The epithermal neutron flux distribution in a nuclear reactor and its effect on epithermal neutron activation analysis

The shape of the epithermal neutron energy distribution has been determined in two irradiation positions of the University of London CONSORT II reactor. The method applied involves cadmium ratio measurements using a series of resonance detectors. Principles of the method and some considerations relative to epithermal neutron activation analysis in connection with the deviation of the epithermal neutron flux distribution from the 1/E law are given.     

Atmospheric pressure deposition of fluorine‐doped SnO2 thin films from organotin fluorocarboxylate precursors

Nine organotin fluorocarboxylates R_nSnO₂CR_f (n = 3, R = Bu, R_f = CF₃, C₂F₅, C₃F₇, C₇F₁₅; R = Et, R_f = CF₃, C₂F₅; R = Me, R_f = C₂F₅; n = 2, R = Me, R_f = CF₃) have been synthesized; key examples have been used to deposit fluorine‐doped SnO₂ thin films by atmospheric pressure chemical vapour deposition. Et₃SnO₂CC₂F₅, in particular, gives high‐quality films with fast deposition rates despite adopting a polymeric, carboxylate‐bridged structure in the solid state, as determined by X‐ray crystallography. Gas‐phase electron diffraction on the model compound Me₃SnO₂CC₂F₅ shows that accessible conformations do not allow contact between tin and fluorine, and that direct transfer is therefore unlikely to be part of the mechanism for fluorine incorporation in SnO₂ films. The structure of Me₂Sn(O₂CCF₃)₂(H₂O) has also been determined and adopts a trans‐Me₂SnO₃ coordination sphere about tin in which each carboxylate group is monodentate. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamics of wire boom oscillations on a spinning satellite Part II,normal modes in spin plane

Harmonic analysis of the normal modes in the spin plane of a satellite with four hinged wire booms each with a tip mass attached is presented. Analytical expressions of normal mode coordinates and frequencies are obtained by solving the matrix eigenvalue equations, using secular determinant and simultaneous diagonalization methods. Translational oscillation of the center body is present in configurations of lower symmetry. The analytical results are in good agreement with computer simulations.

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Zusammenfassung Für einen Satelliten mit vier Drahtentenen, die mit Endgewichten versehen sind, wird die harmonische Analyse der Normalschwingungen ausgeführt. Analytische Ausdrücke für die Normalkoordinaten und-frequenzen werden abgeleitet, in denen die Eigenwert-Matrizengleichungen gelöst werden unter Benutzung der charakteristischen Polynome und simultaner Diagonalisierung. Translative Schwingung des Zentralkörpers existiert für Konfigurationen niedrigerer Symmetrie. Die analytischen Ergebnisse zeigen gute Übereinstimmung mit Komputersimulationen.

     

Synthesis and X-ray structures of new titanium(IV) aryloxides and their exploitation for the ring opening polymerization of epsilon-caprolactone

A series of titanium catecholates have been prepared and characterized by single-crystal X-ray diffraction studies. Complexes 1a-7a were synthesized by the reaction of 1 equiv of ligand with Ti(OiPr)4. All are dimers in the solid-state, in which a catechol bridges between two titanium centers. Electronic (nitro and methoxy groups) and steric (tert-butyl groups) effects of the ligand have been investigated. Complex 1b was synthesized by reaction of 2 equiv of ligand with Ti(OiPr)4. A dimer is again observed with the same bridging ligand together with a terminal catechol moiety. All complexes contain a coordinated 2-propanol ligand on each titanium center forming pseudo-octahedral metal centers. All complexes were tested for the ring-opening-polymerization of epsilon-caprolactone to afford polycaprolactone (PCL). Reasonable yields (up to 79%) were obtained at room temperature, and narrow molecular weight distributions (1.13-1.27) were observed for the PCL produced. The most active complex was found to be complex 1a, containing unsubsituted catechol ligands.     

Fluoride-assisted synthesis of mullite (Al5.65Si0.35O9.175) nanowires

Novel silicon-deficient mullite (Al5.65Si0.35O9.175) single crystal nanowires were synthesized in large quantities on mica substrates assisted by the intermediate fluoride species. The nanowires have diameters in the range 50-100 nm and typical lengths of several microm. Aligned nanowires were observed at the substrate edge. The nanowires have strong photoluminescence (PL) emission bands at 310, 397, 452 and 468 nm.     

Deconvolution of the cellular oxidative stress response with organelle-specific Peptide conjugates

Oxidative stress is a deleterious force that must be combated relentlessly by aerobic organisms and is known to underlie many human diseases including atherosclerosis, Parkinson's disease, and Alzheimer's disease. Information available about the oxidative stress response has come primarily from studies using reactive oxygen species (ROS) with ill-defined locations within the cell. Thus, existing models do not account for possible differences between stress originating within particular regions of the cell. Here, oxidative stress is studied at the subcellular level using ROS-generating compounds localizing within two different organelles: the nucleus and the mitochondrion. Differences in cytotoxicity, gene expression, and survival pathway activation are detected as a function of the subcellular origin of oxidative stress, indicating that independent mechanisms are used to cope with oxidative stress arising in different cellular compartments. These comparative studies, enabled by the development of organelle-specific oxidants, examine the cellular responses to site-specific oxidative stress with heightened precision.     

Automated structure elucidation of two unexpected products in a reaction of an alpha,beta-unsaturated pyruvate

The reaction between an alpha,beta-unsaturated pyruvate and ethyl diazoacetate (EDA) yielded two unexpected products. The structures of these products were determined by automated elucidation of the chemical structures using spectroscopic inputs of a series of 1D and 2D NMR data using the computer program ACD/Structure Elucidator, StrucEluc. The formation of these products is rationalised. Their structures were also confirmed by x-ray crystallography.     

Dipyridyl β-diketonate complexes and their use as metalloligands in the formation of mixed-metal coordination networks

The iron(III) and aluminium(III) complexes of 1,3-di(4-pyridyl)propane-1,3-dionato (dppd) and 1,3-di(3-pyridyl)propane-1,3-dionato (dmppd), [Fe(dppd)(3)] 1, [Fe(dmppd)(3)] 2, [Al(dppd)(3)] 3 and [Al(dmppd)(3)] 4 have been prepared. These complexes adopt molecular structures in which the metal centres contain distorted octahedral geometries. In contrast, the copper(II) and zinc(II) complexes [Cu(dppd)(2)] 5 and [Zn(dmppd)(2)] 6 both form polymeric structures in which coordination of the pyridyl groups into the axial positions of neighbouring metal centres links discrete square-planar complexes into two-dimensional networks. The europium complex [Eu(dmppd)(2)(H(2)O)(4)]Cl·2EtOH·0.5H(2)O 7 forms a structure containing discrete cations that are linked into sheets through hydrogen bonds, whereas the lanthanum complex [La(dmppd)(3)(H(2)O)]·2H(2)O 8 adopts a one-dimensional network structure, connected into sheets by hydrogen bonds. The iron complexes 1 and 2 act as metalloligands in reactions with silver(I) salts, with the nature of the product depending on the counter-ions present. Thus, the reaction between 1 and AgBF(4) gave [AgFe(dppd)(3)]BF(4)·DMSO 9, in which the silver centres link the metalloligands into discrete nanotubes, whereas reactions with AgPF(6) and AgSbF(6) gave [AgFe(dppd)(3)]PF(6)·3.28DMSO 10 and [AgFe(dppd)(3)]SbF(6)·1.25DMSO 11, in which the metalloligands are linked into sheets. In all three cases, only four of the six pyridyl groups present on the metalloligands are coordinated. The reaction between 2 and AgNO(3) gave [Ag(2)Fe(dmppd)(3)(ONO(2))]NO(3)·MeCN·CH(2)Cl(2)12. Compound 12 adopts a layer structure in which all pyridyl groups are coordinated to silver centres and, in addition, a nitrate ion bridges between two silver centres. A similar structure is adopted by [Ag(2)Fe(dmppd)(3)(O(2)CCF(3))]CF(3)CO(2)·2MeCN·0.25CH(2)Cl(2)13, with a bridging trifluoroacetate ion playing the same role as the nitrate ion in 12.     

Synthesis of meso-substituted porphyrins carrying carboranes and oligo(ethylene glycol) units for potential applications in boron neutron capture therapy

Selective delivery of 10B to tumours is one of the major remaining problems in boron neutron capture therapy (BNCT) of cancer. Porphyrins are selectively accumulated in tumours. Thus two series of carborane-carrying porphyrins were constructed, with additional functionality for attachment of uncharged potentially water-solubilising polyethers. 3-(1,2-Dicarbaclosododecaboran(12)-1-ylmethoxy)benzaldehyde was prepared by protection of the aldehyde of 3-(prop-2-ynyloxy)benzaldehyde as a dithioacetal, treatment with decaborane(14) and deprotection. Condensation with a 3-nitrophenyldipyrromethane gave a separable mixture of meso-(3-nitrophenyl)-meso-(3-carboranylmethoxyphenyl)porphyrins, resulting from extensive scrambling at the porphyrinogen stage. Similarly, condensation of 3-(1,2-dicarbaclosododecaboran(12)-1-yl)benzaldehyde with this dipyrromethane gave an analogous mixture of meso-(3-nitrophenyl)-meso-(3-carboranylphenyl)porphyrins. In this second series, the two regioisomeric bis(nitrophenyl)bis(carboranylphenyl)porphyrins could only be distinguished by X-ray crystallography, their NMR spectra being identical. The nitro groups of the mono(nitrophenyl)porphyrins and the bis(nitrophenyl)-porphyrins were reduced to the corresponding amines with tin(II) chloride and the monoamines were coupled with a omega-methoxy poly(ethylene glycol) chloroformate of mean MW 600 to give the MeOPEGylated tricarboranyl porphyrins.