New access to H-phosphonates via metal-catalyzed phosphorus-oxygen bond formation

A novel approach to H-phosphonates from hypophosphorous acid using a transfer hydrogenation process was developed. This method is atom-economical, environmentally friendly, catalytic, and efficient, leading easily to H-phosphonate monoesters or ammonium salt in moderate to good yields.     

ELECTRON GUN FOR LARGE ORBIT GYROTRON (LOG) WITH DECREASED INFLUENCE OF CATHODE PLASMA ON ELECTRON BEAM PROPERTIES

High power Large Orbit Gyrotron (LOG) [1] is now under development at FIR FU. First version of this device was recently manufactured and then assembled with power supply ETIGO-IV [2]. Results of preliminary tests of electron-optic system are presented. The conditions when stableflat form of current pulse realized are discussed. Analytical estimations of cathode-anode distance to achieve small influence of cathode plasma during high voltage (HV) pulse are performed. Two new electron gun versions with decreased influence of the cathode plasma on its impedance and pulse form are suggested and optimized. New optimal magnetic field distributions are found. First gun has quiasi-flat cathode configuration near the anode diaphragm and provides operating current about 60 A. Second one uses blade cathode with operating current about 30 A. Beam quality for both guns is suitable for LOG operation.     

Characterization of graded-index planar waveguides and analysis of modal coupling for the design of integrated optical components produced by ion-exchange in glass and induced by Kerr effect

An experimental analysis of graded-index (GRIN) planar waveguides produced by ion exchange in soda-lime glass is presented. This study is based on a recent model describing nonlinear diffusion. Likewise the modal coupling between planar waveguides, produced in the same substrate, is analyzed in order to design efficient integrated optical components. Finally, waveguiding structures induced by Kerr effect in glass are proposed and analyzed.     

Theoretical investigations on the solvation process

A model to facilitate the computation of the most stable conformer of associated M · H₂O (M being a polar molecule) which depends upon the electrostatic interaction energy between the two associated molecules is proposed and tested. SCF electrostatic potentials for the M molecule and a suitable point charge distribution for H₂O were employed in the model computations. Energies predicted by the model are found to be in good agreement with those resulting from an ab initio minimal STO basis SCF treatment of some conformations of the H₂O dimer.

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Zusammenfassung Ein Modell zur Durchführung der Berechnung des stabilsten Konformeren eines Assoziationskomplexes M · H₂O, wobei M ein polares Molekül ist, wird vorgeschlagen und untersucht. Es basiert auf der elektrostatischen Wechselwirkung zwischen beiden Partnern, und zwar wird für das Molekül M der elektrostatische Anteil seines SCF-Potentials und für H₂O eine angemessene Punktladungsverteilung zugrunde gelegt. Die resultierenden Energien sind in guter Übereinstimmung mit denen, die sich bei einer ab initio Rechnung mit minimaler STO Basis ergeben.

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Work performed with the financial support of the Consiglio Nazionale delle Ricerche, through its Laboratorio di Chimica Quantistica ed Energetica Molecolare.     

The Fermi doublet V2−V3 + V4 of CH3CN as a probe of molecular interactions

The Fermi doublet V₂?V₃ + V₄ of CH₃CN in basic, inert and acidic solvents has been studied by IR and Raman spectroscopy. The values of W, the Fermi coupling coefficient, obtained from IR spectra varies with the nature of the solvent while W evaluated from Raman data remains constant at 12.5 ± 0.5 cm^?1. The similar effects of Bronsted and Lewis acids on the band frequencies and intensities is evidence that the CN group complexes with acids via the N atom “n” electron pair and not the π bond.     

Molecular Imprinting in Sol-Gel Materials: Recent Developments and Applications

Since its inception five decades ago, imprinted sol-gel materials went practically unnoticed, until in the 1970s the conceptual introduction of molecular imprinting in synthetic polymers triggered a new interest in this field. The recent growth in interest in organic–inorganic hybrid materials prepared by sol-gel chemistry and the development of a variety of new strategies for imprinting polymeric matrices have led to a growing activity in what became known as molecularly imprinted sol-gel materials. This paper intends to give an overview of recent progress in molecular imprinting in sol-gel matrices, the potential analytical applications of these tailor-made materials and their limitations, with the aim of drawing attention to useful information and to enhancing interest in this practically unexplored but promising field.     

A traceless solid-phase synthesis of pteridines

The linking of pyrimidines to polystyrene supports via either a 2- or 4-thioether provides access to pteridines through solid-phase synthesis. Oxidative cleavage (dimethyldioxirane) followed by nucleophilic substitution by amines, azide, or water completes a traceless synthesis of pteridines.     

An approximate expression of the electrostatic molecular potential for benzenic compounds

A method for getting approximate but realistic evaluations of the electrostatic molecular potential for benzene derivatives is presented and discussed. The method is based on a partition of the whole molecular observable into directly transferable contributions, which can be calculated without a previous knowledge of the molecular wavefunction. The algorithm, which probably is applicable also to other aromatic compounds, implements a preceding study concerning only unconjugated molecules.     

Determination of lead in the urine of exposed and unexposed adults by extraction and flow-injection/atomic absorption spectrometry

Lead is extracted from urine with ammonium pyrrolidien dithiocrbamate into methyl isobutyl ketone, and 20 μl of the extract is injected into a water carrier stream in a flow-injection/atomic absorption system. The procedure is simple, quick, accurate and reproducible. Recoveries are 96–105%. The mean urine lead contents of 20 unexposed and 20 printing-press lead exposed workers was found to be 39.0 ± 8.3 and 71.7 ± 26.3 μg Pb l^?1, respectively.