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511.
Jack B. Levy Richard C. Walton Ron E. Olsen Courtland Symmes Jr 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):545-548
Abstract Methyllithium displaces a phenyl anion from 10-phenyl-10H-phenoxaphosphine to produce a 70:30 mixture of 10-methyl-10H-phenoxaphosphine and starting phosphine. Butyllithium gives 50% conversion to 10-butyl-10H-phenoxaphosphine. These reactions could take place either by a one-step nucleophilic displacement or by ring cleavage followed by recyclization. To show the feasibility of the two-step process, non-heterocyclic lithiated tertiary phosphines were generated and shown to cyclize to phenoxaphosphines. For example, reaction of 2-phenoxyphenyldiphenylphosphine with phenyllithium produced 10-phenyl-10H-phenoxaphosphine (by lithiation ortho to oxygen followed by cyclization) along with triphenylphosphine (by direct displacement of 2-lithiodiphenyl ether). Other compounds prepared in this work: 2,2′-bis(diphenylphosphino)-diphenyl ether, bis(2-phenoxyphenyl)phenylphosphine, tris(2-phenoxyphenyl)phosphine, 4-carboxy-10-phenyl-10H-phenoxaphosphine, and the oxides and sulfides of the phosphines. 相似文献
512.
Ashbrook SE Cutajar M Pickard CJ Walton RI Wimperis S 《Physical chemistry chemical physics : PCCP》2008,10(37):5754-5764
The high-resolution 27Al and 31P NMR spectra of two as-synthesized forms of the microporous aluminophosphate AlPO-14 and the corresponding calcined-dehydrated form were assigned using both "first-principles" calculations of NMR parameters (GIPAW, as implemented in NMR-CASTEP) and a 27Al-31P heteronuclear correlation NMR experiment (MQ-J-HETCOR) that exploits 27Al multiple-quantum coherences and J couplings to identify Al-O-P linkages. NMR parameters calculated from published AlPO-14 crystal structures, which are derived from powder X-ray diffraction (XRD) data, are in poor agreement with experiment and it was necessary to optimize the structure geometry using energy minimization before satisfactory agreement was obtained. Comparison of simulated powder XRD patterns from the experimental and the energy-minimized structures shows that the changes in relative atomic positions in the optimized structure are relatively small and yield only minor adjustments in the Bragg peak intensities. These results indicate that a combination of NMR spectroscopy and first-principles calculation of NMR parameters may soon be considered a generally useful step in the refinement of the structures of microporous materials derived from powder diffraction data. 相似文献
513.
514.
Walton I Davis M Munro L Catalano VJ Cragg PJ Huggins MT Wallace KJ 《Organic letters》2012,14(11):2686-2689
An N,N-carbonyl-bridged dipyrrinone oxime has been synthesized and studied as a potential sensor for organophosphates. The molecular sensor underwent a drastic colorimetric response upon formation of the adduct. The pesticide dimethoate was found to produce the biggest spectral response, with a limit of detection equal to 4.0 ppm using UV-visible spectroscopy. Minimal fluorescence "turn on" via a PET mechanism was seen, and molecular modeling studies were used to explain the lower than expected PET response. The X-ray crystal structure of the fluorescent dipyrrinone oxime was also obtained. 相似文献
515.
516.
Mountford CP Mount AR Evans SA Su TJ Dickinson P Buck AH Campbell CJ Terry JG Beattie JS Walton AJ Ghazal P Crain J 《Journal of fluorescence》2006,16(6):839-845
Conformational transitions in a 4-way DNA junction when titrated with ionic solutions are studied using time-resolved fluorescence
resonance energy transfer. Parameters characterising the transition in terms of critical ion concentration (c
1/2) and the Hill coefficient for ion binding are obtained by fitting a simple two-state model using steady-state spectra. Data
obtained from a fluorescence lifetime plate reader and analysed by fitting a single exponential to donor fluorescence lifetime
decays are shown to be in good agreement with the parameters obtained from steady-state measurements. Fluorescence lifetimes,
however, offer advantages, particularly in being independent of fluorophore concentration, output intensity, inhomogeneity
in the excitation source and output wavelength. We demonstrate preliminary FRET-FLIM images of DNA junction solutions obtained
using a picosecond gated CCD which are in agreement with results from a fluorescence lifetime plate reader. The results suggest
that time-resolved FRET-FLIM is sensitive to subtle structural changes and may be useful in assays based on 4-way DNA junctions. 相似文献
517.
Terry JG Campbell CJ Ross AJ Livingston AD Buck AH Dickinson P Mountford CP Evans SA Mount AR Beattie JS Crain J Ghazal P Walton AJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(26):11400-11404
This work reports how the use of a standard integrated circuit (IC) fabrication process can improve the potential of silicon nitride layers as substrates for microarray technology. It has been shown that chemical mechanical polishing (CMP) substantially improves the fluorescent intensity of positive control gene and test gene microarray spots on both low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films, while maintaining a low fluorescent background. This results in the improved discrimination of low expressing genes. The results for the PECVD silicon nitride, which has been previously reported as unsuitable for microarray spotting, are particularly significant for future devices that hope to incorporate microelectronic control and analysis circuitry, due to the film's use as a final passivating layer. 相似文献
518.
Surblé S Millange F Serre C Férey G Walton RI 《Chemical communications (Cambridge, England)》2006,(14):1518-1520
EXAFS data measured from amorphous intermediates and crystallisation solutions provides the first evidence that trimeric iron oxide secondary building units remain intact during crystallisation of the metal-organic framework MIL-89 from starting materials to products. 相似文献
519.
Small WR Walton CD Loos J in het Panhuis M 《The journal of physical chemistry. B》2006,110(26):13029-13036
Fabrication of single-walled carbon nanotube (SWNT) networks using evaporation of SDS-SWNT sessile drops on a hydrophobized silicon substrate is reported. It is suggested that the organization of nanotubes during evaporation is controlled by aggregates (in the SDS-SWNT dispersion) and hydrophobicity of the substrate. On hydrophobic substrates, the evaporation of SDS-SWNT sessile drops proceeds through constant contact area. On hydrophilic substrates, nanotube aggregates in SDS-SWNT dispersion stop the contact line from moving, resulting in the formation of "coffee-stains". The (partial) removal of aggregates by centrifugation is essential for a freely moving contact line leading to the organization of nanotubes into a network of homogeneously distributed nanotubes on the most hydrophobic substrate. The evaporation of sessile drops was characterized by microscopic, spectroscopic, and topographical techniques. 相似文献
520.
Stanley AE Walton LJ Kourdi Zerikly M Corre C Challis GL 《Chemical communications (Cambridge, England)》2006,(38):3981-3983
The biosynthetic pathway to 4-methoxy-2,2'-bipyrrole-5-carboxaldehyde (MBC), a key intermediate in the biosynthesis of prodiginine antibiotics in Streptomyces coelicolor, has been elucidated using a combination of gene replacements and feeding experiments with chemically synthesised MBC and a synthetic analogue of a pathway intermediate. 相似文献