2D mapping by Kohonen networks of the air quality data from a large city

The 15-variable environmental data (7 concentrations: CO, SO2, O3, NOx, NO, NO2, particulate matter smaller than 10 micron (PM10), and 8 weather data: cloudiness, rainfall, insolation factor (Isfi), temperature, pressure at two locations, and wind intensity with direction) in a period of 45 days with 1-h intervals were extracted from a larger database of concentrations recorded in minute intervals for the same time period. The monitoring site was located in the City of Buenos Aires in a relatively heavy traffic crossroad of two avenues. The data required special pretreatment where the hourly content of rain, wind intensity, wind velocity, and cloudiness were concerned. The new variable named insolation factor (relative UV radiation) calculated on the basis of the general meteorological data, the geographic position of the monitoring site, cloudiness, date, and the time of the recording was composed. The relative intensity of UV radiation was modeled by a Gaussian function, multiplied by a cloudiness factor. Based on the 14-variable input and the 1-variable output (ozone) data, first, the clustering of all 980 data records was made. The top map clustering showing the ozone concentration was related to the maps of all 14 variables. The link between O3 clusters, NO2, and Isfi weight levels is shown and discussed. As a preliminary result of this study some of the most interesting correlations between the maps and remaining variables are given.     

The influence of intermolecular interactions on the SiH bond vibration in silatrane and its c-substituents

Spectra of the silatrane HSi(OCHRCH₂)₃N and its 3,7,10-trimethyl- and -trifluoromethyl derivatives have been studied. The dependences of frequency and integral intensity of the SiH vibration on solvent polarity and temperature have been established. It has been shown that interaction of silatrane molecules with the solvent is universal in character. The phenomenon of the changing SiH vibration is explained by the possible formation of a three-centered orbital bending the atoms of hydrogen, silicon and nitrogen. In contrast to triethoxysilane, a dependence between v(SiH) and Σσ1 values of substituents in the cycle has been observed for silatranes.     

Rigid cyclophanes that illustrate stereochemical principles

All of the point groups common to organic chemistry except two are illustrated by known compounds that are rigid [2.2]paracyclophane derivatives. Examples are given of transannular directing effects by acetyl, nitro, and acetoxyl substituents attached to [2.2]paracyclophane. In bromination or chloromethylation, proton loss of a sigma complex is rate-determining, and the oxygens already in the molecule remove the proton being substituted. The synthesis of [2.2.2](1,2,4)cyclophane and [3.2.2](1,2,5)cyclophane, and their unusual chemical properties are described. Transannular hydride shifts out of methyl groups due to proximity effects are reported. Torsional racemizations and epimerizations of [2.2]paracyclophane derivatives are reviewed. The diradical intermediates formed have been intercepted by either H· donors, or by addition to substituted olefins. To account for the stereochemical course of addition and substitution reactions in the side-chains of [2.2]- and [4,2]paracyclophanes, new types of bridged carbonium ions are suggested. Conformational equilibria in the four-carbon side-chain of [4.2]paracyclophane derivatives are discussed.     

Chemical changes in polymeric photodielectric media used in holographic recording

Photochemical response of two thick photodielectric holographic recording systems was studied by using a 488 nm argon laser line. These systems are made of poly(methyl methacrylate) or poly(methyl α-cyanoacrylate) with p-benzoquinone as sensitizer. It was found that in both systems, photochemically induced branching, followed by crosslinking of the polymeric chains provide the major effects that modulate the index of refraction of these materials. The change in polymer structure as measured by intrinsic viscosity was correlated to the change in index of refraction, by which the holographic recording process is accomplished.     

Validation of standardized high-performance thin-layer chromatographic methods for quality control and stability testing of herbals

In herbal medicinal products the entire herbal drug or an herbal drug preparation is regarded as the active pharmaceutical ingredient, regardless of whether constituents with defined therapeutic activity are known. In quality control and stability testing of herbal medicinal products, fingerprint chromatograms are used as powerful tools to evaluate and compare the composition of compounds in such products. To fulfill the International Conference on Harmonization and Good Manufacturing Practice-based regulatory requirements in pharmaceutical quality control, chromatographic fingerprint analysis needs to be validated. Based on a standardized methodology, this paper provides a comprehensive concept for evaluating validation parameters for planar chromatographic fingerprinting by considering the stationary phase, sample application, developing solvent, chromatogram development, plate labeling, derivatization, documentation, and chromatographic equipment. Validation parameters addressed include stability of the analyte, selectivity, robustness testing, and method reproducibility.     

Reaction of metalated nitriles with enones

[reaction: see text] There have been a number of reports of the kinetic conjugate (1,4) addition of metalated arylacetonitriles to enones. Several proposals have been made to explain this behavior based on nucleophile structure or aggregation state or on the HSAB properties of the reactants. A reexamination of these studies showed that in each case the 1,4 adducts resulted from equilibration of the kinetically formed 1,2 adducts to the more stable 1,4 adducts. Thus, no conclusions about the origins of 1,4 selectivity can be drawn from these experiments. The 1,2 addition, retro-1,2 addition, 1,4 addition, and retro-1,4 addition of lithiophenylacetonitrile to benzylideneacetone were examined, and a free energy level diagram was constructed for the reaction.     

Solvent-Dependent Lithium Bridging in Allenyl-Propargyllithium Reagents

The solution structures of two allenyl-propargyllithium reagents (6-Li and 7-Li) which give (13)C NMR chemical shifts intermediate between those expected for the allenyl and propargyl isomers have been studied by the Saunders isotope perturbation technique. Variable equilibrium isotope shifts were detected, showing that these reagents adopt structures ranging from equilibrating localized allenyl- and propargyllithium reagents (1A right harpoon over left harpoon 1B) to equilibrating unsymmetrically bridged structures (11) and symmetrically bridged structures (2), depending mostly on the details of solvation.     

Alkali metal intercalated fullerene-like MS(2) (M = W, Mo) nanoparticles and their properties

Layered metal disulfides-MS(2) (M = Mo, W) in the form of fullerene-like nanoparticles and in the form of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal (potassium and sodium) vapor using a two-zone transport method. The composition of the intercalated systems was established using X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The alkali metal concentration in the host lattice was found to depend on the kind of sample and the experimental conditions. Furthermore, an inhomogeneity of the intercalated samples was observed. The product consisted of both nonintercalated and intercalated phases. X-ray diffraction analysis and transmission electron microscopy of the samples, which were not exposed to the ambient atmosphere, showed that they suffered little change in their lattice parameters. On the other hand, after exposure to ambient atmosphere, substantial increase in the interplanar spacing (3-5 A) was observed for the intercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggested as a possible explanation for this large expansion along the c-axis. Deintercalation of the hydrated alkali atoms and restacking of the MS(2) layers was observed in all the samples after prolonged exposure to the atmosphere. Electric field induced deintercalation of the alkali metal atoms from the host lattice was also observed by means of the XPS technique. Magnetic moment measurements for all the samples indicate a diamagnetic to paramagnetic transition after intercalation. Measurements of the transport properties reveal a semiconductor to metal transition for the heavily K intercalated 2H-MoS(2). Other samples show several orders of magnitude decrease in resistivity and two- to five-fold decrease in activation energies upon intercalation. These modifications are believed to occur via charge transfer from the alkali metal to the conduction band of the host lattice. Recovery of the pristine compound properties (diamagnetism and semiconductivity) was observed as a result of deintercalation.     

Spektroskopische Untersuchungen an Siliciumverbindungen. XXXII. Substituenteneinflüsse auf die SiNSi-Bindung in p-substituierten N,N-Bistrimethylsilylanilinen

The influence of the substituents X of the compounds p-X–C₆H₄–N[Si(CH₃)₃]₂ on the positions of the v_s SiNSi vibrational frequencies is described by an empirical equation in dependence on mass and electronic properties of X. The bonding properties of the C? H, Si? C, and Si? N? Si bonds of the disilazane group are discussed by means of complementing informations from ¹³CH coupling constants.     

Über einen Satz von Shl. Sternberg in der Theorie der analytischen Iterationen

Let X=X ₁,...,X _n be the ring of formal power series inn indeterminates over . LetF:XAX+B(X)=(F ⁽¹⁾(X),...,F ⁽ⁿ⁾(X))(X) ⁿ denote an automorphism of X and let ₁,..., _n be the eigenvalues of the linear partA ofF. We will say thatF has an analytic iteration (a. i.) if there exists a family (F _t (itX)) _t of automorphisms such thatF _t(X) has coefficients analytic int and such thatF ₀=X,F ₁=F,F _t+t=F_tF_t for allt,t. Let now a set=(ln₁,...,ln _n ) of determinations of the logarithms be given. We ask if there exists an a. i. ofF such that the eigenvalues of the linear partA(t) ofF _t(X) are . We will give necessary and sufficient conditions forF to have such an a. i., namely thatF is conjugate to a semicanonical formN=T ^–1FT such that inN ^(k)(X) there appear at most monomialsX ₁ ¹ ...X _n ⁿ . This generalizes a result of Shl.Sternberg.

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Herrn Prof. Dr. E. Hlawka zum 60. Geburtstag gewidmet