The Role of a Nonribosomal Peptide Synthetase in l‐Lysine Lactamization During Capuramycin Biosynthesis

Capuramycins are one of several known classes of natural products that contain an l ‐Lys‐derived l ‐α‐amino‐?‐caprolactam (l ‐ACL) unit. The α‐amino group of l ‐ACL in a capuramycin is linked to an unsaturated hexuronic acid component through an amide bond that was previously shown to originate by an ATP‐independent enzymatic route. With the aid of a combined in vivo and in vitro approach, a predicted tridomain nonribosomal peptide synthetase CapU is functionally characterized here as the ATP‐dependent amide‐bond‐forming catalyst responsible for the biosynthesis of the remaining amide bond present in l ‐ACL. The results are consistent with the adenylation domain of CapU as the essential catalytic component for l ‐Lys activation and thioesterification of the adjacent thiolation domain. However, in contrast to expectations, lactamization does not require any additional domains or proteins and is likely a nonenzymatic event. The results set the stage for examining whether a similar NRPS‐mediated mechanism is employed in the biosynthesis of other l ‐ACL‐containing natural products and, just as intriguingly, how spontaneous lactamization is avoided in the numerous NRPS‐derived peptides that contain an unmodified l ‐Lys residue.     

Application of magnetic nanoparticles to gene delivery

Nanoparticle technology is being incorporated into many areas of molecular science and biomedicine. Because nanoparticles are small enough to enter almost all areas of the body, including the circulatory system and cells, they have been and continue to be exploited for basic biomedical research as well as clinical diagnostic and therapeutic applications. For example, nanoparticles hold great promise for enabling gene therapy to reach its full potential by facilitating targeted delivery of DNA into tissues and cells. Substantial progress has been made in binding DNA to nanoparticles and controlling the behavior of these complexes. In this article, we review research on binding DNAs to nanoparticles as well as our latest study on non-viral gene delivery using polyethylenimine-coated magnetic nanoparticles.     

Structural chirality of cholesteric liquid crystal produces atropisomerism: Chiroptical polyisocyanides from achiral monomer in cholesteric liquid crystal matrix

1-Naphthyl isocyanide was polymerized with Ni(II) catalyst in a cholesteric matrix at the liquid crystal (LC) temperature range. The resultant polymers showed optical activity. In this reaction, the structural chirality of cholesteric LC effectively functions to impart one-handed helicity on the corresponding polymers as an optically active atropisomer.     

Catalytic performance of K-promoted Rh/USY catalysts in preferential oxidation of CO in rich hydrogen

K-promoted Rh/USY (molar ratio: K/Rh=3) catalyst was found to exhibit high performance in preferential oxidation of CO in rich hydrogen. Such high performance was maintained in the presence of steam and CO₂. The CO oxidation activity of the K-Rh/USY catalyst was independent of the partial pressure of H₂, while the activity of the unpromoted Rh/USY catalyst was decreased significantly in hydrogen-rich stream. The effect of potassium addition on the catalyst structure was investigated and is discussed in terms of the differences in the catalytic performance.     

Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater

Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O₂) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O₂ MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.     

Shielding effect of double microelectrode tips in a scanning electrochemical microscope

Electrochemical interaction of coaxial double microelectrodes, in which a ring microelectrode was surrounded by another ring microelectrode, was investigated. Mass-transfer reactions that occurred on both inner and outer microelectrodes interfered with each other and showed a “shielding” effect depending on potentials and geometries of microelectrodes. Application of the inner microelectrode of the double microelectrodes for a probing tip of a scanning electrochemical microscope (SECM) revealed that the shielding effect by the outer microelectrode affected the electrochemistry on the inner microelectrode in the vicinity of the substrate surface. The effect was intensified above the insulator but attenuated above the conductor as the microelectrodes approached in feedback mode of the SECM. Approach to a critical interelectrode distance also intensified the shielding effect in the substrate generation/tip collection mode. An SECM line-scan using a platinum/epoxy resin-model substrate was carried out to investigate the shielding effect on current sensitivity and lateral resolution of an SECM image.     

Analysis of proton exchange membrane fuel cell catalyst layers for reduction of platinum loading at Nissan

The biggest issue that must be addressed in promoting widespread use of fuel cell vehicles (FCVs) is to reduce the cost of the fuel cell system. Especially, it is of vital importance to reduce platinum (Pt) loading of catalyst layers (CLs) in the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC). In order to lower the Pt loading of the MEA, mass transport of reactants related to the performance in high current density should be enhanced significantly as well as kinetics of the catalyst, which can result in the better Pt utilization and effectiveness. In this study, we summarized our analytical approach and methods for reduction of Pt loading in CLs. Microstructure, mass transport properties of the reactants, and their relation in CLs were elucidated by applying experimental analyses and computational methods. A simple CL model for I–V performance prediction was then established, where experimentally elucidated parameters of the microstructure and the properties in CLs were taken into account. Finally, we revealed the impact of lowering the Pt loading on the transport properties, polarization, and the I–V performance.     

Effect of styrene–acrylonitrile on the electrical resistivity of polycarbonate/multiwalled carbon nanotube composites

Multiwalled carbon nanotube (MWCNT)‐filled polycarbonate (PC)/styrene–acrylonitrile (SAN) blends with a wide range of blend compositions were prepared by melt mixing in a rotational rheometer, and the effect of SAN on the electrical properties of the PC/MWCNT composites was studied. The structure/electrical property relationship was investigated and explained by a combination of MWCNT localization and blend morphology. Transmission electron micrographs showed selective localization of MWCNTs in the PC phase, regardless of the blend morphology. When the SAN concentration was 10–40 wt %, which corresponded to sea‐island (10–30 wt %) and cocontinuous (40 wt %) blend morphologies (PC was continuous in both structures), the electrical resistivity decreased with increases in the SAN content. The concept of an effective volume concentration of MWCNTs was used to explain this effect. When the SAN concentration was 70 wt % or higher, the electrical resistivity was very high because MWCNTs were confined in the isolated PC particles. In addition, SAN was replaced by other polymers [polystyrene, methyl methacrylate/styrene, and poly(methyl methacrylate)]; these yielded similar blend morphologies and MWCNT localization and showed the generality of the concept of effective concentration in explaining a decrease in the electrical resistivity upon the addition of a second polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.