Nitrogen heterocyclic carbon-rich materials: synthesis and spectroscopic properties of dehydropyridoannulene macrocycles

A new series of nitrogen heterocyclic dehydroannulenes 1-3 have been synthesized and their macrocyclic structures assigned using spectroscopic methods. The chiral and planar ground state conformations of 1 and 3, respectively, were determined by semiempirical theoretical calculations. All dehydropyridoannulenes and precursors possessing four aromatic rings functioned as fluorescent chromophores. A detailed spectroscopic investigation into the cation-binding properties of 3 in dilute solution revealed a particularly selective photoluminescence quenching sensory response for Pd(II) ions. Cycle 3, as well as 1 and 2, also exhibited reversible proton-triggered luminescence quenching behavior. At higher concentrations, 3 afforded a coordination polymer precipitate with Ag(I) ions. Cycles 1 and 2 and precursors 15, 23, and 29 also undergo thermochemical reactions that may potentially lead to carbon-rich polymers. The physicochemical properties of 1-3 suggest that dehydropyridoannulenes may serve as a particularly versatile new class of ligands for the creation of novel heteroatom-containing carbon-rich materials with many potential applications in supramolecular materials science and nanotechnology.     

BSDEs with two reflecting barriers : the general result

In this paper we show the existence of a solution for the BSDE with two reflecting barriers when those latter are completely separated. Neither Mokobodzkis condition nor the regularity of the barriers are supposed. The main tool is the notion of local solution of reflected BSDEs. Applications related to Dynkin games and double obstacle variational inequality are given.Mathematics Subject Classification (2000): 91A15, 60G40, 91A60     

Quinquevalent tungsten as a reducing agent in potentiometric titrations : Estimation of ceric salts,bromate and ferricyanide

Quinquevalent tungsten can be further applied as a reducing agent for the potentiometric estimation of ceric salts, ferricyanide and bromate. Reduction of these oxidants takes place easily when they are present alone or in mixtures containing them together with ferric iron, dichromate or vanadate.     

Subsets with Restricted Movement

Let G be a finite permutation group on a set with no fixed points in and let m and k be integers with 0 < m < k. For a finite subset of the movement of is defined as move() = max_gG| ^g \ |. Suppose further that G is not a 2-group and that p is the least odd prime dividing |G| and move() m for all k-element subsets of . Then either || k + m or k (7m – 5) / 2, || (9m – 3)/2. Moreover when || > k + m, then move() m for every subset of .     

Triterpenoid saponins from leaves of Hedera pastuchowii

Five new triterpenoid saponins, pastuchoside A (1), B (3), C (5), D (7) and E (9), were isolated from the leaves of Hedera pastuchowii. They have oleanolic acid or hederagenin as aglycone. The structures were established by NMR spectroscopy including gs (gradient selected)-COSY, gs-HSQC, gs-HSQC-TOCSY and gs-HMBC experiments, and mass spectrometry (ESI-HR-MS). Heptaoside saponins, compounds 1 and 3, are described for the first time in the genus Hedera.     

The pion–nucleon scattering lengths from pionic hydrogen and deuterium

This is the final publication of the ETH Zurich–Neuchatel–PSI collaboration on the pionic hydrogen and deuterium precision X-ray experiments. We describe the recent hydrogen 3p–1s measurement, report on the determination of the Doppler effect correction to the transition line width, analyze the deuterium shift measurement and discuss implications of the combined hydrogen and deuterium results. From the pionic hydrogen 3p–1s transition experiments we obtain the strong-interaction energy level shift eV and the total decay width eV of the state. Taking into account the electromagnetic corrections we find the hadronic s-wave scattering amplitude for elastic scattering and for single charge exchange, respectively. We then combine the pionic hydrogen results with the 1s level shift measurement on pionic deuterium and test isospin symmetry of the strong interaction: our data are still compatible with isospin symmetry. The isoscalar and isovector scattering lengths (within the framework of isospin symmetry) are found to be and , respectively. Using the GMO sum rule, we obtain from a new value of the coupling constant () from which follows the Goldberger–Treiman discrepancy . The new values of and imply an increase of the nucleon sigma term by at least 9 MeV. Received: 20 April 2001 / Revised version: 6 July 2001 / Published online: 24 August 2001     

Characterization of the polymorph changes in Trimethoprim

Journal of Thermal Analysis and Calorimetry - Polymorphic transformation in Trimethoprim (TMP) drug has been studied employing differential scanning calorimetry (DSC), TG/DSC, X-ray diffraction and...