Journal ArticleDOI
A semi-empirical method of absorption correction
TLDR
An extension of Furnas's method is described in this paper, where the variation of intensity of an axial reflection as the crystal is rotated about the goniometer axis is used to give a curve of relative transmission T against azimuthal angle ϕ for the corresponding reciprocal lattice level.Abstract:
An extension of Furnas's method is described. The variation of intensity of an axial reflection as the crystal is rotated about the goniometer axis is used to give a curve of relative transmission T against azimuthal angle ϕ for the corresponding reciprocal lattice level. Transmission coefficients for any general reflexion hkl are then given approximately by T(hkl) = [T(ϕinc) + T(ϕret)]/2 where ϕinc and ϕret are the azimuthal angles of the incident and reflected beams. Equations are derived for (ϕinc and ϕret and the accuracy of the method is discussed.read more
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Journal ArticleDOI
Structure of methemerythrin at 2.8-Angstrom resolution: computer graphics fit of an averaged electron density map.
TL;DR: The crystal structure of methemerythrin from Themiste dyscritum has been determined at 2.8-Angstrom resolution by single isomorphous replacement technique combined with anomalous scattering from a K2HgI4 derivative.
Journal ArticleDOI
Ribonuclease structure and catalysis: crystal structure of sulfate-free native ribonuclease A at 1.5-A resolution.
TL;DR: Analysis of individual atomic temperature factors indicates that the molecule has become less rigid in general but that some regions were particularly affected by loss of the sulfate, while others were relatively unaffected.
Journal ArticleDOI
Ruthenium-(II)/-(III) terpyridine complexes incorporating imine functionalities. Synthesis, structure, spectroscopic and electrochemical properties
Abstract: A new class of ruthenium terpyridine complexes of the type [RuII(trpy)(L1–6)Cl] 1–6 (trpy = 2, 2′∶6′, 2′′-terpyridine; L1–3 = o-−OC6H3(R)C(R′)NCH2C6H5 and L4–6 = o-−OC6H3(R)CH(R′)NNC6H5; where R = H or p-NO2 and R′ = H or CH3) have been synthesized. The “free” ligands incorporating a NH spacer o-−OC6H3(R)C(R′)NNHC6H5 (HL4–6) have undergone imine to azo tautomerism on co-ordination to the ruthenium terpyridine moiety in the complexes 4–6, whereas those having a CH2 spacer (HL1–3) remain unaltered on co-ordination. The diamagnetic, neutral complexes 1–6 exhibit strong MLCT transitions in the visible region and intraligand transitions in the UV region. A significant shift in MLCT band energy has been observed depending on the ligand field strength of the co-ordinated L. The complexes display a reversible ruthenium(III)–ruthenium(II) couple in the potential range of 0.12–0.63 V and a quasi-reversible ruthenium(IV)–ruthenium(III) couple in the range of 1.21–1.85 V versus SCE. The higher ligand field strength of the co-ordinated L4–6 compared to the co-ordinated L1–3 is reflected in the observed metal redox processes. The reduction of the co-ordinated terpyridine has been observed near −1.3 V. The complexes exhibit moderately strong emissions from the lowest energy MLCT bands in the range 661–690 nm in EtOH–MeOH (4∶1 v/v) at 77 K. The quantum yields of the complexes (Φ = 0.006–0.09) are found to be reasonably sensitive to the nature of the co-ordinated L. The oxidised complexes 3+ and 6+ have been isolated in the solid state as their perchlorate salts. The crystal structure of 3+ exhibits pseudo-octahedral trans geometry with regard to the relative disposition of the imine nitrogen (N4) of L3 and the central pyridyl group of the trpy ligand. The one-electron paramagnetic complexes show 1∶1 conductivity and display ligand-to-metal charge transfer bands near 600 and 400 nm and intraligand transitions in the UV region. The observed rhombic EPR spectra at 77 K corresponding to the distorted octahedral geometry have been analysed to furnish values of axial (Δ) and rhombic (V) distortion parameters as well as the energies of the two expected ligand field transitions (ν1 and ν2) within the t2 shell.
Journal ArticleDOI
Heterometallic Pt-Au complexes with μ-3 S bridging. Syntheses and structures of Pt2 (PPh3)4(μ-SAuCl)2·2CH2Cl2 and Pt2(PPh3)4−(μ-S)(μ-SAuPPh3)NO3·0.5H2O
W. Bos,Jan J. Bour,P. P. J. Schlebos,P. Hageman,W. P. Bosman,Jan M. M. Smits,J. A. C. van Wietmarschen,Paul T. Beurskens +7 more
TL;DR: In this paper, the properties of the three-coordinated S-atoms have been investigated by X-ray diffraction analysis and the crystal and molecular structures of II and the nitrate of IV has been investigated.
Journal ArticleDOI
The three‐dimensional structure of the bifunctional proteinase k/α‐amylase inhibitor from wheat (PKI3) at 2.5 Å resolution
TL;DR: In this article, the three-dimensional structure of proteinase K was solved by molecular replacement on the basis of the atomic coordinates of the homologous Erythrina caffra DE-3 inhibitor, and refined with simulated annealing techniques.
References
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Book
International tables for X-ray crystallography
Norman Fordyce McKerron Henry,Lonsdale, Kathleen, Dame,John S. Kasper,Caroline H. MacGillavry,Gerard D. Rieck,James A. Ibers,Walter C. Hamilton +6 more
ReportDOI
A fortran program for calculating single crystal absorption corrections
D.J. Wehe,W.R. Busing,H.A. Levy +2 more
TL;DR: A Fortran program is described for calculating the absorption correction for application to single crystal x ray or neutron intensity measurements and is available in the form of symbolic punched cards.