbenzene ( 2 ) and 1,4‐diethynyl‐2,5‐bis[2‐(2‐methoxyethoxy)ethoxy]benzene ( 3 ) is carried out to obtain the corresponding polymers consisting of ferrocene, amino acid, and phenyleneethynylene moieties. In the solution state, poly( 1o ‐ 2 ), poly( 1o‐3 ), and poly( 1m ‐ 2 ) exhibit no circular dichroism (CD) signals in N,N‐dimethylformamide (DMF), while poly( 1m‐3 ), poly( 1p ‐ 2 ), and poly( 1p ‐ 3 ) exhibit CD signals assignable to the main chain chromophore, indicating the formation of certain chiral structures. In the solid state, poly( 1o ‐ 2 ), poly( 1o‐3 ), poly( 1m ‐ 2 ), and poly( 1m‐3 ) exhibit CD signals in the solid state, while poly( 1p ‐ 2 ), poly( 1p ‐ 3 ) does not, indicating the different aggregation manners of the polymers in the solution and solid states. The monomer and the polymers exhibit redox properties assignable to the ferrocene moieties. Thermal gravimetry analysis (TGA) measurements reveal that a 30% weight reduction occurs at 500 °C yielding black ferromagnetic solids.     

Efficient growth of multi-walled carbon nanotubes by continuous-wave laser vaporization of graphite containing B4C

Multi-walled carbon nanotubes (MWCNTs), 7–70 nm thick and up to 30 μm long, were efficiently grown by room-temperature continuous-wave laser vaporization of a graphite target containing B₄C in an ambient Ar gas. Adjusting the boron content in the target and Ar gas pressure resulted in a maximum fraction of ∼60% of MWCNTs in the deposits. The straightness of the MWCNTs and graphene layers with an interlayer spacing of ∼0.35 nm indicated that the degree of graphitization was fairly high in the grown MWCNTs. However, the features of D, G, and 2D bands in the Raman spectrum of a deposit suggested boron doping in the MWCNTs. An apparent Young’s modulus of a grown MWCNT was measured to be 0.68 TPa and comparable to those of heat-treated vapor grown carbon nanofibers. MWCNTs are thought to grow on molten boron carbide particles acting as seeds at high temperatures of up to ∼2400 °C.     

Maintenance of hemiround colonies and undifferentiated state of mouse induced pluripotent stem cells on carbon nanotube-coated dishes

Induced pluripotent stem (iPS) cells have attracted worldwide interest. However, there have been only a few studies investigating effective culture substrates for feeder-free culturing for the maintenance of iPS cells. In this study, we cultured mouse iPS cells under feeder-free conditions on carbon nanotube (CNT)-coated dishes and then evaluated the colony morphology and differentiation state of the cells on the dishes. After 5 d of cultivation in a medium containing 15% fetal bovine serum (FBS) and leukemia inhibitory factor (LIF), the colonies on thick films of multi-walled CNTs (MWCNTs) were observed to be hemiround; further, the cells expressed early undifferentiation markers. On the other hand, the colonies on a cell culture polystyrene dish and a collagen-coated polystyrene dish showed indistinct outline and spread well, and most spreading cells only weakly expressed early undifferentiation markers. These results indicate that the thick films of MWCNTs could maintain hemiround colonies and undifferentiated state of mouse iPS cells cultured under feeder-free conditions.     

Phase Diagram and Microstructure in the ZnO–Pr2O3 System

The phase diagram of the ZnO–Pr₂O₃ system with PrO_1.83 contents from 0.5 to 98 mol% was studied via differential thermal analysis (DTA). The system ZnOPr₂O₃ showed a simple eutectic type of phase diagram with no solid solutions and no other compounds. The eutectic temperature was determined to be 1382 ± 5°C. The liquidus line near the eutectic point was determined by a quenching method.     

Fatty Acid Conjugates of Water‐Soluble (±)‐trans‐Selenolane‐3,4‐diol: Effects of Alkyl Chain Length on the Antioxidant Capacity

Fatty acid monoesters of the title compound (DHS^red), of variable carbon chain length (propionate, laurate, myristate, palmitate, and stearate), were synthesized, and their antioxidant capacities were evaluated by means of a lipid peroxidation assay with lecithin/cholesterol liposomes. The selenides with long alkyl chains exhibited significant antioxidant activity (IC₅₀=9–34 μM ) against accumulation of lipid hydroperoxide. Incorporation of the myristate into the liposome was ≈50 % by EPMA analysis. Intermediacy of the selenoxide was examined by NMR. In addition, enhancement of interfacial redox catalytic activity was observed for the myristate, but not for PhSeSePh and edaravone, in a PhCl/H₂O biphasic peroxidation assay. These results suggested that a combination of a hydrophilic selenide moiety as a redox center with a long alkyl chain is an effective approach to selenium antioxidants with interfacial glutathione‐peroxidase‐like (GPx‐like) activity. The activity can be controlled by the alkyl chain length.     

Adaptation of a thermophilic enzyme, 3-isopropylmalate dehydrogenase, to low temperatures

Random mutagenesis coupled with screening of the active enzymeat a low temperature was applied to isolate cold-adapted mutantsof a thermophilic enzyme. Four mutant enzymes with enhancedspecific activities (up to 4.1-fold at 40°C) at a moderatetemperature were isolated from randomly mutated Thermus thermophilus3-isopropylmalate dehydrogenase. Kinetic analysis revealed twotypes of cold-adapted mutants, i.e. k_cat-improved and K_m-improvedtypes. The k_cat-improved mutants showed less temperature-dependentcatalytic properties, resulting in improvement of k_cat (up to7.5-fold at 40°C) at lower temperatures with increased K_mvalues mainly for NAD. The K_m-improved enzyme showed higheraffinities toward the substrate and the coenzyme without significantchange in k_cat at the temperatures investigated (30–70°C).In k_cat-improved mutants, replacement of a residue was foundnear the binding pocket for the adenine portion of NAD. Twoof the mutants retained thermal stability indistinguishablefrom the wild-type enzyme. Extreme thermal stability of thethermophilic enzyme is not necessarily decreased to improvethe catalytic function at lower temperatures. The present strategyprovides a powerful tool for obtaining active mutant enzymesat lower temperatures. The results also indicate that it ispossible to obtain cold-adapted mutant enzymes with high thermalstability.     

Phosphonamidates as thermally latent initiators in the polymerization of epoxides

Summary Phosphonamidates, O,O-di-tert-butyl 1-piperidinyl phosphonamidate (BP-1) and O-tert-butyl di-1-piperidinyl phosphonamidate (BP-2), were synthesized by the reaction of phosphorus oxychloride and piperidine in the presence of triethylamine, followed by the reaction with tert-butyl alcohol in the presence of sodium hydride. The polymerization of GPE was carried out at 110–190 °C for 12 h with BP-1 and BP-2 as thermally latent initiators (3 mol %). The polymerization with O-tert-butyl P-phenyl 1-piperidinyl phosphonamidate (BP) previously reported was also examined for comparison. No polymerization of GPE took place below 110 °C, whereas it proceeded rapidly above the temperature. The activity order was BP-2 > BP > BP-1. Epikote 828 was cured with BP (5 mol %) at 190 °C to afford the solvent-insoluble gelled epoxy resin quantitatively. A mixture of GPE and phosphonamidate BP (3 mol %) did not react at 50 °C for 4 months. Received: 26 February 2001/Revised version: 12 April 2001/Accepted: 13 April 2001     

Synthesis and Properties of Novel Eugenol–Based Polymers

Summary This work deals with the synthesis and characterization of novel eugenol–based polymers. The polymerization of 2–methoxy–4-propenyl–1-prop–2–ynyloxybenzene (1) with Rh, Mo, and W catalysts gave the corresponding polyacetylene [poly(1)], while that using BF₃ catalyst gave poly(1), without affecting the triple bond. A novel cross–linked polyacetylene was synthesized from poly (1) with [(nbd)RhC1]₂–Et₃N catalyst.     

Mechanochemical Synthesis of Ammonium Hexafluorogallate

Mechanochemical reaction between ammonium fluoride (NH₄F) and gallium fluoride trihydrate (GaF₃·3H₂O) at a ratio of 3:1 is conducted by grinding the mixture at room temperature using a planetrary ball mill. A single phase of ammonium hexafluorogallate ((NH₄)₃GaF₆) is obtained as a product of the reaction. Other alkali hexafluorogallates (K₃GaF₆, Na₃GaF₆, and Li₃GaF₆) also can be synthesized by grinding constituent components (AF and GaF₃·3H₂O) under proper grinding conditions. A reaction mechanism related to the dissolution of alkali fluorides in water is suggested.     

Factors Affecting Stable Operation of Counter‐current Multistage Fluidized Bed of Solid‐liquid System — Dimensions of Downspout

For the effective use of an ion exchange resin, a counter‐current multistage fluidized bed has been developed. An appropriate design of the downspout, which works to let particles flow down to next stage, is essential to obtain a stable resin flow. From an experimental study on the particle holdup and pressure drop in the multistage fluidized bed, a method to determine the downspout size has been developed. The relation between the liquid velocity within the downspout and the superficial liquid velocity has been derived from considering the pressure balance between the part of the fluidized bed and that of the downspout.