Colloidal alloys with preassembled clusters and spheres.

PubMed

Ducrot, Étienne; He, Mingxin; Yi, Gi-Ra; Pine, David J

2017-06-01

Self-assembly is a powerful approach for constructing colloidal crystals, where spheres, rods or faceted particles can build up a myriad of structures. Nevertheless, many complex or low-coordination architectures, such as diamond, pyrochlore and other sought-after lattices, have eluded self-assembly. Here we introduce a new design principle based on preassembled components of the desired superstructure and programmed nearest-neighbour DNA-mediated interactions, which allows the formation of otherwise unattainable structures. We demonstrate the approach using preassembled colloidal tetrahedra and spheres, obtaining a class of colloidal superstructures, including cubic and tetragonal colloidal crystals, with no known atomic analogues, as well as percolating low-coordination diamond and pyrochlore sublattices never assembled before.

Conformal Geometry, Hotine’s Conjecture, and Differential Geodesy.

DTIC Science & Technology

1987-07-27

ellipsoid (Stokes Theorem). Rayleigh and Poincare extensively studied tides. Starting around 1900 the close connection between geodesy and mathematics...locally conformal maps on neighborhoods of M ,.’ P -a ,r r’ " % "% J and M’ For example, consider the 2-sphere S and the plane E It 2 2 is well...coordinates where the coordinate surfaces are respectively planes ; planes and cylinders; and planes , spheres, - and cones. we give one less trivial example

Computational study of the electronic structure and magnetic properties of the Ni-C state in [NiFe] hydrogenases including the second coordination sphere.

PubMed

Kampa, Mario; Lubitz, Wolfgang; van Gastel, Maurice; Neese, Frank

2012-12-01

[NiFe] hydrogenases catalyze the reversible formation of H(2). The [NiFe] heterobimetallic active site is rich in redox states. Here, we investigate the key catalytic state Ni-C of Desulfovibrio vulgaris Miyazaki F hydrogenase using a cluster model that includes the truncated amino acids of the entire second coordination sphere of the enzyme. The optimized geometries, computed g tensors, hyperfine coupling constants, and IR stretching frequencies all agree well with experimental values. For the hydride in the bridging position, only a single minimum on the potential energy surface is found, indicating that the hydride bridges and binds to both nickel and iron. The influence of the second coordination sphere on the electronic structure is investigated by comparing results from the large cluster models with truncated models. The largest interactions of the second coordination sphere with the active site concern the hydrogen bonds with the cyanide ligands, which modulate the bond between iron and these ligands. Secondly, the electronic structure of the active site is found to be sensitive to the protonation state of His88. This residue forms a hydrogen bond with the spin-carrying sulfur atom of Cys549, which in turn tunes the spin density at the nickel and coordinating sulfur atoms. In addition, the unequal distribution of spin density over the equatorial cysteine residues results from different orientations of the cysteine side chains, which are kept in their particular orientation by the secondary structure of the protein.

Deconvolution of Raman spectroscopic signals for electrostatic, H-bonding, and inner-sphere interactions between ions and dimethyl phosphate in solution

PubMed Central

Christian, Eric L; Anderson, Vernon E.; Harris, Michael E

2011-01-01

Quantitative analysis of metal ion-phosphodiester interactions is a significant experimental challenge due to the complexities introduced by inner-sphere, outer-sphere (H-bonding with coordinated water), and electrostatic interactions that are difficult to isolate in solution studies. Here, we provide evidence that inner-sphere, H-bonding and electrostatic interactions between ions and dimethyl phosphate can be deconvoluted through peak fitting in the region of the Raman spectrum for the symmetric stretch of non-bridging phosphate oxygens (νsPO 2-). An approximation of the change in vibrational spectra due to different interaction modes is achieved using ions capable of all or a subset of the three forms of metal ion interaction. Contribution of electrostatic interactions to ion-induced changes to the Raman νsPO2- signal could be modeled by monitoring attenuation of νsPO2- in the presence of tetramethylammonium, while contribution of H-bonding and inner-sphere coordination could be approximated from the intensities of altered νsPO2- vibrational modes created by an interaction with ammonia, monovalent or divalent ions. A model is proposed in which discrete spectroscopic signals for inner-sphere, H-bonding, and electrostatic interactions are sufficient to account for the total observed change in νsPO2- signal due to interaction with a specific ion capable of all three modes of interaction. Importantly, the quantitative results are consistent with relative levels of coordination predicted from absolute electronegativity and absolute hardness of alkali and alkaline earth metals. PMID:21334281

Steric hindrance and the enhanced stability of light rare-earth elements in hydrothermal fluids

USGS Publications Warehouse

Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

2009-01-01

A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 ??C and 520 MPa. The REE3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 ??C range. Furthermore, the degree of chloride coordination of REE3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE3+ over heavy REE3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids.

Generalized spherical and simplicial coordinates

NASA Astrophysics Data System (ADS)

Richter, Wolf-Dieter

2007-12-01

Elementary trigonometric quantities are defined in l2,p analogously to that in l2,2, the sine and cosine functions are generalized for each p>0 as functions sinp and cosp such that they satisfy the basic equation cosp([phi])p+sinp([phi])p=1. The p-generalized radius coordinate of a point [xi][set membership, variant]Rn is defined for each p>0 as . On combining these quantities, ln,p-spherical coordinates are defined. It is shown that these coordinates are nearly related to ln,p-simplicial coordinates. The Jacobians of these generalized coordinate transformations are derived. Applications and interpretations from analysis deal especially with the definition of a generalized surface content on ln,p-spheres which is nearly related to a modified co-area formula and an extension of Cavalieri's and Torricelli's indivisibeln method, and with differential equations. Applications from probability theory deal especially with a geometric interpretation of the uniform probability distribution on the ln,p-sphere and with the derivation of certain generalized statistical distributions.

Coordinated Hard Sphere Mixture (CHaSM): A simplified model for oxide and silicate melts at mantle pressures and temperatures

NASA Astrophysics Data System (ADS)

Wolf, Aaron S.; Asimow, Paul D.; Stevenson, David J.

2015-08-01

We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme temperatures and pressures, including deep mantle conditions like those in the early Earth magma ocean. The Coordinated Hard Sphere Mixture (CHaSM) is based on an extension of the hard sphere mixture model, accounting for the range of coordination states available to each cation in the liquid. By utilizing approximate analytic expressions for the hard sphere model, this method is capable of predicting complex liquid structure and thermodynamics while remaining computationally efficient, requiring only minutes of calculation time on standard desktop computers. This modeling framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide range of pressures and temperatures. We find that the typical coordination number of the Mg cation evolves continuously upward from 5.25 at 0 GPa to 8.5 at 250 GPa. The results produced by CHaSM are evaluated by comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHaSM is accurately capturing the dominant physics controlling the behavior of oxide melts at high pressure. Finally, we present a simple quantitative model to explain the universality of the increasing Grüneisen parameter trend for liquids, which directly reflects their progressive evolution toward more compact solid-like structures upon compression. This general behavior is opposite that of solid materials, and produces steep adiabatic thermal profiles for silicate melts, thus playing a crucial role in magma ocean evolution.

Papers from U.S. Department of Energy Science Undergraduate Laboratory Internship Program (SULI) 2010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

2011-06-22

The solvation sphere of halides in water has been investigated using a combination of extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis techniques. The results have indicated that I{sup -} and Br{sup -} both have an asymmetric, 8 water molecule primary solvation spheres. These spheres are identical, with the Br{sup -} sphere about .3 {angstrom} smaller than the I{sup -} sphere. This study utilized near-edge analysis to supplement EXAFS analysis which suffers from signal dampening/broadening due to thermal noise. This paper has reported on the solvation first sphere of I{sup -} and Br{sup -} inmore » water. Using EXAFS and XANES analysis, strong models which describe the geometric configuration of water molecules coordinated to a central anion have been developed. The combination of these techniques has provided us with a more substantiated argument than relying solely on one or the other. An important finding of this study is that the size of the anion plays a smaller role than previously assumed in determining the number of coordinating water molecules. Further experimental and theoretical investigation is required to understand why the size of the anion plays a minor role in determining the number of water molecules bound.« less

Effective transport properties of composites of spheres

NASA Astrophysics Data System (ADS)

Felderhof, B. U.

1994-06-01

The effective linear transport properties of composites of spheres may be studied by the methods of statistical physics. The analysis leads to an exact cluster expansion. The resulting expression for the transport coefficients may be evaluated approximately as the sum of a mean field contribution and correction terms, given by cluster integrals over two-sphere and three-sphere correlation functions. Calculations of this nature have been performed for the effective dielectric constant, as well as the effective elastic constants of composites of spheres. Accurate numerical data for the effective properties may be obtained by computer simulation. An efficient formulation uses multiple expansion in Cartesian coordinates and periodic boundary conditions. Extensive numerical results have been obtained for the effective dielectric constant of a suspension of randomly distributed spheres.

Synthesis, structure, spectroscopic and electrochemical properties of (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)copper(II) monohydrate

NASA Astrophysics Data System (ADS)

Uçar, İbrahim; Karabulut, Bünyamin; Bulut, Ahmet; Büyükgüngör, Orhan

2007-05-01

The (2-amino-4-methylpyrimidine)-(pyridine-2,6-dicarboxylato)copper(II) monohydrate complex was synthesized and characterized by spectroscopic (IR, UV/Vis, EPR), thermal (TG/DTA) and electrochemical methods. X-ray structural analysis of the title complex revealed that the copper ion can be considered to have two coordination spheres. In the first coordination sphere the copper ion forms distorted square-planar geometry with trans-N 2O 2 donor set, and also the metal ion is weakly bonded to the amino-nitrogen in the layer over and to the carboxylic oxygen in the layer underneath in the second coordination sphere. The second coordination environment on the copper ion is attributed to pseudo octahedron. The powder EPR spectra of Cu(II) complex at room and liquid nitrogen temperature were recorded. The calculated g and A parameters have indicated that the paramagnetic centre is axially symmetric. The molecular orbital bond coefficients of the Cu(II) ion in d 9 state is also calculated by using EPR and optical absorption parameters. The cyclic voltammogram of the title complex investigated in DMSO (dimethylsulfoxide) solution exhibits only metal centered electroactivity in the potential range -1.25 to 1.5 V versus Ag/AgCl reference electrode.

ESR, spectroscopic, and quantum-chemical studies on the electronic structures of complexes formed by Cu(I) with radicals (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritsan, N.P.; Usov, O.M.; Shokhirev, N.V.

1986-07-01

The optical and ESR spectra have been examined for complexes of Cu(I) with various radicals, which contain various numbers of Cl/sup -/ ions in the central-atom coordination sphere. The spin-Hamiltonian parameters have been determined for all these radical complexes, and the observed ESR spectra have been compared with those calculated with allowance for second-order effects. The observed values for the isotropic and anisotropic components of the HFI constant from the central ion have been used to estimate the contributions from the 4s and 3d/sup 2//sub z/ orbitals of the copper ion to the unpaired-electron MO. Quantum-chemical calculations have been performedmore » by the INDO method on the electronic structures and geometries of complexes formed by CH/sub 2/OH with Cu(I) for various Cl/sup -/ contents in the coordination sphere. The radical is coordinated by the ..pi.. orbital on the carbon atom, and the stabilities of the radical complexes decrease as the number of Cl/sup -/ ions in the coordination sphere increases. A geometry close to planar for the CuCl/sub 4//sup 3 -/ fragment in a complex containing four Cl/sup -/ ions.« less

Bending nanofibers into nanospirals: coordination chemistry as a tool for shaping hydrophobic assemblies.

PubMed

Kossoy, Elizaveta; Weissman, Haim; Rybtchinski, Boris

2015-01-02

In the current work, we demonstrate how coordination chemistry can be employed to direct self-assembly based on strong hydrophobic interactions. To investigate the influence of coordination sphere geometry on aqueous self-assembly, we synthesized complexes of the amphiphilic perylene diimide terpyridine ligand with the first-row transition-metal centers (zinc, cobalt, and nickel). In aqueous medium, aggregation of these complexes is induced by hydrophobic interactions between the ligands. However, the final shapes of the resulting assemblies depend on the preferred geometry of the coordination spheres typical for the particular metal center. The self-assembly process was characterized by UV/Vis spectroscopy, zeta potential measurements, and cryogenic transmission electron microscopy (cryo-TEM). Coordination of zinc(II) and cobalt(II) leads to the formation of unique nanospiral assemblies, whereas complexation of nickel(II) leads to the formation of straight nanofibers. Notably, coordination bonds are utilized not as connectors between elementary building blocks, but as directing interactions, enabling control over supramolecular geometry. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Competition Between Co(NH3)63+ and Inner Sphere Mg2+ Ions in the HDV Ribozyme

PubMed Central

Gong, Bo; Chen, Jui-Hui; Bevilacqua, Philip C.; Golden, Barbara L.; Carey, Paul R.

2009-01-01

Divalent cations play critical structural and functional roles in many RNAs. While the hepatitis delta virus (HDV) ribozyme can undergo self-cleavage in the presence of molar concentrations of monovalent cations, divalent cations such as Mg2+ are required for efficient catalysis under physiological conditions. Moreover, the cleavage reaction can be inhibited with Co(NH3)63+, an analog of Mg(H2O)62+. Here, the binding of Mg2+ and Co(NH3)63+ to the HDV ribozyme are studied by Raman microscopic analysis of crystals. Raman difference spectra acquired at different metal ion conditions reveal changes in the ribozyme. When Mg2+ alone is introduced to the ribozyme, inner sphere coordination of Mg(H2O)x2+ (x≤5) to non-bridging PO2− oxygen, and changes in base stretches and phosphodiester group conformation are observed. In addition, binding of Mg2+ induces deprotonation of a cytosine assigned to the general acid C75, consistent with solution studies. When Co(NH3)63+ alone is introduced, deprotonation of C75 is again observed, as are distinctive changes in base vibrational ring modes and phosphodiester backbone conformation. In contrast to Mg2+ binding, Co(NH3)63+ binding does not perturb PO2− group vibrations, consistent with its ability to make only outer sphere contacts. Surprisingly, competitive binding studies reveal that Co(NH3)63+ ions displace some inner sphere-coordinated magnesium species, including ions coordinated to PO2− groups or the N7 of a guanine, likely G1 at the active site. These observations contrast with the tenet that Co(NH3)63+ ions displace only outer sphere magnesium ions. Overall, our data support two classes of inner sphere Mg2+-PO2− binding sites: sites that Co(NH3)63+ can displace, and others it cannot. PMID:19888753

A purely Lagrangian method for simulating the shallow water equations on a sphere using smooth particle hydrodynamics

NASA Astrophysics Data System (ADS)

Capecelatro, Jesse

2018-03-01

It has long been suggested that a purely Lagrangian solution to global-scale atmospheric/oceanic flows can potentially outperform tradition Eulerian schemes. Meanwhile, a demonstration of a scalable and practical framework remains elusive. Motivated by recent progress in particle-based methods when applied to convection dominated flows, this work presents a fully Lagrangian method for solving the inviscid shallow water equations on a rotating sphere in a smooth particle hydrodynamics framework. To avoid singularities at the poles, the governing equations are solved in Cartesian coordinates, augmented with a Lagrange multiplier to ensure that fluid particles are constrained to the surface of the sphere. An underlying grid in spherical coordinates is used to facilitate efficient neighbor detection and parallelization. The method is applied to a suite of canonical test cases, and conservation, accuracy, and parallel performance are assessed.

Coordinated Hard Sphere Mixture (CHaSM): A fast approximate model for oxide and silicate melts at extreme conditions

NASA Astrophysics Data System (ADS)

Wolf, A. S.; Asimow, P. D.; Stevenson, D. J.

2015-12-01

Recent first-principles calculations (e.g. Stixrude, 2009; de Koker, 2013), shock-wave experiments (Mosenfelder, 2009), and diamond-anvil cell investigations (Sanloup, 2013) indicate that silicate melts undergo complex structural evolution at high pressure. The observed increase in cation-coordination (e.g. Karki, 2006; 2007) induces higher compressibilities and lower adiabatic thermal gradients in melts as compared with their solid counterparts. These properties are crucial for understanding the evolution of impact-generated magma oceans, which are dominated by the poorly understood behavior of silicates at mantle pressures and temperatures (e.g. Stixrude et al. 2009). Probing these conditions is difficult for both theory and experiment, especially given the large compositional space (MgO-SiO2-FeO-Al2O3-etc). We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme P-T conditions (Wolf et al., 2015). The Coordinated Hard Sphere Mixture (CHaSM) extends the Hard Sphere mixture model, accounting for the range of coordination states for each cation in the liquid. Using approximate analytic expressions for the hard sphere model, this fast statistical method compliments classical and first-principles methods, providing accurate thermodynamic and structural property predictions for melts. This framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide P-T range. Typical Mg-coordination numbers are predicted to evolve continuously from 5.25 (0 GPa) to 8.5 (250 GPa), comparing favorably with first-principles Molecular Dynamics (MD) simulations. We begin extending the model to a simplified mantle chemistry using empirical potentials (generally accurate over moderate pressure ranges, <~30 GPa), yielding predictions rooted in statistical representations of melt structure that compare well with more time-consuming classical MD calculations. This approach also sheds light on the universality of the increasing Grüneisen parameter trend for liquids (opposite that of solids), which directly reflects their progressive evolution toward more compact solid-like structures upon compression.

The structural role of the zinc ion can be dispensable in prokaryotic zinc-finger domains

PubMed Central

Baglivo, Ilaria; Russo, Luigi; Esposito, Sabrina; Malgieri, Gaetano; Renda, Mario; Salluzzo, Antonio; Di Blasio, Benedetto; Isernia, Carla; Fattorusso, Roberto; Pedone, Paolo V.

2009-01-01

The recent characterization of the prokaryotic Cys2His2 zinc-finger domain, identified in Ros protein from Agrobacterium tumefaciens, has demonstrated that, although possessing a similar zinc coordination sphere, this domain is structurally very different from its eukaryotic counterpart. A search in the databases has identified ≈300 homologues with a high sequence identity to the Ros protein, including the amino acids that form the extensive hydrophobic core in Ros. Surprisingly, the Cys2His2 zinc coordination sphere is generally poorly conserved in the Ros homologues, raising the question of whether the zinc ion is always preserved in these proteins. Here, we present a functional and structural study of a point mutant of Ros protein, Ros56–142C82D, in which the second coordinating cysteine is replaced by an aspartate, 5 previously-uncharacterized representative Ros homologues from Mesorhizobium loti, and 2 mutants of the homologues. Our results indicate that the prokaryotic zinc-finger domain, which in Ros protein tetrahedrally coordinates Zn(II) through the typical Cys2His2 coordination, in Ros homologues can either exploit a CysAspHis2 coordination sphere, previously never described in DNA binding zinc finger domains to our knowledge, or lose the metal, while still preserving the DNA-binding activity. We demonstrate that this class of prokaryotic zinc-finger domains is structurally very adaptable, and surprisingly single mutations can transform a zinc-binding domain into a nonzinc-binding domain and vice versa, without affecting the DNA-binding ability. In light of our findings an evolutionary link between the prokaryotic and eukaryotic zinc-finger domains, based on bacteria-to-eukaryota horizontal gene transfer, is discussed. PMID:19369210

Synthesis, Structure, and Physical Properties for a Series of Monomeric Iron(III) Hydroxo Complexes with Varying Hydrogen-Bond Networks

PubMed Central

Mukherjee, Jhumpa; Lucas, Robie L.; Zart, Matthew K.; Powell, Douglas R.; Day, Victor W.; Borovik, A. S.

2013-01-01

Mononuclear iron(III) complexes with terminal hydroxo ligands are proposed to be important species in several metalloproteins, but they have been difficult to isolate in synthetic systems. Using a series of amidate/ureido tripodal ligands, we have prepared and characterized monomeric FeIIIOH complexes with similar trigonal-bipyramidal primary coordination spheres. Three anionic nitrogen donors define the trigonal plane, and the hydroxo oxygen atom is trans to an apical amine nitrogen atom. The complexes have varied secondary coordination spheres that are defined by intramolecular hydrogen bonds between the FeIIIOH unit and the urea NH groups. Structural trends were observed between the number of hydrogen bonds and the Fe–Ohydroxo bond distances: the more intramolecular hydrogen bonds there were, the longer the Fe–O bond became. Spectroscopic trends were also found, including an increase in the energy of the O–H vibrations with a decrease in the number of hydrogen bonds. However, the FeIII/II reduction potentials were constant throughout the series (∼2.0 V vs [Cp2Fe]0/+1), which is ascribed to a balancing of the primary and secondary coordination-sphere effects. PMID:18498155

Analytical solution of the problem of a shock wave in the collapsing gas in Lagrangian coordinates

NASA Astrophysics Data System (ADS)

Kuropatenko, V. F.; Shestakovskaya, E. S.

2016-10-01

It is proposed the exact solution of the problem of a convergent shock wave and gas dynamic compression in a spherical vessel with an impermeable wall in Lagrangian coordinates. At the initial time the speed of cold ideal gas is equal to zero, and a negative velocity is set on boundary of the sphere. When t > t0 the shock wave spreads from this point into the gas. The boundary of the sphere will move under the certain law correlated with the motion of the shock wave. The trajectories of the gas particles in Lagrangian coordinates are straight lines. The equations determining the structure of the gas flow between the shock front and gas border have been found as a function of time and Lagrangian coordinate. The dependence of the entropy on the velocity of the shock wave has been found too. For Lagrangian coordinates the problem is first solved. It is fundamentally different from previously known formulations of the problem of the self-convergence of the self-similar shock wave to the center of symmetry and its reflection from the center, which was built up for the infinite area in Euler coordinates.

Inhibition and oxygen activation in copper amine oxidases.

PubMed

Shepard, Eric M; Dooley, David M

2015-05-19

Copper-containing amine oxidases (CuAOs) use both copper and 2,4,5-trihydroxyphenylalanine quinone (TPQ) to catalyze the oxidative deamination of primary amines. The CuAO active site is highly conserved and comprised of TPQ and a mononuclear type II copper center that exhibits five-coordinate, distorted square pyramidal coordination geometry with histidine ligands and equatorially and axially bound water in the oxidized, resting state. The active site is buried within the protein, and CuAOs from various sources display remarkable diversity with respect to the composition of the active site channel and cofactor accessibility. Structural and mechanistic factors that influence substrate preference and inhibitor sensitivity and selectivity have been defined. This Account summarizes the strategies used to design selective CuAO inhibitors based on active site channel characteristics, leading to either enhanced steric fits or the trapping of reactive electrophilic products. These findings provide a framework to support the future development of candidate molecules aimed at minimizing the negative side effects associated with drugs containing amine functionalities. This is vital given the existence of human diamine oxidase and vascular adhesion protein-1, which have distinct amine substrate preferences and are associated with different metabolic processes. Inhibition of these enzymes by antifungal or antiprotozoal agents, as well as classic monoamine oxidase (MAO) inhibitors, may contribute to the adverse side effects associated with drug treatment. These observations provide a rationale for the limited clinical value associated with certain amine-containing pharmaceuticals and emphasize the need for more selective AO inhibitors. This Account also discusses the novel roles of copper and TPQ in the chemistry of O2 activation and substrate oxidation. Reduced CuAOs exist in a redox equilibrium between the Cu(II)-TPQAMQ (aminoquinol) and Cu(I)-TPQSQ (semiquinone). Elucidating the roles of Cu(I), TPQSQ, and TPQAMQ in O2 activation, for example, distinguishing inner-sphere versus outer-sphere electron transfer mechanisms, has been actively investigated since the discovery of TPQSQ in 1991 and has only recently been clarified. Kinetics and spectroscopic studies encompassing metal substitution, stopped-flow and temperature-jump relaxation methods, and oxygen kinetic isotope experiments have provided strong support for an inner-sphere electron transfer step from Cu(I) to O2. Data for two enzymes support a mechanism wherein O2 prebinds to a three-coordinate Cu(I) site, yielding a [Cu(II)(η(1)-O2(-1))](+) intermediate, with H2O2 generated from ensuing rate-determining proton coupled electron transfer from TPQSQ. While kinetics data from the cobalt-substituted yeast enzyme indicated that O2 is reduced through an outer-sphere process involving TPQAMQ, new findings with a bacterial CuAO demonstrate that both the Cu(II) and Co(II) forms of the enzyme operate via parallel mechanisms involving metal-superoxide intermediates. Structural observations of a coordinated TPQSQ-Cu(I) complex in two CuAOs supports previous indications that Cu(II)/(I) ligand substitution chemistry may be mechanistically relevant. Substantial evidence indicates that rapid and reversible inner-sphere reduction of O2 at a three-coordinate Cu(I) site occurs, but the existence of a coordinated semiquinone in some AOs suggests that, in these enzymes, an outer-sphere reaction between O2 and TPQSQ may also be possible, since this is expected to be energetically favorable compared with outer-sphere electron transfer from TPQAMQ to O2.

An isocenter estimation tool for proton gantry alignment

NASA Astrophysics Data System (ADS)

Hansen, Peter; Hu, Dongming

2017-12-01

A novel tool has been developed to automate the process of locating the isocenter, center of rotation, and sphere of confusion of a proton therapy gantry. The tool uses a Radian laser tracker to estimate how the coordinate frame of the front-end beam-line components changes as the gantry rotates. The coordinate frames serve as an empirical model of gantry flexing. Using this model, the alignment of the front and back-end beam-line components can be chosen to minimize the sphere of confusion, improving the overall beam positioning accuracy of the gantry. This alignment can be performed without the beam active, improving the efficiency of installing new systems at customer sites.

A comparative study of the electrostatic potential of fullerene-like structures of Au 32 and Au 42

NASA Astrophysics Data System (ADS)

Wang, Dong-Lai; Sun, Xiao-Ping; Shen, Hong-Tao; Hou, Dong-Yan; Zhai, Yu-Chun

2008-05-01

By using density functional theory calculations, it is found that the most negative MEP inside the gold cage occurs at the center of the sphere. The largest regions with the most negative MEP outside the sphere are localized in the neighborhood of the bridge sites and the vertex regions of the five-coordinated are more positive. The absolute values of the most negative potentials in both the inner and outer cages as well as the vertex regions of the five-coordinated of Au 32 structure are much larger than those of Au 42, which means Au 32 is preferable for electrophilic attack or nucleophilic processes.

SPHERES National Lab Facility

NASA Technical Reports Server (NTRS)

Benavides, Jose

2014-01-01

SPHERES is a facility of the ISS National Laboratory with three IVA nano-satellites designed and delivered by MIT to research estimation, control, and autonomy algorithms. Since Fall 2010, The SPHERES system is now operationally supported and managed by NASA Ames Research Center (ARC). A SPHERES Program Office was established and is located at NASA Ames Research Center. The SPHERES Program Office coordinates all SPHERES related research and STEM activities on-board the International Space Station (ISS), as well as, current and future payload development. By working aboard ISS under crew supervision, it provides a risk tolerant Test-bed Environment for Distributed Satellite Free-flying Control Algorithms. If anything goes wrong, reset and try again! NASA has made the capability available to other U.S. government agencies, schools, commercial companies and students to expand the pool of ideas for how to test and use these bowling ball-sized droids. For many of the researchers, SPHERES offers the only opportunity to do affordable on-orbit characterization of their technology in the microgravity environment. Future utilization of SPHERES as a facility will grow its capabilities as a platform for science, technology development, and education.

A volumetric conformal mapping approach for clustering white matter fibers in the brain

PubMed Central

Gupta, Vikash; Prasad, Gautam; Thompson, Paul

2017-01-01

The human brain may be considered as a genus-0 shape, topologically equivalent to a sphere. Various methods have been used in the past to transform the brain surface to that of a sphere using harmonic energy minimization methods used for cortical surface matching. However, very few methods have studied volumetric parameterization of the brain using a spherical embedding. Volumetric parameterization is typically used for complicated geometric problems like shape matching, morphing and isogeometric analysis. Using conformal mapping techniques, we can establish a bijective mapping between the brain and the topologically equivalent sphere. Our hypothesis is that shape analysis problems are simplified when the shape is defined in an intrinsic coordinate system. Our goal is to establish such a coordinate system for the brain. The efficacy of the method is demonstrated with a white matter clustering problem. Initial results show promise for future investigation in these parameterization technique and its application to other problems related to computational anatomy like registration and segmentation. PMID:29177252

FAST TRACK COMMUNICATION: Shear coordinate description of the quantized versal unfolding of a D4 singularity

NASA Astrophysics Data System (ADS)

Chekhov, Leonid; Mazzocco, Marta

2010-11-01

In this communication, by using Teichmüller theory of a sphere with four holes/orbifold points, we obtain a system of flat coordinates on the general affine cubic surface having a D4 singularity at the origin. We show that the Goldman bracket on the geodesic functions on the four-holed/orbifold sphere coincides with the Etingof-Ginzburg Poisson bracket on the affine D4 cubic. We prove that this bracket is the image under the Riemann-Hilbert map of the Poisson-Lie bracket on \\oplus _{1}^3\\mathfrak {sl}^\\ast (2,{{\\bb C}}) . We realize the action of the mapping class group by the action of the braid group on the geodesic functions. This action coincides with the procedure of analytic continuation of solutions of the sixth Painlevé equation. Finally, we produce the explicit quantization of the Goldman bracket on the geodesic functions on the four-holed/orbifold sphere and of the braid group action.

The Coulomb problem on a 3-sphere and Heun polynomials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellucci, Stefano; Yeghikyan, Vahagn; Yerevan State University, Alex-Manoogian st. 1, 00025 Yerevan

2013-08-15

The paper studies the quantum mechanical Coulomb problem on a 3-sphere. We present a special parametrization of the ellipto-spheroidal coordinate system suitable for the separation of variables. After quantization we get the explicit form of the spectrum and present an algebraic equation for the eigenvalues of the Runge-Lentz vector. We also present the wave functions expressed via Heun polynomials.

Effects of Measurement Geometry on Spectral Reflectance and Color

DTIC Science & Technology

1998-01-01

calibration of outdoor color imagery were made using integrating sphere and 45°/0° geometry. The differing results are discussed using CIELAB linear... CIELAB color coordinate results were obtained for different measurement geometries. Such results should affect the digital photographic measurements...measurement geometry on spectral reflectance and CIELAB values using integrating sphere and 45°/0° measurement geometries. An example of the phenomenology

Magnesium-binding architectures in RNA crystal structures: validation, binding preferences, classification and motif detection

PubMed Central

Zheng, Heping; Shabalin, Ivan G.; Handing, Katarzyna B.; Bujnicki, Janusz M.; Minor, Wladek

2015-01-01

The ubiquitous presence of magnesium ions in RNA has long been recognized as a key factor governing RNA folding, and is crucial for many diverse functions of RNA molecules. In this work, Mg2+-binding architectures in RNA were systematically studied using a database of RNA crystal structures from the Protein Data Bank (PDB). Due to the abundance of poorly modeled or incorrectly identified Mg2+ ions, the set of all sites was comprehensively validated and filtered to identify a benchmark dataset of 15 334 ‘reliable’ RNA-bound Mg2+ sites. The normalized frequencies by which specific RNA atoms coordinate Mg2+ were derived for both the inner and outer coordination spheres. A hierarchical classification system of Mg2+ sites in RNA structures was designed and applied to the benchmark dataset, yielding a set of 41 types of inner-sphere and 95 types of outer-sphere coordinating patterns. This classification system has also been applied to describe six previously reported Mg2+-binding motifs and detect them in new RNA structures. Investigation of the most populous site types resulted in the identification of seven novel Mg2+-binding motifs, and all RNA structures in the PDB were screened for the presence of these motifs. PMID:25800744

Optimizing conditions for utilization of an H 2 oxidation catalyst with outer coordination sphere functionalities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dutta, Arnab; Ginovska, Bojana; Raugei, Simone

2016-01-01

Hydrogenase enzymes use abundant metals such as nickel and iron to efficiently interconvert H2 and protons. In this work, we demonstrate that a Ni-based catalyst can exceed the rates of enzymes with only slightly higher overpotentials using [Ni(PCy2Narginine2)2]7, containing an amino acid-based outer coordination sphere. Under conditions of high pressure, elevated temperature, and aqueous acidic solutions, conditions similar to those found in fuel cells, this electrocatalyst exhibits the fastest H2 oxidation reported to date for any homogeneous catalyst (TOF 1.1×106 s-1) operating at a moderate overpotential (240 mV). Control experiments demonstrate that both the appended outer coordination sphere and watermore » are important to achieve this impressive catalytic performance. This work was funded by the Office of Science Early Career Research Program through the US Department of Energy, Office of Science, Office of Basic Energy Sciences (AD, WJS), and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (JASR) located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the US Department of Energy.« less

X-ray Absorption Spectroscopy Combined with Time-Dependent Density Functional Theory Elucidates Differential Substitution Pathways of Au(I) and Au(III) with Zinc Fingers.

PubMed

Abbehausen, Camilla; de Paiva, Raphael Enoque Ferraz; Bjornsson, Ragnar; Gomes, Saulo Quintana; Du, Zhifeng; Corbi, Pedro Paulo; Lima, Frederico Alves; Farrell, Nicholas

2018-01-02

A combination of two elements' (Au, Zn) X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TD-DFT) allowed the elucidation of differential substitution pathways of Au(I) and Au(III) compounds reacting with biologically relevant zinc fingers (ZnFs). Gold L 3 -edge XAS probed the interaction of gold and the C-terminal Cys 2 HisCys finger of the HIV-1 nucleocapsid protein NCp7, and the Cys 2 His 2 human transcription factor Sp1. The use of model compounds helped assign oxidation states and the identity of the gold-bound ligands. The computational studies accurately reproduced the experimental XAS spectra and allowed the proposition of structural models for the interaction products at early time points. The direct electrophilic attack on the ZnF by the highly thiophilic Au(I) resulted in a linear P-Au-Cys coordination sphere after zinc ejection whereas for the Sp1, loss of PEt 3 results in linear Cys-Au-Cys or Cys-Au-His arrangements. Reactions with Au(III) compounds, on the other hand, showed multiple binding modes. Prompt reaction between [AuCl(dien)] 2+ and [Au(dien)(DMAP)] 3+ with Sp1 showed a partially reduced Au center and a final linear His-Au-His coordination. Differently, in the presence of NCp7, [AuCl(dien)] 2+ readily reduces to Au(I) and changes from square-planar to linear geometry with Cys-Au-His coordination, while [Au(dien)(DMAP)] 3+ initially maintains its Au(III) oxidation state and square-planar geometry and the same first coordination sphere. The latter is the first observation of a "noncovalent" interaction of a Au(III) complex with a zinc finger and confirms early hypotheses that stabilization of Au(III) occurs with N-donor ligands. Modification of the zinc coordination sphere, suggesting full or partial zinc ejection, is observed in all cases, and for [Au(dien)(DMAP)] 3+ this represents a novel mechanism for nucleocapsid inactivation. The combination of XAS and TD-DFT presents the first direct experimental observation that not only compound reactivity, but also ZnF core specificity, can be modulated on the basis of the coordination sphere of Au(III) compounds.

Methods and considerations to determine sphere center from terrestrial laser scanner point cloud data

NASA Astrophysics Data System (ADS)

Rachakonda, Prem; Muralikrishnan, Bala; Cournoyer, Luc; Cheok, Geraldine; Lee, Vincent; Shilling, Meghan; Sawyer, Daniel

2017-10-01

The Dimensional Metrology Group at the National Institute of Standards and Technology is performing research to support the development of documentary standards within the ASTM E57 committee. This committee is addressing the point-to-point performance evaluation of a subclass of 3D imaging systems called terrestrial laser scanners (TLSs), which are laser-based and use a spherical coordinate system. This paper discusses the usage of sphere targets for this effort, and methods to minimize the errors due to the determination of their centers. The key contributions of this paper include methods to segment sphere data from a TLS point cloud, and the study of some of the factors that influence the determination of sphere centers.

Implementation of Satellite Formation Flight Algorithms Using SPHERES Aboard the International Space Station

NASA Technical Reports Server (NTRS)

Mandy, Christophe P.; Sakamoto, Hiraku; Saenz-Otero, Alvar; Miller, David W.

2007-01-01

The MIT's Space Systems Laboratory developed the Synchronized Position Hold Engage and Reorient Experimental Satellites (SPHERES) as a risk-tolerant spaceborne facility to develop and mature control, estimation, and autonomy algorithms for distributed satellite systems for applications such as satellite formation flight. Tests performed study interferometric mission-type formation flight maneuvers in deep space. These tests consist of having the satellites trace a coordinated trajectory under tight control that would allow simulated apertures to constructively interfere observed light and measure the resulting increase in angular resolution. This paper focuses on formation initialization (establishment of a formation using limited field of view relative sensors), formation coordination (synchronization of the different satellite s motion) and fuel-balancing among the different satellites.

The Problems of Coordination of the International Duties of the Kazakhstan Republic in the Social-Labour Sphere and National Law

ERIC Educational Resources Information Center

Buribayev, Yermek A.; Oryntayev, Zhambyl K.; Bekbossynov, Yermek; Mazhinbekov, Saken; Yessenbekova, Patima; Blasheva, Manshuk

2016-01-01

Background/Objectives: The research topicality is conditioned by the fact that the labour secure of the social and labour human rights is realized not only by the national law but also by the international law that is usually more progressive and establishes the generally accepted standards and norms of human rights in the social-labour sphere.…

Facet-Dependent Cr(VI) Adsorption of Hematite Nanocrystals.

PubMed

Huang, Xiaopeng; Hou, Xiaojing; Song, Fahui; Zhao, Jincai; Zhang, Lizhi

2016-02-16

In this study, the adsorption process of Cr(VI) on the hematite facets was systematically investigated with synchrotron-based Cr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density-functional theory calculation, and surface complexation models. Structural model fitting of EXAFS spectroscopy suggested that the interatomic distances of Cr-Fe were, respectively, 3.61 Å for the chromate coordinated hematite nanoplates with exposed {001} facets, 3.60 and 3.30 Å for the chromate coordinated hematite nanorods with exposed {001} and {110} facets, which were characteristic of inner-sphere complexation. In situ ATR-FTIR spectroscopy analysis confirmed the presence of two inner-sphere surface complexes with C3ν and C2ν symmetry, while the C3ν and C2ν species were assigned to monodentate and bidentate inner-sphere surface complexes with average Cr-Fe interatomic distances of 3.60 and 3.30 Å, respectively. On the basis of these experimental and theoretical results, we concluded that HCrO4(-) as dominated Cr(VI) species was adsorbed on {001} and {110} facets in inner-sphere monodentate mononuclear and bidentate binuclear configurations, respectively. Moreover, the Cr(VI) adsorption performance of hematite facets was strongly dependent on the chromate complexes formed on the hematite facets.

From GLC to double-null coordinates and illustration with static black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nugier, Fabien, E-mail: fnugier@ntu.edu.tw

We present a system of coordinates deriving directly from the so-called Geodesic Light-Cone (GLC) coordinates and made of two null scalars intersecting on a 2-dimensional sphere parameterized by two constant angles along geodesics. These coordinates are shown to be equivalent to the well-known double-null coordinates. As GLC, they present interesting properties for cosmology and astrophysics. We discuss this latter topic for static black holes, showing simple descriptions for the metric or particles and photons trajectories. We also briefly comment on the time of flight of ultra-relativistic particles.

Positional effects of second-sphere amide pendants on electrochemical CO2 reduction catalyzed by iron porphyrins† †Electronic supplementary information (ESI) available: Procedures for synthetic, spectroscopic, and electrochemical experiments. CCDC 1582750. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc04682k

PubMed Central

Nichols, Eva M.; Derrick, Jeffrey S.; Nistanaki, Sepand K.; Smith, Peter T.

2018-01-01

The development of catalysts for electrochemical reduction of carbon dioxide offers an attractive approach to transforming this greenhouse gas into value-added carbon products with sustainable energy input. Inspired by natural bioinorganic systems that feature precisely positioned hydrogen-bond donors in the secondary coordination sphere to direct chemical transformations occurring at redox-active metal centers, we now report the design, synthesis, and characterization of a series of iron tetraphenylporphyrin (Fe-TPP) derivatives bearing amide pendants at various positions at the periphery of the metal core. Proper positioning of the amide pendants greatly affects the electrocatalytic activity for carbon dioxide reduction to carbon monoxide. In particular, derivatives bearing proximal and distal amide pendants on the ortho position of the phenyl ring exhibit significantly larger turnover frequencies (TOF) compared to the analogous para-functionalized amide isomers or unfunctionalized Fe-TPP. Analysis of TOF as a function of catalyst standard reduction potential enables first-sphere electronic effects to be disentangled from second-sphere through-space interactions, suggesting that the ortho-functionalized porphyrins can utilize the latter second-sphere property to promote CO2 reduction. Indeed, the distally-functionalized ortho-amide isomer shows a significantly larger through-space interaction than its proximal ortho-amide analogue. These data establish that proper positioning of secondary coordination sphere groups is an effective design element for breaking electronic scaling relationships that are often observed in electrochemical CO2 reduction. PMID:29732079

Custom Coordination Environments for Lanthanoids: Tripodal Ligands Achieve Near-Perfect Octahedral Coordination for Two Dysprosium-Based Molecular Nanomagnets.

PubMed

Lim, Kwang Soo; Baldoví, José J; Jiang, ShangDa; Koo, Bong Ho; Kang, Dong Won; Lee, Woo Ram; Koh, Eui Kwan; Gaita-Ariño, Alejandro; Coronado, Eugenio; Slota, Michael; Bogani, Lapo; Hong, Chang Seop

2017-05-01

Controlling the coordination sphere of lanthanoid complexes is a challenging critical step toward controlling their relaxation properties. Here we present the synthesis of hexacoordinated dysprosium single-molecule magnets, where tripodal ligands achieve a near-perfect octahedral coordination. We perform a complete experimental and theoretical investigation of their magnetic properties, including a full single-crystal magnetic anisotropy analysis. The combination of electrostatic and crystal-field computational tools (SIMPRE and CONDON codes) allows us to explain the static behavior of these systems in detail.

Synthesis, crystal structures and Hirshfeld surface analyses of two new Salen type nickel/sodium heteronuclear complexes

NASA Astrophysics Data System (ADS)

Mahlooji, Niloofar; Behzad, Mahdi; Tarahhomi, Atekeh; Maroney, Michael; Rudbari, Hadi Amiri; Bruno, Giuseppe; Ghanbari, Bahram

2016-04-01

Two new heteronuclear Nickel(II)/Sodium(I) complexes of a side-off compartmental Schiff base ligand were synthesized and characterized by spectroscopic methods. Crystal structures of both of the complexes were also obtained. The Schiff base ligand was synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with 2-hydroxy-3-methoxybenzaldehyde. In both of the complexes the Ni(II) ion is coordinated to the inner N2O2 coordination sphere with square-planar geometry and the Na(I) ion is coordinated to the outer O2 O2‧ coordination sphere. In Complex (1) with general formula [Ni(L)Na(CH3OH)(ClO4)] the sodium ion is seven coordinated while in (2) with general formula [{Ni(L)Na(OH2)}2(μ-Ni(CN)4)] the sodium ion is six coordinated. Intermolecular interactions in two studied complexes were analyzed using 3D Hirshfeld surfaces and corresponding 2D fingerprint plots. This analysis showed that the H … H and C … H/H … C contacts for both structures (altogether 67.5% of total Hirshfeld surface area for (1) and 77.6% for (2)) and the O … H/H … O (24.2%) for (1) and the N … H/H … N (8.1%) contacts for (2) were the characteristic intermolecular contacts in the related crystal structures.

Development and validation of a multilateration test bench for particle accelerator pre-alignment

NASA Astrophysics Data System (ADS)

Kamugasa, Solomon William; Rothacher, Markus; Gayde, Jean-Christophe; Mainaud Durand, Helene

2018-03-01

The development and validation of a portable coordinate measurement solution for fiducialization of compact linear collider (CLIC) components is presented. This new solution addresses two limitations of high-accuracy state-of-the-art coordinate measuring machines, i.e. lack of portability and limited measurement volume. The solution is based on frequency scanning interferometry (FSI) distances and the multilateration coordinate measurement technique. The developments include a reference sphere for localizing the FSI optical fiber tip and a kinematic mount for repositioning the reference sphere with sub-micrometric repeatability. This design enables absolute distance measurements in different directions from the same point, which is essential for multilateration. A multilateration test bench built using these prototypes has been used to fiducialize a CLIC cavity beam position monitor and 420 mm-long main beam quadrupole magnet. The combined fiducialization uncertainty achieved is 3.5 μm (k  =  1), which is better than the CLIC 5 μm (k  =  1) uncertainty specification.

Brownian self-propelled particles on a sphere

NASA Astrophysics Data System (ADS)

Apaza-Pilco, Leonardo Felix; Sandoval, Mario

We present the dynamics of a Brownian self-propelled particle at low Reynolds number moving on the surface of a sphere. The effects of curvature and self-propulsion on the diffusion of the particle are elucidated by determining (numerically) the mean-square displacement of the particle's angular (azimuthal and polar) coordinates. The results show that the long time behavior of its angular mean-square displacement is linear in time. We also see that the slope of the angular MSD is proportional to the propulsion velocity and inverse to the curvature of the sphere. The angular probability distribution function (PDF) of the particle is also obtained by numerically solving its respective Smoluchowski equation.

DoD Information Assurance and Agile: Challenges and Recommendations Gathered Through Interviews with Agile Program Managers and DoD Accreditation Reviewers

DTIC Science & Technology

2012-11-01

Tradeoff Analysis Method; ATAM, Capability Maturity Model , Capability Maturity Modeling , Carnegie Mellon, CERT, CERT Coordination Center, CMM, CMMI...Hermansen, Product Design, Sphere of Influence (https://www.SphereOfInfluence.com) Joel McAteer, Information Assurance Manager, Modeling ...use of them does introduce some challenges related to delivering software features rapidly and/or in- crementally . • Challenges with respect to

Enhanced CO2 electroreduction efficiency through secondary coordination effects on a pincer iridium catalyst.

PubMed

Ahn, Steven T; Bielinski, Elizabeth A; Lane, Elizabeth M; Chen, Yanqiao; Bernskoetter, Wesley H; Hazari, Nilay; Palmore, G Tayhas R

2015-04-07

An iridium(III) trihydride complex supported by a pincer ligand with a hydrogen bond donor in the secondary coordination sphere promotes the electrocatalytic reduction of CO2 to formate in water/acetonitrile with excellent Faradaic efficiency and low overpotential. Preliminary mechanistic experiments indicate formate formation is facile while product release is a kinetically difficult step.

Coordinating the Provision of Health Services in Humanitarian Crises: a Systematic Review of Suggested Models.

PubMed

Lotfi, Tamara; Bou-Karroum, Lama; Darzi, Andrea; Hajjar, Rayan; El Rahyel, Ahmed; El Eid, Jamale; Itani, Mira; Brax, Hneine; Akik, Chaza; Osman, Mona; Hassan, Ghayda; El-Jardali, Fadi; Akl, Elie

2016-08-03

Our objective was to identify published models of coordination between entities funding or delivering health services in humanitarian crises, whether the coordination took place during or after the crises. We included reports describing models of coordination in sufficient detail to allow reproducibility. We also included reports describing implementation of identified models, as case studies. We searched Medline, PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CINAHL, PsycINFO, and the WHO Global Health Library. We also searched websites of relevant organizations. We followed standard systematic review methodology. Our search captured 14,309 citations. The screening process identified 34 eligible papers describing five models of coordination of delivering health services: the "Cluster Approach" (with 16 case studies), the 4Ws "Who is Where, When, doing What" mapping tool (with four case studies), the "Sphere Project" (with two case studies), the "5x5" model (with one case study), and the "model of information coordination" (with one case study). The 4Ws and the 5x5 focus on coordination of services for mental health, the remaining models do not focus on a specific health topic. The Cluster approach appears to be the most widely used. One case study was a mixed implementation of the Cluster approach and the Sphere model. We identified no model of coordination for funding of health service. This systematic review identified five proposed coordination models that have been implemented by entities funding or delivering health service in humanitarian crises. There is a need to compare the effect of these different models on outcomes such as availability of and access to health services.

UO₂²⁺ uptake by proteins: understanding the binding features of the super uranyl binding protein and design of a protein with higher affinity.

PubMed

Odoh, Samuel O; Bondarevsky, Gary D; Karpus, Jason; Cui, Qiang; He, Chuan; Spezia, Riccardo; Gagliardi, Laura

2014-12-17

The capture of uranyl, UO2(2+), by a recently engineered protein (Zhou et al. Nat. Chem. 2014, 6, 236) with high selectivity and femtomolar sensitivity has been examined by a combination of density functional theory, molecular dynamics, and free-energy simulations. It was found that UO2(2+) is coordinated to five carboxylate oxygen atoms from four amino acid residues of the super uranyl binding protein (SUP). A network of hydrogen bonds between the amino acid residues coordinated to UO2(2+) and residues in its second coordination sphere also affects the protein's uranyl binding affinity. Free-energy simulations show how UO2(2+) capture is governed by the nature of the amino acid residues in the binding site, the integrity and strength of the second-sphere hydrogen bond network, and the number of water molecules in the first coordination sphere. Alteration of any of these three factors through mutations generally results in a reduction of the binding free energy of UO2(2+) to the aqueous protein as well as of the difference between the binding free energies of UO2(2+) and other ions (Ca(2+), Cu(2+), Mg(2+), and Zn(2+)), a proxy for the protein's selectivity over these ions. The results of our free-energy simulations confirmed the previously reported experimental results and allowed us to discover a mutant of SUP, specifically the GLU64ASP mutant, that not only binds UO2(2+) more strongly than SUP but that is also more selective for UO2(2+) over other ions. The predictions from the computations were confirmed experimentally.

Orthogonality of spherical harmonic coefficients

NASA Astrophysics Data System (ADS)

McLeod, M. G.

1980-08-01

Orthogonality relations are obtained for the spherical harmonic coefficients of functions defined on the surface of a sphere. Following a brief discussion of the orthogonality of Fourier series coefficients, consideration is given to the values averaged over all orientations of the coordinate system of the spherical harmonic coefficients of a function defined on the surface of a sphere that can be expressed in terms of Legendre polynomials for the special case where the function is the sum of two delta functions located at two different points on the sphere, and for the case of an essentially arbitrary function. It is noted that the orthogonality relations derived have found applications in statistical studies of the geomagnetic field.

Location dependent coordination chemistry and MRI relaxivity, in de novo designed lanthanide coiled coils† †Electronic supplementary information (ESI) available: Methods, peptide characterization data including mass spectrometry and analytical HPLC, sedimentation equilibrium data, circular dichroism, luminescence, and NMR data. See DOI: 10.1039/c5sc04101e

PubMed Central

Berwick, Matthew R.; Slope, Louise N.; Smith, Caitlin F.; King, Siobhan M.; Newton, Sarah L.; Gillis, Richard B.; Adams, Gary G.; Rowe, Arthur J.; Harding, Stephen E.; Britton, Melanie M.

2016-01-01

Herein, we establish for the first time the design principles for lanthanide coordination within coiled coils, and the important consequences of binding site translation. By interrogating design requirements and by systematically translating binding site residues, one can influence coiled coil stability and more importantly, the lanthanide coordination chemistry. A 10 Å binding site translation along a coiled coil, transforms a coordinatively saturated Tb(Asp)3(Asn)3 site into one in which three exogenous water molecules are coordinated, and in which the Asn layer is no longer essential for binding, Tb(Asp)3(H2O)3. This has a profound impact on the relaxivity of the analogous Gd(iii) coiled coil, with more than a four-fold increase in the transverse relaxivity (21 to 89 mM–1 s–1), by bringing into play, in addition to the outer sphere mechanism present for all Gd(iii) coiled coils, an inner sphere mechanism. Not only do these findings warrant further investigation for possible exploitation as MRI contrast agents, but understanding the impact of binding site translation on coordination chemistry has important repercussions for metal binding site design, taking us an important step closer to the predictable and truly de novo design of metal binding sites, for new functional applications. PMID:29899946

On the Intensity of Radiation of an Electromagnetic Field by a Rotating Ferroelectric Sphere

NASA Astrophysics Data System (ADS)

Gladkov, S. O.; Bogdanova, S. B.

2018-05-01

It is shown that in the case when the spontaneous polarization vector P 0 and the rotational frequency vector ω of a ferroelectric sphere do not coincide, electromagnetic waves will be radiated. The intensity of the radiation is calculated as a function of the coordinates and time, and the anisotropy of this radiation is proven. The distribution of the intensity of radiation is graphically illustrated in the form of a function of the central distance r.

The orbital mechanics of flight mechanics

NASA Technical Reports Server (NTRS)

Dunning, R. S.

1973-01-01

A reference handbook on modern dynamic orbit theory is presented. Starting from the most basic inverse-square law, the law of gravity for a sphere is developed, and the motion of point masses under the influence of a sphere is considered. The reentry theory and the orbital theory are discussed along with the relative motion between two bodies in orbit about the same planet. Relative-motion equations, rectangular coordinates, and the mechanics of simple rigid bodies under the influence of a gravity gradient field are also discussed.

A Bridge to Coordination Isomer Selection in Lanthanide(III) DOTA-tetraamide Complexes

PubMed Central

Vipond, Jeff; Woods, Mark; Zhao, Piyu; Tircso, Gyula; Ren, Jimin; Bott, Simon G.; Ogrin, Doug; Kiefer, Garry E.; Kovacs, Zoltan; Sherry, A.Dean

2008-01-01

Interest in macrocyclic lanthanide complexes such as DOTA is driven largely through interest in their use as contrast agents for MRI. The lanthanide tetraamide derivatives of DOTA have shown considerable promise as PARACEST agents, taking advantage of the slow water exchange kinetics of this class of complex. We postulated that water exchange in these tetraamide complexes could be slowed even further by introducing a group to sterically encumber the space above the water coordination site, thereby hindering the departure and approach of water molecules to the complex. The ligand 8O2-bridged-DOTAM was synthesized in a 34% yield from cyclen. It was found that the lanthanide complexes of this ligand did not possess a water molecule in the inner coordination sphere of the bound lanthanide. The crystal structure of the ytterbium complex revealed that distortions to the coordination sphere were induced by the steric constraints imposed on the complex by the bridging unit. The extent of the distortion was found to increase with increasing ionic radius of the lanthanide ion, eventually resulting in a complete loss of symmetry in the complex. Because this ligand system is bicyclic, the conformation of each ring in the system is constrained by that of the other, in consequence inclusion of the bridging unit in the complexes means only a twisted square antiprismatic coordination geometry is observed for complexes of 8O2-bridged-DOTAM. PMID:17295475

Optimum structure of Whipple shield against hypervelocity impact

NASA Astrophysics Data System (ADS)

Lee, M.

2014-05-01

Hypervelocity impact of a spherical aluminum projectile onto two spaced aluminum plates (Whipple shield) was simulated to estimate an optimum structure. The Smooth Particle Hydrodynamics (SPH) code which has a unique migration scheme from a rectangular coordinate to an axisymmetic coordinate was used. The ratio of the front plate thickness to sphere diameter varied from 0.06 to 0.48. The impact velocities considered here were 6.7 km/s. This is the procedure we explored. To guarantee the early stage simulation, the shapes of debris clouds were first compared with the previous experimental pictures, indicating a good agreement. Next, the debris cloud expansion angle was predicted and it shows a maximum value of 23 degree for thickness ratio of front bumper to sphere diameter of 0.23. A critical sphere diameter causing failure of rear wall was also examined while keeping the total thickness of two plates constant. There exists an optimum thickness ratio of front bumper to rear wall, which is identified as a function of the size combination of the impacting body, front and rear plates. The debris cloud expansion-correlated-optimum thickness ratio study provides a good insight on the hypervelocity impact onto spaced target system.

Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of divalent cation binding to phosphatidylserine membranes. Use of cobalt as a paramagnetic probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

McLaughlin, A.C.

1982-01-01

The paramagnetic divalent cation cobalt has large and well-understood effects on NMR signals from ligands bound in the first coordination sphere, i.e., inner-sphere ligands, and the authors have used these effects to identify divalent cation binding sites at the surface of phosphatidylserine membranes. /sup 31/P NMR results show that 13% of the bound cobalt ions are involved in inner-sphere complexes with the phosphodiester group, while /sup 13/C NMR results show that 54% of the bound cobalt ions are involved in unidentate inner sphere complexes with the carboxyl group. No evidence is found for cobalt binding to the carbonyl groups, butmore » proton release studies suggest that 32% of the bound cobalt ions are involved in chelate complexes that contain both the carboxyl and the amine groups. All of the bound cobalt ions can thus be accounted for in terms of inner sphere complexes with the phosphodiester group or the carboxyl group. They suggest that the unidentate inner-sphere complex between cobalt and the carboxyl group of phosphatidylserine and the inner-sphere complex between cobalt and the phosphodiester group of phosphatidylserine provide reasonable models for complexes between alkaline earth cations and phosphatidylserine membranes.« less

Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of divalent cation binding to phosphatidylserine membranes: use of cobalt as a paramagnetic probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

McLaughlin, A.C.

1982-09-28

The paramagnetic divalent cation cobalt has large and well-understood effects on NMR signals from ligands bound in the first coordination sphere, i.e., inner-sphere ligands, and we have used these effects to identify divalent cation binding sites at the surface of phosphatidylserine membranes. /sup 31/P NMR results show that 13% of the bound cobalt ions are involved in inner-sphere complexes with the phosphodiester group, while /sup 13/C NMR results show that 54% of the bound cobalt ions are involved in unidentate inner sphere complexes with the carboxyl group. No evidence is found for cobalt binding to the carbonyl groups, but protonmore » release studies suggest that 32% of the bound cobalt ions are involved in chelate complexes that contain both the carboxyl and the amine groups. All (i.e., 13% + 54% + 32% = 99%) of the bound cobalt ions can thus be accounted for in terms of inner sphere complexes with the phosphodiester group or the carboxyl group. We suggest that the unidentate inner-sphere complex between cobalt and the carboxyl group of phosphatidylserine and the inner-sphere complex between cobalt and the phosphodiester group of phosphatidylserine provide reasonable models for complexes between alkaline earth cations and phosphatidylserine membranes.« less

A generalized orthogonal coordinate system for describing families of axisymmetric and two-dimensional bodies

NASA Technical Reports Server (NTRS)

Gnoffo, P. A.

1977-01-01

A generalized curvilinear orthogonal coordinate system is presented which can be used for approximating various axisymmetric and two-dimensional body shapes of interest to aerodynamicists. Such body shapes include spheres, ellipses, spherically capped cones, flat-faced cylinders with rounded corners, circular disks, and planetary probe vehicles. A set of transformation equations is also developed whereby a uniform velocity field approaching a body at any angle of attack can be resolved in the transformed coordinate system. The Navier-Stokes equations are written in terms of a generalized orthogonal coordinate system to show the resultant complexity of the governing equations.

Shape-controlled synthesis and properties of dandelion-like manganese sulfide hollow spheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Wei; State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083; Chen, Gen

2012-09-15

Graphical abstract: Dandelion-like MnS hollow spheres assembled with nanorods could be successfully synthesized in large quantities through a simple and convenient hydrothermal synthetic method under mild conditions using soluble hydrated manganese chloride as Mn source, L-cysteine as both a precipitator and complexing reagent. The dandelion-like MnS hollow spheres might have potential applications in microdevices and magnetic cells. Highlights: ► MnS hollow spheres assembled with nanorods could be synthesized. ► The morphologies and sizes of final products could be controlled. ► Possible formation mechanism of MnS hollow spheres is proposed. -- Abstract: Dandelion-like gamma-manganese (II) sulfide (MnS) hollow spheres assembled withmore » nanorods have been prepared via a hydrothermal process in the presence of L-cysteine and polyvinylpyrrolidone (PVP). L-cysteine was employed as not only sulfur source, but also coordinating reagent for the synthesis of dandelion-like MnS hollow spheres. The morphology, structure and properties of as-prepared products have been investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and photoluminescence spectra (PL). The probable formation mechanism of as-prepared MnS hollow spheres was discussed on the basis of the experimental results. This strategy may provide an effective method for the fabrication of other metal sulfides hollow spheres.« less

Computational design of a Zn2+ receptor that controls bacterial gene expression

NASA Astrophysics Data System (ADS)

Dwyer, M. A.; Looger, L. L.; Hellinga, H. W.

2003-09-01

The control of cellular physiology and gene expression in response to extracellular signals is a basic property of living systems. We have constructed a synthetic bacterial signal transduction pathway in which gene expression is controlled by extracellular Zn2+. In this system a computationally designed Zn2+-binding periplasmic receptor senses the extracellular solute and triggers a two-component signal transduction pathway via a chimeric transmembrane protein, resulting in transcriptional up-regulation of a -galactosidase reporter gene. The Zn2+-binding site in the designed receptor is based on a four-coordinate, tetrahedral primary coordination sphere consisting of histidines and glutamates. In addition, mutations were introduced in a secondary coordination sphere to satisfy the residual hydrogen-bonding potential of the histidines coordinated to the metal. The importance of the secondary shell interactions is demonstrated by their effect on metal affinity and selectivity, as well as protein stability. Three designed protein sequences, comprising two distinct metal-binding positions, were all shown to bind Zn2+ and to function in the cell-based assay, indicating the generality of the design methodology. These experiments demonstrate that biological systems can be manipulated with computationally designed proteins that have drastically altered ligand-binding specificities, thereby extending the repertoire of genetic control by extracellular signals.

A hardware investigation of robotic SPECT for functional and molecular imaging onboard radiation therapy systems

PubMed Central

Yan, Susu; Bowsher, James; Tough, MengHeng; Cheng, Lin; Yin, Fang-Fang

2014-01-01

Purpose: To construct a robotic SPECT system and to demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch, as a step toward onboard functional and molecular imaging in radiation therapy. Methods: A robotic SPECT imaging system was constructed utilizing a gamma camera detector (Digirad 2020tc) and a robot (KUKA KR150 L110 robot). An imaging study was performed with a phantom (PET CT PhantomTM), which includes five spheres of 10, 13, 17, 22, and 28 mm diameters. The phantom was placed on a flat-top couch. SPECT projections were acquired either with a parallel-hole collimator or a single-pinhole collimator, both without background in the phantom and with background at 1/10th the sphere activity concentration. The imaging trajectories of parallel-hole and pinhole collimated detectors spanned 180° and 228°, respectively. The pinhole detector viewed an off-centered spherical common volume which encompassed the 28 and 22 mm spheres. The common volume for parallel-hole system was centered at the phantom which encompassed all five spheres in the phantom. The maneuverability of the robotic system was tested by navigating the detector to trace the phantom and flat-top table while avoiding collision and maintaining the closest possible proximity to the common volume. The robot base and tool coordinates were used for image reconstruction. Results: The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector radius of rotation. Without background, all five spheres were visible in the reconstructed parallel-hole image, while four spheres, all except the smallest one, were visible in the reconstructed pinhole image. With background, three spheres of 17, 22, and 28 mm diameters were readily observed with the parallel-hole imaging, and the targeted spheres (22 and 28 mm diameters) were readily observed in the pinhole region-of-interest imaging. Conclusions: Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frames could be an effective means to estimate detector pose for use in SPECT image reconstruction. PMID:25370663

A hardware investigation of robotic SPECT for functional and molecular imaging onboard radiation therapy systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Susu, E-mail: susu.yan@duke.edu; Tough, MengHeng; Bowsher, James

Purpose: To construct a robotic SPECT system and to demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch, as a step toward onboard functional and molecular imaging in radiation therapy. Methods: A robotic SPECT imaging system was constructed utilizing a gamma camera detector (Digirad 2020tc) and a robot (KUKA KR150 L110 robot). An imaging study was performed with a phantom (PET CT Phantom{sup TM}), which includes five spheres of 10, 13, 17, 22, and 28 mm diameters. The phantom was placed on a flat-top couch. SPECT projections were acquired either with a parallel-hole collimator ormore » a single-pinhole collimator, both without background in the phantom and with background at 1/10th the sphere activity concentration. The imaging trajectories of parallel-hole and pinhole collimated detectors spanned 180° and 228°, respectively. The pinhole detector viewed an off-centered spherical common volume which encompassed the 28 and 22 mm spheres. The common volume for parallel-hole system was centered at the phantom which encompassed all five spheres in the phantom. The maneuverability of the robotic system was tested by navigating the detector to trace the phantom and flat-top table while avoiding collision and maintaining the closest possible proximity to the common volume. The robot base and tool coordinates were used for image reconstruction. Results: The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector radius of rotation. Without background, all five spheres were visible in the reconstructed parallel-hole image, while four spheres, all except the smallest one, were visible in the reconstructed pinhole image. With background, three spheres of 17, 22, and 28 mm diameters were readily observed with the parallel-hole imaging, and the targeted spheres (22 and 28 mm diameters) were readily observed in the pinhole region-of-interest imaging. Conclusions: Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frames could be an effective means to estimate detector pose for use in SPECT image reconstruction.« less

Retuning the Catalytic Bias and Overpotential of a [NiFe]-Hydrogenase via a Single Amino Acid Exchange at the Electron Entry/Exit Site

PubMed Central

2017-01-01

The redox chemistry of the electron entry/exit site in Escherichia coli hydrogenase-1 is shown to play a vital role in tuning biocatalysis. Inspired by nature, we generate a HyaA-R193L variant to disrupt a proposed Arg–His cation−π interaction in the secondary coordination sphere of the outermost, “distal”, iron–sulfur cluster. This rewires the enzyme, enhancing the relative rate of H2 production and the thermodynamic efficiency of H2 oxidation catalysis. On the basis of Fourier transformed alternating current voltammetry measurements, we relate these changes in catalysis to a shift in the distal [Fe4S4]2+/1+ redox potential, a previously experimentally inaccessible parameter. Thus, metalloenzyme chemistry is shown to be tuned by the second coordination sphere of an electron transfer site distant from the catalytic center. PMID:28697596

Panoramic stereo sphere vision

NASA Astrophysics Data System (ADS)

Feng, Weijia; Zhang, Baofeng; Röning, Juha; Zong, Xiaoning; Yi, Tian

2013-01-01

Conventional stereo vision systems have a small field of view (FOV) which limits their usefulness for certain applications. While panorama vision is able to "see" in all directions of the observation space, scene depth information is missed because of the mapping from 3D reference coordinates to 2D panoramic image. In this paper, we present an innovative vision system which builds by a special combined fish-eye lenses module, and is capable of producing 3D coordinate information from the whole global observation space and acquiring no blind area 360°×360° panoramic image simultaneously just using single vision equipment with one time static shooting. It is called Panoramic Stereo Sphere Vision (PSSV). We proposed the geometric model, mathematic model and parameters calibration method in this paper. Specifically, video surveillance, robotic autonomous navigation, virtual reality, driving assistance, multiple maneuvering target tracking, automatic mapping of environments and attitude estimation are some of the applications which will benefit from PSSV.

Polynuclear Speciation of Trivalent Cations near the Surface of an Electrolyte Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bera, Mrinal K.; Antonio, Mark R.

Despite long-standing efforts, there is no agreed upon structural model for electrolyte solutions at air-liquid interfaces. We report the simultaneous detection of the near-surface and bulk coordination environments of a trivalent metal cation (europium) in an aqueous solution by use of X-ray absorption spectroscopy. Within the first few nanometers of the liquid surface, the cations exhibit oxygen coordination typical of inner-sphere hydration of an aquated Eu3+ cation. Beyond that, outer-sphere ion-ion correlations are observed that are otherwise not present in the bulk electrolyte. The combination of near-surface and bulk sensitivities to probe metal ion speciation in electrolyte solutions is achievedmore » by detecting electron-yield and X-ray fluorescence signals from an inverted pendant drop. The results provide new knowledge about the near-surface chemistry of aqueous solutions of relevance to aerosols and ion transport processes in chemical separations and biological systems.« less

Controlling Second Coordination Sphere Effects in Luminescent Ruthenium Complexes by Means of External Pressure.

PubMed

Pannwitz, Andrea; Poirier, Stéphanie; Bélanger-Desmarais, Nicolas; Prescimone, Alessandro; Wenger, Oliver S; Reber, Christian

2018-06-04

Two luminescent heteroleptic Ru II complexes with a 2,2'-biimidazole (biimH 2 ) ligand form doubly hydrogen-bonded salt bridges to 4-sulfobenzoate anions in single crystals. The structure of one of these cation-anion adducts shows that the biimH 2 ligand is deprotonated. Its 3 MLCT luminescence band does not shift significantly under the influence of an external hydrostatic pressure, a behavior typical for these electronic transitions. In contrast, hydrostatic pressure on the other crystalline cation-anion adduct induces a shift of proton density from the peripheral N-H groups of biimH 2 towards benzoate, leading to a pronounced redshift of the 3 MLCT luminescence band. Such a significant and pressure-tunable influence from an interaction in the second coordination sphere is unprecedented in artificial small-molecule-based systems. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of zinc binding sites in protein crystal structures.

PubMed

Alberts, I L; Nadassy, K; Wodak, S J

1998-08-01

The geometrical properties of zinc binding sites in a dataset of high quality protein crystal structures deposited in the Protein Data Bank have been examined to identify important differences between zinc sites that are directly involved in catalysis and those that play a structural role. Coordination angles in the zinc primary coordination sphere are compared with ideal values for each coordination geometry, and zinc coordination distances are compared with those in small zinc complexes from the Cambridge Structural Database as a guide of expected trends. We find that distances and angles in the primary coordination sphere are in general close to the expected (or ideal) values. Deviations occur primarily for oxygen coordinating atoms and are found to be mainly due to H-bonding of the oxygen coordinating ligand to protein residues, bidentate binding arrangements, and multi-zinc sites. We find that H-bonding of oxygen containing residues (or water) to zinc bound histidines is almost universal in our dataset and defines the elec-His-Zn motif. Analysis of the stereochemistry shows that carboxyl elec-His-Zn motifs are geometrically rigid, while water elec-His-Zn motifs show the most geometrical variation. As catalytic motifs have a higher proportion of carboxyl elec atoms than structural motifs, they provide a more rigid framework for zinc binding. This is understood biologically, as a small distortion in the zinc position in an enzyme can have serious consequences on the enzymatic reaction. We also analyze the sequence pattern of the zinc ligands and residues that provide elecs, and identify conserved hydrophobic residues in the endopeptidases that also appear to contribute to stabilizing the catalytic zinc site. A zinc binding template in protein crystal structures is derived from these observations.

Pleomorphic copper coordination by Alzheimer's disease amyloid-beta peptide.

PubMed

Drew, Simon C; Noble, Christopher J; Masters, Colin L; Hanson, Graeme R; Barnham, Kevin J

2009-01-28

Numerous conflicting models have been proposed regarding the nature of the Cu(2+) coordination environment of the amyloid beta (Abeta) peptide, the causative agent of Alzheimer's disease. This study used multifrequency CW-EPR spectroscopy to directly resolve the superhyperfine interactions between Cu(2+) and the ligand nuclei of Abeta, thereby avoiding ambiguities associated with introducing point mutations. Using a library of Abeta16 analogues with site-specific (15)N-labeling at Asp1, His6, His13, and His14, numerical simulations of the superhyperfine resonances delineated two independent 3N1O Cu(2+) coordination modes, {N(a)(D1), O, N(epsilon)(H6), N(epsilon)(H13)} (component Ia) and {N(a)(D1), O, N(epsilon)(H6), N(epsilon)(H14)} (component Ib), between pH 6-7. A third coordination mode (component II) was identified at pH 8.0, and simulation of the superhyperfine resonances indicated a 3N1O coordination sphere involving nitrogen ligation by His6, His13, and His14. No differences were observed upon (17)O-labeling of the phenolic oxygen of Tyr10, confirming it is not a key oxygen ligand in the physiological pH range. Hyperfine sublevel correlation (HYSCORE) spectroscopy, in conjunction with site-specific (15)N-labeling, provided additional support for the common role of His6 in components Ia and Ib, and for the assignment of a {O, N(epsilon)(H6), N(epsilon)(H13), N(epsilon)(H14)} coordination sphere to component II. HYSCORE studies of a peptide analogue with selective (13)C-labeling of Asp1 revealed (13)C cross-peaks characteristic of equatorial coordination by the carboxylate oxygen of Asp1 in component Ia/b coordination. The direct resolution of Cu(2+) ligand interactions, together with the key finding that component I is composed of two distinct coordination modes, provides valuable insight into a range of conflicting ligand assignments and highlights the complexity of Cu(2+)/Abeta interactions.

Measurement of the translation and rotation of a sphere in fluid flow

NASA Astrophysics Data System (ADS)

Barros, Diogo; Hiltbrand, Ben; Longmire, Ellen K.

2018-06-01

The problem of determining the translation and rotation of a spherical particle moving in fluid flow is considered. Lagrangian tracking of markers printed over the surface of a sphere is employed to compute the center motion and the angular velocity of the solid body. The method initially calculates the sphere center from the 3D coordinates of the reconstructed markers, then finds the optimal rotation matrix that aligns a set of markers tracked at sequential time steps. The parameters involved in the experimental implementation of this procedure are discussed, and the associated uncertainty is estimated from numerical analysis. Finally, the proposed methodology is applied to characterize the motion of a large spherical particle released in a turbulent boundary layer developing in a water channel.

Cation-Dependent Gold Recovery with α-Cyclodextrin Facilitated by Second-Sphere Coordination.

PubMed

Liu, Zhichang; Samanta, Avik; Lei, Juying; Sun, Junling; Wang, Yuping; Stoddart, J Fraser

2016-09-14

Herein, we report an alkali metal cation-dependent approach to gold recovery, facilitated by second-sphere coordination with eco-friendly α-cyclodextrin (α-CD). Upon mixing eight salts composed of Na(+), K(+), Rb(+), or Cs(+) cations and [AuX4](-) (X = Cl/Br) anions with α-, β-, or γ-CD in water, co-precipitates form selectively from the three (out of 24) aqueous solutions containing α-CD with KAuBr4, RbAuBr4, and CsAuBr4, from which the combination of α-CD and KAuBr4 affords the highest yield. Single-crystal X-ray analyses reveal that in 20 of the 24 adducts CD and [AuX4](-) anions form 2:1 sandwich-type second-sphere adducts driven partially by [C-H···X-Au] interactions between [AuX4](-) anions and the primary faces of two neighboring CDs. In the adduct formed between α-CD and KAuBr4, a [K(OH2)6](+) cation is encapsulated inside the cavity between the secondary faces of two α-CDs, leading to highly efficient precipitation owing to the formation of a cation/anion alternating ion wire residing inside a continuous α-CD nanotube. By contrast, in the other 19 adducts, the cations are coordinated by OH groups and glucopyranosyl ring O atoms in CDs. The strong coordination of Rb(+) and Cs(+) cations by these ligands, in conjunction with the stereoelectronically favorable binding of [AuBr4](-) anions with two α-CDs, facilitates the co-precipitation of the two adducts formed between α-CD with RbAuBr4 and CsAuBr4. In order to develop an efficient process for green gold recovery, the co-precipitation yield of α-CD and KAuBr4 has been optimized regarding both the temperature and the molar ratio of α-CD to KAuBr4.

Coordination Chemistry of Homoleptic Actinide(IV)-Thiocyanate Complexes

DOE PAGES

Carter, Tyler J.; Wilson, Richard E.

2015-09-10

Here, the synthesis, X-ray crystal structure, vibrational and optical spectroscopy for the eight-coordinate thiocyanate compounds, [Et 4N] 4[Pu IV(NCS) 8], [Et 4N] 4[Th IV(NCS) 8], and [Et 4N] 4[Ce III(NCS) 7(H 2O)] are reported. Thiocyanate was found to rapidly reduce plutonium to Pu III in acidic solutions (pH<1) in the presence of NCS –. The optical spectrum of [Et 4N][SCN] containing Pu III solution was indistinguishable from that of aquated Pu III suggesting that inner-sphere complexation with [Et 4N][SCN] does not occur in water. However, upon concentration, the homoleptic thiocyanate complex [Et 4N] 4[Pu IV(NCS) 8] was crystallized when amore » large excess of [Et 4N][NCS] was present. This compound, along with its U IV analogue, maintains inner-sphere thiocyanate coordination in acetonitrile based on the observation of intense ligand-to-metal charge-transfer bands. Spectroscopic and crystallographic data do not support the interaction of the metal orbitals with the ligand π system, but support an enhanced An IV–NCS interaction, as the Lewis acidity of the metal ion increases from Th to Pu.« less

Spectroscopic Characterization of YedY: The Role of Sulfur Coordination in a Mo(V) Sulfite Oxidase Family Enzyme Form

PubMed Central

Yang, Jing; Rothery, Richard; Sempombe, Joseph

2011-01-01

Electronic paramagnetic resonance, electronic absorption, and magnetic circular dichroism spectroscopies have been performed on YedY, a SUOX fold protein with a Mo domain that is remarkably similar to that found in chicken sulfite oxidase, A. thaliana plant sulfite oxidase, and the bacterial sulfite dehydrogenase from S. novella. Low-energy dithiolene→Mo and cysteine thiolate→Mo charge transfer bands have been assigned for the first time in a Mo(V) form of a SUOX fold protein, and the spectroscopic data have been used to interpret the results of bonding calculations. The analysis shows that second coordination sphere effects modulate dithiolene and cysteine sulfur covalency contributions to the Mo bonding scheme. Namely, a more acute Ooxo-Mo-SCys-C dihedral angle results in increased cysteine thiolate S→Mo charge transfer and a high g1 in the EPR spectrum. The spectrosocopic results, coupled with the available structural data, indicate that these second coordination sphere effects may play key roles in modulating the active site redox potential, facilitating hole superexchange pathways for electron transfer regeneration, and affecting the type of reactions catalyzed by sulfite oxidase family enzymes. PMID:19860477

Ligand-Sensitive But Not Ligand-Diagnostic: Evaluating Cr Valence-to-Core X-ray Emission Spectroscopy as a Probe of Inner-Sphere Coordination

PubMed Central

2015-01-01

This paper explores the strengths and limitations of valence-to-core X-ray emission spectroscopy (V2C XES) as a probe of coordination environments. A library was assembled from spectra obtained for 12 diverse Cr complexes and used to calibrate density functional theory (DFT) calculations of V2C XES band energies. A functional dependence study was undertaken to benchmark predictive accuracy. All 7 functionals tested reproduce experimental V2C XES energies with an accuracy of 0.5 eV. Experimentally calibrated, DFT calculated V2C XES spectra of 90 Cr compounds were used to produce a quantitative spectrochemical series showing the V2C XES band energy ranges for ligands comprising 18 distinct classes. Substantial overlaps are detected in these ranges, which complicates the use of V2C XES to identify ligands in the coordination spheres of unknown Cr compounds. The ligand-dependent origins of V2C intensity are explored for a homologous series of [CrIII(NH3)5X]2+ (X = F, Cl, Br, and I) to rationalize the variable intensity contributions of these ligand classes. PMID:25496512

Ag/α-Fe{sub 2}O{sub 3} hollow microspheres: Preparation and application for hydrogen peroxide detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Xinyuan; Wu, Zhiping; Liao, Fang, E-mail: liaozhang2003@163.com

2015-09-15

In this paper, we demonstrated a simple approach for preparing α-Fe{sub 2}O{sub 3} hollow spheres by mixing ferric nitrate aqueous and glucose in 180 °C. The glucose was found to act as a soft template in the process of α-Fe{sub 2}O{sub 3} hollow spheres formation. Ag/α-Fe{sub 2}O{sub 3} hollow nanocomposite was obtained under UV irradiation without additional reducing agents or initiators. Synthesized Ag/α-Fe{sub 2}O{sub 3} hollow composites exhibited remarkable catalytic performance toward H{sub 2}O{sub 2} reduction. The electrocatalytic activity mechanism of Ag/α-Fe{sub 2}O{sub 3}/GCE were discussed toward the reduction of H{sub 2}O{sub 2} in this paper. - Graphical abstract: Glucosemore » is carbonized as carbon balls in the 180 °C hydrothermal carbonization process, which plays a role of a soft template. Carbon spherical shell is rich in many hydroxyls, which have good hydrophilicity and surface reactivity. When Fe(NO{sub 3}){sub 3} is added to the aqueous solution of Glucose, the hydrophilic -OH will adsorb Fe{sup 3+} to form coordination compound by coordination bond. α-FeOOH is formed on the surface of carbon balls by hydrothermal reaction. After calcination at 500 °C, carbon spheres react with oxygen to form carbon dioxide, which disappears in the air. Meanwhile α-FeOOH is calcined to form α-Fe{sub 2}O{sub 3} hollow spheres.« less

[Topical issues of biological safety under current conditions. Part 3. Scientific provision for the national regulation of the biological safety framework in its broad interpretation].

PubMed

Onishchenko, G G; Smolensky, V Yu; Ezhlova, E B; Demina, Yu V; Toporkov, V P; Toporkov, A V; Lyapin, M N; Kutyrev, V V

2014-01-01

Consequent of investigation concerned with biological safety (BS) framework development in its broad interpretation, reflected in the Russian Federation State Acts, identified have been conceptual entity parameters of the up-to-date broad interpretation of BS, which have formed a part of the developed by the authors system for surveillance (prophylaxis, localization, indication, identification, and diagnostics) and control (prophylaxis, localization, and response/elimination) over the emergency situations of biological (sanitary-epidemiological) character. The System functionality is activated through supplying the content with information data which are concerned with monitoring and control of specific internal and external threats in the sphere of BS provision fixed in the Supplement 2 of the International Health Regulations (IHR, 2005), and with the previously characterized nomenclature of hazardous biological factors. The system is designed as a network-based research-and-practice tool for evaluation of the situation in the sphere of BS provision, as well as assessment of efficacy of management decision making as regards BS control and proper State policy implementation. Most of the system elements either directly or indirectly relate to the scope of activities conducted by Federal Service for Surveillance in the Sphere of Consumers Rights Protection and Human Welfare, being substantial argument for allocating coordination functions in the sphere of BS provision to this government agency and consistent with its function as the State Coordinator on IHR (2005). The data collected serve as materials to Draft Federal Law "Concerning biological safety provision of the population".

Review on the Celestial Sphere Positioning of FITS Format Image Based on WCS and Research on General Visualization

NASA Astrophysics Data System (ADS)

Song, W. M.; Fan, D. W.; Su, L. Y.; Cui, C. Z.

2017-11-01

Calculating the coordinate parameters recorded in the form of key/value pairs in FITS (Flexible Image Transport System) header is the key to determine FITS images' position in the celestial system. As a result, it has great significance in researching the general process of calculating the coordinate parameters. By combining CCD related parameters of astronomical telescope (such as field, focal length, and celestial coordinates in optical axis, etc.), astronomical images recognition algorithm, and WCS (World Coordinate System) theory, the parameters can be calculated effectively. CCD parameters determine the scope of star catalogue, so that they can be used to build a reference star catalogue by the corresponding celestial region of astronomical images; Star pattern recognition completes the matching between the astronomical image and reference star catalogue, and obtains a table with a certain number of stars between CCD plane coordinates and their celestial coordinates for comparison; According to different projection of the sphere to the plane, WCS can build different transfer functions between these two coordinates, and the astronomical position of image pixels can be determined by the table's data we have worked before. FITS images are used to carry out scientific data transmission and analyze as a kind of mainstream data format, but only to be viewed, edited, and analyzed in the professional astronomy software. It decides the limitation of popular science education in astronomy. The realization of a general image visualization method is significant. FITS is converted to PNG or JPEG images firstly. The coordinate parameters in the FITS header are converted to metadata in the form of AVM (Astronomy Visualization Metadata), and then the metadata is added to the PNG or JPEG header. This method can meet amateur astronomers' general needs of viewing and analyzing astronomical images in the non-astronomical software platform. The overall design flow is realized through the java program and tested by SExtractor, WorldWide Telescope, picture viewer, and other software.

Acoustical Scattering from an Elastic Sphere in Water: Surface Wave Glory, Resonances, and the Sommerfeld-Watson Transformation for Amplitudes

DTIC Science & Technology

1985-08-01

travels around the sphere (indicated by the dotted rays in Fig. 3). At the point• 2 energy is reradiated into the liquid in the direction of the receiver P...loaded elastic cylinder. 3 58 Using the coordinate system shown in Fig. 1 and au~uing a unit amplitude plane wave traveling in the +t direction the...reflection measured relative to a wave traveling in liquid alon1- the path (r ’ ’., e = 7) (r 0) -0 (r = 9, a ir--y). We have previously obtained results

Alkaline transition of pseudoazurin Met16X mutant proteins: protein stability influenced by the substitution of Met16 in the second sphere coordination.

PubMed

Abdelhamid, Rehab F; Obara, Yuji; Kohzuma, Takamitsu

2008-01-01

Several blue copper proteins are known to change the active site structure at alkaline pH (alkaline transition). Spectroscopic studies of Met16Phe, Met16Tyr, Met16Trp, and Met16Val pseudoazurin variants were performed to investigate the second sphere role through alkaline transition. The visible electronic absorption and resonance Raman spectra of Met16Phe, Met16Tyr, and Met16Trp variants showed the increasing of axial component at pH approximately 11 like wild-type PAz. The visible electronic absorption and far-UV CD spectra of Met16Val demonstrated that the destabilization of the protein structure was triggered at pH>11. Resonance Raman (RR) spectra of PAz showed that the intensity-weighted averaged Cu-S(Cys) stretching frequency was shifted to higher frequency region at pH approximately 11. The higher frequency shift of Cu-S(Cys) bond is implied the stronger Cu-S(Cys) bond at alkaline transition pH approximately 11. The visible electronic absorption and far-UV CD spectra of Met16X PAz revealed that the Met16Val variant is denatured at pH>11, but Met16Phe, Met16Tyr, and Met16Trp mutant proteins are not denatured even at pH>11. These observations suggest that Met16 is important to maintain the protein structure through the possible weak interaction between methionine -SCH3 part and coordinated histidine imidazole moiety. The introduction of pi-pi interaction in the second coordination sphere may be contributed to the enhancement of protein structure stability.

Results of the NIST National Ball Plate Round Robin.

PubMed

Caskey, G W; Phillips, S D; Borchardt, B R

1997-01-01

This report examines the results of the ball plate round robin administered by NIST. The round robin was part of an effort to assess the current state of industry practices for measurements made using coordinate measuring machines. Measurements of a two-dimensional ball plate (240 mm by 240 mm) on 41 coordinate measuring machines were collected and analyzed. Typically, the deviations of the reported X and Y coordinates from the calibrated values were within ± 5 μm, with some coordinate deviations exceeding 20.0 μm. One of the most significant observations from these data was that over 75 % of the participants failed to correctly estimate their measurement error on one or more of the ball plate spheres.

The reduction, verification and interpretation of MAGSAT magnetic data over Canada

NASA Technical Reports Server (NTRS)

Coles, R. L. (Principal Investigator); Haines, G. V.; Vanbeek, G. J.; Walker, J. K.; Newitt, L. R.

1982-01-01

Consideration is being given to representing the magnetic field in the area 40 deg N to 83 deg N by means of functions in spherical coordinates. A solution to Laplace's equation for the magnetic potential over a restricted area was found, and programming and testing are currently being carried out. Magnetic anomaly modelling is proceeding. The program SPHERE, which was adapted to function correctly on the Cyber computer, is now operational, for deriving gravity and magnetic models in a spherical coordinate system.

Connes distance function on fuzzy sphere and the connection between geometry and statistics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devi, Yendrembam Chaoba, E-mail: chaoba@bose.res.in; Chakraborty, Biswajit, E-mail: biswajit@bose.res.in; Prajapat, Shivraj, E-mail: shraprajapat@gmail.com

An algorithm to compute Connes spectral distance, adaptable to the Hilbert-Schmidt operatorial formulation of non-commutative quantum mechanics, was developed earlier by introducing the appropriate spectral triple and used to compute infinitesimal distances in the Moyal plane, revealing a deep connection between geometry and statistics. In this paper, using the same algorithm, the Connes spectral distance has been calculated in the Hilbert-Schmidt operatorial formulation for the fuzzy sphere whose spatial coordinates satisfy the su(2) algebra. This has been computed for both the discrete and the Perelemov’s SU(2) coherent state. Here also, we get a connection between geometry and statistics which ismore » shown by computing the infinitesimal distance between mixed states on the quantum Hilbert space of a particular fuzzy sphere, indexed by n ∈ ℤ/2.« less

It All Depends on Your Attitude.

ERIC Educational Resources Information Center

Kastner, Bernice

1992-01-01

Presents six learning exercises that introduce students to the mathematics used to control and track spacecraft attitude. Describes the geocentric system used for Earthbound location and navigation, the celestial sphere, the spacecraft-based celestial system, time-dependent angles, observer-fixed coordinate axes, and spacecraft rotational axes.…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Shiliang; Liu, Jing; Cowley, Ryan E.

Here, S-Nitrosothiols are known as reagents for NO storage and transportation and as regulators in many physiological processes. Although the S-nitrosylation catalysed by haem proteins is well known, no direct evidence of S-nitrosylation in copper proteins has been reported. Here, we report reversible insertion of NO into a copper–thiolate bond in an engineered copper centre in Pseudomonas aeruginosa azurin by rational design of the primary coordination sphere and tuning its reduction potential by deleting a hydrogen bond in the secondary coordination sphere. The results not only provide the first direct evidence of S-nitrosylation of Cu(II)-bound cysteine in metalloproteins, but alsomore » shed light on the reaction mechanism and structural features responsible for stabilizing the elusive Cu(I)–S(Cys)NO species. The fast, efficient and reversible S-nitrosylation reaction is used to demonstrate its ability to prevent NO inhibition of cytochrome bo 3 oxidase activity by competing for NO binding with the native enzyme under physiologically relevant conditions.« less

Modulation of Active Site Electronic Structure by the Protein Matrix to Control [NiFe] Hydrogenase Reactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Dayle MA; Raugei, Simone; Squier, Thomas C.

2014-09-30

Control of the reactivity of the nickel center of the [NiFe] hydrogenase and other metalloproteins commonly involves outer coordination sphere ligands that act to modify the geometry and physical properties of the active site metal centers. We carried out a combined set of classical molecular dynamics and quantum/classical mechanics calculations to provide quantitative estimates of how dynamic fluctuations of the active site within the protein matrix modulate the electronic structure at the catalytic center. Specifically we focused on the dynamics of the inner and outer coordination spheres of the cysteinate-bound Ni–Fe cluster in the catalytically active Ni-C state. There aremore » correlated movements of the cysteinate ligands and the surrounding hydrogen-bonding network, which modulate the electron affinity at the active site and the proton affinity of a terminal cysteinate. On the basis of these findings, we hypothesize a coupling between protein dynamics and electron and proton transfer reactions critical to dihydrogen production.« less

Modulation of active site electronic structure by the protein matrix to control [NiFe] hydrogenase reactivity.

PubMed

Smith, Dayle M A; Raugei, Simone; Squier, Thomas C

2014-11-21

Control of the reactivity of the nickel center of the [NiFe] hydrogenase and other metalloproteins commonly involves outer coordination sphere ligands that act to modify the geometry and physical properties of the active site metal centers. We carried out a combined set of classical molecular dynamics and quantum/classical mechanics calculations to provide quantitative estimates of how dynamic fluctuations of the active site within the protein matrix modulate the electronic structure at the catalytic center. Specifically we focused on the dynamics of the inner and outer coordination spheres of the cysteinate-bound Ni-Fe cluster in the catalytically active Ni-C state. There are correlated movements of the cysteinate ligands and the surrounding hydrogen-bonding network, which modulate the electron affinity at the active site and the proton affinity of a terminal cysteinate. On the basis of these findings, we hypothesize a coupling between protein dynamics and electron and proton transfer reactions critical to dihydrogen production.

Geometric interpretation of four-wave mixing

NASA Astrophysics Data System (ADS)

Ott, J. R.; Steffensen, H.; Rottwitt, K.; McKinstrie, C. J.

2013-10-01

The nonlinear phenomenon of four-wave mixing (FWM) is investigated using a method, where, without the need of calculus, both phase and amplitudes of the mixing fields are visualized simultaneously, giving a complete overview of the FWM dynamics. This is done by introducing a set of Stokes-like coordinates of the electric fields, which reduce the FWM dynamics to a closed two-dimensional surface, similar to the Bloch sphere of quantum electrodynamics or the Pointcaré sphere in polarization dynamics. The coordinates are chosen so as to use the gauge invariance symmetries of the FWM equations which also give the conservation of action flux known as the Manley-Rowe relations. This reduces the dynamics of FWM to the one-dimensional intersection between the closed two-dimensional surface and the phase-plane given by the conserved Hamiltonian. The analysis is advantageous for visualizing phase-dependent FWM phenomena which are found in a large variety of nonlinear systems and even in various optical communication schemes.

Reversible S-nitrosylation in an engineered azurin

DOE PAGES

Tian, Shiliang; Liu, Jing; Cowley, Ryan E.; ...

2016-04-25

Here, S-Nitrosothiols are known as reagents for NO storage and transportation and as regulators in many physiological processes. Although the S-nitrosylation catalysed by haem proteins is well known, no direct evidence of S-nitrosylation in copper proteins has been reported. Here, we report reversible insertion of NO into a copper–thiolate bond in an engineered copper centre in Pseudomonas aeruginosa azurin by rational design of the primary coordination sphere and tuning its reduction potential by deleting a hydrogen bond in the secondary coordination sphere. The results not only provide the first direct evidence of S-nitrosylation of Cu(II)-bound cysteine in metalloproteins, but alsomore » shed light on the reaction mechanism and structural features responsible for stabilizing the elusive Cu(I)–S(Cys)NO species. The fast, efficient and reversible S-nitrosylation reaction is used to demonstrate its ability to prevent NO inhibition of cytochrome bo 3 oxidase activity by competing for NO binding with the native enzyme under physiologically relevant conditions.« less

Increasing the rate of hydrogen oxidation without increasing the overpotential: A bio-inspired iron molecular electrocatalyst with an outer coordination sphere proton relay

DOE PAGES

Darmon, Jonathan M.; Kumar, Neeraj; Hulley, Elliott B.; ...

2015-03-05

Oxidation of hydrogen (H₂) to protons and electrons for energy production in fuel cells is catalyzed by platinum, but its low abundance and high cost present drawbacks to widespread adoption. Precisely controlled proton delivery and removal is critical in hydrogenase enzymes in nature that catalyze H₂ oxidation using earth-abundant metals (iron and nickel). Here we report a synthetic iron complex, (Cp C5F4N)Fe(P EtN (CH2)3NMe2PEt)(Cl), that serves as a precatalyst for the oxidation of H₂, with turnover frequencies of 290 s⁻¹ in fluorobenzene, under 1 atm of H₂ using 1,4-diazabicyclo[2.2.2]octane (DABCO) as the exogenous base. The cooperative effect of the primary,more » secondary and outer coordination spheres for moving protons in this remarkably fast catalyst emphasizes the key role of pendant amines in mimicking the functionality of the proton pathway in the hydrogenase enzymes.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffeditz, William L.; Katz, Michael J.; Deria, Pravas

Dye-sensitized solar cells (DSCs) are an established alternative photovoltaic technology that offers numerous potential advantages in solar energy applications. However, this technology has been limited by the availability of molecular redox couples that are both noncorrosive/nontoxic and do not diminish the performance of the device. In an effort to overcome these shortcomings, a copper-containing redox shuttle derived from 1,8-bis(2'-pyridyl)-3,6-dithiaoctane (PDTO) ligand and the common DSC additive 4-tert-butylpyridine (TBP) was investigated. Electrochemical measurements, single-crystal X-ray diffraction, and absorption and electron paramagnetic resonance spectroscopies reveal that, upon removal of one metal-centered electron, PDTO-enshrouded copper ions completely shed the tetradentate PDTO ligand andmore » replace it with four or more TBP ligands. Thus, the Cu(I) and Cu(II) forms of the electron shuttle have completely different coordination spheres and are characterized by widely differing Cu(II/I) formal potentials and reactivities for forward versus reverse electron transfer. Notably, the coordination-sphere replacement process is fully reversed upon converting Cu(II) back to Cu(I). In cells featuring an adsorbed organic dye and a nano- and mesoparticulate, TiO2-based, photoelectrode, the dual species redox shuttle system engenders performance superior to that obtained with shuttles based on the (II/I) forms of either of the coordination complexes in isolation.« less

From sticky-hard-sphere to Lennard-Jones-type clusters

NASA Astrophysics Data System (ADS)

Trombach, Lukas; Hoy, Robert S.; Wales, David J.; Schwerdtfeger, Peter

2018-04-01

A relation MSHS →LJ between the set of nonisomorphic sticky-hard-sphere clusters MSHS and the sets of local energy minima ML J of the (m ,n ) -Lennard-Jones potential Vmn LJ(r ) =ɛ/n -m [m r-n-n r-m] is established. The number of nonisomorphic stable clusters depends strongly and nontrivially on both m and n and increases exponentially with increasing cluster size N for N ≳10 . While the map from MSHS→MSHS →LJ is noninjective and nonsurjective, the number of Lennard-Jones structures missing from the map is relatively small for cluster sizes up to N =13 , and most of the missing structures correspond to energetically unfavorable minima even for fairly low (m ,n ) . Furthermore, even the softest Lennard-Jones potential predicts that the coordination of 13 spheres around a central sphere is problematic (the Gregory-Newton problem). A more realistic extended Lennard-Jones potential chosen from coupled-cluster calculations for a rare gas dimer leads to a substantial increase in the number of nonisomorphic clusters, even though the potential curve is very similar to a (6,12)-Lennard-Jones potential.

From sticky-hard-sphere to Lennard-Jones-type clusters.

PubMed

Trombach, Lukas; Hoy, Robert S; Wales, David J; Schwerdtfeger, Peter

2018-04-01

A relation M_{SHS→LJ} between the set of nonisomorphic sticky-hard-sphere clusters M_{SHS} and the sets of local energy minima M_{LJ} of the (m,n)-Lennard-Jones potential V_{mn}^{LJ}(r)=ɛ/n-m[mr^{-n}-nr^{-m}] is established. The number of nonisomorphic stable clusters depends strongly and nontrivially on both m and n and increases exponentially with increasing cluster size N for N≳10. While the map from M_{SHS}→M_{SHS→LJ} is noninjective and nonsurjective, the number of Lennard-Jones structures missing from the map is relatively small for cluster sizes up to N=13, and most of the missing structures correspond to energetically unfavorable minima even for fairly low (m,n). Furthermore, even the softest Lennard-Jones potential predicts that the coordination of 13 spheres around a central sphere is problematic (the Gregory-Newton problem). A more realistic extended Lennard-Jones potential chosen from coupled-cluster calculations for a rare gas dimer leads to a substantial increase in the number of nonisomorphic clusters, even though the potential curve is very similar to a (6,12)-Lennard-Jones potential.

Synchronized Position Hold, Engage, Reorient, Experimental Satellites

NASA Technical Reports Server (NTRS)

Miller, David W.; Wilson, Edward; How, Jonathan; Sanenz-Otero, Alvar; Chamitoff, Gregory

2009-01-01

Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) are bowling-ball sized spherical satellites. They will be used inside the space station to test a set of well-defined instructions for spacecraft performing autonomous rendezvous and docking maneuvers. Three free-flying spheres will fly within the cabin of the station, performing flight formations. Each satellite is self-contained with power, propulsion, computers and navigation equipment. The results are important for satellite servicing, vehicle assembly and formation flying spacecraft configurations. SPHERES is a testbed for formation flying by satellites, the theories and calculations that coordinate the motion of multiple bodies maneuvering in microgravity. To achieve this inside the ISS cabin, bowling-ball-sized spheres perform various maneuvers (or protocols), with one to three spheres operating simultaneously . The Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) experiment will test relative attitude control and station-keeping between satellites, re-targeting and image plane filling maneuvers, collision avoidance and fuel balancing algorithms, and an array of geometry estimators used in various missions. SPHERES consists of three self-contained satellites, which are 18 sided polyhedrons that are 0.2 meter in diameter and weigh 3.5 kilograms. Each satellite contains an internal propulsion system, power, avionics, software, communications, and metrology subsystems. The propulsion system uses CO2, which is expelled through the thrusters. SPHERES satellites are powered by AA batteries. The metrology subsystem provides real-time position and attitude information. To simulate ground station-keeping, a laptop will be used to transmit navigational data and formation flying algorithms. Once these data are uploaded, the satellites will perform autonomously and hold the formation until a new command is given.

Hypersonic merged layer blunt body flows with wakes

NASA Technical Reports Server (NTRS)

Jain, Amolak C.; Dahm, Werner K.

1991-01-01

An attempt is made here to understand the basic physics of the flowfield with wake on a blunt body of revolution under hypersonic rarefied conditions. A merged layer model of flow is envisioned. Full steady-state Navier-Stokes equations in spherical polar coordinate system are computed from the surface with slip and temperature jump conditions to the free stream by the Accelerated Successive Replacement method of numerical integration. Analysis is developed for bodies of arbitrary shape, but actual computations have been carried out for a sphere and sphere-cone body. Particular attention is paid to set the limit of the onset of separation, wake closure, shear-layer impingement, formation and dissipation of the shocks in the flowfield. Validity of the results is established by comparing the present results for sphere with the corresponding results of the SOFIA code in the common region of their validity and with the experimental data.

A new method for recognizing quadric surfaces from range data and its application to telerobotics and automation

NASA Technical Reports Server (NTRS)

Alvertos, Nicolas; Dcunha, Ivan

1992-01-01

A feature set of two dimensional curves is obtained after intersecting symmetric objects like spheres, cones, cylinders, ellipsoids, paraboloids, and parallelepipeds with two planes. After determining the location and orientation of the objects in space, these objects are aligned so as to lie on a plane parallel to a suitable coordinate system. These objects are then intersected with a horizontal and a vertical plane. Experiments were carried out with range images of sphere and cylinder. The 3-D discriminant approach was used to recognize quadric surfaces made up of simulated data. Its application to real data was also studied.

Synthesis, crystal structures and luminescence properties of new multi-component co-crystals of isostructural Co(II) and Zn(II) complexes

NASA Astrophysics Data System (ADS)

Tella, Adedibu C.; Owalude, Samson O.; Omotoso, Mary F.; Olatunji, Sunday J.; Ogunlaja, Adeniyi S.; Alimi, Lukman O.; Popoola, Olugbenga K.; Bourne, Susan A.

2018-04-01

Two novel isostructural compounds containing multi-component co-crystals [M(C6H4NO2)2(H2O)2](C9H6O6)2 (M = Co (1), Zn (2), C6H4NO2 = Picolinic acid, C9H6O6 = Trimesic acid) have been synthesized. The compounds were characterized by elemental analysis, FT-IR, UV-Visible and 1H NMR spectroscopies as well as thermal and single crystal X-ray diffraction analyses. Single crystal X-ray diffraction analysis reveals that 1 and 2 are isostructural. Compound 1 crystallizes in triclinic space group (P-1, with a = 5.154 (10) Å, b = 11.125 (2) Å, c = 14.113 (3) Å, α = 91.01 (3)°, β = 100.54 (3)°, and γ = 102.71 (3)°). In a similar fashion, compound 2 crystallizes in triclinic space group (P-1, with a = 5.1735 (3) Å, b = 11.0930 (10) Å, c = 14.1554 (8) Å, α = 91.70 (3)°, β = 100.26 (3)°, γ = 102.90 (3)°). The metal (II) cation presents distorted MN2O4 octahedral geometry with H2O molecules coordinated to the metal in equatorial position while the picolinic acid molecules are axially coordinated through the pyridine N atom. The two trimesic acid molecules are not part of the first coordination sphere. Compounds 1 and 2 constitute an example of a class of coordination compound of multicomponent crystals having trimesic acid outside the coordination sphere where it is neither protonated or deprotonated. The two compounds were investigated for luminiscence properties.

Crystal structures of three lead(II) acetate-bridged di-amino-benzene coordination polymers.

PubMed

Geiger, David K; Parsons, Dylan E; Zick, Patricia L

2014-12-01

Poly[tris-(acetato-κ(2) O,O')(μ2-acetato-κ(3) O,O':O)tetra-kis-(μ3-acetato-κ(4) O,O':O:O')bis-(benzene-1,2-di-amine-κN)tetra-lead(II)], [Pb4(CH3COO)8(C6H8N2)2] n , (I), poly[(acetato-κ(2) O,O')(μ3-acetato-κ(4) O,O':O:O')(4-chloro-benzene-1,2-diamine-κN)lead(II)], [Pb(CH3COO)2(C6H7ClN2)] n , (II), and poly[(κ(2) O,O')(μ3-acetato-κ(4) O,O':O:O')(3,4-di-amino-benzo-nitrile-κN)lead(II)], [Pb(CH3COO)2(C7H7N3)] n , (III), have polymeric structures in which monomeric units are joined by bridging acetate ligands. All of the Pb(II) ions exhibit hemidirected coordination. The repeating unit in (I) is composed of four Pb(II) ions having O6, O6N, O7 and O6N coordination spheres, respectively, where N represents a monodentate benzene-1,2-di-amine ligand and O acetate O atoms. Chains along [010] are joined by bridging acetate ligands to form planes parallel to (10-1). (II) and (III) are isotypic and have one Pb(II) ion in the asymmetric unit that has an O6N coordination sphere. Pb2O2 units result from a symmetry-imposed inversion center. Polymeric chains parallel to [100] exhibit hydrogen bonding between the amine and acetate ligands. In (III), additional hydrogen bonds between cyano groups and non-coordinating amines join the chains by forming R 2 (2)(14) rings.

An intersecting chord method for minimum circumscribed sphere and maximum inscribed sphere evaluations of sphericity error

NASA Astrophysics Data System (ADS)

Liu, Fei; Xu, Guanghua; Zhang, Qing; Liang, Lin; Liu, Dan

2015-11-01

As one of the Geometrical Product Specifications that are widely applied in industrial manufacturing and measurement, sphericity error can synthetically scale a 3D structure and reflects the machining quality of a spherical workpiece. Following increasing demands in the high motion performance of spherical parts, sphericity error is becoming an indispensable component in the evaluation of form error. However, the evaluation of sphericity error is still considered to be a complex mathematical issue, and the related research studies on the development of available models are lacking. In this paper, an intersecting chord method is first proposed to solve the minimum circumscribed sphere and maximum inscribed sphere evaluations of sphericity error. This new modelling method leverages chord relationships to replace the characteristic points, thereby significantly reducing the computational complexity and improving the computational efficiency. Using the intersecting chords to generate a virtual centre, the reference sphere in two concentric spheres is simplified as a space intersecting structure. The position of the virtual centre on the space intersecting structure is determined by characteristic chords, which may reduce the deviation between the virtual centre and the centre of the reference sphere. In addition,two experiments are used to verify the effectiveness of the proposed method with real datasets from the Cartesian coordinates. The results indicate that the estimated errors are in perfect agreement with those of the published methods. Meanwhile, the computational efficiency is improved. For the evaluation of the sphericity error, the use of high performance computing is a remarkable change.

TH-C-17A-06: A Hardware Implementation and Evaluation of Robotic SPECT: Toward Molecular Imaging Onboard Radiation Therapy Machines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, S; Touch, M; Bowsher, J

Purpose: To construct a robotic SPECT system and demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch. The system has potential for on-board functional and molecular imaging in radiation therapy. Methods: A robotic SPECT imaging system was developed utilizing a Digirad 2020tc detector and a KUKA KR150-L110 robot. An imaging study was performed with the PET CT Phantom, which includes 5 spheres: 10, 13, 17, 22 and 28 mm in diameter. Sphere-tobackground concentration ratio was 6:1 of Tc99m. The phantom was placed on a flat-top couch. SPECT projections were acquired with a parallel-hole collimator andmore » a single pinhole collimator. The robotic system navigated the detector tracing the flat-top table to maintain the closest possible proximity to the phantom. For image reconstruction, detector trajectories were described by six parameters: radius-of-rotation, x and z detector shifts, and detector rotation θ, tilt ϕ and twist γ. These six parameters were obtained from the robotic system by calibrating the robot base and tool coordinates. Results: The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector-to-COR (center-ofrotation) distance. In acquisitions with background at 1/6th sphere activity concentration, photopeak contamination was heavy, yet the 17, 22, and 28 mm diameter spheres were readily observed with the parallel hole imaging, and the single, targeted sphere (28 mm diameter) was readily observed in the pinhole region-of-interest (ROI) imaging. Conclusion: Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frame could be an effective means to estimate detector pose for use in SPECT image reconstruction. PHS/NIH/NCI grant R21-CA156390-01A1.« less

Light-triggered self-assembly of triarylamine-based nanospheres

NASA Astrophysics Data System (ADS)

Moulin, Emilie; Niess, Frédéric; Fuks, Gad; Jouault, Nicolas; Buhler, Eric; Giuseppone, Nicolas

2012-10-01

Tailored triarylamine units modified with terpyridine ligands were coordinated to Zn2+ ions and characterized as discrete dimeric entities. Interestingly, when these complexes were subsequently irradiated with simple visible light in chloroform, they readily self-assembled into monodisperse spheres with a mean diameter of 160 nm.Tailored triarylamine units modified with terpyridine ligands were coordinated to Zn2+ ions and characterized as discrete dimeric entities. Interestingly, when these complexes were subsequently irradiated with simple visible light in chloroform, they readily self-assembled into monodisperse spheres with a mean diameter of 160 nm. Electronic supplementary information (ESI) available: Synthetic procedures and products' characterization (2-4 and 6-9). 1H NMR titration of compound 6 by Zn(OTf)2 to form complex 7. Kinetic measurements by UV-Vis-NIR spectroscopy. Transmission electron microscopy imaging for complexes 8 and 9. UV-Vis-NIR for an Fe2+ analogue of complex 7. Dynamic light scattering and time autocorrelation function for self-assembly of complexes 7-9. Copies of 1H and 13C NMR spectra for compounds 2-4 and 6. See DOI: 10.1039/c2nr32168h

Minimal proton channel enables H2 oxidation and production with a water-soluble nickel-based catalyst.

PubMed

Dutta, Arnab; Lense, Sheri; Hou, Jianbo; Engelhard, Mark H; Roberts, John A S; Shaw, Wendy J

2013-12-11

Hydrogenase enzymes use first-row transition metals to interconvert H2 with protons and electrons, reactions that are important for the storage and recovery of energy from intermittent sources such as solar, hydroelectric, and wind. Here we present Ni(P(Cy)2N(Gly)2)2, a water-soluble molecular electrocatalyst with the amino acid glycine built into the diphosphine ligand framework. Proton transfer between the outer coordination sphere carboxylates and the second coordination sphere pendant amines is rapid, as observed by cyclic voltammetry and FTIR spectroscopy, indicating that the carboxylate groups may participate in proton transfer during catalysis. This complex oxidizes H2 (1-33 s(-1)) at low overpotentials (150-365 mV) over a range of pH values (0.1-9.0) and produces H2 under identical solution conditions (>2400 s(-1) at pH 0.5). Enzymes employ proton channels for the controlled movement of protons over long distances-the results presented here demonstrate the effects of a simple two-component proton channel in a synthetic molecular electrocatalyst.

Experimental and Theoretical Approaches for the Surface Interaction between Copper and Activated Sludge Microorganisms at Molecular Scale

NASA Astrophysics Data System (ADS)

Luo, Hong-Wei; Chen, Jie-Jie; Sheng, Guo-Ping; Su, Ji-Hu; Wei, Shi-Qiang; Yu, Han-Qing

2014-11-01

Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin.

PubMed

Liu, Zhichang; Frasconi, Marco; Lei, Juying; Brown, Zachary J; Zhu, Zhixue; Cao, Dennis; Iehl, Julien; Liu, Guoliang; Fahrenbach, Albert C; Botros, Youssry Y; Farha, Omar K; Hupp, Joseph T; Mirkin, Chad A; Fraser Stoddart, J

2013-01-01

Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH₂)₆][AuBr₄](α-cyclodextrin)₂}n chain superstructure formed during the rapid co-precipitation of α-cyclodextrin and KAuBr₄ in water. This phase change is selective for this gold salt, even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between α-, β- and γ-cyclodextrins with KAuBr₄ and KAuCl₄, we hypothesize that a perfect match in molecular recognition between α-cyclodextrin and [AuBr₄](-) leads to a near-axial orientation of the ion with respect to the α-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr₄](-) and [K(OH₂)₆](+) and drives the co-precipitation of the 1:2 adduct. This discovery heralds a green host-guest procedure for gold recovery from gold-bearing raw materials making use of α-cyclodextrin-an inexpensive and environmentally benign carbohydrate.

Deformed oscillator algebra approach of some quantum superintegrable Lissajous systems on the sphere and of their rational extensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marquette, Ian, E-mail: i.marquette@uq.edu.au; Quesne, Christiane, E-mail: cquesne@ulb.ac.be

2015-06-15

We extend the construction of 2D superintegrable Hamiltonians with separation of variables in spherical coordinates using combinations of shift, ladder, and supercharge operators to models involving rational extensions of the two-parameter Lissajous systems on the sphere. These new families of superintegrable systems with integrals of arbitrary order are connected with Jacobi exceptional orthogonal polynomials of type I (or II) and supersymmetric quantum mechanics. Moreover, we present an algebraic derivation of the degenerate energy spectrum for the one- and two-parameter Lissajous systems and the rationally extended models. These results are based on finitely generated polynomial algebras, Casimir operators, realizations as deformedmore » oscillator algebras, and finite-dimensional unitary representations. Such results have only been established so far for 2D superintegrable systems separable in Cartesian coordinates, which are related to a class of polynomial algebras that display a simpler structure. We also point out how the structure function of these deformed oscillator algebras is directly related with the generalized Heisenberg algebras spanned by the nonpolynomial integrals.« less

Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

PubMed Central

Lancaster, Kyle M.; Zaballa, María-Eugenia; Sproules, Stephen; Sundararajan, Mahesh; DeBeer, Serena; Richards, John H.; Vila, Alejandro J.; Neese, Frank; Gray, Harry B.

2016-01-01

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called “type zero” sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding. PMID:22563915

Ethylene biosynthesis by 1-aminocyclopropane-1-carboxylic acid oxidase: a DFT study.

PubMed

Bassan, Arianna; Borowski, Tomasz; Schofield, Christopher J; Siegbahn, Per E M

2006-11-24

The reaction catalyzed by the plant enzyme 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) was investigated by using hybrid density functional theory. ACCO belongs to the non-heme iron(II) enzyme superfamily and carries out the bicarbonate-dependent two-electron oxidation of its substrate ACC (1-aminocyclopropane-1-carboxylic acid) concomitant with the reduction of dioxygen and oxidation of a reducing agent probably ascorbate. The reaction gives ethylene, CO(2), cyanide and two water molecules. A model including the mononuclear iron complex with ACC in the first coordination sphere was used to study the details of O-O bond cleavage and cyclopropane ring opening. Calculations imply that this unusual and complex reaction is triggered by a hydrogen atom abstraction step generating a radical on the amino nitrogen of ACC. Subsequently, cyclopropane ring opening followed by O-O bond heterolysis leads to a very reactive iron(IV)-oxo intermediate, which decomposes to ethylene and cyanoformate with very low energy barriers. The reaction is assisted by bicarbonate located in the second coordination sphere of the metal.

Coordination of XeF2 to calcium and cadmium hexafluorophosphates(V).

PubMed

Bunic, Tina; Tavcar, Gasper; Tramsek, Melita; Zemva, Boris

2006-02-06

[M(XeF2)5](PF6)2 (M = Ca, Cd) complexes were prepared by the reaction of MF2 and XeF2 under pressure of gaseous PF5 in anhydrous HF as solvent. The coordination sphere of the Ca atom consists of nine fluorine atoms: three from two PF6(-) units (one bidentate and one monodentate) and one from each of six XeF2 molecules. The coordination sphere of the Cd atom consists of eight fluorine atoms: one from each of two PF6(-) units and one from each of six XeF2 molecules. Two of the XeF2 ligands about M in each compound are bridging ligands and are each linked to two M, generating infinite (-M-F-Xe-F-M-F-Xe-F-) chains along the b-axis in the Ca salt and along the c-axis in the Cd compound. The Cd2+ cation is smaller and more electronegative than the Ca2+ cation. These differences account for the higher F ligand coordination in the Ca2+ salt and for other structural features that distinguish them. The different stoichiometry of the PF6(-) salts when compared with their AsF6(-) analogues, which have the composition [M(XeF2)4](AsF6)2 (M = Ca, Cd), is in accord with the lower F ligand charge in the AsF6(-) when compared with that in the PF6(-) compound. Indeed, the AsF6(-) ligand charges appear to be similar to those in the XeF2-bridged species.

Interaction of NaOH solutions with silica surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rimsza, Jessica M.; Jones, Reese E.; Criscenti, Louise J.

Sodium adsorption on silica surfaces depends on the solution counter-ion. Here, we use NaOH solutions to investigate basic environments. Sodium adsorption on hydroxylated silica surfaces from NaOH solutions were investigated through molecular dynamics with a dissociative force field, allowing for the development of secondary molecular species. Furthermore, across the NaOH concentrations (0.01 M – 1.0 M), ~50% of the Na + ions were concentrated in the surface region, developing silica surface charges between –0.01 C/m 2 (0.01 M NaOH) and –0.76 C/m 2 (1.0 M NaOH) due to surface site deprotonation. Five inner-sphere adsorption complexes were identified, including monodentate, bidentate,more » and tridentate configurations and two additional structures, with Na + ions coordinated by bridging oxygen and hydroxyl groups or water molecules. Coordination of Na + ions by bridging oxygen atoms indicates partial or complete incorporation of Na + ions into the silica surface. Residence time analysis identified that Na + ions coordinated by bridging oxygen atoms stayed adsorbed onto the surface four times longer than the mono/bi/tridentate species, indicating formation of relatively stable and persistent Na + ion adsorption structures. Such inner-sphere complexes form only at NaOH concentrations of > 0.5 M. Na + adsorption and lifetimes have implications for the stability of silica surfaces.« less

Interaction of NaOH solutions with silica surfaces

DOE PAGES

Rimsza, Jessica M.; Jones, Reese E.; Criscenti, Louise J.

2018-01-16

Sodium adsorption on silica surfaces depends on the solution counter-ion. Here, we use NaOH solutions to investigate basic environments. Sodium adsorption on hydroxylated silica surfaces from NaOH solutions were investigated through molecular dynamics with a dissociative force field, allowing for the development of secondary molecular species. Furthermore, across the NaOH concentrations (0.01 M – 1.0 M), ~50% of the Na + ions were concentrated in the surface region, developing silica surface charges between –0.01 C/m 2 (0.01 M NaOH) and –0.76 C/m 2 (1.0 M NaOH) due to surface site deprotonation. Five inner-sphere adsorption complexes were identified, including monodentate, bidentate,more » and tridentate configurations and two additional structures, with Na + ions coordinated by bridging oxygen and hydroxyl groups or water molecules. Coordination of Na + ions by bridging oxygen atoms indicates partial or complete incorporation of Na + ions into the silica surface. Residence time analysis identified that Na + ions coordinated by bridging oxygen atoms stayed adsorbed onto the surface four times longer than the mono/bi/tridentate species, indicating formation of relatively stable and persistent Na + ion adsorption structures. Such inner-sphere complexes form only at NaOH concentrations of > 0.5 M. Na + adsorption and lifetimes have implications for the stability of silica surfaces.« less

Structure of 3,4-dihydroxy-2-butanone 4-phosphate synthase from Methanococcus jannaschii in complex with divalent metal ions and the substrate ribulose 5-phosphate: implications for the catalytic mechanism.

PubMed

Steinbacher, Stefan; Schiffmann, Susanne; Richter, Gerald; Huber, Robert; Bacher, Adelbert; Fischer, Markus

2003-10-24

Skeletal rearrangements of carbohydrates are crucial for many biosynthetic pathways. In riboflavin biosynthesis ribulose 5-phosphate is converted into 3,4-dihydroxy-2-butanone 4-phosphate while its C4 atom is released as formate in a sequence of metal-dependent reactions. Here, we present the crystal structure of Methanococcus jannaschii 3,4-dihydroxy-2-butanone 4-phosphate synthase in complex with the substrate ribulose 5-phosphate at a dimetal center presumably consisting of non-catalytic zinc and calcium ions at 1.7-A resolution. The carbonyl group (O2) and two out of three free hydroxyl groups (OH3 and OH4) of the substrate are metal-coordinated. We correlate previous mutational studies on this enzyme with the present structural results. Residues of the first coordination sphere involved in metal binding are indispensable for catalytic activity. Only Glu-185 of the second coordination sphere cannot be replaced without complete loss of activity. It contacts the C3 hydrogen atom directly and probably initiates enediol formation in concert with both metal ions to start the reaction sequence. Mechanistic similarities to Rubisco acting on the similar substrate ribulose 1,5-diphosphate in carbon dioxide fixation as well as other carbohydrate (reducto-) isomerases are discussed.

Long-range Coulomb forces and localized bonds.

PubMed

Preiser; Lösel; Brown; Kunz; Skowron

1999-10-01

The ionic model is shown to be applicable to all compounds in which the atoms carry a net charge and their electron density is spherically symmetric regardless of the covalent character of the bonding. By examining the electric field generated by an array of point charges placed at the positions of the ions in over 40 inorganic compounds, we show that the Coulomb field naturally partitions itself into localized regions (bonds) which are characterized by the electric flux that links neighbouring ions of opposite charge. This flux is identified with the bond valence, and Gauss' law with the valence-sum rule, providing a secure theoretical foundation for the bond-valence model. The localization of the Coulomb field provides an unambiguous definition of coordination number and our calculations show that, in addition to the expected primary coordination sphere, there are a number of weak bonds between cations and the anions in the second coordination sphere. Long-range Coulomb interactions are transmitted through the crystal by the application of Gauss' law at each of the intermediate atoms. Bond fluxes have also been calculated for compounds containing ions with non-spherical electron densities (e.g. cations with stereoactive lone electron pairs). In these cases the point-charge model continues to describe the distant field, but multipoles must be added to the point charges to give the correct local field.

Structural properties of liquid lanthanides using charge hard sphere reference system

NASA Astrophysics Data System (ADS)

Thakora, P. B.; Sonvane, Y. A.; Patel, H. P.; Gajjar, P. N.; Jani, A. R.

2012-06-01

In the present paper Charge Hard Sphere (CHS) system is employed to investigate the structural properties like long wavelength limit S(0), isothermal compressibility (χT) and coordination number n for some liquid lanthanides viz.: La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu. Our well established parameter free model potential is used to describe the electron-ion interaction alongwith sarkar et al. dielectric function. From the present results, it is seen that good agreement between present results and available experimental data have been achieved. At last, we establish the applicability of our parameter free model potential and CHS method to account such structural properties.

Densest local sphere-packing diversity. II. Application to three dimensions

NASA Astrophysics Data System (ADS)

Hopkins, Adam B.; Stillinger, Frank H.; Torquato, Salvatore

2011-01-01

The densest local packings of N three-dimensional identical nonoverlapping spheres within a radius Rmin(N) of a fixed central sphere of the same size are obtained for selected values of N up to N=1054. In the predecessor to this paper [A. B. Hopkins, F. H. Stillinger, and S. Torquato, Phys. Rev. EPLEEE81063-651X10.1103/PhysRevE.81.041305 81, 041305 (2010)], we described our method for finding the putative densest packings of N spheres in d-dimensional Euclidean space Rd and presented those packings in R2 for values of N up to N=348. Here we analyze the properties and characteristics of the densest local packings in R3 and employ knowledge of the Rmin(N), using methods applicable in any d, to construct both a realizability condition for pair correlation functions of sphere packings and an upper bound on the maximal density of infinite sphere packings. In R3, we find wide variability in the densest local packings, including a multitude of packing symmetries such as perfect tetrahedral and imperfect icosahedral symmetry. We compare the densest local packings of N spheres near a central sphere to minimal-energy configurations of N+1 points interacting with short-range repulsive and long-range attractive pair potentials, e.g., 12-6 Lennard-Jones, and find that they are in general completely different, a result that has possible implications for nucleation theory. We also compare the densest local packings to finite subsets of stacking variants of the densest infinite packings in R3 (the Barlow packings) and find that the densest local packings are almost always most similar as measured by a similarity metric, to the subsets of Barlow packings with the smallest number of coordination shells measured about a single central sphere, e.g., a subset of the fcc Barlow packing. Additionally, we observe that the densest local packings are dominated by the dense arrangement of spheres with centers at distance Rmin(N). In particular, we find two “maracas” packings at N=77 and N=93, each consisting of a few unjammed spheres free to rattle within a “husk” composed of the maximal number of spheres that can be packed with centers at respective Rmin(N).

Preparation of Geophysical Fluid Flow Experiments With The Rotating Spherical Gap Flow Model In Space

NASA Astrophysics Data System (ADS)

Egbers, C.

The'GeoFlow' is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluid Mechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field simi- lar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment re- quires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth`s liquid core the experiment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heat- ing the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number.

Redetermination of dicerium(III) tris-(sulfate) tetra-hydrate.

PubMed

Xu, Xin

2007-12-06

Ce(2)(SO(4))(3)(H(2)O)(4) was obtained hydro-thermally from an aqueous solution of cerium(III) oxide, trimethyl-amine and sulfuric acid. The precision of the structure determination has been significantly improved compared with the previous result [Dereigne (1972 ▶). Bull. Soc. Fr. Mineral. Cristallogr.95, 269-280]. The coordination about the two Ce atoms is achieved by seven and six bridging O atoms from sulfate anions. Each S atom makes four S-O-Ce linkages through bridging O atoms. The coordination sphere of each Ce is completed by two water molecules, which act as terminal ligands.

Effect of radiation and magnetohydrodynamic free convection boundary layer flow on a solid sphere with Newtonian heating in a micropolar fluid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alkasasbeh, Hamzeh Taha, E-mail: zukikuj@yahoo.com; Sarif, Norhafizah Md, E-mail: zukikuj@yahoo.com; Salleh, Mohd Zuki, E-mail: zukikuj@yahoo.com

2015-02-03

In this paper, the effect of radiation on magnetohydrodynamic free convection boundary layer flow on a solid sphere with Newtonian heating in a micropolar fluid, in which the heat transfer from the surface is proportional to the local surface temperature, is considered. The transformed boundary layer equations in the form of nonlinear partial differential equations are solved numerically using an implicit finite difference scheme known as the Keller-box method. Numerical solutions are obtained for the local wall temperature and the local skin friction coefficient, as well as the velocity, angular velocity and temperature profiles. The features of the flow andmore » heat transfer characteristics for various values of the Prandtl number Pr, micropolar parameter K, magnetic parameter M, radiation parameter N{sub R}, the conjugate parameter γ and the coordinate running along the surface of the sphere, x are analyzed and discussed.« less

Development of molecular electrocatalysts for CO2 reduction and H2 production/oxidation.

PubMed

Rakowski DuBois, M; DuBois, Daniel L

2009-12-21

The conversion of solar energy to fuels in both natural and artificial photosynthesis requires components for both light-harvesting and catalysis. The light-harvesting component generates the electrochemical potentials required to drive fuel-generating reactions that would otherwise be thermodynamically uphill. This Account focuses on work from our laboratories on developing molecular electrocatalysts for CO(2) reduction and for hydrogen production. A true analog of natural photosynthesis will require the ability to capture CO(2) from the atmosphere and reduce it to a useful fuel. Work in our laboratories has focused on both aspects of this problem. Organic compounds such as quinones and inorganic metal complexes can serve as redox-active CO(2) carriers for concentrating CO(2). We have developed catalysts for CO(2) reduction to form CO based on a [Pd(triphosphine)(solvent)](2+) platform. Catalytic activity requires the presence of a weakly coordinating solvent molecule that can dissociate during the catalytic cycle and provide a vacant coordination site for binding water and assisting C-O bond cleavage. Structures of [NiFe] CO dehydrogenase enzymes and the results of studies on complexes containing two [Pd(triphosphine)(solvent)](2+) units suggest that participation of a second metal in CO(2) binding may also be required for achieving very active catalysts. We also describe molecular electrocatalysts for H(2) production and oxidation based on [Ni(diphosphine)(2)](2+) complexes. Similar to palladium CO(2) reduction catalysts, these species require the optimization of both first and second coordination spheres. In this case, we use structural features of the first coordination sphere to optimize the hydride acceptor ability of nickel needed to achieve heterolytic cleavage of H(2). We use the second coordination sphere to incorporate pendant bases that assist in a number of important functions including H(2) binding, H(2) cleavage, and the transfer of protons between nickel and solution. These pendant bases, or proton relays, are likely to be important in the design of catalysts for a wide range of fuel production and fuel utilization reactions involving multiple electron and proton transfer steps. The generation of fuels from abundant substrates such as CO(2) and water remains a daunting research challenge, requiring significant advances in new inexpensive materials for light harvesting and the development of fast, stable, and efficient electrocatalysts. Although we describe progress in the development of redox-active carriers capable of concentrating CO(2) and molecular electrocatalysts for CO(2) reduction, hydrogen production, and hydrogen oxidation, much more remains to be done.

How should spin-weighted spherical functions be defined?

NASA Astrophysics Data System (ADS)

Boyle, Michael

2016-09-01

Spin-weighted spherical functions provide a useful tool for analyzing tensor-valued functions on the sphere. A tensor field can be decomposed into complex-valued functions by taking contractions with tangent vectors on the sphere and the normal to the sphere. These component functions are usually presented as functions on the sphere itself, but this requires an implicit choice of distinguished tangent vectors with which to contract. Thus, we may more accurately say that spin-weighted spherical functions are functions of both a point on the sphere and a choice of frame in the tangent space at that point. The distinction becomes extremely important when transforming the coordinates in which these functions are expressed, because the implicit choice of frame will also transform. Here, it is proposed that spin-weighted spherical functions should be treated as functions on the spin or rotation groups, which simultaneously tracks the point on the sphere and the choice of tangent frame by rotating elements of an orthonormal basis. In practice, the functions simply take a quaternion argument and produce a complex value. This approach more cleanly reflects the geometry involved, and allows for a more elegant description of the behavior of spin-weighted functions. In this form, the spin-weighted spherical harmonics have simple expressions as elements of the Wigner 𝔇 representations, and transformations under rotation are simple. Two variants of the angular-momentum operator are defined directly in terms of the spin group; one is the standard angular-momentum operator L, while the other is shown to be related to the spin-raising operator ð.

Moments of Inertia of Disks and Spheres without Integration

ERIC Educational Resources Information Center

Hong, Seok-Cheol; Hong, Seok-In

2013-01-01

Calculation of moments of inertia is often challenging for introductory-level physics students due to the use of integration, especially in non-Cartesian coordinates. Methods that do not employ calculus have been described for finding the rotational inertia of thin rods and other simple bodies. In this paper we use the parallel axis theorem and…

Hyperfine coupling constants on inner-sphere water molecules of Gd(III)-based MRI contrast agents.

PubMed

Esteban-Gómez, David; de Blas, Andrés; Rodríguez-Blas, Teresa; Helm, Lothar; Platas-Iglesias, Carlos

2012-11-12

Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Gd(H(2)O)(8)](3+) and different Gd(III)-based magnetic resonance imaging contrast agents such as [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)]. DFT calculations performed on the [Gd(H(2)O)(8)](3+) model system show that both hybrid-GGA functionals (BH&HLYP, B3PW91 and PBE1PBE) and the hybrid meta-GGA functional TPSSh provide (17)O HFCCs in close agreement with the experimental data. The use of all-electron relativistic approaches based on the DKH2 approximation and the use of relativistic effective core potentials (RECP) provide results of essentially the same quality. The accurate calculation of HFCCs on the [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)] complexes requires an adequate description of solvent effects. This was achieved by using a mixed cluster/continuum approach that includes explicitly two second-sphere water molecules. The calculated isotropic (17)O HFCCs (A(iso)) fall within the range 0.40-0.56 MHz, and show deviations from the corresponding experimental values typically lower than 0.05 MHz. The A(iso) values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Gd(III) ion, as well as by the orientation of the water molecule plane with respect to the Gd-O vector. (1)H HFCCs of coordinated water molecules and (17)O HFCCs of second-sphere water molecules take values close to zero. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Identification of Second Shell Coordination in Transition Metal Species Using Theoretical XANES: Example of Ti–O–(C, Si, Ge) Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spanjers, Charles S.; Guillo, Pascal; Tilley, T. Don

X-ray absorption near-edge structure (XANES) is a common technique for elucidating oxidation state and first shell coordination geometry in transition metal complexes, among many other materials. However, the structural information obtained from XANES is often limited to the first coordination sphere. In this study, we show how XANES can be used to differentiate between C, Si, and Ge in the second coordination shell of Ti–O–(C, Si, Ge) molecular complexes based on differences in their Ti K-edge XANES spectra. Experimental spectra were compared with theoretical spectra calculated using density functional theory structural optimization and ab initio XANES calculations. The unique featuresmore » for second shell C, Si, and Ge present in the Ti K pre-edge XANES are attributed to the interaction between the Ti center and the O–X (X = C, Si, or Ge) antibonding orbitals.« less

Forebody and afterbody solutions of the Navier-Stokes equations for supersonic flow over blunt bodies in a generalized orthogonal coordinate system

NASA Technical Reports Server (NTRS)

Gnoffo, P. A.

1978-01-01

A coordinate transformation, which can approximate many different two-dimensional and axisymmetric body shapes with an analytic function, is used as a basis for solving the Navier-Stokes equations for the purpose of predicting 0 deg angle of attack supersonic flow fields. The transformation defines a curvilinear, orthogonal coordinate system in which coordinate lines are perpendicular to the body and the body is defined by one coordinate line. This system is mapped in to a rectangular computational domain in which the governing flow field equations are solved numerically. Advantages of this technique are that the specification of boundary conditions are simplified and, most importantly, the entire flow field can be obtained, including flow in the wake. Good agreement has been obtained with experimental data for pressure distributions, density distributions, and heat transfer over spheres and cylinders in supersonic flow. Approximations to the Viking aeroshell and to a candidate Jupiter probe are presented and flow fields over these shapes are calculated.

Cadmium-1,4-cyclohexanedicarboxylato coordination polymers bearing different di-alkyl-2,2'-bipyridines: syntheses, crystal structures and photoluminescence studies.

PubMed

Rosales-Vázquez, Luis D; Sánchez-Mendieta, Víctor; Dorazco-González, Alejandro; Martínez-Otero, Diego; García-Orozco, Iván; Morales-Luckie, Raúl A; Jaramillo-Garcia, Jonathan; Téllez-López, Antonio

2017-09-26

Four coordination polymers have been synthesized using self-assembly solution reactions under ambient conditions, reacting Cd(ii) ions with 1,4-cyclohexanedicarboxylic acid in the presence of different 2,2'-bipyridine co-ligands: {[Cd(H 2 O)(e,a-cis-1,4-chdc)(2,2'-bpy)]·H 2 O} n (1); [Cd 2 (H 2 O) 2 (e,a-cis-1,4-chdc) 2 (4,4'-dmb) 2 ] n (2); {[Cd(e,a-cis-1,4-chdc)(5,5'-dmb)]·H 2 O·CH 3 OH} n (3) and {[Cd(e,e-trans-1,4-chdc)(4,4'-dtbb)]·CH 3 OH} n (4), where 1,4-chdc = 1,4-cyclohexanedicarboxylato, 2,2'-bpy = 2,2'-bipyridine, 4,4'-dmb = 4,4'-dimethyl-2,2'-bipyridine, 5,5'-dmb = 5,5'-dimethyl-2,2'-bipyridine and 4,4'-dtbb = 4,4'-di-tert-butyl-2,2'-bipyridine. Crystallographic studies show that compound 1 has a 1D structure propagating along the crystallographic b-axis; the Cd ion in 1 is six-coordinated with a distorted-octahedral coordination sphere. Compound 2 has two crystallographic different Cd ions and both are six-coordinated with a distorted-octahedral coordination sphere. Compound 3 exhibits a seven-coordinated Cd ion having a distinctive distorted-monocapped trigonal prismatic geometry. In compound 4, the Cd ion is also seven-coordinated in a distorted monocapped octahedral geometry. Compounds 2, 3 and 4 possess rhombic-shaped dinuclear units (Cd 2 O 2 ) as nodes to generate larger cycles made up of four dinuclear units, a Cd 4 motif, bridged by four 1,4-chdc ligands, accomplishing, thus, 2D structures. Remarkably, in compound 4 the 1,4-chdc ligand conformation changes to the equatorial, equatorial trans, unlike the other compounds where the bridging ligand conformation is the more typical equatorial, axial cis. The solid state luminescence properties of 1-4 were investigated; polymers 3 and 4 exhibited a strong blue emission (λ em = 410-414 nm) compared to 1 and 2; structure-related photoluminescence is attributed to the degree of hydration of the compounds. Furthermore, Cd-polymer 3 suspended in acetone allows the fluorescence selective sensing of acetonitrile over common organic solvents such as alcohols and DMF, based on turn-on fluorescence intensity with a limit of 53 μmol L -1 .

Calcium environment in silicate and aluminosilicate glasses probed by ⁴³Ca MQMAS NMR experiments and MD-GIPAW calculations.

PubMed

Gambuzzi, Elisa; Pedone, Alfonso; Menziani, Maria Cristina; Angeli, Frédéric; Florian, Pierre; Charpentier, Thibault

2015-01-01

⁴³Ca MQMAS NMR spectra of three silica-based glasses in which Ca²⁺ ions play different structural roles have been collected and processed in order to extract the underlying NMR parameter distributions. The NMR parameters have been interpreted with the help of molecular dynamics simulations and DFT-GIPAW calculations. This synergetic experimental-computational approach has allowed us to investigate the Ca environment, to estimate Ca coordination numbers from MD-derived models, and to push further the discussion about ⁴³Ca NMR sensitivity to the first and second coordination spheres: ⁴³Ca δiso and Ca-O distance can be successfully correlated as a function of Ca coordination number. Copyright © 2015 Elsevier Inc. All rights reserved.

The Astronomical Instrument, So-Gahui Invented During King Sejong Period

NASA Astrophysics Data System (ADS)

Lee, Yong-Sam Lee; Kim, Sang-Hyuk

2002-09-01

So-ganui, namely small simplified armillary sphere, was invented as an astronomical instrument by Lee Cheon, Jeong Cho, Jung In-Ji under 16 years' rule of King Sejong. We collect records and observed data on So-ganui. It is designed to measure position of celestial sphere and to determine time. It also can be transformed equatorial to horizontal, and horizontal to equatorial coordinate. It can measure the right ascension, declination, altitude and azimuth. It is composed of Sayu-hwan (Four displacements), Jeokdo-hwan (Equatorial dial), Baekgak-hwan (Ring with one hundred-interval quarters), Gyuhyeong (Sighting aliadade), Yongju (Dragon-pillar) and Bu (Stand). So-ganui was used conveniently portable surveying as well as astronomical instrument and possible to determine time during day and night.

Temperature effect on the structure and conformational fluctuations in two zinc knuckles from the mouse mammary tumor virus.

PubMed

Nedjoua, Drici; Krallafa, Abdelghani Mohamed

2018-06-01

Zinc fingers are small protein domains in which zinc plays a structural role, contributing to the stability of the zinc-peptide complex. Zinc fingers are structurally diverse and are present in proteins that perform a broad range of functions in various cellular processes, such as replication and repair, transcription and translation, metabolism and signaling, cell proliferation, and apoptosis. Zinc fingers typically function as interaction modules and bind to a wide variety of compounds, such as nucleic acids, proteins, and small molecules. In this study, we investigated the structural properties, in solution, of the proximal and distal zinc knuckles of the nucleocapsid (NC) protein from the mouse mammary tumor virus (MMTV) (MMTV NC). For this purpose, we performed a series of molecular dynamics simulations in aqueous solution at 300 K, 333 K, and 348 K. The temperature effect was evaluated in terms of root mean square deviation of the backbone atoms and root mean square fluctuation of the coordinating residue atoms. The stability of the zinc coordination sphere was analyzed based upon the time profile of the interatomic distances between the zinc ions and the chelator atoms. The results indicate that the hydrophobic character of the proximal zinc finger is dominant at 333 K. The low mobility of the coordinating residues suggests that the strong electrostatic effect exerted by the zinc ion on its coordinating residues is not influenced by the increase in temperature. The evolution of the structural parameters of the coordination sphere of the distal zinc finger at 300 K gives us a reasonable picture of the unfolding pathway, as proposed by Bombarda and coworkers (Bombarda et al., 2005), which can predict the binding order of the four conserved ligand-binding residues. Our results support the conclusion that the structural features can vary significantly between the two zinc knuckles of MMTV NC. Copyright © 2018 Elsevier Ltd. All rights reserved.

Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin

PubMed Central

Liu, Zhichang; Frasconi, Marco; Lei, Juying; Brown, Zachary J.; Zhu, Zhixue; Cao, Dennis; Iehl, Julien; Liu, Guoliang; Fahrenbach, Albert C.; Botros, Youssry Y.; Farha, Omar K.; Hupp, Joseph T.; Mirkin, Chad A.; Fraser Stoddart, J.

2013-01-01

Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH2)6][AuBr4](α-cyclodextrin)2}n chain superstructure formed during the rapid co-precipitation of α-cyclodextrin and KAuBr4 in water. This phase change is selective for this gold salt, even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between α-, β- and γ-cyclodextrins with KAuBr4 and KAuCl4, we hypothesize that a perfect match in molecular recognition between α-cyclodextrin and [AuBr4]− leads to a near-axial orientation of the ion with respect to the α-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr4]− and [K(OH2)6]+ and drives the co-precipitation of the 1:2 adduct. This discovery heralds a green host–guest procedure for gold recovery from gold-bearing raw materials making use of α-cyclodextrin—an inexpensive and environmentally benign carbohydrate. PMID:23673640

Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

PubMed Central

Petrenko, Alexander; Stein, Matthias

2017-01-01

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. PMID:28067774

a Numerical Investigation of the Jamming Transition in Traffic Flow on Diluted Planar Networks

NASA Astrophysics Data System (ADS)

Achler, Gabriele; Barra, Adriano

In order to develop a toy model for car's traffic in cities, in this paper we analyze, by means of numerical simulations, the transition among fluid regimes and a congested jammed phase of the flow of kinetically constrained hard spheres in planar random networks similar to urban roads. In order to explore as timescales as possible, at a microscopic level we implement an event driven dynamics as the infinite time limit of a class of already existing model (Follow the Leader) on an Erdos-Renyi two-dimensional graph, the crossroads being accounted by standard Kirchoff density conservations. We define a dynamical order parameter as the ratio among the moving spheres versus the total number and by varying two control parameters (density of the spheres and coordination number of the network) we study the phase transition. At a mesoscopic level it respects an, again suitable, adapted version of the Lighthill-Whitham model, which belongs to the fluid-dynamical approach to the problem. At a macroscopic level, the model seems to display a continuous transition from a fluid phase to a jammed phase when varying the density of the spheres (the amount of cars in a city-like scenario) and a discontinuous jump when varying the connectivity of the underlying network.

Difference method to search for the anisotropy of primary cosmic radiation

NASA Astrophysics Data System (ADS)

Pavlyuchenko, V. P.; Martirosov, R. M.; Nikolskaya, N. M.; Erlykin, A. D.

2018-01-01

The original difference method used in the search for an anisotropy of primary cosmic radiation at the knee region of its energy spectrum is considered. Its methodical features and properties are analyzed. It is shown that this method, in which properties of particle fluxes (rather than an intensity) are investigated, is stable against random experimental errors and allows one to separate anomalies connected with the laboratory coordinate system from anomalies in the celestial coordinate system. The method uses the multiple scattering of charged particles in the magnetic fields of the Galaxy to study the whole celestial sphere, including the regions outside the line of sight of the installation.

Structural study of Cu(II) complexes with benzo[b]furancarboxylic acids

NASA Astrophysics Data System (ADS)

Kalinowska, Diana; Klepka, Marcin T.; Wolska, Anna; Drzewiecka-Antonik, Aleksandra; Ostrowska, Kinga; Struga, Marta

2017-11-01

Four Cu(II) complexes with 2- and 3-benzo[b]furancarboxylic acids have been synthesized and characterized using combination of two spectroscopic techniques. These techniques were: (i) FTIR and (ii) XAFS. FTIR analysis confirmed that complexes were formed and gave insight into identification of possible coordinating groups to the metallic center. XANES analysis indicated that the oxidation state of Cu is +2. EXAFS analysis allowed to identify that the first coordination sphere is formed by 4-5 oxygen atoms with the Cu-O distances around 2 Å. Combining these techniques it was possible to structurally describe novel Cu(II) complexes with benzo[b]furancarboxylic acids.

Redetermination of dicerium(III) tris­(sulfate) tetra­hydrate

PubMed Central

Xu, Xin

2008-01-01

Ce2(SO4)3(H2O)4 was obtained hydro­thermally from an aqueous solution of cerium(III) oxide, trimethyl­amine and sulfuric acid. The precision of the structure determination has been significantly improved compared with the previous result [Dereigne (1972 ▶). Bull. Soc. Fr. Mineral. Cristallogr. 95, 269–280]. The coordination about the two Ce atoms is achieved by seven and six bridging O atoms from sulfate anions. Each S atom makes four S—O—Ce linkages through bridging O atoms. The coordination sphere of each Ce is completed by two water molecules, which act as terminal ligands. PMID:21200451

A Qualitative Analysis of the Spontaneous Volunteer Response to the 2013 Sudan Floods: Changing the Paradigm.

PubMed

Albahari, Amin; Schultz, Carl H

2017-06-01

Introduction While the concept of community resilience is gaining traction, the role of spontaneous volunteers during the initial response to disasters remains controversial. In an attempt to resolve some of the debate, investigators examined the activities of a spontaneous volunteer group called Nafeer after the Sudan floods around the city of Khartoum in August of 2013. Hypothesis Can spontaneous volunteers successfully initiate, coordinate, and deliver sustained assistance immediately after a disaster? This retrospective, descriptive case study involved: (1) interviews with Nafeer members that participated in the disaster response to the Khartoum floods; (2) examination of documents generated during the event; and (3) subsequent benchmarking of their efforts with the Sphere Handbook. Members who agreed to participate were requested to provide all documents in their possession relating to Nafeer. The response by Nafeer was then benchmarked to the Sphere Handbook's six core standards, as well as the 11 minimum standards in essential health services. A total of 11 individuals were interviewed (six from leadership and five from active members). Nafeer's activities included: food provision; delivery of basic health care; environmental sanitation campaigns; efforts to raise awareness; and construction and strengthening of flood barricades. Its use of electronic platforms and social media to collect data and coordinate the organization's response was effective. Nafeer adopted a flat-management structure, dividing itself into 14 committees. A Coordination Committee was in charge of liaising between all committees. The Health and Sanitation Committee supervised two health days which included mobile medical and dentistry clinics supported by a mobile laboratory and pharmacy. The Engineering Committee managed to construct and maintain flood barricades. Nafeer used crowd-sourcing to fund its activities, receiving donations locally and internationally using supporters outside Sudan. Nafeer completely fulfilled three of Sphere's core standards and partially fulfilled the other three, but none of the essential health services standards were fulfilled. Even though the Sphere Handbook was chosen as the best available "gold standard" to benchmark Nafeer's efforts, it showed significant limitations in effectively measuring this group. It appears that independent spontaneous volunteer initiatives, like Nafeer, potentially can improve community resilience and play a significant role in the humanitarian response. Such organizations should be the subject of increased research activity. Relevant bodies should consider issuing separate guidelines supporting spontaneous volunteer organizations. Albahari A , Schultz CH . A qualitative analysis of the spontaneous volunteer response to the 2013 Sudan floods: changing the paradigm. Prehosp Disaster Med. 2017;32(3):240-248.

A study on adsorption mechanism of organoarsenic compounds on ferrihydrite by XAFS

NASA Astrophysics Data System (ADS)

Tanaka, M.; Takahashi, Y.; Yamaguchi, N.

2013-04-01

Anthropogenic organoarsenic compounds which were used such as agrochemicals, pesticides, and herbicides can have a potential as a source of arsenic pollution in water. In the process, the adsorption of arsenic onto mineral surface in soil may play an important role to affect arsenic distribution in solid-water interface. However, adsorption structures of organoarsenic compounds on the iron-(oxyhydr)oxides are not well known. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to know the adsorption structure of methyl- and phenyl-substituted organoarsenic compounds (methylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), and diphenylarsinic acid (DPAA) onto ferrihydrite which can be a strong adsorbent of arsenic. EXAFS analysis suggests that the formation of inner-sphere surface complex for all organoarsenic compounds with ferrihydrite regardless of the organic functional groups and the number of substitution. The As-Fe distances are around 3.27 , which suggests both mono-and bi-dentate inner-sphere complexes by DFT calculations. The corresponding coordination numbers (CNs) are less than two, suggesting that coexistence of both structures of inner-sphere complexes.

Percolation of disordered jammed sphere packings

NASA Astrophysics Data System (ADS)

Ziff, Robert M.; Torquato, Salvatore

2017-02-01

We determine the site and bond percolation thresholds for a system of disordered jammed sphere packings in the maximally random jammed state, generated by the Torquato-Jiao algorithm. For the site threshold, which gives the fraction of conducting versus non-conducting spheres necessary for percolation, we find {{p}\\text{c}}=0.3116(3) , consistent with the 1979 value of Powell 0.310(5) and identical within errors to the threshold for the simple-cubic lattice, 0.311 608, which shares the same average coordination number of 6. In terms of the volume fraction ϕ, the threshold corresponds to a critical value {φ\\text{c}}=0.199 . For the bond threshold, which apparently was not measured before, we find {{p}\\text{c}}=0.2424(3) . To find these thresholds, we considered two shape-dependent universal ratios involving the size of the largest cluster, fluctuations in that size, and the second moment of the size distribution; we confirmed the ratios’ universality by also studying the simple-cubic lattice with a similar cubic boundary. The results are applicable to many problems including conductivity in random mixtures, glass formation, and drug loading in pharmaceutical tablets.

In situ spectroscopic identification of neptunium(V) inner-sphere complexes on the hematite-water interface.

PubMed

Müller, Katharina; Gröschel, Annett; Rossberg, André; Bok, Frank; Franzen, Carola; Brendler, Vinzenz; Foerstendorf, Harald

2015-02-17

Hematite plays a decisive role in regulating the mobility of contaminants in rocks and soils. The Np(V) reactions at the hematite-water interface were comprehensively investigated by a combined approach of in situ vibrational spectroscopy, X-ray absorption spectroscopy and surface complexation modeling. A variety of sorption parameters such as Np(V) concentration, pH, ionic strength, and the presence of bicarbonate was considered. Time-resolved IR spectroscopic sorption experiments at the iron oxide-water interface evidenced the formation of a single monomer Np(V) inner-sphere sorption complex. EXAFS provided complementary information on bidentate edge-sharing coordination. In the presence of atmospherically derived bicarbonate the formation of the bis-carbonato inner-sphere complex was confirmed supporting previous EXAFS findings.1 The obtained molecular structure allows more reliable surface complexation modeling of recent and future macroscopic data. Such confident modeling is mandatory for evaluating water contamination and for predicting the fate and migration of radioactive contaminants in the subsurface environment as it might occur in the vicinity of a radioactive waste repository or a reprocessing plant.

A Computer Program for Mapping Satellite-borne Narrow-Beam Antenna Footprints on Earth. Memorandum Number 72/3.

ERIC Educational Resources Information Center

Stagl, Thomas W.; Singh, Jai P.

Written primarily to define the area of the earth covered by a narrow-beam antenna carried on a synchronous satellite in circular, near equatorial orbits, a computer program has been developed that computes the locus of intersection of a quadric cone and a sphere. The program, which outputs a list of the longitude and latitude coordinates of the…

The mechanism of CO2 hydration: a porous metal oxide nanocapsule catalyst can mimic the biological carbonic anhydrase role.

PubMed

Bandeira, Nuno A G; Garai, Somenath; Müller, Achim; Bo, Carles

2015-11-04

The mechanism for the hydration of CO2 within a Keplerate nanocapsule is presented. A network of hydrogen bonds across the water layers in the first metal coordination sphere facilitates the proton abstraction and nucleophilic addition of water. The highly acidic properties of the polyoxometalate cluster are crucial for explaining the catalysed hydration.

IO Sphere: The Professional Journal of Joint Information Operations. Special Edition 2008

DTIC Science & Technology

2008-01-01

members, disseminate propaganda, videos , brochures, and training materials, as well as to coordinate terrorist acts in an anonymous and...collaboration among larger communities of cyber Porn versus Terror Years ago, authorities noticed that child pornography websites, though often...stepping foot on them. Moreover, video information can be analyzed by computer vision algorithms. Based on technology available today, it’s not

STS (Space Transportation System) Task Simulator.

DTIC Science & Technology

1985-08-15

3 Clohessy - Wiltshire Coordinate System • • -1 1- .M 1°... "p ’. -. .’- 0 . _ -~:Q ~. ... . .o. ., 1. INTRODUCTION The Space Transportation System...motion is obtained by applying the Clohessy - Wiltshire equations for terminal rendezvous/docking with the earth modeled as a uni- form sphere...rotational accelerations to the present quaternions. The Clohessy - Wiltshire equations for terminal rendezvous/dockinq are used to model orbital drift

Adenosine/guanosine-3',5'-bis-phosphates as biocompatible and selective Zn2+-ion chelators. Characterization and comparison with adenosine/guanosine-5'-di-phosphate.

PubMed

Sayer, Alon Haim; Blum, Eliav; Major, Dan Thomas; Vardi-Kilshtain, Alexandra; Levi Hevroni, Bosmat; Fischer, Bilha

2015-04-28

Although involved in various physiological functions, nucleoside bis-phosphate analogues and their metal-ion complexes have been scarcely studied. Hence, here, we explored the solution conformation of 2′-deoxyadenosine- and 2′-deoxyguanosine-3′,5′-bisphosphates, 3 and 4, d(pNp), as well as their Zn(2+)/Mg(2+) binding sites and binding-modes (i.e. inner- vs. outer-sphere coordination), acidity constants, stability constants of their Zn(2+)/Mg(2+) complexes, and their species distribution. Analogues 3 and 4, in solution, adopted a predominant Southern ribose conformer (ca. 84%), gg conformation around C4'-C5' and C5'-O5' bonds, and glycosidic angle in the anti-region (213-270°). (1)H- and (31)P-NMR experiments indicated that Zn(2+)/Mg(2+) ions coordinated to P5' and P3' groups of 3 and 4 but not to N7 nitrogen atom. Analogues 3 and 4 formed ca. 100-fold more stable complexes with Zn(2+)vs. Mg(2+)-ions. Complexes of 3 and 4 with Mg(2+) at physiological pH were formed in minute amounts (11% and 8%, respectively) vs. Zn(2+) complexes (46% and 44%). Stability constants of Zn(2+)/Mg(2+) complexes of analogues 3 and 4 (log KML(M) = 4.65-4.75/2.63-2.79, respectively) were similar to those of the corresponding complexes of ADP and GDP (log KML(M) = 4.72-5.10/2.95-3.16, respectively). Based on the above findings, we hypothesized that the unexpectedly low log K values of Zn(2+)-d(pNp) as compared to Zn(2+)-NDP complexes, are possibly due to formation of outer-sphere coordination in the Zn(2+)-d(pNp) complex vs. inner-sphere in the NDP-Zn(2+) complex, in addition to loss of chelation to N7 nitrogen atom in Zn(2+)-d(pNp). Indeed, explicit solvent molecular dynamics simulations of 1 and 3 for 100 ns supported this hypothesis.

Coordinated HArd Sphere Model (CHASM): A Simplified Model for Silicate and Oxide Liquids at Mantle Conditions

NASA Astrophysics Data System (ADS)

Wolf, A. S.; Asimow, P. D.; Stevenson, D. J.

2013-12-01

Recent first-principles theoretical calculations (Stixrude 2009) and experimental shock-wave investigations (Mosenfelder 2009) indicate that melting perovskite requires significantly less energy than previously thought, supporting the idea of a deep-mantle magma ocean early in Earth's history. The modern-day solid Earth is thus likely the result of crystallization from an early predominantly molten state, a process that is primarily controlled by the poorly understood behavior of silicate melts at extreme pressures and temperatures. Probing liquid thermodynamics at mantle conditions is difficult for both theory and experiment, and further challenges are posed by the large relevant compositional space including at least MgO, SiO2, and FeO. First-principles molecular dynamics has been used with great success to determine the high P-T properties of a small set of fixed composition silicate-oxide liquids including MgO (Karki 2006), SiO2 (Karki 2007), Mg2SiO4 (de Koker 2008), MgSiO3 (Stixrude 2005), and Fe2SiO4 (Ramo 2012). While extremely powerful, this approach has limitations including high computational cost, lower bounds on temperature due to relaxation constraints, as well as restrictions to length scales and time scales that are many orders of magnitude smaller than those relevant to the Earth or experimental methods. As a compliment to accurate first-principles calculations, we have developed the Coordinated HArd Sphere Model (CHASM). We extend the standard hard sphere mixture model, recently applied to silicate liquids by Jing (2011), by accounting for the range of oxygen coordination states available to liquid cations. Utilizing approximate analytic expressions for the hard sphere model, the method can predict complex liquid structure and thermodynamics while remaining computationally efficient. Requiring only minutes on standard desktop computers rather than months on supercomputers, the CHASM approach is well-suited to providing an approximate thermodynamic map of the wide compositional space relevant to early Earth evolution. As a first step on this path, we apply the CHASM formalism to the MgO system. We first demonstrate that the model parameters can be obtained by training on equation of state data for a variety of crystal polymorphs, which discretely sample the continuous range of coordination states available to the liquid; training only on solid data, CHASM thus provides a fully predictive model for oxide liquids. Using the best-fit parameter values, the coordination evolution and equation of state of MgO liquid is determined by free-energy minimization over a wide P-T range. These results are evaluated by favorable comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHASM is accurately capturing the dominant physical mechanism controlling the behavior of high pressure oxide liquids. By combining the CHASM description of MgO liquid with a thermodynamic model for solid MgO periclase, we also compare the MgO melting curve with both first principles computations and shock wave measurements. Future development of the CHASM model will incorporate SiO2, FeO, and Al2O3, providing a simple physical framework that enables both interpretation of experiments and prediction of behavior currently outside our technical or computational capabilities.

Structures of M2(SO2)6B12F12 (M = Ag or K) and Ag2(H2O)4B12F12: Comparison of the Coordination of SO2 versus H2O and of B12F122- versus Other Weakly Coordinating Anions to Metal Ions in the Solid State.

PubMed

Malischewski, Moritz; Peryshkov, Dmitry V; Bukovsky, Eric V; Seppelt, Konrad; Strauss, Steven H

2016-12-05

The structures of three solvated monovalent cation salts of the superweak anion B 12 F 12 2- (Y 2- ), K 2 (SO 2 ) 6 Y, Ag 2 (SO 2 ) 6 Y, and Ag 2 (H 2 O) 4 Y, are reported and discussed with respect to previously reported structures of Ag + and K + with other weakly coordinating anions. The structures of K 2 (SO 2 ) 6 Y and Ag 2 (SO 2 ) 6 Y are isomorphous and are based on expanded cubic close-packed arrays of Y 2- anions with M(OSO) 6 + complexes centered in the trigonal holes of one expanded close-packed layer of B 12 centroids (⊙). The K + and Ag + ions have virtually identical bicapped trigonal prism MO 6 F 2 coordination spheres, with M-O distances of 2.735(1)-3.032(2) Å for the potassium salt and 2.526(5)-2.790(5) Å for the silver salt. Each M(OSO) 6 + complex is connected to three other cationic complexes through their six μ-SO 2 -κ 1 O,κ 2 O' ligands. The structure of Ag 2 (H 2 O) 4 Y is unique [different from that of K 2 (H 2 O) 4 Y]. Planes of close-packed arrays of anions are offset from neighboring planes along only one of the linear ⊙···⊙···⊙ directions of the close-packed arrays, with [Ag(μ-H 2 O) 2 Ag(μ-H 2 O) 2 )] ∞ infinite chains between the planes of anions. There are two nearly identical AgO 4 F 2 coordination spheres, with Ag-O distances of 2.371(5)-2.524(5) Å and Ag-F distances of 2.734(4)-2.751(4) Å. This is only the second structurally characterized compound with four H 2 O molecules coordinated to a Ag + ion in the solid state. Comparisons with crystalline H 2 O and SO 2 solvates of other Ag + and K + salts of weakly coordinating anions show that (i) N[(SO 2 ) 2 (1,2-C 6 H 4 )] - , BF 4 - , SbF 6 - , and Al(OC(CF 3 ) 3 ) 4 - coordinate much more strongly to Ag + than does Y 2- , (ii) SnF 6 2- coordinates somewhat more strongly to K + than does Y 2- , and (iii) B 12 Cl 12 2- coordinates to K + about the same as, if not slightly weaker than, Y 2- .

Gauss-Kronrod-Trapezoidal Integration Scheme for Modeling Biological Tissues with Continuous Fiber Distributions

PubMed Central

Hou, Chieh; Ateshian, Gerard A.

2015-01-01

Fibrous biological tissues may be modeled using a continuous fiber distribution (CFD) to capture tension-compression nonlinearity, anisotropic fiber distributions, and load-induced anisotropy. The CFD framework requires spherical integration of weighted individual fiber responses, with fibers contributing to the stress response only when they are in tension. The common method for performing this integration employs the discretization of the unit sphere into a polyhedron with nearly uniform triangular faces (finite element integration or FEI scheme). Although FEI has proven to be more accurate and efficient than integration using spherical coordinates, it presents three major drawbacks: First, the number of elements on the unit sphere needed to achieve satisfactory accuracy becomes a significant computational cost in a finite element analysis. Second, fibers may not be in tension in some regions on the unit sphere, where the integration becomes a waste. Third, if tensed fiber bundles span a small region compared to the area of the elements on the sphere, a significant discretization error arises. This study presents an integration scheme specialized to the CFD framework, which significantly mitigates the first drawback of the FEI scheme, while eliminating the second and third completely. Here, integration is performed only over the regions of the unit sphere where fibers are in tension. Gauss-Kronrod quadrature is used across latitudes and the trapezoidal scheme across longitudes. Over a wide range of strain states, fiber material properties, and fiber angular distributions, results demonstrate that this new scheme always outperforms FEI, sometimes by orders of magnitude in the number of computational steps and relative accuracy of the stress calculation. PMID:26291492

A Gauss-Kronrod-Trapezoidal integration scheme for modeling biological tissues with continuous fiber distributions.

PubMed

Hou, Chieh; Ateshian, Gerard A

2016-01-01

Fibrous biological tissues may be modeled using a continuous fiber distribution (CFD) to capture tension-compression nonlinearity, anisotropic fiber distributions, and load-induced anisotropy. The CFD framework requires spherical integration of weighted individual fiber responses, with fibers contributing to the stress response only when they are in tension. The common method for performing this integration employs the discretization of the unit sphere into a polyhedron with nearly uniform triangular faces (finite element integration or FEI scheme). Although FEI has proven to be more accurate and efficient than integration using spherical coordinates, it presents three major drawbacks: First, the number of elements on the unit sphere needed to achieve satisfactory accuracy becomes a significant computational cost in a finite element (FE) analysis. Second, fibers may not be in tension in some regions on the unit sphere, where the integration becomes a waste. Third, if tensed fiber bundles span a small region compared to the area of the elements on the sphere, a significant discretization error arises. This study presents an integration scheme specialized to the CFD framework, which significantly mitigates the first drawback of the FEI scheme, while eliminating the second and third completely. Here, integration is performed only over the regions of the unit sphere where fibers are in tension. Gauss-Kronrod quadrature is used across latitudes and the trapezoidal scheme across longitudes. Over a wide range of strain states, fiber material properties, and fiber angular distributions, results demonstrate that this new scheme always outperforms FEI, sometimes by orders of magnitude in the number of computational steps and relative accuracy of the stress calculation.

Bis(dicyclo-hexyl-ammonium) μ-oxalato-κO,O:O,O-bis-[aqua-(oxalato-κO,O)diphenyl-stannate(IV)].

PubMed

Gueye, Ndongo; Diop, Libasse; Molloy, K C Kieran; Kociok-Köhn, Gabrielle

2010-11-24

The structure of the title compound, (C(12)H(24)N)(2)[Sn(2)(C(6)H(5))(4)(C(2)O(4))(3)(H(2)O)(2)], consists of a bischelating oxalate ion, located on an inversion center, which is linked to two SnPh(2) groups. The coordination sphere of the Sn(IV) ion is completed by a monochelating oxalate anion and a water mol-ecule. The Sn(IV) atoms are thus seven-coordinated. The discrete binuclear units are further connected by hydrogen bonds, leading to a supra-molecular crystal structure. The asymmetric unit contains one half dianion and one (Cy(2)NH(2))(+) cation.

Preparation of Geophysical Fluid Flow Experiments ( GeoFlow ) in the Fluid Science Laboratory on ISS

NASA Astrophysics Data System (ADS)

Egbers, C.

The ,,GeoFlow" is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluidmechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field similar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment requires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth's liquid core the exp eriment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heating the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number. Results of preparatory experiments and numerical simulation of the space experiment will be presented. Funding from DLR under grant 50 WM 0122 is greatfully ackwnoledged.

A gadolinium(III) complex of a carboxylic-phosphorus acid derivative of diethylenetriamine covalently bound to inulin, a potential macromolecular MRI contrast agent.

PubMed

Lebdusková, Petra; Kotek, Jan; Hermann, Petr; Vander Elst, Luce; Muller, Robert N; Lukes, Ivan; Peters, Joop A

2004-01-01

A novel conjugate of a polysaccharide and a Gd(III) chelate with potential as contrast agent for magnetic resonance imaging (MRI) was synthesized. The structure of the chelate was derived from H5DTPA by replacing the central pendant arm by a phosphinic acid functional group, which was covalently bound to the polysaccharide inulin. On the average, each monosaccharide unit of the inulin was attached to approximately one (0.9) chelate moiety. The average molecular weight is 23110 and the average number of Gd3+ ions per molecule is 24. The ligand binds the Gd3+ ion in an octadentate fashion via three nitrogen atoms, four carboxylate oxygen atoms, and one P-O oxygen atom, and its first coordination sphere is completed by a water molecule. This compound shows promising properties for application as a contrast agent for MRI thanks to a favorable residence lifetime of this water molecule (170 ns at 298 K), a relatively long rotational correlation time (866 ps at 298 K), and the presence of two water molecules in the second coordination sphere of the Gd3+ ion. Furthermore, its stability toward transmetalation with Zn(II) is as high as that of the clinically used [Gd(DTPA)(H2O)]2-.

The impact of whole human blood on the kinetic inertness of platinum(iv) prodrugs - an HPLC-ICP-MS study.

PubMed

Theiner, Sarah; Grabarics, Márkó; Galvez, Luis; Varbanov, Hristo P; Sommerfeld, Nadine S; Galanski, Markus; Keppler, Bernhard K; Koellensperger, Gunda

2018-04-17

The potential advantage of platinum(iv) complexes as alternatives to classical platinum(ii)-based drugs relies on their kinetic stability in the body before reaching the tumor site and on their activation by reduction inside cancer cells. In this study, an analytical workflow has been developed to investigate the reductive biotransformation and kinetic inertness of platinum(iv) prodrugs comprising different ligand coordination spheres (respectively, lipophilicity and redox behavior) in whole human blood. The distribution of platinum(iv) complexes in blood pellets and plasma was determined by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave digestion. An analytical approach based on reversed-phase (RP)-ICP-MS was used to monitor the parent compound and the formation of metabolites using two different extraction procedures. The ligand coordination sphere of the platinum(iv) complexes had a significant impact on their accumulation in red blood cells and on their degree of kinetic inertness in whole human blood. The most lipophilic platinum(iv) compound featuring equatorial chlorido ligands showed a pronounced penetration into blood cells and a rapid reductive biotransformation. In contrast, the more hydrophilic platinum(iv) complexes with a carboplatin- and oxaliplatin-core exerted kinetic inertness on a pharmacologically relevant time scale with notable amounts of the compound accumulated in the plasma fraction.

Role of second-sphere coordination in anion binding: Synthesis, characterization and X-ray structure of hexaamminecobalt(III) chloride hydrogen phthalate trihydrate and sodium hexaamminecobalt(III) benzoate monohydrate

NASA Astrophysics Data System (ADS)

Sharma, Raj Pal; Bala, Ritu; Sharma, Rajni; Kariuki, B. M.; Rychlewska, Urszula; Warżajtis, Beata

2005-06-01

In an effort to utilize [Co(NH 3) 6] 3+cation as a new host for carboxylate ions, orange coloured crystalline solids of composition [Co(NH 3) 6]Cl(C 8H 5O 4) 2·3H 2O ( 1) and Na[Co(NH 3) 6](C 7H 5O 2) 4·H 2O ( 2) were obtained by reacting hot aqueous solutions of hexaamminecobalt(III) chloride with potassium hydrogen phthalate and sodium benzoate in 1:3 molar ratio, respectively. The title complex salts were characterized by elemental analyses and spectroscopic studies (IR, UV/Visible and NMR). Single crystal X-ray structure determinations revealed the formation of second-sphere coordination complexes based on hydrogen bond interactions. In complex salt 1 only two out of three ionisable chloride ions present in [Co(NH 3) 6]Cl 3 were replaced by two CHO4- ions whereas in complex salt 2 all the three ionisable chloride ions present in [Co(NH 3) 6]Cl 3 were replaced and the final product was an adduct with another mole of sodium benzoate in solid state. The crystal lattice is stabilized by electrostatic forces of attraction and predominantly N-H⋯O interactions.

Geometric Calibration of Full Spherical Panoramic Ricoh-Theta Camera

NASA Astrophysics Data System (ADS)

Aghayari, S.; Saadatseresht, M.; Omidalizarandi, M.; Neumann, I.

2017-05-01

A novel calibration process of RICOH-THETA, full-view fisheye camera, is proposed which has numerous applications as a low cost sensor in different disciplines such as photogrammetry, robotic and machine vision and so on. Ricoh Company developed this camera in 2014 that consists of two lenses and is able to capture the whole surrounding environment in one shot. In this research, each lens is calibrated separately and interior/relative orientation parameters (IOPs and ROPs) of the camera are determined on the basis of designed calibration network on the central and side images captured by the aforementioned lenses. Accordingly, designed calibration network is considered as a free distortion grid and applied to the measured control points in the image space as correction terms by means of bilinear interpolation. By performing corresponding corrections, image coordinates are transformed to the unit sphere as an intermediate space between object space and image space in the form of spherical coordinates. Afterwards, IOPs and EOPs of each lens are determined separately through statistical bundle adjustment procedure based on collinearity condition equations. Subsequently, ROPs of two lenses is computed from both EOPs. Our experiments show that by applying 3*3 free distortion grid, image measurements residuals diminish from 1.5 to 0.25 degrees on aforementioned unit sphere.

Spectroscopic identification of binary and ternary surface complexes of Np(V) on gibbsite.

PubMed

Gückel, Katharina; Rossberg, André; Müller, Katharina; Brendler, Vinzenz; Bernhard, Gert; Foerstendorf, Harald

2013-12-17

For the first time, detailed molecular information on the Np(V) sorption species on amorphous Al(OH)3 and crystalline gibbsite was obtained by in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The results consistently demonstrate the formation of mononuclear inner sphere complexes of the NpO2(+) ion irrespective of the prevailing atmospheric condition. The impact of the presence of atmospheric equivalent added carbonate on the speciation in solution and on the surfaces becomes evident from vibrational data. While the 1:1 aqueous carbonato species (NpO2CO3(-)) was found to become predominant in the circumneutral pH range, it is most likely that this species is sorbed onto the gibbsite surface as a ternary inner sphere surface complex where the NpO2(+) moiety is directly coordinated to the functional groups of the gibbsite's surface. These findings are corroborated by results obtained from EXAFS spectroscopy providing further evidence for a bidentate coordination of the Np(V) ion on amorphous Al(OH)3. The identification of the Np(V) surface species on gibbsite constitutes a basic finding for a comprehensive description of the dissemination of neptunium in groundwater systems.

Crystal structure of tetra­aqua­bis­(pyrimidin-1-ium-4,6-diolato-κO 4)manganese(II)

PubMed Central

Shennara, Khaled A.

2017-01-01

The MnII ion in the structure of the mononuclear title compound, [Mn(C4H3N2O2)2(H2O)4], is situated on an inversion center and is coordinated by two O atoms from two deprotonated 4,6-di­hydroxy­pyrimidine ligands and by four O atoms from water mol­ecules giving rise to a slightly distorted octa­hedral coordination sphere. The complex includes an intra­molecular hydrogen bond between an aqua ligand and the non-protonated N ring atom. The extended structure is stabilized by inter­molecular hydrogen bonds between aqua ligands, by hydrogen bonds between N and O atoms of the ligands of adjacent mol­ecules, and by hydrogen bonds between aqua ligands and the non-coordinating O atom of an adjacent mol­ecule. PMID:28435734

Linked exploratory visualizations for uncertain MR spectroscopy data

NASA Astrophysics Data System (ADS)

Feng, David; Kwock, Lester; Lee, Yueh; Taylor, Russell M., II

2010-01-01

We present a system for visualizing magnetic resonance spectroscopy (MRS) data sets. Using MRS, radiologists generate multiple 3D scalar fields of metabolite concentrations within the brain and compare them to anatomical magnetic resonance imaging. By understanding the relationship between metabolic makeup and anatomical structure, radiologists hope to better diagnose and treat tumors and lesions. Our system consists of three linked visualizations: a spatial glyph-based technique we call Scaled Data-Driven Spheres, a parallel coordinates visualization augmented to incorporate uncertainty in the data, and a slice plane for accurate data value extraction. The parallel coordinates visualization uses specialized brush interactions designed to help users identify nontrivial linear relationships between scalar fields. We describe two novel contributions to parallel coordinates visualizations: linear function brushing and new axis construction. Users have discovered significant relationships among metabolites and anatomy by linking interactions between the three visualizations.

Linked Exploratory Visualizations for Uncertain MR Spectroscopy Data

PubMed Central

Feng, David; Kwock, Lester; Lee, Yueh; Taylor, Russell M.

2010-01-01

We present a system for visualizing magnetic resonance spectroscopy (MRS) data sets. Using MRS, radiologists generate multiple 3D scalar fields of metabolite concentrations within the brain and compare them to anatomical magnetic resonance imaging. By understanding the relationship between metabolic makeup and anatomical structure, radiologists hope to better diagnose and treat tumors and lesions. Our system consists of three linked visualizations: a spatial glyph-based technique we call Scaled Data-Driven Spheres, a parallel coordinates visualization augmented to incorporate uncertainty in the data, and a slice plane for accurate data value extraction. The parallel coordinates visualization uses specialized brush interactions designed to help users identify nontrivial linear relationships between scalar fields. We describe two novel contributions to parallel coordinates visualizations: linear function brushing and new axis construction. Users have discovered significant relationships among metabolites and anatomy by linking interactions between the three visualizations. PMID:21152337

Pseudosymmetric fac-di-aqua-trichlorido[(di-methyl-phosphor-yl)methanaminium-κO]manganese(II).

PubMed

Reiss, Guido J

2013-05-01

In the title compound, [Mn(C3H11NOP)Cl3(H2O)2], the Mn(II) metal center has a distorted o-cta-hedral geometry, coordinated by the three chloride ligands showing a facial arrangement. Two water mol-ecules and the O-coordinated dpmaH cation [dpmaH = (di-methyl-phosphor-yl)methanaminium] complete the coordination sphere. Each complex mol-ecule is connected to its neighbours by O-H⋯Cl and N-H⋯Cl hydrogen bonds. Two of the chloride ligands and the two water ligands form a hydrogen-bonded polymeric sheet in the ab plane. Furthermore, these planes are connected to adjacent planes by hydrogen bonds from the aminium function of cationic dpmaH ligand. A pseudo-mirror plane perpendicular to the b axis in the chiral space group P21 is observed together with inversion twinning [ratio = 0.864 (5):0.136 (5)].

A new class of sonic composites

NASA Astrophysics Data System (ADS)

Munteanu, Ligia; Chiroiu, Veturia; Donescu, Ştefania; Brişan, Cornel

2014-03-01

Transformation acoustics opens a new avenue towards the architecture, modeling and simulation of a new class of sonic composites with scatterers made of various materials and having various shapes embedded in an epoxy matrix. The design of acoustic scatterers is based on the property of Helmholtz equations to be invariant under a coordinate transformation, i.e., a specific spatial compression is equivalent to a new material in a new space. In this paper, the noise suppression for a wide full band-gap of frequencies is discussed for spherical shell scatterers made of auxetic materials (materials with negative Poisson's ratio). The original domain consists of spheres made from conventional foams with positive Poisson's ratio. The spatial compression is controlled by the coordinate transformation, and leads to an equivalent domain filled with an auxetic material. The coordinate transformation is strongly supported by the manufacturing of auxetics which is based on the pore size reduction through radial compression molds.

Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts.

PubMed

Wurster, Benjamin; Grumelli, Doris; Hötger, Diana; Gutzler, Rico; Kern, Klaus

2016-03-23

Developing efficient catalysts for electrolysis, in particular for the oxygen evolution in the anodic half cell reaction, is an important challenge in energy conversion technologies. By taking inspiration from the catalytic properties of single-atom catalysts and metallo-proteins, we exploit the potential of metal-organic networks as electrocatalysts in the oxygen evolution reaction (OER). A dramatic enhancement of the catalytic activity toward the production of oxygen by nearly 2 orders of magnitude is demonstrated for novel heterobimetallic organic catalysts compared to metallo-porphyrins. Using a supramolecular approach we deliberately place single iron and cobalt atoms in either of two different coordination environments and observe a highly nonlinear increase in the catalytic activity depending on the coordination spheres of Fe and Co. Catalysis sets in at about 300 mV overpotential with high turnover frequencies that outperform other metal-organic catalysts like the prototypical hangman porphyrins.

(18-Crown-6)potassium [(1,2,5,6-η)-cyclo-octa-1,5-diene][(1,2,3,4-η)-naph-tha-lene]-ferrate(-I).

PubMed

Brennessel, William W; Ellis, John E

2012-10-01

The title salt, [K(C(12)H(24)O(6))][Fe(C(8)H(12))(C(10)H(8))], is the only known naphthalene complex containing iron in a formally negative oxidation state. Each (naphthalene)(1,5-cod)ferrate(-I) anion is in contact with one (18-crown-6)potassium cation via K⋯C contacts to the outer four carbon atoms of the naphthalene ligand (cod = 1,5-cyclo-octa-diene, 18-crown-6 = 1,4,7,10,13,16-hexa-oxacyclo-octa-deca-ne). When using the midpoints of the coordinating olefin bonds, the overall geometry of the coordination sphere around iron can be best described as distorted tetra-hedral. The naphthalene fold angle between the plane of the iron-coordinating butadiene unit and the plane containing the exo-benzene moiety is 19.2 (1)°.

Fabrication of Pt/Au concentric spheres from triblock copolymer.

PubMed

Koh, Haeng-Deog; Park, Soojin; Russell, Thomas P

2010-02-23

Dispersion of an aqueous H(2)PtCl(6) solution into a trifluorotoluene (TFT) solution of a polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) triblock copolymer produced an emulsion-induced hollow micelle (EIHM), comprising a water nanodroplet stabilized by PEO, H(2)PtCl(6)/P2VP, and PS, sequentially. The following addition of an aqueous LiAuCl(4) solution into the dispersion led to a coordination of LiAuCl(4) and PEO. The resulting spherical EIHM structure was transformed to a hollow cylindrical micelle by the fusion of spherical EIHM with the addition of methanol. This structural transition was reversible by the alternative addition of methanol and TFT. Oxygen plasma was used to generate Pt/Au concentric spheres and hollow cylindrical Pt/Au nano-objects.

Dynamique socio-économique et crise familiale et éducative en côte-d'ivoire de 1960 a 1990

NASA Astrophysics Data System (ADS)

Assy, Edmond Paul

2003-09-01

This article reflects on the crisis affecting the sphere of the family and education in Côte d'Ivoire between 1960 and 1990. The country's family structure has been shaken by the market economy, by the conventional school system and by the modern legal code. This has in turn engendered a crisis of parental authority and a variety of problems connected with the instability of marriages in Côte d'Ivoire. How, then, is it possible to redress the situation and establish a partnership between the family, the educational system and society? The author advances a series of propositions for creating a better coordination between the family and the educational sphere and for reinforcing the educative capacity of the family and of society as a whole.

The Structure of Ethylbenzene, Styrene and Phenylacetylene Determined by Total Neutron Scattering

PubMed Central

Szala‐Bilnik, Joanna; Falkowska, Marta; Bowron, Daniel T.

2017-01-01

Abstract Organic solvents such as phenylacetylene, styrene and ethylbenzene are widely used in industrial processes, especially in the production of rubber or thermoplastics. Despite their important applications detailed knowledge about their structure is limited. In this paper the structures of these three aromatic solvents were investigated using neutron diffraction. The results show that many of their structural characteristics are similar, although the structure of phenylacetylene is more ordered and has a smaller solvation sphere than either ethylbenzene or styrene. Two regions within the first coordination sphere, in which the surrounding molecules show different preferable orientations with respect to the central molecule, were found for each liquid. Additionally, the localisation of the aliphatic chains reveals that they tend to favour closer interactions with each other than to the aromatic rings of the adjacent molecules. PMID:28672104

Mechanical Characterization of Partially Crystallized Sphere Packings

NASA Astrophysics Data System (ADS)

Hanifpour, M.; Francois, N.; Vaez Allaei, S. M.; Senden, T.; Saadatfar, M.

2014-10-01

We study grain-scale mechanical and geometrical features of partially crystallized packings of frictional spheres, produced experimentally by a vibrational protocol. By combining x-ray computed tomography, 3D image analysis, and discrete element method simulations, we have access to the 3D structure of internal forces. We investigate how the network of mechanical contacts and intergranular forces change when the packing structure evolves from amorphous to near perfect crystalline arrangements. We compare the behavior of the geometrical neighbors (quasicontracts) of a grain to the evolution of the mechanical contacts. The mechanical coordination number Zm is a key parameter characterizing the crystallization onset. The high fluctuation level of Zm and of the force distribution in highly crystallized packings reveals that a geometrically ordered structure still possesses a highly random mechanical backbone similar to that of amorphous packings.

A Comparison of Two Yeast MnSODs: Mitochondrial Saccharomyces cerevisiae versus Cytosolic Candida albicans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheng Y.; Cabelli D.; Stich, T.A.

Human MnSOD is significantly more product-inhibited than bacterial MnSODs at high concentrations of superoxide (O{sub 2}{sup -}). This behavior limits the amount of H{sub 2}O{sub 2} produced at high [O{sub 2}{sup -}]; its desirability can be explained by the multiple roles of H{sub 2}O{sub 2} in mammalian cells, particularly its role in signaling. To investigate the mechanism of product inhibition in MnSOD, two yeast MnSODs, one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), were isolated and characterized. ScMnSOD and CaMnSODc are similar in catalytic kinetics, spectroscopy, and redox chemistry, and they both rest predominantlymore » in the reduced state (unlike most other MnSODs). At high [O{sub 2}{sup -}], the dismutation efficiencies of the yeast MnSODs surpass those of human and bacterial MnSODs, due to very low level of product inhibition. Optical and parallel-mode electron paramagnetic resonance (EPR) spectra suggest the presence of two Mn{sup 3+} species in yeast Mn{sup 3+}SODs, including the well-characterized 5-coordinate Mn{sup 3+} species and a 6-coordinate L-Mn{sup 3+} species with hydroxide as the putative sixth ligand (L). The first and second coordination spheres of ScMnSOD are more similar to bacterial than to human MnSOD. Gln154, an H-bond donor to the Mn-coordinated solvent molecule, is slightly further away from Mn in yeast MnSODs, which may result in their unusual resting state. Mechanistically, the high efficiency of yeast MnSODs could be ascribed to putative translocation of an outer-sphere solvent molecule, which could destabilize the inhibited complex and enhance proton transfer from protein to peroxide. Our studies on yeast MnSODs indicate the unique nature of human MnSOD in that it predominantly undergoes the inhibited pathway at high [O{sub 2}{sup -}].« less

A Comparison of Two Yeast MnSODs: Mitochondrial Saccharomyces cerevisiae versus Cytosolic Candida albicans

PubMed Central

Sheng, Yuewei; Stich, Troy A.; Barnese, Kevin; Gralla, Edith B.; Cascio, Duilio; Britt, R. David; Cabelli, Diane E.; Valentine, Joan Selverstone

2011-01-01

Human MnSOD is significantly more product-inhibited than bacterial MnSODs at high concentrations of superoxide (O2−). This behavior limits the amount of H2O2 produced at high [O2−]; its desirability can be explained by the multiple roles of H2O2 in mammalian cells, particularly its role in signaling. To investigate the mechanism of product inhibition in MnSOD, two yeast MnSODs, one from Saccharomyces cerevisiae mitochondria (ScMnSOD) and the other from Candida albicans cytosol (CaMnSODc), were isolated and characterized. ScMnSOD and CaMnSODc are similar in catalytic kinetics, spectroscopy and redox chemistry, and they both rest predominantly in the reduced state (unlike most other MnSODs). At high [O2−] the dismutation efficiencies of the yeast MnSODs surpass those of human and bacterial MnSODs, due to very low level of product inhibition. Optical and parallel-mode electron paramagnetic resonance (EPR) spectra suggest the presence of two Mn3+ species in yeast Mn3+SODs, including the well-characterized 5-coordinate Mn3+ species and a 6-coordinate L-Mn3+ species with hydroxide as the putative sixth ligand (L). The first and second coordination spheres of ScMnSOD are more similar to bacterial than to human MnSOD. Gln154, an H-bond donor to the Mn-coordinated solvent molecule, is slightly further away from Mn in yeast MnSODs, which may result in their unusual resting state. Mechanistically, the high efficiency of yeast MnSODs could be ascribed to putative translocation of an outer-sphere solvent molecule, which could destabilize the inhibited complex and enhance proton transfer from protein to peroxide. Our studies on yeast MnSODs indicate the unique nature of human MnSOD in that it predominantly undergoes the inhibited pathway at high [O2−]. PMID:22077216

Silver(I) complexes with hydantoins and allantoin: synthesis, crystal and molecular structure, cytotoxicity and pharmacokinetics.

PubMed

Puszyńska-Tuszkanow, Mariola; Grabowski, Tomasz; Daszkiewicz, Marek; Wietrzyk, Joanna; Filip, Beata; Maciejewska, Gabriela; Cieślak-Golonka, Maria

2011-01-01

Coordination polymers [Ag(L(1,3))](n) (L(1)=hydantoin, L(3)=5,5-dimethylhydantoin), {[Ag(L(2))](.)0.5H(2)O}(n) (L(2)=1-methylhydantoin) and [Ag(NH(3))(L(4))](n) (L(4)=allantoin) were prepared and characterized by elemental analysis, spectroscopic (IR, FTIR and NMR), thermal and mass spectrometry methods. The crystal structure of {[Ag(1-methylhydantoin)]·0,5H(2)O}(n) was determined and analyzed. Three 1-methylhydantoinate ligands create a T-shape (CN=3) coordination sphere around the Ag(+) ion. Additionally, a short Ag⋯Ag distance of 2.997Å was found in the structure resulting in the expanded [3+2] environment of a distorted square shape. The [Ag(L(2))] entities are bound to each other by the bridging organic ligands. Thus a two-dimensional coordination polymer is created with water molecules located between the layers. In contrast to hydantoins, the allantoin complex contains an additional ammonia molecule in the coordination sphere. Moreover, in the Ag-alla complex the M-organic ligand binding site is shifted to the N-atom of the ureid chain. Free ligands are cytotoxically inactive against human MCF-7 and A549 cancer cell lines and mouse fibroblasts Balb/3T3. The silver hydantoin complexes exhibit a very strong activity against these lines. (The introduction of the methyl groups to the ring slightly increases resistance only against the A549 cell line.) In contrast, the silver complex of allantoin shows only a weak activity which may be related to the presence of the cytotoxic ammonia group in the composition of the compound and/or the different binding site of the ligand. Calculated in silico physiochemical parameters are promising for the future application of the complexes as drugs. Copyright © 2010 Elsevier Inc. All rights reserved.

Alkaline-earth metal carboxylates characterized by 43Ca and 87Sr solid-state NMR: impact of metal-amine bonding.

PubMed

Burgess, Kevin M N; Xu, Yang; Leclerc, Matthew C; Bryce, David L

2014-01-06

A series of calcium and strontium complexes featuring aryl carboxylate ligands has been prepared and characterized by alkaline-earth ((43)Ca and (87)Sr) solid-state NMR experiments in a magnetic field of 21.1 T. In the 11 compounds studied as part of this work, a range of coordination motifs are observed including nitrogen atom binding to Ca(2+) and Sr(2+), a binding mode which has not been investigated previously by (43)Ca or (87)Sr solid-state NMR. (43)Ca isotopic enrichment has enabled the full characterization of the (43)Ca electric field gradient (EFG) and chemical shift tensors of the two calcium sites in calcium p-aminosalicylate (Ca(pams)), where both NMR interactions are affected by the presence of a nitrogen atom in the first coordination sphere of one of the metal sites. The (43)Ca isotropic chemical shift is sensitive to the Ca-N distance as exemplified by the NMR parameters of a second form of Ca(pams) and density functional theory (DFT) calculations. Studies of the strontium analogue, Sr(pams), confirm a similar sensitivity of the (87)Sr EFG tensor to the presence or absence of nitrogen in the first coordination sphere. To our knowledge, this is the first systematic (87)Sr NMR study of strontium complexes featuring organic ligands. The |CQ((87)Sr)| values are found to be sensitive to the coordination number about Sr(2+). In general, this work has also established a larger data set of reliable experimental |CQ((43)Ca)| values which correlate well with those obtained using gauge-including projector-augmented-wave (GIPAW) DFT calculations. It is found that the use of a recently recommended quadrupole moment for (43)Ca, -44.4 mbarn, improves the agreement with experimental values. This contribution lays the groundwork for the interpretation of (43)Ca and (87)Sr NMR spectra of more challenging systems, particularly where nitrogen-alkaline earth metal bonding is occurring.

Coordination- and Redox-Noninnocent Behavior of Ambiphilic Ligands Containing Antimony.

PubMed

Jones, J Stuart; Gabbaï, François P

2016-05-17

Stimulated by applications in catalysis, the chemistry of ambiphilic ligands featuring both donor and acceptor functionalities has experienced substantial growth in the past several years. The unique opportunities in catalysis offered by ambiphilic ligands stem from the ability of their acceptor functionalities to play key roles via metal-ligand cooperation or modulation of the reactivity of the metal center. Ligands featuring group 13 centers, most notably boranes, as their acceptor functionalities have undoubtedly spearheaded these developments, with remarkable results having been achieved in catalytic hydrogenation and hydrosilylation. Motivated by these developments as well as by our fundamental interest in the chemistry of heavy group 15 elements, we became fascinated by the possibility of employing antimony centers as Lewis acids within ambiphilic ligands. The chemistry of antimony-based ligands, most often encountered as trivalent stibines, has historically been considered to mirror that of their lighter phosphorus-based congeners. There is growing evidence, however, that antimony-based ligands may display unique coordination behavior and reactivity. Additionally, despite the diverse Lewis acid and redox chemistry that antimony exhibits, there have been only limited efforts to explore this chemistry within the coordination sphere of a transition metal. By incorporation of antimony into the framework of polydentate ligands in order to enforce the main group metal-transition metal interaction, the effect of redox and coordination events at the antimony center on the structure, electronics, and reactivity of the metal complex may be investigated. This Account describes our group's continuing efforts to probe the coordination behavior, reactivity, and application of ambiphilic ligands incorporating antimony centers. Structural and theoretical studies have established that both Sb(III) and Sb(V) centers in polydentate ligands may act as Z-type ligands toward late transition metals. Although coordinated to a metal, the antimony centers in these complexes retain residual Lewis acidity, as evidenced by their ability to participate in anion binding. Anion binding events at the antimony center have been shown by structural, spectroscopic, and theoretical studies to perturb the antimony-transition metal interaction and in some cases to trigger reactivity at the metal center. Coordinated Sb(III) centers in polydentate ligands have also been found to readily undergo two-electron oxidation, generating strongly Lewis acidic Sb(V) centers in the coordination sphere of the metal. Theoretical studies suggest that oxidation of the coordinated antimony center induces an umpolung of the antimony-metal bond, resulting in depletion of electron density at the metal center. In addition to elucidating the fundamental coordination and redox chemistry of antimony-containing ambiphilic ligands, our work has demonstrated that these unusual behaviors show promise for use in a variety of applications. The ability of coordinated antimony centers to bind anions has been exploited for sensing applications, in which anion coordination at antimony leads to a colorimetric response via a change in the geometry about the metal center. In addition, the capacity of antimony Lewis acids to modulate the electron density of coordinated metals has proved to be key in facilitating photochemical activation of M-X bonds as well as antimony-centered redox-controlled catalysis.

Compaction of granular materials: numerical simulation of "elastic" compression and pressure solution creep

NASA Astrophysics Data System (ADS)

Bernabe, Y.; Evans, J.

2012-12-01

In a previous work we investigated stress transfer in a pair of grain contacts undergoing pressure solution (PS) creep, showed that stress transfer resulted in a significant decrease in overall strain rate, and concluded that PS creep rates of a randomly packed granular aggregate should be affected by packing evolution and the formation of new contacts during creep. To test these conclusions further, we are numerically simulating the "elastic" hydrostatic compression of a random pack of spheres, using a numerical method similar to that of Cundall and Strack [1979]. We assumed that the spheres were frictionless (i.e., spheres in contact only interacted through normal forces) and that the contact forces obeyed the non-linear Digby [1981] model. In order to determine the PS creep compression of the sphere pack subjected to a constant confining pressure pc, we calculated the thicknesses of the dissolved layers at each individual grain contact during a small time increment and, from these, the overall deformation of the sphere pack. We used an analytical expression discussed in our previous paper and originating from Lehner and Leroy [2004]. During these simulations, we also computed the mean coordination number of the grain contact z, the effective bulk modulus K of the sphere pack and others parameters characterizing the topological and mechanical properties of the sphere assembly. Our results show strong non-linear increase of z and K with pc during "elastic" compression and, with time, during PS creep. The packing rearrangements associated with PS creep produce complex time dependence of the overall deformation ɛ(t). We observed a regular transition from ɛ∝t^3/4 at early times (i.e., less than 0.1 years) and ɛ∝t^1/3 at late times (i.e., more than 1000 years). Cundall, P.A., and O.D.L. Strack (1979), A discrete numerical model for granular assemblies, Geotech., 29, 47-65. Digby, P.J. (1981), The effective elastic moduli of porous rocks, J. Appl. Mech., 48, 803-808. Lehner, F.K., and Y. Leroy (2004), Sandstone compaction by intergranular pressure solution, In Mech. Fluid Saturated Rocks (eds. Y. Guéguen and M. Boutéca), Elsevier.

Determination of the Avogadro constant by the XRCD method using a 28Si-enriched sphere

NASA Astrophysics Data System (ADS)

Kuramoto, Naoki; Mizushima, Shigeki; Zhang, Lulu; Fujita, Kazuaki; Azuma, Yasushi; Kurokawa, Akira; Okubo, Sho; Inaba, Hajime; Fujii, Kenichi

2017-10-01

To determine the Avogadro constant N A by the x-ray crystal density method, the density of a 28Si-enriched crystal was determined by absolute measurements of the mass and volume of a 1 kg sphere manufactured from the crystal. The mass and volume were determined by an optical interferometer and a vacuum mass comparator, respectively. The sphere surface was characterized by x-ray photoelectron spectroscopy and spectroscopic ellipsometry to derive the mass and volume of the Si core of the sphere excluding the surface layers. From the mass and volume, the density of the Si core was determined with a relative standard uncertainty of 2.3  ×  10-8. By combining the Si core density with the lattice constant and the molar mass of the sphere reported by the International Avogadro Coordination (IAC) project in 2015, a new value of 6.022 140 84(15)  ×  1023 mol-1 was obtained for N A with a relative standard uncertainty of 2.4  ×  10-8. To make the N A value determined in this work usable for a future adjustment of the fundamental constants by the CODATA Task Group on Fundamental Constants, the correlation of the new N A value with the N A values determined in our previous works was examined. The correlation coefficients with the values of N A determined by IAC in 2011 and 2015 were estimated to be 0.07 and 0.28, respectively. The correlation of the new N A value with the N A value determined by IAC in 2017 using a different 28Si-enriched crystal was also examined, and the correlation coefficient was estimated to be 0.21.

An efficient implementation of a high-order filter for a cubed-sphere spectral element model

NASA Astrophysics Data System (ADS)

Kang, Hyun-Gyu; Cheong, Hyeong-Bin

2017-03-01

A parallel-scalable, isotropic, scale-selective spatial filter was developed for the cubed-sphere spectral element model on the sphere. The filter equation is a high-order elliptic (Helmholtz) equation based on the spherical Laplacian operator, which is transformed into cubed-sphere local coordinates. The Laplacian operator is discretized on the computational domain, i.e., on each cell, by the spectral element method with Gauss-Lobatto Lagrange interpolating polynomials (GLLIPs) as the orthogonal basis functions. On the global domain, the discrete filter equation yielded a linear system represented by a highly sparse matrix. The density of this matrix increases quadratically (linearly) with the order of GLLIP (order of the filter), and the linear system is solved in only O (Ng) operations, where Ng is the total number of grid points. The solution, obtained by a row reduction method, demonstrated the typical accuracy and convergence rate of the cubed-sphere spectral element method. To achieve computational efficiency on parallel computers, the linear system was treated by an inverse matrix method (a sparse matrix-vector multiplication). The density of the inverse matrix was lowered to only a few times of the original sparse matrix without degrading the accuracy of the solution. For better computational efficiency, a local-domain high-order filter was introduced: The filter equation is applied to multiple cells, and then the central cell was only used to reconstruct the filtered field. The parallel efficiency of applying the inverse matrix method to the global- and local-domain filter was evaluated by the scalability on a distributed-memory parallel computer. The scale-selective performance of the filter was demonstrated on Earth topography. The usefulness of the filter as a hyper-viscosity for the vorticity equation was also demonstrated.

Potentiometric and DFT studies of Cu(II) complexes with glycylglycine and methionine of interest for the brain chemistry

NASA Astrophysics Data System (ADS)

Vilhena, Felipe S.; Felcman, Judith; Szpoganicz, Bruno; Miranda, Fabio S.

2017-01-01

A large number of copper (II) complexes have been used as mimetic models for metalloproteins and metalloenzymes. Due to the lack of structural information about copper (II) complexes in aqueous solution, the coordination environment of this metal is not well established. In this work, pKa values of the complexes in the Cu:GlyGly, Cu:Met and Cu:GlyGly:Met systems were calculated by potentiometric titration at 25 °C and ionic strength of 0.1 mol L-1. The coordination modes of the ligands were explored for the main hydrolytic species throught RI-PBE/def2-SVP/COSMO level. In the Cu:GlyGly system, DFT results indicated that the NamineNpept coordination of dipeptide is 2.1 kcal mol-1 more stable than the tridentate NamineNpeptOcarboxy coordination moiety. The deprotonation of the peptide nitrogen is 13.7 kcal mol-1 more favorable than the hydrolysis of the water molecule coordinated to the metal. In the Cu:GlyGly:Met system, the sulfur atom does not belong to the copper (II) coordination sphere. Once the copper ion is incorporated into peptides, another ligand as methionine could bind to this system and carry an antioxidant site to different brain regions.

Wigner functions for nonclassical states of a collection of two-level atoms

NASA Technical Reports Server (NTRS)

Agarwal, G. S.; Dowling, Jonathan P.; Schleich, Wolfgang P.

1993-01-01

The general theory of atomic angular momentum states is used to derive the Wigner distribution function for atomic angular momentum number states, coherent states, and squeezed states. These Wigner functions W(theta,phi) are represented as a pseudo-probability distribution in spherical coordinates theta and phi on the surface of a sphere of radius the square root of j(j +1) where j is the total angular momentum.

Empirical Analysis of the Effectiveness of Teacher Distance Education (TDE) in Ghana: The Perception of Student Teachers, Tutors and Coordinators of the University of Education, Winneba (UEW)

ERIC Educational Resources Information Center

Attah-Mensah, Godwin; Acheampong, Alex Opoku; Nti- Adarkwah, Samuel

2016-01-01

Education has proven to be an effective means of developing the human resource base of most nations and could advance the development of nations. In other to upgrade and train more professionals and non-professionals in the sphere of education, the concept of teacher distance education has gained more attention globally. Therefore, more and new…

Statistics of Stokes variables for correlated Gaussian fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eliyahu, D.

1994-09-01

The joint and marginal probability distribution functions of the Stokes variables are derived for correlated Gaussian fields [an extension of D. Eliyahu, Phys. Rev. E 47, 2881 (1993)]. The statistics depend only on the first moment (averaged) Stokes variables and have a universal form for [ital S][sub 1], [ital S][sub 2], and [ital S][sub 3]. The statistics of the variables describing the Cartesian coordinates of the Poincare sphere are given also.

Lanthanide tris(β-diketonates) as useful probes for chirality determination of biological amino alcohols in vibrational circular dichroism: ligand to ligand chirality transfer in lanthanide coordination sphere.

PubMed

Miyake, Hiroyuki; Terada, Keiko; Tsukube, Hiroshi

2014-06-01

A series of lanthanide tris(β-diketonates) functioned as useful chirality probes in the vibrational circular dichroism (VCD) characterization of biological amino alcohols. Various chiral amino alcohols induced intense VCD signals upon ternary complexation with racemic lanthanide tris(β-diketonates). The VCD signals observed around 1500 cm(-1) (β-diketonate IR absorption region) correlated well with the stereochemistry and enantiomeric purity of the targeted amino alcohol, while the corresponding monoalcohol, monoamine, and diol substrates induced very weak VCD signals. The high-coordination number and dynamic property of the lanthanide complex offer an effective chirality VCD probing of biological substrates. © 2014 Wiley Periodicals, Inc.

Correlation processing of polarization inhomogenous images in laser diagnostics of biological tissues

NASA Astrophysics Data System (ADS)

Trifonyuk, L.

2012-10-01

The model of interaction of laser radiation with biological tissue as a two-component amorphous-crystalline matrix was proposed. The processes of formation of polarization of laser radiation are considered, taking into account birefringence network protein fibrils. Measurement of the coordinate distribution of polarization states in the location of the laser micropolarimetr was conducted .The results of investigating the interrelation between the values of correlation (correlation area, asymmetry coefficient and autocorrelation function excess) and fractal (dispersion of logarithmic dependencies of power spectra) parameters are presented. They characterize the coordinate distributions of polarization azimuth of laser images of histological sections of women's reproductive sphere tissues and pathological changes in human organism. The diagnostic criteria of the prolapse of the vaginal tissue arising are determined.

Post-Flight Estimation of Motion of Space Structures: Part 2

NASA Technical Reports Server (NTRS)

Brugarolas, Paul; Breckenridge, William

2008-01-01

A computer program related to the one described in the immediately preceding article estimates the relative position of two space structures that are hinged to each other. The input to the program consists of time-series data on distances, measured by two range finders at different positions on one structure, to a corner-cube retroreflector on the other structure. Given a Cartesian (x,y,z) coordinate system and the known x coordinate of the retroreflector relative to the y,z plane that contains the range finders, the program estimates the y and z coordinates of the retroreflector. The estimation process involves solving for the y,z coordinates of the intersection between (1) the y,z plane that contains the retroreflector and (2) spheres, centered on the range finders, having radii equal to the measured distances. In general, there are two such solutions and the program chooses the one consistent with the design of the structures. The program implements a Kalman filter. The output of the program is a time series of estimates of the relative position of the structures.

Designing a Dy2 Single-Molecule Magnet with Two Well-Differentiated Relaxation Processes by Using a Nonsymmetric Bis-bidentate Bipyrimidine- N-Oxide Ligand: A Comparison with Mononuclear Counterparts.

PubMed

Díaz-Ortega, Ismael F; Herrera, Juan Manuel; Aravena, Daniel; Ruiz, Eliseo; Gupta, Tulika; Rajaraman, Gopalan; Nojiri, H; Colacio, Enrique

2018-06-04

Herein we report a dinuclear [(μ-mbpymNO){(tmh) 3 Dy} 2 ] (1) single-molecule magnet (SMM) showing two nonequivalent Dy III centers, which was rationally prepared from the reaction of Dy(tmh) 3 moieties (tmh = 2,2,6,6-tetramethyl-3,5-heptanedionate) and the asymmetric bis-bidentate bridging ligand 4-methylbipyrimidine (mbpymNO). Depending on whether the Dy III ions coordinate to the N^O or N^N bidentate donor sets, the Dy III sites present a NO 7 ( D 2 d geometry) or N 2 O 6 ( D 4 d ) coordination sphere. As a consequence, two different thermally activated magnetic relaxation processes are observed with anisotropy barriers of 47.8 and 54.7 K. Ab initio calculations confirm the existence of two different relaxation phenomena and allow one to assign the 47.8 and 54.7 K energy barriers to the Dy(N 2 O 6 ) and Dy(NO 7 ) sites, respectively. Two mononuclear complexes, [Dy(tta) 3 (mbpymNO)] (2) and [Dy(tmh) 3 (phenNO)] (3), have also been prepared for comparative purposes. In both cases, the Dy III center shows a NO 7 coordination sphere and SMM behavior is observed with U eff values of 71.5 K (2) and 120.7 K (3). In all three cases, ab initio calculations indicate that relaxation of the magnetization takes place mainly via the first excited-state Kramers doublet through Orbach, Raman, and thermally assisted quantum-tunnelling mechanisms. Pulse magnetization measurements reveal that the dinuclear and mononuclear complexes exhibit hysteresis loops with double- and single-step structures, respectively, thus supporting their SMM behavior.

Cavity method for force transmission in jammed disordered packings of hard particles.

PubMed

Bo, Lin; Mari, Romain; Song, Chaoming; Makse, Hernán A

2014-10-07

The force distribution of jammed disordered packings has always been considered a central object in the physics of granular materials. However, many of its features are poorly understood. In particular, analytic relations to other key macroscopic properties of jammed matter, such as the contact network and its coordination number, are still lacking. Here we develop a mean-field theory for this problem, based on the consideration of the contact network as a random graph where the force transmission becomes a constraint satisfaction problem. We can thus use the cavity method developed in the past few decades within the statistical physics of spin glasses and hard computer science problems. This method allows us to compute the force distribution P(f) for random packings of hard particles of any shape, with or without friction. We find a new signature of jamming in the small force behavior P(f) ∼ f(θ), whose exponent has attracted recent active interest: we find a finite value for P(f = 0), along with θ = 0. Furthermore, we relate the force distribution to a lower bound of the average coordination number z[combining macron](μ) of jammed packings of frictional spheres with coefficient μ. This bridges the gap between the two known isostatic limits z[combining macron]c (μ = 0) = 2D (in dimension D) and z[combining macron]c(μ → ∞) = D + 1 by extending the naive Maxwell's counting argument to frictional spheres. The theoretical framework describes different types of systems, such as non-spherical objects in arbitrary dimensions, providing a common mean-field scenario to investigate force transmission, contact networks and coordination numbers of jammed disordered packings.

Drastic Effect of the Peptide Sequence on the Copper-Binding Properties of Tripeptides and the Electrochemical Behaviour of Their Copper(II) Complexes.

PubMed

Mena, Silvia; Mirats, Andrea; Caballero, Ana B; Guirado, Gonzalo; Barrios, Leoní A; Teat, Simon J; Rodriguez-Santiago, Luis; Sodupe, Mariona; Gamez, Patrick

2018-04-06

The binding and electrochemical properties of the complexes Cu II -HAH, Cu II -HWH, Cu II -Ac-HWH, Cu II -HHW, and Cu II -WHH have been studied by using NMR and UV/Vis spectroscopies, CV, and density functional calculations. The results obtained highlight the importance of the peptidic sequence on the coordination properties and, consequently, on the redox properties of their Cu II complexes. For Cu II -HAH and Cu II -HWH, no cathodic processes are observed up to -1.2 V; that is, the complexes exhibit very high stability towards copper reduction. This behaviour is associated with the formation of very stable square-planar (5,5,6)-membered chelate rings (ATCUN motif), which enclose two deprotonated amides. In contrast, for non-ATCUN Cu II -Ac-HWH, Cu II -HHW complexes, simulations seem to indicate that only one deprotonated amide is enclosed in the coordination sphere. In these cases, the main electrochemical feature is a reductive irreversible one electron-transfer process from Cu II to Cu I , accompanied with structural changes of the metal coordination sphere and reprotonation of the amide. Finally, for Cu II -WHH, two major species have been detected: one at low pH (<5), with no deprotonated amides, and another one at high pH (>10) with an ATCUN motif, both species coexisting at intermediate pH. The present study shows that the use of CV, using glassy carbon as a working electrode, is an ideal and rapid tool for the determination of the redox properties of Cu II metallopeptides. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic Insight from Calorimetric Measurements of the Assembly of the Binuclear Metal Active Site of Glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes.

PubMed

Pedroso, Marcelo M; Ely, Fernanda; Carpenter, Margaret C; Mitić, Nataša; Gahan, Lawrence R; Ollis, David L; Wilcox, Dean E; Schenk, Gerhard

2017-07-05

Glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes is a binuclear metallohydrolase with a high affinity for metal ions at its α site but a lower affinity at its β site in the absence of a substrate. Isothermal titration calorimetry (ITC) has been used to quantify the Co(II) and Mn(II) binding affinities and thermodynamics of the two sites in wild-type GpdQ and two mutants, both in the absence and in the presence of phosphate. Metal ions bind to the six-coordinate α site in an entropically driven process with loss of a proton, while binding at the β site is not detected by ITC. Phosphate enhances the metal affinity of the α site by increasing the binding entropy and the metal affinity of the β site by enthalpic (Co) or entropic (Mn) contributions, but no additional loss of protons. Mutations of first- and second-coordination sphere residues at the β site increase the metal affinity of both sites by enhancing the binding enthalpy. In particular, loss of the hydrogen bond from second-sphere Ser127 to the metal-coordinating Asn80 has a significant effect on the metal binding thermodynamics that result in a resting binuclear active site with high catalytic activity. While structural and spectroscopic data with excess metal ions have indicated a bridging hydroxide in the binuclear GpdQ site, analysis of ITC data here reveals the loss of a single proton in the assembly of this site, indicating that the metal-bound hydroxide nucleophile is formed in the resting inactive mononuclear form, which becomes catalytically competent upon binding the second metal ion.

Spectroscopic and DFT Studies of Second Sphere Variants of the Type 1 Copper Site in Azurin: Covalent and Non-Local Electrostatic Contributions to Reduction Potentials

PubMed Central

Hadt, Ryan G.; Sun, Ning; Marshall, Nicholas M.; Hodgson, Keith O.; Hedman, Britt; Lu, Yi; Solomon, Edward I.

2012-01-01

The reduction potentials (E0) of type 1 (T1) or blue copper (BC) sites in proteins and enzymes with identical first coordination spheres around the redox active copper ion can vary by ~400 mV. Here, we use a combination of low temperature electronic absorption and magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and S K-edge X-ray absorption spectroscopies to investigate a series of second sphere variants—F114P, N47S, and F114N in Pseudomonas aeruginosa azurin (Az)—which modulate hydrogen bonding to and protein derived dipoles nearby the Cu-S(Cys) bond. Density functional theory (DFT) calculations correlated to the experimental data allow for the fractionation of the contributions to tuning E0 into covalent and non-local electrostatic components. These are found to be significant, comparable in magnitude, and additive for active H-bonds, while passive H-bonds are mostly non-local electrostatic in nature. For dipoles, these terms can be additive to or oppose one another. This study provides a methodology for uncoupling covalency from non-local electrostatics, which, when coupled to X-ray crystallographic data, distinguishes specific local interactions from more long range protein/active interactions, while affording further insight into the second sphere mechanisms available to the protein to tune the E0 of electron transfer sites in biology. PMID:22985400

Le contenu astronomique des Sphériques de Ménélaos

NASA Astrophysics Data System (ADS)

Nadal, Robert; Taha, Abdelkaddous; Pinel, Pierre

2004-07-01

The Spherics were written by Menelaos in the form of a purely mathematical treatise. However, the material developed in the second and third book is closely linked to problems met in astronomy: computation of equatorial coordinates of the Sun, setting up of rising-time tables, study of the motion of the Sun in the sphaera obliqua, simultaneous risings. This link, which remains implicit in the text, was clearly displayed by two arabo-islamic mathematicians and astronomers, who expounded the astronomical meaning of some theorems of the Spherics. We describe, comment and complement their explanations, by classifying the implications of the theorems in three groups: direction of variation of some quantities on the sphere, spherical trigonometry and applications, direction of variation of ratios of some quantities on the sphere. An erratum to this article can be found at http://dx.doi.org/10.1007/s00407-004-0084-7

Design and Implementation of High Precision Temperature Measurement Unit

NASA Astrophysics Data System (ADS)

Zeng, Xianzhen; Yu, Weiyu; Zhang, Zhijian; Liu, Hancheng

2018-03-01

Large-scale neutrino detector requires calibration of photomultiplier tubes (PMT) and electronic system in the detector, performed by plotting the calibration source with a group of designated coordinates in the acrylic sphere. Where the calibration source positioning is based on the principle of ultrasonic ranging, the transmission speed of ultrasonic in liquid scintillator of acrylic sphere is related to temperature. This paper presents a temperature measurement unit based on STM32L031 and single-line bus digital temperature sensor TSic506. The measurement data of the temperature measurement unit can help the ultrasonic ranging to be more accurate. The test results show that the temperature measurement error is within ±0.1°C, which satisfies the requirement of calibration source positioning. Take energy-saving measures, with 3.7V/50mAH lithium battery-powered, the temperature measurement unit can work continuously more than 24 hours.

The Structure of Ethylbenzene, Styrene and Phenylacetylene Determined by Total Neutron Scattering.

PubMed

Szala-Bilnik, Joanna; Falkowska, Marta; Bowron, Daniel T; Hardacre, Christopher; Youngs, Tristan G A

2017-09-20

Organic solvents such as phenylacetylene, styrene and ethylbenzene are widely used in industrial processes, especially in the production of rubber or thermoplastics. Despite their important applications detailed knowledge about their structure is limited. In this paper the structures of these three aromatic solvents were investigated using neutron diffraction. The results show that many of their structural characteristics are similar, although the structure of phenylacetylene is more ordered and has a smaller solvation sphere than either ethylbenzene or styrene. Two regions within the first coordination sphere, in which the surrounding molecules show different preferable orientations with respect to the central molecule, were found for each liquid. Additionally, the localisation of the aliphatic chains reveals that they tend to favour closer interactions with each other than to the aromatic rings of the adjacent molecules. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superspace models for S-3

NASA Astrophysics Data System (ADS)

McKeon, D. G. C.

2003-11-01

The simplest supersymmetric extension of the group SO(4) is discussed. The superalgebra is realized in a superspace whose Bosonic subspace is the surface of a sphere S-3 embedded in four-dimensional Euclidean space. By using Fermionic coordinates in this superspace, which are chiral symplectic Majorana spinors, it proves possible to devise superfield models involving a complex scalar, a pair of chiral symplectic Majorana spinors, and a complex auxiliary scalar. Kinetic terms involve operators that are isometry generators on S-3.

Augmentation of heat and mass transfer in laminar flow of suspensions: A correlation of data

NASA Astrophysics Data System (ADS)

Ahuja, Avtar S.

1980-01-01

The experimental data from literature on the augmentation of heat and gas transport in the laminar flow of suspensions of polystyrene spheres have been correlated on common coordinates. The correlation includes the influences of particle size, tube diameter and length, shear rate of flow, transport properties of diffusing species (heat or gas) in suspending liquids, and of the particle interactions on the augmentation of heat or gas transfer in flowing suspensions.

Alternative Way of Shifting Mass to Move a Spherical Robot

NASA Technical Reports Server (NTRS)

Lux, James

2005-01-01

The method proposed calls for suspending a payload by use of four or more cables that would be anchored to the inner surface of the sphere. In this method, the anchor points would not be diametrically opposite points defining Cartesian axes. The payload, which includes the functional analog of the aforementioned control box, would contain winches that would shorten or lengthen the cables in a coordinated manner to shift the position of the payload within the shell.

A molecular view of cisplatin's mode of action: interplay with DNA bases and acquired resistance.

PubMed

Marques, M Paula M; Gianolio, Diego; Cibin, Giannantonio; Tomkinson, John; Parker, Stewart F; Valero, Rosendo; Pedro Lopes, R; Batista de Carvalho, Luis A E

2015-02-21

The interaction of the widely used anticancer drug cisplatin with DNA bases was studied by EXAFS and vibrational spectroscopy (FTIR, Raman and INS), coupled with DFT/plane-wave calculations. Detailed information was obtained on the local atomic structure around the Pt(ii) centre, both in the cisplatin-purine (adenine and guanine) and cisplatin-glutathione adducts. Simultaneous neutron and Raman scattering experiments allowed us to obtain a reliable and definite picture of this cisplatin interplay with its main pharmacological target (DNA), at the molecular level. The vibrational experimental spectra were fully assigned in the light of the calculated pattern for the most favoured geometry of each drug-purine adduct, and cisplatin's preference for guanine (G) relative to adenine (A) within the DNA double helix was experimentally verified: a complete N by S substitution in the metal coordination sphere was only observed for [cDDP-A2], reflecting a somewhat weaker Pt-A binding relative to Pt-G. The role of glutathione on the drug's pharmacokinetics, as well as on the stability of platinated DNA adducts, was evaluated as this is the basis for glutathione-mediated intracellular drug scavenging and in vivo resistance to Pt-based anticancer drugs. Spectroscopic evidence of the metal's preference for glutathione's sulfur over purine's nitrogen binding sites was gathered, at least two sulfur atoms being detected in platinum's first coordination sphere.

Active Hydrogenation Catalyst with a Structured, Peptide-Based Outer-Coordination Sphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Avijita; Buchko, Garry W.; Reback, Matthew L.

2012-10-05

The synthesis, catalytic activity, and structural features of a rhodium-based hydrogenation catalyst containing a phosphine ligand coupled to a 14-residue peptide are reported. Both CD and NMR spectroscopy show that the peptide adopts a helical structure in 1:1:1 TFE/MeCN/H2O that is maintained when the peptide is attached to the ligand and when the ligand is attached to the metal complex. The metal complex hydrogenates aqueous solutions of 3-butenol to 1-butanol at 360 ± 50 turnovers/Rh/h at 294 K. This peptide- based catalyst represents a starting point for developing and characterizing a peptide-based outer-coordination sphere that can be used to introducemore » enzyme-like features into molecular catalysts. This work was funded by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (AJ, JCL and WJS), the Office of Science Early Career Research Program through the Office of Basic Energy Sciences (GWB, MLR and WJS). Part of the research was conducted at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by U.S. Department of Energy’s Office of Biolog-ical and Environmental Research (BER) program located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the U.S. Department of Energy.« less

Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores

NASA Astrophysics Data System (ADS)

Yang, Guomin; Neretnieks, Ivars; Holmboe, Michael

2017-08-01

During the last four decades, numerous studies have been directed to the swelling smectite-rich clays in the context of high-level radioactive waste applications and waste-liners for contaminated sites. The swelling properties of clay mineral particles arise due to hydration of the interlayer cations and the diffuse double layers formed near the negatively charged montmorillonite (MMT) surfaces. To accurately study the cation hydration in the interlayer nanopores of MMT, solvent-solute and solvent-clay surface interactions (i.e., the solvation effects and the shape effects) on the atomic level should be taken into account, in contrast to many recent electric double layer based methodologies using continuum models. Therefore, in this research we employed fully atomistic simulations using classical molecular dynamics (MD) simulations, the software package GROMACS along with the CLAYFF forcefield and the SPC/E water model. We present the ion distributions and the deformation of the hydrated coordination structures, i.e., the hydration shells of Na+ and Ca2+ in the interlayer, respectively, for MMT in the first-layer, the second-layer, the third-layer, the fourth-layer, and the fifth-layer (1W, 2W, 3W, 4W, and 5W) hydrate states. Our MD simulations show that Na+ in Na-MMT nanopores have an affinity to the ditrigonal cavities of the clay layers and form transient inner-sphere complexes at about 3.8 Å from clay midplane at water contents less than the 5W hydration state. However, these phenomena are not observed in Ca-MMT regardless of swelling states. For Na-MMT, each Na+ is coordinated to four water molecules and one oxygen atom of the clay basal-plane in the first hydration shell at the 1W hydration state, and with five to six water molecules in the first hydration shell within a radius of 3.1 Å at all higher water contents. In Ca-MMT, however each Ca2+ is coordinated to approximately seven water molecules in the first hydration shell at the 1W hydration state and about eight water molecules in the first hydration shell within a radius of 3.3 Å at all higher hydration states. Moreover, the MD results show that the complete hydration shells are nearly spherical with an orthogonal coordination sphere. They could only be formed when the basal spacing d001 ≥ 18.7 Å, i.e., approximately, the interlayer separation h ≥ 10 Å. Comparison between DFT and MD simulations shows that DFT failed to reproduce the outer-sphere complexes in the Stern-layer (within ˜5.0 Å from the clay basal-plane), observed in the MD simulations.

Phosphinic derivative of DTPA conjugated to a G5 PAMAM dendrimer: an 17O and 1H relaxation study of its Gd(III) complex.

PubMed

Lebdusková, Petra; Sour, Angélique; Helm, Lothar; Tóth, Eva; Kotek, Jan; Lukes, Ivan; Merbach, André E

2006-07-28

A DTPA-based chelate containing one phosphinate group was conjugated to a generation 5 polyamidoamine (PAMAM) dendrimer via a benzylthiourea linkage. The Gd(III) complex of this novel conjugate has potential as a contrast agent for magnetic resonance imaging (MRI). The chelates bind Gd3+via three nitrogen atoms, four carboxylates and one phosphinate oxygen, and one water molecule completes the inner coordination sphere. The monomer Gd(III) chelates bearing nitrobenzyl and aminobenzyl groups ([Gd(DTTAP-bz-NO2)(H2O)]2- and [Gd(DTTAP-bz-NH2)(H2O)]2-) as well as the dendrimeric Gd(III) complex G5-(Gd(DTTAP))63) were studied by multiple-field, variable temperature 17O and 1H NMR. The rate of water exchange is faster than that of [Gd(DTPA)(H2O)]2- and very similar on the two monomeric complexes (8.9 and 8.3 x 10(6) s-1 for [Gd(DTTAP-bz-NO2)(H2O)]2- and [Gd(DTTAP-bz-NH2)(H2O)]2-, respectively), while it is decreased on the dendrimeric conjugate (5.0 x 10(6) s-1). The Gd(III) complex of the dendrimer conjugate has a relaxivity of 26.8 mM-1 s-1 at 37 degrees C and 0.47 T (corresponding to 1H Larmor frequency of 20 MHz). Given the contribution of the second sphere water molecules to the overall relaxivity, this value is slightly higher than those reported for similar size dendrimers. The experimental 17O and 1H NMR data were fitted to the Solomon-Bloembergen-Morgan equations extended with a contribution from second coordination sphere water molecules. The rotational dynamics of the dendrimeric conjugate was described in terms of global and local motions with the Lipari-Szabo approach.

Pseudosymmetric fac-di­aqua­trichlorido[(di­methyl­phosphor­yl)methanaminium-κO]manganese(II)

PubMed Central

Reiss, Guido J.

2013-01-01

In the title compound, [Mn(C3H11NOP)Cl3(H2O)2], the MnII metal center has a distorted o­cta­hedral geometry, coordinated by the three chloride ligands showing a facial arrangement. Two water mol­ecules and the O-coordinated dpmaH cation [dpmaH = (di­methyl­phosphor­yl)methanaminium] complete the coordination sphere. Each complex mol­ecule is connected to its neighbours by O—H⋯Cl and N—H⋯Cl hydrogen bonds. Two of the chloride ligands and the two water ligands form a hydrogen-bonded polymeric sheet in the ab plane. Furthermore, these planes are connected to adjacent planes by hydrogen bonds from the aminium function of cationic dpmaH ligand. A pseudo-mirror plane perpendicular to the b axis in the chiral space group P21 is observed together with inversion twinning [ratio = 0.864 (5):0.136 (5)]. PMID:23723764

Synthesis and decomposition of a novel carboxylate precursor to indium oxide

NASA Technical Reports Server (NTRS)

Hepp, Aloysius F.; Andras, Maria T.; Duraj, Stan A.; Clark, Eric B.; Hehemann, David G.; Scheiman, Daniel A.; Fanwick, Phillip E.

1994-01-01

Reaction of metallic indium with benzoyl peroxide in 4-1 methylpyridine (4-Mepy) at 25 C produces an eight-coordinate mononuclear indium(III) benzoate, In(eta(sup 2)-O2CC6H5)3(4-Mepy)2 4H2O (I), in yields of up to 60 percent. The indium(III) benzoate was fully characterized by elemental analysis, spectroscopy, and X-ray crystallography; (I) exists in the crystalline state as discrete eight-coordinate molecules; the coordination sphere around the central indium atom is best described as pseudo-square pyramidal. Thermogravimetric analysis of (I) and X-ray diffraction powder studies on the resulting pyrolysate demonstrate that this new benzoate is an inorganic precursor to indium oxide. Decomposition of (I) occurs first by loss of 4-methylpyridine ligands (100 deg-200 deg C), then loss of benzoates with formation of In2O3 at 450 C. We discuss both use of carboxylates as precursors and our approach to their preparation.

(18-Crown-6)potassium [(1,2,5,6-η)-cyclo­octa-1,5-diene][(1,2,3,4-η)-naph­tha­lene]­ferrate(−I)

PubMed Central

Brennessel, William W.; Ellis, John E.

2012-01-01

The title salt, [K(C12H24O6)][Fe(C8H12)(C10H8)], is the only known naphthalene complex containing iron in a formally negative oxidation state. Each (naphthalene)(1,5-cod)ferrate(−I) anion is in contact with one (18-crown-6)potassium cation via K⋯C contacts to the outer four carbon atoms of the naphthalene ligand (cod = 1,5-cyclo­octa­diene, 18-crown-6 = 1,4,7,10,13,16-hexa­oxacyclo­octa­deca­ne). When using the midpoints of the coordinating olefin bonds, the overall geometry of the coordination sphere around iron can be best described as distorted tetra­hedral. The naphthalene fold angle between the plane of the iron-coordinating butadiene unit and the plane containing the exo-benzene moiety is 19.2 (1)°. PMID:23125569

Dolan Grady relations and noncommutative quasi-exactly solvable systems

NASA Astrophysics Data System (ADS)

Klishevich, Sergey M.; Plyushchay, Mikhail S.

2003-11-01

We investigate a U(1) gauge invariant quantum mechanical system on a 2D noncommutative space with coordinates generating a generalized deformed oscillator algebra. The Hamiltonian is taken as a quadratic form in gauge covariant derivatives obeying the nonlinear Dolan-Grady relations. This restricts the structure function of the deformed oscillator algebra to a quadratic polynomial. The cases when the coordinates form the {\\mathfrak{su}}(2) and {\\mathfrak{sl}}(2,{\\bb {R}}) algebras are investigated in detail. Reducing the Hamiltonian to 1D finite-difference quasi-exactly solvable operators, we demonstrate partial algebraization of the spectrum of the corresponding systems on the fuzzy sphere and noncommutative hyperbolic plane. A completely covariant method based on the notion of intrinsic algebra is proposed to deal with the spectral problem of such systems.

Crystal structure of iron(III) perchlorate nona­hydrate

PubMed Central

Hennings, Erik; Schmidt, Horst; Voigt, Wolfgang

2014-01-01

Since the discovery of perchlorate salts on Mars and the known occurrence of ferric salts in the regolith, there is a distinct possibility that the title compound could form on the surface of Mars. [Fe(H2O)6](ClO4)3·3H2O was crystallized from aqueous solutions at low temperatures according to the solid–liquid phase diagram. It consists of Fe(H2O)6 octa­hedra (point group symmetry -3.) and perchlorate anions (point group symmetry .2) as well as non-coordinating water mol­ecules, as part of a second hydrogen-bonded coordination sphere around the cation. The perchlorate appears to be slightly disordered, with major–minor component occupancies of 0.773 (9):0.227 (9). PMID:25552970

Complexation Enhancement Drives Water-to-Oil Ion Transport: A Simulation Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, Baofu; Ferru, Geoffroy; Ellis, Ross J.

We address the structures and energetics of ion solvation in aqueous and organic solutions to understand liquid-liquid ion transport. Atomistic molecular dynamics (MD) simulations with polarizable force field are performed to study the coordination transformations driving lanthanide (Ln(III)) and nitrate ion transport between aqueous and an alkylamide-oil solution. An enhancement of the coordination behavior in the organic phase is achieved in contrast with the aqueous solution. In particular, the coordination number of Ce3+ increases from 8.9 in the aqueous to 9.9 in the organic solutions (from 8 in the aqueous to 8.8 in the organic systems for Yb3+). Moreover, themore » local coordination environ ment changes dramatically. Potential of mean force calculations show that the Ln(III)-ligand coordination interaction strengths follow the order of Ln(III-)nitrate> Ln(III)-water>Ln(III)-DMDBTDMA. They increase 2-fold in the lipophilic environment in comparison to the aqueous phase, and we attribute this to the shedding of the outer solvation shell. Our findings highlight the importance of outer sphere interactions on the competitive solvation energetics that cause ions to migrate between immiscible phases; an essential ingredient for advancing important applications such as rare earth metal separations. Some open questions in simulating the coordination behavior of heavy metals are also addressed.« less

Existence of frozen-in coordinate systems

NASA Technical Reports Server (NTRS)

Chertkov, A. D.

1995-01-01

The 'frozen-in' coordinate systems were first introduced in the works on 'reconnection' and 'magnetic barrier' theories (see review by M.l.Pudovkin and V.S.Semenov, Space Sci. Rev. 41,1 1985). The idea was to utilize the mathematical apparatus developed for 'general relativity' theory to simplify obtaining solutions to the ideal MHD equations set. Magnetic field (B), plasma velocity (v), and their vector product were used as coordinate vectors. But there exist no stationary solutions of ideal MHD set that satisfies the required boundary conditions at infinity (A.D.Chertkov, Solar Wind Seven Conf.,Pergamon Press,1992,165) having non-zero vector product of v and B where v and B originate from the same sphere. The existence of a solution is the hidden mine of the mentioned theories. The solution is constructed in the coordinate system, which is unknown and indeterminate before obtaining this solution. A substitution of the final solution must be done directly into the initial MHD set in order to check the method. One can demonstrate that 'solutions' of Petschek's problem, obtained by 'frozen-in' coordinate systems, does not satisfy just the 'frozen-in' equation, i.e. induction equation. It stems from the fact that Petschek's 're-connection' model, treated as a boundary problem, is over determined. This problem was incorrectly formulated.

Polarization Utilization in Radar Target Reconstruction: C-Wide (Multi-Frequency) Band Relationship of a Target’s Characteristic Operators with Its Unique Set of Natural Eigenfrequencies.

DTIC Science & Technology

1983-12-14

the left half of the s- plane . These are representation independent. We shall be interested in these poles only. These poles are the complex...on the Left Half Plane Asymptotic Behavior of the SEM Expansion of Surface Currents, Published in Special Issue on the Singularity Expansion Method...precisely, the polarization chart is an orthogonal projection of the Poincare Sphere on a plane , having polar coordinates p= cos (2-) and

Reactivity pathways for nitric oxide and nitrosonium with iron complexes in biologically relevant sulfur coordination spheres.

PubMed

Harrop, Todd C; Song, Datong; Lippard, Stephen J

2007-11-01

The interaction of nitric oxide (NO) with iron-sulfur cluster proteins results in the formation of dinitrosyl iron complexes (DNICs) coordinated by cysteine residues from the peptide backbone or with low molecular weight sulfur-containing molecules like glutathione. Such DNICs are among the modes available in biology to store, transport, and deliver NO to its relevant targets. In order to elucidate the fundamental chemistry underlying the formation of DNICs and to characterize possible intermediates in the process, we have investigated the interaction of NO (g) and NO(+) with iron-sulfur complexes having the formula [Fe(SR)(4)](2-), where R=(t)Bu, Ph, or benzyl, chosen to mimic sulfur-rich iron sites in biology. The reaction of NO (g) with [Fe(S(t)Bu)(4)](2-) or [Fe(SBz)(4)](2-) cleanly affords the mononitrosyl complexes (MNICs), [Fe(S(t)Bu)(3)(NO)](-) (1) and [Fe(SBz)(3)(NO)](-) (3), respectively, by ligand displacement. Mononitrosyl species of this kind were previously unknown. These complexes further react with NO (g) to generate the corresponding DNICs, [Fe(SPh)(2)(NO)(2)](-) (4) and [Fe(SBz)(2)(NO)(2)](-) (5), with concomitant reductive elimination of the coordinated thiolate donors. Reaction of [Fe(SR)(4)](2-) complexes with NO(+) proceeds by a different pathway to yield the corresponding dinitrosyl S-bridged Roussin red ester complexes, [Fe(2)(mu-S(t)Bu)(2)(NO)(4)] (2), [Fe(2)(mu-SPh)(2)(NO)(4)] (7) and [Fe(2)(mu-SBz)(2)(NO)(4)] (8). The NO/NO(+) reactivity of an Fe(II) complex with a mixed nitrogen/sulfur coordination sphere was also investigated. The DNIC and red ester species, [Fe(S-o-NH(2)C(6)H(4))(2)(NO)(2)](-) (6) and [Fe(2)(mu-S-o-NH(2)C(6)H(4))(2)(NO)(4)] (9), were generated. The structures of 8 and 9 were verified by X-ray crystallography. The MNIC complex 1 can efficiently deliver NO to iron-porphyrin complexes like [Fe(TPP)Cl], a reaction that is aided by light. Removal of the coordinated NO ligand of 1 by photolysis and addition of elemental sulfur generates higher nuclearity Fe/S clusters.

Hierarchical NiCo2O4 Hollow Sphere as a Peroxidase Mimetic for Colorimetric Detection of H2O2 and Glucose

PubMed Central

Huang, Wei; Lin, Tianye; Cao, Yang; Lai, Xiaoyong; Peng, Juan; Tu, Jinchun

2017-01-01

In this work, the hierarchical NiCo2O4 hollow sphere synthesized via a “coordinating etching and precipitating” process was demonstrated to exhibit intrinsic peroxidase-like activity. The peroxidase-like activity of NiCo2O4, NiO, and Co3O4 hollow spheres were comparatively studied by the catalytic oxidation reaction of 3,3,5,5-tetramethylbenzidine (TMB) in presence of H2O2, and a superior peroxidase-like activity of NiCo2O4 was confirmed by stronger absorbance at 652 nm. Furthermore, the proposed sensing platform showed commendable response to H2O2 with a linear range from 10 μM to 400 μM, and a detection limit of 0.21 μM. Cooperated with GOx, the developed novel colorimetric and visual glucose-sensing platform exhibited high selectivity, favorable reproducibility, satisfactory applicability, wide linear range (from 0.1 mM to 4.5 mM), and a low detection limit of 5.31 μM. In addition, the concentration-dependent color change would offer a better and handier way for detection of H2O2 and glucose by naked eye. PMID:28124997

Calibration of a flexible measurement system based on industrial articulated robot and structured light sensor

NASA Astrophysics Data System (ADS)

Mu, Nan; Wang, Kun; Xie, Zexiao; Ren, Ping

2017-05-01

To realize online rapid measurement for complex workpieces, a flexible measurement system based on an articulated industrial robot with a structured light sensor mounted on the end-effector is developed. A method for calibrating the system parameters is proposed in which the hand-eye transformation parameters and the robot kinematic parameters are synthesized in the calibration process. An initial hand-eye calibration is first performed using a standard sphere as the calibration target. By applying the modified complete and parametrically continuous method, we establish a synthesized kinematic model that combines the initial hand-eye transformation and distal link parameters as a whole with the sensor coordinate system as the tool frame. According to the synthesized kinematic model, an error model is constructed based on spheres' center-to-center distance errors. Consequently, the error model parameters can be identified in a calibration experiment using a three-standard-sphere target. Furthermore, the redundancy of error model parameters is eliminated to ensure the accuracy and robustness of the parameter identification. Calibration and measurement experiments are carried out based on an ER3A-C60 robot. The experimental results show that the proposed calibration method enjoys high measurement accuracy, and this efficient and flexible system is suitable for online measurement in industrial scenes.

Microcrystalline sphalerite in resin globules suspended in Lake Kivu, East Africa

USGS Publications Warehouse

Degens, E.T.; Okada, H.; Honjo, S.; Hathaway, J.C.

1972-01-01

The origin and chemical nature of micron-sized spheres found as suspended particles in Lake Kivu are examined. It can be shown that the hollow spheres, with a wall thickness of 500 A??, consist of a complex polymeric resinous material which has little functionality, except for hydroxyl groups. The spheres arise in the process of degassing of water samples at depth. Tiny gas bubbles, about 1 micron in size, act as scavengers of dissolved resinous material. The newly created resinous membrane promotes the selective coordination of zinc dissolved in the water column. In the prevailing H2S regime, formation of sphalerite crystals in induced. The size range of the crystals, 5 to 50 A??, corresponds to 1 to 10 unit cells and suggests that the resinous membrane also acts as a template in sphalerite growth processes. The sources of the zinc and dissolved gases (CO2, CH4, H2S) are hydrothermal springs seeping from the lake bottom into the basin. Water discharge is substantial; about 100 years are required to fill the lake to its present level (ca. 550 km3 water). The average Kivu water contains 2 ppm zinc. Thus, 1 million tons of zinc are contained in Lake Kivu in the form of sphalerite. ?? 1972 Springer-Verlag.

Acoustic radiation force of a Bessel beam on a porous sphere.

PubMed

Azarpeyvand, Mahdi

2012-06-01

The possibility of using acoustic Bessel beams to produce an axial pulling force on porous particles is examined in an exact manner. The mathematical model utilizes the appropriate partial-wave expansion method in spherical coordinates, while Biot's model is used to describe the wave motion within the poroelastic medium. Of particular interest here is to examine the feasibility of using Bessel beams for (a) acoustic manipulation of fine porous particles and (b) suppression of particle resonances. To verify the viability of the technique, the radiation force and scattering form-function are calculated for aluminum and silica foams at various porosities. Inspection of the results has shown that acoustic manipulation of low porosity (<0.3) spheres is similar to that of solid elastic spheres, but this behavior significantly changes at higher porosities. Results have also shown a strong correlation between the backscattered form-function and the regions of negative radiation force. It has also been observed that the high-order resonances of the particle can be effectively suppressed by choosing the beam conical angle such that the acoustic contribution from that particular mode vanishes. This investigation may be helpful in the development of acoustic tweezers for manipulation of micro-porous drug delivery carrier and contrast agents.

Synthesis and Characterization of a Series of Structurally and Electronically Diverse Fe(II) Complexes Featuring a Family of Triphenylamido-Amine Ligands

PubMed Central

Paraskevopoulou, Patrina; Ai, Lin; Wang, Qiuwen; Pinnapareddy, Devender; Acharyya, Rama; Dinda, Rupam; Das, Purak; Çelenligil-Çetin, Remle; Floros, Georgios; Sanakis, Yiannis; Choudhury, Amitava; Rath, Nigam P.; Stavropoulos, Pericles

2009-01-01

A family of triphenylamido-amine ligands of the general stoichiometry LxH3 = [R-NH-(2-C6H4)]3N (R = 4-t-BuPh (L1H3), 3,5-t-Bu2Ph (L2H3), 3,5-(CF3)2Ph (L3H3), CO-t-Bu (L4H3) 3,5-Cl2Ph (L5H3), COPh (L6H3), CO-i-Pr (L7H3), COCF3 (L8H3), i-Pr (L9H3)) has been synthesized and characterized, featuring a rigid triphenylamido-amine scaffold and an array of stereoelectronically diverse aryl, acyl and alkyl substituents (R). These ligands are deprotonated by potassium hydride in THF or DMA and reacted with anhydrous FeCl2 to afford a series of ferrous complexes, exhibiting stoichiometric variation and structural complexity. The prevalent [(Lx)Fe(II)–solv]− structures (Lx = L1, L2, L3, L5, solv = THF; Lx = L8, solv = DMA; Lx = L6, L8, solv = MeCN), reveal a distorted trigonal bipyramidal geometry, featuring ligand-derived [N3,amidoNamine] coordination and solvent attachment trans to the Namine atom. Specifically for [(L8)Fe(II)–DMA]−, an Namido residue is coordinated as the corresponding Nimino moiety (Fe–N(Ar)=C(CF3)–O−). In contrast, compounds [(L4)Fe(II)] −, [(L6)2Fe(II)2]2−, [K(L7)2Fe(II)2]22− and [K(L9)Fe]2 are all solvent-free in their coordination sphere and exhibit four-coordinate geometries of significant diversity. In particular, [(L4)Fe(II)]− demonstrates coordination of one amidato residue via the O-atom end (Fe–O–C(t-Bu)=N(Ar)). Furthermore, [(L6)2Fe(II)2]2− and [K(L7)2Fe(II)2]22− are similar structures exhibiting bridging amidato residues (Fe–N(Ar)–C(R)=O–Fe) in dimeric structural units. Finally the structure of [K(L9)Fe]2 is the only example featuring a minimal [N3,amidoNamine] coordination sphere around each Fe(II) site. All compounds have been characterized by a variety of physicochemical techniques, including Mössbauer spectroscopy and electrochemistry, to reveal electronic attributes that are responsible for a range of Fe(II)/Fe(III) redox potentials exceeding 1.0 V. PMID:19950956

Casimir interaction between spheres in ( D + 1)-dimensional Minkowski spacetime

NASA Astrophysics Data System (ADS)

Teo, L. P.

2014-05-01

We consider the Casimir interaction between two spheres in ( D + 1)-dimensional Minkowski spacetime due to the vacuum fluctuations of scalar fields. We consider combinations of Dirichlet and Neumann boundary conditions. The TGTG formula of the Casimir interaction energy is derived. The computations of the T matrices of the two spheres are straightforward. To compute the two G matrices, known as translation matrices, which relate the hyper-spherical waves in two spherical coordinate frames differ by a translation, we generalize the operator approach employed in [39]. The result is expressed in terms of an integral over Gegenbauer polynomials. In contrast to the D=3 case, we do not re-express the integral in terms of 3 j-symbols and hyper-spherical waves, which in principle, can be done but does not simplify the formula. Using our expression for the Casimir interaction energy, we derive the large separation and small separation asymptotic expansions of the Casimir interaction energy. In the large separation regime, we find that the Casimir interaction energy is of order L -2 D+3, L -2 D+1 and L -2 D-1 respectively for Dirichlet-Dirichlet, Dirichlet-Neumann and Neumann-Neumann boundary conditions, where L is the center-to-center distance of the two spheres. In the small separation regime, we confirm that the leading term of the Casimir interaction agrees with the proximity force approximation, which is of order , where d is the distance between the two spheres. Another main result of this work is the analytic computations of the next-to-leading order term in the small separation asymptotic expansion. This term is computed using careful order analysis as well as perturbation method. In the case the radius of one of the sphere goes to infinity, we find that the results agree with the one we derive for sphere-plate configuration. When D=3, we also recover previously known results. We find that when D is large, the ratio of the next-to-leading order term to the leading order term is linear in D, indicating a larger correction at higher dimensions. The methodologies employed in this work and the results obtained can be used to study the one-loop effective action of the system of two spherical objects in the universe.

A Comparative Study of [CaEDTA](2-) and [MgEDTA](2-): Structural and Dynamical Insights from Quantum Mechanical Charge Field Molecular Dynamics.

PubMed

Tirler, Andreas O; Hofer, Thomas S

2015-07-09

Structure and dynamics of [MgEDTA](2-) and [CaEDTA](2-) complexes in aqueous solution have been investigated via quantum mechanical/molecular mechanical (QM/MM) simulations. While for the first a 6-fold octahedral complex has been observed, the presence of an additional coordinating water ligand has been observed in the latter case. Because of rapidly exchanging water molecules, this 7-fold coordination complex was found to form pentagonal bipyramidal as well as capped trigonal prismatic configurations along the simulation interchanging on the picosecond time scale. Also in the case of [MgEDTA](2-) a trigonal prismatic configuration has been observed for a very short time period of approximately 1 ps. This work reports for the first time the presence of trigonal prismatic structures observed in the coordination sphere of [MgEDTA](2-) and [CaEDTA](2-) complexes in aqueous solution. In addition to the detailed characterization of structure and dynamics of the systems, the prediction of the associated infrared spectra indicates that the ion-water vibrational mode found at approximately 250 cm(-1) provides a distinctive measure to experimentally detect the presence of the coordinating water molecule via low-frequency IR setups.

Uranyl coordination in ionic liquids: the competition between ionic liquid anions, uranyl counterions, and Cl- anions investigated by extended X-ray absorption fine structure and UV-visible spectroscopies and molecular dynamics simulations.

PubMed

Gaillard, C; Chaumont, A; Billard, I; Hennig, C; Ouadi, A; Wipff, G

2007-06-11

The first coordination sphere of the uranyl cation in room-temperature ionic liquids (ILs) results from the competition between its initially bound counterions, the IL anions, and other anions (e.g., present as impurities or added to the solution). We present a joined spectroscopic (UV-visible and extended X-ray absorption fine structure)-simulation study of the coordination of uranyl initially introduced either as UO2X2 salts (X-=nitrate NO3-, triflate TfO-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium-based ILs (C4mimA, A-=PF6-, Tf2N-, BF4- and C4mim=1-methyl-3-butyl-imidazolium) as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. The addition of Cl- anions promotes the solubilization of the nitrate and triflate salts in the C4mimPF6 and the C4mimBF4 ILs via the formation of chloro complexes, also formed with other salts. The first coordination sphere of uranyl is further investigated by molecular dynamics (MD) simulations on associated versus dissociated forms of UO2X2 salts in C4mimA ILs as a function of A- and X- anions. Furthermore, the comparison of UO2Cl(4)2-, 2 X- complexes with dissociated X- anions, to the UO2X2, 4 Cl- complexes with dissociated chlorides, shows that the former is more stable. The case of fluoro complexes is also considered, as a possible result of fluorinated IL anion's degradation, showing that UO2F42- should be most stable in solution. In all cases, uranyl is found to be solvated as formally anionic UO2XnAmClp2-n-m-p complexes, embedded in a cage of stabilizing IL imidazolium or ammonium cations.

Metals in proteins: correlation between the metal-ion type, coordination number and the amino-acid residues involved in the coordination.

PubMed

Dokmanić, Ivan; Sikić, Mile; Tomić, Sanja

2008-03-01

Metal ions are constituents of many metalloproteins, in which they have either catalytic (metalloenzymes) or structural functions. In this work, the characteristics of various metals were studied (Cu, Zn, Mg, Mn, Fe, Co, Ni, Cd and Ca in proteins with known crystal structure) as well as the specificity of their environments. The analysis was performed on two data sets: the set of protein structures in the Protein Data Bank (PDB) determined with resolution <1.5 A and the set of nonredundant protein structures from the PDB. The former was used to determine the distances between each metal ion and its electron donors and the latter was used to assess the preferred coordination numbers and common combinations of amino-acid residues in the neighbourhood of each metal. Although the metal ions considered predominantly had a valence of two, their preferred coordination number and the type of amino-acid residues that participate in the coordination differed significantly from one metal ion to the next. This study concentrates on finding the specificities of a metal-ion environment, namely the distribution of coordination numbers and the amino-acid residue types that frequently take part in coordination. Furthermore, the correlation between the coordination number and the occurrence of certain amino-acid residues (quartets and triplets) in a metal-ion coordination sphere was analysed. The results obtained are of particular value for the identification and modelling of metal-binding sites in protein structures derived by homology modelling. Knowledge of the geometry and characteristics of the metal-binding sites in metalloproteins of known function can help to more closely determine the biological activity of proteins of unknown function and to aid in design of proteins with specific affinity for certain metals.

Second-sphere coordination in anion binding: Synthesis, characterization and X-ray structures of bis(diethylenetriamine)cobalt(III) complexes containing benzoates

NASA Astrophysics Data System (ADS)

Bala, Ritu; Kaur, Amrinder; Kashyap, Monika; Janzen, Daron E.

2014-04-01

New complexes of composition s-fac-[Co(dien)2]Cl2(Bz)·H2O (1), s-fac-[Co(dien)2]Cl(p-CBz)2·4.5H2O (2) and mer-[Co(dien)2](p-NBz)3·3H2O (3) were obtained by reacting aqueous solutions of bis(diethylenetriamine)cobalt(III) chloride and sodium salts of benzoates ((Bz = benzoate, CBz = p-chlorobenzoate, NBz = p-nitrobenzoate)) in 1:3 molar ratio. These complexes were characterized by TG analysis and spectroscopic studies (IR, NMR and UV-vis). IR and NMR studies were used for the isomeric identification of [Co(dien)2]3+ in new complexes. This cation, contains ligand diethylenetriamine (dien) bearing H-bond donors, capable of forming hydrogen bonds and its binding properties with benzoates have been studied using standard UV-vis spectroscopic titrations in aqueous medium (log k for Bz = 2.11, p-CBz = 3.64 and p-NBz = 3.66). Single crystal X-ray study of complex 2 and 3 reveals that both the structures are dominantly stabilized by second-sphere coordination through H-bonding interactions of type-NH (dien)⋯O (benzoates) and H (water)⋯O (benzoates) in addition to the electrostatic forces of attractions. Further, the NH (dien)⋯Cl- (counter ion) and NH (dien)⋯O (water) types of interactions are also playing a dominant role to stabilize the crystal lattice in complex 2 and 3 respectively.

Models for the Immediate Environment of Ions in Aqueous Solutions of Neodymium Chloride

NASA Astrophysics Data System (ADS)

Smirnov, P. R.; Grechin, O. V.

2018-01-01

Radial distribution functions of neodymium chloride aqueous solutions in a wide range of concentrations under ambient conditions are calculated from experimental data obtained earlier via X-ray diffraction analysis. Different models of the structural organization of the system are developed. The optimum versions are determined by calculating theoretical functions for each model and comparing their fit to the experimental functions. Such quantitative characteristics of the immediate environment of Nd3+ and Cl- ions as coordination numbers, interparticle distances, and varieties of ion pairs are determined. It is shown that the average number of water molecules in the first coordination sphere of the cation falls from 9 to 6.2 as the concentration rises. The structure of the systems over the whole range of concentrations is determined by ion associates of the noncontact type.

Bis(dicyclo­hexyl­ammonium) μ-oxalato-κ4 O 1,O 2:O 1′,O 2′-bis­[aqua­(oxalato-κ2 O 1,O 2)diphenyl­stannate(IV)

PubMed Central

Gueye, Ndongo; Diop, Libasse; Molloy, K. C. Kieran; Kociok-Köhn, Gabrielle

2010-01-01

The structure of the title compound, (C12H24N)2[Sn2(C6H5)4(C2O4)3(H2O)2], consists of a bischelating oxalate ion, located on an inversion center, which is linked to two SnPh2 groups. The coordination sphere of the Sn(IV) ion is completed by a monochelating oxalate anion and a water mol­ecule. The Sn(IV) atoms are thus seven-coordinated. The discrete binuclear units are further connected by hydrogen bonds, leading to a supra­molecular crystal structure. The asymmetric unit contains one half dianion and one (Cy2NH2)+ cation. PMID:21589314

Tuning structure and mobility of solvation shells surrounding tracer additives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carmer, James; Jain, Avni; Bollinger, Jonathan A.

2015-03-28

Molecular dynamics simulations and a stochastic Fokker-Planck equation based approach are used to illuminate how position-dependent solvent mobility near one or more tracer particle(s) is affected when tracer-solvent interactions are rationally modified to affect corresponding solvation structure. For tracers in a dense hard-sphere fluid, we compare two types of tracer-solvent interactions: (1) a hard-sphere-like interaction, and (2) a soft repulsion extending beyond the hard core designed via statistical mechanical theory to enhance tracer mobility at infinite dilution by suppressing coordination-shell structure [Carmer et al., Soft Matter 8, 4083–4089 (2012)]. For the latter case, we show that the mobility of surroundingmore » solvent particles is also increased by addition of the soft repulsive interaction, which helps to rationalize the mechanism underlying the tracer’s enhanced diffusivity. However, if multiple tracer surfaces are in closer proximity (as at higher tracer concentrations), similar interactions that disrupt local solvation structure instead suppress the position-dependent solvent dynamics.« less

Tuning structure and mobility of solvation shells surrounding tracer additives.

PubMed

Carmer, James; Jain, Avni; Bollinger, Jonathan A; van Swol, Frank; Truskett, Thomas M

2015-03-28

Molecular dynamics simulations and a stochastic Fokker-Planck equation based approach are used to illuminate how position-dependent solvent mobility near one or more tracer particle(s) is affected when tracer-solvent interactions are rationally modified to affect corresponding solvation structure. For tracers in a dense hard-sphere fluid, we compare two types of tracer-solvent interactions: (1) a hard-sphere-like interaction, and (2) a soft repulsion extending beyond the hard core designed via statistical mechanical theory to enhance tracer mobility at infinite dilution by suppressing coordination-shell structure [Carmer et al., Soft Matter 8, 4083-4089 (2012)]. For the latter case, we show that the mobility of surrounding solvent particles is also increased by addition of the soft repulsive interaction, which helps to rationalize the mechanism underlying the tracer's enhanced diffusivity. However, if multiple tracer surfaces are in closer proximity (as at higher tracer concentrations), similar interactions that disrupt local solvation structure instead suppress the position-dependent solvent dynamics.

A new method for registration of heterogeneous sensors in a dimensional measurement system

NASA Astrophysics Data System (ADS)

Zhao, Yan; Wang, Zhong; Fu, Luhua; Qu, Xinghua; Zhang, Heng; Liu, Changjie

2017-10-01

Registration of multiple sensors is a basic step in multi-sensor dimensional or coordinate measuring systems before any measurement. In most cases, a common standard is used to be measured by all sensors, and this may work well for general registration of multiple homogeneous sensors. However, when inhomogeneous sensors detect a common standard, it is usually very difficult to obtain the same information, because of the different working principles of the sensors. In this paper, a new method called multiple steps registration is proposed to register two sensors: a video camera sensor (VCS) and a tactile probe sensor (TPS). In this method, the two sensors measure two separated standards: a chrome circle on a reticle and a reference sphere with a constant distance between them, fixed on a steel plate. The VCS captures only the circle and the TPS touches only the sphere. Both simulations and real experiments demonstrate that the proposed method is robust and accurate in the registration of multiple inhomogeneous sensors in a dimensional measurement system.

Scaling laws for the mechanics of loose and cohesive granular materials based on Baxter's sticky hard spheres

NASA Astrophysics Data System (ADS)

Gaume, Johan; Löwe, Henning; Tan, Shurun; Tsang, Leung

2017-09-01

We have conducted discrete element simulations (pfc3d) of very loose, cohesive, granular assemblies with initial configurations which are drawn from Baxter's sticky hard sphere (SHS) ensemble. The SHS model is employed as a promising auxiliary means to independently control the coordination number zc of cohesive contacts and particle volume fraction ϕ of the initial states. We focus on discerning the role of zc and ϕ for the elastic modulus, failure strength, and the plastic consolidation line under quasistatic, uniaxial compression. We find scaling behavior of the modulus and the strength, which both scale with the cohesive contact density νc=zcϕ of the initial state according to a power law. In contrast, the behavior of the plastic consolidation curve is shown to be independent of the initial conditions. Our results show the primary control of the initial contact density on the mechanics of cohesive granular materials for small deformations, which can be conveniently, but not exclusively explored within the SHS-based assembling procedure.

Accuracy of digital models generated by conventional impression/plaster-model methods and intraoral scanning.

PubMed

Tomita, Yuki; Uechi, Jun; Konno, Masahiro; Sasamoto, Saera; Iijima, Masahiro; Mizoguchi, Itaru

2018-04-17

We compared the accuracy of digital models generated by desktop-scanning of conventional impression/plaster models versus intraoral scanning. Eight ceramic spheres were attached to the buccal molar regions of dental epoxy models, and reference linear-distance measurement were determined using a contact-type coordinate measuring instrument. Alginate (AI group) and silicone (SI group) impressions were taken and converted into cast models using dental stone; the models were scanned using desktop scanner. As an alternative, intraoral scans were taken using an intraoral scanner, and digital models were generated from these scans (IOS group). Twelve linear-distance measurement combinations were calculated between different sphere-centers for all digital models. There were no significant differences among the three groups using total of six linear-distance measurements. When limited to five lineardistance measurement, the IOS group showed significantly higher accuracy compared to the AI and SI groups. Intraoral scans may be more accurate compared to scans of conventional impression/plaster models.

A new method for recognizing quadric surfaces from range data and its application to telerobotics and automation, final phase

NASA Technical Reports Server (NTRS)

Mielke, Roland; Dcunha, Ivan; Alvertos, Nicolas

1994-01-01

In the final phase of the proposed research a complete top to down three dimensional object recognition scheme has been proposed. The various three dimensional objects included spheres, cones, cylinders, ellipsoids, paraboloids, and hyperboloids. Utilizing a newly developed blob determination technique, a given range scene with several non-cluttered quadric surfaces is segmented. Next, using the earlier (phase 1) developed alignment scheme, each of the segmented objects are then aligned in a desired coordinate system. For each of the quadric surfaces based upon their intersections with certain pre-determined planes, a set of distinct features (curves) are obtained. A database with entities such as the equations of the planes and angular bounds of these planes has been created for each of the quadric surfaces. Real range data of spheres, cones, cylinders, and parallelpipeds have been utilized for the recognition process. The developed algorithm gave excellent results for the real data as well as for several sets of simulated range data.

Integration of the shallow water equations on the sphere using a vector semi-Lagrangian scheme with a multigrid solver

NASA Technical Reports Server (NTRS)

Bates, J. R.; Semazzi, F. H. M.; Higgins, R. W.; Barros, Saulo R. M.

1990-01-01

A vector semi-Lagrangian semi-implicit two-time-level finite-difference integration scheme for the shallow water equations on the sphere is presented. A C-grid is used for the spatial differencing. The trajectory-centered discretization of the momentum equation in vector form eliminates pole problems and, at comparable cost, gives greater accuracy than a previous semi-Lagrangian finite-difference scheme which used a rotated spherical coordinate system. In terms of the insensitivity of the results to increasing timestep, the new scheme is as successful as recent spectral semi-Lagrangian schemes. In addition, the use of a multigrid method for solving the elliptic equation for the geopotential allows efficient integration with an operation count which, at high resolution, is of lower order than in the case of the spectral models. The properties of the new scheme should allow finite-difference models to compete with spectral models more effectively than has previously been possible.

Local sensory control of a dexterous end effector

NASA Technical Reports Server (NTRS)

Pinto, Victor H.; Everett, Louis J.; Driels, Morris

1990-01-01

A numerical scheme was developed to solve the inverse kinematics for a user-defined manipulator. The scheme was based on a nonlinear least-squares technique which determines the joint variables by minimizing the difference between the target end effector pose and the actual end effector pose. The scheme was adapted to a dexterous hand in which the joints are either prismatic or revolute and the fingers are considered open kinematic chains. Feasible solutions were obtained using a three-fingered dexterous hand. An algorithm to estimate the position and orientation of a pre-grasped object was also developed. The algorithm was based on triangulation using an ideal sensor and a spherical object model. By choosing the object to be a sphere, only the position of the object frame was important. Based on these simplifications, a minimum of three sensors are needed to find the position of a sphere. A two dimensional example to determine the position of a circle coordinate frame using a two-fingered dexterous hand was presented.

Freezing lines of colloidal Yukawa spheres. II. Local structure and characteristic lengths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gapinski, Jacek, E-mail: gapinski@amu.edu.pl; Patkowski, Adam; NanoBioMedical Center, A. Mickiewicz University, Umultowska 85, 61-614 Poznań

Using the Rogers-Young (RY) integral equation scheme for the static pair correlation functions combined with the liquid-phase Hansen-Verlet freezing rule, we study the generic behavior of the radial distribution function and static structure factor of monodisperse charge-stabilized suspensions with Yukawa-type repulsive particle interactions at freezing. In a related article, labeled Paper I [J. Gapinski, G. Nägele, and A. Patkowski, J. Chem. Phys. 136, 024507 (2012)], this hybrid method was used to determine two-parameter freezing lines for experimentally controllable parameters, characteristic of suspensions of charged silica spheres in dimethylformamide. A universal scaling of the RY radial distribution function maximum is shownmore » to apply to the liquid-bcc and liquid-fcc segments of the universal freezing line. A thorough analysis is made of the behavior of characteristic distances and wavenumbers, next-neighbor particle coordination numbers, osmotic compressibility factor, and the Ravaché-Mountain-Streett minimum-maximum radial distribution function ratio.« less

Lanthanide co-ordination frameworks: Opportunities and diversity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hill, Robert J.; Long, De-Liang; Hubberstey, Peter

2005-08-15

Significant successes have been made over recent years in preparing co-ordination framework polymers that show macroscopic material properties, but in the vast majority of cases this has been achieved with d-block metal-based systems. Lanthanide co-ordination frameworks also offer attractive properties in terms of their potential applications as luminescent, non-linear optical and porous materials. However, lanthanide-based systems have been far less studied to date than their d-block counterparts. One possible reason for this is that the co-ordination spheres of lanthanide cations are more difficult to control and, in the absence of design strategies for lanthanide co-ordination frameworks, it is significantly moremore » difficult to target materials with specific properties. However, this article highlights some of the exciting possibilities that have emerged from the earliest investigations in this field with new topological families of compounds being discovered from relatively simple framework components, including unusual eight, seven and five-connected framework systems. Our own research, as well as others, is leading to a much greater appreciation of the factors that control framework formation and the resultant observed topologies of these polymers. As this understanding develops targeting particular framework types will become more straightforward and the development of designed polyfunctional materials more accessible. Thus, it can be seen that lanthanide co-ordination frameworks have the potential to open up previously unexplored directions for materials chemistry. This article focuses on the underlying concepts for the construction of these enticing and potentially highly important materials.« less

A computer program for converting rectangular coordinates to latitude-longitude coordinates

USGS Publications Warehouse

Rutledge, A.T.

1989-01-01

A computer program was developed for converting the coordinates of any rectangular grid on a map to coordinates on a grid that is parallel to lines of equal latitude and longitude. Using this program in conjunction with groundwater flow models, the user can extract data and results from models with varying grid orientations and place these data into grid structure that is oriented parallel to lines of equal latitude and longitude. All cells in the rectangular grid must have equal dimensions, and all cells in the latitude-longitude grid measure one minute by one minute. This program is applicable if the map used shows lines of equal latitude as arcs and lines of equal longitude as straight lines and assumes that the Earth 's surface can be approximated as a sphere. The program user enters the row number , column number, and latitude and longitude of the midpoint of the cell for three test cells on the rectangular grid. The latitude and longitude of boundaries of the rectangular grid also are entered. By solving sets of simultaneous linear equations, the program calculates coefficients that are used for making the conversion. As an option in the program, the user may build a groundwater model file based on a grid that is parallel to lines of equal latitude and longitude. The program reads a data file based on the rectangular coordinates and automatically forms the new data file. (USGS)

Two conformations of the integrin A-domain (I-domain): a pathway for activation?

PubMed

Lee, J O; Bankston, L A; Arnaout, M A; Liddington, R C

1995-12-15

Integrins are plasma membrane proteins that mediate adhesion to other cells and to components of the extracellular matrix. Most integrins are constitutively inactive in resting cells, but are rapidly and reversibly activated in response to agonists, leading to highly regulated cell adhesion. This activation is associated with conformational changes in their extracellular portions, but the nature of the structural changes that lead to a change in adhesiveness is not understood. The interactions of several integrins with their extracellular ligands are mediated by an A-type domain (generally called the I-domain in integrins). Binding of the I-domain to protein ligands is dependent on divalent cations. We have described previously the structure of the I-domain from complement receptor 3 with bound Mg2+, in which the glutamate side chain from a second I-domain completes the octahedral coordination sphere of the metal, acting as a ligand mimetic. We now describe a new crystal form of the I-domain with bound Mn2+, in which water completes the metal coordination sphere and there is no equivalent of the glutamate ligand. Comparison of the two crystal forms reveals a change in metal coordination which is linked to a large (10 A) shift of the C-terminal helix and the burial of two phenylalanine residues into the hydrophobic core of the Mn2+ form. These structural changes, analogous to those seen in the signal-transducing G-proteins, alter the electrophilicity of the metal, reducing its ability to bind ligand-associated acidic residues, and dramatically alter the surface of the protein implicated in binding ligand. Our observations provide the first atomic resolution view of conformational changes in an integrin domain, and suggest how these changes are linked to a change in integrin adhesiveness. We propose that the Mg2+ form represents the conformation of the domain in the active state and the Mn2+ form the conformation in the inactive state of the integrin.

ATR-FTIR Spectroscopic Evidence for Biomolecular Phosphorus and Carboxyl Groups Facilitating Bacterial Adhesion to Iron Oxides

PubMed Central

Parikh, Sanjai J.; Mukome, Fungai N.D.; Zhang, Xiaoming

2014-01-01

Attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy has been used to probe the binding of bacteria to hematite (α-Fe2O3) and goethite (α-FeOOH). In situ ATR-FTIR experiments with bacteria (Pseudomonas putida, P. aeruginosa, Escherichia coli), mixed amino acids, polypeptide extracts, deoxyribonucleic acid (DNA), and a suite of model compounds were conducted. These compounds represent carboxyl, catecholate, amide, and phosphate groups present in siderophores, amino acids, polysaccharides, phospholipids, and DNA. Due in part to the ubiquitous presence of carboxyl groups in biomolecules, numerous IR peaks corresponding to outer-sphere or unbound (1400 cm−1) and inner-sphere (1310-1320 cm−1) coordinated carboxyl groups are noted following reaction of bacteria and biomolecules with α-Fe2O3 and α-FeOOH. However, the data also reveal that the presence of low-level amounts (i.e., 0.45-0.79%) of biomolecular phosphorous groups result in strong IR bands at ~1043 cm−1, corresponding to inner-sphere Fe-O-P bonds, underscoring the importance of bacteria associated P-containing groups in biomolecule and cell adhesion. Spectral comparisons also reveal slightly greater P-O-Fe contributions for bacteria (Pseudomonad, E. coli) deposited on α-FeOOH, as compared to α-Fe2O3. This data demonstrates that slight differences in bacterial adhesion to Fe oxides can be attributed to bacterial species and Fe-oxide minerals. However, more importantly, the strong binding affinity of phosphate in all bacteria samples to both Fe-oxides results in the formation of inner-sphere Fe-O-P bonds, signifying the critical role of biomolecular P in the initiation of bacterial adhesion. PMID:24859052

Direct Spectroscopic Detection of ATP Turnover Reveals Mechanistic Divergence of ABC Exporters.

PubMed

Collauto, Alberto; Mishra, Smriti; Litvinov, Aleksei; Mchaourab, Hassane S; Goldfarb, Daniella

2017-08-01

We have applied high-field (W-band) pulse electron-nuclear double resonance (ENDOR) and electron-electron double resonance (ELDOR)-detected nuclear magnetic resonance (EDNMR) to characterize the coordination sphere of the Mn 2+ co-factor in the nucleotide binding sites (NBSs) of ABC transporters. MsbA and BmrCD are two efflux transporters hypothesized to represent divergent catalytic mechanisms. Our results reveal distinct coordination of Mn 2+ to ATP and transporter residues in the consensus and degenerate NBSs of BmrCD. In contrast, the coordination of Mn 2+ at the two NBSs of MsbA is similar, which provides a mechanistic rationale for its higher rate constant of ATP hydrolysis relative to BmrCD. Direct detection of vanadate ion, trapped in a high-energy post-hydrolysis intermediate, further supports the notion of asymmetric hydrolysis by the two NBSs of BmrCD. The integrated spectroscopic approach presented here, which link energy input to conformational dynamics, can be applied to a variety of systems powered by ATP turnover. Copyright © 2017 Elsevier Ltd. All rights reserved.

Hydrodynamic synchronization of flagella on the surface of the colonial alga Volvox carteri

NASA Astrophysics Data System (ADS)

Brumley, Douglas; Polin, Marco; Goldstein, Raymond; Pedley, Timothy

2012-11-01

Whether on the surface of unicellular ciliates or in the respiratory epithelium, groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales. The mechanism responsible for the emergence of these metachronal waves is still unclear, mostly because finding an experimental system in which the beating filaments can be followed individually is challenging. We propose the multicellular green alga Volvox carteri as an ideal model system to study metachronal coordination, and report the existence of robust metachronal waves on its surface. Inspired by flagellar tip trajectories of Volvox somatic cells, we model a flagellum using a sphere of radius a elastically bound to a circular orbit of radius r0, perpendicular to a no-slip plane. This elastohydrodynamic model of weakly-coupled self-sustained oscillators can be recast in terms of interacting phase oscillators, offering an intuitive understanding of the mechanism driving the emergence of coordination. Our results confirm that elasticity is fundamental to guarantee fast and robust synchronization, and that sufficiently compliant trajectories lead to the emergence of metachronal waves in a manner essentially independent of boundary conditions.

Database of extended radiation maps and its access system

NASA Astrophysics Data System (ADS)

Verkhodanov, O. V.; Naiden, Ya. V.; Chernenkov, V. N.; Verkhodanova, N. V.

2014-01-01

We describe the architecture of the developed computing web server http://cmb.sao.ru allowing to synthesize the maps of extended radiation on the full sphere from the spherical harmonics in the GLESP pixelization grid, smooth them with the power beam pattern with various angular resolutions in the multipole space, and identify regions of the sky with given coordinates. We describe the server access and administration systems as well as the technique constructing the sky region maps, organized in Python in the Django web-application development framework.

Implementing quantum Ricci curvature

NASA Astrophysics Data System (ADS)

Klitgaard, N.; Loll, R.

2018-05-01

Quantum Ricci curvature has been introduced recently as a new, geometric observable characterizing the curvature properties of metric spaces, without the need for a smooth structure. Besides coordinate invariance, its key features are scalability, computability, and robustness. We demonstrate that these properties continue to hold in the context of nonperturbative quantum gravity, by evaluating the quantum Ricci curvature numerically in two-dimensional Euclidean quantum gravity, defined in terms of dynamical triangulations. Despite the well-known, highly nonclassical properties of the underlying quantum geometry, its Ricci curvature can be matched well to that of a five-dimensional round sphere.

Chirality sensing with stereodynamic biphenolate zinc complexes.

PubMed

Bentley, Keith W; de Los Santos, Zeus A; Weiss, Mary J; Wolf, Christian

2015-10-01

Two bidentate ligands consisting of a fluxional polyarylacetylene framework with terminal phenol groups were synthesized. Reaction with diethylzinc gives stereodynamic complexes that undergo distinct asymmetric transformation of the first kind upon binding of chiral amines and amino alcohols. The substrate-to-ligand chirality imprinting at the zinc coordination sphere results in characteristic circular dichroism signals that can be used for direct enantiomeric excess (ee) analysis. This chemosensing approach bears potential for high-throughput ee screening with small sample amounts and reduced solvent waste compared to traditional high-performance liquid chromatography methods. © 2015 Wiley Periodicals, Inc.

A 3D Ginibre Point Field

NASA Astrophysics Data System (ADS)

Kargin, Vladislav

2018-06-01

We introduce a family of three-dimensional random point fields using the concept of the quaternion determinant. The kernel of each field is an n-dimensional orthogonal projection on a linear space of quaternionic polynomials. We find explicit formulas for the basis of the orthogonal quaternion polynomials and for the kernel of the projection. For number of particles n → ∞, we calculate the scaling limits of the point field in the bulk and at the center of coordinates. We compare our construction with the previously introduced Fermi-sphere point field process.

Effects of Flow and Non-Newtonian Fluids on Nonspherical Cavitation Bubbles,

DTIC Science & Technology

1983-04-10

54 10 Alteration of Streamlines by Sphere for Y2 (8.*). 55 11 Major Components of Optical Cavitation. 61 12 Arrangement of Apparatus. 62 13 Laser ...341small" expansion parameter 111.12 Cnj C external flow time constant (t -c 0) WAS1 o spherical coordinate cone angle a f laser focal angle Figure 13...11.2 Dj - D external flow variable IV.22 Dbeam effective laser beau diameter V.1 De Deborah number Table 5 Ce, e, , e strain rates IV.8-9 Or* •e

Switchable molecular magnets

PubMed Central

SATO, Osamu

2012-01-01

Various molecular magnetic compounds whose magnetic properties can be controlled by external stimuli have been developed, including electrochemically, photochemically, and chemically tunable bulk magnets as well as a phototunable antiferromagnetic phase of single chain magnet. In addition, we present tunable paramagnetic mononuclear complexes ranging from spin crossover complexes and valence tautomeric complexes to Co complexes in which orbital angular momentum can be switched. Furthermore, we recently developed several switchable clusters and one-dimensional coordination polymers. The switching of magnetic properties can be achieved by modulating metals, ligands, and molecules/ions in the second sphere of the complexes. PMID:22728438

Acoustical tweezers using single spherically focused piston, X-cut, and Gaussian beams.

PubMed

Mitri, Farid G

2015-10-01

Partial-wave series expansions (PWSEs) satisfying the Helmholtz equation in spherical coordinates are derived for circular spherically focused piston (i.e., apodized by a uniform velocity amplitude normal to its surface), X-cut (i.e., apodized by a velocity amplitude parallel to the axis of wave propagation), and Gaussian (i.e., apodized by a Gaussian distribution of the velocity amplitude) beams. The Rayleigh-Sommerfeld diffraction integral and the addition theorems for the Legendre and spherical wave functions are used to obtain the PWSEs assuming weakly focused beams (with focusing angle α ⩽ 20°) in the Fresnel-Kirchhoff (parabolic) approximation. In contrast with previous analytical models, the derived expressions allow computing the scattering and acoustic radiation force from a sphere of radius a without restriction to either the Rayleigh (a ≪ λ, where λ is the wavelength of the incident radiation) or the ray acoustics (a ≫λ) regimes. The analytical formulations are valid for wavelengths largely exceeding the radius of the focused acoustic radiator, when the viscosity of the surrounding fluid can be neglected, and when the sphere is translated along the axis of wave propagation. Computational results illustrate the analysis with particular emphasis on the sphere's elastic properties and the axial distance to the center of the concave surface, with close connection of the emergence of negative trapping forces. Potential applications are in single-beam acoustical tweezers, acoustic levitation, and particle manipulation.

A comparative study between evaluation methods for quality control procedures for determining the accuracy of PET/CT registration

NASA Astrophysics Data System (ADS)

Cha, Min Kyoung; Ko, Hyun Soo; Jung, Woo Young; Ryu, Jae Kwang; Choe, Bo-Young

2015-08-01

The Accuracy of registration between positron emission tomography (PET) and computed tomography (CT) images is one of the important factors for reliable diagnosis in PET/CT examinations. Although quality control (QC) for checking alignment of PET and CT images should be performed periodically, the procedures have not been fully established. The aim of this study is to determine optimal quality control (QC) procedures that can be performed at the user level to ensure the accuracy of PET/CT registration. Two phantoms were used to carry out this study: the American college of Radiology (ACR)-approved PET phantom and National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) body phantom, containing fillable spheres. All PET/CT images were acquired on a Biograph TruePoint 40 PET/CT scanner using routine protocols. To measure registration error, the spatial coordinates of the estimated centers of the target slice (spheres) was calculated independently for the PET and the CT images in two ways. We compared the images from the ACR-approved PET phantom to that from the NEMA IEC body phantom. Also, we measured the total time required from phantom preparation to image analysis. The first analysis method showed a total difference of 0.636 ± 0.11 mm for the largest hot sphere and 0.198 ± 0.09 mm for the largest cold sphere in the case of the ACR-approved PET phantom. In the NEMA IEC body phantom, the total difference was 3.720 ± 0.97 mm for the largest hot sphere and 4.800 ± 0.85 mm for the largest cold sphere. The second analysis method showed that the differences in the x location at the line profile of the lesion on PET and CT were (1.33, 1.33) mm for a bone lesion, (-1.26, -1.33) mm for an air lesion and (-1.67, -1.60) mm for a hot sphere lesion for the ACR-approved PET phantom. For the NEMA IEC body phantom, the differences in the x location at the line profile of the lesion on PET and CT were (-1.33, 4.00) mm for the air lesion and (1.33, -1.29) mm for a hot sphere lesion. These registration errors from this study were reasonable compared to the errors reported in previous studies. Meanwhile, the total time required from phantom preparation was 67.72 ± 4.50 min for the ACR-approved PET phantom and 96.78 ± 8.50 min for the NEMA IEC body phantom. When the registration errors and the lead times are considered, the method using the ACR-approved PET phantom was more practical and useful than the method using the NEMA IEC body phantom.

Synthesis and structure of heptaaqua(nitrilotris(methylenephosphonato))(dibarium)sodium monohydrate [Na(H{sub 2}O){sub 3}(μ{sup 6}-NH(CH{sub 2}PO{sub 3}){sub 3})(μ-H{sub 2}O){sub 3}Ba{sub 2}(H{sub 2}O)] · H{sub 2}O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somov, N. V., E-mail: somov@phys.unn.ru; Chausov, F. F., E-mail: xps@ftiudm.ru; Zakirova, R. M., E-mail: ftt@udsu.ru

Crystals of the monohydrate form of heptaaqua(nitrilotris(methylenephosphonato))(dibarium) sodium [Na(H{sub 2}O{sub )3}(µ{sup 6}-NH(CH{sub 2}PO{sub 3}){sub 3})(µ-H{sub 2}O){sub 3}Ba{sub 2}(H{sub 2}O)] · H{sub 2}O are obtained; space group P2{sub 1}/c, Z = 4; a = 13.9117(10) Å, b = 11.54030(10) Å, and c = 24.1784(17) Å, ß = 148.785(18)°. The Na atom is coordinated octahedrally by one oxygen atom of a phosphonate group and five water molecules, including two bridging molecules. Ba atoms occupy two inequivalent crystallographic positions with coordination number eight and nine. The coordination spheres of both Ba atoms include two water molecules. Each ligand is bound to one Namore » atom and five Ba atoms forming three Ba–O–P–O and five Ba–O–P–C–N–C–P–O chelate cycles. In addition to the coordination bonds, molecules, including the solvate water molecule, are involved in hydrogen bonds in the crystal packing.« less

Ambient‐Temperature Synthesis of 2‐Phosphathioethynolate, PCS–, and the Ligand Properties of ECX– (E = N, P; X = O, S)

PubMed Central

Jupp, Andrew R.; Geeson, Michael B.; McGrady, John E.

2015-01-01

Abstract A synthesis of the 2‐phosphathioethynolate anion, PCS–, under ambient conditions is reported. The coordination chemistry of PCO–, PCS– and their nitrogen‐containing congeners is also explored. Photolysis of a solution of W(CO)6 in the presence of PCO– [or a simple ligand displacement reaction using W(CO)5(MeCN)] affords [W(CO)5(PCO)]– (1). The cyanate and thiocyanate analogues, [W(CO)5(NCO)]– (2) and [W(CO)5(NCS)]– (3), are also synthesised using a similar methodology, allowing for an in‐depth study of the bonding properties of this family of related ligands. Our studies reveal that, in the coordination sphere of tungsten(0), the PCO– anion preferentially binds through the phosphorus atom in a strongly bent fashion, while NCO– and NCS– coordinate linearly through the nitrogen atom. Reactions between PCS– and W(CO)5(MeCN) similarly afford [W(CO)5(PCS)]–; however, due to the ambidentate nature of the anion, a mixture of both the phosphorus‐ and sulfur‐bonded complexes (4a and 4b, respectively) is obtained. It was possible to establish that, as with PCO–, the PCS– ion also coordinates to the metal centre in a bent fashion. PMID:27134553

Hyperfine coupling constants on inner-sphere water molecules of a triazacyclononane-based Mn(II) complex and related systems relevant as MRI contrast agents.

PubMed

Patinec, Véronique; Rolla, Gabriele A; Botta, Mauro; Tripier, Raphaël; Esteban-Gómez, David; Platas-Iglesias, Carlos

2013-10-07

We report the synthesis of the ligand H2MeNO2A (1,4-bis(carboxymethyl)-7-methyl-1,4,7-triazacyclononane) and a detailed experimental and computational study of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Mn(MeNO2A)] and related Mn(2+) complexes relevant as potential contrast agents in magnetic resonance imaging (MRI). Nuclear magnetic relaxation dispersion (NMRD) profiles, (17)O NMR chemical shifts, and transverse relaxation rates of aqueous solutions of [Mn(MeNO2A)] were recorded to determine the parameters governing the relaxivity in this complex and the (17)O and (1)H HFCCs. DFT calculations (TPSSh model) performed in aqueous solution (PCM model) on the [Mn(MeNO2A)(H2O)]·xH2O and [Mn(EDTA)(H2O)](2-)·xH2O (x = 0-4) systems were used to determine theoretically the (17)O and (1)H HFCCs responsible for the (17)O NMR chemical shifts and the scalar contributions to (17)O and (1)H NMR relaxation rates. The use of a mixed cluster/continuum approach with the explicit inclusion of a few second-sphere water molecules is critical for an accurate calculation of HFCCs of coordinated water molecules. The impact of complex dynamics on the calculated HFCCs was evaluated with the use of molecular dynamics simulations within the atom-centered density matrix propagation (ADMP) approach. The (17)O and (1)H HFCCs calculated for these complexes and related systems show an excellent agreement with the experimental data. Both the (1)H and (17)O HFCCs (A(iso) values) are dominated by the spin delocalization mechanism. The A(iso) values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Mn(2+) ion, as well as by the orientation of the water molecule plane with respect to the Mn-O vector.

Quantum superintegrable Zernike system

NASA Astrophysics Data System (ADS)

Pogosyan, George S.; Salto-Alegre, Cristina; Wolf, Kurt Bernardo; Yakhno, Alexander

2017-07-01

We consider the differential equation that Zernike proposed to classify aberrations of wavefronts in a circular pupil, whose value at the boundary can be nonzero. On this account, the quantum Zernike system, where that differential equation is seen as a Schrödinger equation with a potential, is special in that it has a potential and a boundary condition that are not standard in quantum mechanics. We project the disk on a half-sphere and there we find that, in addition to polar coordinates, this system separates into two additional coordinate systems (non-orthogonal on the pupil disk), which lead to Schrödinger-type equations with Pöschl-Teller potentials, whose eigen-solutions involve Legendre, Gegenbauer, and Jacobi polynomials. This provides new expressions for separated polynomial solutions of the original Zernike system that are real. The operators which provide the separation constants are found to participate in a superintegrable cubic Higgs algebra.

Spectral Studies of Iron Coordination in Hemeprotein Complexes

PubMed Central

Brill, Arthur S.; Sandberg, Howard E.

1968-01-01

In order to evaluate the feasibility of observing the spectral behavior of protein groups in the coordination sphere of the iron in hemeproteins, criteria are developed to determine whether or not the application of difference absorption spectroscopy to the study of complex formation will be successful. Absolute absorption spectra, 300-1100 mμ, from bacterial catalase complexes are displayed, and the infrared bands correlated with magnetic susceptibility values of similar complexes of other hemeproteins. Dissociation constants for the formation of cyanide and azide complexes of metmyoglobin, methemoglobin, bacterial catalase, and horseradish peroxidase are given. Difference spectra, 210-280 mμ, are displayed for cyanide and azide complexes of these hemeproteins. A band at 235-241 mμ is found in the difference spectra of all low-spin vs. high-spin complexes. The factors which favor the assignment of this band to a transition involving a histidine residue are presented. PMID:5699802

Giant Rugby Ball [{CpBnFe(η5-P5)}24Cu96Br96] Derived from Pentaphosphaferrocene and CuBr2

PubMed Central

2015-01-01

The self-assembly of [CpBnFe(η5-P5)] (CpBn = η5-C5(CH2Ph)5) with CuBr2 leads to the formation of an unprecedented rugby ball-shaped supramolecule consisting of 24 units of the pentaphosphaferrocene and an extended CuBr framework, which does not follow the fullerene topology. The resulting scaffold of 312 noncarbon atoms reveals three different coordination modes of the cyclo-P5 ligand including a novel π-coordination. The outer dimensions of 3.7 × 4.6 nm of the sphere approach the range of the size of proteins. With a value of 32.1 nm3, it is 62 times larger in volume than a C60 molecule. Surprisingly, this giant rugby ball is also slightly soluble in CH2Cl2. PMID:26280785

Noncommutative products of Euclidean spaces

NASA Astrophysics Data System (ADS)

Dubois-Violette, Michel; Landi, Giovanni

2018-05-01

We present natural families of coordinate algebras on noncommutative products of Euclidean spaces R^{N_1} × _R R^{N_2} . These coordinate algebras are quadratic ones associated with an R -matrix which is involutive and satisfies the Yang-Baxter equations. As a consequence, they enjoy a list of nice properties, being regular of finite global dimension. Notably, we have eight-dimensional noncommutative euclidean spaces R4 × _R R4 . Among these, particularly well behaved ones have deformation parameter u \\in S^2 . Quotients include seven spheres S7_u as well as noncommutative quaternionic tori TH_u = S^3 × _u S^3 . There is invariance for an action of {{SU}}(2) × {{SU}}(2) on the torus TH_u in parallel with the action of U(1) × U(1) on a `complex' noncommutative torus T^2_θ which allows one to construct quaternionic toric noncommutative manifolds. Additional classes of solutions are disjoint from the classical case.

Structure and thermodynamics of a mixture of patchy and spherical colloids: A multi-body association theory with complete reference fluid information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bansal, Artee; Asthagiri, D.; Cox, Kenneth R.

A mixture of solvent particles with short-range, directional interactions and solute particles with short-range, isotropic interactions that can bond multiple times is of fundamental interest in understanding liquids and colloidal mixtures. Because of multi-body correlations, predicting the structure and thermodynamics of such systems remains a challenge. Earlier Marshall and Chapman [J. Chem. Phys. 139, 104904 (2013)] developed a theory wherein association effects due to interactions multiply the partition function for clustering of particles in a reference hard-sphere system. The multi-body effects are incorporated in the clustering process, which in their work was obtained in the absence of the bulk medium.more » The bulk solvent effects were then modeled approximately within a second order perturbation approach. However, their approach is inadequate at high densities and for large association strengths. Based on the idea that the clustering of solvent in a defined coordination volume around the solute is related to occupancy statistics in that defined coordination volume, we develop an approach to incorporate the complete information about hard-sphere clustering in a bulk solvent at the density of interest. The occupancy probabilities are obtained from enhanced sampling simulations but we also develop a concise parametric form to model these probabilities using the quasichemical theory of solutions. We show that incorporating the complete reference information results in an approach that can predict the bonding state and thermodynamics of the colloidal solute for a wide range of system conditions.« less

Synthesis and Reactivity of Tripodal Complexes Containing Pendant Bases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blacquiere, Johanna M.; Pegis, Michael L.; Raugei, Simone

2014-09-02

The synthesis of a new tripodal ligand family is reported, with tertiary-amine groups in the second-coordination sphere. The ligands are tris(amido)amine derivatives, with the pendant amines attached via a peptide coupling strategy. They were designed to be used in new catalysts for the oxygen reduction reaction (ORR), in which the pendant acid/base group could improve catalyst performance. Two members of the new ligand family were each metallated with Co(II) and Zn(II) to afford trigonal monopyramidal complexes. Reaction of the cobalt complexes, [Co(L)]-, with dioxygen reversibly generates a small amount of a Co(III)-superoxo species, which was characterized by EPR. Protonation ofmore » the zinc complex Zn[N{CH2CH2NC(O)CH2N(CH2Ph)2}3)-– ([Zn(TNBn)]-) with one equivalent of acid occurs with displacement and dissociation of an amide ligand. Addition of excess acid to the any of the complexes [M(L)]- results in complete proteolysis and formation of the ligands H3L. This decomposition limits the use of these complexes as catalysts for the ORR. An alternative ligand with two pyridyl arms was also prepared but could not be metallated. These studies highlight the importance of stability of the primary-coordination sphere of ORR electrocatalysts to both oxidative and acidic conditions. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.« less

Proton NMR spectroscopic characterization of binary and ternary complexes of cobalt(II) carboxypeptidase A with inhibitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bertini, I.; Luchinat, C.; Messori, L.

The binding of L- and D-phenylalanine and carboxylate inhibitors to cobalt(II)-substituted carboxypeptidase A, Co(II)CPD (E), in the presence and absence of pseudohalogens (X = N/sub 3//sup -/, NCO/sup -/, and NCS/sup -/) has been studied by /sup 1/H NMR spectroscopy. This technique monitors the proton signals of histidine residues bound to cobalt(II) and is therefore sensitive to the interactions of inhibitors that perturb the coordination sphere of the metal. Enzyme-inhibitor complexes, E/times/I, E/times/I/sub 2/, and E/times/I/times/X, each with characteristic NMR features, have been identified. The NMR data suggest that when the carboxylate group of a substrate of inhibitor binds atmore » the active site, a conformational change occurs that allows a second ligand molecule to bind to the metal ion, altering its coordination sphere and thereby attenuating the bidentate behavior of Glu-72. The /sup 1/H NMR signals also reflect alterations in the histidine interactions with the metal upon inhibitor binding. Isotropic shifts in the signals for the C-4 (c) and N protons (a) of one of the histidine ligands are readily observed in all of these complexes. These signals are relatively constant for all E/times/I and E/times/I/times/X complexes, indicating that this ligand is in a relatively fixed or buried conformation. However in the 2:1 carboxylate inhibitor (E/times/I/sub 2/) complexes, both signals are shifted upfield, suggesting a disturbance in the interaction of this histidine with the metal.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Jing-Yun, E-mail: jyunwu@ncnu.edu.tw; Tsai, Chi-Jou; Chang, Ching-Yun

A Zn(II)−salicylaldimine complex [Zn(L{sup salpyca})(H{sub 2}O)]{sub n} (1, where H{sub 2}L{sup salpyca}=4-hydroxy-3-(((pyridin-2-yl)methylimino)methyl)benzoic acid), with a one-dimensional (1D) chain structure, has been successfully converted to a discrete Ni(II)−salicylaldimine complex [Ni(L{sup salpyca})(H{sub 2}O){sub 3}] (2) and an infinite Cu(II)−salicylaldimine complex ([Cu(L{sup salpyca})]·3H{sub 2}O){sub n} (3) through a metal-ion exchange induced structural transformation process. However, such processes do not worked by Mn(II) and Co(II) ions. Solid-state structure analyses reveal that complexes 1–3 form comparable coordinative or supramolecular zigzag chains running along the crystallographic [201] direction. In addition, replacing Zn(II) ion by Ni(II) and Cu(II) ions caused changes in coordination environment and sphere ofmore » metal centers, from a 5-coordinate intermediate geometry of square pyramidal and trigonal bipyramidal in 1 to a 6-coordinate octahedral geometry in 2, and to a 4-coordiante square planar geometry in 3. This study shows that metal-ion exchange serves as a very efficient way of forming new coordination complexes that may not be obtained through direct synthesis. - Graphical abstract: A Zn(II)−salicylaldimine zigzag chain has been successfully converted to a Ni(II)−salicylaldimine supramolecular zigzag chain and a Cu(II)−salicylaldimine coordinative zigzag chain through metal-ion exchange induced structural transformations, which is not achieved by Mn(II) and Co(II) ions.« less

Acid-switched Eu(III) coordination inside reverse aggregates: Insights into a synergistic liquid-liquid extraction system

DOE PAGES

Ellis, Ross J.

2016-08-09

Determining the structure of complex solutions bearing metal ions is challenging, but crucial for developing important technologies such as liquid-liquid extraction for metal refining and separation purposes. Herein, the structure of an organic Eu(III) solution consisting a binary mixture of lipophilic ligands di-2-ethylhexyl phosphoric acid (HDEHP) and tetraoctyl diglycolamide (TODGA) in dodecane is studied using synchrotron small angle X-ray scattering (SAXS) and X-ray absorption fine structure spectroscopy (EXAFS). This system is of technological importance in f-element separation for nuclear fuel cycle applications, where extraction is controlled by varying nitric acid concentration. Extraction is promoted at low and high concentration, butmore » is retarded at intermediate concentration, leading to a U-shaped function; the structural origins of which we investigate. At the nanoscale, the solution is apparently comprised of reverse micelles with polar cores of approximately 1 nm in size, and these remain virtually unchanged as acid concentration is varied. Inside the polar cores, the coordination environment of Eu(III) switches from a 9-coordinate [Eu(TODGA) 3] 3+ motif at high acid, to a 6-coordinate HDEHP-dominated complex resembling Eu(HDEHP·DEHP) 3 at low acid. The results show that extraction is controlled within the coordination sphere, where it is promoted under conditions that favor coordination of either one of the two organic ligands, but is retarded under conditions that encourage mixed complexes. Lastly, our results link solution structure with ion transport properties in a technologically-important liquid-liquid ion extraction system.« less

Optical spectroscopy in turbid media utilizing an integrating sphere: mitochondrial chromophore analysis during metabolic transitions

PubMed Central

Chess, David J.; Billings, Eric; Covian, Raúl; Glancy, Brian; French, Stephanie; Taylor, Joni; de Bari, Heather; Murphy, Elizabeth; Balaban, Robert S.

2013-01-01

Recent evidence suggests that the activity of mitochondrial oxidative phosphorylation Complexes (MOPC) is modulated at multiple sites. Herein, a method of optically monitoring electron distribution within and between MOPC is described using a center-mounted sample in an integrating sphere (to minimize scattering effects) with a rapid-scanning spectrometer. The redox-sensitive MOPC absorbances (~465 to 630 nm) were modeled using linear least squares analysis with individual chromophore spectra. Classical mitochondrial activity transitions (e.g., ADP-induced increase in oxygen consumption) were used to characterize this approach. Most notable in these studies was the observation that intermediates of the catalytic cycle of cytochrome oxidase are dynamically modulated with metabolic state. The MOPC redox state, along with measurements of oxygen consumption and mitochondrial membrane potential, was used to evaluate the conductances of different sections of the electron transport chain. This analysis then was applied to mitochondria isolated from rabbit hearts subjected to ischemia-reperfusion (I/R). Surprisingly, I/R resulted in an inhibition of all measured MOPC conductances, suggesting a coordinated down-regulation of mitochondrial activity with this well-established cardiac perturbation. PMID:23665273

Formation of a disordered solid via a shock-induced transition in a dense particle suspension

NASA Astrophysics Data System (ADS)

Petel, Oren E.; Frost, David L.; Higgins, Andrew J.; Ouellet, Simon

2012-02-01

Shock wave propagation in multiphase media is typically dominated by the relative compressibility of the two components of the mixture. The difference in the compressibility of the components results in a shock-induced variation in the effective volume fraction of the suspension tending toward the random-close-packing limit for the system, and a disordered solid can take form within the suspension. The present study uses a Hugoniot-based model to demonstrate this variation in the volume fraction of the solid phase as well as a simple hard-sphere model to investigate the formation of disordered structures within uniaxially compressed model suspensions. Both models are discussed in terms of available experimental plate impact data in dense suspensions. Through coordination number statistics of the mesoscopic hard-sphere model, comparisons are made with the trends of the experimental pressure-volume fraction relationship to illustrate the role of these disordered structures in the bulk properties of the suspensions. A criterion for the dynamic stiffening of suspensions under high-rate dynamic loading is suggested as an analog to quasi-static jamming based on the results of the simulations.

Synthon preference in the cocrystal of 3,4,5-trifluorophenylboronic acid with urea.

PubMed

Kopczyńska, Karolina; Marek, Paulina H; Banaś, Bartłomiej; Madura, Izabela D

2017-11-01

The comprehensive description of the crystal structure of a novel 1:1 cocrystal of 3,4,5-trifluorophenylboronic acid with urea, C 6 H 4 BF 3 O 2 ·CH 4 N 2 O, is presented. Both components are good candidates for crystal engineering as they can create a variety of supramolecular synthons. The preference for the formation of different hetrosynthons is verified based on theoretical calculations. The syn-anti conformation of boronic acid has been found to be the most favourable in the formation of intermolecular interactions with urea. Moreover, the distortions present in the boron coordination sphere have been described quantitatively based on experimental data according to bond-valence vector model calculations. The results revealed that the deformation of the sphere is typical for a syn-anti conformation of boronic acids. The supramolecular structure of the cocrystal is composed of large synthons in the form of layers made up of O-H...O and N-H...O hydrogen bonds. The layers are joined via N-H...F hydrogen bonds which are unusual for urea cocrystal structures.

Molecular Designs for Controlling the Local Environments around Metal Ions

PubMed Central

Cook, Sarah A.; Borovik, A.S.

2015-01-01

CONSPECTUS The functions of metal complexes are directly linked to the local environment in which they are housed; modifications to the local environment (or secondary coordination sphere) are known to produce changes in key properties of the metal centers that can affect reactivity. Non-covalent interactions are the most common and influential forces that regulate the properties of secondary coordination spheres, which leads to complexities in structure that are often difficult to achieve in synthetic systems. Using key architectural features from the active sites of metalloproteins as inspiration, we have developed molecular systems that enforce intramolecular hydrogen bonds (H-bonds) around a metal center via incorporation of H-bond donors and acceptors into rigid ligand scaffolds. We have utilized these molecular species to probe mechanistic aspects of biological dioxygen activation and water oxidation. This Account describes the stabilization and characterization of unusual M–oxo and heterobimetallic complexes. These types of species have been implicated in a range of oxidative processes in biology but are often difficult to study because of their inherent reactivity. Our H-bonding ligand systems allowed us to prepare an FeIII–oxo species directly from the activation of O2 that was subsequently oxidized to form a monomeric FeIV–oxo species with an S = 2 spin state, similar to those species proposed as key intermediates in non-heme monooxygenases. We also demonstrated that a single MnIII–oxo center that was prepared from water could be converted to a high spin MnV–oxo species via stepwise oxidation—a process that mimics the oxidative charging of the oxygen-evolving complex (OEC) of photosystem II. Current mechanisms for photosynthetic O–O bond formation invoke a MnIV–oxyl species rather than the isoelectronic MnV–oxo system as the key oxidant based on computational studies. However, there is no experimental information to support the existence of an Mn–oxyl radical. We therefore probed the amount of spin density on the oxido ligand of our complexes using EPR spectroscopy in conjunction with oxygen-17 labeling. Our findings showed that there is a significant amount of spin on the oxido ligand, yet the M–oxo bonds are best described as highly covalent and there is no indication that an oxyl radical is formed. These results offer the intriguing possibility that high spin M–oxo complexes are involved in O–O bond formation in biology. Ligand redesign to incorporate H-bond accepting units (sulfonamido groups) simultaneously provided a metal ion binding pocket, adjacent H-bond acceptors, and an auxiliary binding site for a second metal ion. These properties allowed us to isolate a series of heterobimetallic complexes of FeIII and MnIII in which a group II metal ion was coordinated within the secondary coordination sphere. Examination of the influence of the second metal ion on the electron transfer properties of the primary metal center revealed unexpected similarities between CaII and SrII ions—a result with relevance to the OEC. In addition, the presence of a second metal ion was found to prevent intramolecular oxidation of the ligand with an O-atom transfer reagent. PMID:26181849

First-Episode Psychosis and the Criminal Justice System: Using a Sequential Intercept Framework to Highlight Risks and Opportunities.

PubMed

Wasser, Tobias; Pollard, Jessica; Fisk, Deborah; Srihari, Vinod

2017-10-01

In first-episode psychosis there is a heightened risk of aggression and subsequent criminal justice involvement. This column reviews the evidence pointing to these heightened risks and highlights opportunities, using a sequential intercept model, for collaboration between mental health services and existing diversionary programs, particularly for patients whose behavior has already brought them to the attention of the criminal justice system. Coordinating efforts in these areas across criminal justice and clinical spheres can decrease the caseload burden on the criminal justice system and optimize clinical and legal outcomes for this population.

The Downward Continuation to the Earth’s Surface of Truncated Spherical and Ellipsoidal Harmonic Series of the Gravity and Height Anomalies,

DTIC Science & Technology

1981-12-01

triangle OBQ, we obtain r c =COtI ose + sine (411) Hence with (4.10) e 2 sinecose (412)tan ip = (__o__2)_ 1 - e 2sin2 0 Pythagoras ’ theorem then easily...coordinate system. Strictly, this theorem tinds no application in our physical world since it guarantees convergence only outside the sphere enclosing...Junq, 1956, p.54 3 ; Moritz, 1980, p.52) is found, using the above theorem , to be f =E, the focal distance of the ellipsoid, shoving also that the

Shear wave induced resonance elastography of spherical masses with polarized torsional waves

NASA Astrophysics Data System (ADS)

Hadj Henni, Anis; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy

2012-03-01

Shear wave induced resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional shear waves modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an invitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary invivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection.

Shear wave induced resonance elastography of spherical masses with polarized torsional waves.

PubMed

Henni, Anis Hadj; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy

2012-03-26

Shear Wave Induced Resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional shear waves modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an in vitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary in vivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection.

Oxygen-17 NMR Shifts Caused by Cr{Sup ++} in Aqueous Solutions

DOE R&D Accomplishments Database

Jackson, J. A.; Lemons, J. F.; Taube, H.

1962-01-01

Cr{sup ++} in solution produces a paramagnetic shift in the NMR absorption of O{sup 17} in ClO{sub 4}{sup -}, as well as the expected paramagnetic shift for O{sup 17} in H{sub 2}O. As the concentration of ClO{sub 4}{sup -} increases, the shift in the H{sub 2}O{sup 17} absorption is diminished, and eventually changes sign. The effects are ascribed to preferential replacement by ClO{sub 4}{sup -} of water molecules from the axial positions in the first coordination sphere about Cr{sup ++}.

Monoanionic 99mTc-tricarbonyl-aminopolycarboxylate complexes with uncharged pendant groups: Radiosynthesis and evaluation as potential renal tubular tracers.

PubMed

Lipowska, Malgorzata; Klenc, Jeffrey; Jarkas, Nashwa; Marzilli, Luigi G; Taylor, Andrew T

2017-04-01

99m Tc(CO) 3 -nitrilotriacetic acid, 99m Tc(CO) 3 (NTA), is a new renal tubular agent with pharmacokinetic properties comparable to those of 131 I-OIH but the clearance of 99m Tc(CO) 3 (NTA) and 131 I-OIH is still less than the clearance of PAH, the gold standard for the measurement of effective renal plasma flow. At physiological pH, dianionic 99m Tc(CO) 3 (NTA) has a mononegative inner metal-coordination sphere and a mononegative uncoordinated carboxyl group. To evaluate alternate synthetic approaches, we assessed the importance of an uncoordinated carboxyl group, long considered essential for tubular transport, by evaluating the pharmacokinetics of three analogs with the 99m Tc(CO) 3 (NTA) metal-coordination sphere but with uncharged pendant groups. 99m Tc(CO) 3 complexes with N-(2-acetamido)iminodiacetic acid (ADA), N-(2-hydroxyethyl)iminodiacetic acid (HDA) and N-(fluoroethyl)iminodiacetic acid (FEDA) were prepared using a tricarbonyl kit and isolated by HPLC. The pharmacokinetics were evaluated in Sprague-Dawley rats, with 131 I-OIH as an internal control; urine was analyzed for metabolites. Plasma protein binding and erythrocyte uptake were determined from the 10min blood samples. Re(CO) 3 (FEDA), the analog of 99m Tc(CO) 3 (FEDA), was prepared and characterized. 99m Tc(CO) 3 (ADA), 99m Tc(CO) 3 (HDA) and 99m Tc(CO) 3 (FEDA) were efficiently prepared as a single species with high radiochemical purities (>99%). These new monoanionic 99m Tc(CO) 3 tracers with uncharged dangling groups all showed rapid blood clearance and high specificity for renal excretion. Activity in the urine, as a percent of 131 I-OIH at 10 and 60min, was 96% and 99% for ADA, 96% and 100% for HDA, and 100% and 99% for FEDA, respectively. Each new tracer was excreted unchanged in the urine. The Re(CO) 3 (FEDA) structure adds compelling evidence that such 99m Tc(CO) 3 (NTA) analogs have metal-coordination spheres identical to that of 99m Tc(CO) 3 (NTA). New tracers lacking the negatively charged pendant carboxyl group previously thought to be essential for rapid renal extraction, 99m Tc(CO) 3 (ADA), 99m Tc(CO) 3 (HDA) and 99m Tc(CO) 3 (FEDA), exhibit pharmacokinetics in rats comparable to those of 99m Tc(CO) 3 (NTA) and 131 I-OIH. Furthermore, these encouraging results in rats warrant evaluation of this new tracer type in humans. Copyright © 2016 Elsevier Inc. All rights reserved.

Synthetic vaccines.

PubMed

Lerner, R A

1983-02-01

Synthetic vaccines are designed with the help of computer-graphics programs. These displays generated by Arthur J. Olson of the Research Institute of Scripps Clinic show a method whereby parts of a viral protein that are on the surface of a virus, and therefore accessible to antibodies, can be identified. The backbone of the surface domain of the protein on the outer shell of the tomato bushy-stunt virus is displayed (1) on the basis of coordinates determined by Stephen C. Harrison of Harvard University and his colleagues. A single peptide of the protein is picked out in yellow, with the side chains of its component amino acids indicated in atomic detail (2). The peptide is enlarged and a sphere representing a water molecule is displayed (3). The sphere is rolled around the peptide to generate a map of the surface accessible to water (4); it does so, following an algorithm developed by Michael L. Connolly, by placing a dot at each point of its closest contact with the peptide, taking account of the sphere's own van der Waals radius (zone of influence, in effect) and that of each atom of the peptide and the rest of the protein. A similar-dot-surface map is generated to show what parts of the peptide are still accessible to water when three copies of the protein are associated in an array on the surface of the virus (5) and when four such arrays (out of 60) are in position on the outer surface of the virus (6).

YAG glass-ceramic phosphor for white LED (II): luminescence characteristics

NASA Astrophysics Data System (ADS)

Tanabe, Setsuhisa; Fujita, Shunsuke; Yoshihara, Satoru; Sakamoto, Akihiko; Yamamoto, Shigeru

2005-09-01

Optical properties of the Ce:YAG glass-ceramic (GC) phosphor for the white LED were investigated. Concentration dependence of fluorescence intensity of Ce3+:5d→4f transition in the GC showed a maximum at 0.5mol%Ce2O3. Quantum efficiency (QE) of Ce3+ fluorescence in the GC materials, the color coordinate and luminous flux of electroluminescence of LED composite were evaluated with an integrating sphere. QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x,y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd2O3 substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelength shifted to longer side up to Gd/(Y+Gd)=0.40 in molar composition. As a result, the color coordinate locus of the LED with various thickness of the GdYAG-GC shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd3+ ions in the precipitated YAG micro-crystals, leading to the increase of lattice constant of unit cell, which was confirmed by X-ray diffraction.

Large-scale Synchronization in Carpets of Micro-rotors

NASA Astrophysics Data System (ADS)

Kanale, Anup; Guo, Hanliang; Yan, Wen; Kanso, Eva

2017-11-01

Motile cilia are ubiquitous in nature, and have a critical role in biological locomotion and fluid transport. They often beat in an orchestrated wavelike fashion, and theoretical evidence suggests that this coordinated motion could arise from hydrodynamic interactions. Models based on bead-spring oscillators were used to examine the interaction between pairs of cilia, focusing on in-phase or anti-phase synchrony, while models of hydrodynamically-coupled elastic filaments looked at metachronal coordination in large but finite numbers of interacting cilia. The latter models reproduce metachronal wave coordination, but they are not readily amenable to analysis and parametric studies that highlight the origin of the instabilities that lead to wave propagations and wavelength selection. Here, we use a known model in which each cilium is represented by a rigid sphere moving along a circular trajectory close to a wall, hence the term rotor. The rotor is driven by a cilia-inspired force profile. We generalize this model to a doubly-periodic array of rotors, assuming small distance to the bounding wall, and employ Ewald summation techniques to solve for the flow field. Our goal is to examine the conditions that give rise to stable metachronal waves and their associated wavelength.

One dimensional coordination polymers: Synthesis, crystal structures and spectroscopic properties

NASA Astrophysics Data System (ADS)

Karaağaç, Dursun; Kürkçüoğlu, Güneş Süheyla; Şenyel, Mustafa; Şahin, Onur

2016-11-01

Two new one dimensional (1D) cyanide complexes, namely [M(4-aepy)2(H2O)2][Pt(CN)4], (4-aepy = 4-(2-aminoethyl)pyridine M = Cu(II) (1) or Zn(II) (2)), have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. The crystallographic analyses reveal that 1 and 2 are isomorphous and isostructural, and crystallize in the monoclinic system and C2 space group. The Pt(II) ions are coordinated by four cyanide-carbon atoms in the square-planar geometry and the [Pt(CN)4]2- ions act as a counter ion. The M(II) ions display an N4O2 coordination sphere with a distorted octahedral geometry, the nitrogen donors belonging to four molecules of the organic 4-aepy that act as unidentate ligands and two oxygen atoms from aqua ligands. The crystal structures of 1 and 2 are similar each other and linked via intermolecular hydrogen bonding, Pt⋯π interactions to form 3D supramolecular network. Vibration assignments of all the observed bands are given and the spectral features also supported to the crystal structures of the complexes.

2D polymeric cadmium(II) complexes containing 1,3-imidazolidine-2-thione (Imt) ligand, [Cd(Imt)(H2O)2(SO4)]n and [Cd(Imt)2(N3)2]n

NASA Astrophysics Data System (ADS)

Mahmood, Rashid; Ahmad, Saeed; Fettouhi, Mohammed; Roisnel, Thierry; Gilani, Mazhar Amjad; Mehmood, Kashif; Murtaza, Ghulam; Isab, Anvarhusein A.

2018-03-01

The present study aims at preparing and carrying out the structural investigation of two polymeric cadmium(II) complexes of imidazolidine-2-thione (Imt) based on sulfate or azide ions, [Cd(Imt)(H2O)2(SO4)]n (1) and [Cd(Imt)2(N3)2]n (2). The structures of the complexes were determined by single crystal X-ray analysis. Both compounds, 1 and 2 crystallize in the form of 2D coordination polymers and the cadmium(II) ion is six-coordinate having a distorted octahedral geometry in each compound. In 1, the metal ion is bonded to one sulfur atom of Imt and five oxygen atoms with two from water and three of bridging sulfate ions. In 2, the cadmium coordination sphere is completed by two Imt molecules binding through the sulfur atoms and four nitrogen atoms of bridging azide ions. The crystal structures are stabilized by intra and intermolecular hydrogen bonding interactions. The complexes were also characterized by IR and NMR spectroscopy and the spectroscopic data is consistent with the binding of the ligands.

High-speed scanning of critical structures in aviation using coordinate measurement machine and the laser ultrasonic.

PubMed

Swornowski, Pawel J

2012-01-01

Aviation is one of the know-how spheres containing a great deal of responsible sub-assemblies, in this case landing gear. The necessity for reducing production cycle times while achieving better quality compels metrologists to look for new and improved ways to perform inspection of critical structures. This article describes the ability to determine the shape deviation and location of defects in landing gear using coordinate measuring machines and laser ultrasonic with high-speed scanning. A nondestructive test is the basis for monitoring microcrack and corrosion propagation in the context of a damage-tolerant design approach. This article presents an overview of the basics and of the various metrological aspects of coordinate measurement and a nondestructive testing method in terms of high-speed scanning. The new test method (laser ultrasonic) promises to produce the necessary increase in inspection quality, but this is limited by the wide range of materials, geometries, and structure aeronautic parts used. A technique combining laser ultrasonic and F-SAFT (Fourier-Synthetic Aperture Focusing Technique) processing has been proposed for the detection of small defects buried in landing gear. The experimental results of landing gear inspection are also presented. © Wiley Periodicals, Inc.

In situ spectroscopy and spectroelectrochemistry of uranium in high-temperature alkali chloride molten salts.

PubMed

Polovov, Ilya B; Volkovich, Vladimir A; Charnock, John M; Kralj, Brett; Lewin, Robert G; Kinoshita, Hajime; May, Iain; Sharrad, Clint A

2008-09-01

Soluble uranium chloride species, in the oxidation states of III+, IV+, V+, and VI+, have been chemically generated in high-temperature alkali chloride melts. These reactions were monitored by in situ electronic absorption spectroscopy. In situ X-ray absorption spectroscopy of uranium(VI) in a molten LiCl-KCl eutectic was used to determine the immediate coordination environment about the uranium. The dominant species in the melt was [UO 2Cl 4] (2-). Further analysis of the extended X-ray absorption fine structure data and Raman spectroscopy of the melts quenched back to room temperature indicated the possibility of ordering beyond the first coordination sphere of [UO 2Cl 4] (2-). The electrolytic generation of uranium(III) in a molten LiCl-KCl eutectic was also investigated. Anodic dissolution of uranium metal was found to be more efficient at producing uranium(III) in high-temperature melts than the cathodic reduction of uranium(IV). These high-temperature electrolytic processes were studied by in situ electronic absorption spectroelectrochemistry, and we have also developed in situ X-ray absorption spectroelectrochemistry techniques to probe both the uranium oxidation state and the uranium coordination environment in these melts.

Synthesis and coordinating ability of an anionic cobaltabisdicarbollide ligand geometrically analogous to BINAP.

PubMed

Rojo, Isabel; Teixidor, Francesc; Viñas, Clara; Kivekäs, Raikko; Sillanpää, Reijo

2004-10-25

The anionic chelating ligand [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- has been synthesized from [3,3'-Co(1,2-C2B9H11)2]- in very good yield in a one-pot process with an easy work-up procedure. The coordinating ability of this ligand has been studied with Group 11 metal ions (Ag, Au) and with transition-metal ions (Pd, Rh). The two dicarbollide halves of the [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- ligand can swing about one axis in a manner analogous to the constituent parts of BINAP and ferrocenyl phosphine derivatives. All these ligands function as hinges, with the most important property in relation to the coordination requirements of the metal being the PP distance. [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]-, BINAP, ferrocenyl phosphine derivatives, and other hinge ligands present a range of different PP separations, and consequently different coordination spheres and dispositions around metal cations. To account for these differences, the equation Dphi2 = D02 + 4 R2cos2(90-phi/2) has been developed. It relates the PP distance (Dphi) in a complex with the minimum PP distance (D0) that is characteristic of the hinge-type ligand.

The Copper Active Site of CBM33 Polysaccharide Oxygenases

PubMed Central

2013-01-01

The capacity of metal-dependent fungal and bacterial polysaccharide oxygenases, termed GH61 and CBM33, respectively, to potentiate the enzymatic degradation of cellulose opens new possibilities for the conversion of recalcitrant biomass to biofuels. GH61s have already been shown to be unique metalloenzymes containing an active site with a mononuclear copper ion coordinated by two histidines, one of which is an unusual τ-N-methylated N-terminal histidine. We now report the structural and spectroscopic characterization of the corresponding copper CBM33 enzymes. CBM33 binds copper with high affinity at a mononuclear site, significantly stabilizing the enzyme. X-band EPR spectroscopy of Cu(II)-CBM33 shows a mononuclear type 2 copper site with the copper ion in a distorted axial coordination sphere, into which azide will coordinate as evidenced by the concomitant formation of a new absorption band in the UV/vis spectrum at 390 nm. The enzyme’s three-dimensional structure contains copper, which has been photoreduced to Cu(I) by the incident X-rays, confirmed by X-ray absorption/fluorescence studies of both aqueous solution and intact crystals of Cu-CBM33. The single copper(I) ion is ligated in a T-shaped configuration by three nitrogen atoms from two histidine side chains and the amino terminus, similar to the endogenous copper coordination geometry found in fungal GH61. PMID:23540833

Zn(II) and Hg(II) binding to a designed peptide that accommodates different coordination geometries.

PubMed

Szunyogh, Dániel; Gyurcsik, Béla; Larsen, Flemming H; Stachura, Monika; Thulstrup, Peter W; Hemmingsen, Lars; Jancsó, Attila

2015-07-28

Designed metal ion binding peptides offer a variety of applications in both basic science as model systems of more complex metalloproteins, and in biotechnology, e.g. in bioremediation of toxic metal ions, biomining or as artificial enzymes. In this work a peptide (HS: Ac-SCHGDQGSDCSI-NH2) has been specifically designed for binding of both Zn(II) and Hg(II), i.e. metal ions with different preferences in terms of coordination number, coordination geometry, and to some extent ligand composition. It is demonstrated that HS accommodates both metal ions, and the first coordination sphere, metal ion exchange between peptides, and speciation are characterized as a function of pH using UV-absorption-, synchrotron radiation CD-, (1)H-NMR-, and PAC-spectroscopy as well as potentiometry. Hg(II) binds to the peptide with very high affinity in a {HgS2} coordination geometry, bringing together the two cysteinates close to each end of the peptide in a loop structure. Despite the high affinity, Hg(II) is kinetically labile, exchanging between peptides on the subsecond timescale, as indicated by line broadening in (1)H-NMR. The Zn(II)-HS system displays more complex speciation, involving monomeric species with coordinating cysteinates, histidine, and a solvent water molecule, as well as HS-Zn(II)-HS complexes. In summary, the HS peptide displays conformational flexibility, contains many typical metal ion binding groups, and is able to accommodate metal ions with different structural and ligand preferences with high affinity. As such, the HS peptide may be a scaffold offering binding of a variety of metal ions, and potentially serve for metal ion sequestration in biotechnological applications.

Systematic Perturbations of Binuclear Non-heme Iron Sites: Structure and Dioxygen Reactivity of de Novo Due Ferri Proteins

DOE PAGES

Snyder, Rae Ana; Betzu, Justine; Butch, Susan E.; ...

2015-07-08

We report that DFsc (single-chain due ferri) proteins allow for modeling binuclear non-heme iron enzymes with a similar fold. Three 4A → 4G variants of DFsc were studied to investigate the effects of (1) increasing the size of the substrate/solvent access channel (G4DFsc), (2) including an additional His residue in the first coordination sphere along with three additional helix-stabilizing mutations [3His-G4DFsc(Mut3)], and (3) the three helix-stabilizing mutations alone [G4DFsc-(Mut3)] on the biferrous structures and their O 2 reactivities. Near-infrared circular dichroism and magnetic circular dichroism (MCD) spectroscopy show that the 4A → 4G mutations increase coordination of the diiron sitemore » from 4-coordinate/5-coordinate to 5-coordinate/5-coordinate, likely reflecting increased solvent accessibility. While the three helix-stabilizing mutations [G4DFsc(Mut3)] do not affect the coordination number, addition of the third active site His residue [3His-G4DFsc(Mut3)] results in a 5-coordinate/6-coordinate site. Although all 4A → 4G variants have significantly slower pseudo-first-order rates when reacting with excess O 2 than DFsc (~2 s ₋1), G4DFsc and 3His-G4DFsc(Mut3) have rates (~0.02 and ~0.04 s ₋1) faster than that of G4DFsc(Mut3) (~0.002 s ₋1). These trends in the rate of O 2 reactivity correlate with exchange coupling between the Fe(II) sites and suggest that the two-electron reduction of O 2 occurs through end-on binding at one Fe(II) rather than through a peroxy-bridged intermediate. Finally, UV–vis absorption and MCD spectroscopies indicate that an Fe(III)Fe(III)-OH species first forms in all three variants but converts into an Fe(III)-μ-OH-Fe(III) species only in the 2-His forms, a process inhibited by the additional active site His ligand that coordinatively saturates one of the iron centers in 3His-G4DFsc(Mut3).« less

Systematic Perturbations of Binuclear Non-heme Iron Sites: Structure and Dioxygen Reactivity of de Novo Due Ferri Proteins.

PubMed

Snyder, Rae Ana; Betzu, Justine; Butch, Susan E; Reig, Amanda J; DeGrado, William F; Solomon, Edward I

2015-08-04

DFsc (single-chain due ferri) proteins allow for modeling binuclear non-heme iron enzymes with a similar fold. Three 4A → 4G variants of DFsc were studied to investigate the effects of (1) increasing the size of the substrate/solvent access channel (G4DFsc), (2) including an additional His residue in the first coordination sphere along with three additional helix-stabilizing mutations [3His-G4DFsc(Mut3)], and (3) the three helix-stabilizing mutations alone [G4DFsc(Mut3)] on the biferrous structures and their O2 reactivities. Near-infrared circular dichroism and magnetic circular dichroism (MCD) spectroscopy show that the 4A → 4G mutations increase coordination of the diiron site from 4-coordinate/5-coordinate to 5-coordinate/5-coordinate, likely reflecting increased solvent accessibility. While the three helix-stabilizing mutations [G4DFsc(Mut3)] do not affect the coordination number, addition of the third active site His residue [3His-G4DFsc(Mut3)] results in a 5-coordinate/6-coordinate site. Although all 4A→ 4G variants have significantly slower pseudo-first-order rates when reacting with excess O2 than DFsc (∼2 s(-1)), G4DFsc and 3His-G4DFsc(Mut3) have rates (∼0.02 and ∼0.04 s(-1)) faster than that of G4DFsc(Mut3) (∼0.002 s(-1)). These trends in the rate of O2 reactivity correlate with exchange coupling between the Fe(II) sites and suggest that the two-electron reduction of O2 occurs through end-on binding at one Fe(II) rather than through a peroxy-bridged intermediate. UV-vis absorption and MCD spectroscopies indicate that an Fe(III)Fe(III)-OH species first forms in all three variants but converts into an Fe(III)-μ-OH-Fe(III) species only in the 2-His forms, a process inhibited by the additional active site His ligand that coordinatively saturates one of the iron centers in 3His-G4DFsc(Mut3).

Structural changes at the metal ion binding site during the phosphoglucomutase reaction.

PubMed

Ray, W J; Post, C B; Liu, Y; Rhyu, G I

1993-01-12

An electron density map of the reactive, Cd2+ form of crystalline phosphoglucomutase from X-ray diffraction studies shows that the enzymic phosphate donates a nonbridging oxygen to the ligand sphere of the bound metal ion, which appears to be tetracoordinate. 31P and 113Cd NMR spectroscopy are used to assess changes in the properties of bound Cd2+ produced by substrate/product and by substrate/product analog inhibitors. The approximately 50 ppm downfield shift of the 113Cd resonance on formation of the complex of dephosphoenzyme and glucose 1,6-bisphosphate is associated with the initial sugar-phosphate binding step and likely involves a change in the geometry of the coordinating ligands. This interpretation is supported by spectral studies involving various complexes of the active Co2+ and Ni(2+)-enzyme. In addition, there is a loss of the 31P-113Cd J coupling that characterizes the monophosphate complexes of the Cd2+ enzyme either during or immediately after the PO3- transfer step that produces the bisphosphate complex, indicating a further change at the metal binding site. The implications of these observations with respect to the PO3- transfer process in the phosphoglucomutase reaction are considered. The apparent plasticity of the ligand sphere of the active site metal ion in this system may allow a single metal ion to act as a chaperone for a nonbridging oxygen during PO3- transfer or to allow a change in metal ion coordination during catalysis. A general NMR line shape/chemical-exchange analysis for evaluating binding in protein-ligand systems when exchange is intermediate to fast on the NMR time scale is described. Its application to the present system involves multiple exchange sites that depend on a single binding rate, thereby adding further constraints to the analysis.

The role of vanadium in biology.

PubMed

Rehder, Dieter

2015-05-01

Vanadium is special in at least two respects: on the one hand, the tetrahedral anion vanadate(v) is similar to the phosphate anion; vanadate can thus interact with various physiological substrates that are otherwise functionalized by phosphate. On the other hand, the transition metal vanadium can easily expand its sphere beyond tetrahedral coordination, and switch between the oxidation states +v, +iv and +iii in a physiological environment. The similarity between vanadate and phosphate may account for the antidiabetic potential of vanadium compounds with carrier ligands such as maltolate and picolinate, and also for vanadium's mediation in cardiovascular and neuronal defects. Other potential medicinal applications of more complex vanadium coordination compounds, for example in the treatment of parasitic tropical diseases, may also be rooted in the specific properties of the ligand sphere. The ease of the change in the oxidation state of vanadium is employed by prokarya (bacteria and cyanobacteria) as well as by eukarya (algae and fungi) in respiratory and enzymatic functions. Macroalgae (seaweeds), fungi, lichens and Streptomyces bacteria have available haloperoxidases, and hence enzymes that enable the 2-electron oxidation of halide X(-) with peroxide, catalyzed by a Lewis-acidic V(V) center. The X(+) species thus formed can be employed to oxidatively halogenate organic substrates, a fact with implications also for the chemical processes in the atmosphere. Vanadium-dependent nitrogenases in bacteria (Azotobacter) and cyanobacteria (Anabaena) convert N2 + H(+) to NH4(+) + H2, but are also receptive for alternative substrates such as CO and C2H2. Among the enigmas to be solved with respect to the utilization of vanadium in nature is the accumulation of V(III) by some sea squirts and fan worms, as well as the purport of the nonoxido V(IV) compound amavadin in the fly agaric.

Two pathways for electrocatalytic oxidation of hydrogen by a nickel bis(diphosphine) complex with pendant amines in the second coordination sphere.

PubMed

Yang, Jenny Y; Smith, Stuart E; Liu, Tianbiao; Dougherty, William G; Hoffert, Wesley A; Kassel, W Scott; Rakowski DuBois, M; DuBois, Daniel L; Bullock, R Morris

2013-07-03

A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(P(Cy)2N(t-Bu)2)2](BF4)2 (P(Cy)2N(t-Bu)2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni(II) complex gives three isomers of the doubly protonated Ni(0) complex [Ni(P(Cy)2N(t-Bu)2H)2](BF4)2. Using the pKa values and Ni(II/I) and Ni(I/0) redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(P(Cy)2N(t-Bu)2)2](2+) was determined to be -7.9 kcal mol(-1). The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s(-1) is observed at 23 °C.

99 Tc NMR determination of the oxygen isotope content in 18 O-enriched water.

PubMed

Tarasov, Valerii P; Kirakosyan, Gayana А; German, Konstantin E

2018-03-01

99 Tc NMR has been suggested as an original method of evaluating the content of oxygen isotopes in oxygen-18-enriched water, a precursor for the production of radioisotope fluorine-18 used in positron emission tomography. To this end, solutions of NH 4 TcO 4 or NaTcO 4 (up to 0.28 mol/L) with natural abundance of oxygen isotopes in virgin or recycled 18 O-enriched water have been studied by 99 Tc NMR. The method is based on 16 O/ 17 O/ 18 O intrinsic isotope effects in the 99 Tc NMR chemical shifts, and the statistical distribution of oxygen isotopes in the coordination sphere of TcO 4 - and makes it possible to quantify the composition of enriched water by measuring the relative intensities of the 99 Tc NMR signals of the Tc 16 O 4-n 18 O n - isotopologues. Because the oxygen exchange between TcO 4 - and enriched water in neutral and alkaline solutions is characterized by slow kinetics, gaseous HCl was bubbled through a solution for a few seconds to achieve the equilibrium distribution of oxygen isotopes in the Tc coordination sphere without distortion of the oxygen composition of the water. Pertechnetate ion was selected as a probe due to its high stability in solutions and the significant 99 Tc NMR shift induced by a single 16 O→ 18 O substitution (-0.43 ± 0.01 ppm) in TcO 4 - and spin coupling constant 1 J( 99 Tc- 17 O) (131.46 Hz) favourable for the observation of individual signals of Tc 16 O 4-n 18 O n - isotopologues. Copyright © 2017 John Wiley & Sons, Ltd.

SU-E-J-79: Evaluation of Prostate Volume Changes During Radiotherapy Using Implanted Markers and On-Board Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ispir, B; Akdeniz, Y; Ugurluer, G

2015-06-15

Purpose: To evaluate prostate volume changes during radiation therapy using implanted gold markers and on-board imaging. Methods: Twenty-five patients were included who underwent an implantation of three gold markers. Cartesian coordinates of markers were assessed in kV-images. The coordinates of centers of two markers were measured on kV-images from the center of the marker at the apex which was reference. The distances between the markers were extrapolated from the coordinates using the Euclid formula. The radius of the sphere through markers was calculated using sinus theorem. The prostate volume for the first and last fraction was substituted with a spheremore » model and was calculated for each patient. The t-test was used for analysis. Results: The mean prostate volume for first and last fraction was 24.65 and 20.87 cc, respectively (p≤0.05). The prostate volume was smaller for 23 patients, whereas there was an expansion for 2 patients. Fifteen patients had androgen deprivation during radiotherapy (H group) and ten did not (NH group). The mean prostate volume for the first and last fraction for the NH group was 30.73 cc and 24.89 cc and for the H group 20.84 cc and 18.19 cc, respectively. There was a 15.8% volume change during treatment for the NH group and 12.2% for the H group, but the difference was not statistically significant. The radius difference of the theoretical sphere for the first and last fraction was 0.98 mm (range, 0.09–2.95 mm) and remained below 2 mm in 88% of measurements. Conclusion: There was a significant volume change during prostate radiotherapy. The difference between H group and NH group was not significant. The radius changes did not exceed 3 mm and it was below adaptive treatment requirements. Our results indicate that prostate volume changes during treatment should be taken into account during contouring and treatment planning.« less

Biometal binding-site mimicry with modular, hetero-bifunctionally modified architecture encompassing a Trp/His motif: insights into spatiotemporal noncovalent interactions from a comparative spectroscopic study.

PubMed

Yang, Chi Ming

2011-03-28

Metal-site Trp/His interactions are crucial to diverse metalloprotein functions. This paper presents a study using metal-motif mimicry to capture and dissect the static and transient components of physicochemical properties underlying the Trp/His aromatic side-chain noncovalent interactions across the first- and second-coordination spheres of biometal ions. Modular biomimetic constructs, EDTA-(L-Trp, L-His) or EWH and DTPA-(L-Trp, L-His) or DWH, featuring a function-significant Trp/His pair, enabled extracting the putative hydrophobic/hydrophilic aromatic interactions surrounding metal centers. Fluorescence, circular dichroism (CD) spectroscopic titrations and ESI mass spectrometry demonstrated that both the constructs stoichiometrically bind to Ca(2+), Co(2+), Cu(2+), Ni(2+), Mn(2+), Zn(2+), Cd(2+), and Fe(2+), and such binding was strongly coupled to stereospecific side-chain structure reorientations of the Trp indole and His imidazole rings. A mechanistic dichotomy corresponding to the participation of the indole unit in the binding event was revealed by a scaffold-platform correlation of steady-state fluorescence-response landscape, illuminating that secondary-coordination-sphere ligand cation-π interactions were immediately followed by subsequent transient physicochemical processes including through-space energy transfer, charge transfer and/or electron transfer, depending on the type of metals. The fluorescence quenching of Trp side chain by 3d metal ions can be ascribed to through-space d-π interactions. While the fluorescence titration was capable of illuminating a two-component energetic model, clean isosbestic/isodichroic points in the CD titration spectra indicated that the metallo-constructs, such as Cu(2+)-EWH complex, fold thermodynamically by means of a two-state equilibrium. Further, the metal-ion dependence of Trp conformational variation in the modular architecture of metal-bound scaffolds was evidenced unambiguously by the CD spectra and supported by MMFF calculations; both were capable of distinguishing between the coordination geometry and the preference for metal binding mode. The study thus helps understand how aromatic rings around metal-sites have unique capabilities through the control of the spatiotemporal distribution of noncovalent interaction elements to achieve diverse chemical functionality.

The transformation of amorphous calcium carbonate, ACC, to crystalline phases as function of time and temperature.

NASA Astrophysics Data System (ADS)

Gies, Hermann; Happel, Marian; Niedermayr, Andrea; Immenhauser, Adrian

2017-04-01

We present results from a structural study of the transformation of freeze dried amorphous calcium carbonate, ACC, in crystalline material using pair distribution function analysis, PDF analysis, of X-ray powder diffraction data, XPD data. PDF analysis allows for the analysis of local order of structural subunit in the range between molecular unit (1. and 2. coordination sphere) and long range periodicity as in crystalline materials. ACC was precipitated from aqueous solutions at 298 K and 278 K using different amounts of Mg cations as stabilizer. The samples were immediately separated from the solution and freeze dried. For the transformation study, the samples were heated and analysed using XPD until they were crystallized. The radial distribution obtained from the XPD data were compared to simulated radial distributions of the calcium carbonate polymorphs and their hydrated phases. An ACC precipitated from a solution with Ca:Mg:CO3 = 1:5:4 at 298 K (ration in mmol, pH = 8.2) and freeze dried right after isolation from the solution revealed a close resemblance with ikaite in its local order. Another ACC with Ca:Mg:CO3 = 1:10:1.4 (T = 298, pH = 8.7) showed distinctly different local order resembling monohydrocalcite. Both ACC, however, still had considerable amounts of water dominating the Ca-coordination sphere. During the transformation to calcite, the structural changes in the sample concerned the hydrate water coordinating Ca which was removed and replaced by the carbonate oxygens. The study shows that ACC obtained from different starting solutions show specific local order. Freeze drying leads to solid ACC powder which still contain considerable amounts of hydrate water. Structural subunits are distinct in ACC and different from the crystalline phase. The study supplements recent reports presented by Konrad et al., Purgstaller et al., and Tobler et al.. F. Konrad et al., Cryst. Growth Des. 16, 6310-6317(2016) B. Purgstaller et al., Geochimica et Cosmochimica Acta 174, 180-195(2016) DJ. Tobler et al., Cryst. Growth Des. 16, 4500-4508(2016)

SPHERES: Design of a Formation Flying Testbed for ISS

NASA Astrophysics Data System (ADS)

Sell, S. W.; Chen, S. E.

2002-01-01

The SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellites) payload is an innovative formation-flying spacecraft testbed currently being developed for use internally aboard the International Space Station (ISS). The purpose of the testbed is to provide a cost-effective, long duration, replenishable, and easily reconfigurable platform with representative dynamics for the development and validation of metrology, formation flying, and autonomy algorithms. The testbed components consist of three 8-inch diameter free-flying "satellites," five ultrasound beacons, and an ISS laptop workstation. Each satellite is self-contained with on-board battery power, cold-gas propulsion (CO2), and processing systems. Satellites use two packs of eight standard AA batteries for approximately 90 minutes of lifetime while beacons last the duration of the mission powered by a single AA battery. The propulsion system uses pressurized carbon dioxide gas, stored in replaceable tanks, distributed through an adjustable regulator and associated tubing to twelve thrusters located on the faces of the satellites. A Texas Instruments C6701 DSP handles control algorithm data while an FPGA manages all sensor data, timing, and communication processes on the satellite. All three satellites communicate with each other and with the controlling laptop via a wireless RF link. Five ultrasound beacons, located around a predetermined work area, transmit ultrasound signals that are received by each satellite. The system effectively acts as a pseudo-GPS system, allowing the satellites to determine position and attitude and to navigate within the test arena. The payload hardware are predominantly Commercial Off The Shelf (COTS) products with the exception of custom electronics boards, selected propulsion system adaptors, and beacon and satellite structural elements. Operationally, SPHERES will run in short duration test sessions with approximately two weeks between each session. During operations, satellites will autonomously perform various maneuvers with one to three satellites operating simultaneously, involving a crew member only to upload protocols and replace satellite consumables (gas and power) during the test session. Once completed, data will be downlinked to the ground for analysis by the SPHERES team, facilitating the iterative process of new and/or modified protocols being uplinked for use in the next test session. SPHERES has prior flight experience on the NASA KC-135 Reduced Gravity aircraft and has also been in constant use in laboratory air table testing for almost two years. Slated for launch to the International Space Station on ISS12A.1, SPHERES will use its six-month flight to conduct risk-reduction investigations involving the coordinated motion of multiple satellites in a micro-gravity environment.

Gas-phase study of new organozinc reagents by IRMPD-spectroscopy, computational modelling and tandem-MS.

PubMed

Massah, Ahmad R; Dreiocker, Frank; Jackson, Richard F W; Pickup, Barry T; Oomens, Jos; Meijer, Anthony J H M; Schäfer, Mathias

2011-08-07

An extensive set of organozinc iodides, useful for Negishi-type cross-coupling reactions, are investigated as respective cations after formal loss of iodide in the gas phase. Firstly, two new alkylzinc compounds derived from Tyrosine (Tyr) and Tryptophan (Trp) are closely examined. Secondly, the influence of specific protecting groups on the subtle balance between intra- and intermolecular coordination of zinc in these reagents is probed through trifluoroacetyl (TFA)-derivatized alkylzinc compounds. Finally, the influence of the strongly coordinating bidentate ligand N,N,N',N'-tetramethylethylenediamine (TMEDA) on the structure of alkylzinc cations is further explored in order to better understand the stability of the respective complexes towards water. A combination of electrospray (ESI)-MS/MS, accurate ion mass measurements, infrared multiple-photon dissociation (IRMPD) spectroscopy and computational modelling allowed the full characterisation of all dimethylformamide (DMF)-solvated and TMEDA-coordinated alkylzinc cations in the gas phase. The calculations indicate that the zinc cation in gas-phase alkylzinc-DMF or TMEDA-complex ions preferentially adopts a tetrahedral coordination sphere with four ligands. Additionally, conformers with only three binding partners bound to zinc but with effectively combined hydrogen-bond interactions are also found. Collision induced dissociation (CID) patterns demonstrate that the zinc-DMF interaction in tetrahedral four-coordinate mono-DMF-zinc complex ions as well as the interaction between TMEDA and zinc in the corresponding complex ions is even stronger than typical covalent bonds. In most cases, all major features of the IRMPD spectra are consistent with only a single major isomer, allowing secured identification and assignment. This journal is © the Owner Societies 2011

Disclosure of key stereoelectronic factors for efficient H2 binding and cleavage in the active site of [NiFe]-hydrogenases.

PubMed

Bruschi, Maurizio; Tiberti, Matteo; Guerra, Alessandro; De Gioia, Luca

2014-02-05

A comparative analysis of a series of DFT models of [NiFe]-hydrogenases, ranging from minimal NiFe clusters to very large systems including both the first and second coordination sphere of the bimetallic cofactor, was carried out with the aim of unraveling which stereoelectronic properties of the active site of [NiFe]-hydrogenases are crucial for efficient H2 binding and cleavage. H2 binding to the Ni-SIa redox state is energetically favored (by 4.0 kcal mol(-1)) only when H2 binds to Ni, the NiFe metal cluster is in a low spin state, and the Ni cysteine ligands have a peculiar seesaw coordination geometry, which in the enzyme is stabilized by the protein environment. The influence of the Ni coordination geometry on the H2 binding affinity was then quantitatively evaluated and rationalized analyzing frontier molecular orbitals and populations. Several plausible reaction pathways leading to H2 cleavage were also studied. It turned out that a two-step pathway, where H2 cleavage takes place on the Ni-SIa redox state of the enzyme, is characterized by very low reaction barriers and favorable reaction energies. More importantly, the seesaw coordination geometry of Ni was found to be a key feature for facile H2 cleavage. The discovery of the crucial influence of the Ni coordination geometry on H2 binding and activation in the active site of [NiFe]-hydrogenases could be exploited in the design of novel biomimetic synthetic catalysts.

Theoretical crystal chemistry of M{sub x}(TO{sub 4}){sub y} sulfates and selenates: Topological analysis and classification of suprapolyhedral invariants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilyushin, G. D.; Blatov, V. A.

2006-05-15

A geometric topological analysis of orthotetrahedral phases M{sub x}(TO{sub 4}){sub y} (T = S or Se) is performed for 46 sulfates and 17 selenates with the TOPOS 3.2 software package. The values of coordination sequences {l_brace}N{sub k}{r_brace} of T atoms are used as classification parameters of topologically different MTO nets. The crystal structures are analyzed within 12 coordination spheres of T sites and assigned to 26 topological types. It is established that only 7 types are common for the structures of sulfates and selenates, 16 types include only sulfates, and 3 types include only selenates. The average values of themore » bond lengths are determined: = 1.48(2) A and = 1.63(2) A. The hierarchical ordering of the crystal structure is performed using the concept of a polyhedral microensemble of the structure.« less

Spectroscopic and structural study of novel interaction product of pyrrolidine-2-thione with molecular iodine. Presumable mechanisms of oxidation

NASA Astrophysics Data System (ADS)

Chernov'yants, Margarita S.; Burykin, Igor V.; Starikova, Zoya A.; Tereznikov, Alexander Yu.; Kolesnikova, Tatiana S.

2013-09-01

Synthesis, spectroscopic and structural characterization of novel interaction product of pyrrolidine-2-thione with molecular iodine is reported. The ability of pyrrolidine-2-thione to form the outer-sphere charge-transfer complex C4H7NS·I2 with iodine molecule in dilute chloroform solution has been studied by UV/vis spectroscopy. Oxidative desulfurization promotes ring fusion of two pyrrolidine-2-thione molecules. The product of iodine induced oxidative desulfurization has been studied by X-ray diffraction method. The crystal structure of the reaction product is formed by 5-(2-thioxopyrrolidine-1-yl)-3,4-dihydro-2H-pyrrolium (C8H13N2S+) cations and pentaiodide anions I5-, which are linked by the intermolecular I⋯Hsbnd C and I⋯C close contacts. The angular pentaiodide anions can be considered as structures formed by coordination of two iodine molecules to the iodide ion (type 1) or by the coordination of iodine molecule to the triiodide ion (type 2).

XAFS investigation of polyamidoxime-bound uranyl contests the paradigm from small molecule studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayes, Richard T.; Piechowicz, Marek; Lin, Zekai

In this study, limited resource availability and population growth have motivated interest in harvesting valuable metals from unconventional reserves, but developing selective adsorbents for this task requires structural knowledge of metal binding environments. Amidoxime polymers have been identified as the most promising platform for large-scale extraction of uranium from seawater. However, despite more than 30 years of research, the uranyl coordination environment on these adsorbents has not been positively identified. We report the first XAFS investigation of polyamidoxime-bound uranyl, with EXAFS fits suggesting a cooperative chelating model, rather than the tridentate or η 2 motifs proposed by small molecule andmore » computational studies. Samples exposed to environmental seawater also display a feature consistent with a μ 2-oxo-bridged transition metal in the uranyl coordination sphere, suggesting in situ formation of a specific binding site or mineralization of uranium on the polymer surface. These unexpected findings challenge several long-held assumptions and have significant implications for development of polymer adsorbents with high selectivity.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alí-Torres, Jorge; Mirats, Andrea; Maréchal, Jean-Didier

Amyloid plaques formation and oxidative stress are two key events in the pathology of the Alzheimer disease (AD), in which metal cations have been shown to play an important role. In particular, the interaction of the redox active Cu{sup 2+} metal cation with Aβ has been found to interfere in amyloid aggregation and to lead to reactive oxygen species (ROS). A detailed knowledge of the electronic and molecular structure of Cu{sup 2+}-Aβ complexes is thus important to get a better understanding of the role of these complexes in the development and progression of the AD disease. The computational treatment ofmore » these systems requires a combination of several available computational methodologies, because two fundamental aspects have to be addressed: the metal coordination sphere and the conformation adopted by the peptide upon copper binding. In this paper we review the main computational strategies used to deal with the Cu{sup 2+}-Aβ coordination and build plausible Cu{sup 2+}-Aβ models that will afterwards allow determining physicochemical properties of interest, such as their redox potential.« less

Two Ti13-oxo-clusters showing non-compact structures, film electrode preparation and photocurrent properties.

PubMed

Hou, Jin-Le; Luo, Wen; Wu, Yin-Yin; Su, Hu-Chao; Zhang, Guang-Lin; Zhu, Qin-Yu; Dai, Jie

2015-12-14

Two benzene dicarboxylate (BDC) and salicylate (SAL) substituted titanium-oxo-clusters, Ti13O10(o-BDC)4(SAL)4(O(i)Pr)16 (1) and Ti13O10(o-BDC)4(SAL-Cl)4(O(i)Pr)16 (2), are prepared by one step in situ solvothermal synthesis. Single crystal analysis shows that the two Ti13 clusters take a paddle arrangement with an S4 symmetry. The non-compact (non-sphere) structure is stabilized by the coordination of BDC and SAL. Film photoelectrodes are prepared by the wet coating process using the solution of the clusters and the photocurrent response properties of the electrodes are studied. It is found that the photocurrent density and photoresponsiveness of the electrodes are related to the number of coating layers and the annealing temperature. Using ligand coordinated titanium-oxo-clusters as the molecular precursors of TiO2 anatase films is found to be effective due to their high solubility, appropriate stability in solution and hence the easy controllability.

XAFS investigation of polyamidoxime-bound uranyl contests the paradigm from small molecule studies

DOE PAGES

Mayes, Richard T.; Piechowicz, Marek; Lin, Zekai; ...

2015-11-12

In this study, limited resource availability and population growth have motivated interest in harvesting valuable metals from unconventional reserves, but developing selective adsorbents for this task requires structural knowledge of metal binding environments. Amidoxime polymers have been identified as the most promising platform for large-scale extraction of uranium from seawater. However, despite more than 30 years of research, the uranyl coordination environment on these adsorbents has not been positively identified. We report the first XAFS investigation of polyamidoxime-bound uranyl, with EXAFS fits suggesting a cooperative chelating model, rather than the tridentate or η 2 motifs proposed by small molecule andmore » computational studies. Samples exposed to environmental seawater also display a feature consistent with a μ 2-oxo-bridged transition metal in the uranyl coordination sphere, suggesting in situ formation of a specific binding site or mineralization of uranium on the polymer surface. These unexpected findings challenge several long-held assumptions and have significant implications for development of polymer adsorbents with high selectivity.« less

Determination of the Molecular Structures of Ferric Enterobactin and Ferric Enantioenterobactin Using Racemic Crystallography.

PubMed

Johnstone, Timothy C; Nolan, Elizabeth M

2017-10-25

Enterobactin is a secondary metabolite produced by Enterobacteriaceae for acquiring iron, an essential metal nutrient. The biosynthesis and utilization of enterobactin permits many Gram-negative bacteria to thrive in environments where low soluble iron concentrations would otherwise preclude survival. Despite extensive work carried out on this celebrated molecule since its discovery over 40 years ago, the ferric enterobactin complex has eluded crystallographic structural characterization. We report the successful growth of single crystals containing ferric enterobactin using racemic crystallization, a method that involves cocrystallization of a chiral molecule with its mirror image. The structures of ferric enterobactin and ferric enantioenterobactin obtained in this work provide a definitive assignment of the stereochemistry at the metal center and reveal secondary coordination sphere interactions. The structures were employed in computational investigations of the interactions of these complexes with two enterobactin-binding proteins, which illuminate the influence of metal-centered chirality on these interactions. This work highlights the utility of small-molecule racemic crystallography for obtaining elusive structures of coordination complexes.

Supramolecular photochemistry and solar cells

PubMed

Iha

2000-01-01

Supramolecular photochemistry as well as solar cells are fascinating topics of current interest in Inorganic Photochemistry and very active research fields which have attracted wide attention in last two decades. A brief outline of the investigations in these fields carried out in our Laboratory of Inorganic Photochemistry and Energy Conversion is given here with no attempt of an exhaustive coverage of the literature. The emphasis is placed on recent work and information on the above mentioned subjects. Three types of supramolecular systems have been the focus of this work: (i) cage-type coordination compounds; (ii) second-sphere coordination compounds, exemplified by ion-pair photochemistry of cobalt complexes and (iii) covalently-linked systems. In the latter, modulation of the photoluminescence and photochemistry of some rhenium complexes are discussed. Solar energy conversion and development of thin-layer photoelectrochemical solar cells based on sensitization of nanocrystalline semiconductor films by some ruthenium polypyridyl complexes are presented as an important application that resulted from specifically engineered artificial assemblies.

Toward understanding the chloroquine action at the molecular level in antimalarial therapy--X-ray absorption studies in acetic acid solution.

PubMed

Walczak, Monika S; Lawniczak-Jablonska, Krystyna; Wolska, Anna; Sikora, Marcin; Sienkiewicz, Andrzej; Suárez, Liliana; Kosar, Aaron J; Bellemare, Marie-Josee; Bohle, D Scott

2011-04-21

The local atomic structure around the central iron of the synthetic soluble analog of malarial pigment in acetic acid solution and with addition of chloroquine as found by X-ray absorption spectroscopy is reported. The special interest was drawn to the axial linkage between the central iron atom of the ferriprotoporphyrin IX (FePPIX) coordinated axially to the propionate group of the adjacent FePPIX. This kind of bonding is typical for hematin anhydride. Detailed analysis revealed differences in oxygen coordination sphere (part of dimer linkage bond) between synthetic equivalent of hemozoin in the powder state and dissolved in acetic acid and water at different concentrations mimicking the physiological condition of the parasite's food vacuole. The results of performed studies suggest that the molecular structure of synthetic analogue of hemozoin is no longer dimer-like in acidic solution. Further changes in atomic order around Fe are seen after addition of the antimalarial drug chloroquine.

Summary of PhysPAG Activity

NASA Astrophysics Data System (ADS)

Nousek, John A.

2014-01-01

The Physics of the Cosmos Program Analysis Group (PhysPAG) is responsible for solicitiing and coordinating community input for the development and execution of NASA's Physics of the Cosmos (PCOS) program. In this session I will report on the activity of the PhysPAG, and solicit community involvement in the process of defining PCOS objectives, planning SMD architecture, and prioritizing PCOS activities. I will also report on the activities of the PhysPAG Executive Committee, which include the chairs of the Science Analysis Groups/ Science Interest Groups which fall under the PhysPAG sphere of interest. Time at the end of the presentation willl be reserved for questions and discussion from the community.

CONTRASTING BEHAVIOR OF CONFORMATIONALLY LOCKED CARBOCYCLIC NUCLEOSIDES OF ADENOSINE AND CYTIDINE AS SUBSTRATES FOR DEAMINASES

PubMed Central

Schroeder, Gottfried K.; Ludek, Olaf R.; Siddiqui, Maqbool A.; Ezzitouni, Abdallah; Wolfenden, Richard

2010-01-01

In addition to the already known differences between adenosine deaminase (ADA) and cytidine deaminase (CDA) in terms of their tertiary structure, the sphere of Zn+2 coordination, and their reverse stereochemical preference, we present evidence that the enzymes also differ significantly in terms of the North/South conformational preferences for their substrates and the extent to which the lack of the O(4’) oxygen affects the kinetics of the enzymatic deamination of carbocyclic substrates. The carbocyclic nucleoside substrates used in this study have either a flexible cyclopentane ring or a rigid bicyclo[3.1.0]hexane scaffold. PMID:20183605

PICsar: Particle in cell pulsar magnetosphere simulator

NASA Astrophysics Data System (ADS)

Belyaev, Mikhail A.

2016-07-01

PICsar simulates the magnetosphere of an aligned axisymmetric pulsar and can be used to simulate other arbitrary electromagnetics problems in axisymmetry. Written in Fortran, this special relativistic, electromagnetic, charge conservative particle in cell code features stretchable body-fitted coordinates that follow the surface of a sphere, simplifying the application of boundary conditions in the case of the aligned pulsar; a radiation absorbing outer boundary, which allows a steady state to be set up dynamically and maintained indefinitely from transient initial conditions; and algorithms for injection of charged particles into the simulation domain. PICsar is parallelized using MPI and has been used on research problems with 1000 CPUs.

Zernike Basis to Cartesian Transformations

NASA Astrophysics Data System (ADS)

Mathar, R. J.

2009-12-01

The radial polynomials of the 2D (circular) and 3D (spherical) Zernike functions are tabulated as powers of the radial distance. The reciprocal tabulation of powers of the radial distance in series of radial polynomials is also given, based on projections that take advantage of the orthogonality of the polynomials over the unit interval. They play a role in the expansion of products of the polynomials into sums, which is demonstrated by some examples. Multiplication of the polynomials by the angular bases (azimuth, polar angle) defines the Zernike functions, for which we derive transformations to and from the Cartesian coordinate system centered at the middle of the circle or sphere.

Solvation structure of the halides from x-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antalek, Matthew; Hedman, Britt; Sarangi, Ritimukta, E-mail: ritis@slac.stanford.edu

2016-07-28

Three-dimensional models for the aqueous solvation structures of chloride, bromide, and iodide are reported. K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near edge (MXAN) analyses found well-defined single shell solvation spheres for bromide and iodide. However, dissolved chloride proved structurally distinct, with two solvation shells needed to explain its strikingly different X-ray absorption near edge structure (XANES) spectrum. Final solvation models were as follows: iodide, 8 water molecules at 3.60 ± 0.13 Å and bromide, 8 water molecules at 3.40 ± 0.14 Å, while chloride solvation included 7 water molecules at 3.15 ± 0.10 Å, andmore » a second shell of 7 water molecules at 4.14 ± 0.30 Å. Each of the three derived solvation shells is approximately uniformly disposed about the halides, with no global asymmetry. Time-dependent density functional theory calculations simulating the chloride XANES spectra following from alternative solvation spheres revealed surprising sensitivity of the electronic state to 6-, 7-, or 8-coordination, implying a strongly bounded phase space for the correct structure during an MXAN fit. MXAN analysis further showed that the asymmetric solvation predicted from molecular dynamics simulations using halide polarization can play no significant part in bulk solvation. Classical molecular dynamics used to explore chloride solvation found a 7-water solvation shell at 3.12 (−0.04/+0.3) Å, supporting the experimental result. These experiments provide the first fully three-dimensional structures presenting to atomic resolution the aqueous solvation spheres of the larger halide ions.« less

Monodisperse NixFe3-xO4 nanospheres: Metal-ion-steered size/composition control mechanism, static magnetic and enhanced microwave absorbing properties

NASA Astrophysics Data System (ADS)

Jiang, Kedan; Liu, Yun; Pan, Yefei; Wang, Ru; Hu, Panbing; He, Rujia; Zhang, Lingli; Tong, Guoxiu

2017-05-01

An easy metal-ion-steered solvothermal method was developed for the one-step synthesis of monodisperse, uniform NixFe3-xO4 polycrystalline nanospheres with tunable sphere diameter (40-400 nm) and composition (0 ≤ x ≤ 0.245) via changing just Ni2+/Fe3+ molar ratio (γ). With g increased from 0:1 to 2:1, sphere diameter gradually decreased and crystal size exhibited an inversed U-shaped change tendency, followed by increased Ni/Fe atom ratio from 0% to 0.0888%. An in situ-reduction, coordination-precipitation transformation mechanism was proposed to interpret the metal-ion-steered growth. Size- and composition-dependent static magnetic and microwave absorbing properties were systematically investigated. Saturation magnetization declines with g in a Boltzmann model due to the changes of crystal size, sphere diameter, and Ni content. The coercivity reaches a maximum at γ = 0.75:1 because of the critical size of Fe3O4 single domain (25 nm). Studies on microwave absorption reveal that 150-400 nm Fe3O4 nanospheres mainly obey the quarter-wavelength cancellation model with the single-band absorption; 40-135 nm NixFe3-xO4 nanospheres (0 ≤ x ≤ 0.245) obey the one and three quarter-wavelength cancellation model with the multi-band absorption. 150 nm Fe3O4 nanospheres exhibit the optimal EM wave-absorbing property with an absorbing band of 8.94 GHz and the maximum RL of -50.11 dB.

Comparison of contact and non-contact asphere surface metrology devices

NASA Astrophysics Data System (ADS)

DeFisher, Scott; Fess, Edward M.

2013-09-01

Metrology of asphere surfaces is critical in the precision optics industry. Surface metrology serves as feedback into deterministic grinding and polishing platforms. Many different techniques and devices are used to qualify an asphere surface during fabrication. A contact profilometer is one of the most common measurement technologies used in asphere manufacturing. A profilometer uses a fine stylus to drag a diamond or ruby tip over the surface, resulting in a high resolution curved profile. Coordinate measuring machines (CMM) apply a similar concept by touching the optic with a ruby or silicon carbine sphere. A CMM is able to move in three dimensions while collecting data points along the asphere surface. Optical interferometers use a helium-neon laser with transmission spheres to compare a reflected wavefront from an asphere surface to a reference spherical wavefront. Large departure aspheres can be measured when a computer generated hologram (CGH) is introduced between the interferometer and the optic. OptiPro Systems has developed a non-contact CMM called UltraSurf. It utilizes a single point non-contact sensor, and high accuracy air bearings. Several different commercial non-contact sensors have been integrated, allowing for the flexibility to measure a variety of surfaces and materials. Metrology of a sphere and an asphere using a profilometer, CMM, Interferometer with a CGH, and the UltraSurf will be presented. Cross-correlation of the measured surface error magnitude and shape will be demonstrated. Comparisons between the techniques and devices will be also presented with attention to accuracy, repeatability, and overall measurement time.

Efficient Implementation of the Invariant Imbedding T-Matrix Method and the Separation of Variables Method Applied to Large Nonspherical Inhomogeneous Particles

NASA Technical Reports Server (NTRS)

Bi, Lei; Yang, Ping; Kattawar, George W.; Mishchenko, Michael I.

2012-01-01

Three terms, ''Waterman's T-matrix method'', ''extended boundary condition method (EBCM)'', and ''null field method'', have been interchangeable in the literature to indicate a method based on surface integral equations to calculate the T-matrix. Unlike the previous method, the invariant imbedding method (IIM) calculates the T-matrix by the use of a volume integral equation. In addition, the standard separation of variables method (SOV) can be applied to compute the T-matrix of a sphere centered at the origin of the coordinate system and having a maximal radius such that the sphere remains inscribed within a nonspherical particle. This study explores the feasibility of a numerical combination of the IIM and the SOV, hereafter referred to as the IIMþSOV method, for computing the single-scattering properties of nonspherical dielectric particles, which are, in general, inhomogeneous. The IIMþSOV method is shown to be capable of solving light-scattering problems for large nonspherical particles where the standard EBCM fails to converge. The IIMþSOV method is flexible and applicable to inhomogeneous particles and aggregated nonspherical particles (overlapped circumscribed spheres) representing a challenge to the standard superposition T-matrix method. The IIMþSOV computational program, developed in this study, is validated against EBCM simulated spheroid and cylinder cases with excellent numerical agreement (up to four decimal places). In addition, solutions for cylinders with large aspect ratios, inhomogeneous particles, and two-particle systems are compared with results from discrete dipole approximation (DDA) computations, and comparisons with the improved geometric-optics method (IGOM) are found to be quite encouraging.

Structure and Bonding in Uranyl(VI) Peroxide and Crown Ether Complexes; Comparison of Quantum Chemical and Experimental Data.

PubMed

Vallet, Valérie; Grenthe, Ingmar

2017-12-18

The structure, chemical bonding, and thermodynamics of alkali ions in M[12-crown-4] + , M[15-crown-5] + , and M[18-crown-6] + , M[UO 2 (O 2 )(OH 2 ) 2 ] + 4,5 , and M[UO 2 (O 2 )(OH)(OH 2 )] n 1-n (n = 4, 5) complexes have been explored by using quantum chemical (QC) calculations at the ab initio level. The chemical bonding has been studied in the gas phase in order to eliminate solvent effects. QTAIM analysis demonstrates features that are very similar in all complexes and typical for electrostatic M-O bonds, but with the M-O bonds in the uranyl peroxide systems about 20 kJ mol -1 stronger than in the corresponding crown ether complexes. The regular decrease in bond strength with increasing M-O bond distance is consistent with predominantly electrostatic contributions. Energy decomposition of the reaction energies in the gas phase and solvent demonstrates that the predominant component of the total attractive (ΔE elec + ΔE orb ) energy contribution is the electrostatic component. There are no steric constraints for coordination of large cations to small rings, because the M + ions are located outside the ring plane, [O n ], formed by the oxygen donors in the ligands; coordination of ions smaller than the ligand cavity results in longer than normal M-O distances or in a change in the number of bonds, both resulting in weaker complexes. The Gibbs energies, enthalpies, and entropies of reaction calculated using the conductor-like screening model, COSMO, to account for solvent effects deviate significantly from experimental values in water, while those in acetonitrile are in much better agreement. Factors that might affect the selectivity are discussed, but our conclusion is that present QC methods are not accurate enough to describe the rather small differences in selectivity, which only amount to 5-10 kJ mol -1 . We can, however, conclude on the basis of QC and experimental data that M[crown ether] + complexes in the strongly coordinating water solvent are of outer-sphere type, [M(OH 2 ) n + ][crown ether], while those in weakly coordinating acetonitrile are of inner-sphere type, [M-crown ether] + . The observation that the M[UO 2 (O 2 )(OH)(OH 2 )] n 1-n complexes are more stable in solution than those of M[crown ether] + is an effect of the different charges of the rings.

Uranyl adsorption and surface speciation at the imogolite-water interface: Self-consistent spectroscopic and surface complexation models

USGS Publications Warehouse

Arai, Y.; McBeath, M.; Bargar, J.R.; Joye, J.; Davis, J.A.

2006-01-01

Macro- and molecular-scale knowledge of uranyl (U(VI)) partitioning reactions with soil/sediment mineral components is important in predicting U(VI) transport processes in the vadose zone and aquifers. In this study, U(VI) reactivity and surface speciation on a poorly crystalline aluminosilicate mineral, synthetic imogolite, were investigated using batch adsorption experiments, X-ray absorption spectroscopy (XAS), and surface complexation modeling. U(VI) uptake on imogolite surfaces was greatest at pH ???7-8 (I = 0.1 M NaNO3 solution, suspension density = 0.4 g/L [U(VI)]i = 0.01-30 ??M, equilibration with air). Uranyl uptake decreased with increasing sodium nitrate concentration in the range from 0.02 to 0.5 M. XAS analyses show that two U(VI) inner-sphere (bidentate mononuclear coordination on outer-wall aluminol groups) and one outer-sphere surface species are present on the imogolite surface, and the distribution of the surface species is pH dependent. At pH 8.8, bis-carbonato inner-sphere and tris-carbonato outer-sphere surface species are present. At pH 7, bis- and non-carbonato inner-sphere surface species co-exist, and the fraction of bis-carbonato species increases slightly with increasing I (0.1-0.5 M). At pH 5.3, U(VI) non-carbonato bidentate mononuclear surface species predominate (69%). A triple layer surface complexation model was developed with surface species that are consistent with the XAS analyses and macroscopic adsorption data. The proton stoichiometry of surface reactions was determined from both the pH dependence of U(VI) adsorption data in pH regions of surface species predominance and from bond-valence calculations. The bis-carbonato species required a distribution of surface charge between the surface and ?? charge planes in order to be consistent with both the spectroscopic and macroscopic adsorption data. This research indicates that U(VI)-carbonato ternary species on poorly crystalline aluminosilicate mineral surfaces may be important in controlling U(VI) mobility in low-temperature geochemical environments over a wide pH range (???5-9), even at the partial pressure of carbon dioxide of ambient air (pCO2 = 10-3.45 atm). ?? 2006 Elsevier Inc. All rights reserved.

Molecular-Scale Study of Aspartate Adsorption on Goethite and Competition with Phosphate.

PubMed

Yang, Yanli; Wang, Shengrui; Xu, Yisheng; Zheng, Binghui; Liu, Jingyang

2016-03-15

Knowledge of the interfacial interactions between aspartate and minerals, especially its competition with phosphate, is critical to understanding the fate and transport of amino acids in the environment. Adsorption reactions play important roles in the mobility, bioavailability, and degradation of aspartate and phosphate. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) measurements and density functional theory (DFT) calculations were used to investigate the interfacial structures and their relative contributions in single-adsorbate and competition systems. Our results suggest three dominant mechanisms for aspartate: bidentate inner-sphere coordination involving both α- and γ-COO(-), outer-sphere complexation via electrostatic attraction and H-bonding between aspartate NH2 and goethite surface hydroxyls. The interfacial aspartate is mainly governed by pH and is less sensitive to changes of ionic strength and aspartate concentration. The phosphate competition significantly reduces the adsorption capacity of aspartate on goethite. Whereas phosphate adsorption is less affected by the presence of aspartate, including the relative contributions of diprotonated monodentate, monoprotonated bidentate, and nonprotonated bidentate structures. The adsorption process facilitates the removal of bioavailable aspartate and phosphate from the soil solution as well as from the sediment pore water and the overlying water.

Helium-like magnesium embedded in strongly coupled plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharyya, Sukhamoy

2016-05-06

In recent days, with the advent of the x-ray free electron laser (FEL) with Linac coherent light source (LCLS) and the Orion laser, experimental studies on atomic systems within strongly coupled plasma environment with remarkable improvement in accuracy as compared to earlier experiments have become possible. In these kinds of experiments, hydrogen-like and helium-like spectral lines are used for determination of plasma parameters such as temperature, density. Accurate theoretical calculations are, therefore, necessary for such kind of studies within a dense plasma environment. In this work, ab initio calculations are carried out in the framework of the Rayleigh-Ritz variation principlemore » to estimate the ground state energy of helium-like magnesium within strongly coupled plasma environment. Explicitly correlated wave functions in Hylleraas coordinates have been used to incorporate the effect of electron correlation. The ion-sphere model potential that confines the central positive ion in a finite domain filled with plasma electrons has been adopted to mimic the strongly coupled plasma environment. Thermodynamic pressure ’felt’ by the ion in the ground states due to the confinement inside the ion spheres is also estimated.« less

Conformal Robotic Stereolithography

PubMed Central

Stevens, Adam G.; Oliver, C. Ryan; Kirchmeyer, Matthieu; Wu, Jieyuan; Chin, Lillian; Polsen, Erik S.; Archer, Chad; Boyle, Casey; Garber, Jenna

2016-01-01

Abstract Additive manufacturing by layerwise photopolymerization, commonly called stereolithography (SLA), is attractive due to its high resolution and diversity of materials chemistry. However, traditional SLA methods are restricted to planar substrates and planar layers that are perpendicular to a single-axis build direction. Here, we present a robotic system that is capable of maskless layerwise photopolymerization on curved surfaces, enabling production of large-area conformal patterns and the construction of conformal freeform objects. The system comprises an industrial six-axis robot and a custom-built maskless projector end effector. Use of the system involves creating a mesh representation of the freeform substrate, generation of a triangulated toolpath with curved layers that represents the target object to be printed, precision mounting of the substrate in the robot workspace, and robotic photopatterning of the target object by coordinated motion of the robot and substrate. We demonstrate printing of conformal photopatterns on spheres of various sizes, and construction of miniature three-dimensional objects on spheres without requiring support features. Improvement of the motion accuracy and development of freeform toolpaths would enable construction of polymer objects that surpass the size and support structure constraints imparted by traditional SLA systems. PMID:29577062

State health managers' perceptions of the Public Health Action Organizational Contract in the State of Ceará, Brazil.

PubMed

Goya, Neusa; Andrade, Luiz Odorico Monteiro de; Pontes, Ricardo José Soares; Tajra, Fábio Solon; Barreto, Ivana Cristina de Holanda Cunha

2017-04-01

The Public Health Action Organizational Contract (COAP) / Decree 7.508/2011 aimed to seal health agreements made between federated entities to promote the cooperative governance and management of Health Regions. A qualitative study was carried out adopting a hermeneutic approach to understand state health managers' perceptions of the elaboration and effects of the COAP in the State of Ceará. Open-ended interviewees and documental analysis were conducted. It was observed that the COAP led to the strengthening of regionalization in the government sphere; institutional gains through the implementation of ombudsmen and the National System of Pharmaceutical Care Management; increased information about the state health system's workforce; and health budget transparency. The following problems were (re)visited: institutional weakness in the operation of the network; limited state capacity for regulation of care; and underfunding. Regional governance was restricted to the government sphere, coordinated by the state, and was characterized by a predominantly bureaucratic and hierarchical governance structure. The COAP inaugurated a contractual interfederative model of regionalization, but revealed the institutional weaknesses of the SUS and its lacks of capacity to fulfill its principles as the structural problems of the three-tiered model go unaddressed.

Complexation of carboxylate on smectite surfaces.

PubMed

Liu, Xiandong; Lu, Xiancai; Zhang, Yingchun; Zhang, Chi; Wang, Rucheng

2017-07-19

We report a first principles molecular dynamics (FPMD) study of carboxylate complexation on clay surfaces. By taking acetate as a model carboxylate, we investigate its inner-sphere complexes adsorbed on clay edges (including (010) and (110) surfaces) and in interlayer space. Simulations show that acetate forms stable monodentate complexes on edge surfaces and a bidentate complex with Ca 2+ in the interlayer region. The free energy calculations indicate that the complexation on edge surfaces is slightly more stable than in interlayer space. By integrating pK a s and desorption free energies of Al coordinated water calculated previously (X. Liu, X. Lu, E. J. Meijer, R. Wang and H. Zhou, Geochim. Cosmochim. Acta, 2012, 81, 56-68; X. Liu, J. Cheng, M. Sprik, X. Lu and R. Wang, Geochim. Cosmochim. Acta, 2014, 140, 410-417), the pH dependence of acetate complexation has been revealed. It shows that acetate forms inner-sphere complexes on (110) in a very limited mildly acidic pH range while it can complex on (010) in the whole common pH range. The results presented in this study form a physical basis for understanding the geochemical processes involving clay-organics interactions.

Thermodynamic and Spectroscopic Studies of Trivalent f -element Complexation with Ethylenediamine- N,N '-di(acetylglycine)- N,N '-diacetic Acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heathman, Colt R.; Grimes, Travis S.; Zalupski, Peter R.

In this study, the coordination behavior and thermodynamic features of complexation of trivalent lanthanides and americium by ethylenediamine- N,N'-di(acetylglycine)- N,N'-diacetic acid (EDDAG-DA) (bisamide-substituted-EDTA) were investigated by potentiometric and spectroscopic techniques. Acid dissociation constants (K a) and complexation constants (β) of lanthanides (except Pm) were determined by potentiometric analysis. Absorption spectroscopy was used to determine stability constants for the binding of trivalent americium and neodymium by EDDAG-DA under similar conditions. The potentiometry revealed 5 discernible protonation constants and 3 distinct metal–ligand complexes (identified as ML –, MHL, and MH 2L +). Time-resolved fluorescence studies of Eu-(EDDAG-DA) solutions (at varying pH) identifiedmore » a constant inner-sphere hydration number of 3, suggesting that glycine functionalities contained in the amide pendant arms are not involved in metal complexation and are protonated under more acidic conditions. The thermodynamic studies identified that f-element coordination by EDDAG-DA is similar to that observed for ethylenediamine- N,N,N',N'-tetraacetic acid (EDTA). However, coordination via two amidic oxygens of EDDAG-DA lowers its trivalent f-element complex stability by roughly 3 orders of magnitude relative to EDTA.« less

Thermodynamic and Spectroscopic Studies of Trivalent f -element Complexation with Ethylenediamine- N,N '-di(acetylglycine)- N,N '-diacetic Acid

DOE PAGES

Heathman, Colt R.; Grimes, Travis S.; Zalupski, Peter R.

2016-03-21

In this study, the coordination behavior and thermodynamic features of complexation of trivalent lanthanides and americium by ethylenediamine- N,N'-di(acetylglycine)- N,N'-diacetic acid (EDDAG-DA) (bisamide-substituted-EDTA) were investigated by potentiometric and spectroscopic techniques. Acid dissociation constants (K a) and complexation constants (β) of lanthanides (except Pm) were determined by potentiometric analysis. Absorption spectroscopy was used to determine stability constants for the binding of trivalent americium and neodymium by EDDAG-DA under similar conditions. The potentiometry revealed 5 discernible protonation constants and 3 distinct metal–ligand complexes (identified as ML –, MHL, and MH 2L +). Time-resolved fluorescence studies of Eu-(EDDAG-DA) solutions (at varying pH) identifiedmore » a constant inner-sphere hydration number of 3, suggesting that glycine functionalities contained in the amide pendant arms are not involved in metal complexation and are protonated under more acidic conditions. The thermodynamic studies identified that f-element coordination by EDDAG-DA is similar to that observed for ethylenediamine- N,N,N',N'-tetraacetic acid (EDTA). However, coordination via two amidic oxygens of EDDAG-DA lowers its trivalent f-element complex stability by roughly 3 orders of magnitude relative to EDTA.« less

Insulin mimesis of vanadium derivatives. Oxidation of cysteine by V(V) oxo diperoxo complexes.

PubMed

Ballistreri, F P; Barbuzzi, E G; Tomaselli, G A; Toscano, R M

2000-05-30

Kinetics of the oxidation of cysteine to cystine by four V(V) oxo diperoxo complexes [VO(O2)2L] possessing insulin mimetic activity, where L = oxalate(oxa), picolinate (pic), bipyridil (bipy), phenanthroline(phen), were performed in water at 10 degrees C by the UV or stopped-flow technique. 51V NMR spectra indicate that oxa undergoes a total ligand dissociation differently from pic, bipy and phen which hold their ligands also in solution. The observed reactivity is deeply affected by the identity of the ligand. The process seems to require coordination of the cysteine to the metal, followed by oxidation within the coordination sphere. In this respect phen and bipy make the coordination of cysteine much easier than oxa and pic. It is suggested, also on the basis of some preliminary observations concerning the oxidation of C6H5CH2SH, that the oxidation process is triggered by an electron transfer step. The rate of this step would be higher for oxa and pic than for phen and bipy. The observation that the oxidative ability of these vanadium peroxo complexes is dependent upon the nature of the ligands might match the analogous finding that their insulin mimetic activity is also modulated by the ligand identities.

[Complexity of social and healthcare coordination in addictions and the role of the nurse].

PubMed

Molina Fernández, Antonio Jesús; González Riera, Javier; Montero Bancalero, Francisco José; Gómez-Salgado, Juan

2016-01-01

The present article discusses the psychosocial impact of basic and advanced concepts, such as social support and prevention, as well as to establish a link between theoretical models related to the social sphere on one side, and the health aspects on the other. This work is based on the context of the influence on health shared by community psychology and social psychology. Starting from the historical background of current approaches, a review is presented of those first actions focused on the care plan and they are framed in a reaction model to the drug problem, which progressed to the current healthcare network model, through the creation of Spanish National Action Plan on Drugs. The complexity of the problem is then broken down into the following key elements: Multifactorial Model of Drugs and Addictions, importance of prevention, and social support. Subsequently, a description is presented on the different levels of the healthcare network, with their different resources. This is also illustrated using a coordination protocol. Finally, it features the nursing approach to drugs, with its contributions, particularly as regards the coordination of resources, and aspects that must be developed for improvement in this area. Copyright © 2015 Elsevier España, S.L.U. All rights reserved.

Crystallographic studies on complexes of potassium iodide and copper perchlorate with N, Nʹ-dicyclohexylurea tethered to a benzo-12-crown-4

NASA Astrophysics Data System (ADS)

Tripathi, Garima; Ramanathan, Gurunath

2018-03-01

The N, N‧-dicyclohexylurea-capped benzo-12-crown-4 (compound 1) has been synthesized. The coordination behaviour of this compound (1) has been studied by crystallizing it with KI (2) and Cu(ClO4)2 (3) salts. The crystallographic studies were performed with all three compounds. The presence of metal ions significantly affects the crystal packing of the compound 1. The crystal lattice of compound 1 was stabilized by Csbnd H⋯π and Cdbnd O⋯Hsbnd N hydrogen bonding. The presence of KI in compound 2 results in a dimer structure in which iodide anion behaves as a bridging ligand. The K+ forms a perching structure with the crown ring. In the compound 3, Cu2+ ion and ligand molecule (1) crystallized independently. They were connected through hydrogen bonding. Interestingly, Cu2+ adopts two different geometries with the coordination number 5 and 6. The centre Cu2+ (Cu1) adopted an octahedral geometry whereas the terminal Cu2+ (Cu2) acquired square pyramidal geometry. The coordination sphere of Cu2+ contains ClO4- anion and water molecules. Cu2+ ion forms a chain structure through ClO4- anion and water molecules involve in hydrogen bonding with the ligand molecule.

Asymptotic symmetries on Killing horizons

NASA Astrophysics Data System (ADS)

Koga, Jun-Ichirou

2001-12-01

We investigate asymptotic symmetries regularly defined on spherically symmetric Killing horizons in Einstein theory with or without the cosmological constant. These asymptotic symmetries are described by asymptotic Killing vectors, along which the Lie derivatives of perturbed metrics vanish on a Killing horizon. We derive the general form of the asymptotic Killing vectors and find that the group of asymptotic symmetries consists of rigid O(3) rotations of a horizon two-sphere and supertranslations along the null direction on the horizon, which depend arbitrarily on the null coordinate as well as the angular coordinates. By introducing the notion of asymptotic Killing horizons, we also show that local properties of Killing horizons are preserved not only under diffeomorphisms but also under nontrivial transformations generated by the asymptotic symmetry group. Although the asymptotic symmetry group contains the Diff(S1) subgroup, which results from supertranslations dependent only on the null coordinate, it is shown that the Poisson brackets algebra of the conserved charges conjugate to asymptotic Killing vectors does not acquire nontrivial central charges. Finally, by considering extended symmetries, we discuss the fact that unnatural reduction of the symmetry group is necessary in order to obtain the Virasoro algebra with nontrivial central charges, which is not justified when we respect the spherical symmetry of Killing horizons.

Binding of dinitrogen to an iron-sulfur-carbon site

NASA Astrophysics Data System (ADS)

Čorić, Ilija; Mercado, Brandon Q.; Bill, Eckhard; Vinyard, David J.; Holland, Patrick L.

2015-10-01

Nitrogenases are the enzymes by which certain microorganisms convert atmospheric dinitrogen (N2) to ammonia, thereby providing essential nitrogen atoms for higher organisms. The most common nitrogenases reduce atmospheric N2 at the FeMo cofactor, a sulfur-rich iron-molybdenum cluster (FeMoco). The central iron sites that are coordinated to sulfur and carbon atoms in FeMoco have been proposed to be the substrate binding sites, on the basis of kinetic and spectroscopic studies. In the resting state, the central iron sites each have bonds to three sulfur atoms and one carbon atom. Addition of electrons to the resting state causes the FeMoco to react with N2, but the geometry and bonding environment of N2-bound species remain unknown. Here we describe a synthetic complex with a sulfur-rich coordination sphere that, upon reduction, breaks an Fe-S bond and binds N2. The product is the first synthetic Fe-N2 complex in which iron has bonds to sulfur and carbon atoms, providing a model for N2 coordination in the FeMoco. Our results demonstrate that breaking an Fe-S bond is a chemically reasonable route to N2 binding in the FeMoco, and show structural and spectroscopic details for weakened N2 on a sulfur-rich iron site.

Color-coded topography and shaded relief map of the lunar near side and far side hemispheres

USGS Publications Warehouse

,

2003-01-01

This publication is a set of three sheets of topographic maps that presents color-coded topographic data digitally merged with shaded relief data. Adopted figure: The figure for the Moon, used for the computation of the map projection, is a sphere with a radius of 1737.4 km. Because the Moon has no surface water, and hence no sea level, the datum (the 0 km contour) for elevations is defined as the radius of 1737.4 km. Coordinates are based on the mean Earth/polar axis (M.E.) coordinates system, the z axis is the axis of the Moon's rotation, and the x axis is the mean Earth direction. The center of mass is the origin of the coordinate system. The equator lies in the x-y plane and the prime meridian lies in the x-z plane with east longitude values being positive. Projection: The projection is Lambert Azimuthal Equal Area Projection. The scale factor at the central latitude and central longitude point is 1:10,000,000. For the near side hemisphere the central latitude and central longitude point is at 0° and 0°. For the far side hemisphere the central latitude and central longitude point is at 0° and 180°.

Synthesis, crystal structure, and magnetic properties of two-dimensional divalent metal glutarate/dipyridylamine coordination polymers, with a single crystal-to-single crystal transformation in the copper derivative

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montney, Matthew R.; Supkowski, Ronald M.; Staples, Richard J.

Hydrothermal reaction of divalent metal chlorides with glutaric acid and 4,4'-dipyridylamine (dpa) has afforded an isostructural family of coordination polymers with formulation [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate). Square pyramidal coordination is seen in 1-3, with semi-ligation of a sixth donor to produce a '5+1' extended coordination sphere. Neighboring metal atoms are linked into 1D [M(glu)]{sub n} neutral chains through chelating/monodentate bridging glutarate moieties with a syn-anti binding mode, and semi-chelation of the pendant carboxylate oxygen. These chains further connect into 2D layers through dipodal dpa ligands. Neighboring layers stack into the pseudo 3D crystal structure ofmore » 1-3 through supramolecular hydrogen bonding between dpa amine units and the semi-chelated glutarate oxygen atoms. The variable temperature magnetic behavior of 1-3 was explored and modeled as infinite 1D Heisenberg chains. Notably, complex 3 undergoes a thermally induced single crystal-to-single crystal transformation between centric and acentric space groups, with a conformationally disordered unilayer structure at 293 K and an ordered bilayer structure at 173 K. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analyses. - Graphical abstract: The coordination polymers [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate, dpa=4,4'-dipyridylamine) exhibit 2D layer structures based on 1D [M(glu)]{sub n} chains linked through dpa tethers. Antiferromagnetic coupling is observed for 2 and 3, while ferromagnetism is predominant in 1. Compound 3 undergoes a thermally induced single crystal-to-single crystal transformation from an acentric to a centrosymmetric space group.« less

Hydrothermal recrystallization of transition metal nitroprussides. Formation of the most stable phases

NASA Astrophysics Data System (ADS)

Echevarría, F.; Reguera, L.; González M, M.; Galicia, J.; Ávila, M.; Reguera, E.

2018-02-01

Hydrothermal recrystallization appears to be an appropriate treatment to explore the structural diversity of porous coordination polymers. In this contribution, such a post-synthesis treatment is applied to divalent transition metal nitroprussides, T[Fe(CN)5NO]•xH2O with T =Mn, Fe, Co, Ni, Cu, Zn, Cd. This family of compounds forms an interesting series of nanoporous coordination polymers with a wide structural diversity, related to the synthesis route used and the solid hydration degree (x). The effect of a hydrothermal recrystallization of previously prepared fine powders using the precipitation method, on their crystal structure and related properties is herein discussed. In this series of coordination polymers, for Fe, Co, Ni the precipitated powders are obtained as cubic phase, with a high porosity related to presence of systematic vacancies for building unit [Fe(CN)5NO]. For Fe and Co a structural transition, from cubic to orthorhombic, was observed, which is associated to formation of a most compact structure. The crystal structure for the new orthorhombic phases was refined from the collected powder HR-XRD patterns. For Ni, the cubic phase remains stable even for large heating time, which is ascribed to the high polarizing power of this metal. The high porosity for the cubic phase allows an easy accommodation for the local deformations around the Ni atom coordination sphere. The structural information from XRD was complemented with CO2 and H2 adsorption and TG data, IR and UV-vis spectra, and magnetic measurements. The magnetic data, through the presence of spin-orbit coupling for Fe and Co in the two phases, provide fine details on the coordination environment for the metal linked at the N ends of the CN group.

Freeform metrology using subaperture stitching interferometry

NASA Astrophysics Data System (ADS)

Supranowitz, Chris; Lormeau, Jean-Pierre; Maloney, Chris; Murphy, Paul; Dumas, Paul

2016-11-01

As applications for freeform optics continue to grow, the need for high-precision metrology is becoming more of a necessity. Currently, coordinate measuring machines (CMM) that implement touch probes or optical probes can measure the widest ranges of shapes of freeform optics, but these measurement solutions often lack sufficient lateral resolution and accuracy. Subaperture stitching interferometry (SSI™) extends traditional Fizeau interferometry to provide accurate, high-resolution measurements of flats, spheres, and aspheres, and development is currently on-going to enable measurements of freeform surfaces. We will present recent freeform metrology results, including repeatability and cross-test data. We will also present MRF® polishing results where the stitched data was used as the input "hitmap" to the deterministic polishing process.

Metal-dependent inhibition of HIV-1 integrase by 5CITEP inhibitor: A theoretical QM/MM approach

NASA Astrophysics Data System (ADS)

do Nascimento, Josenaide P.; Araújo Silva, José Rogério; Lameira, Jerônimo; Alves, Cláudio N.

2013-09-01

HIV-1 integrase (IN) is a potential target for developing drugs against AIDS. In this letter, QM/MM approach was used to study the inhibition of IN by 5CITEP inhibitor in presence of divalent cations (Mg2+ or Mn2+). In addition, the main interactions occurring in 5CITEP-IN complex and the influence of divalent cations (Mg2+ or Mn2+) in enzymatic inhibition were investigated using B3LYP/6-31+G(d,p)/MM. The results suggest that the Asp64, Asp116 and four crystal water molecules plays a crucial role in cation (Mg2+ or Mn2+) coordination sphere.

Influence of conformational changes on spin crossover properties and superstructure formation in 2D coordination polymers [Fe(hbtz)2(RCN)2](ClO4)2.

PubMed

Książek, Maria; Kusz, Joachim; Białońska, Agata; Bronisz, Robert; Weselski, Marek

2015-11-14

2D structurally related iron(ii) coordination networks {[Fe(hbtz)2(RCN)2](ClO4)2}∞ featuring, besides tetrazol-2-yl rings in the first coordination sphere, also axially coordinated propionitrile or allyl cyanide molecules (R = C3H5-, 1; R = C2H5-, 2) were synthesized. Thermally induced spin crossover (SCO) in 1 takes place in two poorly resolved stages (T(1)1/2(↓) = T(1)1/2(↑) = 198 K, T(2)1/2(↓) = 170 K, T(2)1/2(↑) = 171 K) whereas in 2 complete and relatively gradual one step SCO (T1/2(↓) = T1/2(↑) = 160 K) occurs. Diversification of the SCO properties of the complexes originates from the ability of coordinated allyl cyanide in 1 to undergo conformational alterations, which is not observed for propionitrile molecules in 2. SCO in 1 is accompanied by a non-monotonic change of the contribution of allyl cyanide conformers which is related to reconstruction of the network of intermolecular contacts established between polymeric layers. The coordination network 1 exhibits extraordinary elasticity and in the second stage SCO, accompanied by conformational changes of allyl cyanide, triggers a crystallographic phase transition which leads to the formation of a superstructure. What is important, the formation of the superstructure is not caused by long range ordering of HS and LS iron(ii) ions. The structural alteration is associated with corrugation of the polymeric skeleton and disappearance of nitrile disorder. Irradiation of a single crystal of 1 at 15 K with laser light (520 nm) allowed producing a novel low temperature HS phase of 1 in which, contrary to the high temperature HS phase, disordering of anion and allyl cyanide molecules is not observed and the corrugated nature of the polymeric layer, characteristic of the LS phase, is preserved.

The Behavior of the Ru-bda Water Oxidation Catalysts at Low Oxidation States.

PubMed

Matheu, Roc; Ghaderian, Abolfazl; Francas, Laia; Chernev, Petko; Ertem, Mehmed; Benet-Buchholz, Jordi; Batista, Victor; Haumann, Michael; Gimbert-Suriñach, Carolina; Sala, Xavier; Llobet, Antoni

2018-06-13

The Ru complex [RuII(bda-κ-N2O2)(N-NH2)2], 1, (bda2- = (2,2'-bipyridine)-6,6'-dicarboxylate; N-NH2 = 4-(pyridin-4-yl)aniline) is used as a synthetic intermediate to prepare Ru-bda complexes that contain the NO+, acetonitrile (MeCN) or H2O ligands at oxidation states II and III. Complex 1 reacts with excess NO+ to form a Ru complex where the aryl amine ligands N-NH2 in 1 are transformed into diazonium salts (N-N2+ = 4-(pyridin-4-yl)benzenediazonium)) together with the formation of a new Ru-NO group at the equatorial zone, to generate [RuII(bda-κ-N2O)(NO)(N-N2)2]3+, 23+. Similarly, complex 1 can also react with a coordinating solvent, such as MeCN, at room temperature leading to complex [RuII(bda-κ-N2O)(MeCN)(N-NH2)2], 3. Finally in acidic aqueous solutions solvent water coordinates the Ru center forming {[RuII(bda-κ-(NO)3)(H2O)(N-NH3)2](H2O)n}2+, 42+, that is strongly hydrogen bonded with additional water molecules at the second coordination sphere. We have additionally characterized the one electron oxidized complex {[RuIII(bda-κ-(NO)3.5)(H2O)(N-NH3)2](H2O)n}3+, 53+. The coordination mode of the complexes has been studied both in the solid state and in solution through single-crystal XRD, X-ray absorption spectroscopy, variable-temperature NMR and DFT calculations. While the κ-N2O is the main coordination mode for 23+ and 3, an equilibrium that involves isomers with κ-N2O and κ-NO2 coordination modes and neighboring hydrogen bonded water molecules is observed for 42+ and 53+. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Intrinsic viscosity and the electrical polarizability of arbitrarily shaped objects

NASA Astrophysics Data System (ADS)

Mansfield, Marc L.; Douglas, Jack F.; Garboczi, Edward J.

2001-12-01

The problem of calculating the electric polarizability tensor αe of objects of arbitrary shape has been reformulated in terms of path integration and implemented computationally. The method simultaneously yields the electrostatic capacity C and the equilibrium charge density. These functionals of particle shape are important in many materials science applications, including the conductivity and viscosity of filled materials and suspensions. The method has been validated through comparison with exact results (for the sphere, the circular disk, touching spheres, and tori), it has been found that 106 trajectories yield an accuracy of about four and three significant figures for C and αe, respectively. The method is fast: For simple objects, 106 trajectories require about 1 min on a PC. It is also versatile: Switching from one object to another is easy. Predictions have also been made for regular polygons, polyhedra, and right circular cylinders, since these shapes are important in applications and since numerical calculations of high stated accuracy are available. Finally, the path-integration method has been applied to estimate transport properties of both linear flexible polymers (random walk chains of spheres) and lattice model dendrimer molecules. This requires probing of an ensemble of objects. For linear chains, the distribution function of C and of the trace (αe), are found to be universal in a size coordinate reduced by the chain radius of gyration. For dendrimers, these distribution functions become increasingly sharp with generation number. It has been found that C and αe provide important information about the distribution of molecular size and shape and that they are important for estimating the Stokes friction and intrinsic viscosity of macromolecules.

[Polar and non polar notations of refraction].

PubMed

Touzeau, O; Gaujoux, T; Costantini, E; Borderie, V; Laroche, L

2010-01-01

Refraction can be expressed by four polar notations which correspond to four different combinations of spherical or cylindrical lenses. Conventional expressions of refraction (plus and minus cylinder notation) are described by sphere, cylinder, and axis. In the plus cylinder notation, the axis visualizes the most powerful meridian. The axis usually corresponds to the bow tie axis in curvature maps. Plus cylinder notation is also valuable for all relaxing procedures (i.e., selective suture ablation, arcuate keratotomy, etc.). In the cross-cylinder notation, two orthogonal cylinders can describe (without the sphere component) the actual refraction of both the principal meridians. This notation must be made before performing the vertex calculation. Using an association of a Jackson cross-cylinder and a spherical equivalent, refraction can be broken down into two pure components: astigmatism and sphere. All polar notations of refraction may perfectly characterize a single refraction but are not suitable for statistical analysis, which requires nonpolar expression. After doubling the axis, a rectangular projection breaks down the Jackson cross-cylinder, which has a polar axis, into two Jackson cross-cylinders on the 0 degrees /90 degrees and 45 degrees /135 degrees axis. This procedure results in the loss of the directional nature of the data. Refraction can be written in a nonpolar notation by three rectangular coordinates (x,y,z), which can also represent the spherocylinder by one point in a dioptric space. These three independent (orthogonal) variables have a concrete optical significance: a spherical component, a direct/inverse (WTR/ATR) component, and an oblique component of the astigmatism. Finally, nonpolar notations are useful for statistical analysis and graphical representation of refraction. Copyright (c) 2009 Elsevier Masson SAS. All rights reserved.

Ionic Asymmetry and Solvent Excluded Volume Effects on Spherical Electric Double Layers: A Density Functional Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G.

In this article we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids (J. Chem. Phys. 124, 154506). It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilizemore » a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the Mean Spherical Approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that predicted by the Stern model.« less

Theoretical studies of UO(2)(OH)(H(2)O)(n) (+), UO(2)(OH)(2)(H(2)O)(n), NpO(2)(OH)(H(2)O)(n), and PuO(2)(OH)(H(2)O)(n) (+) (n

PubMed

Cao, Zhiji; Balasubramanian, K

2009-10-28

Extensive ab initio calculations have been carried out to study equilibrium structures, vibrational frequencies, and the nature of chemical bonds of hydrated UO(2)(OH)(+), UO(2)(OH)(2), NpO(2)(OH), and PuO(2)(OH)(+) complexes that contain up to 21 water molecules both in first and second hydration spheres in both aqueous solution and the gas phase. The structures have been further optimized by considering long-range solvent effects through a polarizable continuum dielectric model. The hydrolysis reaction Gibbs free energy of UO(2)(H(2)O)(5) (2+) is computed to be 8.11 kcal/mol at the MP2 level in good agreement with experiments. Our results reveal that it is necessary to include water molecules bound to the complex in the first hydration sphere for proper treatment of the hydrated complex and the dielectric cavity although water molecules in the second hydration sphere do not change the coordination complex. Structural reoptimization of the complex in a dielectric cavity seems inevitable to seek subtle structural variations in the solvent and to correlate with the observed spectra and thermodynamic properties in the aqueous environment. Our computations reveal dramatically different equilibrium structures in the gas phase and solution and also confirm the observed facile exchanges between the complex and bulk solvent. Complete active space multiconfiguration self-consistent field followed by multireference singles+doubles CI (MRSDCI) computations on smaller complexes confirm predominantly single-configurational nature of these species and the validity of B3LYP and MP2 techniques for these complexes in their ground states.

A micro-CMM with metrology frame for low uncertainty measurements

NASA Astrophysics Data System (ADS)

Brand, Uwe; Kirchhoff, Juergen

2005-12-01

A conventional bridge-type coordinate measuring machine (CMM) with an opto-tactile fibre probe for the measurement of microstructures has been equipped with a metrology frame in order to reduce its measurement uncertainty. The frame contains six laser interferometers for high-precision position and guiding deviation measurements, a Zerodur cuboid with three measuring surfaces for the laser interferometers to which the fibre probe is fixed, and an invar frame which supports the measuring objects and to which the reference mirrors of the interferometers are fixed. The orthogonality and flatness deviations of the Zerodur measuring surfaces have been measured and taken into account in the equation of motion of the probing sphere. As a first performance test, the flatness of an optical flat has been measured with the fibre probe. Measuring-depth-dependent and probing-force-dependent shifts of the probing position were observed. In order to reduce the scattering of the probing points, 77 measurements were averaged for one coordinate point to be measured. This has led to measuring times of several hours for one plane and strong thermal drifts of the measured probing points.

A Rare Terminal Dinitrogen Complex of Chromium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mock, Michael T.; Chen, Shentan; Rousseau, Roger J.

The reduction of dinitrogen to ammonia from N2 and H2 is currently carried out by the Haber-Bosch process, an energy intensive process that requires high pressures and high temperatures and accounts for the production of millions of tons of ammonia per year. The development of a catalytic, energy-efficient process for N2 reduction is of great interest and remains a formidable challenge. In this communication, we are reporting the preparation, characterization and computational electronic structure analysis of a rare 'Chatt-type' ((P-P)2M(N2)2, P-P = diphosphine ligand) complex of chromium, cis-[Cr(N2)2(PPh2NBn2)2] and its reactivity with CO. This complex is supported by the diphosphinemore » ligand PPh2NBn2, containing non-coordinating pendant amine bases, to serve as proton relays. Future studies for this complex are aimed at answering fundamental questions regarding the role of proton relays in the second coordination sphere in their ability to facilitate proton movement from an external acid to metal-bound dinitrogen ligands in the challenging multi-proton/electron reduction of N2 to ammonia.« less

MD studies of electron transfer at ambient and elevated pressures

NASA Astrophysics Data System (ADS)

Giles, Alex; Spooner, Jacob; Weinberg, Noham

2013-06-01

The effect of pressure on the rate constants of outer-sphere electron transfer reactions has often been described using the Marcus-Hush theory. This theory agrees well with experiment when internal reorganization of the ionic system is negligible, however it does not offer a recipe for calculation of the effects that result from significant solute restructuring. We have recently developed a molecular dynamics technique that accurately describes structural dependence of molecular volumes in non-polar and weakly polar systems. We are now extending this approach to the case of highly polar ionic systems where both solvent and solute restructuring components are important. For this purpose we construct pressure-dependent two-dimensional surfaces for electron transfer reactions in coordinate system composed of interionic distance and Marcus-type solvent polarization coordinate, and use these surfaces to describe pressure effects on reaction kinetics. R.A. Marcus. J. Chem. Phys. 24, 966 (1956); 24, 979 (1956); 26, 867 (1957). Discuss. Faraday Soc. 29, 21 (1960). Faraday Discuss. Chem. Soc. 74, 7 (1982); N.S. Hush. Trans. Faraday Soc. 57, 557 (1961).

Spectroscopic and computational investigation of actinium coordination chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrier, Maryline Ghislaine; Batista, Enrique Ricardo; Berg, John M.

Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac III reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac–O H2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively.more » The X-ray absorption spectroscopy comparisons between Ac III and Am III in HCl solutions indicate Ac III coordinates more inner-sphere Cl 1– ligands (3.2±1.1) than Am III (0.8±0.3). Finally, these results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac III chemical behaviour.« less

Crystal structure of di-chlorido-{4-[(E)-(meth-oxy-imino-κN)meth-yl]-1,3-thia-zol-2-amine-κN (3)}palladium(II).

PubMed

Dyakonenko, Viktorita V; Zholob, Olga O; Orysyk, Svitlana I; Pekhnyo, Vasily I

2015-01-01

In the title compound, [PdCl2(C5H7N3OS)], the Pd(II) atom adopts a distorted square-planar coordination sphere defined by two N atoms of the bidentate ligand and two Cl atoms. The mean deviation from the coordination plane is 0.029 Å. The methyl group is not coplanar with the plane of the metallacycle [torsion angle C-O-N-C = 20.2 (4)°]. Steric repulsion between the methyl group and atoms of the metallacycle is manifested by shortened intra-molecular H⋯C contacts of 2.27, 2.38 and 2.64 Å, as compared with the sum of the van der Waals radii of 2.87 Å. The amino group participates via one H atom in the formation of an intra-molecular N-H⋯Cl hydrogen bond. In the crystal, the other H atom of the amino group links mol-ecules via bifurcated N-H⋯(Cl,O) hydrogen bonds into chains parallel to [001].

Electronic structure and optical properties of Eu(III) tris-β-diketonate adducts with 1,10-phenanthroline

NASA Astrophysics Data System (ADS)

Shurygin, A. V.; Korochentsev, V. V.; Cherednichenko, A. I.; Mirochnik, A. G.; Kalinovskaya, I. V.; Vovna, V. I.

2018-03-01

Adducts of tris-β-diketonates of the rare earth metal Eu(III) with 1,10-phenanthroline are studied by photoelectron spectroscopy and quantum chemistry methods. The electronic structure, peculiarities of the nature of chemical bonds, and the geometric structure of the adducts are determined. The interpretation of UV photoelectron spectra of vapors and X-ray photoelectron spectra of solid is carried out with the chosen technique. DFT/TDDFT methods make it possible to study the 1,10-phenanthroline molecule influence on the adduct electronic structure and to analyze the electronic effects of substitution of methyl groups by trifluoromethyl groups in the ligands. At transition from the tris-β-diketonate complexes to the adducts, it is observed an increase of the absorption region and a decrease in the energy gap that contributes to the efficiency growth in electronic excitation energy transfer in the ligand-metal. Moreover, phenanthroline displaces water groups, that are luminescence quenchers, from the first coordination sphere, closes coordination in the adduct, and blocks their further attachment. Both factors contribute to an increase in the luminescence intensity.

Spectroscopic and computational investigation of actinium coordination chemistry

DOE PAGES

Ferrier, Maryline Ghislaine; Batista, Enrique Ricardo; Berg, John M.; ...

2016-08-17

Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac III reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac–O H2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively.more » The X-ray absorption spectroscopy comparisons between Ac III and Am III in HCl solutions indicate Ac III coordinates more inner-sphere Cl 1– ligands (3.2±1.1) than Am III (0.8±0.3). Finally, these results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac III chemical behaviour.« less

Non-covalent and coordination interactions in Cu(II) systems with uridine, uridine 5'-monophosphate and triamine or tetramine as biogenic amine analogues in aqueous solutions.

PubMed

Łomozik, Lechosław; Jastrzab, Renata

2003-10-01

Reactions of metallation and non-covalent interactions have been studied in ternary systems of Cu(II) ions with uridine, uridine 5'-monophosphate and diamines or triamines. It has been found that in metal-free systems the reaction centres of the nucleoside with the polyamine are the donor nitrogen atoms N(3) and protonated -NH(x) groups of the amines. In comparison to systems with adenosine or cytidine, the pH range of complex formation is shifted towards higher values. It is a consequence of significantly higher basicity of uridine and in agreement with the ion-ion, ion-dipole interaction model assumed. Formation of molecular complexes of uridine 5'-monophosphate with polyamines at a low pH is the result of activity of the phosphate group which plays the role of a negatively charged reaction site. Non-covalent interactions interfere in processes of bioligand metallation. Centres of weak interactions are simultaneously binding sites of metal ions. In protonated Cu(Urd)(PA)H(x) complexes, coordination has been found to involve the N(3) atom from the nucleoside and two donor nitrogen atoms from the polyamine (PA). In the heteroligand species Cu(Urd)(PA), despite deprotonation of all amine groups, one of these groups is located outside the inner coordination sphere. In complexes with uridine-5'-monophosphate, the phosphate group is active in metallation. Moreover, in certain coordination compounds this group is engaged in non-covalent interactions with PA molecules, despite binding Cu ions, as has been shown on the basis of equilibrium and spectral studies.

Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.

PubMed Central

Deutsch, E; Elder, R C; Lange, B A; Vaal, M J; Lay, D G

1976-01-01

Reduction of pertechnetate by tin(II) in the presence of dimethylglyoxime is shown, by single crystal x-ray analysis, to yield a technetium-tin-dimethylglyoxime complex in which tin and technetium are intimately connected by a triple bridging arrangement. One bridge consists of a single oxygen atom and it is hypothesized that this bridge arises from the inner sphere reduction of technetium by tin(II), the electrons being transferred through a technetium "yl" oxygen which eventually becomes the bridging atom. Two additional bridges arise from two dimethylglyoxime ligands that function as bidentate nitrogen donors towards Tc and monodentate oxygen donors towards Sn. The tin atom can thus be viewed as providing a three-pronged "cap" on one end of the Tc-dimethylglyoxime complex. The additional coordination sites around Tc are occupied by the two nitrogens of a third dimethylglyoxime ligand, making the Tc seven-coordinate. The additional coordination sites around Sn are occupied by three chloride anions, giving the Sn a fac octahedral coordination environment. From indirect evidence the oxidation states of tin and technetium are tentatively assigned to be IV and V, respectively. Since most 99mTc-radiopharmaceuticals are synthesized by the tin(II) reduction of pertechnetate, it is likely that the Sn-O-Tc linkage described in this work is an important feature of the chemistry of these species. This linkage also provides a ready rationale for the close association of tin and technetium observed in many 99mTc-radiopharmaceuticals. PMID:1069984

The coordination structure of the extracted copper(II) complex with a synergistic mixture containing dinonylnaphthalene sulfonic acid and n-hexyl 3-pyridinecarboxylate ester

NASA Astrophysics Data System (ADS)

Zhu, Shan; Hu, Huiping; Hu, Jiugang; Li, Jiyuan; Hu, Fang; Wang, Yongxi

2017-09-01

In continuation of our interest in the coordination structure of the nickel(II) complex with dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexyl 4-pyridinecarboxylate ester (4PC), it was observed that the coordination sphere was completed by the coordination of two N atoms of pyridine rings in ligands 4PC and four water molecules while no direct interaction between Ni(II) and deprotonated HDNNS was observed. To investigate whether the coordination structure of nickel(II) with the synergistic mixture containing HDNNS and 4PC predominates or not in the copper(II) complex with the synergistic mixtures containing HDNNS and pyridinecarboxylate esters, a copper(II) synergist complex with n-hexyl 3-pyridinecarboxylate ester (L) and naphthalene-2-sulfonic acid (HNS, the short chain analogue of HDNNS), was prepared and studied by X-ray single crystal diffraction, elemental analyses and thermo gravimetric analysis (TGA), respectively. It was shown that the composition of the copper(II) synergist complex was [Cu(H2O)2(L)2(NS)2] and formed a trans-form distorted octahedral coordination structure. Two oxygen atoms of the two coordinated water molecules and two N atoms of the pyridine rings in the ligands L defined the basal plane while two O atoms from two sulfonate anions of the deprotonated HNS ligands occupied the apical positions by direct coordination with Cu(II), which was distinguished from the coordination structure of the nickel(II) synergist complex as reported in our previous work. In the crystal lattice, neighboring molecules [Cu(H2O)2L2(NS)2] were linked through the intermolecular hydrogen bonds between the hydrogen atoms of the coordinated water molecules and the oxygen atoms of the sulfonate anions in the copper(II) synergist complex to form a 2D plane. In order to bridge the gap between the solid state structure of the copper(II) synergist complex and the solution structure of the extracted copper(II) complex with the actual synergistic mixture containing L and HDNNS in the non-polar organic phase, the structures of the two copper(II) complexes were further investigated by Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS), and the results indicated that the extracted copper(II) complex in the non-polar organic phase might possess a similar coordination structure as the copper(II) synergist complex.

Crystallographic comparison of manganese- and iron-dependent homoprotocatechuate 2,3-dioxygenases.

PubMed

Vetting, Matthew W; Wackett, Lawrence P; Que, Lawrence; Lipscomb, John D; Ohlendorf, Douglas H

2004-04-01

The X-ray crystal structures of homoprotocatechuate 2,3-dioxygenases isolated from Arthrobacter globiformis and Brevibacterium fuscum have been determined to high resolution. These enzymes exhibit 83% sequence identity, yet their activities depend on different transition metals, Mn2+ and Fe2+, respectively. The structures allow the origins of metal ion selectivity and aspects of the molecular mechanism to be examined in detail. The homotetrameric enzymes belong to the type I family of extradiol dioxygenases (vicinal oxygen chelate superfamily); each monomer has four betaalphabetabetabeta modules forming two structurally homologous N-terminal and C-terminal barrel-shaped domains. The active-site metal is located in the C-terminal barrel and is ligated by two equatorial ligands, H214NE1 and E267OE1; one axial ligand, H155NE1; and two to three water molecules. The first and second coordination spheres of these enzymes are virtually identical (root mean square difference over all atoms, 0.19 A), suggesting that the metal selectivity must be due to changes at a significant distance from the metal and/or changes that occur during folding. The substrate (2,3-dihydroxyphenylacetate [HPCA]) chelates the metal asymmetrically at sites trans to the two imidazole ligands and interacts with a unique, mobile C-terminal loop. The loop closes over the bound substrate, presumably to seal the active site as the oxygen activation process commences. An "open" coordination site trans to E267 is the likely binding site for O2. The geometry of the enzyme-substrate complexes suggests that if a transiently formed metal-superoxide complex attacks the substrate without dissociation from the metal, it must do so at the C-3 position. Second-sphere active-site residues that are positioned to interact with the HPCA and/or bound O2 during catalysis are identified and discussed in the context of current mechanistic hypotheses.

Long distance electron-transfer mechanism in peptidylglycine alpha-hydroxylating monooxygenase: a perfect fitting for a water bridge.

PubMed

de la Lande, Aurélien; Martí, Sergio; Parisel, Olivier; Moliner, Vicent

2007-09-26

The active sites of copper enzymes have been the subject of many theoretical and experimental investigations from a number of years. Such studies have embraced topics devoted to the modeling of the first coordination sphere at the metallic cations up to the development of biomimetic, or bioinspired, catalytic systems. At least from the theoretical viewpoint, fewer efforts have been dedicated to elucidate how the two copper cations act concertedly in noncoupled dicopper enzymes such as peptidylglycine alpha-hydroxylating monooxygenase (PHM) and dopamine beta-monooxygenase (DbetaM). In these metalloenzymes, an electronic transfer is assumed between the two distant copper cations (11 A). Recent experimental results suggest that this transfer occurs through water molecules, a phenomenon which has been theoretically evidenced to be of high efficiency in the case of cytochrome b5 (Science, 2005, 310, 1311). In the present contribution dedicated to PHM, we overpass the common theoretical approaches dedicated to the electronic and geometrical structures of sites CuM or CuH restricted to their first coordination spheres and aim at directly comparing theoretical results to the experimentally measured activity of the PHM enzyme. To achieve this goal, molecular dynamics simulations were performed on wild-type and various mutants of PHM. More precisely, we provide an estimate of the electron-transfer efficiency between the CuM and CuH sites by means of such molecular dynamics simulations coupled to Marcus theory joined to the Beratan model to approximate the required coupling matrix elements. The theoretical results are compared to the kinetics measurements performed on wild and mutated PHM. The present work, the dynamic aspects of which are essential, accounts for the experimental results issued from mutagenesis. It supports the conclusion that an electronic transfer can occur between two copper(I) sites along a bridge involving a set of hydrogen and chemical bonds. Residue Gln170 is evidenced to be the keystone of this water-mediated pathway.

Small-Body Extensions for the Satellite Orbit Analysis Program (SOAP)

NASA Technical Reports Server (NTRS)

Carnright, Robert; Stodden, David; Coggi, John

2008-01-01

An extension to the SOAP software allows users to work with tri-axial ellipsoid-based representations of planetary bodies, primarily for working with small, natural satellites, asteroids, and comets. SOAP is a widely used tool for the visualization and analysis of space missions. The small body extension provides the same visualization and analysis constructs for use with small bodies. These constructs allow the user to characterize satellite path and instrument cover information for small bodies in both 3D display and numerical output formats. Tri-axial ellipsoids are geometric shapes the diameters of which are different in each of three principal x, y, and z dimensions. This construct provides a better approximation than using spheres or oblate spheroids (ellipsoids comprising two common equatorial diameters as a distinct polar diameter). However, the tri-axial ellipsoid is considerably more difficult to work with from a modeling perspective. In addition, the SOAP small-body extensions allow the user to actually employ a plate model for highly irregular surfaces. Both tri-axial ellipsoids and plate models can be assigned to coordinate frames, thus allowing for the modeling of arbitrary changes to body orientation. A variety of features have been extended to support tri-axial ellipsoids, including the computation and display of the spacecraft sub-orbital point, ground trace, instrument footprints, and swathes. Displays of 3D instrument volumes can be shown interacting with the ellipsoids. Longitude/latitude grids, contour plots, and texture maps can be displayed on the ellipsoids using a variety of projections. The distance along an arbitrary line of sight can be computed between the spacecraft and the ellipsoid, and the coordinates of that intersection can be plotted as a function of time. The small-body extension supports the same visual and analytical constructs that are supported for spheres and oblate spheroids in SOAP making the implementation of the more complex algorithms largely transparent to the user.

Analysis of Magnetic Anisotropy and the Role of Magnetic Dilution in Triggering Single-Molecule Magnet (SMM) Behavior in a Family of CoII YIII Dinuclear Complexes with Easy-Plane Anisotropy.

PubMed

Palacios, María A; Nehrkorn, Joscha; Suturina, Elizaveta A; Ruiz, Eliseo; Gómez-Coca, Silvia; Holldack, Karsten; Schnegg, Alexander; Krzystek, Jurek; Moreno, José M; Colacio, Enrique

2017-08-25

Three new closely related Co II Y III complexes of general formula [Co(μ-L)(μ-X)Y(NO 3 ) 2 ] (X - =NO 3 - 1, benzoate 2, or 9-anthracenecarboxylato 3) have been prepared with the compartmental ligand N,N',N''-trimethyl-N,N''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H 2 L). In these complexes, Co II and Y III are triply bridged by two phenoxide groups belonging to the di-deprotonated ligand (L 2- ) and one ancillary anion X - . The change of the ancillary bridging group connecting Co II and Y III ions induces small differences in the trigonally distorted CoN 3 O 3 coordination sphere with a concomitant tuning of the magnetic anisotropy and intermolecular interactions. Direct current magnetic, high-frequency and -field EPR (HFEPR), frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) measurements, and ab initio theoretical calculations demonstrate that Co II ions in compounds 1-3 have large and positive D values (≈50 cm -1 ), which decrease with increasing the distortion of the pseudo-octahedral Co II coordination sphere. Dynamic ac magnetic susceptibility measurements indicate that compound 1 exhibits field-induced single-molecule magnet (SMM) behavior, whereas compounds 2 and 3 only display this behavior when they are magnetically diluted with diamagnetic Zn II (Zn/Co=10:1). In view of this, it is always advisable to use magnetically diluted complexes, in which intermolecular interactions and quantum tunneling of magnetism (QTM) would be at least partly suppressed, so that "hidden single-ion magnet (SIM)" behavior could emerge. Field- and temperature-dependence of the relaxation times indicate the prevalence of the Raman process in all these complexes above approximately 3 K. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

103Rh NMR spectroscopy and its application to rhodium chemistry.

PubMed

Ernsting, Jan Meine; Gaemers, Sander; Elsevier, Cornelis J

2004-09-01

Rhodium is used for a number of large processes that rely on homogeneous rhodium-catalyzed reactions, for instance rhodium-catalyzed hydroformylation of alkenes, carbonylation of methanol to acetic acid and hydrodesulfurization of thiophene derivatives (in crude oil). Many laboratory applications in organometallic chemistry and catalysis involve organorhodium chemistry and a wealth of rhodium coordination compounds is known. For these and other areas, 103Rh NMR spectroscopy appears to be a very useful analytical tool. In this review, most of the literature concerning 103Rh NMR spectroscopy published from 1989 up to and including 2003 has been covered. After an introduction to several experimental methods for the detection of the insensitive 103Rh nucleus, a discussion of factors affecting the transition metal chemical shift is given. Computational aspects and calculations of chemical shifts are also briefly addressed. Next, the application of 103Rh NMR in coordination and organometallic chemistry is elaborated in more detail by highlighting recent developments in measurement and interpretation of 103Rh NMR data, in relation to rhodium-assisted reactions and homogeneous catalysis. The dependence of the 103Rh chemical shift on the ligands at rhodium in the first coordination sphere, on the complex geometry, oxidation state, temperature, solvent and concentration is treated. Several classes of compounds and special cases such as chiral rhodium compounds are reviewed. Finally, a section on scalar coupling to rhodium is provided. 2004 John Wiley & Sons, Ltd.

Plasticity of Cl-Te-Cl Fragments. Synthesis, Single-Crystal X-ray, and NBO Study of (1-Thia-2-tellura-1-phenyl-4-chloro)cyclopentane 2,2,2-Trichloride.

PubMed

Sundberg, Markku R.; Laitalainen, Tarja; Bergman, Jan; Uggla, Rolf; Matikainen, Jorma; Kaltia, Seppo

1998-06-01

Tellurium tetrachloride and allylphenyl sulfide react to form (1-thia-2-tellura-1-phenyl-4-chloro)cyclopentane 2,2,2-trichloride. The crystal and molecular structure were determined by single-crystal X-ray techniques. The crystals belong to the monoclinic system, space group P2(1)/c (No. 14) with a = 6.020(3) Å, b = 11.46(1) Å, c = 20.156(2) Å, beta = 97.53(2) degrees, V = 1379(1) Å(3), and Z = 4. The structure was refined to the final R value of 0.036. The coordination around Te(IV) is distorted psi octahedral with three Cl atoms in the equatorial positions. The axial Te(1)-C(1) bond opposite to the lone pair of electrons at the Te(IV) atom completes the coordination polyhedron. The intramolecular Te-S distance is 2.903(3) Å. Symmetric and asymmetric deformation modes were established to describe the plasticity of the Cl-Te-Cl fragments extracted from the Cambridge Structural Database. The hypervalency of Te(IV) manifests itself as plasticity in the equatorial plane of the coordination sphere. The NBO calculations show that all of the equatorial Te-Cl bonds are highly polarized and the electrons reside mainly on the Cl atoms.

The effect of local atomic structure on the optical properties of GeSi self-assembled islands buried in silicon matrix

NASA Astrophysics Data System (ADS)

Demchenko, I. N.; Lawniczak-Jablonska, K.; Kret, S.; Novikov, A. V.; Laval, J.-Y.; Zak, M.; Szczepanska, A.; Yablonskiy, A. N.; Krasilnik, Z. F.

2007-03-01

The local atomic structure of GeSi self-assembled islands buried in a silicon matrix strongly influences the optical properties of such systems. In the present paper this structure was determined by x-ray absorption fine-structure (XAFS) spectroscopy and high resolution transmission electron microscopy (HRTEM) and used to build a schematic description of the band structure model. Quantitative analysis of the extended XAFS (EXAFS) spectrum was performed for three coordination shells around the Ge absorbing atom with multiple scattering taken into account. It was proved that the coordination number of elements in an alloy resulting from EXAFS analysis for all three coordination spheres (i.e. 'mixing degree' parameters) cannot be taken as the concentration of alloy but can be used together with a proper model of the alloy unit cell to calculate a realistic concentration. The fraction of Ge calculated in this way is consistent with HRTEM results. The found model of the unit cell was used to generate a x-ray absorption near edge structure spectrum by ab initio calculations. This approach yielded a spectrum in good agreement with the experimental one. The information gained from XAFS and HRTEM was then used for calculation of the band structure diagram. Results of the calculation are discussed and compared with the experimental photoluminescence spectrum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frankaer, Christian Grundahl; Mossin, Susanne; Ståhl, Kenny

The level of structural detail around the metal sites in Ni{sup 2+} and Cu{sup 2+} T{sub 6} insulin derivatives was significantly improved by using a combination of single-crystal X-ray crystallography and X-ray absorption spectroscopy. Photoreduction and subsequent radiation damage of the Cu{sup 2+} sites in Cu insulin was followed by XANES spectroscopy. Using synchrotron radiation (SR), the crystal structures of T{sub 6} bovine insulin complexed with Ni{sup 2+} and Cu{sup 2+} were solved to 1.50 and 1.45 Å resolution, respectively. The level of detail around the metal centres in these structures was highly limited, and the coordination of water inmore » Cu site II of the copper insulin derivative was deteriorated as a consequence of radiation damage. To provide more detail, X-ray absorption spectroscopy (XAS) was used to improve the information level about metal coordination in each derivative. The nickel derivative contains hexacoordinated Ni{sup 2+} with trigonal symmetry, whereas the copper derivative contains tetragonally distorted hexacoordinated Cu{sup 2+} as a result of the Jahn–Teller effect, with a significantly longer coordination distance for one of the three water molecules in the coordination sphere. That the copper centre is of type II was further confirmed by electron paramagnetic resonance (EPR). The coordination distances were refined from EXAFS with standard deviations within 0.01 Å. The insulin derivative containing Cu{sup 2+} is sensitive towards photoreduction when exposed to SR. During the reduction of Cu{sup 2+} to Cu{sup +}, the coordination geometry of copper changes towards lower coordination numbers. Primary damage, i.e. photoreduction, was followed directly by XANES as a function of radiation dose, while secondary damage in the form of structural changes around the Cu atoms after exposure to different radiation doses was studied by crystallography using a laboratory diffractometer. Protection against photoreduction and subsequent radiation damage was carried out by solid embedment of Cu insulin in a saccharose matrix. At 100 K the photoreduction was suppressed by ∼15%, and it was suppressed by a further ∼30% on cooling the samples to 20 K.« less

Extraction of water and speciation of trivalent lanthanides and americium in organophosphorus extractants

DOE PAGES

Gullekson, Brian J.; Breshears, Andrew T.; Brown, M. Alex; ...

2016-11-29

Complexes of the trivalent lanthanides and Am with di-2-ethylhexylphosphoric acid (HDEHP) dissolved in an aliphatic diluent were probed with UV–vis, X-ray absorption fine structure, and time-resolved fluorescence spectroscopy while the water concentration was determined by Karl Fischer titrations. In particular, our work focuses on the Nd-hypersensitive UV–vis absorbance region to identify the cause of changing absorbance values at 570 and 583 nm in relation to the pseudooctahedral Nd environment when coordinated with three HDEHP dimers. In contrast to recently reported interpretations, we establish that while impurities have an effect on this electronic transition band, a high water content can causemore » distortion of the pseudooctahedral symmetry of the six-coordinate Nd, resembling the reported spectra of the seven-coordinate Nd compounds. Extended X-ray absorption fine structure analysis of the Nd in high-concentration HDEHP solutions also points to an increase in the coordination number from 6 to 7. The spectral behavior of other lanthanides (Pr, Ho, Sm, and Er) and Am III as a function of the HDEHP concentration suggests that water coordination with the metal likely depends on the metal’s effective charge. Fluorescence data using lifetime studies and excitation and emission spectra support the inclusion of water in the Eu coordination sphere. Further, the role of the effective charge was confirmed by a comparison of the Gibbs free energies of six- and seven-coordinate La-HDEHP–H 2O and Lu-HDEHP–H 2O complexes using density functional theory. In contrast, HEH[EHP], the phosphonic acid analogue of HDEHP, exhibits a smaller capacity for water, and the electronic absorption spectra of Nd or Am appear to be unchanged, although the Pr spectra show a noticeable change in intensity as a function of the water content. As a result, electronic absorption extinction coefficients of Am III, Nd III, Pr III, Sm III, Er III, and Ho III as a function of the HDEHP concentration are reported for the first time.« less

Extraction of water and speciation of trivalent lanthanides and americium in organophosphorus extractants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gullekson, Brian J.; Breshears, Andrew T.; Brown, M. Alex

Complexes of the trivalent lanthanides and Am with di-2-ethylhexylphosphoric acid (HDEHP) dissolved in an aliphatic diluent were probed with UV–vis, X-ray absorption fine structure, and time-resolved fluorescence spectroscopy while the water concentration was determined by Karl Fischer titrations. In particular, our work focuses on the Nd-hypersensitive UV–vis absorbance region to identify the cause of changing absorbance values at 570 and 583 nm in relation to the pseudooctahedral Nd environment when coordinated with three HDEHP dimers. In contrast to recently reported interpretations, we establish that while impurities have an effect on this electronic transition band, a high water content can causemore » distortion of the pseudooctahedral symmetry of the six-coordinate Nd, resembling the reported spectra of the seven-coordinate Nd compounds. Extended X-ray absorption fine structure analysis of the Nd in high-concentration HDEHP solutions also points to an increase in the coordination number from 6 to 7. The spectral behavior of other lanthanides (Pr, Ho, Sm, and Er) and Am III as a function of the HDEHP concentration suggests that water coordination with the metal likely depends on the metal’s effective charge. Fluorescence data using lifetime studies and excitation and emission spectra support the inclusion of water in the Eu coordination sphere. Further, the role of the effective charge was confirmed by a comparison of the Gibbs free energies of six- and seven-coordinate La-HDEHP–H 2O and Lu-HDEHP–H 2O complexes using density functional theory. In contrast, HEH[EHP], the phosphonic acid analogue of HDEHP, exhibits a smaller capacity for water, and the electronic absorption spectra of Nd or Am appear to be unchanged, although the Pr spectra show a noticeable change in intensity as a function of the water content. As a result, electronic absorption extinction coefficients of Am III, Nd III, Pr III, Sm III, Er III, and Ho III as a function of the HDEHP concentration are reported for the first time.« less

On holographic entanglement density

NASA Astrophysics Data System (ADS)

Gushterov, Nikola I.; O'Bannon, Andy; Rodgers, Ronnie

2017-10-01

We use holographic duality to study the entanglement entropy (EE) of Conformal Field Theories (CFTs) in various spacetime dimensions d, in the presence of various deformations: a relevant Lorentz scalar operator with constant source, a temperature T , a chemical potential μ, a marginal Lorentz scalar operator with source linear in a spatial coordinate, and a circle-compactified spatial direction. We consider EE between a strip or sphere sub-region and the rest of the system, and define the "entanglement density" (ED) as the change in EE due to the deformation, divided by the sub-region's volume. Using the deformed CFTs above, we show how the ED's dependence on the strip width or sphere radius, L, is useful for characterizing states of matter. For example, the ED's small- L behavior is determined either by the dimension of the perturbing operator or by the first law of EE. For Lorentz-invariant renormalization group (RG) flows between CFTs, the "area theorem" states that the coefficient of the EE's area law term must be larger in the UV than in the IR. In these cases the ED must therefore approach zero from below as L→∞. However, when Lorentz symmetry is broken and the IR fixed point has different scaling from the UV, we find that the ED often approaches the thermal entropy density from above, indicating area theorem violation.

General relativistic satellite astrometry. II. Modeling parallax and proper motion

NASA Astrophysics Data System (ADS)

de Felice, F.; Bucciarelli, B.; Lattanzi, M. G.; Vecchiato, A.

2001-07-01

The non-perturbative general relativistic approach to global astrometry introduced by de Felice et al. (\\cite{defetal}) is here extended to account for the star motions on the Schwarzschild celestial sphere. A new expression of the observables, i.e. angular distances among stars, is provided, which takes into account the effects of parallax and proper motions. This dynamical model is then tested on an end-to-end simulation of the global astrometry mission GAIA. The results confirm the findings of our earlier work, which applied to the case of a static (angular coordinates only) sphere. In particular, measurements of large arcs among stars (each measurement good to ~ 100 mu arcsec, as expected for V ~ 17 mag stars) repeated over an observing period comparable to the mission lifetime foreseen for GAIA, can be modeled to yield estimates of positions, parallaxes, and annual proper motions good to ~ 15 mu arcsec. This second round of experiments confirms, within the limitations of the simulation and the assumptions of the current relativistic model, that the space-born global astrometry initiated with Hipparcos can be pushed down to the 10-5 arcsec accuracy level proposed with the GAIA mission. Finally, the simplified case we have solved can be used as reference for testing the limiting behavior of more realistic models as they become available.

Numerical simulation of a sphere moving down an incline with identical spheres placed equally apart

USGS Publications Warehouse

Ling, Chi-Hai; Jan, Chyan-Deng; Chen, Cheng-lung; Shen, Hsieh Wen

1992-01-01

This paper describes a numerical study of an elastic sphere moving down an incline with a string of identical spheres placed equally apart. Two momentum equations and a moment equation formulated for the moving sphere are solved numerically for the instantaneous velocity of the moving sphere on an incline with different angles of inclination. Input parameters for numerical simulation include the properties of the sphere (the radius, density, Poison's ratio, and Young's Modulus of elasticity), the coefficient of friction between the spheres, and a damping coefficient of the spheres during collision.

Water Surface Impact and Ricochet of Deformable Elastomeric Spheres

NASA Astrophysics Data System (ADS)

Hurd, Randy C.

Soft and deformable silicone rubber spheres ricochet from a water surface when rigid spheres and disks (or skipping stones) cannot. This dissertation investigates why these objects are able to skip so successfully. High speed cameras allow us to see that these unique spheres deform significantly as they impact the water surface, flattening into pancake-like shapes with greater area. Though the water entry behavior of deformable spheres deviates from that of rigid spheres, our research shows that if this deformation is accounted for, their behavior can be predicted from previously established methods. Soft spheres skip more easily because they deform significantly when impacting the water surface. We present a diagram which enables the prediction of a ricochet from sphere impact conditions such as speed and angle. Experiments and mathematical representations of the sphere skipping both show that these deformable spheres skip more readily because deformation momentarily increases sphere area and produces an attack angle with the water which is favorable to skipping. Predictions from our mathematical representation of sphere skipping agree strongly with observations from experiments. Even when a sphere was allowed to skip multiple times in the laboratory, the mathematical predictions show good agreement with measured impact conditions through subsequent skipping events. While studying multiple impact events in an outdoor setting, we discovered a previously unidentified means of skipping, which is unique to deformable spheres. This new skipping occurs when a relatively soft sphere first hits the water at a high speed and low impact angle and the sphere begins to rotate very quickly. This quick rotation causes the sphere to stretch into a shape similar to an American football and maintain this shape while it spins. The sphere is observed to move nearly parallel with the water surface with the tips of this "football" dipping into the water as it rotates and the sides passing just over the surface. This sequence of rapid impact events give the impression that the sphere is walking across the water surface.

Unusual mode of protein binding by a cytotoxic π-arene ruthenium(ii) piano-stool compound containing an O,S-chelating ligand.

PubMed

Hildebrandt, Jana; Görls, Helmar; Häfner, Norman; Ferraro, Giarita; Dürst, Matthias; Runnebaum, Ingo B; Weigand, Wolfgang; Merlino, Antonello

2016-08-02

A new pseudo-octahedral π-arene ruthenium(ii) piano-stool compound, containing an O,S-bidentate ligand (compound 1) and showing significant cytotoxic activity in vitro, was synthesized and characterized. In solution stability and interaction with the model protein bovine pancreatic ribonuclease (RNase A) were investigated by using UV-Vis absorption spectroscopy. Its crystal structure and that of the adduct formed upon reaction with RNase A were obtained by X-ray crystallography. The comparison between the structure of purified compound 1 and that of the fragment bound to RNase A reveals an unusual mode of protein binding that includes ligand exchange and alteration of coordination sphere geometry.

A symmetric integral identity for Bessel functions with applications to integral geometry

NASA Astrophysics Data System (ADS)

Salman, Yehonatan

2017-12-01

In the article of Kunyansky (Inverse Probl 23(1):373-383, 2007) a symmetric integral identity for Bessel functions of the first and second kind was proved in order to obtain an explicit inversion formula for the spherical mean transform where our data is given on the unit sphere in Rn . The aim of this paper is to prove an analogous symmetric integral identity in case where our data for the spherical mean transform is given on an ellipse E in R2 . For this, we will use the recent results obtained by Cohl and Volkmer (J Phys A Math Theor 45:355204, 2012) for the expansions into eigenfunctions of Bessel functions of the first and second kind in elliptical coordinates.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schoendorff, George E.; De Jong, Wibe A.; Gordon, Mark S.

The formation of uranyl dicationic complexes containing water and nitrile (acetonitrile, propionitrile, and benzonitrile) ligands, [UO2(H2O)n(RCN)m]2+, has been studied using density functional theory (DFT) with a relativistic effective core potential (RECP) to account for scalar relativistic effects on uranium. It is shown that nitrile addition is favored over the addition of water ligands. Decomposition of these complexes to [UO2OH(H2O)n(RCN)m]+ by the loss of either H3O+ or (RCN+H)+ is also examined. It is found that this reaction occurs when the coordination sphere of uranyl is unsaturated. Additionally, this reaction is influenced by the size of the nitrile ligand with reactions involvingmore » acetonitrile being the most prevalent.« less

Laser backscattering analytical model of Doppler power spectra about rotating convex quadric bodies of revolution

NASA Astrophysics Data System (ADS)

Gong, YanJun; Wu, ZhenSen; Wang, MingJun; Cao, YunHua

2010-01-01

We propose an analytical model of Doppler power spectra in backscatter from arbitrary rough convex quadric bodies of revolution (whose lateral surface is a quadric) rotating around axes. In the global Cartesian coordinate system, the analytical model deduced is suitable for general convex quadric body of revolution. Based on this analytical model, the Doppler power spectra of cones, cylinders, paraboloids of revolution, and sphere-cones combination are proposed. We analyze numerically the influence of geometric parameters, aspect angle, wavelength and reflectance of rough surface of the objects on the broadened spectra because of the Doppler effect. This analytical solution may contribute to laser Doppler velocimetry, and remote sensing of ballistic missile that spin.

Standardization Tests of NACA No. 1 Wind Tunnel

NASA Technical Reports Server (NTRS)

Reid, Elliott G

1925-01-01

The tests described in this report were made in the 5-foot atmospheric wind tunnel of the National Advisory Committee for Aeronautics, at Langley Field. The primary objective of collecting data on the characteristics of this tunnel for comparison with those of others throughout the world, in order that, in the future, the results of tests made in all the principle laboratories may be interpreted, compared, and coordinated on a basis of scientifically established relationships, a process hitherto impossible due to the lack of comparable data. The work includes tests of a disk, spheres, cylinders, and airfoils, explorations of the test section for static pressure and velocity distribution, and determination of the variations of air flow direction throughout the operating range of the tunnel. (author)

Crystal structure of fac-tri-chlorido-[tris-(pyridin-2-yl-N)amine]-chromium(III).

PubMed

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol-ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris-(pyridin-2-yl)amine; C15H12N4], the Cr(III) ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa-hedral coordination sphere. The average Cr-N and Cr-Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol-ecule is located on a mirror plane. In the crystal, a combination of C-H⋯N and C-H⋯Cl hydrogen-bonding inter-actions connect the mol-ecules into a three-dimensional network.

Crystal structure of fac-aquatricarbonyl[(S)-valin-ato-κ(2) N,O]-rhenium(I).

PubMed

Piletska, Kseniia O; Domasevitch, Kostiantyn V; Shtemenko, Alexander V

2016-04-01

In the mol-ecule of the title compound, [Re(C5H10NO2)(CO)3(H2O)], the Re(I) atom adopts a distorted octa-hedral coordination sphere defined by one aqua and three carbonyl ligands as well as one amino N and one carboxyl-ate O atom of the chelating valinate anion. The carbonyl ligands are arranged in a fac-configuration around the Re(I) ion. In the crystal, an intricate hydrogen-bonding system under participation of two O-H, two N-H and one C-H donor groups and the carboxyl-ate and carbonyl O atoms as acceptor groups contribute to the formation of a three-dimensional supra-molecular network.

Analytic theory of photoacoustic wave generation from a spheroidal droplet.

PubMed

Li, Yong; Fang, Hui; Min, Changjun; Yuan, Xiaocong

2014-08-25

In this paper, we develop an analytic theory for describing the photoacoustic wave generation from a spheroidal droplet and derive the first complete analytic solution. Our derivation is based on solving the photoacoustic Helmholtz equation in spheroidal coordinates with the separation-of-variables method. As the verification, besides carrying out the asymptotic analyses which recover the standard solutions for a sphere, an infinite cylinder and an infinite layer, we also confirm that the partial transmission and reflection model previously demonstrated for these three geometries still stands. We expect that this analytic solution will find broad practical uses in interpreting experiment results, considering that its building blocks, the spheroidal wave functions (SWFs), can be numerically calculated by the existing computer programs.

Collinear swimmer propelling a cargo sphere at low Reynolds number.

PubMed

Felderhof, B U

2014-11-01

The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes equations in the presence of a sphere with a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.

Stem/progenitor cells derived from the cochlear sensory epithelium give rise to spheres with distinct morphologies and features.

PubMed

Diensthuber, Marc; Oshima, Kazuo; Heller, Stefan

2009-06-01

Nonmammalian vertebrates regenerate lost sensory hair cells by means of asymmetric division of supporting cells. Inner ear or lateral line supporting cells in birds, amphibians, and fish consequently serve as bona fide stem cells resulting in high regenerative capacity of hair cell-bearing organs. Hair cell regeneration does not happen in the mammalian cochlea, but cells with proliferative capacity can be isolated from the neonatal cochlea. These cells have the ability to form clonal floating colonies, so-called spheres, when cultured in nonadherent conditions. We noticed that the sphere population derived from mouse cochlear sensory epithelium cells was heterogeneous, consisting of morphologically distinct sphere types, hereby classified as solid, transitional, and hollow. Cochlear sensory epithelium-derived stem/progenitor cells initially give rise to small solid spheres, which subsequently transition into hollow spheres, a change that is accompanied by epithelial differentiation of the majority of sphere cells. Only solid spheres, and to a lesser extent, transitional spheres, appeared to harbor self-renewing stem cells, whereas hollow spheres could not be consistently propagated. Solid spheres contained significantly more rapidly cycling Pax-2-expressing presumptive otic progenitor cells than hollow spheres. Islet-1, which becomes upregulated in nascent sensory patches, was also more abundant in solid than in hollow spheres. Likewise, hair cell-like cells, characterized by the expression of multiple hair cell markers, differentiated in significantly higher numbers in cell populations derived from solid spheres. We conclude that cochlear sensory epithelium cell populations initially give rise to small solid spheres that have self-renewing capacity before they subsequently convert into hollow spheres, a process that is accompanied by loss of stemness and reduced ability to spontaneously give rise to hair cell-like cells. Solid spheres might, therefore, represent the most suitable sphere type for cell-based assays or animal model transplantation studies aimed at development of cell replacement therapies.

Insight into the coordination and the binding sites of Cu(2+) by the histidyl-6-tag using experimental and computational tools.

PubMed

Watly, Joanna; Simonovsky, Eyal; Wieczorek, Robert; Barbosa, Nuno; Miller, Yifat; Kozlowski, Henryk

2014-07-07

His-tags are specific sequences containing six to nine subsequent histydyl residues, and they are used for purification of recombinant proteins by use of IMAC chromatography. Such polyhistydyl tags, often used in molecular biology, can be also found in nature. Proteins containing histidine-rich domains play a critical role in many life functions in both prokaryote and eukaryote organisms. Binding mode and the thermodynamic properties of the system depend on the specific metal ion and the histidine sequence. Despite the wide application of the His-tag for purification of proteins, little is known about the properties of metal-binding to such tag domains. This inspired us to undertake detailed studies on the coordination of Cu(2+) ion to hexa-His-tag. Experiments were performed using the potentiometric, UV-visible, CD, and EPR techniques. In addition, molecular dynamics (MD) simulations and density functional theory (DFT) calculations were applied. The experimental studies have shown that the Cu(2+) ion binds most likely to two imidazoles and one, two, or three amide nitrogens, depending on the pH. The structures and stabilities of the complexes for the Cu(2+)-Ac-(His)6-NH2 system using experimental and computational tools were established. Polymorphic binding states are suggested, with a possibility of the formation of α-helix structure induced by metal ion coordination. Metal ion is bound to various pairs of imidazole moieties derived from the tag with different efficiencies. The coordination sphere around the metal ion is completed by molecules of water. Finally, the Cu(2+) binding by Ac-(His)6-NH2 is much more efficient compared to other multihistidine protein domains.

Hydrogen Bonding Rescues Overpotential in Seven-Coordinated Ru Water Oxidation Catalysts

DOE PAGES

Matheu, Roc; Ertem, Mehmed Z.; Gimbert-Surinach, Carolina; ...

2017-08-15

In this paper, we describe the synthesis, structural characterization, and redox properties of two new Ru complexes containing the dianionic potentially pentadentate [2,2':6',2"-terpyridine]-6,6"-dicarboxylate (tda 2–) ligand that coordinates Ru at the equatorial plane and with additional pyridine or dmso acting as monondentate ligand in the axial positions: [Ru II(tda-κ-N 3O)(py)(dmso)], 1 II and [Ru III(tda-κ-N 3O 2)(py)(H 2O) ax] +, 2 III(H 2O) +. Complex 1 II has been characterized by single-crystal XRD in the solid state and in solution by NMR spectroscopy. The redox properties of 1 II and 2 III(H 2O) + have been thoroughly investigated by meansmore » of cyclic voltammetry and differential pulse voltammetry. Complex 2 II(H 2O) displays poor catalytic activity with regard to the oxidation of water to dioxygen, and its properties have been analyzed on the basis of foot of the wave analysis and catalytic Tafel plots. The activity of 2 II(H 2O) has been compared with related water oxidation catalysts (WOCs) previously described in the literature. Despite its moderate activity, 2 II(H 2O) constitutes the cornerstone that has triggered the rationalization of the different factors that govern overpotentials as well as efficiencies in molecular WOCs. The present work uncovers the interplay between different parameters, namely, coordination number, number of anionic groups bonded to the first-coordination sphere of the metal center, water oxidation catalysis overpotential, p K a and hydrogen bonding, and the performance of a given WOC. It thus establishes the basic principles for the design of efficient WOCs operating at low overpotentials.« less

The use of a genetic algorithm-based search strategy in geostatistics: application to a set of anisotropic piezometric head data

NASA Astrophysics Data System (ADS)

Abedini, M. J.; Nasseri, M.; Burn, D. H.

2012-04-01

In any geostatistical study, an important consideration is the choice of an appropriate, repeatable, and objective search strategy that controls the nearby samples to be included in the location-specific estimation procedure. Almost all geostatistical software available in the market puts the onus on the user to supply search strategy parameters in a heuristic manner. These parameters are solely controlled by geographical coordinates that are defined for the entire area under study, and the user has no guidance as to how to choose these parameters. The main thesis of the current study is that the selection of search strategy parameters has to be driven by data—both the spatial coordinates and the sample values—and cannot be chosen beforehand. For this purpose, a genetic-algorithm-based ordinary kriging with moving neighborhood technique is proposed. The search capability of a genetic algorithm is exploited to search the feature space for appropriate, either local or global, search strategy parameters. Radius of circle/sphere and/or radii of standard or rotated ellipse/ellipsoid are considered as the decision variables to be optimized by GA. The superiority of GA-based ordinary kriging is demonstrated through application to the Wolfcamp Aquifer piezometric head data. Assessment of numerical results showed that definition of search strategy parameters based on both geographical coordinates and sample values improves cross-validation statistics when compared with that based on geographical coordinates alone. In the case of a variable search neighborhood for each estimation point, optimization of local search strategy parameters for an elliptical support domain—the orientation of which is dictated by anisotropic axes—via GA was able to capture the dynamics of piezometric head in west Texas/New Mexico in an efficient way.

Inner and Outer Coordination Shells of Mg(2+) in CorA Selectivity Filter from Molecular Dynamics Simulations.

PubMed

Kitjaruwankul, Sunan; Wapeesittipan, Pattama; Boonamnaj, Panisak; Sompornpisut, Pornthep

2016-01-28

Structural data of CorA Mg(2+) channels show that the five Gly-Met-Asn (GMN) motifs at the periplasmic loop of the pentamer structure form a molecular scaffold serving as a selectivity filter. Unfortunately, knowledge about the cation selectivity of Mg(2+) channels remains limited. Since Mg(2+) in aqueous solution has a strong first hydration shell and apparent second hydration sphere, the coordination structure of Mg(2+) in a CorA selectivity filter is expected to be different from that in bulk water. Hence, this study investigated the hydration structure and ligand coordination of Mg(2+) in a selectivity filter of CorA using molecular dynamics (MD) simulations. The simulations reveal that the inner-shell structure of Mg(2+) in the filter is not significantly different from that in aqueous solution. The major difference is the characteristic structural features of the outer shell. The GMN residues engage indirectly in the interactions with the metal ion as ligands in the second shell of Mg(2+). Loss of hydrogen bonds between inner- and outer-shell waters observed from Mg(2+) in bulk water is mostly compensated by interactions between waters in the first solvation shell and the GMN motif. Some water molecules in the second shell remain in the selectivity filter and become less mobile to support the metal binding. Removal of Mg(2+) from the divalent cation sensor sites of the protein had an impact on the structure and metal binding of the filter. From the results, it can be concluded that the GMN motif enhances the affinity of the metal binding site in the CorA selectivity filter by acting as an outer coordination ligand.

Measurement of the Casimir Force between Two Spheres

NASA Astrophysics Data System (ADS)

Garrett, Joseph L.; Somers, David A. T.; Munday, Jeremy N.

2018-01-01

Complex interaction geometries offer a unique opportunity to modify the strength and sign of the Casimir force. However, measurements have traditionally been limited to sphere-plate or plate-plate configurations. Prior attempts to extend measurements to different geometries relied on either nanofabrication techniques that are limited to only a few materials or slight modifications of the sphere-plate geometry due to alignment difficulties of more intricate configurations. Here, we overcome this obstacle to present measurements of the Casimir force between two gold spheres using an atomic force microscope. Force measurements are alternated with topographical scans in the x -y plane to maintain alignment of the two spheres to within approximately 400 nm (˜1 % of the sphere radii). Our experimental results are consistent with Lifshitz's theory using the proximity force approximation (PFA), and corrections to the PFA are bounded using nine sphere-sphere and three sphere-plate measurements with spheres of varying radii.

CD and MCD of CytC3 and taurine dioxygenase: role of the facial triad in alpha-KG-dependent oxygenases.

PubMed

Neidig, Michael L; Brown, Christina D; Light, Kenneth M; Fujimori, Danica Galonić; Nolan, Elizabeth M; Price, John C; Barr, Eric W; Bollinger, J Martin; Krebs, Carsten; Walsh, Christopher T; Solomon, Edward I

2007-11-21

The alpha-ketoglutarate (alpha-KG)-dependent oxygenases are a large and diverse class of mononuclear non-heme iron enzymes that require FeII, alpha-KG, and dioxygen for catalysis with the alpha-KG cosubstrate supplying the additional reducing equivalents for oxygen activation. While these systems exhibit a diverse array of reactivities (i.e., hydroxylation, desaturation, ring closure, etc.), they all share a common structural motif at the FeII active site, termed the 2-His-1-carboxylate facial triad. Recently, a new subclass of alpha-KG-dependent oxygenases has been identified that exhibits novel reactivity, the oxidative halogenation of unactivated carbon centers. These enzymes are also structurally unique in that they do not contain the standard facial triad, as a Cl- ligand is coordinated in place of the carboxylate. An FeII methodology involving CD, MCD, and VTVH MCD spectroscopies was applied to CytC3 to elucidate the active-site structural effects of this perturbation of the coordination sphere. A significant decrease in the affinity of FeII for apo-CytC3 was observed, supporting the necessity of the facial triad for iron coordination to form the resting site. In addition, interesting differences observed in the FeII/alpha-KG complex relative to the cognate complex in other alpha-KG-dependent oxygenases indicate the presence of a distorted 6C site with a weak water ligand. Combined with parallel studies of taurine dioxygenase and past studies of clavaminate synthase, these results define a role of the carboxylate ligand of the facial triad in stabilizing water coordination via a H-bonding interaction between the noncoordinating oxygen of the carboxylate and the coordinated water. These studies provide initial insight into the active-site features that favor chlorination by CytC3 over the hydroxylation reactions occurring in related enzymes.

Ultrahigh-resolution crystal structures of Z-DNA in complex with Mn(2+) and Zn(2+) ions.

PubMed

Drozdzal, Pawel; Gilski, Miroslaw; Kierzek, Ryszard; Lomozik, Lechoslaw; Jaskolski, Mariusz

2013-06-01

X-ray crystal structures of the spermine(4+) form of the Z-DNA duplex with the self-complementary d(CG)3 sequence in complexes with Mn(2+) and Zn(2+) cations have been determined at the ultrahigh resolutions of 0.75 and 0.85 Å, respectively. Stereochemical restraints were only used for the sperminium cation (in both structures) and for nucleotides with dual conformation in the Zn(2+) complex. The Mn(2+) and Zn(2+) cations at the major site, designated M(2+)(1), bind at the N7 position of G6 by direct coordination. The coordination geometry of this site was octahedral, with complete hydration shells. An additional Zn(2+)(2) cation was bis-coordinated in a tetrahedral fashion by the N7 atoms of G10 and G12 from a symmetry-related molecule. The coordination distances of Zn(2+)(1) and Zn(2+)(2) to the O6 atom of the guanine residues were 3.613 (6) and 3.258 (5) Å, respectively. Moreover, a chloride ion was also identified in the coordination sphere of Zn(2+)(2). Alternate conformations were observed in the Z-DNA-Zn(2+) structure not only at internucleotide linkages but also at the terminal C3'-OH group of G12. The conformation of the sperminium chain in the Z-DNA-Mn(2+) complex is similar to the spermine(4+) conformation in analogous Z-DNA-Mg(2+) structures. In the Z-DNA-Zn(2+) complex the sperminium cation is disordered and partially invisible in electron-density maps. In the Z-DNA-Zn(2+) complex the sperminium cation only interacts with the phosphate groups of the Z-DNA molecules, while in the Z-DNA-Mn(2+) structure it forms hydrogen bonds to both the phosphate groups and DNA bases.

QM/MM structural and spectroscopic analysis of the di-iron(II) and di-iron(III) ferroxidase site in M ferritin.

PubMed

Harris, Travis V; Morokuma, Keiji

2013-08-05

Ferritins are cage-like proteins composed of 24 subunits that take up iron(II) and store it as an iron(III) oxide mineral core. A critical step is the ferroxidase reaction, in which oxygen reacts with a di-iron(II) site, proceeding through a peroxo intermediate, to form μ-oxo/hydroxo-bridged di-iron(III) products. The recent crystal structures of copper(II)- and iron(III)-bound frog M ferritin at 2.8 Å resolution [Bertini; et al. J. Am. Chem. Soc. 2012, 134, 6169-6176] provided an opportunity to theoretically investigate the detailed structures of the reactant state and products. In this study, the quantum mechanical/molecular mechanical ONIOM method is used to structurally optimize a series of single-subunit models with various hydration, protonation, and coordination states of the ferroxidase site. Calculated exchange coupling constants (J), Mössbauer parameters, and time-dependent density functional theoretical (TD-DFT) circular dichroism spectra with electronic embedding are compared with the available experimental data. The di-iron(II) model with the most experimentally consistent structural and spectroscopic parameters has 5-coordinate iron centers with Glu23, Glu58, His61, and two waters completing one coordination sphere, and His54, Glu58, Glu103, and Asp140 completing the other. In contrast to a previously proposed structure, Gln137 is not directly coordinated, but it is involved in hydrogen bonding with several iron ligands. For the di-iron(III) products, we find that a μ-oxo-bridged and two doubly bridged (μ-hydroxo and μ-oxo/hydroxo) species are likely coproduced. Although four quadrupole doublets were observed experimentally, we find that two doublets may arise from a single asymmetrically coordinated ferroxidase site. These proposed key structures will help to explore the pathway connecting the di-Fe(II) state to the peroxo intermediate and the branching mechanisms leading to the multiple products.

Lead and aluminum bonding in Pb-AI metaphosphate glasses.

PubMed

Tsuchida, J E; Schneider, J; Pizani, P S; Oliveira, S L

2008-01-21

The bonding properties of cations in phosphate glasses determine many short- and medium-range structural features in the glass network, hence influencing bulk properties. In this work, Pb-Al-metaphosphate glasses (1 - x)Pb(PO(3))(2).xAI(PO(3))(3) with 0 < or = x < or = 1 were analyzed to determine the effect of the substitution of Pb by AI on the glass structure in the metaphosphate composition. The glass transition temperature and density were measured as a function of the Al concentration. The vibrational and structural properties were probed by Raman spectroscopy and nuclear magnetic resonance of (31)P, (27)AI, and (207)Pb. Aluminum incorporates homogeneously in the glass creating a stiffer and less packed network. The average coordination number for AI decreases from 5.9 to 5.0 as x increases from 0.1 to 1, indicating more covalent AI-O bonds. The coordination number of Pb in these glasses is greater than 8, showing an increasing ionic behavior for compositions richer in AI. A quantitative analysis of the phosphate speciation shows definite trends in the bonding of AIO(n) groups and phosphate tetrahedra. In glasses with x < 0.48, phosphate groups share preferentially only one nonbridging O corner with an AIO(n) coordination polyhedron. For x > 0.48 more than one nonbridging O can be linked to AIO(n) polyhedra. There is no corner sharing of O between AIO(n) and PbO(n) polyhedra nor between AIO(n) themselves throughout the compositional range. The PbO(n) coordination polyhedra show considerable nonbridging O sharing, with each O participating in the coordination sphere of at least two Pb. The bonding preferences determined for Al are consistent with the behavior observed in Na-AI and Ca-AI metaphosphates, indicating this may be a general behavior for ternary phosphate glasses.

Viscous constraints on predator:food size ratios in microscale feeding

NASA Astrophysics Data System (ADS)

Jabbarzadeh, Mehdi; Fu, Henry

2014-11-01

Small organisms such as protists or copepods may try to capture food by manipulating food with cilia, limbs, or feeding appendages. At these small scales, viscous flow may complicate the ability of a feeding appendage to closely approach a food particle. As a simplified but tractable model of such feeding approach, we consider the problem of two spheres approaching in a Stokes fluid. The first ``feeding'' sphere, which represents a body part or feeding appendage, is pushed with a constant force towards a force-free ``food'' sphere. When the feeding sphere reaches within a cutoff distance of the food sphere we assume that nonhydrodynamic interactions lead to capture. We examine approach for a range of size ratios between the feeding and food sphere. To investigate the approach efficiency, we examine the time required for the feeding sphere to capture the food sphere, as well as how far the feeding sphere must move before it captures the food sphere. We also examine the effect of varying the cutoff distance for capture. We find that hydrodynamic interactions strongly affect the results when the size of the spheres is comparable. We describe what relative sizes between feeding sphere and food particles may be most effective for food capture.

High temperature insulation for ceramic matrix composites

DOEpatents

Merrill, Gary B.; Morrison, Jay Alan

2001-01-01

A ceramic composition is provided to insulate ceramic matrix composites under high temperature, high heat flux environments. The composition comprises a plurality of hollow oxide-based spheres of various dimensions, a phosphate binder, and at least one oxide filler powder, whereby the phosphate binder partially fills gaps between the spheres and the filler powders. The spheres are situated in the phosphate binder and the filler powders such that each sphere is in contact with at least one other sphere. The spheres may be any combination of Mullite spheres, Alumina spheres, or stabilized Zirconia spheres. The filler powder may be any combination of Alumina, Mullite, Ceria, or Hafnia. Preferably, the phosphate binder is Aluminum Ortho-Phosphate. A method of manufacturing the ceramic insulating composition and its application to CMC substrates are also provided.

High temperature insulation for ceramic matrix composites

DOEpatents

Merrill, Gary B.; Morrison, Jay Alan

2000-01-01

A ceramic composition is provided to insulate ceramic matrix composites under high temperature, high heat flux environments. The composite comprises a plurality of hollow oxide-based spheres of varios dimentions, a phosphate binder, and at least one oxide filler powder, whereby the phosphate binder partially fills gaps between the spheres and the filler powders. The spheres are situated in the phosphate binder and the filler powders such that each sphere is in contact with at least one other sphere. The spheres may be any combination of Mullite spheres, Alumina spheres, or stabilized Zirconia spheres. The filler powder may be any combination of Alumina, Mullite, Ceria, or Hafnia. Preferably, the phosphate binder is Aluminum Ortho-Phosphate. A method of manufacturing the ceramic insulating composition and its application to CMC substates are also provided.

High temperature insulation for ceramic matrix composites

DOEpatents

Merrill, Gary B.; Morrison, Jay Alan

2004-01-13

A ceramic composition is provided to insulate ceramic matrix composites under high temperature, high heat flux environments. The composition comprises a plurality of hollow oxide-based spheres of various dimensions, a phosphate binder, and at least one oxide filler powder, whereby the phosphate binder partially fills gaps between the spheres and the filler powders. The spheres are situated in the phosphate binder and the filler powders such that each sphere is in contact with at least one other sphere. The spheres may be any combination of Mullite spheres, Alumina spheres, or stabilized Zirconia spheres. The filler powder may be any combination of Alumina, Mullite, Ceria, or Hafnia. Preferably, the phosphate binder is Aluminum Ortho-Phosphate. A method of manufacturing the ceramic insulating composition and its application to CMC substrates are also provided.

Electromagnetic Energy Localization and Characterization of Composites

DTIC Science & Technology

2013-01-01

polyhedrons ), and [39] (spheres and a complex yet symmetric structure). With time-domain EM analysis, regular shapes, such as cubes, spheres, and regular...spheres), [40] (spheres, crosses, cylinders, and polyhedrons ), and [41] (spheres and cylinders); and 3-D random mixtures using a frequency-domain finite...element method [42] ( polyhedrons ), and [43], [44] (spheres). Such steady-state analyses are limited as they, for example, do not capture temporal

Movements of a Sphere Moving Over Smooth and Rough Inclines

NASA Astrophysics Data System (ADS)

Jan, Chyan-Deng

1992-01-01

The steady movements of a sphere over a rough incline in air, and over smooth and rough inclines in a liquid were studied theoretically and experimentally. The principle of energy conservation was used to analyze the translation velocities, rolling resistances, and drag coefficients of a sphere moving over the inclines. The rolling resistance to the movement of a sphere from the rough incline was presumed to be caused by collisions and frictional slidings. A varnished wooden board was placed on the bottom of an experimental tilting flume to form a smooth incline and a layer of spheres identical to the sphere moving over them was placed on the smooth wooden board to form a rough incline. Spheres used in the experiments were glass spheres, steel spheres, and golf balls. Experiments show that a sphere moving over a rough incline with negligible fluid drag in air can reach a constant translation velocity. This constant velocity was found to be proportional to the bed inclination (between 11 ^circ and 21^circ) and the square root of the sphere's diameter, but seemingly independent of the sphere's specific gravity. Two empirical coefficients in the theoretical expression of the sphere's translation velocity were determined by experiments. The collision and friction parts of the shear stress exerted on the interface between the moving sphere and rough incline were determined. The ratio of collision to friction parts appears to increase with increase in the bed inclination. These two parts seem to be of the same order of magnitude. The rolling resistances and the relations between the drag coefficient and Reynolds number for a sphere moving over smooth and rough inclines in a liquid, such as water or salad oil, were determined by a regression analysis based on experimental data. It was found that the drag coefficient for a sphere over the rough incline is larger than that for a sphere over the smooth incline, and both of which are much larger than that for a sphere in free fall. The relative magnitudes of the shear stresses due to drag, collision, and friction were also determined in terms of the Reynolds number.

Phase diagram of heteronuclear Janus dumbbells

NASA Astrophysics Data System (ADS)

O'Toole, Patrick; Giacometti, Achille; Hudson, Toby

Using Aggregation-Volume-Bias Monte Carlo simulations along with Successive Umbrella Sampling and Histogram Re-weighting, we study the phase diagram of a system of dumbbells formed by two touching spheres having variable sizes, as well as different interaction properties. The first sphere ($h$) interacts with all other spheres belonging to different dumbbells with a hard-sphere potential. The second sphere ($s$) interacts via a square-well interaction with other $s$ spheres belonging to different dumbbells and with a hard-sphere potential with all remaining $h$ spheres. We focus on the region where the $s$ sphere is larger than the $h$ sphere, as measured by a parameter $1\\le \\alpha\\le 2 $ controlling the relative size of the two spheres. As $\\alpha \\to 2$ a simple fluid of square-well spheres is recovered, whereas $\\alpha \\to 1$ corresponds to the Janus dumbbell limit, where the $h$ and $s$ spheres have equal sizes. Many phase diagrams falling into three classes are observed, depending on the value of $\\alpha$. The $1.8 \\le \\alpha \\le 2$ is dominated by a gas-liquid phase separation very similar to that of a pure square-well fluid with varied critical temperature and density. When $1.3 \\le \\alpha \\le 1.8$ we find a progressive destabilization of the gas-liquid phase diagram by the onset of self-assembled structures, that eventually lead to a metastability of the gas-liquid transition below $\\alpha=1.2$.

A Conventional Mean Pole

NASA Astrophysics Data System (ADS)

Stamatakos, N. G.; McCarthy, D. D.

2016-12-01

A CONVENTIONAL MEAN POLE PATH The gradual drift of the pole associated with the rotational axis of the Earth in a terrestrial reference frame is characterized by the motion of a "mean pole." The IERS Conventions (2010) does not provide a formal definition of such a "mean pole." In its glossary it defines the terminology "mean pole" in the celestial frame by using the definition "the position on the celestial sphere towards which the Earth's axis points at a particular epoch, with the oscillations due to precession-nutation removed." The need for a terrestrial mean pole is mentioned in Section 7.1.4 of the IERS Conventions, which outlines the procedure to account for the variation in terrestrial site coordinates caused by the pole tide. It states, that an estimate of the wander of the mean pole to within about 10 milliarc-seconds is needed to ensure that the geopotential field is aligned to the long term mean pole. Historically the angular coordinates of this "mean pole" were calculated by averaging the observed angular coordinates of the rotational pole over six years, the beat period of the annual and approximately 14-month Chandler motions of the rotational pole. The IERS Conventions (2010) realization of the mean pole is composed of a cubic fit of the polar coordinates valid over 1976-2010 and a linear model for extrapolation after 2010.0. Further it notes that in the future, the IERS conventional mean pole will be revised as needed with sufficient advance notice. However, this document leaves open the formal definition of a conventional terrestrial mean pole, the spectral frequency content to be expected in such a definition and a procedure to be used to realize the coordinates of the path for users. Background is provided regarding past realizations of a "mean pole," and the requirements for a realization of a mean pole path are reviewed. Possible definitions and potential mathematical models to provide mean pole coordinates in the future are outlined. In addition, the authors hope that this poster will serve to open a discussion, which will identify geodesy disciplines that require a mean pole and what type of definition would be suitable to their needs.

Ruthenium(II) Complexes Containing Lutidine-Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of C-N bonds.

PubMed

Hernández-Juárez, Martín; López-Serrano, Joaquín; Lara, Patricia; Morales-Cerón, Judith P; Vaquero, Mónica; Álvarez, Eleuterio; Salazar, Verónica; Suárez, Andrés

2015-05-11

A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C-N bond assisted either by the pincer ligand or a second coordinated H2 molecule. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design and reactivity of Ni-complexes using pentadentate neutral-polypyridyl ligands: Possible mimics of NiSOD.

PubMed

Snider, Victoria G; Farquhar, Erik R; Allen, Mark; Abu-Spetani, Ayah; Mukherjee, Anusree

2017-10-01

Superoxide plays a key role in cell signaling, but can be cytotoxic within cells unless well regulated by enzymes known as superoxide dismutases (SOD). Nickel superoxide dismutase (NiSOD) catalyzes the disproportion of the harmful superoxide radical into hydrogen peroxide and dioxygen. NiSOD has a unique active site structure that plays an important role in tuning the potential of the nickel center to function as an effective catalyst for superoxide dismutation with diffusion controlled rates. The synthesis of structural and functional analogues of NiSOD provides a route to better understand the role of the nickel active site in superoxide dismutation. In this work, the synthesis of a series of nickel complexes supported by nitrogen rich pentadentate ligands is reported. The complexes have been characterized through absorption spectroscopy, mass spectrometry, and elemental analysis. X-ray absorption spectroscopy was employed to establish the oxidation state and the coordination geometry around the metal center. The reactivity of these complexes toward KO 2 was evaluated to elucidate the role of the coordination sphere in controlling superoxide dismutation reactivity. Copyright © 2017 Elsevier Inc. All rights reserved.

Coupling Influences SMM Properties for Pure 4 f Systems.

PubMed

Zhang, Xuejing; Liu, Shuang; Vieru, Veacheslav; Xu, Na; Gao, Chen; Wang, Bing-Wu; Shi, Wei; Chibotaru, Liviu F; Gao, Song; Cheng, Peng; Powell, Annie K

2018-04-20

Increasing both the energy barrier for magnetization reversal and the coercive field of the hysteresis loop are significant challenges in the field of single-molecule magnets (SMMs). Coordination geometries of lanthanide ions and magnetic interactions between lanthanide ions are both important for guiding the magnetic behavior of SMMs. We report a high energy barrier of 657 K (457 cm -1 ) in a diamagnetic-ion-diluted lanthanide chain compound with a constrained bisphenoid symmetry (D 2d ); this energy barrier is substantially higher than the barrier of 567 K (394 cm -1 ) of the non-diluted chain compound with intrachain ferromagnetic interactions. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops, which is crucial for the rational design of high-performance SMMs. Factors related to the coordination sphere of the lanthanide center, which govern the high magnetic relaxation barriers through the second excited Kramer's doublets and the magnetic interactions that affect the hysteresis loops, were revealed through ab initio calculations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Terminal energy distribution of blast waves from bursting spheres

NASA Technical Reports Server (NTRS)

Adamczyk, A. A.; Strehlow, R. A.

1977-01-01

The calculation results for the total energy delivered to the surroundings by the burst of an idealized massless sphere containing an ideal gas are presented. The logic development of various formulas for sphere energy is also presented. For all types of sphere bursts the fraction of the total initial energy available in the sphere that is delivered to the surroundings is shown to lie between that delivered for the constant pressure addition of energy to a source region and that delivered by isentropic expansion of the sphere. The relative value of E sub/Q increases at fixed sphere pressure/surrounding pressure as sphere temperature increases because the velocity of sound increases.

New Langevin and gradient thermostats for rigid body dynamics.

PubMed

Davidchack, R L; Ouldridge, T E; Tretyakov, M V

2015-04-14

We introduce two new thermostats, one of Langevin type and one of gradient (Brownian) type, for rigid body dynamics. We formulate rotation using the quaternion representation of angular coordinates; both thermostats preserve the unit length of quaternions. The Langevin thermostat also ensures that the conjugate angular momenta stay within the tangent space of the quaternion coordinates, as required by the Hamiltonian dynamics of rigid bodies. We have constructed three geometric numerical integrators for the Langevin thermostat and one for the gradient thermostat. The numerical integrators reflect key properties of the thermostats themselves. Namely, they all preserve the unit length of quaternions, automatically, without the need of a projection onto the unit sphere. The Langevin integrators also ensure that the angular momenta remain within the tangent space of the quaternion coordinates. The Langevin integrators are quasi-symplectic and of weak order two. The numerical method for the gradient thermostat is of weak order one. Its construction exploits ideas of Lie-group type integrators for differential equations on manifolds. We numerically compare the discretization errors of the Langevin integrators, as well as the efficiency of the gradient integrator compared to the Langevin ones when used in the simulation of rigid TIP4P water model with smoothly truncated electrostatic interactions. We observe that the gradient integrator is computationally less efficient than the Langevin integrators. We also compare the relative accuracy of the Langevin integrators in evaluating various static quantities and give recommendations as to the choice of an appropriate integrator.

Eu(III) Complex with DO3A-amino-phosphonate Ligand as a Concentration-Independent pH-Responsive Contrast Agent for Magnetic Resonance Spectroscopy (MRS).

PubMed

Krchová, Tereza; Herynek, Vít; Gálisová, Andrea; Blahut, Jan; Hermann, Petr; Kotek, Jan

2017-02-20

A new DOTA-like ligand H 5 do3aNP with a 2-[amino(methylphosphonic acid)]ethyl-coordinating pendant arm was prepared, and its coordinating properties were studied by NMR spectroscopy and potentiometry. The study revealed a rare slow exchange (on the 1 H and 31 P NMR time scale) between protonated and unprotonated complex species with a corresponding acidity constant pK A ∼ 8.0. This unusually slow time scale associated with protonation is caused by a significant geometric change from square-antiprismatic (SA) arrangement observed for protonated complex SA-[Eu(Hdo3aNP)] - to twisted-square-antiprismatic (TSA) arrangement found for deprotonated complex TSA-[Eu(do3aNP)] 2- . This behavior results in simultaneous occurrence of the signals of both species in the 31 P NMR spectra at approximately -118 and +70 ppm, respectively. Such an unprecedented difference in the chemical shifts between species differing by a proton is caused by a significant movement of the principal magnetic axis and by a change of phosphorus atom position in the coordination sphere of the central Eu(III) ion (i.e., by relative movement of the phosphorus atom with respect to the principal magnetic axis). It changes the sign of the paramagnetic contribution to the 31 P NMR chemical shift. The properties discovered can be employed in the measurement of pH by MRS techniques as presented by proof-of-principle experiments on phantoms.

Water-soluble platinum nanoparticles stabilized by sulfonated N-heterocyclic carbenes: influence of the synthetic approach.

PubMed

Baquero, Edwin A; Tricard, Simon; Coppel, Yannick; Flores, Juan C; Chaudret, Bruno; de Jesús, Ernesto

2018-03-28

The synthesis of metal nanoparticles (NPs) under controlled conditions in water remains a challenge in nanochemistry. Two different approaches to obtain platinum NPs, which involve the treatment of aqueous solutions of preformed sulfonated (NHC)Pt(ii) dimethyl complexes with carbon monoxide, and of (NHC)Pt(0) diolefin complexes with dihydrogen (NHC = N-heterocyclic carbene), are disclosed here. The resulting NPs were found to be highly stable in water under air for an indefinite time period. Coordination of the NHC ligands to the platinum surface via the carbenic carbon was monitored by solid-state NMR spectroscopy, and the presence of a platinum-carbon bond was unambiguously evidenced by the determination of a 13 C- 195 Pt coupling constant (1106 and 1050 Hz for NPs containing 13 C labeled-NHC ligands and prepared under CO and H 2 , respectively). The coordination of CO to the (NHC)Pt(ii) precursors prior to formation of the NPs was confirmed by NMR spectroscopy. When using a disulfonated NHC ligand, a second coordination sphere containing bis(NHC)Pt(ii) complexes is described. Under CO, the formation of NPs was found to be slower than in a previously reported thermal method (Angew. Chem., Int. Ed., 2014, 53, 13220-13224), but led to NPs of similar sizes, whereas under H 2 , the synthesis of platinum NPs progressed even more slowly and produced larger NPs. In addition to the influence of the synthetic approach, the present study highlights the importance of ligand design for NP stabilization.

Crystal structure of a mixed-ligand dinuclear Ba-Zn complex with 2-meth-oxy-ethanol having tri-phenyl-acetate and chloride bridges.

PubMed

Utko, Józef; Sobocińska, Maria; Dobrzyńska, Danuta; Lis, Tadeusz

2015-07-01

The dinuclear barium-zinc complex, μ-chlorido-1:2κ(2) Cl:Cl-chlorido-2κCl-bis-(2-meth-oxy-ethanol-1κO)bis-(2-meth-oxy-ethanol-1κ(2) O,O')bis-(μ-tri-phenyl-acetato-1:2κ(2) O:O')bariumzinc, [BaZn(C20H15O2)2Cl2(C3H8O2)4], has been synthesized by the reaction of barium tri-phenyl-acetate, anhydrous zinc chloride and 2-meth-oxy-ethanol in the presence of toluene. The barium and zinc metal cations in the dinuclear complex are linked via one chloride anion and carboxyl-ate O atoms of the tri-phenyl-acetate ligands, giving a Ba⋯Zn separation of 3.9335 (11) Å. The irregular nine-coordinate BaO8Cl coordination centres comprise eight O-atom donors, six of them from 2-meth-oxy-ethanol ligands (four from two bidentate O,O'-chelate inter-actions and two from monodentate inter-actions), two from bridging tri-phenyl-acetate ligands and one from a bridging Cl donor. The distorted tetra-hedral coordination sphere of zinc comprises two O-atom donors from the tri-phenyl-acetate ligands and two Cl donors (one bridging and one terminal). In the crystal, O-H⋯Cl, O-H⋯O and C-H⋯Cl inter-molecular inter-actions form a layered structure, lying parallel to (001).

Spectroscopic evidence for ternary surface complexes in the lead(II)-malonic acid-hematite system

USGS Publications Warehouse

Lenhart, J.J.; Bargar, J.R.; Davis, J.A.

2001-01-01

Using extended X-ray absorption fine structure (EXAFS) and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) measurements, we examined the sorption of Pb(II) to hematite in the presence of malonic acid. Pb LIII-edge EXAFS measurements performed in the presence of malonate indicate the presence of both Fe and C neighbors, suggesting that a major fraction of surface-bound malonate is bonded to adsorbed Pb(II). In the absence of Pb(II), ATR-FTIR measurements of sorbed malonate suggest the formation of more than one malonate surface complex. The dissimilarity of the IR spectrum of malonate sorbed on hematite to those for aqueous malonate suggest at least one of the sorbed malonate species is directly coordinated to surface Fe atoms in an inner-sphere mode. In the presence of Pb, little change is seen in the IR spectrum for sorbed malonate, indicating that geometry of malonate as it coordinates to sorbed Pb(II) adions is similar to the geometry of malonate as it coordinates to Fe in the hematite surface. Fits of the raw EXAFS spectra collected from pH 4 to pH 8 result in average Pb-C distances of 2.98 to 3.14 A??, suggesting the presence of both four- and six-membered Pb-malonate rings. The IR results are consistent with this interpretation. Thus, our results suggest that malonate binds to sorbed Pb(II) adions, forming ternary metal-bridging surface complexes. ?? 2001 Academic Press.

Crystal structure of tris­(trans-1,2-cyclo­hexa­ne­diamine-κ2 N,N′)chromium(III) tetra­chlorido­zincate chloride trihydrate from synchrotron data

PubMed Central

Moon, Dohyun; Choi, Jong-Ha

2016-01-01

The structure of the title double salt, [Cr(rac-chxn)3][ZnCl4]Cl·3H2O (chxn is trans-1,2-cyclo­hexa­nedi­amine; C6H14N2), has been determined from synchrotron data. The CrIII ion is coordinated by six N atoms of three chelating chxn ligands, displaying a slightly distorted octa­hedral coordination environment. The distorted tetra­hedral [ZnCl4]2− anion, the isolated Cl− anion and three lattice water mol­ecules remain outside the coordination sphere. The Cr—N(chxn) bond lengths are in a narrow range between 2.0737 (12) and 2.0928 (12) Å; the mean N—Cr—N bite angle is 82.1 (4)°. The crystal packing is stabilized by hydrogen-bonding inter­actions between the amino groups of the chxn ligands and the water mol­ecules as donor groups, and O atoms of the water mol­ecules, chloride anions and Cl atoms of the [ZnCl4]2− anions as acceptor groups, leading to the formation of a three-dimensional network. The [ZnCl4]2− anion is disordered over two sets of sites with an occupancy ratio of 0.94:0.06. PMID:27308016

Versatile chelating behavior of benzil bis(thiosemicarbazone) in zinc, cadmium, and nickel complexes.

PubMed

López-Torres, Elena; Mendiola, Ma Antonia; Pastor, César J; Pérez, Beatriz Souto

2004-08-23

Reactions of benzil bis(thiosemicarbazone), LH(6), with M(NO(3))(2).nH(2)O (M = Zn, Cd, and Ni), in the presence of LiOH.H(2)O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH(4)] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH(6) acts as a N(2)S(2) ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, (1)H, and (13)C NMR spectroscopies and for the cadmium complex by (113)Cd NMR in solution and in the solid state.

Using a motion capture system for spatial localization of EEG electrodes

PubMed Central

Reis, Pedro M. R.; Lochmann, Matthias

2015-01-01

Electroencephalography (EEG) is often used in source analysis studies, in which the locations of cortex regions responsible for a signal are determined. For this to be possible, accurate positions of the electrodes at the scalp surface must be determined, otherwise errors in the source estimation will occur. Today, several methods for acquiring these positions exist but they are often not satisfyingly accurate or take a long time to perform. Therefore, in this paper we describe a method capable of determining the positions accurately and fast. This method uses an infrared light motion capture system (IR-MOCAP) with 8 cameras arranged around a human participant. It acquires 3D coordinates of each electrode and automatically labels them. Each electrode has a small reflector on top of it thus allowing its detection by the cameras. We tested the accuracy of the presented method by acquiring the electrodes positions on a rigid sphere model and comparing these with measurements from computer tomography (CT). The average Euclidean distance between the sphere model CT measurements and the presented method was 1.23 mm with an average standard deviation of 0.51 mm. We also tested the method with a human participant. The measurement was quickly performed and all positions were captured. These results tell that, with this method, it is possible to acquire electrode positions with minimal error and little time effort for the study participants and investigators. PMID:25941468

Green Color Purification in Tb(3+) Ions through Silica Inverse Opal Heterostructure.

PubMed

Shrivastava, Vishnu Prasad; Sivakumar, Sri; Kumar, Jitendra

2015-06-10

The ordered SiO2:Tb(3+) inverse opal heterostructure films are fabricated through polystyrene spheres hetero-opal template using the convective self-assembly method to examine their potential for color purification. Their optical properties and photoluminescence have been investigated and compared with individual single inverse opals and reference (SiO2:Tb(3+) powder). The heterostructures are shown to possess two broad photonic stop bands separated by an effective pass band, causing suppression of blue, orange, and red emission bands corresponding to (5)D4 → (7)F(j); j = 6, 4, 3 transitions, respectively and an enhancement of green emission (i.e., (5)D4 → (7)F5). Although the suppression of various emission occurs because of its overlap with the photonic band gaps (PSBs), the enhancement of green radiation is observed because of its location matching with the pass band region. The Commission International de l'Eclairage (CIE) chromaticity coordinates of the emission spectrum of the heterostructure based on polystyrene sphere of 390 and 500 nm diameter are x = 0.2936, y = 0.6512 and lie closest to those of standard green color (wavelength 545 nm). In addition, a significant increase observed in luminescence lifetime for (5)D4 level of terbium in inverse opal heterostructures vis-à-vis reference (SiO2:Tb(3+) powder) is attributed to the change in the effective refractive index.

Vertical discretization with finite elements for a global hydrostatic model on the cubed sphere

NASA Astrophysics Data System (ADS)

Yi, Tae-Hyeong; Park, Ja-Rin

2017-06-01

A formulation of Galerkin finite element with basis-spline functions on a hybrid sigma-pressure coordinate is presented to discretize the vertical terms of global Eulerian hydrostatic equations employed in a numerical weather prediction system, which is horizontally discretized with high-order spectral elements on a cubed sphere grid. This replaces the vertical discretization of conventional central finite difference that is first-order accurate in non-uniform grids and causes numerical instability in advection-dominant flows. Therefore, a model remains in the framework of Galerkin finite elements for both the horizontal and vertical spatial terms. The basis-spline functions, obtained from the de-Boor algorithm, are employed to derive both the vertical derivative and integral operators, since Eulerian advection terms are involved. These operators are used to discretize the vertical terms of the prognostic and diagnostic equations. To verify the vertical discretization schemes and compare their performance, various two- and three-dimensional idealized cases and a hindcast case with full physics are performed in terms of accuracy and stability. It was shown that the vertical finite element with the cubic basis-spline function is more accurate and stable than that of the vertical finite difference, as indicated by faster residual convergence, fewer statistical errors, and reduction in computational mode. This leads to the general conclusion that the overall performance of a global hydrostatic model might be significantly improved with the vertical finite element.

Electronic Structure of p- and n-Type Doping Impurities in Cubic Gallium Nitride

NASA Astrophysics Data System (ADS)

Pentaleri, E. A.; Gubanov, V. A.; Fong, C. Y.; Klein, B. M.

1996-03-01

LMTO-TB calculations were performed to investigate the electronic structure of C, Be, Mg, Si, Zn, and Cd substitutional impurities in cubic GaN (c-GaN). The calculations used 128-site supercells consisting of 64-atoms. Empty spheres of two types occupied the remaining sites. Semi-core Ga 3d states were treated explicitly as valence states. Both amphoteric substitutions were considered for C and Si impurities, while only cation-site substitutions were considered for Be, Mg, Zn, and Cd. All metal impurities formed partially occupied impurity states at the VB edge, which may result in p-type conductivity. C and Si impurities substituted at anion sites form sharp resonances in the gap, and are inactive in creating either p- or n-type carriers. Likewise, cation-site C substitutions introduce to the middle of the band gap strongly localized states that are inactive in carrier formation. Cation-site Si substitutions form an impurity sub-band at the CB edge, leading to n-type conductivity. The DOS at the Fermi level for each impurity-doped c-GaN crystal is used to estimate the most effective p-type doping impurities. The wave-function composition, space, and energy localization is analyzed for different impurities via projections onto the orbital basis and atomic coordinational spheres, and by examining calculated charge-density distributions.

Eu(III) Complexes of Octadentate 1-Hydroxy-2-pyridinones: Stability and Improved Photophysical Performance[].

PubMed

Moore, Evan G; D'Aléo, Anthony; Xu, Jide; Raymond, Kenneth N

2009-10-13

The luminescence properties of lanthanoid ions can be dramatically enhanced by coupling them to antenna ligands that absorb light in the UV/visible and then efficiently transfer the energy to the lanthanoid center. The synthesis and the complexation of Ln(III) cations (Ln=Eu; Gd) for a ligand based on four 1-hydroxy-2-pyridinone (1,2-HOPO) chelators appended to a ligand backbone derived by linking two L-lysine units (3LI-bis-LYS) is described. This octadentate Eu(III) complex ([Eu(3LI-bis-LYS-1,2-HOPO)](-)) has been evaluated in terms of its thermodynamic stability, UV/visible absorption and luminescence properties. For this complex the conditional stability constant (pM) is 19.9, which is an order of magnitude higher than diethylenetriaminepentacetic acid (DTPA) at pH= 7.4. This Eu(III) complex also shows an almost two-fold increase in its luminescence quantum yield in aqueous solution (pH= 7.4) when compared to other octadentate ligands. Hence, despite a slight decrease of the molar absorption coefficient, a much higher brightness is obtained for [Eu(3LI-bis-LYS-1,2-HOPO)](-). This overall improvement was achieved by saturating the coordination sphere of the Eu(III) cation, yielding an increased metal centered efficiency by excluding solvent water molecules from the metal's inner sphere.

High-accuracy process based on the corrective calibration of removal function in the magnetorheological finishing

NASA Astrophysics Data System (ADS)

Zhong, Xianyun; Fan, Bin; Wu, Fan

2017-08-01

The corrective calibration of the removal function plays an important role in the magnetorheological finishing (MRF) high-accuracy process. This paper mainly investigates the asymmetrical characteristic of the MRF removal function shape and further analyzes its influence on the surface residual error by means of an iteration algorithm and simulations. By comparing the ripple errors and convergence ratios based on the ideal MRF tool function and the deflected tool function, the mathematical models for calibrating the deviation of horizontal and flowing directions are presented. Meanwhile, revised mathematical models for the coordinate transformation of an MRF machine is also established. Furthermore, a Ø140-mm fused silica plane and a Ø196 mm, f/1∶1, fused silica concave sphere samples are taken as the experiments. After two runs, the plane mirror final surface error reaches PV 17.7 nm, RMS 1.75 nm, and the polishing time is 16 min in total; after three runs, the sphere mirror final surfer error reaches RMS 2.7 nm and the polishing time is 70 min in total. The convergence ratios are 96.2% and 93.5%, respectively. The spherical simulation error and the polishing result are almost consistent, which fully validate the efficiency and feasibility of the calibration method of MRF removal function error using for the high-accuracy subaperture optical manufacturing.

Mechanisms of boron removal from hydraulic fracturing wastewater by aluminum electrocoagulation.

PubMed

Sari, Mutiara Ayu; Chellam, Shankararaman

2015-11-15

Boron uptake from highly saline hydraulic fracturing wastewater by freshly precipitated amorphous Al(OH)3 precipitates is due to ligand exchange and complexation with surface hydroxyl groups. Consequently, aluminum electrocoagulation can be a feasible approach to remove boron from flowback/produced water. Actual hydraulic fracturing wastewater containing ∼120mg/L boron from the Eagle Ford shale play was employed. Electrocoagulation was performed over a range of aluminum dosages (0-1350mg/L), pH 6.4 and 8, and high current densities (20-80mA/cm(2)) using a cylindrical aluminum anode encompassed by a porous cylindrical 316-stainless steel cathode. Direct measurements of boron uptake along with its chemical state and coordination were made using Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-Ray Photoelectron Spectroscopy. Boron removal increased monotonically with aluminum dosage and was higher at pH 8, but remained relatively constant at ⩾20mA/cm(2). Chloride ions induced anodic pitting and super-Faradaic (131% efficiency) aluminum dissolution and their electrooxidation produced free chlorine. ATR-FTIR suggested outer-sphere and inner-sphere complexation of trigonal B(OH)3 with Al(OH)3, which was confirmed by the BO bond shifting toward lower binding energies in XPS. Severe AlO interferences precluded evidence for tetrahedral B(OH)4(-) complexation. No evidence for co-precipitation was obtained. Copyright © 2015 Elsevier Inc. All rights reserved.

Colloquium: Toward living matter with colloidal particles

NASA Astrophysics Data System (ADS)

Zeravcic, Zorana; Manoharan, Vinothan N.; Brenner, Michael P.

2017-07-01

A fundamental unsolved problem is to understand the differences between inanimate matter and living matter. Although this question might be framed as philosophical, there are many fundamental and practical reasons to pursue the development of synthetic materials with the properties of living ones. There are three fundamental properties of living materials that we seek to reproduce: The ability to spontaneously assemble complex structures, the ability to self-replicate, and the ability to perform complex and coordinated reactions that enable transformations impossible to realize if a single structure acted alone. The conditions that are required for a synthetic material to have these properties are currently unknown. This Colloquium examines whether these phenomena could emerge by programming interactions between colloidal particles, an approach that bootstraps off of recent advances in DNA nanotechnology and in the mathematics of sphere packings. The argument is made that the essential properties of living matter could emerge from colloidal interactions that are specific—so that each particle can be programmed to bind or not bind to any other particle—and also time dependent—so that the binding strength between two particles could increase or decrease in time at a controlled rate. There is a small regime of interaction parameters that gives rise to colloidal particles with lifelike properties, including self-assembly, self-replication, and metabolism. The parameter range for these phenomena can be identified using a combinatorial search over the set of known sphere packings.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors.

PubMed

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J; Mijowska, Ewa

2012-05-29

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

NASA Astrophysics Data System (ADS)

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J.; Mijowska, Ewa

2012-05-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Anti-gravity device

NASA Technical Reports Server (NTRS)

Palsingh, S. (Inventor)

1975-01-01

An educational toy useful in demonstrating fundamental concepts regarding the laws of gravity is described. The device comprises a sphere 10 of radius r resting on top of sphere 12 of radius R. The center of gravity of sphere 10 is displaced from its geometrical center by distance D. The dimensions are so related that D((R+r)/r) is greater than r. With the center of gravity of sphere 10 lying on a vertical line, the device is in equilibrium. When sphere 10 is rolled on the surface of sphere 12 it will return to its equilibrium position upon release. This creates an illusion that sphere 10 is defying the laws of gravity. In reality, due to the above noted relationship of D, R, and r, the center of gravity of sphere 10 rises from its equilibrium position as it rolls a short distance up or down the surface of sphere 12.

CMM Interim Check Design of Experiments (U)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montano, Joshua Daniel

2015-07-29

Coordinate Measuring Machines (CMM) are widely used in industry, throughout the Nuclear Weapons Complex and at Los Alamos National Laboratory (LANL) to verify part conformance to design definition. Calibration cycles for CMMs at LANL are predominantly one year in length and include a weekly interim check to reduce risk. The CMM interim check makes use of Renishaw’s Machine Checking Gauge which is an off-the-shelf product simulates a large sphere within a CMM’s measurement volume and allows for error estimation. As verification on the interim check process a design of experiments investigation was proposed to test a couple of key factorsmore » (location and inspector). The results from the two-factor factorial experiment proved that location influenced results more than the inspector or interaction.« less

PDB-NMA of a protein homodimer reproduces distinct experimental motility asymmetry.

PubMed

Tirion, Monique M; Ben-Avraham, Daniel

2018-01-16

We have extended our analytically derived PDB-NMA formulation, Atomic Torsional Modal Analysis or ATMAN (Tirion and ben-Avraham 2015 Phys. Rev. E 91 032712), to include protein dimers using mixed internal and Cartesian coordinates. A test case on a 1.3 [Formula: see text] resolution model of a small homodimer, ActVA-ORF6, consisting of two 112-residue subunits identically folded in a compact 50 [Formula: see text] sphere, reproduces the distinct experimental Debye-Waller motility asymmetry for the two chains, demonstrating that structure sensitively selects vibrational signatures. The vibrational analysis of this PDB entry, together with biochemical and crystallographic data, demonstrates the cooperative nature of the dimeric interaction of the two subunits and suggests a mechanical model for subunit interconversion during the catalytic cycle.

Near-neighbor mixing and bond dilation in mechanically alloyed Cu-Fe

NASA Astrophysics Data System (ADS)

Harris, V. G.; Kemner, K. M.; Das, B. N.; Koon, N. C.; Ehrlich, A. E.; Kirkland, J. P.; Woicik, J. C.; Crespo, P.; Hernando, A.; Garcia Escorial, A.

1996-09-01

Extended x-ray-absorption fine-structure (EXAFS) measurements were used to obtain element-specific, structural, and chemical information of the local environments around Cu and Fe atoms in high-energy ball-milled CuxFe1-x samples (x=0.50 and 0.70). Analysis of the EXAFS data shows both Fe and Cu atoms reside in face-centered-cubic sites where the first coordination sphere consists of a mixture of Fe and Cu atoms in a ratio which reflects the as-prepared stoichiometry. The measured bond distances indicate a dilation in the bonds between unlike neighbors which accounts for the lattice expansion measured by x-ray diffraction. These results indicate that metastable alloys having a positive heat of mixing can be prepared via the high-energy ball-milling process.

PDB-NMA of a protein homodimer reproduces distinct experimental motility asymmetry

NASA Astrophysics Data System (ADS)

Tirion, Monique M.; ben-Avraham, Daniel

2018-03-01

We have extended our analytically derived PDB-NMA formulation, Atomic Torsional Modal Analysis or ATMAN (Tirion and ben-Avraham 2015 Phys. Rev. E 91 032712), to include protein dimers using mixed internal and Cartesian coordinates. A test case on a 1.3 {\\mathringA} resolution model of a small homodimer, ActVA-ORF6, consisting of two 112-residue subunits identically folded in a compact 50 {\\mathringA} sphere, reproduces the distinct experimental Debye-Waller motility asymmetry for the two chains, demonstrating that structure sensitively selects vibrational signatures. The vibrational analysis of this PDB entry, together with biochemical and crystallographic data, demonstrates the cooperative nature of the dimeric interaction of the two subunits and suggests a mechanical model for subunit interconversion during the catalytic cycle.

Navigation system for flexible endoscopes

NASA Astrophysics Data System (ADS)

Hummel, Johann; Figl, Michael; Birkfellner, Wolfgang; Häfner, Michael; Kollmann, Christian; Bergmann, Helmar

2003-05-01

Endoscopic Ultrasound (EUS) features flexible endoscopes equipped with a radial or linear array scanhead allowing high resolution examination of organs adjacent to the upper gastrointestinal tract. An optical system based on fibre-glass or a CCD-chip allows additional orientation. However, 3-dimensional orientation and correct identification of the various anatomical structures may be difficult. It therefore seems desirable to merge real-time US images with high resolution CT or MR images acquired prior to EUS to simplify navigation during the intervention. The additional information provided by CT or MR images might facilitate diagnosis of tumors and, ultimately, guided puncture of suspicious lesions. We built a grid with 15 plastic spheres and measured their positions relatively to five fiducial markers placed on the top of the grid. For this measurement we used an optical tracking system (OTS) (Polaris, NDI, Can). Two sensors of an electromagnetic tracking system (EMTS) (Aurora, NDI, Can) were mounted on a flexible endoscope (Pentax GG 38 UX, USA) to enable a free hand ultrasound calibration. To determine the position of the plastic spheres in the emitter coordinate system of the EMTS we applied a point-to-point registration (Horn) using the coordinates of the fiducial markers in both coordinate systems (OTS and EMTS). For the transformation between EMTS to the CT space the Horn algorithm was adopted again using the fiducial markers. Visualization was enabled by the use of the AVW-4.0 library (Biomedical Imaging Resource, Mayo Clinic, Rochester/MN, USA). To evaluate the suitability of our new navigation system we measured the Fiducial Registration Error (FRE) of the diverse registrations and the Target Registration Error (TRE) for the complete transformation from the US space to the CT space. The FRE for the ultrasound calibration amounted to 4.3 mm +/- 4.2 mm, resulting from 10 calibration procedures. For the transformation from the OTS reference system to the EMTS emitter space we found an average FRE of 0.8 mm +/- 0.2 mm. The FRE for the CT registration was 1.0 mm +/- 0.3 mm. The TRE was found to be 3.8 mm +/- 1.3 mm if we target the same spheres which where used for the calibration procedure. A movement of the phantom results in higher TREs because of the orientation sensitivity of the sensor. In that case the TRE in the area where the biopsy is supposed to be taken place was found to be 7.9 mm +/- 3.2 mm. Our system provides the interventionist with additional information about position and orientation of the used flexible instrument. Additionally, it improves the marksmanship of biopsies. The use of the miniaturized EMTS enables for the first time the navigation of flexible instruments in this way. For the successful application of navigation systems in interventional radiology, an accuracy in the range of 5 mm is desirable. The accuracy of the localization of a point in CT space are just 3 mm too high as required. One of the possibilities to overcome this difference is to mount the two sensors in such a way that the interference of their electromagnetic fields is minimized. A considerable restraint constitutes the small characteristic volume (360mm x 600mm x 600mm), which requires for most application an additional optical system.

Intercomparison of General Circulation Models for Hot Extrasolar Planet Atmospheres

NASA Astrophysics Data System (ADS)

Cho, James

2013-11-01

In this collaborative work with I. Polichtchouk, C. Watkins, H. Th. Thrastarson, O. M. Umurhan, and M. de la Torre-Juárez, we compare five general circulation models (GCMs) which have been recently used to study hot extrasolar planet atmospheres (BOB, CAM, IGCM, MITgcm, and PEQMOD), under three test cases useful for assessing model convergence and accuracy. Such a broad, detailed intercomparison has not been performed thus far for extrasolar planets study. The models considered all solve the traditional primitive equations, but employ different numerical algorithms or grids (e.g., pseudospectral and finite volume, with the latter separately in longitude-latitude and ``cubed-sphere'' grids). The test cases are chosen to cleanly address specific aspects of the behaviors typically reported in hot extrasolar planet simulations: 1) steady-state, 2) nonlinearly evolving baroclinic wave, and 3) response to fast timescale thermal relaxation. When initialized with a steady jet, all models maintain the steadiness, as they should--except MITgcm in cubed-sphere grid. A very good agreement is obtained for a baroclinic wave evolving from an initial instability in spectral models (only). However, exact numerical convergence is still not achieved across the spectral models: amplitudes and phases are observably different. When subject to a typical ``hot-Jupiter''-like forcing, all five models show quantitatively different behavior--although qualitatively similar, time-variable, quadrupole-dominated flows are produced. Hence, as have been advocated in several past studies, specific quantitative predictions (such as the location of large vortices and hot regions) by GCMs should be viewed with caution. Overall, in the tests considered here, spectral models in pressure coordinate (PEBOB and PEQMOD) perform the best and MITgcm in cubed-sphere grid performs the worst. This work has been supported by the Science and Technology Facilities Council, Westfield Small Grant, NASA Postdoctoral Program, and Institute for Theory and Computation, Harvard College Observatory.

An Unusual Rolling-Sphere Phenomenon.

ERIC Educational Resources Information Center

Cromer, Alan

1996-01-01

Discusses the theory behind a study of motion where a hollow plastic sphere racing against a steel sphere in two parallel sections of inclined channeling always reaches the bottom first; once on the floor, however, the steel sphere travels faster, speeding past the plastic sphere when both are about one meter from the base of the track. (JRH)

Porous Ceramic Spheres From Cation Exchange Beads

NASA Technical Reports Server (NTRS)

Dynys, Fred

2005-01-01

This document is a slide presentation that examines the use of a simple templating process to produce hollow ceramic spheres with a pore size of 1 to 10 microns. Using ion exchange process it was determined that the method produces porous ceramic spheres with a unique structure: (i.e., inner sphere surrounded by an outer sphere.)

Finite-size radiation force correction for inviscid spheres in standing waves.

PubMed

Marston, Philip L

2017-09-01

Yosioka and Kawasima gave a widely used approximation for the acoustic radiation force on small liquid spheres surrounded by an immiscible liquid in 1955. Considering the liquids to be inviscid with negligible thermal dissipation, in their approximation the force on the sphere is proportional to the sphere's volume and the levitation position in a vertical standing wave becomes independent of the size. The analysis given here introduces a small correction term proportional to the square of the sphere's radius relative to the aforementioned small-sphere force. The significance of this term also depends on the relative density and sound velocity of the sphere. The improved approximation is supported by comparison with the exact partial-wave-series based radiation force for ideal fluid spheres in ideal fluids.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

PubMed Central

2012-01-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors. PMID:22643113

Dispersivity of Bidisperse Packings of Spheres and Evidence for Distinct Random Structures

NASA Astrophysics Data System (ADS)

Scheven, U. M.

2018-05-01

The intrinsic longitudinal and transverse dispersivity of bidisperse random packings of spheres with size ratio 5 ∶1 was determined by pulsed field gradient nuclear magnetic resonance, in the dilute regime where small spheres occupy between 0% and 5% of the packings' volume. Small spheres plugging pores systematically raise the mechanical transverse and longitudinal dispersivity above that of reference packings of monodisperse spheres. NMR-derived porosities, widths of velocity distributions, and dispersivities reveal distinct states of structural disorder above and below a relative sphere concentration n /N =1 , where n and N are the number densities of small and large spheres.

Biomolecule-assisted construction of cadmium sulfide hollow spheres with structure-dependent photocatalytic activity.

PubMed

Wei, Chengzhen; Zang, Wenzhe; Yin, Jingzhou; Lu, Qingyi; Chen, Qun; Liu, Rongmei; Gao, Feng

2013-02-25

In this study, we report the synthesis of monodispersive solid and hollow CdS spheres with structure-dependent photocatalytic abilities for dye photodegradation. The monodispersive CdS nanospheres were constructed with the assistance of the soulcarboxymthyi chitosan biopolymer under hydrothermal conditions. The solid CdS spheres were corroded by ammonia to form hollow CdS nanospheres through a dissolution-reprecipitation mechanism. Their visible-light photocatalytic activities were investigated, and the results show that both the solid and the hollow CdS spheres have visible-light photocatalytic abilities for the photodegradation of dyes. The photocatalytic properties of the CdS spheres were demonstrated to be structure dependent. Although the nanoparticles comprising the hollow spheres have larger sizes than those comprising the solid spheres, the hollow CdS spheres have better photocatalytic performances than the solid CdS spheres, which can be attributed to the special hollow structure. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microwave-Assisted Solvothermal Synthesis of VO2 Hollow Spheres and Their Conversion into V2O5 Hollow Spheres with Improved Lithium Storage Capability.

PubMed

Pan, Jing; Zhong, Li; Li, Ming; Luo, Yuanyuan; Li, Guanghai

2016-01-22

Monodispersed hierarchically structured V2O5 hollow spheres were successfully obtained from orthorhombic VO2 hollow spheres, which are in turn synthesized by a simple template-free microwave-assisted solvothermal method. The structural evolution of VO2 hollow spheres has been studied and explained by a chemically induced self-transformation process. The reaction time and water content in the reaction solution have a great influence on the morphology and phase structure of the resulting products in the solvothermal reaction. The diameter of the VO2 hollow spheres can be regulated simply by changing vanadium ion content in the reaction solution. The VO2 hollow spheres can be transformed into V2O5 hollow spheres with nearly no morphological change by annealing in air. The nanorods composed of V2O5 hollow spheres have an average length of about 70 nm and width of about 19 nm. When used as a cathode material for lithium-ion batteries, the V2O5 hollow spheres display a diameter-dependent electrochemical performance, and the 440 nm hollow spheres show the highest specific discharge capacity of 377.5 mAhg(-1) at a current density of 50 mAg(-1) , and are better than the corresponding solid spheres and nanorod assemblies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Triassico: A Sphere Positioning System for Surface Studies with IBA Techniques

NASA Astrophysics Data System (ADS)

Fontana, Cristiano L.; Doyle, Barney L.

We propose here a novel device, called the Triassico, to microscopically study the entire surface of millimeter-sized spheres. The sphere dimensions can be as small as 1 mm, and the upper limit defined only by the power and by the mechanical characteristics of the motors used. Three motorized driving rods are arranged so an equilateral triangle is formed by the rod's axes, on such a triangle the sphere sits. Movement is achieved by rotating the rods with precise relative speeds and by exploiting the friction between the sphere and the rods surfaces. The sphere can be held in place by gravity or by an opposing trio of rods. By rotating the rods with specific relative angular velocities, a net torque can be exerted on the sphere which then rotates. No repositioning of the sphere or of the motors is needed to cover the full surface with the investigating tools. An algorithm was developed to position the sphere at any arbitrary polar and azimuthal angle. The algorithm minimizes the number of rotations needed by the rods, in order to efficiently select a particular position on the sphere surface. A prototype Triassico was developed for the National Ignition Facility, of the Lawrence Livermore National Laboratory (Livermore, California, USA), as a sphere manipulation apparatus for ion microbeam analysis at Sandia National Laboratories (Albuquerque, NM, USA) of Xe-doped DT inertial confinement fusion fuel spheres. Other applications span from samples orientation, ball bearing manufacturing, or jewelry.

Porous Si spheres encapsulated in carbon shells with enhanced anodic performance in lithium-ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hui; Wu, Ping, E-mail: zjuwuping@njnu.edu.cn; Shi, Huimin

2014-07-01

Highlights: • In situ magnesiothermic reduction route for the formation of porous Si@C spheres. • Unique microstructural characteristics of both porous sphere and carbon matrix. • Enhanced anodic performance in term of cycling stability for lithium-ion batteries. - Abstract: A novel type of porous Si–C micro/nano-hybrids, i.e., porous Si spheres encapsulated in carbon shells (porous Si@C spheres), has been constructed through the pyrolysis of polyvinylidene fluoride (PVDF) and subsequent magnesiothermic reduction methodology by using SiO{sub 2} spheres as precursors. The as-synthesized porous Si@C spheres have been applied as anode materials for lithium-ion batteries (LIBs), and exhibit enhanced anodic performance inmore » term of cycling stability compared with bare Si spheres. For example, the porous Si@C spheres are able to exhibit a high reversible capacity of 900.0 mA h g{sup −1} after 20 cycles at a current density of 0.05 C (1 C = 4200 mA g{sup −1}), which is much higher than that of bare Si spheres (430.7 mA h g{sup −1})« less

Second-Sphere Effects in Dinuclear FeIIIZnII Hydrolase Biomimetics: Tuning Binding and Reactivity Properties.

PubMed

Camargo, Tiago Pacheco; Neves, Ademir; Peralta, Rosely A; Chaves, Cláudia; Maia, Elene C P; Lizarazo-Jaimes, Edgar H; Gomes, Dawidson A; Bortolotto, Tiago; Norberto, Douglas R; Terenzi, Hernán; Tierney, David L; Schenk, Gerhard

2018-01-02

Herein, we report the synthesis and characterization of two dinuclear Fe III Zn II complexes [Fe III Zn II LP1] (1) and [Fe III Zn II LP2] (2), in which LP1 and LP2 are conjugated systems containing one and two pyrene groups, respectively, connected via the diamine -HN(CH 2 ) 4 NH- spacer to the well-known N 5 O 2 -donor H 2 L ligand (H 2 L = 2-bis{[(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl}-4-methylphenol). The complex [Fe III Zn II L1] (3), in which H 2 L was modified to H 2 L1, with a carbonyl group attached to the terminal phenol group, was included in this study for comparison purposes. 1 Both complexes 1 and 2 were satisfactorily characterized in the solid state and in solution. Extended X-ray absorption fine structure data for 1 and 3 in an acetonitrile solution show that the multiply bridged structure seen in the solid state of 3 is retained in solution. Potentiometric and UV-vis titration of 1 and 2 show that electrostatic interaction between the protonated amino groups and coordinated water molecules significantly decreases the pK a of the iron(III)-bound water compared to those of 3. On the other hand, catalytic activity studies using 1 and 2 in the hydrolysis of the activated substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) resulted in a significant increase in the association of the substrate (K ass ≅ 1/K M ) compared to that of 3 because of electrostatic and hydrophobic interactions between BDNPP and the side-chain diaminopyrene of the ligands H 2 LP1 and H 2 LP2. In addition, the introduction of the pyrene motifs in 1 and 2 enhanced their activity toward DNA and as effective antitumor drugs, although the biochemical mechanism of the latter effect is currently under investigation. These complexes represent interesting examples of how to promote an increase in the activity of traditional artificial metal nucleases by introducing second-coordination-sphere effects.

Evaluating the role of acidic, basic, and polar amino acids and dipeptides on a molecular electrocatalyst for H 2 oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boralugodage, Nilusha Priyadarshani; Arachchige, Rajith Jayasingha; Dutta, Arnab

Amino acids and peptides have been shown to have a significant influence on the H2 production and oxidation reactivity of Ni(P R 2N R’ 2) 2, where P R 2N R’ 2 = 1,5-diaza-3,7-diphosphacyclooctane, R is either phenyl (Ph) or cyclohexyl (Cy), and R’ is either an amino acid or peptide. Most recently, the Ni(P Cy 2Naminoacid 2) 2 complexes (CyAA) have shown enhanced H 2 oxidation rates, water solubility, and in the case of arginine (CyArg) and phenylalanine (CyPhe), electrocatalytic reversibility. Both the backbone –COOH and side chain interactions were shown to be critical to catalytic performance. Here wemore » further investigate the roles of the outer coordination sphere by evaluating amino acids with acidic, basic, and hydrophilic side chains, as well as dipeptides which combine multiple successful features from previous complexes. Six new complexes were prepared, three containing single amino acids: aspartic acid (CyAsp), lysine (CyLys), and serine (CySer) and three containing dipeptides: glycine-phenylalanine (Cy(GlyPhe)), phenylalanine-glycine (Cy(PheGly)), and aspartic acid-phenylananine (Cy(AspPhe)). The resulting catalytic performance demonstrates that complexes need both interactions between side chain and –COOH groups for fast, efficient catalysis. The fastest of all of the catalysts, Cy(AspPhe), had both of these features, while the other dipeptide complexes with an amide replacing the -COOH were both slower; however, the amide group was demonstrated to participate in the proton pathway when side chain interactions are present to position it. Both the hydrophilic and basic side chains, notably lacking in side chain interactions, significantly increased the overpotential, with only modest increases in TOF. Of all of the complexes, only CyAsp was reversible at room temperature, and only in water, the first of these complexes to demonstrate room temperature reversibility in water. These results continue to provide and solidify design rules for controlling reactivity and efficiency of Ni(P 2N 2) 2 complexes with the outer coordination sphere.« less

Axial zero-field splitting in mononuclear Co(ii) 2-N substituted N-confused porphyrin: Co(2-NC3H5-21-Y-CH2C6H4CH3-NCTPP)Cl (Y = o, m, p) and Co(2-NC3H5-21-CH2C6H5-NCTPP)Cl.

PubMed

Lai, Ya-Yuan; Chang, Yu-Chang; Chen, Jyh-Horung; Wang, Shin-Shin; Tung, Jo-Yu

2016-03-21

The inner C-benzyl- and C-o-xylyl (or m-xylyl, p-xylyl)-substituted cobalt(ii) complexes of a 2-N-substituted N-confused porphyrin were synthesized from the reaction of 2-NC3H5NCTPPH (1) and CoCl2·6H2O in toluene (or o-xylene, m-xylene, p-xylene). The crystal structures of diamagnetic chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-hydrogen-21-carbaporphyrinato-N,N',N'')zinc(ii) [Zn(2-NC3H5-21-H-NCTPP)Cl; 3 ] and paramagnetic chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-benzyl-21-carbaporphyrinato-N,N',N'')cobalt(ii) [Co(2-NC3H5-21-CH2C6H5NCTPP)Cl; 7], and chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-Y-xylyl-21-carbaporphyrinato-N,N',N'')cobalt(ii) [Co(2-NC3H5-21-Y-CH2C6H4CH3NCTPP)Cl] [Y = o (8), m (9), p (10)] were determined. The coordination sphere around the Zn(2+) (or Co(2+)) ion in 3 (or 7-10) is a distorted tetrahedron (DT). The free energy of activation at the coalescence temperature Tc for the exchange of phenyl ortho protons o-H (26) with o-H (22) in 3 in a CDCl3 solvent is found to be ΔG = 61.4 kJ mol(-1) through (1)H NMR temperature-dependent measurements. The axial zero-field splitting parameter |D| was found to vary from 35.6 cm(-1) in 7 (or 30.7 cm(-1) in 8) to 42.0 cm(-1) in 9 and 46.9 cm(-1) in 10 through paramagnetic susceptibility measurements. The magnitude of |D| can be related to the coordination sphere at the cobalt sites.

Secondary coordination sphere interactions within the biomimetic iron azadithiolate complexes related to Fe-only hydrogenase: dynamic measure of electron density about the Fe sites.

PubMed

Liu, Yu-Chiao; Tu, Ling-Kuang; Yen, Tao-Hung; Lee, Gene-Hsiang; Yang, Shu-Ting; Chiang, Ming-Hsi

2010-07-19

A series of iron azadithiolate complexes possessing an intramolecular secondary coordination sphere interaction and an ability to reduce HOAc at the potential near the first electron-transfer process are reported. A unique structural feature in which the aza nitrogen has its lone pair point toward the apical carbonyl carbon is observed in [Fe(2)(mu-S(CH(2))(2)NR(CH(2))(2)S)(CO)(6-x)L(x)](2) (R = (n)Pr, x = 0, 1a; R = (i)Pr, x = 0, 1b; R = (n)Pr, L = PPh(3), x = 1, 2; R = (n)Pr, L = P(n)Bu(3), x = 1, 3) as biomimetic models of the active site of Fe-only hydrogenase. The presence of this weak N...C(CO(ap)) interaction provides electronic perturbation at the Fe center. The distance of the N...C(CO(ap)) contact is 3.497 A in 1a. It increases by 0.455 A in 2 when electronic density of the Fe site is slightly enriched by a weak sigma-donating ligand, PPh(3). A longer distance (4.040 A) is observed for the P(n)Bu(3) derivative, 3. This N...C(CO(ap)) distance is thus a dynamic measure of electronic nature of the Fe(2) core. Variation of electronic richness within the Fe(2) moiety among the complexes reflects on their electrochemical response. Reduction of 2 is recorded at the potential of -2.17 V, which is 270 mV more negative than that of 1. Complex 3 requires additional 150 mV for the same reduction. Such cathodic shift results from CO substitution by phosphines. Electrocatalytic hydrogen production from HOAc by both kinds of complexes (all-CO and phosphine-substituted species) requires the potential close to that for reduction of the parent molecules in the absence of acids. The catalytic mechanism of 1a is proposed to involve proton uptake at the Fe(0)Fe(I) redox level instead of the Fe(0)Fe(0) level. This result is the first observation among the all-CO complexes with respect to electrocatalysis of HOAc.

Comparison of NiS2 and α-NiS hollow spheres for supercapacitors, non-enzymatic glucose sensors and water treatment.

PubMed

Wei, Chengzhen; Cheng, Cheng; Cheng, Yanyan; Wang, Yan; Xu, Yazhou; Du, Weimin; Pang, Huan

2015-10-21

NiS2 hollow spheres are successfully prepared by a one-step template free method. Meanwhile, α-NiS hollow spheres can also be synthesized via the calcination of the pre-obtained NiS2 hollow spheres at 400 °C for 1 h in air. The electrochemical performances of the as-prepared NiS2 and α-NiS hollow sphere products are evaluated. When used for supercapacitors, compared with NiS2 hollow spheres, the α-NiS hollow sphere electrode shows a large specific capacitance of 717.3 F g(-1) at 0.6 A g(-1) and a good cycle life. Furthermore, NiS2 and α-NiS hollow spheres are successfully applied to fabricate non-enzymatic glucose sensors. In particular, the α-NiS hollow spheres exhibit good catalytic activity for the oxidation of glucose, a fast amperometric response time of less than 5 s, and the detection limit is estimated to be 0.08 μM. More importantly, compared with other normally co-existing interfering species, such as ascorbic acid, uric acid and dopamine, the electrode modified with α-NiS hollow spheres shows good selectivity. Moreover, the α-NiS hollow spheres also present good capacity to remove Congo red organic pollutants from wastewater by their surface adsorption ability.

Interaction of a shock wave with multiple spheres suspended in different arrangements

NASA Astrophysics Data System (ADS)

Zhang, Li-Te; Sui, Zhen-Zhen; Shi, Hong-Hui

2018-03-01

In this study, the unsteady drag force, Fd, drag coefficient, Cd, and the relevant dynamic behaviors of waves caused by the interaction between a planar incident shock wave and a multi-sphere model are investigated by using imbedded accelerometers and a high-speed Schlieren system. The shock wave is produced in a horizontal 200 mm inner diameter circular shock tube with a 2000 mm × 200 mm × 200 mm transparent test section. The time history of Cd is obtained based on band-block and low-pass Fast Fourier Transformation filtering combined with Savitzky-Golay polynomial smoothing for the measured acceleration. The effects of shock Mach number, Ms, geometry of multi-sphere model, nondimensional distance between sphere centers, H, and channel blockage are analyzed. We find that all time histories of Cd have a similar double-peak shaped main structure. It is due to wave reflection, diffraction, interference, and convergence at different positions of the spheres. The peak Fd increases, whereas the peak Cd decreases monotonically with increasing Ms. The increase of shock strength due to shock focusing by upstream spheres increases the peak Fd of downstream spheres. Both the increase in sphere number and the decrease in distance between spheres promote wave interference between neighboring spheres. As long as the wave interference times are shorter than the peak times, the peak Fd and Cd are higher compared to a single sphere.

The effect of disorder of small spheres on the photonic properties of the inverse binary NaCl-like structure

NASA Astrophysics Data System (ADS)

Pattabhiraman, Harini; Dijkstra, Marjolein

2017-09-01

Inverse opal structures are experimentally realisable photonic band gap materials. They suffer from the drawback of possessing band gaps that are extremely susceptible to structural disorders. A binary colloidal NaCl lattice, which is also experimentally realisable, is a promising alternative to these opals. In this work, we systematically analyse the effect of structural disorder of the small spheres on the photonic properties of an inverse binary NaCl lattice with a size ratio of 0.30 between the small and large spheres. The types of structural disorders studied include the position of the small spheres in the octahedral void of the large spheres, polydispersity in size of the small spheres, and the fraction of small spheres in the crystal. We find a low susceptibility of the band gap of the inverse NaCl lattice to the disorder of the small spheres.

Identification of tumor-initiating cells derived from two canine rhabdomyosarcoma cell lines

PubMed Central

KISHIMOTO, Takuya Evan; YASHIMA, Shoko; NAKAHIRA, Rei; ONOZAWA, Eri; AZAKAMI, Daigo; UJIKE, Makoto; OCHIAI, Kazuhiko; ISHIWATA, Toshiyuki; TAKAHASHI, Kimimasa; MICHISHITA, Masaki

2017-01-01

Cancer stem cells or tumor-initiating cells (TICs) are a small subpopulation of cells that have the capacity to self-renew, differentiate and initiate tumors. These cells may function in tumor initiation, aggression and recurrence. Whether spheres derived from canine rhabdomyosarcoma cells have stem cell-like properties is unclear. We induced sphere formation in the canine rhabdomyosarcoma cell lines, CMS-C and CMS-J, and characterized the spheres in vitro and in vivo. Sphere-forming cells were more resistant to vincristine, mitoxantrone and doxorubicin than adherent cells. Xenograft transplantation demonstrated that 1 × 103 sphere-forming cells derived from CMS-C were sufficient for tumor formation. The sphere assay showed that the sphere-forming cells were present in these tumors. These results suggest that the spheres derived from canine rhabdomyosarcoma cells may possess characteristics of TICs. This study provides the foundation for elucidating the contribution of TICs to rhabdomyosarcoma tumorigenesis. PMID:28529244

Identification of tumor-initiating cells derived from two canine rhabdomyosarcoma cell lines.

PubMed

Kishimoto, Takuya Evan; Yashima, Shoko; Nakahira, Rei; Onozawa, Eri; Azakami, Daigo; Ujike, Makoto; Ochiai, Kazuhiko; Ishiwata, Toshiyuki; Takahashi, Kimimasa; Michishita, Masaki

2017-07-07

Cancer stem cells or tumor-initiating cells (TICs) are a small subpopulation of cells that have the capacity to self-renew, differentiate and initiate tumors. These cells may function in tumor initiation, aggression and recurrence. Whether spheres derived from canine rhabdomyosarcoma cells have stem cell-like properties is unclear. We induced sphere formation in the canine rhabdomyosarcoma cell lines, CMS-C and CMS-J, and characterized the spheres in vitro and in vivo. Sphere-forming cells were more resistant to vincristine, mitoxantrone and doxorubicin than adherent cells. Xenograft transplantation demonstrated that 1 × 10 3 sphere-forming cells derived from CMS-C were sufficient for tumor formation. The sphere assay showed that the sphere-forming cells were present in these tumors. These results suggest that the spheres derived from canine rhabdomyosarcoma cells may possess characteristics of TICs. This study provides the foundation for elucidating the contribution of TICs to rhabdomyosarcoma tumorigenesis.

Specific surface area of overlapping spheres in the presence of obstructions

NASA Astrophysics Data System (ADS)

Jenkins, D. R.

2013-02-01

This study considers the random placement of uniform sized spheres, which may overlap, in the presence of another set of randomly placed (hard) spheres, which do not overlap. The overlapping spheres do not intersect the hard spheres. It is shown that the specific surface area of the collection of overlapping spheres is affected by the hard spheres, such that there is a minimum in the specific surface area as a function of the relative size of the two sets of spheres. The occurrence of the minimum is explained in terms of the break-up of pore connectivity. The configuration can be considered to be a simple model of the structure of a porous composite material. In particular, the overlapping particles represent voids while the hard particles represent fillers. Example materials are pervious concrete, metallurgical coke, ice cream, and polymer composites. We also show how the material properties of such composites are affected by the void structure.

Specific surface area of overlapping spheres in the presence of obstructions.

PubMed

Jenkins, D R

2013-02-21

This study considers the random placement of uniform sized spheres, which may overlap, in the presence of another set of randomly placed (hard) spheres, which do not overlap. The overlapping spheres do not intersect the hard spheres. It is shown that the specific surface area of the collection of overlapping spheres is affected by the hard spheres, such that there is a minimum in the specific surface area as a function of the relative size of the two sets of spheres. The occurrence of the minimum is explained in terms of the break-up of pore connectivity. The configuration can be considered to be a simple model of the structure of a porous composite material. In particular, the overlapping particles represent voids while the hard particles represent fillers. Example materials are pervious concrete, metallurgical coke, ice cream, and polymer composites. We also show how the material properties of such composites are affected by the void structure.

Generating perfect fluid spheres in general relativity

NASA Astrophysics Data System (ADS)

Boonserm, Petarpa; Visser, Matt; Weinfurtner, Silke

2005-06-01

Ever since Karl Schwarzschild’s 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star—a static spherically symmetric blob of fluid with position-independent density—the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres.

In vitro and in vivo study of the application of volvox spheres to co-culture vehicles in liver tissue engineering.

PubMed

Chang, Siou Han; Huang, Han Hsiang; Kang, Pei Leun; Wu, Yu Chian; Chang, Ming-Huang; Kuo, Shyh Ming

2017-11-01

Volvox sphere is a biomimetic concept of a natural Volvox, wherein a large outer sphere contains smaller inner spheres, which can encapsulate cells and provide a double-layer three-dimensional environment for culturing cells. This study simultaneously encapsulated rat mesenchymal stem cells (MSCs) and AML12 hepatocytes in volvox spheres and extensively evaluated the effects of various culturing modes on cell functions and fates. The results showed that compared with a static flask culture, MSCs encapsulated in volvox spheres differentiated into hepatocyte-like cells with a 2-fold increase in albumin (ALB) expression and a 2.5-fold increase in cytokeratin 18 expression in a dynamic bioreactor. Moreover, the restorative effects of volvox spheres encapsulating cells on retrorsine-exposed CCl 4 -induced liver injuries in rats were evaluated. The data presented significant reductions in AST and ALT levels after the implantation of volvox spheres encapsulating both MSCs and AML12 hepatocytes in vivo. In contrast to the negative control group, histopathological analysis demonstrated liver repair and formation of the new liver tissue in groups implanted with volvox spheres containing cells. These results demonstrate that liver cells implanted with volvox spheres encapsulating both MSCs and AML12 hepatocytes promote liver repair and liver tissue regeneration in liver failure caused by necrotizing agents such as retrorsine and CCl 4 . Hence, volvox spheres encapsulating MSCs and liver cells can be a promising and clinically effective therapy for liver injury. In this study, we used a volvox sphere, which is a unique design that mimics the natural Volvox, that consists of a large outer sphere that contains smaller inner spheres, which provide a three-dimensional environment to culture cells. The purpose of this study is to co-culture mesenchymal stem cells (MSCs) and AML12 liver cells in volvox spheres and evaluate two different culture methods, dynamic bioreactor and static culture flask,on the cultured cells. In addition, we aimed to evaluate the restorative effects of volvox spheres encapsulating MSCs and/or AML12 liver cells on rats with retrorsine-exposed CCl 4 -induced liver injuries. The results showed that MSCs encapsulated in volvox spheres differentiated into hepatocyte-like cells with a 2-fold increase in albumin expression and a 2.5-fold increase in cytokeratin 18 expression ina dynamic bioreactor. Moreover, the data presented significant reductions in AST and ALT levels after the implantation of volvox spheres encapsulating both MSCs and AML12 hepatocytes in vivo. In contrast to the negative control group, histopathological analysis demonstrated liver repair and formation of new liver tissue in groups implanted with volvox spheres containing cells. These results demonstrate that liver cells implanted with volvox spheres encapsulating both MSCs and AML12 hepatocytes promote liver repair and liver tissue regeneration in liver failure caused by necrotizing agents such as retrorsine and CCl 4 . Hence, volvox spheres encapsulating MSCs and liver cells can be a promising and clinically effective therapy for liver injury. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sphericity determination using resonant ultrasound spectroscopy

DOEpatents

Dixon, Raymond D.; Migliori, Albert; Visscher, William M.

1994-01-01

A method is provided for grading production quantities of spherical objects, such as roller balls for bearings. A resonant ultrasound spectrum (RUS) is generated for each spherical object and a set of degenerate sphere-resonance frequencies is identified. From the degenerate sphere-resonance frequencies and known relationships between degenerate sphere-resonance frequencies and Poisson's ratio, a Poisson's ratio can be determined, along with a "best" spherical diameter, to form spherical parameters for the sphere. From the RUS, fine-structure resonant frequency spectra are identified for each degenerate sphere-resonance frequency previously selected. From each fine-structure spectrum and associated sphere parameter values an asphericity value is determined. The asphericity value can then be compared with predetermined values to provide a measure for accepting or rejecting the sphere.

Sphericity determination using resonant ultrasound spectroscopy

DOEpatents

Dixon, R.D.; Migliori, A.; Visscher, W.M.

1994-10-18

A method is provided for grading production quantities of spherical objects, such as roller balls for bearings. A resonant ultrasound spectrum (RUS) is generated for each spherical object and a set of degenerate sphere-resonance frequencies is identified. From the degenerate sphere-resonance frequencies and known relationships between degenerate sphere-resonance frequencies and Poisson's ratio, a Poisson's ratio can be determined, along with a 'best' spherical diameter, to form spherical parameters for the sphere. From the RUS, fine-structure resonant frequency spectra are identified for each degenerate sphere-resonance frequency previously selected. From each fine-structure spectrum and associated sphere parameter values an asphericity value is determined. The asphericity value can then be compared with predetermined values to provide a measure for accepting or rejecting the sphere. 14 figs.

Sphere based fluid systems

NASA Technical Reports Server (NTRS)

Elleman, Daniel D. (Inventor); Wang, Taylor G. (Inventor)

1989-01-01

Systems are described for using multiple closely-packed spheres. In one system for passing fluid, a multiplicity of spheres lie within a container, with all of the spheres having the same outside diameter and with the spheres being closely nested in one another to create multiple interstitial passages of a known size and configuration and smooth walls. The container has an inlet and outlet for passing fluid through the interstitial passages formed between the nested spheres. The small interstitial passages can be used to filter out material, especially biological material such as cells in a fluid, where the cells can be easily destroyed if passed across sharp edges. The outer surface of the spheres can contain a material that absorbs a constitutent in the flowing fluid, such as a particular contamination gas, or can contain a catalyst to chemically react the fluid passing therethrough, the use of multiple small spheres assuring a large area of contact of these surfaces of the spheres with the fluid. In a system for storing and releasing a fluid such as hydrogen as a fuel, the spheres can include a hollow shell containing the fluid to be stored, and located within a compressable container that can be compressed to break the shells and release the stored fluid.

Establishment of prostate cancer spheres from a prostate cancer cell line after phenethyl isothiocyanate treatment and discovery of androgen-dependent reversible differentiation between sphere and neuroendocrine cells.

PubMed

Chen, Yamei; Cang, Shundong; Han, Liying; Liu, Christina; Yang, Patrick; Solangi, Zeeshan; Lu, Quanyi; Liu, Delong; Chiao, J W

2016-05-03

Prostate cancer can transform from androgen-responsive to an androgen-independent phenotype. The mechanism responsible for the transformation remains unclear. We studied the effects of an epigenetic modulator, phenethyl isothiocyanate (PEITC), on the androgen-responsive LNCaP cells. After treatment with PEITC, floating spheres were formed with characteristics of prostate cancer stem cells (PCSC). These spheres were capable of self-renewal in media with and without androgen. They have been maintained in both types of media as long term cultures. Upon androgen deprivation, the adherent spheres differentiated to neuroendocrine cells (NEC) with decreased proliferation, expression of androgen receptor, and PSA. NEC reverse differentiated to spheres when androgen was replenished. The sphere cells expressed surface marker CD44 and had enhanced histone H3K4 acetylation, DNMT1 down-regulation and GSTP1 activation. We hypothesize that PEITC-mediated alteration in epigenomics of LNCaP cells may give rise to sphere cells, whereas reversible androgenomic alterations govern the shuttling between sphere PCSC and progeny NEC. Our findings identify unrecognized properties of prostate cancer sphere cells with multi-potential plasticity. This system will facilitate development of novel therapeutic agents and allow further exploration into epigenomics and androgenomics governing the transformation to hormone refractory prostate cancer.

Diagnosis of a Poorly Performing Liquid Hydrogen Bulk Storage Sphere

NASA Technical Reports Server (NTRS)

Krenn, Angela G.

2011-01-01

There are two 850,000 gallon Liquid Hydrogen (LH2) storage spheres used to support the Space Shuttle Program; one residing at Launch Pad A and the other at Launch Pad B. The LH2 Sphere at Pad B has had a high boiloff rate since being brought into service in the 1960's. The daily commodity loss was estimated to be approximately double that of the Pad A sphere, and well above the minimum required by the sphere's specification. Additionally, after being re-painted in the late 1990's a "cold spot" appeared on the outer sphere which resulted in a poor paint bond, and mold formation. Thermography was used to characterize the area, and the boiloff rate was continually evaluated. All evidence suggested that the high boiloff rate was caused by an excessive heat leak into the inner sphere due to an insulation void in the annulus. Pad B was recently taken out of Space Shuttle program service which provided a unique opportunity to diagnose the sphere's poor performance. The sphere was drained and inerted, and then opened from the annular relief device on the top where a series of boroscoping operations were accomplished. Boroscoping revealed a large Perlite insulation void in the region of the sphere where the cold spot was apparent. Perlite was then trucked in and off-loaded into the annular void region until the annulus was full. The sphere has not yet been brought back into service.

Unusual undecanuclear heterobimetallic Zn4Ln7 (Ln = Gd, Dy) nano-sized clusters encapsulating two peroxide anions through spontaneous intake of dioxygen.

PubMed

Ke, Hongshan; Lu, Xiaohua; Wei, Wen; Wang, Wenyuan; Xie, Gang; Chen, Sanping

2017-06-27

The synthesis, characterization and properties of two unprecedented undecanuclear heterobimetallic Zn 4 Ln 7 complexes of formula [Zn 4 Ln 7 (L) 8 (O 2 ) 2 (OH) 4 (Cl) 4 (H 2 O) 4 ]·Cl·4H 2 O·4CH 3 CN (Ln = Gd (1), Dy (2)) encapsulating two peroxide anions are presented, representing a very rare example of a 3d-peroxo-Ln system and expanding the realm of metal-peroxo complexes. These eleven metal ions are arranged in a peculiar structural motif, where Zn 4 is located at the peripheral shell wrapping Ln 7 in the inner core. The Zn ions are penta-coordinate in all cases, linked to the NO 2 donor atoms from the L 2- ligand and to a hydroxyl group, and the apical position is occupied by a chloride anion. All Ln III ions in these systems are octa-coordinate with LnO 8 and LnNO 7 coordination spheres. Magnetocaloric effect (MCE) behavior has been found in the Gd analogue due to multiple low lying excited states arising from antiferromagnetic Gd-Gd exchange interactions. The Dy derivative shows frequency dependent out-of-phase signals indicating the presence of slow relaxation of magnetization below 8 K under zero applied direct current (dc) field, but without reaching a maximum, which is due to a faster quantum tunneling relaxation. The effective barrier extracted from the frequency dependent data is U eff = 11.2 K and a τ 0 of 4.18 × 10 -6 s.

Spin state switching in iron coordination compounds

PubMed Central

Gaspar, Ana B; Garcia, Yann

2013-01-01

Summary The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices. The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligo- and polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property. PMID:23504535

Synthesis, crystal structure, antibacterial activity and theoretical studies on a novel mononuclear cobalt(II) complex based on 2,4,6-tris(2-pyridyl)-1,3,5-triazine ligand

NASA Astrophysics Data System (ADS)

Maghami, Mahboobeh; Farzaneh, Faezeh; Simpson, Jim; Ghiasi, Mina; Azarkish, Mohammad

2015-08-01

A cobalt complex was prepared from CoCl2·6H2O and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in methanol and designated as [Co(tptz)(CH3OH)Cl2]·CH3OH·0.5H2O (1). It was characterized by several techniques including TGA analysis and FT-IR, UV-Vis and 1H NMR spectral studies. The crystal structure of 1 was determined by single-crystal X-ray diffraction. The Co(II) metal center in 1 is six coordinated with a distorted octahedral geometry. The tptz ligand is tridentate and coordinates to the cobalt through coplanar nitrogen atoms from the triazine and two pyridyl rings. Two chloride anions and a methanol molecule complete the inner coordination sphere of the metal ion. The optimized geometrical parameters obtained by DFT calculation are in good agreement with single XRD data. The in vitro antibacterial activity of various tptz complexes of Co(II), Ni(II), Cu(II), Mn(II) and Rh(III) were evaluated against Gram-positive (Bacillus subtilis, Staphylococcus aureus and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Whereas all complexes exhibited good activity in comparison to standard antibacterial drugs, the inhibitory effects of complexes were found to be more than that of the parent ligand. Overall, the obtained results strongly suggest that the cobalt(II) complex is a suitable candidate for counteracting antibiotic resistant microorganisms.

Redox reactions of [FeFe]-hydrogenase models containing an internal amine and a pendant phosphine.

PubMed

Zheng, Dehua; Wang, Mei; Chen, Lin; Wang, Ning; Sun, Licheng

2014-02-03

A diiron dithiolate complex with a pendant phosphine coordinated to one of the iron centers, [(μ-SCH2)2N(CH2C6H4-o-PPh2){Fe2(CO)5}] (1), was prepared and structurally characterized. The pendant phosphine is dissociated together with a CO ligand in the presence of excess PMe3, to afford [(μ-SCH2)2N(CH2C6H4-o-PPh2){Fe(CO)2(PMe3)}2] (2). Redox reactions of 2 and related complexes were studied in detail by in situ IR spectroscopy. A series of new Fe(II)Fe(I) ([3](+) and [6](+)), Fe(II)Fe(II) ([4](2+)), and Fe(I)Fe(I) (5) complexes relevant to Hox, Hox(CO), and Hred states of the [FeFe]-hydrogenase active site were detected. Among these complexes, the molecular structures of the diferrous complex [4](2+) with the internal amine and the pendant phosphine co-coordinated to the same iron center and the triphosphine diiron complex 5 were determined by X-ray crystallography. To make a comparison, the redox reactions of an analogous complex, [(μ-SCH2)2N(CH2C6H5){Fe(CO)2(PMe3)}2] (7), were also investigated by in situ IR spectroscopy in the absence or presence of extrinsic PPh3, which has no influence on the oxidation reaction of 7. The pendant phosphine in the second coordination sphere makes the redox reaction of 2 different from that of its analogue 7.

Precise and Fast Computation of the Gravitational Field of a General Finite Body and Its Application to the Gravitational Study of Asteroid Eros

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukushima, Toshio, E-mail: Toshio.Fukushima@nao.ac.jp

In order to obtain the gravitational field of a general finite body inside its Brillouin sphere, we developed a new method to compute the field accurately. First, the body is assumed to consist of some layers in a certain spherical polar coordinate system and the volume mass density of each layer is expanded as a Maclaurin series of the radial coordinate. Second, the line integral with respect to the radial coordinate is analytically evaluated in a closed form. Third, the resulting surface integrals are numerically integrated by the split quadrature method using the double exponential rule. Finally, the associated gravitationalmore » acceleration vector is obtained by numerically differentiating the numerically integrated potential. Numerical experiments confirmed that the new method is capable of computing the gravitational field independently of the location of the evaluation point, namely whether inside, on the surface of, or outside the body. It can also provide sufficiently precise field values, say of 14–15 digits for the potential and of 9–10 digits for the acceleration. Furthermore, its computational efficiency is better than that of the polyhedron approximation. This is because the computational error of the new method decreases much faster than that of the polyhedron models when the number of required transcendental function calls increases. As an application, we obtained the gravitational field of 433 Eros from its shape model expressed as the 24 × 24 spherical harmonic expansion by assuming homogeneity of the object.« less

Cavitation and radicals drive the sonochemical synthesis of functional polymer spheres

DOE PAGES

Narayanan, Badri; Deshmukh, Sanket A.; Shrestha, Lok Kumar; ...

2016-07-25

Sonochemical synthesis can lead to a dramatic increase in the kinetics of formation of polymer spheres (templates for carbon spheres) compared to the modified Stober silica method applied to produce analogous polymer spheres. Reactive molecular dynamics simulations of the sonochemical process indicate a significantly enhanced rate of polymer sphere formation starting from resorcinol and formaldehyde precursors. The associated chemical reaction kinetics enhancement due to sonication is postulated to arise from the localized lowering of atomic densities, localized heating, and generation of radicals due to cavitation collapse in aqueous systems. This dramatic increase in reaction rates translates into enhanced nucleation andmore » growth of the polymer spheres. Finally, the results are of broad significance to understanding mechanisms of sonication induced synthesis as well as technologies utilizing polymers spheres.« less

Cavitation and radicals drive the sonochemical synthesis of functional polymer spheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narayanan, Badri, E-mail: bnarayanan@anl.gov; Deshmukh, Sanket A.; Sankaranarayanan, Subramanian K. R. S., E-mail: ssankaranarayanan@anl.gov

2016-07-25

Sonochemical synthesis can lead to a dramatic increase in the kinetics of formation of polymer spheres (templates for carbon spheres) compared to the modified Stöber silica method applied to produce analogous polymer spheres. Reactive molecular dynamics simulations of the sonochemical process indicate a significantly enhanced rate of polymer sphere formation starting from resorcinol and formaldehyde precursors. The associated chemical reaction kinetics enhancement due to sonication is postulated to arise from the localized lowering of atomic densities, localized heating, and generation of radicals due to cavitation collapse in aqueous systems. This dramatic increase in reaction rates translates into enhanced nucleation andmore » growth of the polymer spheres. The results are of broad significance to understanding mechanisms of sonication induced synthesis as well as technologies utilizing polymers spheres.« less

Effect of vaginal spheres and pelvic floor muscle training in women with urinary incontinence: a randomized, controlled trial.

PubMed

Porta-Roda, Oriol; Vara-Paniagua, Jesús; Díaz-López, Miguel A; Sobrado-Lozano, Pilar; Simó-González, Marta; Díaz-Bellido, Paloma; Reula-Blasco, María C; Muñoz-Garrido, Francisco

2015-08-01

To compare the efficacy and safety of Kegel exercises performed with or without, vaginal spheres as treatment for women with urinary incontinence. Multicentre parallel-group, open, randomized controlled trial. Women were allocated to either a pelvic floor muscle-training program consisting of Kegel exercises performed twice daily, 5 days/week at home, over 6 months with vaginal spheres, or to the same program without spheres. The primary endpoint was women's report of urinary incontinence at 6 months using the International Consultation on Incontinence Questionnaire-Short Form (ICIQ-UI-SF). Secondary outcome measures were the 1 hr pad-test, King's Health Questionnaire (KHQ) and a five-point Likert scale for subjective evaluation. Adherence was measured with the Morisky-Green test. Thirty-seven women were randomized to the spheres group and 33 to the control group. The primary endpoint was evaluated in 65 women (35 in the spheres group vs. 30 controls). ICIQ-UI-SF results improved significantly at 1-month follow-up in the spheres group (P < 0.01) and at 6 months in the controls. The 1 hr pad-test improved in the spheres group but not in the control group. No significant differences were found in the KHQ results or in the subjective evaluation of efficacy and safety. Adherence was higher in the spheres group but differences were not significant. Mild transient side effects were reported in four patients in the spheres group and one in the control group. Both treatments improved urinary incontinence but women who performed the exercises with vaginal spheres showed an earlier improvement. Vaginal spheres were well tolerated and safe. © 2014 Wiley Periodicals, Inc.

Filter Bed of Packed Spheres

NASA Technical Reports Server (NTRS)

Elleman, D. D.; Wang, T. G.

1986-01-01

Spheres sized and treated for desired sieve properties. Filter constructed from densely packed spheres restrained by screens. Hollow gas-filled plastic or metal spheres normally used. Manufactured within one percent or better diameter tolerance. Normally, all spheres in filter of same nominal diameter. Filter used as sieve to pass only particles smaller than given size or to retain particles larger than that size. Options available under filter concept make it easy to design for specific applications.

Forming MOFs into spheres by use of molecular gastronomy methods.

PubMed

Spjelkavik, Aud I; Aarti; Divekar, Swapnil; Didriksen, Terje; Blom, Richard

2014-07-14

A novel method utilizing hydrocolloids to prepare nicely shaped spheres of metal-organic frameworks (MOFs) has been developed. Microcrystalline CPO-27-Ni particles are dispersed in either alginate or chitosan solutions, which are added dropwise to solutions containing, respectively, either divalent group 2 cations or base that act as gelling agents. Well-shaped spheres are immediately formed, which can be dried into spheres containing mainly MOF (>95 wt %). The spheronizing procedures have been optimized with respect to maximum specific surface area, shape, and particle density of the final sphere. At optimal conditions, well-shaped 2.5-3.5 mm diameter CPO-27-Ni spheres with weight-specific surface areas <10 % lower than the nonformulated CPO-27-Ni precursor, and having sphere densities in the range 0.8 to 0.9 g cm(-3) and particle crushing strengths above 20 N, can be obtained. The spheres are well suited for use in fixed-bed catalytic or adsorption processes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

iSAP: Interactive Sparse Astronomical Data Analysis Packages

NASA Astrophysics Data System (ADS)

Fourt, O.; Starck, J.-L.; Sureau, F.; Bobin, J.; Moudden, Y.; Abrial, P.; Schmitt, J.

2013-03-01

iSAP consists of three programs, written in IDL, which together are useful for spherical data analysis. MR/S (MultiResolution on the Sphere) contains routines for wavelet, ridgelet and curvelet transform on the sphere, and applications such denoising on the sphere using wavelets and/or curvelets, Gaussianity tests and Independent Component Analysis on the Sphere. MR/S has been designed for the PLANCK project, but can be used for many other applications. SparsePol (Polarized Spherical Wavelets and Curvelets) has routines for polarized wavelet, polarized ridgelet and polarized curvelet transform on the sphere, and applications such denoising on the sphere using wavelets and/or curvelets, Gaussianity tests and blind source separation on the Sphere. SparsePol has been designed for the PLANCK project. MS-VSTS (Multi-Scale Variance Stabilizing Transform on the Sphere), designed initially for the FERMI project, is useful for spherical mono-channel and multi-channel data analysis when the data are contaminated by a Poisson noise. It contains routines for wavelet/curvelet denoising, wavelet deconvolution, multichannel wavelet denoising and deconvolution.

Development of response models for the Earth Radiation Budget Experiment (ERBE) sensors. Part 2: Analysis of the ERBE integrating sphere ground calibration

NASA Technical Reports Server (NTRS)

Halyo, Nesim; Taylor, Deborah B.

1987-01-01

An explicit solution of the spectral radiance leaving an arbitrary point on the wall of a spherical cavity with diffuse reflectivity is obtained. The solution is applicable to spheres with an arbitrary number of openings of any size and shape, an arbitrary number of light sources with possible non-diffuse characteristics, a non-uniform sphere wall temperature distribution, non-uniform and non-diffuse sphere wall emissivity and non-uniform but diffuse sphere wall spectral reflectivity. A general measurement equation describing the output of a sensor with a given field of view, angular and spectral response measuring the sphere output is obtained. The results are applied to the Earth Radiation Budget Experiment (ERBE) integrating sphere. The sphere wall radiance uniformity, loading effects and non-uniform wall temperature effects are investigated. It is shown that using appropriate interpretation and processing, a high-accuracy short-wave calibration of the ERBE sensors can be achieved.

Ceramic Spheres From Cation Exchange Beads

NASA Technical Reports Server (NTRS)

Dynys, F. W.

2003-01-01

Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.

Simulations of two sedimenting-interacting spheres with different sizes and initial configurations using immersed boundary method

NASA Astrophysics Data System (ADS)

Liao, Chuan-Chieh; Hsiao, Wen-Wei; Lin, Ting-Yu; Lin, Chao-An

2015-06-01

Numerical investigations are carried out for the drafting, kissing and tumbling (DKT) phenomenon of two freely falling spheres within a long container by using an immersed-boundary method. The method is first validated with flows induced by a sphere settling under gravity in a small container for which experimental data are available. The hydrodynamic interactions of two spheres are then studied with different sizes and initial configurations. When a regular sphere is placed below the larger one, the duration of kissing decreases in pace with the increase in diameter ratio. On the other hand, the time duration of the kissing stage increases in tandem with the increase in diameter ratio as the large sphere is placed below the regular one, and there is no DKT interactions beyond threshold diameter ratio. Also, the gap between homogeneous spheres remains constant at the terminal velocity, whereas the gaps between the inhomogeneous spheres increase due to the differential terminal velocity.

Beyond-proximity-force-approximation Casimir force between two spheres at finite temperature

NASA Astrophysics Data System (ADS)

Bimonte, Giuseppe

2018-04-01

A recent experiment [J. L. Garrett, D. A. T. Somers, and J. N. Munday, Phys. Rev. Lett. 120, 040401 (2018), 10.1103/PhysRevLett.120.040401] measured for the first time the gradient of the Casimir force between two gold spheres at room temperature. The theoretical analysis of the data was carried out using the standard proximity force approximation (PFA). A fit of the data, using a parametrization of the force valid for the sphere-plate geometry, was used by the authors to place a bound on deviations from PFA. Motivated by this work, we compute the Casimir force between two gold spheres at finite temperature. The semianalytic formula for the Casimir force that we construct is valid for all separations, and can be easily used to interpret future experiments in both the sphere-plate and sphere-sphere configurations. We describe the correct parametrization of the corrections to PFA for two spheres that should be used in data analysis.

Development and fabrication of insulator seals for thermionic diodes

NASA Technical Reports Server (NTRS)

Poirier, V. L.

1972-01-01

Eight different types of cermet seals for thermionic diodes were investigated: (1) 1 micron Al2O3 with Nb spheres; (2) 200 A Al2O3 with Nb spheres; (3) 1 micron Al2O3 with Nb 1% Zr spheres; (4) 200 A Al2O3 with Nb 1% Zr spheres; (5) Pure Y2O3 with Nb 1% Zr spheres; (6) Y2O3 3% ZrO2 with Nb 1% Zr spheres; (7) Y2O3 10% ZrO2 with Nb 1% Zr spheres; and (8) ZrO2 12% Y2O3 with Nb 1% Zr spheres. Investigations were made to determine the most favorable fabrication techniques and the effect of the bonding cycle, (length of bonding time and shutdown sequences). The analysis of the seals included tensile test, vacuum test, electrical test and metallurgical examination. At the conclusion of the development phase, 36 seals were fabricated for delivery for evaluation.

Carbonaceous spheres—an unusual template for solid metal oxide mesoscale spheres: Application to ZnO spheres

NASA Astrophysics Data System (ADS)

Patrinoiu, Greta; Calderón-Moreno, Jose Maria; Culita, Daniela C.; Birjega, Ruxandra; Ene, Ramona; Carp, Oana

2013-06-01

A green template route for the synthesis of mesoscale solid ZnO spheres was ascertained. The protocol involves a double coating of the carbonaceous spheres with successive layers of zinc-containing species by alternating a non-ultrasound and ultrasound-assisted deposition, followed by calcination treatments. The composites were characterized by FTIR spectroscopy, thermal analysis, scanning electron microscopy while the obtained ZnO spheres by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, N2 adsorption-desorption isotherms and photoluminescence investigations. A growth mechanism of the solid spheres is advanced based on these results. While the spheres' diameters and the mean size values of ZnO are independent on deposition order, the surface area and the external porosity are fairly dependent. The photoluminescence measurements showed interesting emission features, with emission bands in the violet to orange region. The spheres present high photocatalytical activity towards the degradation of phenol under UV irradiation, the main reaction being its mineralization.

Bis(tetraphenylarsonium) hexachloridozirconate(IV) acetonitrile tetrasolvate

DOE PAGES

Borjas, Rosendo; Mariappan Balasekaran, Samundeeswari; Poineau, Frederic

2018-04-06

The bis(tetraphenylarsonium) hexachloridozirconate(IV) salt, (AsPh 4 ) 2 [ZrCl 6 ] (Ph = C 6 H 5 ), was prepared more than 25 years ago [Esmadi & Sutcliffe (1991). Indian J. Chem. 30 A , 99–101], but its crystal structure was never reported. By following a similar experimental procedure, the compound was synthesized and its crystal structure was investigated as a acetonitrile tetrasolvate, (As(C 6 H 5 ) 4 ) 2 [ZrCl 6 ]·4CH 3 CN, by single-crystal X –ray diffraction. The [ZrCl 6 ] 2− anion adopts a slightly distorted octahedral coordination sphere, with Zr—Cl bond lengths of 2.4586 (6), 2.4723 (6),more » and 2.4818 (5) Å, and Cl—Zr—Cl angles ranging from 89.602 (19) to 90.397 (19)°.« less

Lanthanides in molecular magnetism: old tools in a new field.

PubMed

Sorace, Lorenzo; Benelli, Cristiano; Gatteschi, Dante

2011-06-01

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems.

Reactive trajectories of the Ru2+/3+ self-exchange reaction and the connection to Marcus' theory.

PubMed

Tiwari, Ambuj; Ensing, Bernd

2016-12-22

Outer sphere electron transfer between two ions in aqueous solution is a rare event on the time scale of first principles molecular dynamics simulations. We have used transition path sampling to generate an ensemble of reactive trajectories of the self-exchange reaction between a pair of Ru 2+ and Ru 3+ ions in water. To distinguish between the reactant and product states, we use as an order parameter the position of the maximally localised Wannier center associated with the transferring electron. This allows us to align the trajectories with respect to the moment of barrier crossing and compute statistical averages over the path ensemble. We compare our order parameter with two typical reaction coordinates used in applications of Marcus theory of electron transfer: the vertical gap energy and the solvent electrostatic potential at the ions.

Computerized implementation of higher-order electron-correlation methods and their linear-scaling divide-and-conquer extensions.

PubMed

Nakano, Masahiko; Yoshikawa, Takeshi; Hirata, So; Seino, Junji; Nakai, Hiromi

2017-11-05

We have implemented a linear-scaling divide-and-conquer (DC)-based higher-order coupled-cluster (CC) and Møller-Plesset perturbation theories (MPPT) as well as their combinations automatically by means of the tensor contraction engine, which is a computerized symbolic algebra system. The DC-based energy expressions of the standard CC and MPPT methods and the CC methods augmented with a perturbation correction were proposed for up to high excitation orders [e.g., CCSDTQ, MP4, and CCSD(2) TQ ]. The numerical assessment for hydrogen halide chains, polyene chains, and first coordination sphere (C1) model of photoactive yellow protein has revealed that the DC-based correlation methods provide reliable correlation energies with significantly less computational cost than that of the conventional implementations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Crystal structure of fac-tri­chlorido­[tris­(pyridin-2-yl-N)amine]­chromium(III)

PubMed Central

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol­ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris­(pyridin-2-yl)amine; C15H12N4], the CrIII ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa­hedral coordination sphere. The average Cr—N and Cr—Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol­ecule is located on a mirror plane. In the crystal, a combination of C—H⋯N and C—H⋯Cl hydrogen-bonding inter­actions connect the mol­ecules into a three-dimensional network. PMID:25705455

Kinetic and mechanism of the oxidation of chromium(III) complex with anthranil- N, N-diacetic acid by periodate ion in acidic aqueous solutions

NASA Astrophysics Data System (ADS)

Ali, Ismat H.

2015-06-01

The kinetics of oxidation of [CrIII(atda)(H2O)2] (atda = anthranil- N, N-diacetato) complex by IO{4/-} was studied spectrophotometrically in aqueous solutions with pH range 2.20-3.34, 0.30 M ionic strength and in 20.0-40.0°C temperature range. The rate law of the reaction exhibited saturation kinetics. Values of the rate constant for the electron transfer process, the equilibrium constant for dissociation of [CrIII (atda)(H2O)2] to [CrIII (atda) (H2O)OH]+ + H+ and the pre-equilibrium formation constant were calculated. The thermodynamic activation parameters are reported. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of the IVII to chromium(III).

Bis(tetraphenylarsonium) hexachloridozirconate(IV) acetonitrile tetrasolvate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borjas, Rosendo; Mariappan Balasekaran, Samundeeswari; Poineau, Frederic

The bis(tetraphenylarsonium) hexachloridozirconate(IV) salt, (AsPh 4 ) 2 [ZrCl 6 ] (Ph = C 6 H 5 ), was prepared more than 25 years ago [Esmadi & Sutcliffe (1991). Indian J. Chem. 30 A , 99–101], but its crystal structure was never reported. By following a similar experimental procedure, the compound was synthesized and its crystal structure was investigated as a acetonitrile tetrasolvate, (As(C 6 H 5 ) 4 ) 2 [ZrCl 6 ]·4CH 3 CN, by single-crystal X –ray diffraction. The [ZrCl 6 ] 2− anion adopts a slightly distorted octahedral coordination sphere, with Zr—Cl bond lengths of 2.4586 (6), 2.4723 (6),more » and 2.4818 (5) Å, and Cl—Zr—Cl angles ranging from 89.602 (19) to 90.397 (19)°.« less

Crystal structures of fac-tri-chlorido-tris-(tri-methyl-phosphane-κP)rhodium(III) monohydrate and fac-tri-chlorido-tris-(tri-methyl-phosphane-κP)rhodium(III) methanol hemisolvate: rhodium structures that are isotypic with their iridium analogs.

PubMed

Merola, Joseph S; Franks, Marion A

2015-02-01

The crystal structures of two solvates of fac-tri-chlorido-tris-(tri-methyl-phosphane-κP)rhodium(III) are reported, i.e. one with water in the crystal lattice, fac-[RhCl3(Me3P)3]·H2O, and one with methanol in the crystal lattice, fac-[RhCl3(Me3P)3]·0.5CH3OH. These rhodium compounds exhibit distorted octahedral coordination spheres at the metal and are isotypic with the analogous iridium compounds previously reported by us [Merola et al. (2013 ▶). Polyhedron, 54, 67-73]. Comparison is made between the rhodium and iridium compounds, highlighting their isostructural relationships.

Tuning Reactivity and Electronic Properties through Ligand Reorganization within a Cerium Heterobimetallic Framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, Jerome R.; Gordon, Zachary; Booth, Corwin H.

2014-06-24

Cerium compounds have played vital roles in organic, inorganic, and materials chemistry due to their reversible redox chemistry between trivalent and tetravalent oxidation states. However, attempts to rationally access molecular cerium complexes in both oxidation states have been frustrated by unpredictable reactivity in cerium(III) oxidation chemistry. Such oxidation reactions are limited by steric saturation at the metal ion, which can result in high energy activation barriers for electron transfer. An alternative approach has been realized using a rare earth/alkali metal/1,1'-BINOLate (REMB) heterobimetallic framework, which uses redox-inactive metals within the secondary coordination sphere to control ligand reorganization. The rational syntheses ofmore » functionalized cerium(IV) products and a mechanistic examination of the role of ligand reorganization in cerium(III) oxidation are presented.« less

Zonally averaged model of dynamics, chemistry and radiation for the atmosphere

NASA Technical Reports Server (NTRS)

Tung, K. K.

1985-01-01

A nongeostrophic theory of zonally averaged circulation is formulated using the nonlinear primitive equations on a sphere, taking advantage of the more direct relationship between the mean meridional circulation and diabatic heating rate which is available in isentropic coordinates. Possible differences between results of nongeostrophic theory and the commonly used geostrophic formulation are discussed concerning: (1) the role of eddy forcing of the diabatic circulation, and (2) the nonlinear nearly inviscid limit vs the geostrophic limit. Problems associated with the traditional Rossby number scaling in quasi-geostrophic formulations are pointed out and an alternate, more general scaling based on the smallness of mean meridional to zonal velocities for a rotating planet is suggested. Such a scaling recovers the geostrophic balanced wind relationship for the mean zonal flow but reveals that the mean meridional velocity is in general ageostrophic.

Thiourea derivatives as chelating agents for bioconjugation of rhenium and technetium.

PubMed

Gomez, J D Castillo; Hagenbach, A; Gerling-Driessen, U I M; Koksch, B; Beindorff, N; Brenner, W; Abram, U

2017-10-31

Potential tetradentate thiocarbamoylbenzamidine derivatives H 4 L have been synthesized from the corresponding benzimidoyl chlorides and triglycine. They are suitable chelating agents for the oxidotechnetium(v) and oxidorhenium(v) cores and form stable, neutral [MO(HL)] complexes with an equatorial SN 3 coordination sphere and an additional, uncoordinated carboxylic group, which can be used for bioconjugation. Representatives of the rhenium and 99 Tc products have been isolated and analyzed with spectroscopic methods and X-ray diffraction. Bioconjugates of these complexes with angiotensin-II have been synthesized and structurally characterized. Analogous 99m Tc complexes have been produced and tested in vitro and in vivo. The experiments confirm a considerable stability for the [ 99m Tc(HL)] product as well as for its bioconjugate and recommend this class of compounds for further bioconjugation studies towards clinical applications.

Solving Partial Differential Equations on Overlapping Grids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henshaw, W D

2008-09-22

We discuss the solution of partial differential equations (PDEs) on overlapping grids. This is a powerful technique for efficiently solving problems in complex, possibly moving, geometry. An overlapping grid consists of a set of structured grids that overlap and cover the computational domain. By allowing the grids to overlap, grids for complex geometries can be more easily constructed. The overlapping grid approach can also be used to remove coordinate singularities by, for example, covering a sphere with two or more patches. We describe the application of the overlapping grid approach to a variety of different problems. These include the solutionmore » of incompressible fluid flows with moving and deforming geometry, the solution of high-speed compressible reactive flow with rigid bodies using adaptive mesh refinement (AMR), and the solution of the time-domain Maxwell's equations of electromagnetism.« less

Active Control of Vortex Induced Vibrations of a Tethered Sphere in a Uniform Air Flow

NASA Astrophysics Data System (ADS)

van Hout, Rene; Greenblatt, David; Zvi Katz, Amit

2011-11-01

VIV of two heavy tethered spheres (D = 40 mm, m* = msphere/ ρfVsphere = 21 and 67, L* = L / D = 2.50) were studied in a wind tunnel under uniform free stream velocities up to U* = U /fn D = 15.9, with and without acoustic control. Control was achieved using two speakers mounted on either side of the spheres and driven in-phase at f= 35Hz (f* = 22.3). In the non-controlled case, the bifurcation map of transverse sphere oscillation amplitude, Ay, showed stationary motion as well as periodic and non-stationary oscillations with increasing U*. For m* = 21, Aymax was about twice as large as for m* = 67. Acoustic control dampened Aymax in the periodic region (m* = 67) and increased Aymax in the non-stationary region for both spheres. Sphere boundary layer dynamics in the three different bifurcation regions were studied using time resolved PIV with a horizontal laser sheet positioned at the center of the sphere. The field of view was 55 × 55 mm2 containing one quarter of the sphere. Results will be presented on the vortex dynamics near the sphere's surface with and without acoustic control.

Hollow spheres: crucial building blocks for novel nanostructures and nanophotonics

NASA Astrophysics Data System (ADS)

Zhong, Kuo; Song, Kai; Clays, Koen

2018-03-01

In this review, we summarize the latest developments in research specifically derived from the unique properties of hollow microspheres, in particular, hollow silica spheres with uniform shells. We focus on applications in nanosphere (colloidal) lithography and nanophotonics. The lithography from a layer of hollow spheres can result in nanorings, from a multilayer in unique nano-architecture. In nanophotonics, disordered hollow spheres can result in antireflection coatings, while ordered colloidal crystals (CCs) of hollow spheres exhibit unique refractive index enhancement upon infiltration, ideal for optical sensing. Furthermore, whispering gallery mode (WGM) inside the shell of hollow spheres has also been demonstrated to enhance light absorption to improve the performance of solar cells. These applications differ from the classical applications of hollow spheres, based only on their low density and large surface area, such as catalysis and chemical sensing. We provide a brief overview of the synthesis and self-assembly approaches of the hollow spheres. We elaborate on their unique optical features leading to defect mode lasing, optomicrofluidics, and the existence of WGMs inside shell for light management. Finally, we provide a perspective on the direction towards which future research relevant to hollow spheres might be directed.

Localization of source with unknown amplitude using IPMC sensor arrays

NASA Astrophysics Data System (ADS)

Abdulsadda, Ahmad T.; Zhang, Feitian; Tan, Xiaobo

2011-04-01

The lateral line system, consisting of arrays of neuromasts functioning as flow sensors, is an important sensory organ for fish that enables them to detect predators, locate preys, perform rheotaxis, and coordinate schooling. Creating artificial lateral line systems is of significant interest since it will provide a new sensing mechanism for control and coordination of underwater robots and vehicles. In this paper we propose recursive algorithms for localizing a vibrating sphere, also known as a dipole source, based on measurements from an array of flow sensors. A dipole source is frequently used in the study of biological lateral lines, as a surrogate for underwater motion sources such as a flapping fish fin. We first formulate a nonlinear estimation problem based on an analytical model for the dipole-generated flow field. Two algorithms are presented to estimate both the source location and the vibration amplitude, one based on the least squares method and the other based on the Newton-Raphson method. Simulation results show that both methods deliver comparable performance in source localization. A prototype of artificial lateral line system comprising four ionic polymer-metal composite (IPMC) sensors is built, and experimental results are further presented to demonstrate the effectiveness of IPMC lateral line systems and the proposed estimation algorithms.

Analysis of the detailed configuration of hydrated lanthanoid(III) ions in aqueous solution and crystalline salts by using K- and L(3)-edge XANES spectroscopy.

PubMed

D'Angelo, Paola; Zitolo, Andrea; Migliorati, Valentina; Persson, Ingmar

2010-01-11

The structural properties of the hydrated lanthanoid(III) ions in aqueous solution and in the isostructural trifluoromethanesulfonate salts have been investigated by a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the K- and L(3)-edges. The XANES analysis has provided a clear description of the variation of lanthanoid(III) hydration properties across the series. It was found that all of the lanthanoid(III) hydration complexes retain a tricapped trigonal prism (TTP) geometry, and along the series two of the capping water molecules become less and less strongly bound, before finally, on average, one of them leaves the hydration cluster. This gives rise to an eight-coordinated distorted bicapped trigonal prism with two different Ln--O capping distances for the smallest lanthanoid(III) ions. This systematic study has shown that for lanthanoid compounds more accurate structural information is obtained from the analysis of the L(3)-edge than from K-edge XANES data. Moreover, whereas the second hydration shells provide a detectable contribution to the L(3)-edge XANES spectra of the lighter lanthanoid ions, the K-edge spectra are insensitive to the more distant coordination spheres.

Protonation of carboxyl groups in EuDOTA-tetraamide complexes results in catalytic prototropic exchange and quenching of the CEST signal

NASA Astrophysics Data System (ADS)

Zhang, Lei; Evbuomwan, Osasere M.; Tieu, Michael; Zhao, Piyu; Martins, Andre F.; Sherry, A. Dean

2017-10-01

The CEST properties of EuDOTA-tetraamide complexes bearing pendant carboxylate and carboxyl ethyl esters were measured as a function of pH. The CEST signal from the Eu3+-bound water molecule decreased in intensity between pH 8.5 and 4.5 while the proton exchange rates (kex) increased over this same pH range. In comparison, the CEST signal in the corresponding carboxyl ester derivatives was nearly constant. Both observations are consistent with stepwise protonation of the four carboxylic acid groups over this same pH range. This indicates that negative charges on the carboxyl groups above pH 6 facilitate the formation of a strong hydrogen-bonding network in the coordination second sphere above the single Eu3+-bound water molecule, thereby decreasing prototropic exchange of protons on the bound water molecule with bulk water protons. The percentage of square antiprismatic versus twisted square antiprism coordination isomers also decreased as the appended carboxylic acid groups were positioned further away from the amide. The net effect of lowering the pH was an overall increase in kex and a quenching of the CEST signal. This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.

Cation binding to a Bacillus (1,3-1,4)-beta-glucanase. Geometry, affinity and effect on protein stability.

PubMed

Keitel, T; Meldgaard, M; Heinemann, U

1994-05-15

The hybrid Bacillus (1,3-1,4)-beta-glucanase H(A16-M), consisting of 16 N-terminal amino acids derived from the mature form of the B. amyloliquefaciens enzyme and of 198 C-proximal amino acids from the B. macerans enzyme, binds a calcium ion at a site at its molecular surface remote from the active center [T. Keitel, O. Simon, R. Borriss & U. Heinemann (1993) Proc. Natl Acad. Sci. USA 90, 5287-5291]. X-ray diffraction analysis at 0.22-nm resolution of crystals grown in the absence of calcium and in the presence of EDTA shows this site to be occupied by a sodium ion. Whereas the calcium ion has six oxygen atoms in its coordination sphere, two of which are from water molecules, sodium is fivefold coordinated with a fifth ligand belonging to a symmetry-related protein molecule in the crystal lattice. The affinity of H(A16-M) for calcium over sodium has been determined calorimetrically. Calcium binding stabilizes the native three-dimensional structure of the protein as shown by guanidinium chloride unfolding and thermal inactivation experiments. The enhanced enzymic activity of Bacillus beta-glucanases at elevated temperatures in the presence of calcium ions is attributed to a general stabilizing effect by the cation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Streltsov, Victor A.; Titmuss, Stephen J.; Epa, V. Chandana

Neurodegeneration observed in Alzheimer disease (AD) is believed to be related to the toxicity from reactive oxygen species (ROS) produced in the brain by the amyloid-{beta} (A{beta}) protein bound primarily to copper ions. The evidence for an oxidative stress role of A{beta}-Cu redox chemistry is still incomplete. Details of the copper binding site in A{beta} may be critical to the etiology of AD. Here we present the structure determined by combining x-ray absorption spectroscopy (XAS) and density functional theory analysis of A{beta} peptides complexed with Cu{sup 2+} in solution under a range of buffer conditions. Phosphate-buffered saline buffer salt (NaCl)more » concentration does not affect the high-affinity copper binding mode but alters the second coordination sphere. The XAS spectra for truncated and full-length A{beta}-Cu{sup 2+} peptides are similar. The novel distorted six-coordinated (3N3O) geometry around copper in the A{beta}-Cu{sup 2+} complexes include three histidines: glutamic, or/and aspartic acid, and axial water. The structure of the high-affinity Cu{sup 2+} binding site is consistent with the hypothesis that the redox activity of the metal ion bound to A{beta} can lead to the formation of dityrosine-linked dimers found in AD.« less

Structure-from-motion approach for characterization of bioerosion patterns using UAV imagery.

PubMed

Genchi, Sibila A; Vitale, Alejandro J; Perillo, Gerardo M E; Delrieux, Claudio A

2015-02-04

The aim of this work is to evaluate the applicability of the 3D model obtained through Structure-from-Motion (SFM) from unmanned aerial vehicle (UAV) imagery, in order to characterize bioerosion patterns (i.e., cavities for roosting and nesting) caused by burrowing parrots on a cliff in Bahía Blanca, Argentina. The combined use of SFM-UAV technology was successfully applied for the 3D point cloud model reconstruction. The local point density, obtained by means of a sphere of radius equal to 0.5 m, reached a mean value of 9749, allowing to build a high-resolution model (0.013 m) for resolving fine spatial details in topography. To test the model, we compared it with another point cloud dataset which was created using a low cost do-it-yourself terrestrial laser scanner; the results showed that our georeferenced model had a good accuracy. In addition, an innovative method for the detection of the bioerosion features was implemented, through the processing of data provided by SFM like color and spatial coordinates (particularly the y coordinate). From the 3D model, we also derived topographic calculations such as slope angle and surface roughness, to get associations between the surface topography and bioerosion features.

Structure-from-Motion Approach for Characterization of Bioerosion Patterns Using UAV Imagery

PubMed Central

Genchi, Sibila A.; Vitale, Alejandro J.; Perillo, Gerardo M. E.; Delrieux, Claudio A.

2015-01-01

The aim of this work is to evaluate the applicability of the 3D model obtained through Structure-from-Motion (SFM) from unmanned aerial vehicle (UAV) imagery, in order to characterize bioerosion patterns (i.e., cavities for roosting and nesting) caused by burrowing parrots on a cliff in Bahía Blanca, Argentina. The combined use of SFM-UAV technology was successfully applied for the 3D point cloud model reconstruction. The local point density, obtained by means of a sphere of radius equal to 0.5 m, reached a mean value of 9749, allowing to build a high-resolution model (0.013 m) for resolving fine spatial details in topography. To test the model, we compared it with another point cloud dataset which was created using a low cost do-it-yourself terrestrial laser scanner; the results showed that our georeferenced model had a good accuracy. In addition, an innovative method for the detection of the bioerosion features was implemented, through the processing of data provided by SFM like color and spatial coordinates (particularly the y coordinate). From the 3D model, we also derived topographic calculations such as slope angle and surface roughness, to get associations between the surface topography and bioerosion features. PMID:25658392

A finite element method for solving the shallow water equations on the sphere

NASA Astrophysics Data System (ADS)

Comblen, Richard; Legrand, Sébastien; Deleersnijder, Eric; Legat, Vincent

Within the framework of ocean general circulation modeling, the present paper describes an efficient way to discretize partial differential equations on curved surfaces by means of the finite element method on triangular meshes. Our approach benefits from the inherent flexibility of the finite element method. The key idea consists in a dialog between a local coordinate system defined for each element in which integration takes place, and a nodal coordinate system in which all local contributions related to a vectorial degree of freedom are assembled. Since each element of the mesh and each degree of freedom are treated in the same way, the so-called pole singularity issue is fully circumvented. Applied to the shallow water equations expressed in primitive variables, this new approach has been validated against the standard test set defined by [Williamson, D.L., Drake, J.B., Hack, J.J., Jakob, R., Swarztrauber, P.N., 1992. A standard test set for numerical approximations to the shallow water equations in spherical geometry. Journal of Computational Physics 102, 211-224]. Optimal rates of convergence for the P1NC-P1 finite element pair are obtained, for both global and local quantities of interest. Finally, the approach can be extended to three-dimensional thin-layer flows in a straightforward manner.

SPHERES HALO

NASA Image and Video Library

2017-06-23

iss052e006482 (6/23/2017) --- Astronaut Peggy Whitson is photographed during a test session of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Halo investigation in the Kibo module. The SPHERES Halo investigation studies the possibility of launching several separate components and then attaching them once they are in space. The investigation upgrades the International Space Station’s fleet of SPHERES to enable each SPHERE to communicate with six external objects at the same time, testing new control and remote assembly methods.

Finite Element in Angle Unit Sphere Meshing for Charged Particle Transport.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortega, Mario Ivan; Drumm, Clifton R.

Finite element in angle formulations of the charged particle transport equation require the discretization of the unit sphere. In Sceptre, a three-dimensional surface mesh of a sphere is transformed into a two-dimensional mesh. Projection of a sphere onto a two-dimensional surface is well studied with map makers spending the last few centuries attempting to create maps that preserve proportion and area. Using these techniques, various meshing schemes for the unit sphere were investigated.

Eddy currents in a conducting sphere

NASA Technical Reports Server (NTRS)

Bergman, John; Hestenes, David

1986-01-01

This report analyzes the eddy current induced in a solid conducting sphere by a sinusoidal current in a circular loop. Analytical expressions for the eddy currents are derived as a power series in the vectorial displacement of the center of the sphere from the axis of the loop. These are used for first order calculations of the power dissipated in the sphere and the force and torque exerted on the sphere by the electromagnetic field of the loop.

The electromagnetic radiation from simple sources in the presence of a homogeneous dielectric sphere

NASA Technical Reports Server (NTRS)

Mason, V. B.

1973-01-01

In this research, the effect of a homogeneous dielectric sphere on the electromagnetic radiation from simple sources is treated as a boundary value problem, and the solution is obtained by the technique of dyadic Green's functions. Exact representations of the electric fields in the various regions due to a source located inside, outside, or on the surface of a dielectric sphere are formulated. Particular attention is given to the effect of sphere size, source location, dielectric constant, and dielectric loss on the radiation patterns and directivity of small spheres (less than 5 wavelengths in diameter) using the Huygens' source excitation. The computed results are found to closely agree with those measured for waveguide-excited plexiglas spheres. Radiation patterns for an extended Huygens' source and for curved electric dipoles located on the sphere's surface are also presented. The resonance phenomenon associated with the dielectric sphere is studied in terms of the modal representation of the radiated fields. It is found that when the sphere is excited at certain frequencies, much of the energy is radiated into the sidelobes. The addition of a moderate amount of dielectric loss, however, quickly attenuates this resonance effect. A computer program which may be used to calculate the directivity and radiation pattern of a Huygens' source located inside or on the surface of a lossy dielectric sphere is listed.

Delivery of chemotherapeutics using spheres made of bioengineered spider silks derived from MaSp1 and MaSp2 proteins.

PubMed

Jastrzebska, Katarzyna; Florczak, Anna; Kucharczyk, Kamil; Lin, Yinnan; Wang, Qin; Mackiewicz, Andrzej; Kaplan, David L; Dams-Kozlowska, Hanna

2018-02-01

Analysis of the properties and chemotherapeutics delivery potential of spheres made of bioengineered spider silks MS1 and MS2. MS1 and MS2 derived from Nephila clavipes dragline silks - MaSp1 and MaSp2, respectively - formed spheres that were compared in terms of physicochemical properties, cytotoxicity and loading/release of chemotherapeutics. MS2 spheres were more dispersed, smaller, of solid core, of higher beta-sheet structure content, and of opposite (negative) charge than MS1 spheres. Preloaded MS2 showed greater applicability for mitoxantrone, while postloaded for etoposide delivery compared with MS1 spheres. However, MS1 spheres were a better choice for doxorubicin delivery than MS2. Bioengineered silks can be tailored to develop a system with optimal drug loading and release properties.

On a Microscopic Representation of Space-Time V

NASA Astrophysics Data System (ADS)

Dahm, R.

2017-01-01

In previous parts of this publication series, starting from the Dirac algebra and SU*(4), the ’dual’ compact rank-3 group SU(4) and Lie theory, we have developed some arguments and the reasoning to use (real) projective and (line) Complex geometry directly. Here, we want to extend this approach further in terms of line and Complex geometry and give some analytical examples. As such, we start from quadratic Complexe which we’ve identified in parts III and IV already as yielding naturally the ’light cone’ x_12 + x_22 + x_32 - x_02 = 0 when being related to (homogeneous) point coordinates x_α ^2 and infinitesimal dynamics by tetrahedral Complexe (or line elements). This introduces naturally projective transformations by preserving anharmonic ratios. We summarize some old work of Plücker relating quadratic Complexe to optics and discuss briefly their relation to spherical (and Schrödinger-type) equations as well as an obvious interpretation based on homogeneous coordinates and relations to conics and second order surfaces. Discussing (linear) symplectic symmetry and line coordinates, the main purpose and thread within this paper, however, is the identification and discussion of special relativity as direct invariance properties of line/Complex coordinates as well as their relation to ’quantum field theory’ by complexification of point coordinates or Complexe. This can be established by the Lie mapping1 which relates lines/Complexe to sphere geometry so that SU(2), SU(2)×U(1), SU(2)×SU(2) and the Dirac spinor description emerge without additional assumptions. We give a short outlook in that quadratic Complexe are related to dynamics e.g. power expressions in terms of six-vector products of Complexe, and action principles may be applied. (Quadratic) products like {Fμ ν }{Fμ ν }{{ or }}{Fα {{ }μ ν }}Fμ ν ^α ,1 ≤ α ≤ 3 are natural quadratic Complex expressions which may be extended by line constraints λk · ɛ = 0 with respect to an ’action principle’ so that we identify ’quantum field theory’ with projective or line/Complex geometry having applied the Lie mapping.

Sparkle model for the calculation of lanthanide complexes: AM1 parameters for Eu(III), Gd(III), and Tb(III).

PubMed

Freire, Ricardo O; Rocha, Gerd B; Simas, Alfredo M

2005-05-02

Our previously defined Sparkle model (Inorg. Chem. 2004, 43, 2346) has been reparameterized for Eu(III) as well as newly parameterized for Gd(III) and Tb(III). The parameterizations have been carried out in a much more extensive manner, aimed at producing a new, more accurate model called Sparkle/AM1, mainly for the vast majority of all Eu(III), Gd(III), and Tb(III) complexes, which possess oxygen or nitrogen as coordinating atoms. All such complexes, which comprise 80% of all geometries present in the Cambridge Structural Database for each of the three ions, were classified into seven groups. These were regarded as a "basis" of chemical ambiance around a lanthanide, which could span the various types of ligand environments the lanthanide ion could be subjected to in any arbitrary complex where the lanthanide ion is coordinated to nitrogen or oxygen atoms. From these seven groups, 15 complexes were selected, which were defined as the parameterization set and then were used with a numerical multidimensional nonlinear optimization to find the best parameter set for reproducing chemical properties. The new parameterizations yielded an unsigned mean error for all interatomic distances between the Eu(III) ion and the ligand atoms of the first sphere of coordination (for the 96 complexes considered in the present paper) of 0.09 A, an improvement over the value of 0.28 A for the previous model and the value of 0.68 A for the first model (Chem. Phys. Lett. 1994, 227, 349). Similar accuracies have been achieved for Gd(III) (0.07 A, 70 complexes) and Tb(III) (0.07 A, 42 complexes). Qualitative improvements have been obtained as well; nitrates now coordinate correctly as bidentate ligands. The results, therefore, indicate that Eu(III), Gd(III), and Tb(III) Sparkle/AM1 calculations possess geometry prediction accuracies for lanthanide complexes with oxygen or nitrogen atoms in the coordination polyhedron that are competitive with present day ab initio/effective core potential calculations, while being hundreds of times faster.

Incorporation of star measurements for the determination of orbit and attitude parameters of a geosynchronous satellite: An iterative application of linear regression

NASA Astrophysics Data System (ADS)

Phillips, D.

1980-10-01

Currently on NOAA/NESS's VIRGS system at the World Weather Building star images are being ingested on a daily basis. The image coordinates of the star locations are measured and stored. Subsequently, the information is used to determine the attitude, the misalignment angles between the spin axis and the principal axis of the satellite, and the precession rate and direction. This is done for both the 'East' and 'West' operational geosynchronous satellites. This orientation information is then combined with image measurements of earth based landmarks to determine the orbit of each satellite. The method for determining the orbit is simple. For each landmark measurement one determines a nominal position vector for the satellite by extending a ray from the landmark's position towards the satellite and intersecting the ray with a sphere with center coinciding with the Earth's center and with radius equal to the nominal height for a geosynchronous satellite. The apparent motion of the satellite around the Earth's center is then approximated with a Keplerian model. In turn the variations of the satellite's height, as a function of time found by using this model, are used to redetermine the successive satellite positions by again using the Earth based landmark measurements and intersecting rays from these landmarks with the newly determined spheres. This process is performed iteratively until convergence is achieved. Only three iterations are required.

Adsorption of fatty acids on iron (hydr)oxides from aqueous solutions.

PubMed

Chernyshova, Irina V; Ponnurangam, Sathish; Somasundaran, Ponisseril

2011-08-16

The interaction of iron (hydr)oxides with fatty acids is related to many industrial and natural processes. To resolve current controversies about the adsorption configurations of fatty acids and the conditions of the maximum hydrophobicity of the minerals, we perform a detailed study of the adsorption of sodium laurate (dodecanoate) on 150 nm hematite (α-Fe(2)O(3)) particles as a model system. The methods used include in situ FTIR spectroscopy, ex situ X-ray photoelectron spectroscopy (XPS), measurements of the adsorption isotherm and contact angle, as well as the density functional theory (DFT) calculations. We found that the laurate adlayer is present as a mixture of inner-sphere monodentate mononuclear (ISMM) and outer-sphere (OS) hydration shared complexes independent of the solution pH. Protonation of the OS complexes does not influence the conformational order of the surfactant tails. One monolayer, which is filled through the growth of domains and is reached at the micellization/precipitation edge of laurate, makes the particles superhydrophobic. These results contradict previous models of the fatty acid adsorption and suggest new interpretation of literature data. Finally, we discovered that the fractions of both the OS laurate and its molecular form increase in D(2)O, which can be used for interpreting complex spectra. We discuss shortcomings of vibrational spectroscopy in determining the interfacial coordination of carboxylate groups. This work advances the current understanding of the oxide-carboxylate interactions and the research toward improving performance of fatty acids as surfactants, dispersants, lubricants, and anticorrosion reagents.

Constructing the quantum Hall system on the Grassmannians Gr2(CN)

NASA Astrophysics Data System (ADS)

Ballı, F.; Behtash, A.; Kürkçüoğlu, S.; Ünal, G.

2015-04-01

In this talk, we give the formulation of Quantum Hall Effects (QHEs) on the complex Grassmann manifolds Gr2(CN). We set up the Landau problem in Gr2(CN), solve it using group theoretical techniques and provide the energy spectrum and the eigenstates in terms of the SU(N) Wigner D-functions for charged particles on Gr2(CN) under the influence of abelian and non-abelian background magnetic monopoles or a combination of these thereof. For the simplest case of Gr2(C4) we provide explicit constructions of the single and many- particle wavefunctions by introducing the Plucker coordinates and show by calculating the two-point correlation function that the lowest Landau level (LLL) at filling factor v = 1 forms an incompressible fluid. Finally, we heuristically identify a relation between the U(1) Hall effect on Gr2(C4) and the Hall effect on the odd sphere S5, which is yet to be investigated in detail, by appealing to the already known analogous relations between the Hall effects on CP3 and CP7 and those on the spheres S4 and S8, respectively. The talk is given by S. Kürkçüoğlu at the Group 30 meeting at Ghent University, Ghent, Belgium in July 2014 and based on the article by F.Ballı, A.Behtash, S. Kürkçüoğlu, G.Ünal [1].

Structure evolution of mononuclear tungsten and molybdenum species in the protonation process: Insight from FPMD and DFT calculations

NASA Astrophysics Data System (ADS)

Zhang, Ning; Yi, Haibo; Zeng, Dewen; Zhao, Zhongwei; Wang, Wenlei; Costanzo, Francesca

2018-03-01

In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4-) may partially exist as a five-coordinated WO3(OH)(H2O)- species except for the four-coordinated WO3(OH)- species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol-1) for the WO3(OH)(H2O)- and WO3(OH)- species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)- species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO42- is more easily protonated than the MoO42- anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy.

Contributions of the S100A9 C-Terminal Tail to High-Affinity Mn(II) Chelation by the Host-Defense Protein Human Calprotectin

PubMed Central

Brophy, Megan Brunjes; Nakashige, Toshiki G.; Gaillard, Aleth; Nolan, Elizabeth M.

2014-01-01

Human calprotectin (CP) is an antimicrobial protein that coordinates Mn(II) with high affinity in a Ca(II)-dependent manner at an unusual histidine-rich site (site 2) formed at the S100A8/S100A9 dimer interface. We present a 16-member CP mutant family where mutations in the S100A9 C-terminal tail (residues 96–114) are employed to evaluate the contributions of this region, which houses three histidines and four acidic residues, to Mn(II) coordination at site 2. The results from analytical size-exclusion chromatography, Mn(II) competition titrations, and electron paramagnetic resonance spectroscopy establish that the C-terminal tail is essential for high-affinity Mn(II) coordination by native CP in solution. The studies indicate that His103 and His105 (HXH motif) of the tail complete the Mn(II) coordination sphere in solution, affording an unprecedented biological His6 site. These solution studies are in agreement with a Mn(II)-CP crystal structure reported recently (PNAS 2013, 110, 3841). Remarkably high-affinity Mn(II) binding is retained when either H103 or H105 are mutated to Ala, when the HXH motif is shifted from positions 103–105 to 104–106, and when the human tail is substituted by the C-terminal tail of murine S100A9. Nevertheless, antibacterial activity assays employing human CP mutants reveal that the native disposition of His residues is important for conferring growth inhibition against Escherichia coli and Staphylococcus aureus. Within the S100 family, the S100A8/S100A9 heterooligomer is essential for providing high-affinity Mn(II) binding; the S100A7ox, S100A9(C3S), S100A12, and S100B homodimers do not exhibit such Mn(II)-binding capacity. PMID:24245608

Heteroleptic complexes of Zn(II) based on 1-(5-bromo-2-hydroxybenzylidene)-4-phenylthiosemicarbazide: Synthesis, structural characterization, theoretical studies and antibacterial activity

NASA Astrophysics Data System (ADS)

Azarkish, Mohammad; Akbari, Alireza; Sedaghat, Tahereh; Simpson, Jim

2017-04-01

Four new ternary complexes, [ZnL (2,2‧-bipy)] (1), Zn2L2(4,4‧-bipy)] (2), [ZnL(Imd)]·H2O (3) and [ZnL3(MeImd)] (4), have been synthesized from the reaction of Zn(II) acetate with 1-(5-bromo-2-hydroxybenzylidene)-4-phenylthiosemicarbazide (H2L) in the presence of a heterocyclic base, 2,2‧-bipyridine, 4,4‧-bipyridine, imidazole or 2-methylimidazole, as an auxiliary ligand. The complexes have been investigated by elemental analysis and FT-IR, UV-Vis and 1HNMR spectroscopy. These data show that the thiosemicarbazone acts as a tridentate dianionic ligand and coordinates via the thiol group, imine nitrogen, and phenolic oxygen. The coordination sphere was completed by the nitrogen atom(s) of the secondary ligand. The structure of 1 was also confirmed by X-ray crystallography and shown to be a five coordinate complex with coordination geometry between the square-pyramidal and trigonal-bipyramidal. Density functional theory (DFT) calculations including geometry optimization, vibrational frequencies and electronic absorptions have been performed for 1 with the B3LYP functional at the TZP(6-311G*) basis set using the Gaussian 03 or ADF 2009 packages. The optimization calculation showed that the crystallographically determined geometry parameters can be reproduced with that basis set. Experimental IR frequencies and calculated vibration frequencies also support each other. The in vitro antibacterial activities of the ligand and complexes have been evaluated against Gram-positive (B. subtilis and S. aureus) and Gram-negative (P. aeruginosa) bacteria and compared with the standard antibacterial drugs. The results reveal that all of the complexes show much better activity in comparison to the individual thiosemoicarbazone ligand (H2L), against all bacterial strains used, with complex 3 showing the most promising results.

Smart SPHERES: A Telerobotic Free-Flyer for Intravehicular Activities in Space

NASA Technical Reports Server (NTRS)

Fong, Terrence; Micire, Mark J.; Morse, Ted; Park, Eric; Provencher, Chris; To, Vinh; Wheeler, D. W.; Mittman, David; Torres, R. Jay; Smith, Ernest

2013-01-01

Smart SPHERES is a prototype free-flying space robot based on the SPHERES platform. Smart SPHERES can be remotely operated by astronauts inside a spacecraft, or by mission controllers on the ground. We developed Smart SPHERES to perform a variety of intravehicular activities (IVA), such as operations inside the International Space Station (ISS). These IVA tasks include environmental monitoring surveys (radiation, sound levels, etc.), inventory, and mobile camera work. In this paper, we first discuss the motivation for free-flying space robots. We then describe the development of the Smart SPHERES prototype, including avionics, software, and data communications. Finally, we present results of initial flight tests on-board the ISS.

Remote measurement of material properties from radiation force induced vibration of an embedded sphere.

PubMed

Chen, Shigao; Fatemi, Mostafa; Greenleaf, James F

2002-09-01

A quantitative model is presented for a sphere vibrated by two ultrasound beams of frequency omega1 and omega2. Due to the interference of two sound beams, the radiation force has a dynamic component of frequency omega2-omega1. The radiation impedance and mechanical impedance of the sphere are then used to compute the vibration speed of the sphere. Vibration speed versus vibration frequency is measured by laser vibrometer on several spheres, both in water and in gel phantom. These experimental results are used to verify the model. This method can be used to estimate the material properties of the medium (e.g., shear modulus) surrounding the sphere.

Smart SPHERES: A Telerobotic Free-Flyer for Intravehicular Activities in Space

NASA Technical Reports Server (NTRS)

Fong, Terrence; Micire, Mark J.; Morse, Ted; Park, Eric; Provencher, Chris

2013-01-01

Smart SPHERES is a prototype free-flying space robot based on the SPHERES platform. Smart SPHERES can be remotely operated by astronauts inside a spacecraft, or by mission controllers on the ground. We developed Smart SPHERES to perform a variety of intravehicular activities (IVA), such as operations inside the International Space Station (ISS). These IVA tasks include environmental monitoring surveys (radiation, sound levels, etc.), inventory, and mobile camera work. In this paper, we first discuss the motivation for free- flying space robots. We then describe the development of the Smart SPHERES prototype, including avionics, software, and data communications. Finally, we present results of initial flight tests on-board the ISS.

The effects of inter-cavity separation on optical coupling in dielectric bispheres.

PubMed

Ashili, Shashanka P; Astratov, Vasily N; Sykes, E Charles H

2006-10-02

The optical coupling between two size-mismatched spheres was studied by using one sphere as a local source of light with whispering gallery modes (WGMs) and detecting the intensity of the light scattered by a second sphere playing the part of a receiver of electromagnetic energy. We developed techniques to control inter-cavity gap sizes between microspheres with ~30nm accuracy. We demonstrate high efficiencies (up to 0.2-0.3) of coupling between two separated cavities with strongly detuned eigenstates. At small separations (<1 microm) between the spheres, the mechanism of coupling is interpreted in terms of the Fano resonance between discrete level (true WGMs excited in a source sphere) and a continuum of "quasi"-WGMs with distorted shape which can be induced in the receiving sphere. At larger separations the spectra detected from the receiving sphere originate from scattering of the radiative modes.

Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.

PubMed

Rodríguez-López, Tonalli; del Río, Fernando

2012-01-28

In this work we study a set of soft-sphere systems characterised by a well-defined variation of their softness. These systems represent an extension of the repulsive Lennard-Jones potential widely used in statistical mechanics of fluids. This type of soft spheres is of interest because they represent quite accurately the effective intermolecular repulsion in fluid substances and also because they exhibit interesting properties. The thermodynamics of the soft-sphere fluids is obtained via an effective hard-sphere diameter approach that leads to a compact and accurate equation of state. The virial coefficients of soft spheres are shown to follow quite simple relationships that are incorporated into the equation of state. The approach followed exhibits the rescaling of the density that produces a unique equation for all systems and temperatures. The scaling is carried through to the level of the structure of the fluids.

Recent progress in hollow sphere-based electrodes for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Zhao, Yan; Chen, Min; Wu, Limin

2016-08-01

Hollow spheres have drawn much attention in the area of energy storage and conversion, especially in high-performance supercapacitors owing to their well-defined morphologies, uniform size, low density and large surface area. And quite some significant breakthroughs have been made in advanced supercapacitor electrode materials with hollow sphere structures. In this review, we summarize and discuss the synthesis and application of hollow spheres with controllable structure and morphology as electrode materials for supercapacitors. First, we briefly introduce the fabrication strategies of hollow spheres for electrode materials. Then, we discuss in detail the recent advances in various hollow sphere-based electrode materials for supercapacitors, including single-shelled, yolk-shelled, urchin-like, double-shelled, multi-shelled, and mesoporous hollow structure-based symmetric and asymmetric supercapacitor devices. We conclude this review with some perspectives on the future research and development of the hollow sphere-based electrode materials.