Application of Microwave Energy to Cleavage of Sulfur Bonds in the S8Ring in the Simplest Amide Solvents

Microwave energy has been employed for cleavage of sulfur bonds in the S₈ring. Cleavage of S–S bonds was carried out in extraction of elemental sulfur in simple amide solvents. Due to the use of microwave energy and the polarity of amides, up to, 100 times lower concentration of a nucleophilic reducer, such as azide or nitrite, may be used to cleave the sulfur bonds. The time needed for cleavage of sulfur bonds at sulfur concentration higher than 0.1 mg S/100 mg solvent was reduced from hours to minutes. This cleavage was quantitative when carried out in a Teflon container in a microwave oven with continuous or pulsed heating. UV spectra show from which value of absorption there will be a sulfur sol at different sulfur concentrations. This allows us to adjust the microwave exposure power and time to avoid sulfur sol formation and not destroy the sample.     

Die Struktur des Pentaphenyldisilans

Structure of Pentaphenyldisilane For the first time Pentaphenyldisilane was prepared by Gilman and Goodman. It is produced by the reaction of Ph₃SiLi with Ph₂ClSiH. The crystal structure presents an ideally staggered conformation. The distance d(Si? Si) = 235.7 pm corresponds to a normal single bond length. This emphasizes the complete relief of the central Si? Si bond by the insertion of only one hydrogen atom.     

The third-order electric susceptibilities of NaCl and KCl monocrystals

The dispersion of the third-order electric susceptibilities(; , , –) and(; , 0, 0) of NaCl and KCl monocrystals has been calculated by means of experimental data on the electro-optic Kerr effect. The result has been obtained by using semi-classical models of anharmonic oscillators. An ionic contribution to the electro-optic coefficients has been presented. From the result obtained it follows that the third-order electric susceptibilities are of the order of 10^–22 m² V^–2.     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. 46 [1]. 29Si-NMR-chemische Verschiebungen von Trialkoxysilylthioderivaten der Permethylpolysilane

Contributions to the Chemistry of Silicon-Sulphur Compounds. 46. ²⁹Si-N.M.R. Chemical Shifts of Trialkoxysilylthio Derivatives of Permethylpolysilanes ²⁹Si-N.M.R. chemical shifts of trialkoxysilythio derivatives of permethylpolysilanes of the two series: α, ω-(RO)₃SiS(SiMe₂)_nSSi(OR)₃, n = 2, 3, 4, 6 and 1-(RO)₃SiS(SiMe₂)_nMe, n = 2, 4; R = i-Pr, t-Bu and also ³¹C-NMR shifts are given. The relationship of ²⁹Si-NMR chemical shift from the netto charge at the silicon atom q(Si) which value has been corrected according to the Sandorfy C quantum-chemical model is discussed. The greater reduction of the electron density at silicon in compounds with Si? X bond (X = S, P, Cl) has been explained by a conjugation of the lone of sulphur with the Si? X bonding pair.     

RESOLUTION OF TWO EMISSION SPECTRA FOR TRYPTOPHAN USING FREQUENCY-DOMAIN PHASE-MODULATION SPECTRA

We describe a novel application of frequency-domain fluorometry which allows resolution of the decay times and emission spectra of samples which display multi-exponential decay kinetics. This method does not require any previous knowledge about the decay times or any assumptions about the shape of the emission spectra. We record the wavelength-dependent phase angles and modulations (phase angle and modulation spectra) using a number of light modulation frequencies. The data is analyzed by non-linear least-squares to recover the emission spectra and their associated decay times. Phase and modulation spectra (PM Spec) were used to recover the emission spectra associated with the two decay times of tryptophan at pH = 7 (0.54 and 3.44 ns). The emission spectra of these components are centered at 340 and 355 nm, respectively, with the amplitude of the 0.54 ns component contributing 6% to the total emission. These results are in agreement with previous time-resolved studies by Szabo and Rayner [J. Am. Chem. Soc. 102, 554-563 (1980)]. Control experiments were performed on mixtures of N-acetyl-L-tryptophanamide (NATA) and PPD, which demonstrate our ability to recover the spectra and decay times from two component mixtures. NATA itself displayed a single decay time and only one emission spectrum.     

On the implementation of Sμ U(2) action in the irreducible representations of twisted canonical commutation relations

The natural S U(2) action on the creation and annihilation operators satisfying twisted canonical commutation relations (TCCR) is investigated. It is shown that the Fock representation is the only covariant irreducible representation of TCCR.Partially supported by the program RP.1.10.     

Metamagnetism

This is a review of the physical properties of metamagnets. These are antiferromagnets which, upon the application of a magnetic field, can undergo first-order magnetic phase transitions to a state with a relatively large magnetic moment. The treatments of mean field theory describing these materials are reviewed, as are the treatments of more modern theories. The experimental properties of the known metamagnets are discussed, with emphasis on the variety of means by which the metamagnetic transitions have been observed and studied. For some materials, there have been studies of the tricritical behaviour, and a discussion of the experimental results of these studies is given, along with a comparison of the results with the present theory.     

Subtraction Menger algebras

We give an abstract characterization of algebras of partial functions from A ⁿ to A endowed with the operations of the Menger superposition and the set-theoretic difference of functions as subsets of A ⁿ⁺¹.     

Reduction of Phenyl-Substituted Pyridinium Methoiodides with Sodium Borohydride. Formation of Amine-Borane Complexes in Water

Reduction of phenyl-substituted pyridinium methoiodides with sodium borohydride in water afforded besides the desired tetrahydropyridines substantial amounts of amine-borane complexes. Reduction in methanol afforded tetrahydropyridines in high yield, with almost no amine-boranes formed.