Search results for "Orthorhombic crystal system"
showing 10 items of 205 documents
Expanding the 2, 2’-bipyrimidine bridged 1D homonuclear coordination polymers family: [MIIbpymCl2] (M=Fe, Co) magnetic and structural characterization
2013
One pot reaction of hydrated chloride salts of Fe(II) and Co(II) with stoichiometric amounts of 2, 2’-bipyrimidine (bpym) in a methanol/ acetonitrile mixture afforded the corresponding 1D homonuclear coordination polymers, [μ-(bpym)MCl2]n. Crystal structures of both complexes are isomorphous in the highly symmetric orthorhombic space group Fddd. The 1D coordination polymers are composed of almost orthogonal alternating bipyrimidine bridges linking the {MCl2} units. The magnetic behaviour of the Fe(II)compound can be well understood as a uniform S=2 chain with antiferromagnetic exchange interaction between metal ion sites. In the case of the Co(II) ion, also an antiferromagnetic interaction …
A novel caryophyllene type sesquiterpene lactone from Asparagus falcatus (Linn.); Structure elucidation and anti-angiogenic activity on HUVECs
2011
Abstract In this study the novel caryophyllene type sesquiterpene lactone (aspfalcolide) has been isolated from the leaves of Asparagus falcatus (Linn.) and characterized by IR, 1D NMR, 2D NMR, EI–MS, HR–ESI–MS and X-ray single crystal diffraction analysis. The aspfalcolide crystallizes in the orthorhombic space group P212121 with a = 6.37360(10), b = 7.6890(2), c = 27.3281(6) A, α = β = γ = 90° and Z = 4. One intermolecular O–H⋯O hydrogen bond enforces these natural molecules to form infinite chains through the crystal. Aspfalcolide was screened for its anti-angiogenic activity in human umbilical vein endothelial cells (HUVECs) and the result showed the remarkable inhibitory effect of aspf…
Vibrational analysis of iron and zinc phosphate conversion coating constituents
2001
Abstract The FT-MIR/FT-FIR and NIR-FT-Raman spectra of orthorhombic α -Zn 3 (PO 4 ) 2 ·4H 2 O (α-hopeite) and monoclinic Zn 2 Fe(PO 4 ) 2 ·4H 2 O (phosphophyllite), including deuterated samples, have been measured in the polycrystalline state at room temperature and below. The distribution of vibrational levels was related to the results of complete unit-cell group analyses. The number of uncoupled OD stretching modes of α-hopeite (isotopically dilute samples) strongly exceeds that expected from the number of hydrogen positions of the structure reported. In contrast, unequivocal assignment of the four hydrogen bonds of phosphophyllite has been performed. The distortion of the phosphate tetr…
Synthesis and characterization of novel bile-acid – heteroaryl conjugates with N-(2-aminoethyl)amido linker
2008
Abstract Four novel bile acid conjugates N-[2-([2,2′]-bithiophen-5-ylmethyl)aminoethyl]-3α-hydroxy-5β-cholan-24-amide (1), N-[2-([2,2′]-bithiophen-5-ylmethyl)aminoethyl]-3α,7α,12α-trihydroxy-5β-cholan-24-amide (2), N-[2-(1H-pyrrol-2-ylmethyl)aminoethyl]-3α-hydroxy-5β-cholan-24-amide (3), N-[2-(pyridin-2-ylmethyl)aminoethyl]-3α-hydroxy-5β-cholan-24-amide (4) have been synthesized in moderate to good yields, and their structures have been characterized by 1H, 13C, 13C DEPT-135, PFG 1H,13C HMQC, and PFG 1H,13C HMBC NMR spectra. Their molecular weights and elemental compositions have been determined by ESI-TOF mass spectrometry and elemental analyses. Crystal structure of 1 characterized with o…
Morphology and Band Structure of Orthorhombic PbS Nanoplatelets: An Indirect Band Gap Material
2021
PbS quantum dots and nanoplatelets (NPLs) are of enormous interest in the development of optoelectronic devices. However, some important aspects of their nature remain unclear. Recent studies have revealed that colloidal PbS NPLs may depart from the rock-salt crystal structure of bulk and form an orthorhombic (Pnma) modification instead. To gain insight into the implications of such a change over the optoelectronic properties, we have synthesized orthorhombic PbS NPLs and determined the lattice parameters by means of selected area electron diffraction measurements. We have then calculated the associated band structure using density functional theory with Perdew–Burke–Ernzerhof functional fo…
New insight into the haemoglobin superfamily: preliminary crystallographic characterization of human cytoglobin.
2003
Human cytoglobin, present in almost all tissue types, is a newly identified member of the Hb superfamily. A double mutant, having both cysteines replaced by serines, has been overexpressed in Escherichia coli, purified and crystallized. A highly redundant SAD data set has been collected at the haem Fe-atom absorption edge (lambda = 1.720 A) to 2.60 A resolution. The crystals belong to the orthorhombic P2(1)2(1)2(1) space group, with unit-cell parameters a = 46.8, b = 73.1, c = 98.9 A and two molecules per asymmetric unit. The anomalous difference Patterson map clearly reveals the position of the haem Fe-atom sites, thus paving the way for SAD structure determination.
Raman study of the phase transitions sequence in pure WO3 at high temperature and in HxWO3 with variable hydrogen content
1999
Abstract An extensive investigation of the temperature dependence of Raman spectra has been carried out on WO 3 powders from room temperature to 800°C. In particular the orthorhombic-to-tetragonal phase transition occurring at about 740°C has been studied for the first time. The Raman active mode at 710 cm −1 of the orthorhombic phase disappears from the spectrum at temperature below the phase transition point and the Raman activity in the tetragonal phase results very low. A comparative study of hydrogenated tungsten bronzes H x WO 3 ( x ≤0.23), where the same transition sequence is driven by an increase of the proton concentration from x =0 to 0.23, reveals similar behaviour of the high f…
Structural Changes in Nanoporous MFI Zeolites Induced by Tetrachloroethene Adsorption: A Joint Experimental and Simulation Study
2011
A joint experimental and molecular simulation study was performed to investigate the adsorption of tetrachloroethene on two MFI zeolites, ZSM-5 with a Si/Al ratio of 26.5, and silicalite-1, which is the pure silica form of ZSM-5. Adsorption isotherms and isosteric heats of adsorption of tetrachloroethene were measured and compared to molecular simulation results. Experimental curves for both MFI zeolites show a step at loading of 4 molecules·uc−1 that was interpreted in terms of a structural change of the host framework. A thermodynamic analysis based on the osmotic ensemble scheme allowed attributing this step to a symmetry change from ORTHO (orthorhombic form with Pnma symmetry) to PARA (…
Electrochemical deposition of Ag2Se nanostructures
2017
Abstract AgSe based nanostructures (nanowires or nanotubes) were obtained by electrodeposition. A systematic investigation was carried out, varying concentration of the precursors, pH of the electrolytic solution, ligands, and deposition mode, to study the effect of all these parameters on the growth of nanostructures. Nanostructure morphology depends also on the type of metal that was used as support, due to the secondary reaction of hydrogen evolution. On Ni support, the H2 evolution reaction led to formation of only nanotubes, while on copper substrate also nanowires were obtained. Composition of nanostructures depends strongly on solution pH. X-ray diffraction and Raman spectroscopy sho…
ChemInform Abstract: Synthesis and Characterization of NdNiO3 Prepared by Low Temperature Methods.
2010
Abstract NdNiO3 has been prepared with an orthorhombic perovskite structure by a low temperature and low oxygen pressure method starting from a nickel(III) oxide precursor, β-NiO(OH). The compound LaNiO3 has also been obtained by this method. This chemical-precursor-based synthesis overcomes problems related to the use of high oxygen pressures in the synthesis.