Easily assembled,modular N,O-chelating ligands for Ta(V) complexation: a comparative study of ligand effects in hydroaminoalkylation with N-methylaniline and 4-methoxy-N-methylaniline

The influence of structurally related N,O-chelating ligands with additional heteroatoms (N, O, P, S) on the reactivity of in situ generated tantalum complexes for the hydroaminoalkylation of amines has been explored. Reactivity was probed by evaluating the catalytic ability of these N,O-chelating systems with N-methylaniline and 4-methoxy-N-methylaniline substrates. Enhanced reactivity is observed with amide proligands bearing an ortho-methoxyphenyl group on the nitrogen. 4-Methoxy-N-methylaniline is found to be more prone to undergo C–H functionalization via hydroaminoalkylation than N-methylaniline. The use of the related substrate 2-methoxy-N-methylaniline is not tolerated, and instead C(sp³)–O bond cleavage was observed.     

Nichteuklidische Geometrie und Volumina hyperbolischer Polyeder

Zusammenfassung. In dieser Arbeit wird der Volumenbegriff in der nichteuklidischen Geometrie charakterisiert. Damit verknüpft ist das dritte Hilbertsche Problem über die Zerlegungsgleichheit von Polygonen und Polyedern in R?umen konstanter Krümmung. Es wird ein elementarer Zugang unter besonderer Berücksichtigung des hyperbolischen Falls beschrieben. Eingegangen am 2.2.1996 / Angenommen am 16.4.1996     

Electrochemical performance of the (Ni, Cr) doped spinel material as cathode in lithium cells

The (Ni:Cr) doped lithiated manganese oxide electrode is prepared by wet chemical route using citric acid as the precursor material. The various physical and chemical properties of the prepared electrode material were studied by DSC, XRD, FTIR, Raman and SEM measurements. The electrical conducting property of the electrode was studied by the d.c. conductivity measurements. The electrochemical property was also evaluated by using test cells with the (Ni:Cr) doped spinel electrode. The cycle life was found to be increased upon increasing dopant concentration. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

通向3-D之路

在2000年早期，42寸的等离子体电视刚刚出现在市场时，其标价超过一万美元。而今年，LCD超过了等离子体（图1），3-DTV也正在步入普通家庭。     

Riemannian nilmanifolds and the trace formula

This paper examines the clean intersection hypothesis required for the expression of the wave invariants, computed from the asymptotic expansion of the classical wave trace by Duistermaat and Guillemin. The main result of this paper is the calculation of a necessary and sufficient condition for an arbitrary Riemannian two-step nilmanifold to satisfy the clean intersection hypothesis. This condition is stated in terms of metric Lie algebra data. We use the calculation to show that generic two-step nilmanifolds satisfy the clean intersection hypothesis. In contrast, we also show that the family of two-step nilmanifolds that fail the clean intersection hypothesis are dense in the family of two-step nilmanifolds. Finally, we give examples of nilmanifolds that fail the clean intersection hypothesis.

     

Diastereoselective alkylations of β-tetrazolyl propionic acids

A new procedure for the diastereoselective alkylations of β-tetrazolyl propionic acids is described. A seven-membered chelation model is proposed to rationalize the observed high level of syn selectivity.     

A note on the hyperbolic 4-orbifold of minimal volume

Paper withdrawn by author after original posting date of July 16, 2004 and prior to preparation of the printed issue.

     

Two-photon absorption coefficients of several liquids at 264 nm

The nonlinear absorption of water (H₂O), heavy water (D ₂O), ethanol, methanol, hexane, cyclohexane, 1, 2-dichloroethane, and chloroform at 264 nm was studied using femtosecond laser pulses. The two-photon absorption coefficients for these liquids were found to be between (34 ± 3) × 10^-11 cm/W and (95 ± 11) × 10^-11 cm/W     

Adsorption behavior of noble metal ions (Au, Ag, Pd) on nanometer-size titanium dioxide with ICP-AES.

The adsorption behavior of gold (Au), silver (Ag) and palladium (Pd) on nanometer-size titanium dioxide (NSTD) at low concentrations was studied using inductively coupled plasma atomic emission spectrometry (ICP-AES). A preconcentration procedure of the analytes was carried out using NSTD as a solid-phase extractant before their determination by ICP-AES. The optimum conditions for adsorption were studied in detail, and under the condition that Au, Ag and Pd ions could be adsorbed and recovered quantitatively. The static adsorption capacities of Au, Ag and Pd on NSTD were 22.63, 14.06 and 11.82 mg/g, respectively. For the elution of gold, silver and palladium, a mixture of 5% thiourea solution and 3 mol L(-1) HNO3 was used. The parameters tested included: pH conditions, contact time of the analytes with NSTD, flow rate, adsorption capacity and sorption kinetics. According to the definition of IUPAC, the detection limits (3sigma) of this method for Au, Ag and Pd with an enrichment factor of 50 were (0.016), (0.006) and (0.012) microg mL(-1), respectively, the relative standard deviations (RSD) were 8.7%, 4.5% and 7.4%, respectively (n = 6). Some geological samples were determined with satisfactory results.