Quinazolines. XI. Synthesis of 2,4-diamino-5, 10-diliydrobenzo[g] quinazolines

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.     

Association between ammonium monovanadate and β-cyclodextrin as seen by NMR and transport techniques

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.     

Rapid analysis for polynuclear aromatic hydrocarbons by linear-sweep differential pulse voltammetry

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.     

The synthesis of platinum and palladium cluster compounds with isocyanide or functionalised phosphine ligands. Crystal structures of [Pt5(CO)(μ-CO)5{Ph2PCH2C(O) Ph}4 and [Pt5(μ-CNC6H3Me2-2, 6)3(CNC6H3Me2-2, 6)5 {Ph2PCH2C(O) Ph}2]

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.     

Synthesis, spectra and photophysics of some free base tetrafluoroalkyl and tetrafluoroaryl porphyrins with potential applications in imaging

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.     

The visible absorption spectrum of OBrO, investigated by Fourier transform spectroscopy

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.     

Diffusion coefficients of sodium dodecyl sulfate in water swollen cross-linked polyacrylamide membranes

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.     

Spectral and photophysical studies of substituted indigo derivatives in their keto forms.

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.     

The synthesis and structure of terpyridine-N-oxide complexes of copper(II) perchlorate

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.     

Measuring complexation by single-molecule fluorescence anisotropy

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.