Synthesis and characterization of tris(cyclopentylcyclopentadienyl)lanthanide complexes (C5H9C5H4)(3)NdBrLi(THF)(3) and (C5H9C5H4)(3)SmTHF

(C5H9C5H4)(3)NdBrLi(THF)(4)(1)(C5H9=cyclopentyl) was obtained from the reaction of NdCl3 with C5H9C5H4Na and LiBr (Nd:Na:Li=1:2:1 molar ratio) in THE X-ray crystallography showed that the ten-coordinated neodymium atom is bonded to three cyclopentylcyclopentadienyl(eta(5)) rings and a single bromine atom bridging a lithium which is bonded to three THF molecules. Complex 1 is triclinic, P1 space group with unit dimensions of a= 12.048(2), b= 13.498(3), c= 13.831(3)Angstrom, a = 104.16(3), beta = 104.07(3), gamma =95.96(3)degrees, V=2083.3(7)Angstrom(3), Z=2, D-c=1.35Mg/m(3) and F(000)=874. (C5H9C5H4)(3)SmTHF (2) was synthesized by reaction of anhydrous SmCl3 with C5H9C5H4Na at a molar ratio of 1:3. The structure was determined by X-ray crystallography. The ten-coordinated samarium atom is bonded to three cycloperrtylcyclopentadienyl rings and one oxygen of THF molecule to form a pseudo-tetrahedron. Complex 2 is orthorhombic, Fdd2 space group with unit cell dimensions of a =28.175(5)Angstrom, b =46.24(2) Angstrom, c =9.167(4) Angstrom(3), V=11943(8)Angstrom(3), Z= 16, D-c = 1.38Mg/m(3) and F(000)=5136.

Au on (111) and (110) surfaces of CeO2: A density-functional theory study

The atomic structures of gold supported on (111) and (110) surfaces of CeO2 have been studied using density-functional theory calculations. A single Au atom is placed on three adsorption sites on the surfaces; the stoichiometric surfaces, an oxygen vacancy and a Ce-vacancy. It is found that (i) the Au adsorption energies are in the following order: E-ad(Ce-vacancy) > E-ad(O-vacancy) > E-ad(stoichiometric surface); and (ii) the Au atom adsorption on the Ce-vacancy activates O atoms nearby. One 0 atom is less stable than that in O-2 in the gas phase and another O atom is much easier to remove compared to that of the stoichiometric surfaces. These results suggest that the Au adsorption on Ce-vacancies not only creates an O-vacancy but also activates an O atom nearby. This provides a piece of direct evidence that Au adsorption on a Ce-vacancy may be responsible for some unique catalytic properties of Au/CeO2. (C) 2008 Elsevier B.V. All rights reserved.

The crystal and molecular structure of bis (pyridoxamine) copper (II) dinitrate monohydrate

The crystal structure of Cu(PM)2(N03hoH20 (where PM is pyridoxamine, CSHI2N202) has been determined from three dimensional x-ray diffraction data. The crystals are triclinic, space group pI, a = 14.248 (2), b = 8.568 (1), c = 9.319 (1) 1, a = 94.08 (1), e = 89.73 (1), y~~ 99.18 (1)°, z = 2, jl(MoK) = 10.90 em-I, Po = 1.61 g/cm3 and Pc = 1.61 g/em3• The structure a was solved by Patterson techniques from data collected on a Picker 4-circle diffractometer to 26max = 45°. All atoms, including hydrogens, have been located. Anisotropic thermal parameters have been refined for all nonhydrogen atoms. For the 2390 independent reflections with F ? 3cr(F) , R = 0.0408. The results presented here provide the first detailed structural information of a metal complex with PM itself. The copper atoms are located on centres of symmetry and each is chela ted by two PM zwitterions through the amino groups and phenolate oxygen atoms. The zwitterionic form found in this structure involves the loss of a proton from the phenolate group and protonation of the pyridine ring nitrogen atoms. The two independent Cu(PM)2 moieties are symmetrically bridged by a single oxygen atom from one of the nitrate groups. The second nitrate group is not coordinated to the copper atoms but is central to an extensive hydrogen bonding network involving the water molecule and uncoordinated functional groups of PM.

Theory of enhanced magnetic anisotropy induced by Pt adatoms on two-dimensional Co clusters supported on a Pt(111) substrate

Calculations are reported of the magnetic anisotropy energy of two-dimensional (2D) Co nanostructures on a Pt(111) substrate. The perpendicular magnetic anisotropy (PMA) of the 2D Co clusters strongly depends on their size and shape, and rapidly decreases with increasing cluster size. The PMA calculated is in reasonable agreement with experimental results. The sensitivity of the results to the Co-Pt spacing at the interface is also investigated and, in particular, for a complete Co monolayer we note that the value of the spacing at the interface determines whether PMA or in-plane anisotropy occurs. We find that the PMA can be greatly enhanced by the addition of Pt adatoms to the top surface of the 2D Co clusters. A single Pt atom can induce in excess of 5 meV to the anisotropy energy of a cluster. In the absence of the Pt adatoms the PMA of the Co clusters falls below 1 meV/Co atom for clusters of about 10 atoms whereas, with Pt atoms added to the surface of the clusters, a PMA of 1 meV/Co atom can be maintained for clusters as large as about 40 atoms. The effect of placing Os atoms on the top of the Co clusters is also considered. The addition of 5d atoms and clusters on the top of ferromagnetic nanoparticles may provide an approach to tune the magnetic anisotropy and moment separately.

Catena-Poly[bis(ethane-1,2-diammonium) [manganese(II)-di-mu-phosphato-kappa O-4 : O ']]: a one-dimensional manganese phosphate

The title compound,{(C2H10N2)(2)[Mn(PO4)(2)]}(n), contains anionic square-twisted chains of formula [Mn(PO4)(2)](4-) constructed from corner-sharing four-membered rings of alternating MnO4 and PO4 units. The Mn and P atoms have distorted tetrahedral coordination and the Mn atom lies on a twofold axis. The linear manganese-phosphate chains are held together by hydrogen-bonding interactions involving the framework O atoms and the H atoms of the ethane-1,2-diammonium cations, which lie in the interchain spaces.

Copper(II) complexes of benzene-1,2-dioxyacetic acid (bdoaH2): X-ray crystal structure of [Cu2(bdoa)(phen)4]bdoa·13H2O (phen = 1,10-phenanthroline)

Copper(II) acetate reacts with benzene-1,2-dioxyacetic acid (bdoaH2) in aqueous media to give [Cu(bdoa)(H2O)2] (1). Complex 1 reacts with the N-donor ligands pyridine (py), ammonia and 1,10-phenanthroline (phen) to give [Cu(bdoa)(NH3)2]·H2O (2), [Cu(bdoa)(py)2]·H2O (3) and [Cu2(bdoa)(phen)4]bdoa·13H2O (4), respectively. The X-ray crystal structure of the dicopper(II,II) complex 4 shows each copper atom at the centre of a distorted trigonal bipyramid comprising four nitrogen atoms from two chelating phen ligands and a single oxygen atom from one of the carboxylate moieties of the bridging bdoa2− ligand. The cyclic voltammogram of 4 shows a single reversible wave for the Cu2+/Cu+ couple at E = + 115 mV (vs Ag/AgCl). Spectroscopic and magnetic data for the complexes are given.

Phosphonate ligands in extended inorganic hybrids and as radical units in complexes

Phosphonatliganden in erweiterten anorganischen Hybridmaterialien undrnals Radikalträgern in KomplexenrnrnAnorganisch-organische Hybridmaterialien sind in der Regel extrem vielseitig. Die systematische Darstellung von niederdimensionalen Materialien (eindimensionale Kettenverbindungen oder zweidimensionalen Schichtverbindungen) mit einer Kontrolle über die Art der Verbindung,rnbietet neue Möglichkeiten im Bereich des molekularen Magnetismus. Hier im Fall von Metall-Phosphonat Verbindungen in erweiterten anorganischen Hybriden wurde der pH - Wert während der Reaktion eingestellt, wodurch der Grad der Protonierung des Phosphonatliganden kontrolliert wurde. Aufgrund der Tatsache, dass alle erhaltenen Metall Phosphonatverbindungen neutral waren, konnte das Ligand zu Metallverhältnis erstmals vorhergesagt werden. So wurden mehrere neue Metall–Phosphonat Verbindungen im Bereich von Null-dimensionalen (I0O0, Co-Kristallisation von M(H2O)6 mitrndeprotonierten Phosphonatligand), über eindimensionalen (I1O0, Kettenstrukturen) bis hin zu zweidimensionalen (I2O0, Schichtstrukturen) ausführlich diskutiert in Bezug auf ihr magnetisches Verhalten. Im Allgemeinen sind die erwarteten Austauschwechselwirkungen in einem erweiterten anorganischen Hybridmaterial stark, weil oft ein Superaustausch durch ein einzelnes Sauerstoffatom möglich ist. Hier waren oft mehrere konkurrierende Austauschwechselwirkungen vorhanden, so dass kompliziertere magnetische Verhalten beobachtet wurden.rnrnDarüber hinaus wurden drei neue Beispiele von Nitronyl-Nitroxidradikale dargestellt, in denen eine zusätzliche saure Funktionalität eingeführt war. Die Auswirkungen des sauren Charakters der zusätzlich eingeführten Sulfonsäure oder Phosphonsäure-Gruppe auf das Nitronyl-Nitroxidradikal wurden im Detail zum ersten Mal untersucht. Die mit der Phosphonsäure-Gruppe versehenen Nitronyl-Nitroxidradikale sind perfekte Proben für die Untersuchung einer Spin-Verschiebung in Nitronyl-Nitroxidradikale durch EPR-Spektroskopie, aufgrund des eingeführten Phosphors. Auch der Protonierungsgrad der zusätzlich eingeführten Phosphonsäure-Gruppe wurde berücksichtigt. In dieser Arbeit wurden die ersten Metallkomplexe der neuen substituierten sauren Nitronyl-Nitroxidradikale vorgestellt. Die Koordination von Nickel(II) Metallionen an die saure, zweite funktionelle Gruppe des Nitronyl–Nitroxid Radikal wurde beschrieben. Die magnetische Austauschwechselwirkung der Metallionen untereinander und die Metall-Radikal-Austauschwechselwirkungen wurden untersucht. rnrnIm Allgemeinen können interessante molekulare magnetische Materialien dadurch dargestellt werden, dass die Dimension der Metall-Phosphonat-Verbindungen als Beispiele für die erweiterten anorganischen Hybridmaterialien gesteuert werden kann. Mit Nitronyl-Nitroxidradikale als organische Liganden können in Zukunft noch mehr Spin-Träger in anorganisch-organischen Gerüstmaterialien integriert werden um die magnetischen Eigenschaften zu verbesseren.rn

Thermoelektrische und strukturelle Eigenschaften gefüllter Skutterudite, sowie Verbesserung ihres Gütefaktors durch Nanostrukturierung

Gefüllte Skutterudite mit der Summenformel MxCo4Sb12 sind vielversprechende thermoelektrische Materialien. Die Standardsynthese führt jedoch oft zur Bildung von MSbx, Sb, CoSb oder CoSb2 als Nebenphasen. In dieser Arbeit wird eine neue zweistufige Synthese vorgestellt, bei der die Bildung des Kieftits (CoSb3) getrennt von dem topotaktischen Füllen mit dem Metallatom M erfolgt. Dieser Ansatz erlaubt eine Durchführung der Reaktion bei niedrigeren Temperaturen mit kürzeren Reaktionszeiten. Ein geringer Antimon-Unterschuss im so erhaltenen Kieftit erhöht die Anzahl der Ladungsträger und unterdrückt die Bildung von Verunreinigungsphasen. Zunächst wurden Skutteruditproben mit der nominellen Zusammensetzung InxCo4Sb12 mit x = 0,12; 0,15; 0,18 und 0,20 in hoher Reinheit hergestellt und mit Spark Plasma Sintering (SPS) kompaktiert. Messaufnahmen mit Potential- und Seebeck-Mikrosonde und Rasterelektronenmikroskop zeigten eine hohe Probenhomogenität. Produkte waren nahezu phasenrein, was eine Untersuchung der Transporteigenschaften ohne Verfälschung durch Nebenphasen ermöglichte. Die quantitative Phasenanalyse mittels Synchrotron-Beugungsdaten zeigte < 0,1 % InSb bei In0,18Co4Sb12 und In0,20Co4Sb12, sowie eine lineare Korrelation zwischen dem wahren Füllgrad und der Gitterkonstante. Die Bindung von < 0,1 % InSb verringerte den Füllgrad der nominellen In0,20Co4Sb12-Probe auf x = 0,144. Die nominelle In0,18Co4Sb12-Probe mit dem wahren Gehalt x = 0,160 hatte den höchsten zT-Wert nahe eins bei 420 °C. Es konnte anschließend die Anwendbarkeit der Synthesemethode für Barium- und mehrfach gefüllte (Na+In) Skutterudite gezeigt werden. Die Na-gefüllte Probe war gegenüber der thermischen Behandlung in der SPS oder der Charakterisierung instabil. Alle Verbindungen wurden gesintert und ihre Transporteigenschaften wurden charakterisiert. Des weiterem wurde der Einfluss der Konzentration der Korngrenzen bei den Mischungen von zu Nanomaßstab vermahlenem In0,18Co4Sb12 (Partikelgrößen zwischen 20 und 100 nm) mit dem ursprünglichen Bulk untersucht. Proben mit verschiedenen Anteilen von Nanopulver wurden gesintert, ihre thermoelektrischen und strukturellen Eigenschaften wurden untersucht. Die Gütezahl zT von 1,39 bei 375 °C wurde bei der Probe mit gleichen Anteilen des Nano- und des unbehandelten Pulvers erreicht. Die Komposite mit Anteilen <10 % oder >75 % des Nanopulvers zeigten keine Verbesserung gegenüber der unbehandelten Verbindung.rn

Structure at 2.7 Å resolution of the Paracoccus denitrificans two-subunit cytochrome c oxidase complexed with an antibody FV fragment

The aa3 type cytochrome c oxidase consisting of the core subunits I and II only was isolated from the soil bacterium Paracoccus denitrificans and crystallized as complex with a monoclonal antibody Fv fragment. Crystals could be grown in the presence of a number of different nonionic detergents. However, only undecyl-β-d-maltoside and cyclohexyl-hexyl-β-d-maltoside yielded well-ordered crystals suitable for high resolution x-ray crystallographic studies. The crystals belong to space group P212121 and diffract x-rays to at least 2.5 Å (1 Å = 0.1 nm) resolution using synchrotron radiation. The structure was determined to a resolution of 2.7 Å using molecular replacement and refined to a crystallographic R-factor of 20.5% (Rfree = 25.9%). The refined model includes subunits I and II and the 2 chains of the Fv fragment, 2 heme A molecules, 3 copper atoms, and 1 Mg/Mn atom, a new metal (Ca) binding site, 52 tentatively identified water molecules, and 9 detergent molecules. Only four of the water molecules are located in the cytoplasmic half of cytochrome c oxidase. Most of them are near the interface of subunits I and II. Several waters form a hydrogen-bonded cluster, including the heme propionates and the Mg/Mn binding site. The Fv fragment binds to the periplasmic polar domain of subunit II and is critically involved in the formation of the crystal lattice. The crystallization procedure is well reproducible and will allow for the analysis of the structures of mechanistically interesting mutant cytochrome c oxidases.

Molecular determinants of tissue selectivity in estrogen receptor modulators

Interaction of the estrogen receptor/ligand complex with a DNA estrogen response element is known to regulate gene transcription. In turn, specific conformations of the receptor-ligand complex have been postulated to influence unique subsets of estrogen-responsive genes resulting in differential modulation and, ultimately, tissue-selective outcomes. The estrogen receptor ligands raloxifene and tamoxifen have demonstrated such tissue-specific estrogen agonist/antagonist effects. Both agents antagonize the effects of estrogen on mammary tissue while mimicking the actions of estrogen on bone. However, tamoxifen induces significant stimulation of uterine tissue whereas raloxifene does not. We postulate that structural differences between raloxifene and tamoxifen may influence the conformations of their respective receptor/ligand complexes, thereby affecting which estrogen-responsive genes are modulated in various tissues. These structural differences are 4-fold: (A) the presence of phenolic hydroxyls, (B) different substituents on the basic amine, (C) incorporation of the stilbene moiety into a cyclic benzothiophene framework, and (D) the imposition of a carbonyl “hinge” between the basic amine-containing side chain and the olefin. A series of raloxifene analogs that separately exemplify each of these differences have been prepared and evaluated in a series of in vitro and in vivo assays. This strategy has resulted in the development of a pharmacophore model that attributes the differences in effects on the uterus between raloxifene and tamoxifen to a low-energy conformational preference imparting an orthogonal orientation of the basic side chain with respect to the stilbene plane. This three-dimensional array is dictated by a single carbon atom in the hinge region of raloxifene. These data indicate that differences in tissue selective actions among benzothiophene and triarylethylene estrogen receptor modulators can be ascribed to discrete ligand conformations.

Microscopic theory for quantum mirages in quantum corrals

Scanning tunneling microscopy permits us to image the Kondo resonance of a single magnetic atom adsorbed on a metallic surface. When the magnetic impurity is placed at the focus of an elliptical quantum corral, a Kondo resonance has been recently observed both on top of the impurity and on top of the focus where no magnetic impurity is present. This projection of the Kondo resonance to a remote point on the surface is referred to as quantum mirage. We present a quantum mechanical theory for the quantum mirage inside an ideal quantum corral and predict that the mirage will occur in corrals with shapes other than elliptical.

Storage of classical information in quantum spins

Digital magnetic recording is based on the storage of a bit of information in the orientation of a magnetic system with two stable ground states. Here we address two fundamental problems that arise when this is done on a quantized spin: quantum spin tunneling and backaction of the readout process. We show that fundamental differences exist between integer and semi-integer spins when it comes to both reading and recording classical information in a quantized spin. Our findings imply fundamental limits to the miniaturization of magnetic bits and are relevant to recent experiments where a spin-polarized scanning tunneling microscope reads and records a classical bit in the spin orientation of a single magnetic atom.

Crystal structure of P450cin in a complex with its substrate, 1,8-cineole, a close structural homologue to D-camphor, the substrate for P450cam

Cytochrome P450cin catalyzes the monooxygenation of 1,8-cineole, which is structurally very similar to D-camphor, the substrate for the most thoroughly investigated cytochrome P450, cytochrome P450cam. Both 1,8-cineole and D-camphor are C-10 monoterpenes containing a single oxygen atom with very similar molecular volumes. The cytochrome P450cin-substrate complex crystal structure has been solved to 1.7 Angstrom resolution and compared with that of cytochrome P450cam. Despite the similarity in substrates, the active site of cytochrome P450cin is substantially different from that of cytochrome P450cam in that the B' helix, essential for substrate binding in many cytochrome P450s including cytochrome P450cam, is replaced by an ordered loop that results in substantial changes in active site topography. In addition, cytochrome P450cin does not have the conserved threonine, Thr252 in cytochrome P450cam, which is generally considered as an integral part of the proton shuttle machinery required for oxygen activation. Instead, the analogous residue in cytochrome P450cin is Asn242, which provides the only direct protein H-bonding interaction with the substrate. Cytochrome P450cin uses a flavodoxin-like redox partner to reduce the heme iron rather than the more traditional ferredoxin-like Fe2S2 redox partner used by cytochrome P450cam and many other bacterial P450s. It thus might be expected that the redox partner docking site of cytochrome P450cin would resemble that of cytochrome P450BM3, which also uses a flavodoxin-like redox partner. Nevertheless, the putative docking site topography more closely resembles cytochrome P450cam than cytochrome P450BM3.

Spin-charge conductance in nanoscale electronic devices

We introduce a spin-charge conductance matrix as a unifying concept underlying charge and spin transport within the framework of the Landauer-Buttiker conductance formula. It turns out that the spin-charge conductance matrix provides a natural and gauge covariant description for electron transport through nanoscale electronic devices. We demonstrate that the charge and spin conductances are gauge invariant observables which characterize transport phenomena arising from spin-dependent scattering. Tunnelling through a single magnetic atom is discussed to illustrate our theory.

Bioquímica quântica na diferenciação dos níveis de ativação de receptores AMPA por agonistas parciais Wilardina

In the central nervous system (CNS) of mammalian, fast synaptic transmission between nerve cells is performed primarily by α-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) receptors, an ionotropic glutamate receptor that is related with learning, memory and homeostasis of the nervous system. Impairments in their functions are correlated with development of many brain desorders, such as epilepsy, schizophrenia, autism, Parkinson and Alzheimer. The use of willardiine analogs has been shown a powerful tool to understanding of activation and desensitization mechanisms of this receptors, because the modification of a single ligand atom allows the observation of varying levels of efficacy. In this work, taking advantage of Fluorine Willardiine (1.35Å), Hydrogen Willardiine (1.65Å), Bromine Willardiine (1.8Å) and Iodine Willardiine (2.15Å) structures co-crystalized with GluA2 with codes 1MQI, 1MQJ, 1MQH and 1MQG, we attempted to energetically differentiate the four ligands efficacy. The complexes were submitted to energetic calculations based on density functional theory (DFT), under the optics of molecular fractionation with conjugate caps (MFCC) method. Obtained results show a relationship between the energetic values and willardiines efficacy order (FW> HW > BrW > IW), also show the importance of E705, R485, Y450, S654, T655, T480 e P478 as the amino acids that contribute most strongly with the interaction of four partial agonists. Furthermore, we outlined the M708 behaviour, attracted by FW and HW ligands, and repels by BrW and IW. With the datas reported on this work, it is possible for a better understanding of the AMPA receptor, which can serve as an aid in the development of new drugs for this system.