Electrochemical and spectroelectrochemical properties of neptunium(VI) ions in nitric acid solution

A benchmark study was carried out to verify whether MCNP is useful in the design stage of a PGNAA facility for large samples up to 1 m length and 0.15 m diameter, using a 2.54 cm diameter thermal neutron beam. For this facility neutron self-shielding and gamma-attenuation correction methods have to be developed. The relative spatial neutron-density distributions within three samples with different macroscopic scattering and absorption cross sections were studied in a comparison between an MCNP simulation and an irradiation experiment using copper wires as neutron monitors. The neutron density in the sample was within statistical agreement between experiment and simulation. Typically the relative spatial neutron-density distributions agreed to within 1%. Therefore, MCNP can be used in design studies for the development of a large sample PGNAA facility as specified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ab initio integrated multi-center molecular orbitals method for large cluster systems: total energy and normal vibration

A new computational scheme integrating multi-center ab initio molecular orbitals for determining total energy and normal vibration of large cluster systems is presented. This method can be used to treat large cluster systems such as solvents by quantum mechanics. The geometry parameters, the total energies, the relative energies, and the normal vibrations for four models of water cluster, the hydrated hydronium ion complex, and the transition state of proton transfer are calculated by the present method and are compared with those obtained by the full ab initio MO method. The results agree very well. The scheme proposed in this article is also intended to be used in modeling computer cluster systems using parallel algorithms.     

Furopyridines. VIII. Molecular structure and two-dimensional NMR spectral assignment of 2,14-dimethyl-8aβ-hydroxy-7,10-dioxo-5β,6β-(propano)-6α,8α-(ethanoimino)-trans-perhydroisoquinoline

This paper reports the two-dimensional nmr spectral assignment and the X-ray structural determination of 2,14-dimethyl-8β-hydroxy-7,10-dioxo-5β,6β-(propano)-6α,8α-(ethanoimino)-trans-perhydroisoquinoline V which was obtained from 7,10-dimethyl-2β-hydroxy-14-oxo-2,3-(methanoiminoethano)-3β,4β-(propano)-3,4,5,6,7,8-hexahydro-2H-pyrano[2,3-c]pyridine IV by isomerization with hydrochloric acid. Both the compounds IV and V afforded the same dimethiodide IV -2MeI, while the configurational isomer 2,14-dimethyl-8aβ-hydroxy-7,10-dioxo-5α,6β-(propano)-6α,8α-(ethanoimino)-trans-perhydroisoquinoline III gave monomethiodide III -Mel. The structures of these methiodides were also confirmed by X-ray analysis.     

Micro-HPLC/TLC/FTIR

Identification problems often encountered in high performance liquid chromatography (HPLC)/Fourier transform infrared spectrometry (FTIR) can be circumvented through the use of a thin-layer chromatographic (TLC) plate as deposition and infra-red sampling medium. The combination of complementary separation modes is shown to demonstrate increased resolution of the components of complex mixtures. In this particular work, the effluent from a reversed-phase microcolumn is continuously deposited on a TLC plate with alumina stationary phase. The solute remains on the plate as a continuous record of the HPLC separation, which is then analyzed by diffuse reflectance FTIR. When the HPLC separation is inadequate for full separation of the components, the immobilized HPLC chromatogram serves as a starting point for subsequent TLC separation. A number of FTIR reconstructed chromatograms and spectra which are derived from the TLC plate aid in the interpretation.     

Chemical reactivity of two-photon excited trimethylsilylacetylene in aerosol particle formation with acrolein

Under irradiation with N₂ laser light, a gaseous mixture of trimethylsilylacetylene (ethynyltrimethylsilane) (TMeSiA) and acrolein (AC) produced sedimentary aerosol particles with a mean diameter of 1.0 μm. Nucleation process of the aerosol particles was studied by measuring monitor (He–Ne laser) light intensity scattered by the aerosol particles as formed under N₂ laser light irradiation. With increasing partial pressure of TMeSiA, the nucleation reaction of aerosol particles was accelerated due to additional generation of reactive species from TMeSiA molecules by a two-photon process. FT-IR spectra of the sedimentary particles showed that TMeSiA molecules were incorporated into polymerization reaction of AC by forming –Si–O–C– bond from R(CH₃)₂Si radicals. Two-photon processes of both AC and TMeSiA molecules under N₂ laser light irradiation were briefly discussed.     

Long-range electron transfer over 4 nm governed by an inelastic hopping mechanism in self-assembled monolayers of helical peptides

Well-ordered self-assembled monolayers (SAMs) were prepared on gold from helical peptides carrying a ferrocene (Fc) moiety at the N- or C-terminal end, and long-range electron transfer (ET) from Fc to gold was investigated. Electrochemical studies revealed that an inelastic hopping mechanism dominated over the superexchange mechanism in the ET reactions in the present SAMs and the dipole moment of the helix accelerated the ET reactions probably due to the lowering of the barrier height between the gold surface and peptide layer.     

Ambident effect of a p-sulfinyl group for the introduction of two carbon substituents to phenol rings: a convergent synthesis of diverse benzofuran neolignans

A convergent synthesis of diversely substituted benzofuran neolignans (8) is described employing a single p-sulfinyl group on the phenols (3) as an ambident functional group for two types of carbon-carbon bond-forming reactions: (i) the direct synthesis of the dihydrobenzofuran skeletons through an aromatic Pummerer-type reaction and (ii) the ipso-substitution of the sulfur functional group by carbon substituents through a ligand exchange reaction.     

SPECTRAL SENSITIZATION OF SnO2 THIN FILM ELECTRODE BY THE J-AGGREGATE OF CYANINE DYES IN MONOLAYERS

Arachidic acid monolayers containing 5,6,5',6'-dibenzo-I,I-diethyl-2,2'-cyanine chloride were prepared by the spreading method and deposited on the SnO₂ surface using the Langmuir-Blodgett technique. The SnO₂ : dye assembly prepared in this manner was used as a photoelectrode of the conventional electrochemical cell. A distinct J-band was observed in the action spectra of sensitized anodic and cathodic photocurrents. Effects of calcium arachidate barriers inserted between dye layer and either SnO₂ electrode (inside barrier) or electrolyte solution (outside barrier) on the photocurrent were examined. Although the inside barrier was effective in decreasing both anodic and cathodic photocurrents, the outside barrier did not suppress cathodic photocurrent. The following mechanism involving a molecular exciton of the J-aggregate is proposed for the sensitized photocurrent. The anodic photocurrent is caused by hole trapping by some reducing agent and concomitant injection of the electron from molecular exciton to the conduction band of SnO₂. Extraction of conduction-band electron of SnO₂ by molecular exciton and supplying to some oxidizing agent such as dissolved oxygen are responsible for the cathodic photocurrent.     

A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N₂) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.