Determination of polynuclear aromatic hydrocarbons in micellar solution by electrogenerated chemiluminescence

When polarized cathodically in aqueous acetate solution (pH 7.0) containing peroxodisulfate, a micelle-forming surfactant (Brij-35) and a polynuclear aromatic hydrocarbon, an oxide-covered aluminum electrode produces an intense electroluminescence where the emitting species is the micelle-encapsulated hydrocarbon. The detection limit is ca. 10^?8 M for 9,10- diphenylanthracene.     

Study on the Chemistry and Structure of (Na(1−x)Bix)(Nb(1−y)Mny)O3 Ceramics by XPS, AES and EPMA

The (Na_1–xBi_x)(Mn_yNb_1–y)O₃ ceramics are new compounds, obtained for the first time, on the base of sodium niobate with substitution of bismuth manganite. It was shown that the solubility limit for Mn ions in sodium niobate lattice does not exceed 1% at. Therefore, the co-doping with Bi ions was proposed to increase this limit. Bismuth ions are expected to replace Na ions and to ensure charge compensation in the formed compound, thus enhancing possibility of accumulation of the Mn ions in solution without losing the appropriate electrical and optical properties. To study the morphology of produced ceramic four methods of sample characterization were used: X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron microprobe analysis (EPMA) and Scanning Electron Microscopy (SEM).     

The role of amine in the mechanism of pentathiepin (polysulfur) antitumor agents

A computational and experimental study is presented, which provides the first evidence that amine has an opportunity to engage in bonding with pentathiepin to promote its decomposition. The study provides mechanistic insight into the process that gives rise to pentathiepin biological activity. Primary or secondary amine will allow for an intramolecular addition to the pentathiepin ring at the nearest sulfur (S1). In contrast, tertiary amine adds reversibly to S1, because nitrogen cannot lose its positive charge by deprotonation. This precludes the amine promotion step. An energetically low-lying process is characterized, corresponding to S3-loss triggered by nucleophilic activation with a primary or secondary amine. Pentathiepin desulfurization via S3-unit transfer is supported by a trapping study with norbornene. That the amine may confer an enhanced reactivity in the natural products varacin, 1, and lissoclinotoxin A, 2, adds to the understanding of the pathway for pentathiepin activation and may provide new design concepts that have potential applications for this class of biocides.     

Vibrational spectra and chemical quantum calculations for 2-adamantylamino-5-nitropyridine crystals--a novel material for laser Raman converters

Polycrystalline infrared and polarized FT-Raman spectra have been measured for 2-adamantylamino-5-nitropyridine, a novel organic material for laser Raman converters. The assignment of IR and Raman bands is given on the basis of DFT calculations. The spectroscopic studies have not indicated the presence of any significant intermolecular interactions in the crystal structure of this compound. The lines observed in the stimulated Raman spectrum of this crystal are assigned to the respective molecular vibrations.     

Instrumentally simple flow detector for the determination of traces of electroluminescent compounds in aqueous solutions

A flow detector based on the observation of the cathodic electroluminescence at an oxide-covered aluminium electrode is described. The detector responds only to electroluminescent compounds in aqueous eluents, and additional selectivity can be achieved by making use of optical filters for wavelength discrimination. The optimum detection conditions were determined by using the cathodic electroluminescence induced by a polynuclear aromatic hydrocarbon in micellar solutions as the model electroluminescence. This instrumentally simple detector can be used to determine electroluminescent compounds in a wide concentration range with good precision. For instance, its detection limit, dynamic range and precision (i.e., relative standard deviation for 20 successive measurements of 1 × 10^?7 M samples) for the determination of micelle-encapsulated 9,10-diphenylanthracene were found to be 1 × 10^?8 M, four orders of magnitude and 7%, respectively.     

Low-lying excited singlet states and S2→S0 luminescence of dipyrido[3,4-b: 2,3-d]phenazine

The absorption, fluorescence and excitation fluorescence spectra dipyrido[3,4-b:2,3-d]-phenazine (DPPZ1) have been measured in non-polar and polar matrices at room temperature, and were taken into account to explain the origin of the relatively weak emission of this molecule in both type of environment. The electronic structure of DPPZ1 was calculated using a modified INDO CI method. The geometry optimization has been performed using the MNDO method. According to the spectra and the results of calculations, the lowest excited singlet state S₁ of DPPZ1 molecule is of n,π^*-type and the next one, S₂ state, is of π,π^*-type. The energy gap ΔE_calc is equal 4770 cm⁻¹. The low efficiency of the emission observed in the hydroxylic solvent can be interpreted in terms of thermal quenching of the π,π^*-type fluorescence. However, experimental results obtained suggest that in nonpolar solvents the emission of the molecule examined is an anomalous S₂→S₀ fluorescence.     

Organolithium-induced enantioselective alkylative double ring-opening of epoxides: synthesis of enantioenriched unsaturated amino alcohols

The use of (−)-sparteine as an external chiral ligand in enantioselective organolithium-induced alkylative double ring-opening of dihydropyrrole epoxides and 7-azanorbornene-type epoxides gives unsaturated acyclic amino alcohols, and amino cyclohexenols in up to 87% ee.     

Total synthesis of new indolo[2,3-a]quinolizine alkaloids sempervirine type, potential pharmaceuticals

Total synthesis of the two series of new pentacycilc cycloalk[g]indolo[2,3-a]quinolizine alkaloids (modified sempervirine possessing the wide range of activity), has been elaborated in five steps from 5-acetyl-3-methylthio-1,2,4-triazine (obtained from the simple acyclic materials). In the two key steps: inverse electron demand Diels-Alder reaction of precursor with cyclic enamines and the following Fischer indolization of 3-acetyl-1-methylthiocycloalka[c]pyridines, the AB-DE synthons, has been obtained. The final stages: desulfuration, and formation of the C-ring via the Gribble method have led to the expected zwitterionic alkaloids. Model syntheses of the indolopyridocoline and its methoxy analogue from 2-acetylpyridine have been performed for investigation of the microwave-induced Fischer synthesis of sensitive indoles and for obtaining compounds for comparative study of spectroscopic data.     

On the magnetization fluctuations in the completely disordered paramagnetic medium

The space extension of a single magnetization fluctuation in the disordered paramagnetic medium defined within the coherent potential approximation is discussed. The thermodynamical potential functional for the subspace of nearly completely disordered configurations is derived.