Broad-spectrum radical cyclizations boosted by polarity matching. Carbonylative access to alpha-stannylmethylene lactams from azaenynes and CO

Free-radical mediated stannylcarbonylation of azaenynes provides a general [n + 1]-type annulation approach leading to alpha-stannylmethylene lactams. The cyclization is unusual in its breadth, covering 4-exo, 5-exo, 6-exo, 7-exo, and 8-exo modes.     

Electrostatic Interactions That Determine the Rate of Pseudorotation Processes in Oxyphosphorane Intermediates: Implications with Respect to the Roles of Metal Ions in the Enzymatic Cleavage of RNA

The enzymatic cleavage of RNA takes place via a cyclic pentacoordinate oxyphosphorane intermediate/transition state. We carried out ab initio investigations on the neutral cyclic oxyphosphorane, which exists as a stable intermediate. As a consequence of the conformational preferences of the pentacoordinate trigonal bipyramidal intermediates, the rotation of the P-OH bonds is strongly coupled with the reaction coordinate for the pseudorotation process. In addition, the neutral PF(4)OH species has a higher barrier to pseudorotation than the corresponding anionic species PF(4)O(-). These findings are related to the positive charge of the hydrogen atoms on the equatorial oxygens in the trigonal bipyramidal structures: the hydrogen atoms preferably adopt eclipsed positions relative to the axial ligands. Fixing the cationic species in these regions causes an increase in the barrier heights for pseudorotation processes and, thus, prevents isomerization by pseudorotation. Consequently, metal coordination in the double-metal ion mechanism for enzymatic cleavage of RNA should serve to exclusively stabilize the trigonal bipyramidal intermediate/transition state for the in-line attack and departure process.     

Synthesis,hydrophilicity, and oxygen permeability of poly[(trimethylsilyl)propyne]-gr-poly(N,N-dimethylacrylamide)

N,N-dimethylacrylamide (DMAA) was graft copolymerized on poly[(trimethylsilyl)propyne] (PTMSP) by single electron reduction of PTMSP with potassium naphthalenide (K-Naph), followed by anion polymerization of DMAA from the carbanion formed in the reduction. A hard and practically non-water-swelling PTMSP-gr-poly(DMAA) was obtained under the conditions using controlled amount of K-Naph and DMAA. The graft copolymer was characterized with regard to structure, number-averaged molecular weight, and the amount of grafting poly(DMAA) determined by the relative absorbance of the IR absorption band assigned to the CO and SiC H functionalities (A_CO/A_{SiC H}). The oxygen permeability and water contact angle (θ) of the graft copolymer were evaluated while varying the amount of grafting poly(DMAA). The graft copolymer proved to be highly oxygen permeable (165 Barrers) and hydrophilic (θ = 27°). Its transparency was also elucidated with UV–vis spectra. This graft copolymer was proposed as a promising candidate for use as a hard contact lens material. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 603–610, 1998     

Development and validation of a liquid chromatographic method for the analysis of positron emission tomography radiopharmaceuticals with Ru(bpy)(3)(2+)-KMnO(4) chemiluminescence detection.

A sensitive, selective and rapid high-performance liquid chromatographic (HPLC) method with chemiluminescence (CL) detection was developed and validated for the analysis of positron emission tomography (PET) radiopharmaceuticals. This method is based on the CL reaction of PET compounds with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] and acidic potassium permanganate [KMnO(4)]. After optimization of the reaction conditions, 12 of the 14 PET compounds investigated could be successfully detected and showed good performance in terms of sensitivity, linearity and reproducibility. In particular, for compounds with a tertiary amine functional group, the limits of detection were ppb levels for a 20 microL injection volume. Finally, this method was used to determine PET compounds for calculating of specific radioactivity in pharmaceutical samples.     

Chemical states of dodecanethiolate-passivated Au nanoparticles: synchrotron-radiation photoelectron spectroscopy

We have carried out a photoemission study using synchrotron radiation of dodecanethiolate (DT)-passivated Au nanoparticles supported on the highly oriented pyrolytic graphite substrates. From detailed line-shape analyses of Au 4f core-level photoemission spectra of DT-passivated Au nanoparticles, it was found that Au 4f core-level spectra consist of two components. We attribute these components to the inner Au atoms and surface Au atoms bonded to surface dodecanethiolates. From these results, we discuss the chemical states of the present DT-passivated Au nanoparticles.     

Characterization of boron carbon nitride film modified by excimer laser annealing

Boron carbon nitride (BCN) shows promise as a field emitter material because of its mechanical hardness, chemical inertness, and low electron affinity. This study investigated the modification of a BCN film with an amorphous area using KrF excimer laser (wavelength: 248 nm, photon energy: 5.0 eV) annealing without substrate heating. This achieved significant variation in characteristics, such as an increase in bandgap energy and decrease in electron affinity. Laser annealing reduced electron affinity from 0.7 to 0.3 eV. The results indicate that the modification of the BCN film by KrF excimer laser annealing achieves characteristics similar to hexagonal BN (h-BN) film without losing the desirable properties of the BCN film, such as physical stability.     

Raman study of vibrational relaxation of acetonitrile in solution

Line widths of isotropic Raman spectra of the ν₁ (a₁) CH or CD stretching bands of acetonitrile CH₃CN and CD₃CN were measured in a number of solvents. The vibrational dephasing theory, modified for use in binary mixtures, predicts quantitatively the solvent dependence of the Raman line widths.     

Conversion from arenes having a benzene ring to those having a picolinic acid by simple growing cell reactions using Escherichia coli that expressed the six bacterial genes involved in biphenyl catabolism

The comprehensive bioconversion of aromatic compounds with a benzene ring to a picolinic acid was achieved with a recombinant Escherichia coli strain that expressed the six genes involved in biphenyl catabolism, these being the bphA1(2072)A2A3A4 genes encoding the evolved biphenyl dioxygenase, the bphB gene encoding dihydrodiol dehydrogenase, and the bphC gene encoding catechol 2,3-dioxygenase.