Altered expression of polyhydroxyalkanoate synthase gene and its effect on poly[(R)-3-hydroxybutyrate] synthesis in recombinant Escherichia coli

Polyhydroxyalkanoate (PHA) synthase (PhaC) from Wautersia eutropha was expressed in a wide range of production level in Escherichia coli XL1-Blue cells and its effects on PhaC activity, poly[(R)-3-hydroxybutyrate] [P(3HB)] production and its molecular weights were investigated. The production level of PhaC was controlled both by the amount of chemical inducer (isopropyl-β-d-thiogalactopyranoside, IPTG) added into the medium and the use of different copy number of plasmids. In a flask experiment, as PhaC production level in the cells increased, the PhaC activity also increased in the range of low PhaC concentration. However, PhaC activity did not further increase in the range of high PhaC concentration, probably due to the formation of inclusion body in the cells. The molecular weight of P(3HB) was found to decrease with increasing PhaC activity. This trend was also verified in high cell density cultivation using 10-l jar fermentor. Furthermore, we demonstrated that the use of low copy number plasmid and appropriate induction of PhaC expression were effective in achieving both high productivity and high molecular weight of P(3HB).     

Structural developments in synthetic rubbers during uniaxial deformation by in situ synchrotron X‐ray diffraction

The molecular orientation and strain‐induced crystallization of synthetic rubbers—polyisoprene rubber, polybutadiene rubber, and butyl rubber [poly(isobutylene isoprene)]—during uniaxial deformation were studied with in situ synchrotron wide‐angle X‐ray diffraction. The high intensity of the synchrotron X‐rays and the new data analysis method made it possible to estimate the mass fractions of the strain‐induced crystals and amorphous chain segments in both the oriented and unoriented states. Contrary to the conventional concept, the majority of the molecules (50–75%) remained in an unoriented amorphous state at high strains. Each synthetic rubber showed a different behavior of strain‐induced crystallization and molecular orientation during extension and retraction. Our results confirmed the occurence of strain‐induced networks in the synthetic rubbers due to the inhomogeneity of the crosslink distribution. The strain‐induced networks containing microfibrillar crystals and oriented amorphous tie chains were responsible for the ultimate mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 956–964, 2004     

Terahertz time-domain spectra of aromatic carboxylic acids incorporated in nano-sized pores of mesoporous silicate.

Terahertz time-domain spectroscopy (THz-TDS) is used to study the intra- and intermolecular vibrational modes of aromatic carboxylic acids, for example, o-phthalic acid, benzoic acid, and salicylic acid, which form either intra- or intermolecular hydrogen bond(s) in different ways. Incorporating the target molecules in nano-sized spaces in mesoporous silicate (SBA-16) is found to be effective for the separate detection of intramolecular hydrogen bonding modes and intermolecular modes. The results are supported by an analysis of the differences in the peak shifts, which depend on temperature, caused by the different nature of the THz absorption. Raman spectra revealed that incorporating the molecules in the nano-sized pores of SBA-16 slightly changes the molecular structures. In the future, THz-TDS using nanoporous materials will be used to analyze the intra- and intermolecular vibrational modes of molecules with larger hydrogen bonding networks such as proteins or DNA.     

Quantitative assessment of solid oxide electrochemical doping

Quantitative analysis of metal cation doping by solid oxide electrochemical doping (SOED) has been performed under galvanostatic doping conditions. A M–β″-Al₂O₃ (M=Ag, Na) microelectrode (contact radius: about 10 μm) was used as cation source to attain a homogeneous solid–solid contact between the β″-Al₂O₃ and doping target. In Ag doping into alkali borate glass, the measured dopant amount closely matched the theoretical value. High Faraday efficiencies of above 90% were obtained. This suggests that the dopant amount can be precisely controlled on a micromole scale by the electric charge during electrolysis. On the other hand, current efficiencies of Na doping into Bi₂Sr₂CaCu₂O_y (BSCCO) ceramics depended on the applied constant current. Efficiencies of above 80% were achieved at a constant current of 10 μA (1.6 A cm⁻²). The relatively low efficiencies were explained by the saturation of BSCCO grain boundaries with Na. By contrast, excess Na was detected on the anodic surface of ceramics at a constant current of 100 μA (16 A cm⁻²). In the present study, we demonstrate that SOED enables micromole-scale control over dopant amount.     

Thermal properties and fracture toughness of a liquid‐crystalline epoxy resin cured with an aromatic diamine crosslinker having a mesogenic group

A mesogenic‐type curing agent was synthesized to introduce a mesogenic group not only into epoxy resin backbones but also into the crosslink units. In the mesogenic curing agent system, the domain size became larger, and the network arrangement in each domain existed to a greater extent than that in a system cured with the ordinary diamine curing system according to the evidence from polarized optical micrographs and polarized Fourier transform infrared mapping measurements. Moreover, the fracture toughness of the system was considerably improved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2486–2494, 2006     

Thermoanalytical characterization of carbon/carbon hybrid material, Apple Woodceramics

Woodceramics, a carbon/carbon composite of plant-originated carbon reinforced by glassy carbon from phenolic resin, was prepared from apple pomace at carbonizing temperatures of 1073 K (AWC800) and 1473 K (AWC1200), and characterized by thermoanalytical methods and X-ray diffraction (XRD). Simultaneous differential scanning calorimetry (DSC) and thermogravimetric (TG) showed complicated overlapping reactions similar to those of coal. The initial temperature of pyrolysis was obtained by fitting logistic functions to observed TG data. The results suggested that AWC1200 contained more volatile matter than AWC800. In an inert atmosphere, complicated devolatilization takes place. In an oxidizing atmosphere, thermal change occurs roughly in four steps: desorption of physically adsorbed matter; pyrolysis into aliphatic and aromatic fragments; ignition; combustion of char. The oxidation resistance of AWC1200 was superior to AWC800.     

Remarkably large positive and negative allosteric effects on ion recognition by the formation of a novel helical pseudocryptand

In supramolecular chemistry, a great deal of attention has focused on regulating guest binding via an external stimulus. To utilize the same effector for both highly guest-selective positive and negative allosteric effects, however, stricter and more precise regulation of the host structure is required. A novel allosteric host 1 binds Fe(II) to afford the pseudocryptand, 1.Fe(II), which bears a cavity that is surrounded by three polyether chains in a helical fashion. The binding selectivity of 1 (Na+ > K+ > Rb+ > Cs+) is the opposite of 1.Fe(II) (Cs+ > Rb+ > K+ > Na+). Single-ion transport through a liquid membrane shows ion selectivity similar to the equilibrium constants. To the best of our knowledge, this is the first example of an allosteric recognition system, in which the same effector, that is, Fe(II), exhibits both large positive and negative allosteric effects on equilibrium and dynamic recognition events. The X-ray analysis and 1H NMR examination indicate that the combination of the macrobicyclic effect and the intramolecular interchain interactions (CH-pi interaction and steric hindrance) finely controls the positive and negative allosteric effects, which depend on the size of the guest. The helical framework opens a new general method for constructing more sophisticated, controllable receptors for helical biomolecules, for example, DNA and proteins, and helical molecular devices such as a molecular coil or spring responding to a stimulus.     

Selective capture of 1α,25-(OH)2-previtamin D3 utilizing polymer-supported trialkylsilyl triflate in the synthesis of 1α,25-(OH)2-vitamin D3

Catch and release method utilizing polymer-support was investigated in the separation of 1α,25-(OH)₂ pre- and provitamin D₃. Polymer-supported alkyldiisopropylsilyl triflate selectively captured the previtamin D₃ from a 26:74 mixture of pre- and provitamin D₃ produced by photoisomerization of provitamin D₃.     

Friction coefficient and structural transition in a poly(acrylamide) gel

The friction coefficient between the polymer network of an opaque poly(acrylamide) gel and water is measured as a function of the mole fraction of cross linker. The friction coefficients of opaque gels are 4 to 5 orders of magnitude smaller than those of the transparent gels. This drastic decrease in friction occurs when the mole fraction of cross linker is 0.2. In opaque gels, the friction coefficient of gels and the mole fraction of cross linker are related by a power law. The network structure of the opaque gels used in the friction measurements is examined with a confocal laser scanning microscope. The opaque gel network consists of a fractal aggregate of colloidal particles. The radius of particles and the volume occupied by the particles depend on the mole fraction of cross linker. Both relationships are well described by the power laws. The power law of the friction coefficient is well explained in terms of the power laws of the structural parameters and the Stokes equation of the hydrodynamic friction for the spherical particle. It indicates that the friction of the opaque gel is determined simply by the structure of the polymer network.