Structural and spectroscopic studies of transition metal nitrite complexes. IX.Crystal structures and spectroscopic properties of polymeric [Ni(C2H8N2)2-(NO2)] ClO4, its mononuclear zinc analogue, cis-Bis(ethane-1,2-diamine)(nitrito-O,O')zinc(II) perchlorate, and the complexes cis-(N,N,N',N'-Tetramethylethane-1,2-diamine)di(nitrito-O,O')-nickel(II) and -zinc(II)

1981 ◽  
Vol 34 (10) ◽  
pp. 2159 ◽  
Author(s):  
AJ Finney ◽  
MA Hitchman ◽  
CL Raston ◽  
GL Rowbottom ◽  
AH White
Keyword(s):  
Nickel Complex ◽  
Zinc Complex ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Amine Nitrogen ◽  
Alternative Description ◽  
Distorted Octahedral ◽  
Steric Factors ◽  
The Difference ◽  
Infrared Frequencies

The crystal structures of the title compounds are reported. The complex [Ni(C2H8N2)2(NO2)] ClO4 is found to be an infinite polymer with trans N,O-bridging nitrite groups. The zinc analogue of this contains mononuclear units involving a symmetrically chelated nitrite group. The two compounds formed with N,N,N',N'-tetramethylethane-1,2-diamine are isostructural, with the metal having a distorted octahedral ligand environment provided by the amine nitrogen atoms and two chelating nitrite groups. However, while the nitrite ions in the nickel complex are chelated approximately symmetrically, the Zn-O bonds trans to the amine nitrogen atoms (2.30 �) are much longer than those in the cis positions (2.07 �), and an alternative description of the geometry of the zinc complex is as a highly distorted tetrahedral arrangement involving essentially monodentate nitrito groups. The difference in stereochemistry between these two complexes is apparently caused by electronic rather than steric factors, and comparison is also made with the geometry reported for the iso-structural copper complex. The electronic spectra of the two nickel(II) complexes are discussed in relation to their structures, and the infrared frequencies reported for the nitrite groups are correlated with the observed coordination geometries.

Structural and spectroscopic studies of transition metal nitrite complexes. VI. Crystal structures and spectra of Hexakis(imidazole)nickel(II) dinitrate, trans-Tetrakis(2-methylimidazole)dinitritonickel(II) and cis-Tetrakis(2-methylimidazole)-(nitrito-O,O')nickel(II) nitrate-methanol (2/1)

1981 ◽  
Vol 34 (10) ◽  
pp. 2113 ◽  
Author(s):  
AJ Finney ◽  
MA Hitchman ◽  
CL Raston ◽  
GL Rowbottom ◽  
AH White
Keyword(s):  
Crystal Structures ◽  
Symmetry Axis ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Ligand Field ◽  
Coordination Geometry ◽  
Distorted Octahedral ◽  
Relative Field ◽  
Ligand Coordination ◽  
Fourfold Symmetry

The crystal structures and spectroscopic properties of the complexes cis-tetrakis(2-methy1imidazole)-(nitrito-O,O')nickel(II) nitrate-methanol (2/1) and trans-tetrakis(2-methylimidazole)dinitritonickel(II) are reported. The nitrite group in the former compound chelates, giving a distorted octahedral ligand coordination geometry. The ligand stereochemistry in the second complex is also a distorted octahedron, with both anions coordinating as trans nitrito groups though with significantly different Ni-O bond lengths and the nickel(II) ion being raised out of the plane of the four imidazole ligand nitrogen atoms towards the closer nitrite group. The Ni-O bond directions also deviate substantially from the fourfold symmetry axis in this latter complex. These distortions apparently occur in order to minimize ligand-ligand repulsions, particularly those associated with the amine methyl substituents. The electronic spectra of both complexes show significant band splittings due to the departure of the ligand field from regular octahedral symmetry and these are discussed in terms of the relative field strengths of the imidazole and nitrito ligands. The structure of hexakis(imidazole)nickel(II) nitrate (redetermination) is also reported.

Optical Spectroscopic Studies of a Soluble Fluorene-Based Conjugated Polymer: A Hydrostatic Pressure and Temperature Study

2001 ◽  
Vol 708 ◽  
Author(s):  
S. Guha ◽  
J.D. Rice ◽  
C. M. Martin ◽  
W. Graupner ◽  
M. Chandrasekhar ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Conjugated Polymer ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Phonon Interaction ◽  
Optical Studies ◽  
Strong Electron ◽  
Conjugated Molecules ◽  
Electron Phonon Interaction ◽  
Backbone Conformation

ABSTRACTSpectroscopic properties of conjugated molecules/polymers have varying degrees of sensitivity to backbone conformation. Optical studies are presented as a function of temperature and hydrostatic pressure, using photoluminescence and Raman scattering from two polymers with distinct differences in their backbone conformation, namely, polyfluorene (PF) and ladder type poly(para-phenylene)(m-LPPP). In contrast to the photoluminescence (PL) vibronics in mLPPP, the 0-0 PL vibronic peak in PF shows a red-shift with increasing temperatures. Pressure studies reveal that the PL spectrum of PF red-shifts and broadens with increasing pressures. The phonon lines in PF show an antiresonance effect at higher pressures indicating a strong electron-phonon interaction.

Structural and spectroscopic studies of transition metal nitrite complexes. V. Crystal structures and spectra of trans-Tetrakis(pyridine)dinitritonickel(II)-pyridine (1/2), trans-Tetrakis(4-methylpyridine)dinitritonickel(II) and trans-Tetrakis(pyrazole)-dinitritonickel(II)

1981 ◽  
Vol 34 (10) ◽  
pp. 2095 ◽  
Author(s):  
AJ Finney ◽  
MA Hitchman ◽  
CL Raston ◽  
GL Rowbottom ◽  
BW Skelton ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Transition Metal ◽  
Crystal Structures ◽  
Electronic Spectra ◽  
Spectroscopic Studies ◽  
Molecular Structures ◽  
Aromatic Rings ◽  
Paddle Wheel ◽  
Crystal And Molecular Structures ◽  
Infrared Frequencies

The crystal and molecular structures of the compounds [Ni(py)4(ONO)2],2py, [Ni(γmpy),(ONO)2] and [Ni(prz)4(ONO)2] are reported.�All three are trans nitrito complexes, the pyridine (py) compound containing two pyridine molecules of solvation. The aromatic rings in the first two complexes adopt 'paddle wheel' conformations with pitch angles varying between 40 and 70�. The nitrite ions are positioned so as to minimize repulsive interactions with the amines, and it seems likely that these groups bond through oxygen rather than nitrogen because this allows a lesser degree of interligand steric interference. The amine rings in [Ni(prz)4(ONO)2] are orthogonal to the plane containing the nickel and coordinated pyrazole nitrogen atoms; the nitrito groups are disordered between two inequivalent positions, each of which involves hydrogen bonding with the pyrazole NH groups. The nitrite infrared frequencies are similar to those observed for other nickel(II) nitrito complexes except that the antisymmetric NO stretching mode of one of the groups in the pyrazole complex is much lower in energy than expected, being in the range normally associated with a nitrogen-bonded or chelated nitrite group. It is suggested that this deviation may be caused by the hydrogen bonding in the complex. The electronic spectra of the compounds yield 10Dq values of 9100 and 8500 cm-1 for the nitrite ligands in [Ni(py)4(ONO)2] and Ni(prz)4(ONO)2], respectively, placing the nitrito group towards the weaker end of the spectro-chemical series.

Synthesis and Characterization of the Manganese Pyroarsenate Mn2As2O7 · 2H2O

2001 ◽  
Vol 56 (4-5) ◽  
pp. 359-363 ◽  
Author(s):  
N. Stock ◽  
G. D. Stucky ◽  
A. K. Cheetham
Keyword(s):  
Three Dimensional ◽  
Spectroscopic Studies ◽  
Mean Value ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Raman Spectroscopic ◽  
Distorted Octahedral ◽  
Ir And Raman ◽  
Hydrothermal Methods

Abstract The manganese pyroarsenate hydrate, Mn2As2O7 · 2 H2O, has been obtained as a single phase product using hydrothermal methods and the structure has been determined by single crystal X-ray diffraction. The title compound crystallizes in the monoclinic space group P21/n with a = 6.6576(4), b = 14.555(1), c = 7.8147(5) Å, β = 94.935(1)°, V = 754.46(8) Å3 and Z = 4. The manganese ions are each coordinated to five oxygen atoms and a water molecule in a distorted octahedral arrangement. Edge-sharing MnO6 octahedra form chains which are connected to a three-dimensional framework by As2O74- ions. The pyroarsenate anion, which attains a nearly eclipsed conformation, has a mean As-O distance for the terminal As-O bonds of 1.669(2) Å, while for the bridging oxygen atom a mean value of 1.757(2) Å is observed. Magnetic susceptibility measurements indicate the presence of high-spin Mn2+ ions. Thermogravimetric as well as IR and Raman spectroscopic studies of Mn2As2O7 · 2 H2O are presented.

scholarly journals NO binding kinetics in myoglobin investigated by picosecond Fe K-edge absorption spectroscopy

2015 ◽  
Vol 112 (42) ◽  
pp. 12922-12927 ◽  
Author(s):  
Mahsa Silatani ◽  
Frederico A. Lima ◽  
Thomas J. Penfold ◽  
Jochen Rittmann ◽  
Marco E. Reinhard ◽  
...  
Keyword(s):  
Active Center ◽  
Absorption Spectroscopy ◽  
Spectroscopic Studies ◽  
Pump Probe ◽  
X Ray ◽  
The Difference ◽  
Direct Sensitivity ◽  
X Ray Absorption ◽  
Recombination Kinetics ◽  
532 Nm

Diatomic ligands in hemoproteins and the way they bind to the active center are central to the protein’s function. Using picosecond Fe K-edge X-ray absorption spectroscopy, we probe the NO-heme recombination kinetics with direct sensitivity to the Fe-NO binding after 532-nm photoexcitation of nitrosylmyoglobin (MbNO) in physiological solutions. The transients at 70 and 300 ps are identical, but they deviate from the difference between the static spectra of deoxymyoglobin and MbNO, showing the formation of an intermediate species. We propose the latter to be a six-coordinated domed species that is populated on a timescale of ∼200 ps by recombination with NO ligands. This work shows the feasibility of ultrafast pump–probe X-ray spectroscopic studies of proteins in physiological media, delivering insight into the electronic and geometric structure of the active center.

Electrical and Raman Spectroscopic Studies on Aurivillius Layered-Pervoskite Ceramics

2019 ◽  
Vol 1154 ◽  
pp. 80-90
Author(s):  
Mohammed Abdul Basheer ◽  
Vagmare Gangadhar ◽  
Guduru Prasad ◽  
Gobburu Subramanya Kumar ◽  
Nandi Venkata Prasad
Keyword(s):  
Rare Earth ◽  
Complex Impedance ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Rare Earth Ions ◽  
X Ray Diffraction ◽  
Raman Spectroscopic ◽  
Solid State Route ◽  
A Site ◽  
Rare Earth La

Double rare-earth (La; Sm/Gd) substituted Aurivillius family of Bismuth Layered Structured Ferroelectrics (BLSF) namely Bi2.6Sm0.2La0.2TiNbO9 (BSLT; sample-A), Bi2.6Gd0.2La0.2TiNbO9 (BGLT; sample-B), single phase ceramics were prepared by solid state route. In addition, intergrowth (x BSLT - (1-x) BGLT, where x=0.49; sample-C) and solid solution (BSLT­x - BGLTy; where x + y=0.4; sample-D) materials were prepared. Dielectric, ferroelectric and Raman spectroscopic properties were studied on the said above materials. The X-ray diffraction analysis and Raman spectra revealed well-formation of stable structure. Though, the sample-C and sample-D have lower coercive field, compared to the sample-A and sample-B, but they exhibited sharp hysterisis loop. Therefore the instrinsic defects of sample-D inhabits more sensitivity towards the ferroelectric behaviour. The results were corroborated to the impedance and dielectrical data. The results were consistent with the SEM micrographs and complex impedance plots. An attempt is made to understand the effect of rare-earth ions on A-site of layered-pervoskite structure, defined as: (Bi2O2)2+(An-1BnO3n+1)2-.The term n represents number of pervoskite blocks interleaved with the bismuth oxide layers.

scholarly journals Significance of Conformation Changes During the Binding and Release of Chromium(III) from Human Serum Transferrin

2020 ◽  
Vol 4 (Supplement_2) ◽  
pp. 1798-1798
Author(s):  
Kyle Edwards ◽  
John Vincent
Keyword(s):  
Metal Binding ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Turnover Time ◽  
Time Intervals ◽  
Paramagnetic Resonance ◽  
Funding Sources ◽  
Research Award ◽  
Conformation Changes ◽  
Multiple Conformations

Abstract Objectives Transferrin, Tf, the protein that transports iron from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Recently, the presence of multiple conformations was suggested by spectroscopic studies. The objective of this work is confirm whether various conformers of Cr(III)2-Tf exist and their potential significance for Cr(III) transport. Methods Cr(III) was added to apoTf in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37 °C. After time intervals, ultraviolet spectra were collected, or aliquots were removed and frozen for analysis by electron paramagnetic resonance (EPR) spectroscopy, which can distinguish free Cr(III) and Cr(III) bound to the two metal binding sites of Tf. To model the acidification of the endosome that triggers release of metal ions from Tf, the Cr(III)2-Tf conformer solutions were acidified by the addition of hydrochloric acid to pH 4.5 or 5.5. At time intervals after acidification, samples were again analyzed by ultraviolet and EPR spectroscopies. Results A combination of electronic and EPR studies reveal that the addition of Cr(III) to apoTf at near neutral pH in the presence of 25 mM bicarbonate results in the rapid binding of two Cr(III) accompanied and then followed by a series of conformation changes in Cr(III)2-Tf. These multiple conformations give rise to different spectroscopic properties and upon acidification different rates of Cr(III) release. Conclusions The conformer of Cr(III)2-Tf used in most previous studies and giving rise to EPR features at g ∼ 5.1, 5.4, and 5.6 forms too slowly to be physiologically relevant; however, two previously unknown conformers of Cr(III)2-Tf, giving rise to an EPR feature at g ∼2 and at g ∼ 5.4, respectively, were identified. The latter of these conformers has a lifespan similar to the turnover time of transferrin and releases Cr(III) rapidly, suggesting it is probably the most physiologically significant conformer of Cr(III)2-Tf. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

scholarly journals The emission of corrosive vapours by wood. Hot - water - extracted O - acetylated hemicelluloses from sweet chestnut (Castanea sativa) and wych elm (Ulmus glabrau) and a discussion of O-acetyl-group changes occurring in these woods during incubation at 48° and 100% relative humidity

1969 ◽  
Vol 113 (2) ◽  
pp. 253-257
Author(s):  
G. C. Cochrane ◽  
J. D. Gray ◽  
P. C. Arni
Keyword(s):  
Cell Walls ◽  
Castanea Sativa ◽  
Hot Water ◽  
Dimethyl Sulphoxide ◽  
Green Wood ◽  
Sweet Chestnut ◽  
Steric Factors ◽  
Acetyl Group ◽  
The Difference ◽  
Wych Elm

1. O-Acetylated polysaccharides were obtained from green wood of both sweet chestnut and wych elm by treatment of the residue remaining after dimethyl sulphoxide extraction with water at 98°. This gives a mixture of polysaccharides containing xylose, galactose, glucose and uronic acids. Analysis of these and their fractionated products suggest that only xylans in green sweet chestnut and green wych elm are O-acetylated. 2. The isolated O-acetylated xylans are not representative of the total O-acetylated xylans occurring in sweet chestnut and wych elm. 3. Application of the method developed by Bouveng for the location of O-acetyl groups to all four O-acetylated xylans obtained in this series of investigations by dimethyl sulphoxide extraction showed that those from sweet chestnut and wych elm, under the same conditions of incubation, lost: 74·2 and 43·4% of acetyl groups respectively, at C-2; 58·0 and 28·5% of acetyl groups respectively at C-3; 41·8 and 82·2% of acetyl groups respectively at C-2 and C-3. 4. A consideration of electronic and steric factors indicates that there does not appear to be a purely chemical reason for the difference in loss of O-acetyl groups between sweet chestnut and wych elm. It is suggested that the location of O-acetylated xylans in the wood cell walls and the presence of extractive may play some part in this difference.

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