bluuebunny/crossref_metadata_2025 huggingface dataset:
Stable isotope composition of dissolved inorganic carbon and particulate organic carbon in sea ice from the Ross Sea, Antarctica
Authors: Munro David R. , Dunbar Robert B. , Mucciarone David A. , Arrigo Kevin R. , Long Matthew C.
Published: September 2010

We examined controls on the carbon isotopic composition of sea ice brines and organic matter during cruises to the Ross Sea, Antarctica in November/December 1998 and November/December 2006. Brine samples were analyzed for salinity, nutrients, total dissolved inorganic carbon (ΣCO2), and the 13C/12C ratio of ΣCO2 Particulate organic matter from sea ice cores was analyzed for percent particulate organic carbon (POC), percent total particulate nitrogen (TPN), and stable carbon isotopic composition (δ13CPOC). ΣCO2 in sea ice brines ranged from 1368 to 7149 μmol kg−1, equivalent to 1483 to 2519 μmol kg−1 when normalized to 34.5 psu salinity (sΣCO2), the average salinity of Ross Sea surface waters. Sea ice primary producers removed up to 34% of the available ΣCO2, an amount much higher than the maximum removal observed in sea ice free water. Carbonate precipitation and CO2 degassing may reduce sΣCO2 by a similar amount (e.g., 30%) in the most hypersaline sea ice environments, although brine volumes are low in very cold ice that supports these brines. Brine ranged from −2.6 to +8.0‰ while δ13CPOC ranged from −30.5 to −9.2‰. Isotopic enrichment of the ΣCO2 pool via net community production accounts for some but not all carbon isotopic enrichment of sea ice POC. Comparisons of sΣCO2, and δ13CPOC within sea ice suggest that εp (the net photosynthetic fractionation factor) for sea ice algae is ∼8‰ smaller than the εp observed for phytoplankton in open water regions of the Ross Sea. These results have implications for modeling of carbon uptake and transformation in the ice‐covered ocean and for reconstruction of past sea ice extent based on stable isotopic composition of organic matter in sediment cores.
Serum microRNA characterization identifies miR-885-5p as a potential marker for detecting liver pathologies
Authors: Gui Junhao , Tian Yaping , Wen Xinyu , Zhang Wenhui , Zhang Pengjun , Gao Jing , Run Wei , Tian Liyuan , Jia Xingwang , Gao Yanhong
Published: September 2010

Circulating miRNAs (microRNAs) are emerging as promising biomarkers for several pathological conditions, and the aim of this study was to investigate the feasibility of using serum miRNAs as biomarkers for liver pathologies. Real-time qPCR (quantitative PCR)-based TaqMan MicroRNA arrays were first employed to profile miRNAs in serum pools from patients with HCC (hepatocellular carcinoma) or LC (liver cirrhosis) and from healthy controls. Five miRNAs (i.e. miR-885-5p, miR-574-3p, miR-224, miR-215 and miR-146a) that were up-regulated in the HCC and LC serum pools were selected and further quantified using real-time qPCR in patients with HCC, LC, CHB (chronic hepatitis B) or GC (gastric cancer) and in normal controls. The present study revealed that more than 110 miRNA species in the serum samples and wide distribution ranges of serum miRNAs were observed. The levels of miR-885-5p were significantly higher in sera from patients with HCC, LC and CHB than in healthy controls or GC patients. miR-885-5p yielded an AUC [the area under the ROC (receiver operating characteristic) curve] of 0.904 [95% CI (confidence interval), 0.837–0.951, P<0.0001) with 90.53% sensitivity and 79.17% specificity in discriminating liver pathologies from healthy controls, using a cut off value of 1.06 (normalized). No correlations between increased miR-885-5p and liver function parameters [AFP (α-fetoprotein), ALT (alanine aminotransferase), AST (aspartate aminotransferase) and GGT (γ-glutamyl transpeptidase)] were observed in patients with liver pathologies. In summary, miR-885-5p is significantly elevated in the sera of patients with liver pathologies, and our data suggest that serum miRNAs could serve as novel complementary biomarkers for the detection and assessment of liver pathologies.
Theory of radiative shocks in the mixed, optically thick-thin case
Authors: McClarren Ryan G. , Drake R. Paul , Morel J. E. , Holloway James Paul
Published: September 2010

A theory of radiating shocks that are optically thick in the downstream (postshock) state and optically thin in the upstream (preshock) state, which are called thick-thin shocks, is presented. Relations for the final temperature and compression, as well as the postshock temperature and compression as a function of the shock strength and initial pressure, are derived. The model assumes that there is no radiation returning to the shock from the upstream state. Also, it is found that the maximum compression in the shock scales as the shock strength to the 1/4 power. Shock profiles for the material downstream of the shock are computed by solving the fluid and radiation equations exactly in the limit of no radiation returning to the shock. These profiles confirm the validity and usefulness of the model in that limit.
Study on the core/cladding interface in Cr:YAG double-clad crystal fibers grown by the codrawing laser-heated pedestal growth method
Authors: Lai Chien-Chih , Lin Yen-Sheng , Huang Kuang-Yao , Huang Sheng-Lung
Published: September 2010

This study reports, for the first time, atomic-scale high-resolution transmission electron microscope (HRTEM) microstructure studies on the interface between the crystal core and polycrystalline inner cladding and strain relaxation mechanism of high-quality Cr:YAG double-clad crystal fibers grown by a codrawing laser-heated pedestal growth method. HRTEM analysis indicates that the core has high crystallinity and a sharp core/inner-cladding interface, exhibiting coherent planes with a preferred orientation relationship to the γ-Al2O3 nanocrystals in the inner cladding. The slightly distorted γ-Al2O3 lattice facilitates the release of residual strain, and eliminates misfit dislocation at the interface. Lattice strain analysis and image processing reveal a ∼18.2 nm layer near the interface for strain relaxation.
Product gas evolution above planar microstructured model catalysts—A combined scanning mass spectrometry, Monte Carlo, and Computational Fluid Dynamics study
Authors: Roos M. , Bansmann J. , Zhang D. , Deutschmann O. , Behm R. J.
Published: September 2010

The transport and distribution of reaction products above catalytically active Pt microstructures was studied by spatially resolved scanning mass spectrometry (SMS) in combination with Monte Carlo simulation and fluid dynamics calculations, using the oxidation of CO as test reaction. The spatial gas distribution above the Pt fields was measured via a thin quartz capillary connected to a mass spectrometer. Measurements were performed in two different pressure regimes, being characteristic for ballistic mass transfer and diffusion involving multiple collisions for the motion of CO2 product molecules between the sample and the capillary tip, and using differently sized and shaped Pt microstructures. The tip height dependent lateral resolution of the SMS measurements as well as contributions from shadowing effects, due to the mass transport limitations between capillary tip and sample surface at close separations, were evaluated and analyzed. The data allow to define measurement and reaction conditions where effects induced by the capillary tip can be neglected (“minimal invasive measurements”) and provide a basis for the evaluation of catalyst activities on microstructured model systems, e.g., for catalyst screening or studies of transport effects.
Triple-frequency intermittent contact atomic force microscopy characterization: Simultaneous topographical, phase, and frequency shift contrast in ambient air
Authors: Solares Santiago D. , Chawla Gaurav
Published: September 2010

We present computational simulation and experimental results of ambient air atomic force microscopy (AFM) characterization with simultaneous excitation and control of three eigenmodes of a rectangular microcantilever beam. Trimodal characterization combining amplitude and frequency modulation is an enhancement of the capabilities of the AFM technique, which could allow the rapid acquisition of topographical, phase, and frequency shift contrast with a single surface scan at normal scan rates. The results suggest that, in general, the phase and frequency shift contrast are affected similarly but in opposite directions by the tip-sample interactions, although deviations from this trend are often observed in the experiments, such that all available sources of contrast could provide complementary information on surface properties.
On the kinetics of tautomerism in drugs: New application of broadband dielectric spectroscopy
Authors: Wojnarowska Z. , Wlodarczyk P. , Kaminski K. , Grzybowska K. , Hawelek L. , Paluch M.
Published: September 2010

There are a number of chemical compounds that readily convert to other isomers when their crystalline structure is lost (e.g., during melting or dissolution). This phenomenon, commonly known as tautomerism, is a subject of intense research. It is an important problem especially in pharmaceutical industry because various isomers of a drug may have different pharmacological activity. Therefore, it is important to find appropriate experimental technique which enables the determination of the isomerization ability of compounds. In this communication, we demonstrate that broadband dielectric spectroscopy (BDS) method has the potential of detection and monitoring of tautomerism of drugs. To investigate the tautomerism phenomenon we have chosen one of the hypoglycemic agents that belong to the class II of sulfonylurea drugs. Based on density functional theory (DFT) calculations we have analyzed two possible tautomerization pathways of glibenclamide. By using BDS as a tool, we show it can detect the conversion between the isomeric forms through time dependence in the dielectric properties. The activation energy (Ea) of this process is in good agreement with that obtained from DFT analysis. Finally, we discuss the possible effects of tautomerism on basic pharmaceutical parameters such as biological activity or bioavailability in the case of the glibenclamide drug.
Optical and thermal depth profile reconstructions of inhomogeneous photopolymerization in dental resins using photothermal waves
Authors: Martínez-Torres P. , Mandelis A. , Alvarado-Gil J. J.
Published: September 2010

Photopolymerization is a process that depends, among other factors, on the optical properties of polymerized materials. In turn, this process affects longitudinal light transport in these materials, thereby altering their optical absorption coefficient which is thus expected to exhibit depth dependence. Furthermore, polymerization affects the thermal properties of these materials. A robust theoretical approach to the study of the depth-dependent optical absorption coefficient, β(x), and thermal diffusivity, α(x), in materials exhibiting depth profiles of these parameters has been developed through the photothermal inverse problem based on the concept of the thermal-harmonic oscillator. Using this concept in the frequency-domain nonhomogeneous photothermal-wave boundary-value problem, the simultaneous reconstruction of arbitrary simultaneous optical and thermal depth profiles was achieved using a multiparameter fitting method to the experimental amplitude and phase. As a first application of the theory to partially polymerized Alert Composite (shade A3) dental resin, with curing induced by a blue light-emitting diode, the β(x) and α(x) depth profiles were reconstructed from photothermal radiometric frequency-scanned data. A strong anticorrelation of these two depth profiles was observed and was interpreted in terms of photochemical processes occurring during the optical (photocuring) creation of long polymeric chains in the resin. The photothermally reconstructed depth profiles may have implications for the optimization of blue light curing methods using such resins in dental clinical practice.
Switched capacitor charge pump reduces hysteresis of piezoelectric actuators over a large frequency range
Authors: Huang Liang , Ma Yu Ting , Feng Zhi Hua , Kong Fan Rang
Published: September 2010

Piezoelectric actuators exhibit large hysteresis between the applied voltage and their displacement. A switched capacitor charge pump is proposed to reduce hysteresis and linearize the movement of piezoelectric actuators. By pumping the same amount of charges into the piezoelectric actuator quantitatively, the actuator will be forced to change its length with constant step. Compared with traditional voltage and charge driving, experimental results demonstrated that the piezoelectric stack driven by the charge pump had less hysteresis over a large frequency range, especially at ultralow frequencies. A hysteresis of less than 2.01% was achieved over a frequency range of 0.01–20 Hz using the charge pump driver.
Self-diffusion of poly(propylene glycol) in nanoporous glasses studied by pulsed field gradient NMR: A study of molecular dynamics and surface interactions
Authors: Schönhals A. , Rittig F. , Kärger J.
Published: September 2010

Pulsed field gradient NMR is applied to investigate the self-diffusion of poly(proypylene glycol) in nanoporous glasses (nominal pore sizes of 2.5–7.5 nm). In general, the diffusion is slowed down by the confinement compared to the bulk. For native pore surfaces covered by hydroxyl groups the spin echo attenuation Ψ displays a bimodal behavior versus q2t (q-norm of a generalized scattering vector). This was explained assuming spatial regions of different diffusivities in a two-phase model. The slow component is assigned to segments forming a surface layer close to the pore walls in which the segments have a lower mobility than those located in the center of the pores. By variation of observation time it was concluded that time constant for the dynamic exchange of segments between these two regions is around 100 ms at room temperature. For silanized pores, the bimodal behavior in the spin echo attenuation Ψ shows a stretched exponential decay versus q2t. The estimated diffusion coefficients decrease strongly with decreasing pore size. The temperature dependence of the diffusion coefficient can be approximated by an Arrhenius law where the activation energy increases with decreasing pore size. The observed pore size dependence for the diffusion of poly(propylene glycol) in silanized nanoporous glasses can be discussed assuming interaction and confining size effects.
The role of ultrathin AlN barrier in the reduction in the hot electron and self-heating effects for GaN-based double-heterojunction high electron mobility transistors
Authors: Wang L. , Hu W. D. , Chen X. S. , Lu W.
Published: September 2010

We propose an AlN/GaN/InGaN/GaN double-heterojunction high electron mobility transistor (DH-HEMT) structure with a 4 nm thin AlN barrier layer. The performance of the DH-HEMT device is investigated by using two-dimensional numerical simulation. The conduction band profile is obtained by using the Poisson’s equation and Fermi–Dirac statistics in combination with the polarization charges. Due to large conduction-band offset of the AlN/GaN interface and strong polarization of AlN, the minor channel at GaN/InGaN interface can be eliminated. Further, the hot electron and self-heating effects on the transport properties of this DH-HEMT are investigated by using hydrodynamic model. In comparison with the AlGaN barrier DH-HEMT and conventional HEMT, this kind of DH-HEMT can effectively reduce the hot electron effect under high voltage. The reason is that the maximum field strength is far below the critical value for the existence of the hot electron effect in the AlGaN barrier DH-HEMTs and conventional HEMTs with the same voltage 6 V. The simulation results also show that the ultrathin AlN barrier layer can significantly reduce thermal impedance, and then lower the self-heating effect. Furthermore, the passivation layer has significant role in the self-heating effect of the ultrathin barrier DH-HEMTs.
Raman scattering determination of the energy difference between Γ and L conduction band minima in Ga1−xInxAsySb1−y
Authors: Cuscó R. , Ibáñez J. , Artús L.
Published: September 2010

We report a Raman scattering determination of the energy difference EΓ−L between the Γ conduction-band minimum and the L valley minima in n-type Ga1−xInxAsySb1−y lattice matched to GaSb (x=0.15, y=0.13). A frequency downshift in the L+ phonon–plasmon coupled mode is observed between 80 K and room temperature that is attributed to electron transfer from the Γ to the L valleys. We use the L+ frequency shift to evaluate EΓ−L by performing Lindhard–Mermin L+ line-shape fits for different EΓ−L values. The EΓ−L value increases with electron concentration due to band gap renormalization. A value EΓ−L=154 meV is derived for intrinsic material.
Interface electronic structures of 2-amino-4,5-imidazoledicarbonitrile on Ag and Al surfaces
Authors: Nakayama Yasuo , Huang Yen-Hao , Wei Ching-Hsuan , Kubo Takuya , Machida Shin-ichi , Pi Tun-Wen , Tang S.-J. , Noguchi Yutaka , Ishii Hisao
Published: September 2010

2-amino-4,5-imidazoledicarbonitrile (AIDCN) has been considered as a promising material toward organic nonvolatile memory application. Aiming for achieving a deep understanding of the origins of the bistable electric behavior of the AIDCN-based memory devices and, in particular, of the reported drastic improvement of the device performance by replacement of the Al top-electrode material with Ag, we elucidated the electronic structures of the interfaces between AIDCN and electrode metals (Ag and Al), as well as the bulk of AIDCN, by photoemission spectroscopy (PES). Ionization energy of AIDCN was determined to be 6.6 eV that was also certified by photoelectron yield spectroscopy measurements. For the AIDCN/Ag interface, the highest occupied molecular orbital (HOMO)-derived peak was clearly resolved in the PES spectra even when the thickness of the AIDCN overlayers were below the monolayer. The peak position showed significant shifting (∼0.5 eV) to the higher binding energy side with formation of the multilayers. Probing angle dependent spectra revealed that the AIDCN monolayer on Ag shows different molecular orientation from that of the multilayers. These results strongly suggest that a sharp interface was formed between the Ag surface and AIDCN overlayers. In contrast, the PES spectra of the AIDCN/Al interface showed not a peak but a diffuse tailing structure in the HOMO region until the bulklike phase was formed. No angular dependent change appeared on the PES spectra in the low coverage region, which suggests the molecular orientation was random. The hole injection barriers, derived from energy offsets between the edges of the HOMO-derived spectral features and the Fermi level, of AIDCN/Ag and AIDCN/Al interfaces are estimated to be 2.0 eV and 1.0 eV, respectively.
Use of square waves incident on magnetic nanoparticles to induce magnetic hyperthermia for therapeutic cancer treatment
Authors: Morgan Sean M. , Victora R. H.
Published: September 2010

Magnetic hyperthermia for treatment of tumors would benefit greatly from increased heating of the magnetic particles relative to the incident electromagnetic wave power. Micromagnetic simulations including thermal fluctuations show that the use of an incident square wave, as opposed to the usual sine wave, increases the normalized heat by at least 50%, with the possibility of much greater improvement for the usual case of particle ensembles that have a distribution of magnetic anisotropies, volumes, and angles to the incident radiation. It is shown that even replacement of the square wave by a limited number of harmonics is highly beneficial.
Piezoelectric-actuated, piezoresistive-sensed circular micromembranes for label-free biosensing applications
Authors: Alava T. , Mathieu F. , Rameil P. , Morel Y. , Soyer C. , Remiens D. , Nicu L.
Published: September 2010

In this paper, we report on the fabrication and characterization of the dynamic behavior of circular micromembranes integrating a piezoelectric thin film for actuation and a boron-doped silicon piezoresistor for sensing purposes. Resonant frequencies corresponding to high-order modes of vibration are measured, respectively, in air and deionized water. The measurements are compared with theoretical values calculated using the extended Lamb’s model [H. Lamb, Proc. R. Soc. London 98, 205 (1920)] adapted to the microscale. Moreover, label-free detection of Bacillus atrophaeus (or B. atrophaeus) with a concentration of 108 spores/mL is repeatedly performed in real-time which assesses the biosensing potential of microscale circular membranes bearing actuation and sensing elements.
Mid- and far-infrared intersubband absorption in quantum dash nanostructures
Authors: Crnjanski J. V. , Gvozdić D. M.
Published: September 2010

The authors calculate and analyze intersubband absorption in InAs/GaAs quantum dash ensemble. The absorption spectrum dominantly occupies the mid- and extends to the far-infrared region. As far as the wetting layer is taken into account, the electron concentration significantly affects the absorption and the spectrum can be tailored by adjusting spacer layers. It is shown that size fluctuation of dashes causes spectrum broadening and its asymmetry, while the increase in the wetting layer thickness leads to a redshift in the spectrum and decrease in the absorption.
Charge injection barrier and interface dipole formation in pentacene/semimetal heterostructures
Authors: Hatch Richard C. , Sanchez Casey W. , Höchst Hartmut
Published: September 2010

Heterostructures containing pentacene (Pn) and the semimetals Bi and Sb were grown using molecular beam epitaxy. We used photoemission spectroscopy to measure the evolution of the vacuum level, hole-injection barrier, interface dipole, and work function changes as a function of Pn and semimetal coverage. The energy levels of the semimetal/Pn/semimetal sandwich structures show symmetric final values. The Pn/semimetal interfaces are very abrupt and established after a single monolayer (∼15 Å), whereas the semimetal/Pn interfaces extend over ∼100 Å.
High power terahertz emission from a single gate AlGaN/GaN field effect transistor with periodic Ohmic contacts for plasmon coupling
Authors: Onishi Toshikazu , Tanigawa Tatsuya , Takigawa Shinichi
Published: September 2010

We report on room temperature terahertz (THz) emission by a single, short gate AlGaN/GaN field effect transistor with grating Ohmic contacts. The fingers of metal contacts are fabricated at the nanoscale in length and spacing in order to work as a radiation coupler of electron plasmons in the THz range. Spectrum analysis revealed a broadband emission centered at 1.5 THz with a controlled polarization by the grating contacts. The measured output power is linearly increased with the drain input power and reached up to 1.8 μW.
A contactless method for measuring the recombination velocity of an individual grain boundary in thin-film photovoltaics
Authors: Mendis B. G. , Bowen L. , Jiang Q. Z.
Published: September 2010

A cathodoluminescence-based, contactless method for extracting the bulk minority carrier diffusion length and reduced recombination velocity of an individual grain boundary is applied to vapor grown CdTe epitaxial films. The measured diffusion length was within the range of 0.4–0.6 μm and the grain boundary recombination velocity varied from 500 to 750 cm/s. The technique can be used to investigate the effect of grain boundaries on photovoltaic performance.
Stereo-Electronic Effects in Substituted Phosphines: a Molecular Orbital Study
Authors: Magnusson E
Published: September 2010

Substituent effects from directly bonded and remote groups in phosphines have been studied by ab initio molecular orbital methods in an attempt to discriminate between the electronic and steric effects of attached groups and determine how they are transmitted to
phosphorus. Results of calculations are compared with experimentally determined basicities and acidities, ionization energies, inversion barriers and 31P N.M.R. results. The electronic consequences of steric effects are comparable in importance to direct electronic effects; in the PHn(CH3)3-n, series steric effects account for about half of the substituent effect on basicities and ionization potentials. The effects of steric bulk, modelled by bond angle constraint, are concentrated in the HOMO; by contrast, electronic effects on the HOMO are often minimal. Conformational changes include changes in geometry but the electronic response exceeds what would be expected for geometrical change alone and in NH2- and OH-substituted model compounds of the PH2X and PX3 series may be as great as that produced by changing the substituent. In remote substitution the effects are mainly due to charge displacement at phosphorus. Directly bound groups more often exert their effects by altering the balance between s and p orbitals in the bonding and in the non-bonding parts of the electron distribution but in ways which preclude correlation with electronegativity or other single-parameter measures of substituent properties. Donor/acceptor interactions are weaker in phosphorus(III) compounds than in the first-row analogues but the response to substitution in the density profile is much stronger around the more polarizable second-row element which explains why the alkyl substituent effect is greater for the donor properties of phosphines than amines while the effects of fluoro-substitution are weaker.
Substituent Effects and Structure in Substituted Dibenzonaphthyrones
Authors: Becker H , Raston CL , Skelton BW , White AH
Published: September 2010

The crystal and molecular structures of [1]benzopyrano[4,3- c][1]benzopyran-5,11-done (dibenzo-naphthyrone) and three of its symmetrically tetrasubstituted derivatives have been determined by single-crystal X-ray diffraction methods. Only the tetra-t-butyl-substituted dibenzonaphthyrone was found to deviate significantly from planarity by having the two carbonyl groups folded and 'syn'-oriented relative to the plane of the connecting ethylene double bond. The dihedral angle between the two aromatic rings was found to be 25. The molecular geometry of all the other dibenzo-naphthyrones in their crystalline states is characterized by planarity, and their structures are centrosymmetric.
Anthracyclines. XII. The preparation of (—)-(7R)-7-Acetyl-7-(t-butyldimethylsilyoxy-1(4H)-one and (+)-(6R)-6-Acetyl-6-(t-butyldimethylsilyloxy)- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalene-1(4H)-one: an Improved Route to Chiral AB Synthons for 7-Deoxydaunomycinone
Authors: Russell RA , Krauss AS , Irvine RW , Warrener RN
Published: September 2010

The title dienones (2) and (5) were prepared from the chiral alcohols (7a) and (7b) respectively. These key starting materials were in turn available from the reduction of 3-acetyl-5-benzyloxy-8-methoxy-1,2- dihydronaphthalene (6a) and 3-acetyl-8-benzyloxy-5-methoxy-1,2- dihydronaphthalene (6b) with lithium aluminium hydride modified with (—)-N- methylephedrine and N- ethylaniline . Chiral phase high-pressure liquid chromatography was used to analyse the enantioselectivity of these reductions which were shown to yield variable results depending upon the origin of the reducing agent.
Chemistry of buprestins A and B. Bitter principles of jewel beetles (Coleoptera: Buprestidae)
Authors: Brown WV , Jones AJ , Lacey MJ , Moore BP
Published: September 2010

The isolation an
structural elucidation of β-D- glucopyranose 1,2,6- tris (pyrrole-2-carboxylate) ( buprestin A) (1) and β-D- glucopyranose 6- (4-hydroxybenzoate) 1,2-bis(pyrrole-2-carboxylate) ( buprestin B) (3), bitter principles of beetles of the family Buprestidae , are reported.
Crystal Structure of Bis(2,2':6',2"-terpyridine)iron(II) Bis(perchlorate) Hydrate
Authors: Baker AT , Goodwin HA
Published: September 2010

The crystal structure of bis (2,2′:6′,2″-terpyridine)iron(II) bis ( perchlorate ) hydrate has been determined by single-crystal X-ray diffractometry . The compound is monoclinic, space group P21, with two molecules in a unit cell of dimensions a 8.830(3), b 8.914(1), c 20.037(6)Ǻ, β 100.82(1)°. The structure was refined by least squares to a residual of 0.048 for 2007 observed reflections. The cation is found to have approximate D2d symmetry, with the principal distortion from octahedral symmetry being an axial compression. The lattice water molecule and anions are oriented towards the interligand pockets of the cation. There is hydrogen bonding between the water molecule and one anion.
Addition of Alkynes to the Metal-Metal Double Bond in (η-C5Me,5)2Rh2(µ-CO)2; Crystal and Molecular Structure of the Complex (η-C5Me5)2Rh2(µ-CO){µ-C(O)C2(CF3)2}.
Authors: Dickson RS , Evans GS , Fallon GD
Published: September 2010

Various alkynes (EtC2Et,
MeO2CC2CO2Me, CF3C2CF3,
PhC2Ph, C6F5C2C6F5,
PhC2Me, PhC2C6-F5, PhC2CO2Me)
react with (η-C5Me5)2Rh2(μ-CO)2
in acetone at room temperature; no reaction was observed with ButC2But.
The σ-bridging alkyne complex, trans-(η-C5Me5)2Rh2(CO)2(μ-η1:η1C6F5C2C6F5),
was obtained from the reaction with C6F5C2C6F5.
With the other alkynes, dimetallaeneone complexes,
(η-C5Me5)2Rh2(μ-CO){μ-η2:η2-C(O)C2RR′},
are formed. Some of these 'eneone' complexes co-exist with (η- C5Me5)2Rh2(CO)2(μ-η1:η1-RC2R�)
in the solid state (RC2R� = PhC2C6F5)
and/or in solution (EtC2Et, CF3C2CF3,
PhC2C6F5); others (MeO2CC2CO2Me,
PhC2Ph, PhC2Me, PhC2CO2Me) exist
exclusively as (η-C5Me5)2Rh2(μ-CO){μ-η2:η2-
C(O)C2RR′} in both the solid and solution states. The geometry of
the bridging group in (η-C5Me5)2Rh2(μ-CO){μ-η2:η2-C(O)C2(CF3)2}
has been determined from an X-ray diffraction study. The compound crystallizes with
four molecules in the monoclinic space group P21/n in a unit cell of
dimensions a 9.451(4), b 15.287(5), c 18.821(8)Ǻ, β 98.66(5)°. The
structure was solved by conventional heavy atom methods and refined to R 0.066
based on 4356 observed reflections above background. The structure contains a metalla-eneone ring, Rh -C(=O)-C(CF3)=C(CF3),
with the alkene bond η2-attached to the
second rhodium atom. Variable temperature N.M.R .
measurements establish that the complexes (η- C5Me5)2Rh2(μ-CO){μ-η2:η2-C(O)C2R2}(R
= CF3 or CO2Me) are fluxional in solution. Facile cleavage
of a C(O)-C(R) bond enables the metalla-eneone ring to shift rapidly from one rhodium atom to the
other.
Other products formed in the reactions between (η-C5Me5)2Rh2(μ-CO)2
and RC2R′ include. (η-C5Me5) Rh {C4(CF3)4CO}, (η-C5Me5) Rh (η4-C6R6) (R = CF3
or CO2Me), (η-C5Me5)2Rh2-(C4R2R′2)
(R = R′ = CO2Me; or R, R′ = Ph, C6F5), (η-
C5Me5)2Rh2(CO2C2Ph2),
(η-C5Me5)- Rh (C4Ph4CO2),
(η-C5Me5)2Rh2(CO)2{C4(CF3)4},
(η-C5Me5)2Rh2(CO)(μ-CO){COC4(C6F5)4}
and C6R3R′3 (R = R′ = Ph or CO2Me;
R = Ph and R′ = Me). Reactions between (η-C5Me5)2-Co2(μ-CO)2
and alkynes at room temperature or above yield mononuclear cyclopentadienone
complexes (η-C5Me5)Co{C4R4CO}(R
= Me, CF3 or C6F5), and the mononuclear arene complex (η-C5Me5)Co{C6(CF3)6}.
Methanation of Carbon Monoxide with Water over Supported Rhodium Catalysts.
Authors: Tanaka Y , Iizuka T
Published: September 2010

The formation of methane in the reaction of CO and H2O over Rh supported on ZrO2, Al2O3, TiO2, SiO2 and MgO was examined. The high activity was achieved over Rh/ZrO2 and Rh/TiO2 at 300°C and CO dissociation ability of the catalyst was concluded to be an important factor to obtain high activity. At low temperature (c. 200°C), CO was not hydrogenated effectively but CO2 formed by the water gas shift reaction was hydrogenated after the conversion of CO into CO2 was completed. The formation of CH4 appears to occur through the water gas shift reaction, followed by the hydrogenation of carbonaceous species formed by the dissociation of CO or CO2.
Pyrazine Chemistry. IV. Oxidation of 3,6-Dibenzylpiperazine-2,5-diones
Authors: Marcuccio SM , Elix JA
Published: September 2010

The autoxidation of (�) cis- and trans-3,6-dibenzyl-1,4- dimethylpiperazine-2,5-diones (6) and (8) has been shown to give (�)-6- benzyl-1,4-dimethylpiperazine-2,3,5-trione (12). Oxidation of a (2) cis-trans mixture of 1,4-diacetyl-3,6-dibenzylpiperazine-2,5-diones, (5) and (7), with elemental sulfur was shown to give (�)-(Z)-1-acetyl- 6-benzyl-3-benzylidenepiperazine-2,5-dione (10).
Structural Studies on Catalysts and Catalyst Precursors. II. The X-Ray Structure Determination of Chloro(Pentante-2,4-dithionato)(tributylphosphine)nickel(II), Ni(sacsac)(PBu3)Cl
Authors: Cavell KJ , Hay DG , Masters AF , Williams GA
Published: September 2010

The preparation and characterization of Ni( sacsac )(PBu3) Cl by single crystal X-ray diffraction [refined to R 0.052, R? 0.042 with 1325 data having I ≥ 3σ(I)], are reported. The compound crystallizes as discrete molecules in the orthorhombic space group P bca, with a 15.526(4), b 15.774(4), c 18.377(8)Ǻ, U 4500.7 Ǻ3, and Z 8. The nickel-donor atom bond distances are Ni-S (trans Cl ) 2.097(3), Ni-S (trans P) 2.138(3), Ni- Cl 2.216(3) and Ni-P 2.237(3)Ǻ, with the ligands subtending angles S-Ni-S 98.6(1), S-Ni- Cl 85.4(1), S-Ni-P 89.5(1) and Cl -Ni-P 86.8(1). The coordination about the nickel(II) centre is planar; however, one butyl group of the phosphine is oriented so that a hydrogen is directed towards the apical position of the nickel. The structure is correlated with the N.M.R . spectra in both solid and solution phases and compared with the structures of related com- pounds. The Ni-S bonds are shown to be short and the Ni-P bond long relative to such dimensions in comparable compounds.
The Nucleophilic Substitution Reactions of 5- and 7-Chloro-4,6-dinitrobenzofurazan 1-Oxide by Aromatic Amines.
Authors: Read RW , Norris WP
Published: September 2010

7-Chloro-4,6-dinitrobenzofurazan 1-oxide is a powerful electrophile which reacts with a variety of primary and secondary aromatic amines, even those with deactivating substituents , to give arylamino - benzofurazan oxides under mild conditions. Tertiary aromatic amines react through carbon to give aminoarylbenzofurazan oxides. During, or as a consequence of, the substitution reactions, tautomerism occurs to give in all but one example an equilibrium mixture of 5- and 7-substituted 4,6-dinitrobenzofurazan oxides in which the latter predominates. Thus 5-chloro-4,6-dinitrobenzofurazan 1-oxide and 7- chloro-4,6-dinitrobenzofurazan 1-oxide both react with aniline to yield the same isomeric mixture of products: 4,6-dinitro-7- phenylaminobenzofurazan oxide (predominantly 1-oxide) (major) and 4,6- dinitro-5-phenylaminobenzofurazan 1-oxide (minor). The 5- and 7- phenylamino 4,6-dinitrobenzofurazans were prepared to assist in structural assignment of the N-oxides.
Isoflavones from Podocarpus amarus
Authors: Carman RM , Russell-Maynard JKL , Schumann RC
Published: September 2010

The isoflavone irisolidone is a major constituent of Podocarpus amarus heartwood. Its structure has been securely established by 13C n.m.r . studies upon a range of derivatives. The isoflavones biochanin A, genistein and daidzein are also present in the tree.
vic-Iodo Thiocyanates and Iodo Isothiocyanates. IX. A Synthesis of Penam and Other Polycyclic Β-Lactams
Authors: Cambie RC , Clark GR , Jones TC , Rutledge PS , Strange GA , Woodgate PD
Published: September 2010

Penam (4-thia-1-azabicyclo[3.2.0]heptan-7-one) and 2,3-disubstituted penams are prepared conveniently from vic-iodo isothiocyanates beginning with the facile cyclization of the latter with di -t-butyl sodiomalonates. Treatment of the resulting di -t-butyl 2-(thiazolidin-2- ylene ) malonates with trifluoroacetic acid gives t-butyl 2-thiazolin-2- ylacetate derivatives which are reduced to the corresponding thiazolidines with aluminium amalgam. Cleavage of these t-butyl esters with hydrogen chloride affords β-amino acid hydrochlorides, which are cyclized to penam and its derivatives with 1-[3-( dimethylamino ) propyl ]- 3-ethylcarbodiimide hydrochloride. The structures of the (2α,3aβ,7aβ)- thiazolidine (5) and of the tricyclic β- lactam (41) have been confirmed by X-ray
crystallography.
Synthesis of 1H-[1]Benzothieno[3,2-d]azonine and [1]Benzothieno[3,2-d]azecine Derivatives
Authors: Browne EJ
Published: September 2010

Derivatives of two new [1] benzothieno medium-ring heterocyclic systems have been prepared by ring degradation using cyanogen bromide-induced solvolysis of tetracyclic precursors. Reaction of a hexahydro -[1] benzothieno [3,2-g] indolizine (4a) and a hexahydro-2H-[1] benzo-thieno [2,3-a] quinolizine (4b) with cyanogen bromide and magnesium oxide under solvolytic conditions yielded the hexahydro-1H-[1] benzothieno [3,2-d] azonines (5a) and (6a) and the octahydro -[1] benzothieno [3,2-d] azecines (5b) and (6b), respectively. Functional group interconversions of these medium-ring systems are described, including oxidations to the cyclic ketones (7) and (9). The 11b-phenyl derivative (13) of (4a) reacted under similar conditions to give both solvolysis (14) and (16) and elimination (15) medium-ring products, the ratios depending on the solvent. By contrast the analogous 9a-phenylthienoindolizine derivative (17) under these conditions gave only the medium-ring elimination product (18) in aqueous medium, and only the equivalent solvolysis product in methanol. Both the thieno and [1] benzothienoazonine elimination products (18) and (15) appear to be mixtures of E and Z isomers. The [1] benzothieno [3,2-g] indolizine bases (4a) and (13) are the first reported examples of this ring system.
Ab Initio Studies on Amides: Cyanamide, Dicyanamide and Tricyanamide
Authors: Riggs NV , Radom L
Published: September 2010

Optimization of the geometry of cyanamide with the 3-21G basis set leads to a planar (C2v) structure, whereas the STO-3G, 6-31G* and 6- 31G** basis sets lead to a pyramidal structure at the amido -nitrogen atom. The 6-31G* and 6-31G** geometries are reasonably close to the experimental geometry, and the calculated barriers to inversion (4.5 and 3.4 kJ mol-1, respectively) are also close to experimental values (5.4-5.6 kJ mol-1), but the STO-3G value (13.9 kJ mol-1) is much too high. Dicyanamide is far from planar at the STO-3G level but planar at the more definitive 6-31G* level, whereas tricyanamide is planar even at the STO-3G level. The prediction is that, in contrast to cyanamide itself, dicyanamide and tricyanamide are planar molecules. Calculated increases in N-C bond-lengths and decreases in C≡N bond-lengths for dicyanamide and tricyanamide as compared with the planar form of cyanamide are used to predict experimental lengths for these bonds in di - and tri- cyanamide.
The Deoxygenation of Some Derivatives of Methyl 3-Amino-3-deoxy-α-D-glucopyranoside
Authors: Patroni JJ , Stick RV
Published: September 2010

The deoxygenation, at C2, of methyl 3-acetylamino-4,6-O-benzylidene-3- deoxy-α-D-glucoside is described, and the subsequent conversion of the product into 3-acetylamino-2,3-dideoxy-D-arabino-hexose. Attempts at further deoxygenation (at C6), even the use of trifluoroacetylamino derivatives, were unsuccessful.
New Alkaloids of the ent-Kaurene Type from Anopterus Species. III. A 2D-N.M.R. Study of Anopterine and the Determination of Structure of Six Minor Alkaloids by N.M.R
Authors: John SR , Lamberton JA , Suares H , Willing RI
Published: September 2010

A number of homonuclear and heteronuclear 2D-n.m.r.
techniques have been used to interpret completely the 1H n.m.r . spectrum and to reinterpret the 13C n.m.r . spectrum of the alkaloid anopterine. Comparison of the n.m.r . data for anopterine with those of six minor alkaloids from Anopterus macleayanus has allowed the assignment of the structures, 7β-hydroxyanopteryl 11α,l2α-ditiglate, 7β-hydroxyanopteryl 11α-(E)-4′-hydroxy-2′-methylbut-2′-enoate 12α-tiglate, anopteryl 12α- tiglate , anopteryl 11α-4′-hydroxybenzoate 12α-tiglate, 7β- hydroxyanopteryl 11α-4′-hydroxybenzoate 12α-tiglate and 7β- hydroxyanopteryl 11α-benzoate 12α-tiglate to the minor alkaloids.
Crystal Structure of Dimethyl-[tris(N-methylimidazol-2-yl)methanol-N,N']-gold(III) Nitrate
Authors: Byers PK , Canty AJ , Skelton BW , White AH
Published: September 2010

Crystals of dimethyl [ tris (N-methylimidazol-2-yl) methano -N,N′]gold(III) nitrate are monoclinic, P21/c, a 8.217(3), b 14.010(5), c 16.800(6) Ǻ, β 101.93(3)𕢲, Z 4. The cations have the ligand coordinated as an N,N′- bidentate to cis-Me2AuIII, giving square-planar geometry for gold, together with an uncoordinated N-methylimidazol-2-yl ring above the coordination plane.
Divalent Metal Complexes of 2-Formylphenoxyacetic Acid: The Crystal Structures of 2-Formylphenoxyacetic Acid, and the Isomorphous Cobalt(II) and Zinc(II) 2-Formylphenoxyacetates
Authors: Kennard CHL , O'Reilly EJ , Smith G , Mak TCW
Published: September 2010

The crystal structures of 2-formylphenoxyacetic acid ( ofpaH ), tetraaquabis (2-formylphenoxyacetato)-cobalt(II) (1) and tetraaquabis (2- formylphenoxyacetato )zinc(II) (2) have been determined by X-ray diffraction and refined to residuals R 0.039, 0.058 and 0.045 for 1197, 1178 and 1230 observed reflections respectively. 2-Formylphenoxyacetic acid crystallizes in a monoclinic cell, space group P21/n with a 8.066(2), b 7.375(1), c 14.206(2) Ǻ, β 98.12(1)° and Z 4. The planar molecules form unusual hydrogen-bonded chain polymers (O…O 2.694(3)Ǻ] linked through the carboxyl groups. The complexes (1) and (2) are isomorphous, the comparative cells being a 5.036(1), b 13.463(3), c 15.083(4) Ǻ, β 96.88(2)° for (1), and a 5.044(1), b 13.481(3), c 15.055(4) Ǻ, β 96.95(2)° for (2), with Z 2 and space group P21. The complexes have four waters and two trans-related carboxyl oxygens [mean M-O distances 2.129(5) and 2.117(3) Ǻ respectively] completing almost regular octahedral stereochemistries . The nickel(II) complex [Ni( ofpa )(H2O)4] is probably not isostructural with (1) and (2), and the copper(II) complex is also different, with formula [Cu( ofpa )2(H2O)2].
A 13C N.M.R. Study of Some Methyl Chlorodeoxy-α-D-aldohexopyranosides
Authors: Toufeili IA , Dziedzic SZ
Published: September 2010

13 C n.m.r . data for six chlorinated methyl α-D- aldohexopyranoside derivatives and the parent sugars are presented. The effects on the C3 chemical shift as a result of replacement of hydroxyl by chlorine at C3 differ from previously reported α-substitution shifts.
The Synthesis of Hallachrome Leucotriacetate (2,7,8-Triacetoxy-1-methoxy-3-methylanthracene)
Authors: Comber MF , Sargent MV
Published: September 2010

The synthesis of 2,7,8-triacetoxy-1-methoxy-3-methylanthracene (30), a derivative of hallachrome (7-hydroxy-8-methoxy-6-methylanthracene-1,2- quinone ) (1), the red pigment of the marine worm Halla parthenopeia ( Delle Chiaje ), is described. The key step in the synthesis relied on the alkylation of the aryl cuprate derived from the oxazoline (13) with the benzyl bromide (19), thus ultimately providing the benzylbenzoic acid (25) and thence the anthracene (30).
Unexpected Transaminations of Some Aminopyrimidin-4(3H)-ones
Authors: Cowden WB
Published: September 2010

Transamination reactions of 6-amino-2-methylthiopyrimidin-4-(3H)-one and some 2,6-diaminopyrimidin-4(3H)-ones with secondary amines are reported. The syntheses of various 6-amino-2-disubstituted aminopyrimidin-4(3H)-ones are described.
An ab initio Study of Butyrolactone and 3-Hydroxybutyrolactone. Semiempirical Calculations on Proton Coupling Constants in These Molecules
Authors: Riggs NV
Published: September 2010

Optimization with the 3-21G basis set of the geometry of the envelope conformation of butyrolactone leads to a structure with an out-of-plane angle of 29.7° for the flap. Similar optimization of the twisted-ring conformation leads to a structure lying only 0.2 kJ mol-1 higher in energy and having a twist angle of 18.7°. These structures differ mainly in a vertical translation of C3 and C4 by c. 0.14 Ǻ with respect to the C2-C1-O2 plane. The ring may be twisted or bent at low energy- cost, and the barrier to inversion via the planar-ring (CS) structure is only 4.7 kJ mol-1. It is suggested that the envelope conformation is but one of many transient structures in a rapid ring-inversion process. For 3-hydroxybutyrolactone, the optimized twisted-ring conformation with twist angle 22.0° lies 0.3 kJ mol-1 below the optimized envelope conformation with out-of-plane angle 33.7° again these structures differ mainly in a vertical translation of C 3 and C 4 by c. 0.15 Ǻ with respect to the C 2-C 1-O2 plane. Moderate ring twisting and bending are rather more costly than in butyrolactone itself, and the hydroxy group clearly occupies the pseudo-axial position on C 3. Calculated bond lengths and angles for both molecules are mostly within the corresponding experimental ranges for a series of γ-lactones. Proton- proton spin coupling constants calculated by the FINITE/INDO method for the optimized 3-hydroxybutyrolactone structures are in moderate-to-good agreement with experimental values, and agreement is improved by application of a thermal population-averaging procedure. Thermally averaged values for butyrolactone are also presented.
Pyrazine Chemistry. V. Synthesis of Methylanhydropicroroccellin and Dimethylpicroroccellin
Authors: Marcuccio SM , Elix JA
Published: September 2010

The structure of the lichen diketopiperazine, picroroccellin, has been studied by the synthesis of several of its degradation products. The three possible formulations of methylanhydropicroroccellin (3), (4) and (5) were synthesized and from the physical and chemical properties, the former two compounds were shown to be dissimilar from the naturally derived material. Furthermore, the reactivity of the 3- methoxypiperazine-2,5-dione (5) entirely paralleled that reported for picroroccellin and was consistent with the oxygen functions being located at the 3- and 6-positions of the piperazine-2,5-dione ring. Dimethylpicroroccellin (23) was synthesized, so establishing the trans- stereochemistry of this compound. The properties of (23) were identical with those recorded for the naturally derived material. Hence we conclude that picroroccellin should be reformulated as (2).
The Determination of Fluoride-Ion Activities in Moderately Concentrated Aqueous Hydrogen-Fluoride
Authors: Mctigue P , Odonnell TA , Verity B
Published: September 2010

A lead-lead chlorofluoride electrode has been used to determine fluoride ion activities, aF-, in 0-6 M aqueous HF. Our data show that aF- increases, passes through a maximum and then decreases with increasing HF concentration. The conductivities of concentrated HF- water mixtures have also been measured. Both the conductometric and potentiometric data are used in the development of a quantitative model of the equilibria existing between fluoride ions and HF molecules in the solutions studied. The data support the view that the ions (HF)2F-, (HF)3F- and (HF)4F- are important species in moderately concentrated aqueous HF.
1,2,4-Triazines. 1. The Use of C-13 Nuclear-Magnetic-Resonance Spectroscopy to Determine the Methylation Products of 3-Methylthio-1,2,4-Triazin-5(2h)-One
Authors: Jacobsen NW , Rose SE
Published: September 2010

Carbon-13 nuclear magnetic resonance spectroscopy utilizing both proton coupled and decoupled spectra has been found to be a useful method to determine unequivocally the sites of methylation in the 1,2,4-triazine series. Specifically, the method identified the methylation products of 3-methylthio-1,2,4-triazin-5(2H)-one as the new zwitterion 1-methyl-3- methylthio-1,2,4-triazinium-5-olate and the previously reported N2, N4- and O-methyl isomers.