A facile three-step synthesis of (±)-crispine A via an acyliminium ion cyclisation

A high yielding cyclisation of the readily available N-(4,4-diethoxybutyl)-2-(3,4-dimethoxyphenyl)acetamide to 8,9-bis(methyloxy)-2,3,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-5(1H)-one is described. The latter can be reduced with either AlH₃ or BH₃ to (±)-crispine A in an overall yield of 55%.     

Electron transport across the alkanethiol self-assembled monolayer/Au(111) interface: role of the chemical anchor

Alkanethiol self-assembled monolayers (SAMs) on Au(111) are model systems for molecular electronics. We probe the role of the chemisorption bond on electron dynamics at the SAM/Au interface using time-resolved two-photon photoemission. Formation of the Au-S bond is evidenced by a localized sigma resonance, which broadens and shifts upward in energy when the lying-down chemisorbed molecules stand up. The localized chemisorption bond does not affect the electronic coupling between delocalized image resonances and the metal substrate. Instead, lifetimes of image resonances are decreased due to scattering with S atoms within the thiol or thiolate monolayer.     

Dark induction of haem oxygenase messenger RNA by haematoporphyrin derivative and zinc phthalocyanine; agents for photodynamic therapy.

Haematoporphyrin derivative is one of the main drugs currently used in clinical trials involving photodynamic therapy of cancer, and zinc phthalocyanine is being considered as one of several possible alternatives. We show that incubation of cultured human fibroblasts populations with either of the two drugs will lead to a sharp increase in the accumulation of the messenger RNA corresponding to haem oxygenase. Only cells incubated with haematoporphyrin derivative show additional enhancement of expression of this specific gene on exposure to red light. Since haem oxygenase induction appears to be a specific stress response that may be involved in cellular defence, such observations should be confirmed under conditions which would allow the clinical implications to be fully evaluated.     

Analysis of ion binding on humic substances and the determination of intrinsic affinity distributions

Humic substances are characterized by a variable electric potential and by a variety of binding sites leading to chemical heterogeneity. Binding of ions to these substances is influenced by both factors. A methodology based on acid—base titrations at several salt levels is presented that allows for the assessment of an appropriate electrostatic double-layer model and the intrinsic proton affinity distribution. The double-layer model is used for the conversion of pH to pH_S for each data point, where H_S is the proton concentration in the diffuse layer near the binding site. It is shown that with an appropriate double-layer model the proton binding curves at different salt levels converge into one “master curve” when plotted as a function of pH_S. The intrinsic proton affinity distribution can then be derived from the “master curve” using the LOGA method. A rigorous analysis of metal binding to humic substances is complex and in practice is not feasible. Under two different (simplifying) assumptions, namely fully coupled and uncoupled binding, it is shown how intrinsic metal ion affinity distributions can be obtained. Model calculations show that apparent metal ion affinity distributions do not resemble the intrinsic metal ion affinity distribution.     

A study of the water-soluble proteins of the seeds of the cotton plants Gossypium hirsutum and G. barbadense

It has been shown by electrophoresis in polyacrylamide gel that different enzymes with similar electrophoretic mobilities may be localized in one and the same zone of water-soluble cottonseed proteins. Some zones not stained by the usual protein dyes also possess enzymatic activity. It has been established that the majority of the electrophoretic fractions consist of a series of polypeptides with different molecular weights, mainly of low-molecular-weight nature. The results are given of an investigation of the peroxidase, α-amylase, lipase, NADH-DCPIP oxidoreductase, and NADPH-DCPIP oxidoreductase activities of the water soluble fraction of the proteins of the seeds of the species mentioned.     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.     

Determination of trace inpurities high-purity aluminum oxide by inductively-coupled plasma atomic emission-spectrometry

Trace impurities (Ca, Cu, Fe, Mg, Mn, Na and Si) in 99.99% aluminum oxide were determined by inductively-coupled plasma atomic emission spectrometry (i.c.p./a.e.s.). The sample was fused with lithium carbonate/boric acid to determine Ca, Cu, Mg, Mn, Na and Si or dissolved in phosphoric/sulphuric acids to determine iron. Matrix effects on the calibration graphs for each element were studied: for accurate determinations, calibration solutions must contain lithium and boric acid (or aluminium and phosphoric and sulphuric acids for iron).     

Plasma polymerization. V. A systematic investigation of the inductively coupled RF plasma polymerization of the isomeric tetrafluorobenzenes

A systematic investigation has been made of the composition, gross structural features, and rates of deposition of plasma polymer films produced from the excitation of inductively coupled RF plasmas in the isomeric tetrafluorobenzenes. ESCA data reveal that the dominant reaction involves rearrangement such that under a wide variety of experimental conditions the composition of the crosslinked products remains essentially the same as that of the starting material. Small differences in rates of deposition are observed for the different isomers, and theoretical SCF MO studies at the MNDO level provides a basis for discussion of the experimental data.     

The use of magnesium perchlorate as desiccant in the syringe injection technique for determination of mercury by cold-vapour atomic absorption spectrometry

The method developed earlier was found to suffer a loss in sensitivity when the magnesium perchlorate desiccant became damp. The most sensitive and consistent results were obtained when the magnesium perchlorate was removed from the sample injection manifold. Under most circumstances a desiccant is not required.     

Chlorine nitrate photolysis by a new technique: very low pressure photolysis

Very low pressure photolysis (VLPØ) of chlorine nitrate was performed in a quartz Knudsen cell. The light source was a 2500 W high-pressure xenon lamp, and a modulated molecular-beam mass spectrometer was used to monitor the concentration of ClONO₂ and photolysis products. Because of the low pressures used (? 10^?3 torr) and the short residence time in the cell (≈1 s), secondary reactions were unimportant and the primary products could be directly identified. The primary photolysis products (λ ≈ 2700 Å) are atomic chlorine and NO₃ free radical. Chlorine atoms were identified both by the appearance of Cl₂ (wall recombination product; the walls were not poisoned) and by HCl produced when C₂H₆ was added to the cell. Nitrate free radical was directly identified as a mass peak at m/e = 62, as well as by chemical titration with nitric oxide: NO₃ + NO → 2NO₂. It was verified by direct tests that the peak at m/e = 62 did not arise from possible HNO₃ contamination or from N₂O₅, a possible secondary product. This titration reaction was used to measure quantitatively a lower limit to the primary quantum yield, φ ? 0.5 ± 0.3. This represents a lower limit because of the unknown extent of the secondary photolysis of NO₃ under our conditions. We believe this to be the first observation using mass spectrometry of the NO₃ free radical. The quantum yield for atomic chlorine is φ = 1.0 ± 0.2. N₂O was used to test for O(¹D) according to the reaction, O(¹D) + N₂O → products; none was observed. Triplet oxygen, O(³P) was observed to the extent of ≈ 10% by the reaction O(³P) + NO₂ → NO + O₂, but this yield can also be due to the photolysis of NO₃ free radical produced in the primary step. We conclude that the predominant reaction pathway is

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