Reactivity of nucleophilic uracil derivatives

The reactivity of uracil derivatives bearing acidic methylene groups at N1 was investigated. On treatment with strong base, compounds with nitrile as the activating group underwent extensive dimerisation to give new tricyclic systems. Ester-activated compounds also produced dimers in the absence of an external electrophile, but their monomeric carbanions could be trapped by prompt addition of benzyl bromide to give normally alkylated products.     

Guettardine,a possible biogenetic intermediate in the formation of corynanthe-cinchona alkaloids

The structure of guettardine 1, an indole alkaloid isolated from the bark of $\text{Guettarda heterosepala}$ (Rubiaceae), was determined from an analysis of its MS, ¹H and ¹³C NMR spectral data, and by a chemical correlation with dihydrocorynantheol 7. Guettardine 1 can be considered to be an intermediate between the Corynanthé and the cinchonamine groups of alkaloids which are precursors of quinine and its derivatives.     

2-Cyano Δ3 piperidines1 II : total synthesis in the (±) ervitsine α-acylindole alkaloid series

The first total synthesis in the ervitsine α-acylindole alkaloid series was achieved via two successive nucleophilic substitutions on the relevant 2-cyano Δ³ piperidine by an indole moiety.     

Extractive scintillating polymer sensors for trace-level detection of uranium in contaminated ground water

This contribution describes the synthesis of robust extractive scintillating resin and its use in a flow-cell detector for the direct detection of uranium in environmental waters. The base poly[(4-methyl styrene)-co-(4-vinylbenzyl chloride)-co-(divinylbenzene)-co-(2-(1-napthyl)-4-vinyl-5-phenyloxazole)] resin contains covalently bound fluorophores. Uranium-binding functionality was added to the resin by an Arbuzov reaction followed by hydrolysis via strong acid or trimethylsilyl bromide (TMSBr)-mediated methanolysis. The resin was characterized by Fourier-transform infrared spectroscopy and spectrofluorometry. Fluorophore degradation was observed in the resin hydrolyzed by strong acid, while the resin hydrolyzed by TMSBr-mediated methanolysis maintained luminosity and showed hydrogen bonding-induced Stokes' shift of ∼100 nm. The flow cell detection efficiency for uranium of the TMSBr-mediated methanolysis resin was evaluated at pH 4, 5 and 6 in DI water containing 500 Bq L⁻¹ uranium-233 and demonstrated flow cell detection efficiencies of 23%, 16% and 7%. Experiments with pH 4, synthetic groundwater with 50 Bq L⁻¹ uranium-233 exhibited a flow cell detection efficiency of 17%. The groundwater measurements show that the resins can concentrate the uranyl cation from waters with high concentrations of competitor ions at near-neutral pH. Findings from this research will lay the groundwork for development of materials for real-time environmental sensing of alpha- and beta-emitting radionuclides.     

Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

This report covers studies in trivalent lanthanide complexation by two simple cyclohexanetriols that are models of the two coordination sites found in sugars and derivatives. Several complexes of trivalent lanthanide ions with cis,cis-1,3,5-trihydroxycyclohexane (L(1)()) and cis,cis-1,2,3-trihydroxycyclohexane (L(2)()) have been characterized in the solid state, and some of them have been studied in organic solutions. With L(1)(), Ln(L)(2) complexes are obtained when crystallization is performed from acetonitrile solutions whatever the nature of the salt (nitrate or triflate) [Ln(L(1)())(2)(NO(3))(2)](NO(3)) (Ln = Pr, Nd); [Ln(L(1)())(2)(NO(3))H(2)O](NO(3))(2) (Ln = Eu, Ho, Yb); [Ln(L(1)())(2)(OTf)(2)(H(2)O)](OTf) (Ln = Nd, Eu). Lanthanum nitrate itself gives a mixed complex [La(L(1)())(2)(NO(3))(2)][LaL(1)()(NO(3))(4)] from acetonitrile solution while [La(L(1)())(2)(NO(3))(2)](NO(3)) is obtained using dimethoxyethane as reaction solvent and crystallization medium. With L(2)(), Ln(L)(2) complexes have also been crystallized from methanol solution [Ln(L(2)())(2)(NO(3))(2)]NO(3), (Ln = Pr, Nd, Eu). Single-crystal X-ray diffraction analyses are reported for these complexes. Complex formation in solution has been studied for several triflate salts (La, Pr, Nd, Eu, and Yb) with L(1 )()and L(2)(), respectively in acetonitrile and in methanol. In contrast to the solid state, both structures Ln(L) and Ln(L)(2) equilibrate in solution, as was demonstrated by low-temperature (1)H NMR and electrospray ionization mass spectrometry experiments. Competing experiments in complexing abilities of L(1)() and L(2)() with trivalent lanthanide cations have shown that only L(2)() exhibits a small selectivity (Nd > Pr > Yb > La > Eu) in methanol.     

Ueber den mikrochemischen Blutnachweis

Ohne Zusammenfassung     

An Improved Method for Calculating Zeta-Potentials from Measurements of the Electrokinetic Sonic Amplitude

The surface electric properties of the commercially available silica, Monospher 1000 (Fa. Merck), have been studied by conductivity and ESA (electrokinetic sonic amplitude) experiments. It could be shown that accounting for the contribution of the stagnant layer to surface conductivity is indispensable in the interpretation of electrokinetic data at low ionic strength. A general method has been put forward which allows to take into account the total, experimentally accessible surface conductivity in the evaluation of ESA data of moderately concentrated suspensions. This includes additional conductivity measurements which serve for the independent estimation of the total relative surface conductivity. The resulting zeta-potentials are clearly higher than those obtained after neglecting the contribution of the stagnant layer to surface conductivity. In addition, the ionic mobilities of potassium and magnesium in the hydrodynamically stagnant layer have been investigated in some detail. It has been found that the ionic mobility of potassium is of the same order of magnitude as in the bulk solution while the mobility of magnesium is significantly reduced. Copyright 2000 Academic Press.     

2-cyano Δ3 piperidines IV: Spiroannelation in the piperidine series

The preparation of piperidines $\text{7}$ and $\text{11}$ spirosubstituted at C-2 from the 2-cyano Δ³ piperidine $\text{5}$ is described. The mechanism of their formation is discussed.