Pyramidal Sites Research Articles

Changes in Corticospinal Efficacy Contribute to the Locomotor Plasticity Observed After Unilateral Cutaneous Denervation of the Hindpaw in the Cat

We used microwire electrodes chronically implanted into the hindlimb representation of the motor cortex as well as into the pyramidal tract to test the hypothesis that the corticospinal system contributes to the locomotor plasticity that is observed after cutaneous denervation of the cat hindpaw. A total of 23 electrodes implanted into the motor cortex in three cats trained to walk on a treadmill produced phase-dependent, short-latency, twitch responses in hindlimb flexor and extensor muscles during locomotion. After a unilateral cutaneous denervation of the hindpaw, the cats showed transient deficits in locomotion, including a dragging of the hindpaw along the treadmill belt during the swing phase. This deficit rapidly recovered over the course of a few days. The recovery of locomotion was accompanied by an increase in the magnitude of the responses evoked in different muscles by the cortical stimulation at all 23 cortical sites. Response magnitude increased rapidly within the first 1-2 wk postdenervation before attaining a plateau at > or =3 wk. In two cats, for which detailed information was obtained, response magnitude in the knee flexor, semitendinosus (St), was increased by >250% at 14/18 sites (mean increase = 1,235%). Increased responses in the St to stimulation were also observed at two of the four pyramidal tract sites after the denervation but were relatively smaller (max = 593%) than those evoked by the cortical stimulation. We suggest that the denervation produces changes in both cortical and spinal excitability that, together, produce a change in corticospinal efficacy that contributes to the recovery of locomotor function.

Crystal and Magnetic Structures of the Mn3+ Orbital Ordered Manganite YBaMn2O5.5

The compound YBaMn2O5.5, having only Mn3+, has been prepared by carefully oxidizing/reducing YBaMn2O5/YBaMn2O6. We have determined its crystal (Icma, a ≈ 8.161, b ≈ 7.546, c ≈ 15.279 A) and magnetic (collinear antiferromagnetic) structures using neutron powder diffraction as a function of temperature. The compound is an insulator at all measured temperatures, showing an activated conductivity, Ea ≈ 0.22 eV. According to bond valence calculations, two Jahn−Teller distorted Mn3+ are associated with MnO6 octahedra and MnO5 pyramids. The signs of the exchange interactions deduced from the corresponding orbital ordering are in good agreement with the observed magnetic structure. The magnetic moment, at low temperature, of the two kinds of Mn3+ ions are slightly different: 3.5(1) μB for the pyramidal site and 3.7(1) μB for the octahedral site. The reduction with respect to the expected moment is due to a combination of covalence and zero-point fluctuations of the AF structure.

Structure and magnetic properties in the La 1− xEu xBaFeCuO 5+ δ system

The solid solution La 1− x Eu x BaFeCuO 5+ δ synthesized in air with 0 ⩽ δ ⩽ 0.13 was studied by X-ray diffraction, 57Fe Mössbauer spectroscopy and susceptibility measurements. Double perovskite with YBaFeCuO 5-type structure was observed except for x = 0 composition which has a cubic cell. Fe and Cu are generally in square pyramidal environments which differ by their distortion: axially compressed for Fe and elongated for Cu. Mössbauer studies showed the existence of pyramidal Fe 3+, Fe 3+ y and octahedral Fe 4+. Electric field gradient calculations allowed to better understand the origin of the distortion of the two pyramidal iron sites.

Magnetization and neutron diffraction studies on FeCrP

Crystal structure and magnetic behaviour of FeCrP have been investigated using magnetization and neutron diffraction measurements. FeCrP crystallizes in orthorhombic FeZrP type structure (Pnma space group,Z = 4) in which Cr atoms occupy the pyramidal site and Fe atoms occupy the tetrahedral site with total preference. Structural parameters including positional parameters have been refined. The refined values of positional parameters for Fe and Cr are quite different from those in FeZrP. The nature of magnetization-temperature curve is suggestive of antiferromagnetic nature withTN = 280 (±10) K. Preliminary analysis of neutron diffraction pattern at 13 K is indicative of a rather complicated magnetic structure.

Synthesis, crystal structure, and magnetic investigations of FePb 1−xBa xP 2O 7 (0≤x

The new solid solution Fe(Pb 1−xBa x)P 2O 7 has been synthesized by solid reactions. In the whole experimental range (0≤x<1 ; T=850 °C), this solid solution is isotypic to the pure phase FePbP 2O 7 and closely related to αCa 2P 2O 7. The structures of FePbP 2O 7 ( x=0) and FePb 0.2Ba 0.8P 2O 7 ( x=0.8) have been determined from a single crystal and refined to R=0.041 and R=0.034, respectively. FePbP 2O 7 and FePb 0.2Ba 0.8P 2O 7 crystallize in the monoclinic space group P2 1/n, with a=5.3800(11) Å, b=8.3100(17) Å, c=12.800(3) Å, β=91.00(3)° and a=5.5333(2) Å, b=8.4196(3) Å, c=12.8238(2) Å and β=91.16(2)°, respectively. The most salient feature of the FePbP 2O 7 structure is the presence of an isolated 4+1 square pyramidal site occupied by Fe 2+. The connections between FeO 5 units and P 2O 7 diphosphate groups define tunnels along [100] where Pb 2+ cations are located and give rise to a three-dimensional framework. The cationic distribution (Pb 2+, Ba 2+) has been determined for the isostructral compounds Fe(Pb 1−xBa x)P 2O 7 (0≤x<1). FePbP 2O 7 is antiferromagnetic : T N=10 K; this is consistent with the fact that the magnetic interactions arise only from the Fe–O–P–O–Fe superexchange mechanism.

&lt;b&gt;Synthesis and characterization of monomeric manganese(II) and cobalt(III) complexes of the hexadentate amine ligand N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine, C&lt;sub&gt;26&lt;/sub&gt;H&lt;sub&gt;28&lt;/sub&gt;N&lt;sub&gt;6&lt;/sub&gt; (tpen)&lt;/b&gt;

The syntheses and characterization of complexes of manganese(II) and cobalt(III) with the potentially hexadentate ligand N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine, C26H28N6 (tpen), are described. The monomeric manganese(II) complex [Mn(C26H28N6)(H2O)](ClO4)2 (1) crystallizes in the monoclinic space group C2/c with 4 formula units in a cell of dimensions a = 15.080(1) Å, b = 10.101(1) Å, c = 19.426(2) Å and b = 94.6l(l)°. The structure has been refined to a final value of the conventional R-factor of 0.0401 based on 2586 observed independent reflections. The geometry at the manganese center is seven-coordinate, and is best described as a capped trigonal pyramid with the water molecule forming the cap and the six nitrogen atoms of the tpen ligand occupying the pyramidal sites. The manganese atom and the water molecule lie on a crystallographic twofold axis. The related cobalt(III) complex, [Co(C26H28N6)] (C1O4)3 (4) crystallizes in the monoclinic space group P21/n with 4 formula units in a cell of dimensions a = 9.829(2) Å, b = 18.364(4) Å, c = 18.128(4) Å and b = 93.64(3)°. The structure has been refined to a final value of the conventional R-factor of 0.0526 based on 3574 observed independent reflections. The complex is approximately octahedral, the coordination being provided by the six nitrogen atoms of the tpen ligand. The EPR spectrum of 1 diluted into the corresponding Cd(II) host has been simulated with the parameters g = 2.00, A = 0.0080 cm-1, D = 0.116 cm-1, and E = 0.0013 cm-1. The small value of E/D is consistent with the observed symmetry of the complex. KEY WORDS: Monomeric manganese(II) complex, Monomeric cobalt(III) complex, Hexadentate ligand, N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine Bull. Chem. Soc. Ethiop. 2004, 18(1), 17-28.

Calcium and Strontium Hexaluminates: NMR Evidence that “Pentacoordinate” Cation Sites Are Four‐Coordinated.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Calcium and Strontium Hexaluminates: NMR Evidence that “Pentacoordinate” Cation Sites Are Four-Coordinated

We report new, high-resolution solid state 27Al NMR data for two members of the magnetoplumbite group of structures, strontium hexaluminate (SrAl12O19, “SA6”) and calcium hexaluminate (CaAl12O19, “CA6,” synthetic hibonite), acquired at 14.1 and 18.8 T fields. The high-field data allow, for the first time, the accurate observation of the NMR signal from the Al(2) sites, which have been previously described as “pentacoordinate” but which appear instead to be very distorted tetrahedra, which give rise to 27Al isotropic chemical shifts of about 57 ppm and nuclear quadrupolar coupling constants of about 21 MHz. This finding is fully consistent with “split-atom” refinements of these crystal structures, in which the most probable position of the Al atom is displaced away from the average trigonal pyramidal site center, along the crystallographic 3-fold axis. The NMR data also demonstrate, however, that the “splitting” is the result of static, not dynamical, disorder among these sites.

A three-dimensional bimetallic oxide constructed from octamolybdate clusters and copper–ligand cation polymer subunits. A comment on the stability of the octamolybdate isomers

Hydrothermal reactions of CuSO 4·5H 2O, MoO 3 and tetra-2-pyridylpyrazine (tpyrpyz) yield the three-dimensional bimetallic oxide hybrid material [{Cu 2(tpyrpyz)} 2{ζ-Mo 8O 26}]·7H 2O ( 1·7H 2O). The framework structure is constructed from {Cu 2(tpyrpyz)} n 2 n+ cationic polymer chains linked through octamolybdate clusters. The ζ-isomer of {Mo 8O 26} 4−, consisting of four octahedral and four square pyramidal sites is present as the cluster building block. There are now seven isomeric forms of the {Mo 8O 26} 4− cluster, and calculations of their relative energies and interconversions are presented. Crystal data: C 48H 46Cu 4Mo 8N 12O 33 ( 1·7H 2O), monoclinic C2/ c, a=26.678(1), b=10.8981(4), and c=25.4109(9) Å, β=116.855(1)°, V=6591.2(4) Å 3, Z=4, D calc=2.359 g cm −3.

Photodarkening effect in glassy As2S3 and As2O3

Photodarkening, or the shift of the optical absorption edge to smaller energies after excitation with light whose energy is near that of the optical band edge, has been studied in the chalcogenide glasses for many years. Recently we have conducted high field nuclear magnetic resonance (NMR) studies at 17 T and nuclear quadrupole resonance (NQR) studies of 75As in glassy As2S3. We have compared the 75As NMR and NQR lineshapes in glassy As2S3 and As2O3 before and after irradiation. An increase in the asymmetry parameter would have implied an increase in the departure from cylindrical symmetry in the bonding at the arsenic pyramidal sites. The null result reported here is inconsistent with microscopic models of photodarkening that involve switching of large numbers of As–Chalcogen bonds.

HREM and CIP Characterization of Complex Superstructures in Cu‐Co Related Perovskites

AbstractTwo compositions in the La‐Ba‐Cu‐Co‐O system − La2Ba3Cu2Co3O13 and La2Ba3Cu3Co2O13 − have been synthesized and characterized by means of SAED (Selected Area Electron Diffraction) and HREM (High Resolution Electron Microscopy). The La2Ba3Cu2Co3O13 phase leads to a fivefold perovskite superstructure along the c axis, which can be described as formed by the recurrent intergrowth of the two alternating blocks ···PP··· and ···POhP··· (P = pyramid and Oh = octahedron). Pyramidal and octahedral sites are randomly occupied by Cu/Co cations, while La/Ba cations exhibit an ordered distribution. The La2Ba3Cu3Co2O13 composition gives rise to a mixture of phases in which a new phase showing a threefold superstructure due to the sequence ···POhP··· coexists with a fivefold superstructure with the same polyhedra sequence (···PPPOhP···) as the previous one, but a disordered arrangement of lanthanum‐barium cations. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis and characterization of La 4BaCu 5O 13+ δ and La 4BaCu 5− xMxO 13+ δ: M=Fe, Co, Ni, Zn

La 4BaCu 5− x M x O 13+ δ : M=Fe, Co, Ni, Zn were prepared by the solid-state route at 1000°C. Solid solution limits of x=1.0(1) [Fe], x=1.1(1) [Co], x=1.56(7) [Ni] and x=0.47(1) [Zn] were determined from XRD and EPMA results. Rietveld refinement of combined XRD/neutron powder diffraction data was carried out on undoped La 4BaCu 5O 13+ δ and x=1 for M=Fe, Co, Ni. For La 4BaCu 5O 13+ δ , which is an oxygen-deficient perovskite, the presence of square planar CuO 4 groups, disordered over the Cu(2) sites with CuO 5 square pyramids, is indicated, together with, for δ<0, either square planar CuO 4 or square pyramidal CuO 5 and octahedral CuO 6 groups disordered over the Cu(1) sites. For M=Fe, Ni, there was preferential substitution onto the one-fold octahedral site; for M=Co, substitution took place on both the one-fold octahedral and four-fold square pyramidal sites.

Effect of iron doping on the properties of TbBaCo2O5.5 layered perovskite

The properties of the TbBa(Co2−xFex−)O5+δ (0&amp;lt;x⩽1) system, exhibiting the giant magnetoresistance effect, were studied by magnetization, thermogravimetric analysis (TGA), and resistivity measurements as well as by Mössbauer spectroscopy. It was found that the properties of this system dramatically change at x&amp;gt;0.1, at which a concentration-dependent orthorhombic–tetragonal transition takes place. The orthorhombic composition with x=0.1 exhibits a transition from an antiferromagnetic to weak ferromagnetic state at a temperature Ti=200 K on warming and at 160 K on cooling, and a transition from a weak ferromagnetic to paramagnetic state at TN=304 K. A metal–insulator transition occurs at TM=348 K on warming. Transformation into a tetragonal phase (x⩾0.12) leads to the disappearance of both the weak ferromagnetic state and the metal–insulator phase transition. Also, the Néel point drops. The orthorhombic and tetragonal phases coexist in the concentrational range (0.1&amp;lt;x&amp;lt;0.12). Mössbauer spectroscopy has shown that Fe3+ ions preferentially occupy two low-symmetry positions that are interpreted to be pyramidal sites with fivefold coordination. Both Mössbauer spectroscopy and TGA data revealed that the increase of Fe content leads to the decrease of oxygen content according to the formula TbBa(Co2−xFex)O5.5−x/2. It is supposed that at x⩾0.12 a change of the type of oxygen vacancy ordering occurs.

Oxygen Vacancies and Intermediate Spin Trivalent Cobalt Ions in Lithium-Overstoichiometric LiCoO2

Thermal treatments under a very wide range of oxygen pressures were used to probe the composition and defect nature of a lithium-overstoichiometric “Lix0CoO2” (x0 > 1) sample using X-ray powder diffraction, 7Li NMR, and electrochemical tests. It was found that at 900 °C, under atmospheric and elevated oxygen pressures, the lithium-overstoichiometric sample gradually transformed to stoichiometric LiCoO2 by losing excess lithium in the form of Li2O. In addition, it was shown that the defect associated with Co2+ and oxygen deficiency as reported by Gorshkov et al. and Karelina et al. had a different NMR signature than that present in Li-overstoichiometric samples. Therefore, it is believed that oxygen vacancies are present but Co2+ ions are not present in Lix0CoO2 (x0 > 1). This leads to a formula [Li]interslab[CoIII1-3tCo3+(IS)2tLit]slab[O2-t], involving an intermediate spin configuration for 2t Co3+ ions in a square-based pyramidal site. This new model was supported by the NMR and magnetic data of the lithium-overstoichiometric sample and its deintercalated compounds. The effect of the defect on the end-of-discharge voltage profile during cycling was also discussed.

Nuclear quadrupole resonance study of the glassy As xSe 1− x system

Nuclear quadrupole resonance (NQR) of 75 As has been used to study the local bonding structure of glassy arsenic–selenium systems. We have studied the glassy system As x Se 1− x with x=0.08, 0.15, 0.27, 0.32, 0.36, 0.40, 0.50, and 0.60 using 75 As NQR at liquid nitrogen temperature (77 K). The 75 As NQR spin-echo spectra from x=0.08 up to x=0.40 each consist of a single broad line. As the concentration of arsenic increases, the positions of the peaks decrease approximately linearly from 63 MHz at x=0.08 to 58 MHz at x=0.40. For x=0.50, the spectrum, consists of a very broad asymmetric peak near 81 MHz. The spectrum for x=0.60 consists of three well-resolved, narrow peaks, but otherwise extends over a similar frequency range as that of x=0.50. By comparison with NQR spectra that occur in crystalline arsenic–selenium compounds, these three peaks have been interpreted as due to three fold co-ordinated, pyramidal arsenic sites with, varying numbers of arsenic–arsenic bonds.

Characterization of Chromium-Substituted Zeolite BEA

Abstract Chromium-incorporated BEA zeolite samples (CAB) are synthesized via a hydrothermal procedure, and their chemical compositions are analyzed by both the ICP-AES and EDX techniques. Synthesized samples are characterized for the local environment of chromium through FTIR, thermal analysis and cyclic voltammetry. An observation of a notable band in FTIR (at 955 cm-1) of calcined/acetic acid-washed samples of CAB revealed that at least a part of chromium is associated with the framework. In a thermal analysis, a high-temperature (643–773 K) desorption peak of TEA+ was noticed; the peak size increased along with an increase in the chromium content. Cyclic voltammograms of as-synthesized, calcined and acetic acid-treated samples gave ample evidence for the incorporation of chromium into the framework. Acid-washed CAB samples showed framework-stabilized chromium in a zeolite BEA structure, possibly under two different local environments, i.e. tetrahedral and square pyramidal sites.

Structural Change at Metal-Insulator Transition of Tb2Ba2Co4O11

Temperature variation of the crystal structure has been investigated for Tb 2 Ba 2 Co 4 O 11 , which shows a metal-insulator (MI) transition at T MI = 340 K. The compound has a layered-type double-perovskite structure along the c -axis, with alternating the CoO 6 octahedron and the CoO 5 pyramids along the a -axis. With decrease of temperature below T MI , the distortion of the octahedral and pyramidal sites is fairly released, suggesting that spin state transition of the Co 3+ ions is the origin for the MI transition.

Comparison of the dynamics of hydrogen and deuterium dissolved in crystalline Pd 9Si 2 and Pd 3P 0.8

The bonding potentials of hydrogen and deuterium dissolved in the crystalline alloys Pd 9Si 2 and Pd 3P 0.8 have been studied by neutron scattering techniques. Neutron powder diffraction verifies that, in both alloys, the principal type of interstitial absorption site is the quadrilateral base of a Pd-defined pyramid situated on the face of an empty triangular prism. The neutron vibrational spectroscopy results indicate that, although the H and D vibrational energies parallel to the Pd pyramidal base appear to be similar for both alloys, the H and D vibrational energies perpendicular to the Pd pyramidal base for Pd 9Si 2 are ≈15% softer than the corresponding energies for Pd 3P 0.8. Both neutron vibrational spectroscopy and quasielastic neutron scattering show that hydrogen hopping between the two pyramidal absorption sites associated with different faces of the same prism is much more rapid in Pd 9Si 2 than in Pd 3P 0.8. This may be directly attributable to the observed softer potential along the hopping trajectory (i.e. perpendicular to the Pd pyramidal base) for the interstitial site in Pd 9Si 2 compared to that in Pd 3P 0.8.

Magnetic behaviour of alloys in the series (Fe 1− xCo x) 2P

Magnetization and Mössbauer spectroscopic measurements are reported on five alloys in the series (Fe 1− x Co x ) 2P (corresponding to x=0.03, 0.10, 0.30, 0.50 and 0.70). All the five alloys are ferromagnetically ordered. With increasing cobalt, the Curie temperature initially increases becoming maximum for x=0.30 at 480 K and then drops. In going from x=0.10 to 0.30, when the crystalline symmetry changes from Fe 2P-like hexagonal one to Co 2P-like orthorhombic one, the magnetic moment on the pyramidal metallic site tilts off the V zz -axis. In all the compositions, substitution of cobalt reduces the internal magnetic field at the tetrahedral site whereas that at the pyramidal site shows little change. The system with x=0.03 exhibits temporal relaxation of magnetization over a long period of time. Mössbauer spectra of this alloy exhibit a reduction in linewidth with increasing temperature from 80 to 125 to 160 K. These observations are indicative of the existence of magnetic clusters.

Submersible Observations of the Hydrothermal Vent Communities on the Iheya Ridge, Mid Okinawa Trough, Japan

During the Dives Nos. 409, 410, 480 and 481 of the Japanese submersible Shinkai 2000, conducted on June 10 and 11, 1989 and on May 16 and 17, 1990, several hydrothermal vents and prosperous vent associated biological communities were found on the northern slope of the Iheya Ridge in the Mid-Okinawa Trough (27°32.5′ N, 126°58.5′ E: depth 1,400 m). The first site we found, the “Calyptogena Site”, was characterized by a relatively thick blanket of sediments, pleated and/or laminated lava flows, with occasional lobate pillows and white and yellow stains. Although no remarkable shimmering water and thermal anomalies were detected during the observations, the extraordinarily dense community must be related to hydrothermal activities. The community was dominated by the giant white clam, Calyptogena okutanii, in biomass, and by Neolepas-type primitive scalpellids and slender vestimentiferan tube-worms in number. The second site, the “Pyramid Site”, situated only 200 m northward from the Calyptogena Site has typical clear smokers emitting hot water over 200°C, and is characterized by a hard substratum of volcanic rocks and hydrothermal slabs. No noteworthy succession was perceived at the Calyptogena Site over a year. Many of the vent members occurred at both sites. However, Calyptogena okutanii, which were confined to the sediment bottom, Neolepas spp. and larger vestimentiferan tube-worms were found to thrive only at the Calyptogena Site, being only minor elements in the Pyramid Site. The global distribution of several groups of organisms is discussed preliminarily in zoogeographical terms based on comparison with other submersible missions and surveys done by surface vessels.