bluuebunny/crossref_metadata_2025 huggingface dataset:
Site-specific modification of calmodulin Ca2+ affinity tunes the skeletal muscle ryanodine receptor activation profile
Authors: Jiang Jie , Zhou Yubin , Zou Jin , Chen Yanyi , Patel Priya , Yang Jenny J. , Balog Edward M.
Published: September 2010

The skeletal muscle isoform of the ryanodine receptor Ca2+-release channel (RyR1) is regulated by Ca2+ and CaM (calmodulin). CaM shifts the biphasic Ca2+-dependence of RyR1 activation leftward, effectively increasing channel opening at low Ca2+ and decreasing channel opening at high Ca2+. The conversion of CaM from a RyR1 activator into an inhibitor is due to the binding of Ca2+ to CaM; however, which of CaM's four Ca2+-binding sites serves as the switch for this conversion is unclear. We engineered a series of mutant CaMs designed to individually increase the Ca2+ affinity of each of CaM's EF-hands by increasing the number of acidic residues in Ca2+-chelating positions. Domain-specific Ca2+ affinities of each CaM variant were determined by equilibrium fluorescence titration. Mutations in sites I (T26D) or II (N60D) in CaM's N-terminal domain had little effect on CaM Ca2+ affinity and regulation of RyR1. However, the site III mutation N97D increased the Ca2+-binding affinity of CaM's C-terminal domain and caused CaM to inhibit RyR1 at a lower Ca2+ concentration than wild-type CaM. Conversely, the site IV mutation Q135D decreased the Ca2+-binding affinity of CaM's C-terminal domain and caused CaM to inhibit RyR1 at higher Ca2+ concentrations. These results support the hypothesis that Ca2+ binding to CaM's C-terminal acts as the switch converting CaM from a RyR1 activator into a channel inhibitor. These results indicate further that targeting CaM's Ca2+ affinity may be a valid strategy to tune the activation profile of CaM-regulated ion channels.
Influence of disorder on localization and density of states in amorphous carbon nitride thin films systems rich in π-bonded carbon atoms
Authors: Alibart F. , Lejeune M. , Durand Drouhin O. , Zellama K. , Benlahsen M.
Published: September 2010

We discuss in this paper the evolution of both the density of states (DOS) located between the band-tail states and the DOS around the Fermi level N(EF) in amorphous carbon nitride films (a-CNx) as a function of the total nitrogen partial pressure ratio in the Ar/N2 plasma mixture. The films were deposited by three different deposition techniques and their microstructure was characterized using a combination of infrared and Raman spectroscopy and optical transmission experiments, completed with electrical conductivity measurements, as a function of temperature. The observed changes in the optoelectronic properties are attributed to the modification in the atomic bonding structures, which were induced by N incorporation, accompanied by an increase in the sp2 carbon bonding configurations and their relative disorder. The electrical conductivity variation was interpreted in terms of local effects on the nature and energy distribution of π and π∗ states.
Analytic expressions for the inelastic scattering and energy loss of electron and proton beams in carbon nanotubes
Authors: Emfietzoglou D. , Kyriakou I. , Garcia-Molina R. , Abril I. , Kostarelos K.
Published: September 2010

We have determined “effective” Bethe coefficients and the mean excitation energy of stopping theory (I-value) for multiwalled carbon nanotubes (MWCNTs) and single-walled carbon nanotube (SWCNT) bundles based on a sum-rule constrained optical-data model energy loss function with improved asymptotic properties. Noticeable differences between MWCNTs, SWCNT bundles, and the three allotropes of carbon (diamond, graphite, glassy carbon) are found. By means of Bethe’s asymptotic approximation, the inelastic scattering cross section, the electronic stopping power, and the average energy transfer to target electrons in a single inelastic collision, are calculated analytically for a broad range of electron and proton beam energies using realistic excitation parameters.
Bilayer metal gate electrodes with tunable work function: Adhesion and interface characterization
Authors: Birringer Ryan P. , Lu Ching-Huang , Deal Michael , Nishi Yoshio , Dauskardt Reinhold H.
Published: September 2010

The dependence of Pt film thickness and forming gas annealing on the interface fracture properties and interface composition of Ti/Pt bilayer gate electrode films on a HfO2 gate dielectric are reported. These fracture properties and composition results are directly compared to work function tuning behavior witnessed in metal-oxide semiconductor (MOS) capacitors fabricated from the same films. The interface fracture energy of the metal bilayer/gate dielectric interface is strongly dependent on thickness after a forming gas anneal but shows no thickness dependence in the as-deposited case. The flat-band voltage increases abruptly and then remains constant as the thickness of the Pt film is increased in the as-deposited case but varies gradually with increasing Pt thickness after a forming gas anneal. Angle-resolved x-ray photoelectron spectroscopy characterization of the resulting fracture surfaces confirms that Ti diffusion to the metal bilayer/gate dielectric interface is responsible for these effects.
Reduced leakage current in BiFeO3–BiCrO3 nanocomposite films formed by chemical solution deposition
Authors: Singh Sushil K. , Shanthy S. , Ishiwara H.
Published: September 2010

BiFeO 3 – BiCrO 3 nanocomposite films were formed by depositing sol-gel solutions on Pt/Ti/SiO2/Si(100) structures. It was found from x-ray diffraction analysis that the films annealed at 550 °C in air and O2 atmosphere formed by polycrystalline composites of BiFeO3 (BFO) and BiCrO3 (BCO) without any other impurity phase in films. The BFO–BCO composite films annealed in O2/air showed small grains approximately 120 nm and 80 nm in diameter, respectively, and these nanograins were effective in suppressing leakage current in the films. We observed for the first time the leakage current in the range of 10−6 A/cm2 at an applied field 600 kV/cm, which is more than four order of magnitude lower than BFO films at similar applied electric field. The low leakage current density in BFO–BCO films annealed in air/O2 atmosphere might be due to the low oxygen vacancies, domination of the Ohmic conduction and intergrain depletion in grain boundary limited conduction. The remanent polarizations as large as 30 μC/cm2 at an applied electric field of 1200 kV/cm were obtained in the films and the films showed much improved fatigue response up to 108 measured switching cycles.
Phase-space dynamics of runaway electrons in tokamaks
Authors: Guan Xiaoyin , Qin Hong , Fisch Nathaniel J.
Published: September 2010

The phase-space dynamics of runaway electrons is studied, including the influence of loop voltage, radiation damping, and collisions. A theoretical model and a numerical algorithm for the runaway dynamics in phase space are developed. Instead of standard integrators, such as the Runge–Kutta method, a variational symplectic integrator is applied to simulate the long-term dynamics of a runaway electron. The variational symplectic integrator is able to globally bound the numerical error for arbitrary number of time-steps, and thus accurately track the runaway trajectory in phase space. Simulation results show that the circulating orbits of runaway electrons drift outward toward the wall, which is consistent with experimental observations. The physics of the outward drift is analyzed. It is found that the outward drift is caused by the imbalance between the increase of mechanical angular momentum and the input of toroidal angular momentum due to the parallel acceleration. An analytical expression of the outward drift velocity is derived. The knowledge of trajectory of runaway electrons in configuration space sheds light on how the electrons hit the first wall, and thus provides clues for possible remedies.
Fast vibrational configuration interaction using generalized curvilinear coordinates and self-consistent basis
Authors: Scribano Yohann , Lauvergnat David M. , Benoit David M.
Published: September 2010

In this paper, we couple a numerical kinetic-energy operator approach to the direct-vibrational self-consistent field (VSCF)/vibrational configuration interaction (VCI) method for the calculation of vibrational anharmonic frequencies. By combining this with fast-VSCF, an efficient direct evaluation of the ab initio potential-energy surface (PES), we introduce a general formalism for the computation of vibrational bound states of molecular systems exhibiting large-amplitude motion such as methyl-group torsion. We validate our approach on an analytical two-dimensional model and apply it to the methanol molecule. We show that curvilinear coordinates lead to a significant improvement in the VSCF/VCI description of the torsional frequency in methanol, even for a simple two-mode coupling expansion of the PES. Moreover, we demonstrate that a curvilinear formulation of the fast-VSCF/VCI scheme improves its speed by a factor of two and its accuracy by a factor of 3.
Relaxation, dispersion, attenuation, and finite propagation speed in viscoelastic media
Authors: Seredyńska M. , Hanyga Andrzej
Published: September 2010

Dispersion and attenuation functions in a linear viscoelastic medium with a positive relaxation spectrum are given by integral representations in terms of a positive Radon measure satisfying a growth condition. Kramers–Kronig dispersion relations with one subtraction can be derived from the integral representations of the dispersion and attenuation functions. The dispersion and attenuation functions have sublinear growth in the high frequency range. The wave number vector can have a linear component in addition to the dispersion function. In this case the viscoelastic waves propagate with a bounded speed. In the other cases viscoelastic wave propagation has a diffusion-like character.
Argon pair potential at basis set and excitation limits
Authors: Patkowski Konrad , Szalewicz Krzysztof
Published: September 2010

A new ab initio interaction potential for the electronic ground state of argon dimer has been developed. The potential is a sum of contributions corresponding to various levels of the coupled-cluster theory up to the full coupled-cluster method with single, double, triple, and quadruple excitations. All contributions have been calculated in larger basis sets than used in the development of previous Ar2 potentials, including basis sets optimized by us up to the septuple(sextuple)-zeta level for the frozen-core (all-electron) energy. The diffuse augmentation functions have also been optimized. The effects of the frozen-core approximation and the relativistic effects have been computed at the CCSD(T) level. We show that some basis sets used in literature to compute these corrections may give qualitatively wrong results. Our calculations also show that the effects of high excitations do not necessarily converge significantly faster (in absolute values) in basis set size than the effects of lower excitations, as often assumed in literature. Extrapolations to the complete basis set limits have been used for most terms. Careful examination of the basis set convergence patterns enabled us to determine uncertainties of the ab initio potential. The interaction energy at the near-minimum interatomic distance of 3.75 Å amounts to −99.291±0.32 cm−1. The ab initio energies were fitted to an analytic potential which predicts a minimum at 3.762 Å with a depth of 99.351 cm−1. Comparisons with literature potentials indicate that the present one is the most accurate representation of the argon-argon interaction to date.
Three-dimensional superconductivity in nominal composition Fe1.03Se with Tczero up to 10.9 K induced by internal strain
Authors: Ge Junyi , Cao Shixun , Yuan Shujuan , Kang Baojuan , Zhang Jincang
Published: September 2010

Iron selenide with the nominal composition Fe1.03Se was synthesized by a self-flux solution method which shows a zero resistance temperature up to 10.9 K and a Tconset (90% ρn, ρn: normal state resistivity) up to 13.3 K. The residual resistivity ratio RRR=R(300 K)/R0=12. Scanning electron microscopy-EDX study shows that the composition of as grown sample is near stoichiometric FeSe. The decrease in superconducting transition temperature by heat treatment indicates that internal crystallographic strain which plays the same effect as external pressure is the origin of its high Tc. The fluctuation conductivity was studied which could be well described by three-dimensional (3D) Aslamazov–Larkin power law. The estimated value of coherence length ξc=9.2 Å is larger than the distance between conducting layers (∼6.0 Å), indicating the 3D nature of superconductivity in this compound.
Lab-on-a-chip flow cytometer employing color-space-time coding
Authors: Cho Sung Hwan , Qiao Wen , Tsai Frank S. , Yamashita Kenichi , Lo Yu-Hwa
Published: September 2010

We describe a fluorescent detection technique for a lab-on-a-chip flow cytometer. Fluorescent emission is encoded into a time-dependent signal as a fluorescent cell or bead traverses a waveguide array with integrated spatial filters and color filters. Different from conventional colored filters with well-defined transmission spectral window, the integrated color filters are designed to have broad transmission characteristics, similar to the red-green-blue photoreceptors in the retina of human eye. This unique design allows us to detect multiple fluorescent colors with only three color filters based on the technique of color-space-time coding using only one single photomultiplier tube or avalanche photodetector.
Charge effect in S enhanced CO adsorption: A theoretical study of CO on Au, Ag, Cu, and Pd (111) surfaces coadsorbed with S, O, Cl, and Na
Authors: Gan Li-Yong , Zhao Yu-Jun
Published: September 2010

The extraordinary sulfur enhanced CO adsorption on Au surface creates curiosity to many scientists in the field, and is expected to have potential applications in catalyst design. In this work, we have investigated the interactions of the coadsorption of CO and various adatoms X (X=Na, S, O, and Cl) on Au and Pd(111) surfaces and made further comparison with CO adsorption on charged Au and Pd surfaces by a first-principles study. We find out that the enhancement of CO adsorption by S on Au originates from S-induced positive polarization of Au surface. The d band of metal atoms in the positively polarized Au surface shifts up toward the Fermi level (EF) without remarkable changes of its shape and occupation. In contrast, in the negatively polarized Au(111) surface, achieved by electropositive adatom such as Na adsorption or artificially adding additional electrons to the substrate, d bands shift down relative to EF, and thus CO adsorption is weakened. Further study of CO coadsorption with X on two other noble metal (Ag and Cu) surfaces manifests that Ag shows the same behavior as Au does, while the situation of Cu is just between that on Au and Pd. It suggests that the extraordinary S-induced enhancement of CO adsorption on Au/Ag, different from other transition metals (TMs), ultimately results from the inertness of d bands buried below EF. The S-induced charge can introduce a significant d band shift on Au/Ag with respect to EF due to their narrow density of states at EF and thus strengthens CO adsorption subsequently.
Coulomb effect inhibiting spontaneous emission in charged quantum dot
Authors: Gradkowski Kamil , Ochalski Tomasz J. , Pavarelli Nicola , Williams David P. , Huyet Guillaume , Liang Baolai , Huffaker Diana L.
Published: September 2010

We investigate the emission dynamics of InAs/GaAs quantum dots (QDs) coupled to an InGaAs quantum well in a tunnel injection scheme by means of time-resolved photoluminescence. Under high-power excitation we observe a redshift in the QD emission of the order of 20 meV. The optical transition intensity shows a complex evolution, where an initial plateau phase is followed by an increase in intensity before a single-exponential decay. We attribute this behavior to the Coulomb interactions between the carriers in a charged QD and corroborate the experimental results with both a rate equation model and self-consistent eight-band k⋅p calculations.
Microstrip superconducting quantum interference device amplifiers with submicron Josephson junctions: Enhanced gain at gigahertz frequencies
Authors: DeFeo M. P. , Bhupathi P. , Yu K. , Heitmann T. W. , Song C. , McDermott R. , Plourde B. L. T.
Published: September 2010

We present measurements of an amplifier based on a dc superconducting quantum interference device (SQUID) with submicron Al–AlOx–Al Josephson junctions. The small junction size reduces their self-capacitance and allows for the use of relatively large resistive shunts while maintaining nonhysteretic operation. This leads to an enhancement of the SQUID transfer function compared to SQUIDs with micron-scale junctions. The device layout is modified from that of a conventional SQUID to allow for coupling signals into the amplifier with a substantial mutual inductance for a relatively short microstrip coil. Measurements at 310 mK exhibit gain of 32 dB at 1.55 GHz.
Nonlinear optical performance of periodic structures made from composites of polymers and Co3O4 nanoparticles
Authors: Zhu X. , Wang J. , Lau P. , Nguyen D. , Norwood R. A. , Peyghambarian N.
Published: September 2010

The nonlinear optical performance of specially designed periodic structures made from composites of optical polymers and Co3O4 nanoparticles is investigated. The refractive indices of the alternating layers are designed to be close and no photonic band gap (PBG) is formed at low power density. Under high power illumination, the index difference becomes large because of the high optical nonlinearities of the Co3O4 nanoparticles. Consequently, enhanced nonlinear optical performance is obtained with the formation and the strengthening of the PBG. Nonlinear reflection and nonlinear transmission as well as reduced nonlinear threshold are observed in the PBG structures.
Calcium-enhanced exocytosis of gold nanoparticles
Authors: Chen Ran , Huang George , Ke Pu Chun
Published: September 2010

This paper examines the exocytosis of nanoparticles, an important but rarely documented aspect of cell responses to engineered nanomaterials. Specifically, HT-29 mammalian cells were labeled with a lipophilic Laurdan dye, and the membrane fluidity in the presence of gold nanoparticles was evaluated by the generalized polarization (GP) values derived from the fluorescence spectra of the dye. The concentration of excreted gold nanoparticles increased with increasing extracellular calcium, directly demonstrating exocytosis of nanoparticles and corroborating the inference made from the GP values of the Laurdan dye. This study provides additional information for understanding the fate of nanomaterials in biological systems.
Stereoselectivity in the Reactions between the Anion of 4-Phenyl-5,6-dihydro-2H-thiopyran 1-Oxide and Electrophiles
Authors: Crumbie RL , Ridley DD , Steel PJ
Published: September 2010

Treatment of the anion(17), prepared from the six- membered ring allylic sulfoxide 4-phenyl-5,6-dihydro-2H-thiopyran 1-oxide (8) with primary alkyl halides at -78°, affords trans-2-alkyl-4-phenyl-5,6-dihydro-2H-thiopyran 1-oxides exclusively. The stereospecificity of these reactions thus corresponds to that obtained from the related saturated cyclic sulfoxides . However, when the anion (17) is treated with 2-iodopropane (-78° → 20°) a mixture of 2-cis and 2-trans products results. Independent experiments indicate that the lack of stereoselectivity is due to anion exchange reactions at the higher temperature required to effect alkylation. 2-cis and 2-trans Adducts also are obtained in reactions of the anion (17) with benzaldehydes (-78° → 0°), and from X-ray crystallographic analyses it has been established that the cis adducts predominate, with little selectivity in attack on the two enantiotopic faces of the aldehyde.
The Determination of Substituent Effects by 13C Nuclear Magnetic Resonance Spectrometry. The Effect of Solvent on CH2X Groups
Authors: Happer DAR , Steenson BE
Published: September 2010

A previous study of the effect of meta- and para-CH2X substituents on the 13C n.m.r. chemical shifts of the α and β side-chain carbons of β- methoxycarbonylstyrenes (methyl cinnamates ) in ethanol has been extended to cover five additional solvents (Me2SO, Me2CO, CDCl3, CCl4 and C6H6). The results support the earlier claim that, for most substituents , the magnitudes of the substituent -induced shifts are proportional to the inductive effect of X. The major contributor to the latter appears to be the field effect generated by the C-X dipole, with the lines of force passing mainly through the molecule. In non-polar solvents, however, there is evidence that lines of force passing directly through the solvent can also influence the shifts in both the meta and para series.
The Reactions of Alkoxide-Alkanol Negative Ions with Ketene. An ab initio and Ion Cyclotron Resonance Study
Authors: Hayes RN , Sheldon JC , Bowie JH
Published: September 2010

Alkanol-alkoxide negative ions [RO----HOR] react with ketene to form stable species H-C≡C-O----HOR. The initial intermediate in the reaction sequence is produced by the formation of a hydrogen bond between the negatively charged oxygen of [RO----HOR] and a hydrogen of ketene. This intermediate decomposes by competing reactions, viz. ( i ) a minor pathway involving direct elimination of ROH, and (ii) a major pathway involving a rearrangement sequence. Intermediates and product ions have been defined by using ab initio calculations at the 4-31G level. The differences between the reactions of [RO----HOR]/ketene and [RO---- HOR]/acetaldehyde systems are discussed.
Synthesis, Properties and Crystal Structure Determination of a Perchloroheptafulvalene Isomer
Authors: Hugel HM , Horn E , Snow MR
Published: September 2010

Crystals of the syn-perchloroheptafulvalene isomer, C14Cl12, crystallize in the space group C2/c with a 12.376(6), b 10.980(4), c 15.242(4)Ǻ and β 100.54(3)°. The structure analysis of the isomer indicates molecular packing disorder into two orientations about the centre of symmetry. In the final full-matrix least-squares refinement the conventional R value converged at 0.042. Formation of the syn isomer is most likely to proceed through the perchloroheptatrienyl anion which can dimerize and form syn-perchloroheptafulvalene by cis elimination of lithium chloride.
Potential Antimalarials. III. N4-Substituted 7-Bromo-1,5-naphthyridin-4-amines
Authors: Barlin GB , Tan W
Published: September 2010

A series of new N4-substituted
7-bromo-1,5-naphthyridin-4-amines has been prepared from nicotinic acid through 3-bromo-8-chloro- 1,5- naphthyridine by nucleophilic replacement of the
8-chloro substituent with appropriate amines. Several of these compounds, namely 7-bromo-N- (4′-diethylamino-1′-methylbutyl)-1,5-naphthy-ridin-4-amine (′5-azabromoquine'), 4-(7′-bromo-1′,5′-naphthyridin-4′-ylamino)-2-(diethylamino-methyl)phenol and 7-bromo-N-(2′-diethylaminoethyl)-1,5- naphthyridin-4-amine showed significant antimalarial acivity. Apparent cures were effected when these test chemicals were injected intra-peritoneally in a single dose of 200
mg/kg to mice infected with Plasmodium vinckei vinckei.
Iron(II) and Nickel(II) Complexes of 4,4′-Bithiazole: Spectral, Magnetic and Structural Studies
Authors: Baker AT , Goodwin HA
Published: September 2010

Iron(II) and nickel(II) complexes of 4,4′-bithiazole (L) have been prepared. Salts of [FeL3]2+ undergo thermally induced spin-state transitions, in the solid state and in solution. The structures of both [FeL3] [ClO4]2 and [NiL3] [ClO4]2 have been determined by single-crystal X-ray diffractometry . The compounds are isomorphous : monoclinic with space group C2/c, with four molecules in a unit cell of dimensions (Fe, Ni): a 17.250(3), 17.379(3); b 9.8168(9), 9.685(1); c 16.867(3), 17.135(3) Ǻ; β 105.943(7), 104.860(7)°. The structures were refined by least-squares methods to residuals of 0.033 (Fe) and 0.033 (Ni) for 1917 (Fe) and 2017 (Ni) observed reflections. The cations have a distorted octahedral structure with the average Ni-N bond length being 0.11 Ǻ longer than the average Fe-N bond length.
Potential Antimalarials. IV. 4-[7'-Bromo(and Chloro)-1′,5′-Naphthyridin-4′-Ylamino]Phenols and N4-Substituted 7-Chloro-1,5-Naphthyridin-4-Amines
Authors: Barlin G , Tan W
Published: September 2010

A series of nine mono- and di-Mannich bases, for example 4-(7′-bromo-1′,5′-naphthyridin-4′-ylamino)-2,6-bis( dimethylaminomethyl )phenol derived from 4-(7′-bromo-1′,5′-naphthyridin-4′-ylamino)phenol and several other N4-substituted 7-bromo- and 7-chloro-1,5-naphthyridin-4- amines have been prepared. ′All these compounds showed significant antimalarial activity when injected intraperitoneally in a single dose of 100-200 mg/kg to mice infected with Plasmodium vinckei vinckei. The di-Mannich bases appeared to be the most potent and effective in parasite control; however, no deaths were observed in infected mice treated with the mono- Mannich compounds.
Phenyl Ring Orientations in Two Tetracyclone Adducts; X-Ray Crystal Structures of exo-and endo-1,7,8,9-Tetraphenyltricyclo-[5.2.1.02,6]deca-3,8-dien-10-ones
Authors: Coxon JM , O'Connell MJ , Steel PJ
Published: September 2010

The crystal structures of exo- and endo- 1,7,8,9- tetraphenyltricyclo [5.2.1.02,6]deca-3,8-dien-10-one (8) and (9) are reported. Crystals of the exo adduct (8) are triclinic: Pī , a 9.863(2), b 10.738(2), c 13.634(2) Ǻ, α 82.90(1), β 68.87(1), γ 66.87(1)°, Z 2; crystals of the endo adduct (9) are monoclinic: P21/c, a 11.610(1), b 7.862(2), c 27.675(3) Ǻ, β 100.223(9)°, Z 4. The structures were refined to R 0.039 and 0.049 respectively. The relative orientations of the four phenyl rings in the two structures are similar.
An X-Ray Photoelectron Study of Doped and Supported Nickel Oxide
Authors: Cochran SJ , Larkins FP
Published: September 2010

The surfaces of lithium-and chromium-doped nickel oxide and of nickel oxide supported on alumina have been examined by X-ray photoelectron spectroscopy. The concentration of the nickel(III) species increased for the lithium-doped oxide and decreased for the chromium-doped oxide relative to the undoped oxide. The effects of doping were manifested most clearly however by the amount of oxygen-containing species adsorbed on the oxide surface rather than by variations in the nickel(III) peak intensity. Lithium-doped oxides were also shown to reduce more readily than undoped or chromium-doped oxides in the presence of carbon-containing impurities. The rate of reduction is influenced by the activation energy for electron transport which is related to the availability of the nickel(III) species. Supported oxides showed significant surface enhancement of nickel(II) as well as an absence of the nickel(III) species. The nickel(II) species in the supported oxide was not easily reduced to nickel(0).
Crystallographic Characterization of a Hydrated Form of Copper(I) Cyanide
Authors: Kildea JD , Skelton BW , White AH
Published: September 2010

The crystal structure of a crystalline artefact of a reaction involving copper(I), cyanide and water under conditions of high temperature and pressure has been determined by single-crystal X-ray diffraction methods at 295 K, and refined by full matrix least-squares to a residual of 0.046 for 572 independent 'observed' reflections; the composition is suggested to be [Cu3(CN)3(H2O)]∞, comprising a two- dimensional polymer with both linearly coordinated and bridging cyanide groups. Crystals are monoclinic, probable space group C2/c, a 19.048(7), b 6.798(3), c 13.223(7) Ǻ, β 125.72(3)°, Z 8.
Synthetic Approaches to Mycorrhizin A and Gilmicolin. III A Synthesis of Tricyclic Enones Epimeric with and Identical with the Key Synthetic Intermediate of Koft and Smith
Authors: Brown RFC , Caldwell KB , Gatehouse BM , Teo PYT
Published: September 2010

The cyclopentadiene adduct (2) derived from the benzofuranol (1) undergoes selective deprotonation with lithium diisopropylamide at C 8a, leading with allyl bromide to the 8a-allyl derivative (3) and with Me3SiCl to the silyl ether (8). Reduction and methanolysis of (8) gives the epimeric hydroxy ketones (9) and (10) which by pyrolysis and O-silylation can be converted into the epimeric triethylsilyloxy tricyclic enones (13) and (15); the latter enone is identical with the key synthetic intermediate of Koft and Smith, but is the minor product. Attempted Mitsunobu inversion of the hydroxy enone (12) effects isomerization to the saturated 4,7-dione (18). The structure of the 8a- allyl derivative (3) is established by X-ray crystallography.
Unsaturated Cembrane Acids From Cleome viscosa L. (Capparidaceae)
Authors: Kosela S , Ghisalberti E , Jefferies P , Skelton B , White A
Published: September 2010

Two new unsaturated cembrane acids have been isolated from Cleome viscosa L. X-ray crystallographic methods show one to be (1R*,3E,7Z, 12R*)-20-hydroxycembra-3,7,15-trien-19-oic acid (2). The structure of the second compound has been deduced from spectroscopic data to be (3E,7Z,11Z)-17,20-dihydroxycembra-3,7,11,15-tetraen-19-oic acid (3).
Crystal Structures of the 1:1 Adducts of N,N,N′,N′- Tetramethyl-o-phenylenediamine with Zinc(II) Bromide and Mercury(II) Bromide and Iodide
Authors: Hughes CM , Favas MC , Skelton BW , White AH
Published: September 2010

The 1:1 adducts of o-Me2N.C6H4.NMe2 (≡ L″) with ZnI2, HgBr2 and HgI2 are isomorphous and their crystal structures have been established by single-crystal X-ray diffraction methods, being refined to residuals of 0.045, 0.050, 0.035, for 1759, 1617, 1911 'observed' reflections respectively. Crystals are monoclinic P21/c,Z = 4, with a ~ 8.5, b ~ 21, c ~ 8 Ǻ, β ~ 95°. In L″ZnI2, {Zn-I} is 2.538, {Zn-N} 2.09 Ǻ, with I-Zn-I 115.36(6), N-Zn-N 84.6(3), and I-Zn-N 108.3(2)-118.3(2)°. In L″HgBr2, (Hg-Br) is 2.523, {Hg-N} 2.42 Ǻ, with Br-Hg-Br 123.04(8), N-Hg-N 73.2(4) and Br-Hg-N 98.9(3)-131.2(3)°. In L″HgI2, {Hg-I} is 2.661, {Hg-N} 2.44 Ǻ, with I-Hg-I 128.92 (3), N-Hg-N 72.8(3), and I-Hg-N 101.8(2)- 122.9(2). X-Hg-X angles are unexpectedly small and this is attributed to incipient dimer formation through an inversion centre, this tendency being greatest in (2) where the Hg…Br approach is 3.456(3) Ǻ and the immediate HgBr2N environment of the mercury is trigonal planar.
Applications of Cd N.M.R to Polycadmium Complexes. III. Effects of Zn/Cd and of Se/S Substitution in the Tetra-Adamantanoid Cage [S4Cd10(Sph)16]4- in Relation to Heterometal Metallothioneins
Authors: Dance IG
Published: September 2010

Cadmium-113 n.m.r . spectra at 66.6 MHz of various mixtures of the six cage compounds [X4M10( SPh )16]4-
(1; X = S, Se; M = Zn, Cd ) and [M4( SPh )10]2- (M = Zn, Cd ), have revealed the exchange reactions of M and of X which occur within the different structural elements of (1), namely the triply bridging chalcogenide ligands X, the inner metal atoms Mi, and the outer metal atoms Mo. At laboratory temperature the exchange time scales range from days (X) through hours (Mi) to seconds (Mo and SPh ), according to the extent of atomic connection to each of these structural components of the aggregate. Metal exchange does not always follow random statistics, with biases towards equilibrium association of the same metal. The M- and X-substituted products, with lower symmetry than the high-symmetry precursors, reveal the mutual influences of the various structural elements on Cd chemical shift: S → Se substitution causes changes ( ΔδCd ) of -37 ppm at one bond, -3 ppm and -1.5 ppm at three bonds, and + 1 ppm five bonds distant; Cd → Zn substitution causes δCd
to change by + 13 ppm and + 5 ppm at a connection of two bonds and by -3 ppm over four bonds. These effects of adjacent Cd → Zn substitution on δCd provide well defined models in support of the hypothesis of similar effects in the Cd n.m.r . spectra of mixed Zn, Cd metallothionein proteins.
Organolanthanoids .VIII. Some Ligand-Exchange Reactions of Pentafluorophenyllanthanoids and Bis(Phenylethynyl)Ytterbium(II)
Authors: Deacon GB , Newnham RH
Published: September 2010

The cyclopentadienyl - and indenyl-lanthanoids, (C5H5)2Yb( dme ) ( dme = 1,2- dimethoxyethane ), (C9H7)2Yb( thf )2 ( thf = tetrahydrofuran ), (C5H5)2Eu( thf )n (n = 0.5 or 1), (C9H7)2Eu( thf ), (C5H5)3Sm, (MeC5H4)3Sm, and (C9H7)3Sm( thf ) have been prepared by ligand exchange reactions of (C6F5)2Yb, (C6F5)2Eu, and a pentafluorophenylsamarium species with cyclopentadiene , methylcyclopentadiene , or indene. This synthetic method has particular significance for the indenyllanthanoids . An explosive product was obtained from (C6F5)2Yb and methylcyclopentadiene. Reactions of ( PhCC )2Yb with cyclopentadienes and indene have yielded (C5H5)2Yb( dme ), (MeC5H4)2Yb( dme ), and (C9H7)2Yb( thf )2, but (C5H5)2Yb did not undergo ligand exchange with phenylacetylene.
Studies in Bile Salt Solutions .XIII. Hydrophobic Substrate Effects on the Esterase Activity of Bile-Salt-Stimulated Human-Milk Lipase. Hydrolysis of 4-Nitrophenyl Alkanoates and Alkyl 4-Nitrobenzoates
Authors: Oconnor CJ , Mitha ASH , Walde P
Published: September 2010

The pseudo-first-order rate constants of hydrolysis of a series of 4-nitrophenyl alkanoates and a series of n-alkyl esters of 4-nitrobenzoic acid and of 4-nitrophenyl hexahydrobenzoate and cyclohexyl 4-nitrobenzoate, catalysed by bile-salt-stimulated human milk lipase in the absence and presence (2 mmol dm-3) of sodium cholate/cholic acid and sodium taurocholate , have been measured at pH 7.3, 310.5 K. It has been shown that the enzyme possesses a specific esterase acyl binding site which almost completely excludes the binding therein of a cyclohexyl group. There is also present a specific alkyl binding site which can fully accommodate a cyclohexyl ring. Both binding sites are hydrophobic in nature, but although the hydrophobic nature of the alkyl binding site is affected by bile-salt stimulation, that of the acyl site is not. Hydrophobicity parameters have been calculated for hydrocarbon chains lying in the acyl and alkyl binding positions of bile-salt-stimulated human milk lipase.
The Diastereomeric 8,9-Epoxides of Limonene (the 8,9-Epoxy-p-menth-1-enes)
Authors: Carman RM , Devoss JJ , Greenfield KL
Published: September 2010

The stereochemistry of the 8,9-epoxy-p-menth-1-enes has been unambiguously determined by relating them to the corresponding p- menth-1-ene-8,9-diols( uroterpenol ) of known configuration. Mild conditions for the hydrolysis of epoxides with hydroxide ion are described.
Studies of Some Cadmium(II) and Mercury(II) Complexes With Dicyclohexylphosphino-N-Phenylthioformamide, LH: Crystal and Molecular-Structures of [Cdl2(LH)]2, ([HgCl2(LH)]2.CH2Cl2) And HgCl2(LH)2
Authors: Cowan SW , Dakternieks D , Gable RW , Hoskins BF , Rolls CL , Tiekink ERT
Published: September 2010

The crystal and molecular structures of the title compounds, [CdI2(LH)]2, (1), [HgCl2(LH)]2.CH2Cl2(2), and HgCl2(LH)2(3)[where LH = dicyclohexylphosphino-N-phenyl-thioformamide,* (c-C6H11)2PC(S)N(H)Ph] have been determined by single-crystal X-ray diffraction techniques. Crystals of (1) are monoclinic, space group P21/n, a 13.051(2), b 10.183(1), c 18.106(1)Ǻ and β 101.55(8)° with Z 2; R and Rw were 0.047 and 0.044 respectively for 2320 unique, observed reflections. The unit cell contains two equivalent centrosymmetric, halogen-bridged cadmium dimers. Crystals of (2) are triclinic, space group Pī, with a 10.668(4), b 14.978(3), c 16.838(4)Ǻ,
and α 111.80(2), β 101.03(2), γ 92.06(2)° with Z 2; R and Rw were 0.069 and 0.067 respectively for 3379 unique observed reflections. The structure shows two independent centrosymmetric halogen-bridged dimers within the unit cell. Crystals of (3) are monoclinic, space group C2/c, a 24.719(6), b 12.247(3), c 26.818(6)
Ǻ, and β 94.62(2)° with Z 8; R and Rw were 0.075 and 0.071 respectively for 2698 unique, observed reflections. The structure shows the complex to be monomeric. In all three compounds the metal atom is in an approximately tetrahedral environment with the potentially multidentate ligand, LH, coordinating only through the phosphorus atom. The mercury compounds show a much larger deviation from ideal tetrahedral geometry than does the cadmium compound.
Nucleophilic-Substitution Reactions in Benzo[C][1,8]Naphthyridines
Authors: Deady LW , Werden DM
Published: September 2010

The reactions of 1-chloro-3-methyl-6-(p- methylphenoxy ) benzo [c][1,8] naphthyridine with a variety of nucleophiles are reported. The relative reactivity of the 1- and 6-positions depends on the nucleophile and reaction conditions. Anilines, and alkyl and aryl thioxides react at position 1, alkylamines and alkoxide at position 6, and acidified alcohol at both 1 and 6. Some possible reasons for these positional reactivities are discussed.
Further Reactions in the Tetrahydroazocin-2(1h)-one Series
Authors: Ridley DD , Simpson GW
Published: September 2010

5,6,7,8-Tetrahydroazocin-2(1H)-one and the 3-phenylthio- and 3- phenylsulfonyl-substituted derivatives have been converted into the corresponding 2-ethoxy-5,6,7,8-tetrahydroazocines with Meerwein's reagent. Upon irradiation under mercury lamp at longer wavelengths (Pyrex vessels) these compounds are inert, but at shorter wavelengths (quartz vessels) polymeric materials form with no evidence of intramolecular ring cyclization. Reaction of the lactams with bases, and with t-butyl hypochlorite, are reported, and these reactions lead to a variety of azocin-2(1H)-one derivatives.
Vibrational-Spectra of Crystalline Ammonium-Nitrate
Authors: Carrick MT , James DW
Published: September 2010

The low-temperature Raman spectra of NH4NO3 and ND4NO3 give evidence of one phase (phase V) with the phase transition from phase IV being sluggish and occuring over a temperature range of some 100 K with pronounced hysteresis . The spectra were consistent with the reported powder structure of P42. The internal vibrations of the nitrate ion showed both site and factor group components while the internal motions of the ammonium ion showed evidence of two different coulombic sites with a small site splitting evident for both sites. In the higher temperature phase some evidence relating to heteroionic coupling of Ag site components in phase IV is presented and the site splitting of internal nitrate bands in CsCl type structures of phases V, IV, II and I is discussed.
Rearrangement of the Fulminate Anion (CNO-) to the Cyanate Anion (OCN-). Possible Intermediacy of the Oxazirinyl Anion
Authors: Li WK , Baker J , Radom L
Published: September 2010

The rearrangement of the
fulminate anion (CNO-) to the cyanate
anion (OCN-) has been examined by using high-level ab initio molecular orbital calculations which include a diffuse-function-augmented polarization basis set and electron correlation incorporated at the full fourth-order Moller-Plesset level (MP4). The reaction is predicted to be exothermic by 275 kJ mol-1. Our best calculations indicate theinvolvement of a metastable cyclic oxazirinyl anion intermediate. However, this lies in an extremely shallow potential well and, in contrast to the predictions of semiempirical calculations, is unlikely to have more than a fleeting existence. The fulminate and cyanate anions are calculated to be stable with respect to electron loss and stable with respect to intramolecular rearrangement; accordingly, both should be observable gas-phase species.
Lewis-Base Adducts of Group-1B Metal(I) Compounds. XXIII. Synthesis and Structures of the 'Tris(3,5-Dimethylpyridine)Copper(I) Halides, [(C7H9N)3CuX], X = Cl, Br, I
Authors: Dyason JM , Engelhardt LM , Healy PC , White AH
Published: September 2010

The crystal structures of the title compounds, (C7H9N)3CuX, X = Cl , Br, I [(1), (2), (3)], have been determined by single-crystal X-ray methods at 295 K, being refined to residuals of 0.022, 0.053, 0.047 for 151, 312, 720 independent 'observed' reflections respectively. The three structures containing 3,5-dimethylpyridine have an interesting relationship in symmetry: (1) is rhombohedral , R3m, a
9.050(3)Ǻ, α 110.89(3)°, Z 1; (2) is rhombohedral, R3c, a 10.328(5)Ǻ, α 95.60(4), Z 2; and (3), derived from (2), is monoclinic, Cc, a 13.233(6), b 15.083(7), c 11.491(6)Ǻ, β 98.27(4)°, Z 4. The distances Cu- Cl , Br, I are 2.412(9), 2.51(1), 2.683(3)Ǻ, with Cu-N 2.08(1), 2.02(1), 1.98(2)- 2.15(4)Ǻ respectively. In (1), the symmetry of the molecule, containing pseudo- tetrahedrally coordinated copper, N3CuX, is a full 3 m, with the ligands lying in mirror planes containing the 3 axis; in (2), the ligands rotate about the Cu-N bonds so that the molecular symmetry is 3; and in (3) further distortion of this kind causes total loss of crystallographically imposed symmetry. This descent in symmetry is the converse of that observed in the rhombohedral series [(C6H7N)3CuX] (C6H7N = 3-methylpyridine), and the possible underlying reasons are explored in terms of intra- and inter-molecular X...H interactions.
Light-Induced Electron-Transfer Reactions Involving the Tris(2,2'-Bipyridine)Ruthenium Dication and Related Complexes. 3. Improved Synthesis of 2,2'-Bipyridine-4,4'-Dicarboxylic Acid and Photoreduction of Water by Bis(2,2'-Bipyridine)(2,2'-Bipyridine-4,4'-Dicarboxylic Acid)Ruthenium(II)
Authors: Launikonis A , Lay PA , Mau AWH , Sargeson AM , Sasse WHF
Published: September 2010

The oxidation of 4,4′-dimethyl-2,2′-bipyridine with potassium permanganate in water gives 2,2′-bipyridine-4,4′-dicarboxylic acid and 4′-methyl-2,2?-bipyridine-4-carboxylic acid. The latter acid is oxidized to the diacid by boiling nitric acid. Complexes of the type Ru ( bpy )2L2+ have been prepared where L is 2,2′-bipyridine-4,4′- dicarboxylic acid, diethyl 2,2′-bipyridine-4,4′-dicarboxylate, 4′- methyl-2,2′-bipyridine-4-carboxylic acid and ethyl 4′-methyl-2,2′- bipyridine-4-carboxylate. These complexes have been compared with [ Ru ( bpy )3]2+ as sensitizers for the photoreduction of water. Stern- Volmer analysis has been applied to the quenching of their luminescence by methylviologen (mv2+), [Co(sep)]3+ (sep is 1,3,6,8,10,13,16,19- octaazabicyclo [6.6.6] icosane ) and [Co( CLsar )]3+ ( CLsar is 1-chloro- 3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane ). Changes in the Stern-Volmer constants have been related to the free energy changes associated with the oxidative quenching and the overall charges of the ruthenium complexes. The rates of formation of hydrogen compared favourably in sacrificial cycles with the ruthenium complexes as sensitizers, mv2+, Co(sep)3+ as electron-transfer agents, platinum/poly(vinyl alcohol) as catalyst, and ethylenediaminetetraacetic acid as electron donor. The results obtained have been discussed in terms of variations in the efficiencies of cage escape in the oxidative quenching and competition between electron transfer and energy transfer.
NMR-Spectra and Solution Structures of Some Piperazine-2,5-Diones. X-Ray Crystal-Structure of Threo-1-Acetyl-3-(Alpha-Bromobenzyl)-3-Methoxy-Piperazine-2,5-Dione
Authors: Elix JA , Fallon GD , Marcuccio SM , Rae ID
Published: September 2010

3-(α- Bromobenzyl )-3-methoxypiperazine-2,5-diones are prepared by the reaction of 3-benzylidenepiperazine-2,5-diones with N- bromosuccinimide in methanol. The crystal structure of the threo-1-acetyl compound shows the side chain in the EN conformation, with the bromine above the heterocyclic ring, the latter ring system being almost planar. This conformer predominates in CDCl3 solution also, but in (CD3)2SO the piperazine-2,5-dione ring adopts a boat conformation. Both the erythro isomer and an N(4)-methyl derivative exist in solution predominantly as folded conformers. The importance of repulsive interactions in predicting the conformation of substituted piperazine-2,5-diones is discussed.
Base Hydrolysis of Coordinated Trimethyl Phosphate
Authors: Hendry P , Sargeson AM
Published: September 2010

The novel metal complex ions pentaammine ( trimethyl phosphate)- rhodium(III) and -iridium(III) have been synthesized and their hydrolysis in basic solution studied. The hydrolyses yield coordinated dimethyl phosphate ( dmp ), exclusively for the iridium complex, but accompanied by metal-oxygen bond rupture in the case of the rhodium complex. The reaction of the iridium complex proceeds with phosphorus-oxygen cleavage. The hydrolyses in the absence of nucleophiles other than hydroxide obey simple rate laws, v = k1[(NH3)5Ir( tmp )][OH-] for the iridium complex and v = (k1 + k2[OH-])[(NH3)5Rh( tmp )] for rhodium. Both complexes hydrolyse
to yield coordinated dmp approximately 400 times faster than the analogous reaction for uncoordinated tmp. In butylamine -buffered solutions of [(NH3)5Rh( tmp )]3+, N- methylated butylamine is produced presumably as a result of nucleophilic attack of butylamine at a carbon centre of coordinated trimethyl phosphate.
Trifluoromethyl Complexes of Osmium(II) by Halogen Oxidation of an Osmium(0) Difluorocarbene Compound and the Structures of Os(CF3)Cl2(NO)(PPh3)2
and Os(CF3)Cl0.666I1.333(NO)(PPh3)2
Authors: Clark GR , Greene TR , Roper WR
Published: September 2010

Oxidation of Os(=CF2) Cl (NO)(PPh3)2 by the halogens X2(X = Cl , I), unexpectedly yields the trifluoromethyl complexes Os(CF3)CIX(NO)(PPh3)2 in a low yield which is improved by the addition of LiF to the reaction mixture. The crystal structures of both Os(CF3)Cl2(NO)(PPh3)2 and Os(CF3)Cl0.666I1.333(NO)(PPh3)2 have been determined. Crystals of Os(CF3)Cl2(NO)(PPh3)2 are monoclinic, a 24.543(5), b 9.685(1), c 15.951(1) Ǻ, β 115.81(1)°, Z 4, space group C2/c. Least-squares refinement has returned a residual, R, of 0.048 for 3371 observed reflections. The molecule lies on a twofold axis, with the CF3-group and one Cl-ligand statistically interchanged. Crystals of Os(CF3)Cl0.666 I1.333(NO)(PPh3)2 are monoclinic, a 24.562(4), b 9.690(1), c 16.385(2) Ǻ, β 115.51(1)°, Z 4, space group C2/c. Least-squares refinement has returned a residual of 0.058 for 4087 observed reflections. This crystal structure is best described as a 2 : 1 mixture of Os(CF3) ClI (NO)(PPh3)2 and s(CF3)I2(NO)(PPh3)2, (both with CF3 and I statistically disordered about the diad axis, as above). Both complexes exhibit octahedral coordination geometries.
15N and 195Pt NMR-Study of the Effect of Chain-Length, n, on the Reactions of Amino-Acids, +NH3(CH2)NCO2 (N = 1, 2, 3), With Platinum(II) Ammine Complexes
Authors: Appleton TG , Hall JR , Ralph SF
Published: September 2010

15N and 195Pt n.m.r. have been used to study the reactions in solution of cis -Pt(15NH3)2(H2O)22+ (1), cis -Pt(15NH3)2(OH)2 (2), cis -Pt(15NH3)2Cl2 (3), Pt(15NH3)3(H2O)2+ (4) and Pt(15NH3)3(OH)+ (5) with the amino acids +NH3(CH2)nCO2- (LH) [n = 1 ( glycine, glyH ); n = 2 (β- alanine , βalaH ), n = 3 (γ- aminobutyric acid, abaH )]. While glycine with (1) gives initially cis -Pt(NH3)2( glyH -O)(H2O)2+, with facile ring closure to Pt(NH3)2( gly - N,O)+, β- alanine and γ- aminobutyric acid with (1) give solutions containing a mixture of cis -Pt(NH3)2(LH-O)(H2O)2+, cis -Pt(NH3)2(LH.O)22+, and {Pt(NH3)2}2(μO,O-LH)(μ-OH)3+, which are quite stable kinetically under mildly acid conditions. Ring closure to Pt(NH3)2(L-N,O)+ becomes increasingly difficult as n increases. At 37°C and initial pH 7, (3) with glycine gives Pt(NH3)2( gly -N,O)+, but β- alanine and γ- aminobutyric acid give predominantly cis -Pt(NH3)2Cl(LH-O)+. Compound (4) with glycine gives initially Pt(NH3)3( glyH -O)2+, which then isomerizes to Pt(NH3)3( glyH -N)2+. In corresponding reactions with β- alanine and γ- aminobutyric acid, Pt(NH3)3(LH-O)2+ is stable indefinitely under mildly acid conditions. Differences in reactivity of the amino acids with (2) and (5) in alkaline solutions may be correlated with decreasing nucleophilicity of the amine group of NH2(CH2)nCO2- as n increases.