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排序方式: 共有296条查询结果,搜索用时 15 毫秒
131.
Andre Rosowsky Elizabeth P. Burrows Ping C. Huang Edward J. Modest 《Journal of heterocyclic chemistry》1972,9(6):1239-1244
An unequivocal synthesis of 2,4-diamino-5,10-dihydrobenzo[g]quinazolines is described, starting from methyl 2-tetralone-3-carboxylates. Condensation with guanidine yielded 2-amino-4-hydroxy derivatives, which were thiated with phosphorus pentasulfide and S-alkylated with dimethyl sulfate. The resultant 2-amino-4-methylthio compounds were converted into 2,4-diamino derivatives by amination at elevated temperature and pressure. Attempted synthesis from 3-cyano-1,4-dihydro-2-methoxynaphthalene and guanidine was unsuccessful. 相似文献
132.
Association between ammonium monovanadate and β-cyclodextrin as seen by NMR and transport techniques
A.C.F. Ribeiro V.M.M. Lobo A.J.M. Valente S.M.N. Simes A.J.F.N. Sobral M.L. Ramos H.D. Burrows 《Polyhedron》2006,25(18):3581-3587
The interaction between vanadium (V) and the carbohydrate β-cyclodextrin (β-CD) has been studied in aqueous solutions (pH ≈ 7.5, 298.15 K) using multinuclear NMR spectroscopy, coupled with measurements of diffusion coefficients and electrical conductivity. The transport properties of vanadate ion solutions are markedly influenced by the presence of β-CD. Data from 51V, 1H and 13C NMR spectroscopy show that these effects are due to strong interactions between this carbohydrate and vanadate due to formation of 2:1 (β-CD:vanadate) complexes. The formation of such 2:1 complexes is also supported by molecular mechanics calculations. Complexation is seen by conductometric and diffusion techniques to lead to a significant decrease in the molar conductivity and diffusion coefficient of vanadate solutions in the presence of β-CD. Using the above stoichiometry, it has been possible to calculate the association constant, leading to the value K = 4.3 × 104 M−2 from the analysis of the conductivity data. 相似文献
133.
Rapid-scan linear-sweep differential pulse voltammetry at scan rates of up to 200 mV s-1 is evaluated for the rapid analysis of polynuclear aromatic hydrocarbon mixtures in acetonitrile at a platinum working electrode. Three- and four-component mixtures with appropriate peak potential separation between the components can be readily separated and quantified at the 1–5-ppm concentration level. A major advantage of the method is the short time requirement. A four-component mixture which requires a 1.2-V range to cover all peaks can be scanned in only 6 s instead of the 5–10 min required by conventional differential pulse voltammetry. 相似文献
134.
Jean Bernard Ballif Pierre Braunstein Andrew D. Burrows Richard D. Adams Wengan Wuz 《Journal of Cluster Science》1994,5(3):443-466
The reaction of the ketophosphine ligand Ph2PCH2C(O)Ph (P~O) with [PtCl2(NCMe)2] and carbon monoxide in THF in the presence of an excess of zinc afforded the 70 electron pentanuclear cluster [Pt5(CO)(μ-CO)5(P~O)4] (1). Reaction of the palladium(0) complex [Pd2(dba)3] CHCl3 (dba = dibenzylideneacetone) with Ph2PCH2C(O)R [R = Ph or C5H4Fe(C5H5)] under SO2 led to the pentapalladium cluster compounds [Pd5(μ3-SO2)2 (μ-SO2)2 {Ph2PCH2C(O)R}5] (2a,R = Ph;2b,R = C5H4Fe(C5H5)), Cluster (1) reacts with 2,6-xylyl isocyanide, CNC6H3Me2-2,6 to give a red cluster of formula [Pt5(μ-CNC6H3Me2-2, 6)3 (CNC6H3Me2-2, 6)5 (P~O)2] (3) and a green complex (4). The corresponding complexes (6) and (7) were also obtained by using PPh3 instead of P~O. Clusters (2a) and (2b) react with [NEt3Bz] Cl to give[NEt3Bz][Pd3(μ-SO2)2 (μ-Cl){Ph2PCH2C(O)R}3](8a,R = Ph;8b,R = C5H4Fe(C5H5)). The molecular structures of (1) and (3) were determined by single-crystal X-ray diffraction analyses. 相似文献
135.
Grancho JC Pereira MM Miguel Mda G Rocha GA Burrows HD 《Photochemistry and photobiology》2002,75(3):249-256
The synthesis, characterization and photophysical properties of two perfluoroalkyl (5,10,15,20-tetrakis-[trifluoromethyl]- and [heptafluoropropyl]-porphyrin) and two perfluoroaryl (5,10,15,20-tetrakis-[2,6-difluorophenyl]- and [pentafluorophenyl]-porphyrin) are described, with reference to their potential in both photodynamic therapy (PDT) and in vivo imaging by fluorescence and 19F nuclear magnetic resonance spectroscopy. Absorption and fluorescence spectra, fluorescence lifetimes and triplet-singlet difference spectra are reported. Triplet yields have been obtained by flash photolysis and pulse radiolysis, whereas yields of sensitized singlet oxygen formation have been determined by time-resolved phosphorimetry. All four compounds show high yields of triplet formation and singlet oxygen sensitization. The spectral properties, stability and attractive solubility characteristics of the perfluoroalkyl derivatives make them particularly suitable candidates for future study for applications in PDT. 相似文献
136.
Fleischmann OC Meyer-Arnek J Burrows JP Orphal J 《The journal of physical chemistry. A》2005,109(23):5093-5103
By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm(-1). A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)-X(2B1). Vibrational constants have been determined for the C(2A2) state (omega(1) = 648.3 +/- 1.9 cm(-1) and omega 2 = 212.8 +/- 1.2 cm(-1)) and for the X(2B1) state (omega 1 = 804.1 +/- 0.8 cm(-1) and omega 2 = 312.2 +/- 0.5 cm(-1)). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By modeling the band contours, predissociation lifetimes have been estimated. Further, an estimate for the absorption cross-section of OBrO has been made by assessing the bromine budget within the gas mixture, and atmospheric lifetimes of OBrO have been calculated using a photochemical model. 相似文献
137.
Diffusion of aqueous sodium dodecyl sulfate (SDS) across cross-linked polyacrylamide hydrogel membranes has been studied by electrical conductivity measurements. Initial rapid sorption of SDS (as unimer) into the membranes is observed. The effect of SDS concentration, and of cross-linker fraction on the degree of swelling of the gels is studied and associated with binding of the surfactant to the polymer, with surface bound water suggested to be involved in these interactions. Below the surfactant critical micelle concentration, volume collapse of less cross-linked membranes is observed, and associated with aggregate formation. Fluorescence measurements using pyrene as a probe show that micellar aggregates do not diffuse through the membrane, and only overall unimer diffusion is observed. The effect of cross-linking on the diffusion process is discussed. 相似文献
138.
J Sérgio Seixas de Melo Raquel Rond?o Hugh D Burrows Maria J Melo Suppiah Navaratnam Ruth Edge Gundula Voss 《Chemphyschem》2006,7(11):2303-2311
The spectral and photophysical properties of indigo derivatives with di-, tetra-, and hexa-substitution in their neutral (keto) form are investigated in solution. The study comprises absorption and emission spectra, together with quantitative measurements of quantum yields of fluorescence (phi(F)) and singlet oxygen formation (phi(Delta)) and fluorescence lifetimes. The energy difference between the HOMO and LUMO orbitals is dependent on the degree (number of groups) and relative position of substitution. The phi(F) and phi(Delta) values were found to be very low S(0) internal conversion yields and thus, with the other data, to determine the rate constants for all decay processes. From these, several conclusions are drawn. Firstly, the radiationless rate constants, k(NR) , clearly dominate over the radiative rate constants, k(F) , (and processes). Secondly, the main deactivation channel for the compounds in their keto form is the radiationless S(1) approximately approximately -->S(0) internal conversion process. Finally, although the changes are relatively small, internal conversion yield seems to be independent of the overall pattern of substitution. A more detailed investigation of the decay profiles with collection at the blue and red emission of the fluorescence band of indigo and one di-substituted indigo reveals the decays to be bi-exponential and that at longer emission wavelengths these appear to be associated with both rise and decay times indicating that two excited species exist, which is consistent with a keto-excited form giving rise (by fast proton transfer) to the enol-form of indigo. Evidence is presented which supports the idea that intramolecular (and possibly some intermolecular) proton transfer can explain the high efficiency of internal conversion in indigo. 相似文献
139.
Amoroso AJ Burrows MW Coles SJ Haigh R Farley RD Hursthouse MB Jones M Malik KM Murphy DM 《Dalton transactions (Cambridge, England : 2003)》2008,(4):506-513
The co-ordination of a series of terpyridine-N-oxide ligands to the Cu(ii) ion is reported. Addition of two equivalents of ligand results in the formation of the expected 2 : 1 six co-ordinate product, while the addition of one equivalent of ligand allows the isolation of 1 : 1 species if the ligand has a meridonal binding mode. The five complexes isolated were characterised in the solid state by X-ray crystallography while they are studied in solution using EPR, UV-vis spectroscopy and IR spectroscopy. 相似文献
140.
The complexation of a fluorescent probe by a target protein was observed by single-molecule fluorescence anisotropy. Free and bound states, heterogeneities, and rare binding events can all be observed by this approach. Fluorophore-conjugated biotin was used to bind to NeutrAvidin as a proof-of-concept case. Molecular interactions were observed that could not be elucidated with conventional (ensemble) measurements. 相似文献