Evaluation of reactivity for nitroxide radical trapping by correlation analysis using steric substituent parameter (ΩS)

The reactivity of nitroxide radical trapping (NRT), where stable nitroxide radicals react with transient carbon-centered radicals to form diamagnetic molecules, was evaluated. This was done with the use of the steric substituent parameter of both radicals by correlation analysis on the basis of the reactivity data determined by Ingold's group. In the case where the transient carbon-centered radicals were not resonance stabilized, the rate constant could be well correlated by using only Ω_S parameters of R₂NO⋅ and U⋅. If the transient radicals were stabilized by resonance, the parameter to estimate the amount of the resonance stabilization of U⋅ was necessary in the regression equation to evaluate the reactivity correctly. When the spin density, calculated by PM3 UHF molecular orbital calculations, was used as the resonance stabilization parameter, the rate constant could be well evaluated by a dual-parameter regression equation. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 215–221, 1998.     

Bipyridine-Modified DNA Three-Way Junctions with Amide linkers: Metal-Dependent Structure Induction and Self-Sorting

DNA three-way junction (3WJ) structures are essential building blocks for the construction of DNA nanoarchitectures. We have synthesized a bipyridine (bpy)-modified DNA 3WJ by using a newly designed bpy-modified nucleoside, U_bpy- 3 , in which a bpy ligand is tethered via a stable amide linker. The thermal stability of the bpy-modified 3WJ was greatly enhanced by the formation of an interstrand Ni^II(bpy)₃ complex at the junction core (ΔT_m=+17.7 °C). Although the stereochemistry of the modification site differs from that of the previously reported bpy-modified nucleoside U_bpy- 2 , the degree of the Ni^II-mediated stabilization observed with U_bpy- 3 was comparable to that of U_bpy- 2 . Structure induction of the 3WJs and the duplexes was carried out by the addition or removal of Ni^II ions. Furthermore, Ni^II-mediated self-sorting of 3WJs was performed by using the bpy-modified strands and their unmodified counterparts. Both transformations were driven by the formation of Ni^II(bpy)₃ complexes. The structural induction and self-sorting of bpy-modified 3WJs are expected to have many potential applications in the development of metal-responsive DNA materials.     

Enzymatic Formation of Indolactam Scaffold by C−N Bond-Forming Cytochrome P450 Oxidases in Teleocidin Biosynthesis

Teleocidins are potent protein kinase C activators, and possess a unique indole-fused nine-membered lactam structure. Teleocidin biosynthesis starts from the formation of a dipeptide by non-ribosomal peptide synthetase (NRPS), followed by oxidative C−N bond formation by a cytochrome P450 oxidase, reverse-prenylation by a prenyltransferase, and methylation-initiated terpene cyclization by a C-methyltransferase. This minireview focuses on recent research progress toward the elucidation of the molecular basis for the remarkable P450-catalyzed intramolecular C−N bond-forming reaction, which is challenging in synthetic chemistry, to generate the indolactam scaffold. In addition, precursor-directed biosynthesis with the promiscuous P450 enzymes led to the formation of a series of unnatural and novel molecular scaffolds, including a sulfur-substituted indolactam with a different conformation from that of indolactam V.     

Exploiting a C–N Bond Forming Cytochrome P450 Monooxygenase for C–S Bond Formation

C–S bond formation reactions are widely distributed in the biosynthesis of biologically active molecules, and thus have received much attention over the past decades. Herein, we report intramolecular C–S bond formation by a P450 monooxygenase, TleB, which normally catalyzes a C?N bond formation in teleocidin biosynthesis. Based on the proposed reaction mechanism of TleB, a thiol‐substituted substrate analogue was synthesized and tested in the enzyme reaction, which afforded the unprecedented sulfur‐containing thio‐indolactam V, in addition to an unusual indole‐fused 6/5/8‐tricyclic product whose structure was determined by the crystalline sponge method. Interestingly, conformational analysis revealed that the SOFA conformation is stable in thio‐indolactam V, in sharp contrast to the major TWIST form in indolactam V, resulting in differences in their biological activities.     

High mobility organic thin-film transistors on plastic substrate

We have fabricated organic thin-film transistors (OTFTs) based on di-n-decyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) on a polyimide gate dielectric coated on a polycarbonate substrate with a bottom-gate, top-contact configuration. Mobilities of the C₁₀-DNTT-based TFTs were as high as 2.4 cm² V^?1 s^?1, which are much better than those of the parent dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)-based TFTs (mobility ～ 0.5 cm²/V) fabricated on the same substrate. Compared to the C₁₀-DNTT-TFTs on the conventional Si/SiO₂ substrate, the present mobility of C₁₀-DNTT-TFTs are somewhat reduced, which can be attributed to reduced crystallinity on the polyimide gate dielectric, although the crystalline phase on the polyimide is the same as on the Si/SiO₂ substrate.     

Experimental results of DPIS with a new RFQ

We have developed a new heavy ion production system which uses a combination of an RFQ and a laser ion source. Induced plasma by a laser shot is delivered to the RFQ without an extraction electrode. We named this new idea ‘direct plasma injection scheme (DPIS)’. In 2004, a new RFQ was built for demonstrating the capability of the DPIS. After a few months of commissioning period, we could obtain more than 60 mA of carbon beam from the RFQ. This new scheme could be applied to cancer therapy facilities and high energy nuclear physics accelerator complexes.     

Pattern-effect-free all-optical wavelength conversion using a hydrogenated amorphous silicon waveguide with ultra-fast carrier decay

Ultra-fast carrier decay, recently discovered in a hydrogenated amorphous silicon waveguide, can be exploited for pattern-effect-free all-optical signal processing based on optical Kerr nonlinearity. In this study, we utilized a 10 Gbit/s RZ-OOK data stream as a pump for degenerate four-wave mixing in a low-loss hydrogenated amorphous silicon waveguide. The propagation loss of the waveguide used was 1.0±0.2 dB/cm at 1550 nm. Unlike crystalline silicon waveguides, no noticeable difference was observed in the BER characteristics between the cases of PRBS 2(7)-1 and 2(31)-1.     

SDS‐PAGE and two‐dimensional maps in a radial gel format

A novel method for performing 2‐D map analysis is here reported, consisting in a modification of the second dimension run, which is performed not in a conventional square‐ or rectangular‐size gel, but in a radial surface. This has the advantage of permitting resolution of closely adjacent bands, representing strings of isoforms of similar or identical mass but of closely spaced isoelectric points. When used in a mono‐dimensional, SDS‐PAGE format, this system allows the simultaneous running of 62 sample tracks. Examples are given of separation of plasma and urinary proteins.