4-bromo-5-methyl-(2H)-1,2,6-thiadiazin-3(6H)one 1,1-dioxides

The title compounds, bearing an alkyl and/or bromine substituent on nitrogen, were synthesized. Unlike 5-bromo-6-methyluracil, 4-bromo-5-methyl-(2H)-1,2,6-thiadiazin-3-(6H)one 1,1-dioxides have the ability to act as a bromonium ion source.     

Active site reactant center geometry in the Co(II)-product radical pair state of coenzyme B12-dependent ethanolamine deaminase determined by using orientation-selection electron spin-echo envelope modulation spectroscopy

The distances and orientations among reactant centers in the active site of coenzyme B12-dependent ethanolamine deaminase from Salmonella typhimurium have been characterized in the Co(II)-product radical pair state by using X-band electron paramagnetic resonance (EPR) and two-pulse electron spin-echo envelope modulation (ESEEM) spectroscopies in the disordered solid state. The unpaired electron spin in the product radical is localized on C2. Our approach is based on the orientation-selection created in the EPR spectrum of the biradical by the axial electron-electron dipolar interaction. Simulation of the EPR line shape yielded a best-fit Co(II)-C2 distance of 9.3 A. ESEEM spectroscopy performed at four magnetic field values addressed the hyperfine coupling of the unpaired electron spin on C2 with 2H in the C5' methyl group of 5'-deoxyadenosine and in the beta-2H position at C1 of the radical. Global ESEEM simulations (over the four magnetic fields) were weighted by the orientation dependence of the EPR line shape. A Nelder-Mead direct search fitting algorithm was used to optimize the simulations. The results lead to a partial model of the active site, in which C5' is located a perpendicular distance of 1.6 A from the Co(II)-C2 axis, at distances of 6.3 and 3.5 A from Co(II) and C2, respectively. The van der Waals contact of the C5'-methyl group and C2 indicates that C5' remains close to the radical species during the rearrangement step. The C2-Hs-C5' angle including the strongly coupled hydrogen, Hs, and the C5'-Hs orientation relative to the C1-C2 axis are consistent with a linear hydrogen atom transfer coordinate and an in-line acceptor p-orbital orientation. The trigonal plane of the C2 atom defines sub-spaces within the active site for C5' radical migration and hydrogen atom transfers (side of the plane facing Co(II)) and amine migration (side of the plane facing away from Co(II)).     

Fluordiazadiphosphetidine, 3. Mitt.: Die thermische Behandlung von 2,2,2,4,4,4-Hexafluoro-1,3-dimethyl-1,3,2,4-diazadiphosphetidin unter Druck in Gegenwart von Phosphor(V)fluorid und Alkalimetallfluoriden

Prolonged heating of (CH₃NPF₃)₂ in a sealed tube at 120°C yields (CH₃N)₄P₃F₇ and PF₅. Under the experimental conditions these compounds react to (CH₃N)₄P₃F₆ ⁺PF₆ ^–. Reaction of (CH₃NPF₃)₂ in the presence of PF₅ leads to a marked decrease in the formation of the ionic compound. The influence of the fluoride donating saltsMF (M=Li, Na, K, Cs) is investigated.

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Früher: Alkyliminophosphorsäuretrihalogenide, 1. und 2. Mitt.     

Metallierungsreaktionen an cyclometallierten komplexen des typs Mo-C6H4CH2PR2)2(M = Pd,Pt)

The complexes of type $\text{M}\text{o}\text{-C}{}_6\text{H}{}_4\text{CH}{}_2\text{P}$R₂)₂ (M = Pd, Pt) are readily deprotonated by n-Buli under various conditions yielding μ-C-bis-dilithiated species. The resulting carbanions are attacked by the electrophiles Mel, Me₃SiCl and Ph₂PCl to form the corresponding disubstituted derivatives. The reaction with AuCl . PPh₃ yields heterobimetallic complexes with two different MC σ-bonds. The compounds obtained are analytically and spectroscopically characterized.     

Studies of protein hydration in aqueous solution by high-resolution nuclear magnetic resonance spectroscopy

Individual hydration water molecules in aqueous protein solutions have been observed using experimental schemes for homonuclear two-dimensional and heteronuclear three-dimensional NMR experiments in H₂O solution, which do not require suppression of the solvent line by presaturation. In these experiments, the location of the hydration waters is determined from their nuclear Overhauser effects (NOE s) with individual hydrogen atoms of distinct amino acid residues. In the basic pancreatic trypsin inhibitor (BPTI ), four internal water molecules that had been reported in three different crystal forms were also found to be in the same locations in the solution structure, with lifetimes with respect to exchange of the water protons in excess of 0.3 ns. Additional NOE s with polypeptide protons located on the protein surface may involve either hydration water molecules or hydroxyl protons of amino acid side chains. Their total number is small compared to the number of NOE s expected from the hydration water molecules identified in the crystal structures of BPTI .     

Improved ultrasonic extraction procedure for the determination of polycyclic aromatic hydrocarbons in sediments

The aim of this work was to optimize an ultrasonic extraction procedure for the determination of polycyclic aromatic hydrocarbons (PAHs) in sediments and to compare it with the reflux procedure using methanolic potassium hydroxide. Sample extracts were purified with a miniaturized silica gel chromatographic column and analyzed by gas chromatography-mass spectrometry (GC-MS). Ultrasonication using n-hexane-acetone (1:1, v/v) solvent mixture on dried homogenized marine sediment gave better precision (smaller relative standard deviation (RSD) values) and comparable quantities of individual PAH's compared to the reflux procedure. Ultrasonication with the n-hexane-acetone (1:1, v/v) mixture, utilizing four 15 min extraction cycles, was found to be sufficient for extracting PAHs from wet sediments. The optimized ultrasonic extraction procedure extracted aliphatic and aromatic hydrocarbons from the National Institute of Standards and Technology SRM 1941a with recoveries greater than 90%. The major advantages of ultrasonication compared to the reflux method are the lower extraction times, simplicity of the apparatus and extraction procedure. The optimized ultrasonication procedure has been used in our laboratory to extract hydrocarbons from naturally wet sediments from rivers, and coastal and marine areas.     

Triphenylphosphinimino‐triphenylstiboniumchlorid, [Ph3PNSbPh3Cl], und seine Reaktion mit FeCl3

[Ph₃PNSbPh₃Cl] ( 1 ) was prepared by oxidative addition of ClNPPh₃ to triphenylstibine in dichloromethane solution. The compound is characterized by IR spectroscopy and by an X‐ray structure determination. 1 crystallizes in the monoclinic space group P2₁/c with four formula units per unit cell. Lattice dimensions at 193 K: a = 925.3(1), b = 1777.2(1), c = 1825.5(1) pm, β = 94.07(1)°, R₁ = 0.0228. 1 forms monomeric molecules with tetrahedrally coordinated phosphorus and trigonal‐bipyramidally coordinated antimony atom, the atoms N and Cl being in axial positions. The bond lengths PN and SbN are 155.0(2) and 198.4(2) pm, respectively, the PNSb angle is 138.6(1)°. 1 reacts with iron trichloride to give the known phosphoraneiminato complex [FeCl₂(NPPh₃)]₂.     

On the construction of primitive elements in field extensions

The subject of this article are a priori constructions of primitive elements in field extensions. Consider the totality of all separable polynomialsf of degreen over a fieldK with rootsx ₁,...,x _n and prescribed Galois groupG. A vector (b ₁,...,b _n )K ⁿ is called stably primitive (forG), if, for each suchf,b ₁ x ₁+...+b _n x _n generates the splitting field off. We develop representation theoretical devices to investigate the set of stably primitive vectors geometrically. A fundamental observation is that is either very large or very small (or even empty). These two cases are illustrated by various examples. Moreover, criteria are given to decide which case holds. For a number of groups where is recognized to be small we show.     

Band structure effects on the plasmon dispersion in simple metals

The real part of the effective dielectric function is derived analytically in the pseudopotential approximation. For anyk-direction, the theory allows the evaluation of the plasmon dispersion, _p (k), which is found to be anisotropic in general due to band structure effects. Application of the theory to Al yields an isotropic shift atk=0 of _p (0) _v – 0.3 eV and explains the recently observed anisotropic behaviour of the dispersion very well fork < 0.6k _F .     

Funktionalisierte Alkinkomplexe von Wolfram(VI). Synthese und Kristallstrukturen von [WCl4(Et?Se?CC?Se?Et)(THF)] und [WCl4(Et?Te?CC?Te?Et)(THF)]

Functionalized Alkyne Complexes of Tungsten(VI). Syntheses and Crystal Structures of [WCl₄(Et? Se? C?C? Se? Et)(THF)] and [WCl₄(Et? Te? C?C? Te? Et)(THF)] The title compounds have been prepared by reactions of [WCl₄(SEt₂)₂] with the alkynes Et? X? C?C? X? Et (X = Se, Te) in CCl₄ solution and subsequent addition of tetrahydrofurane. Both complexes were characterized by crystal structure determinations. [WCl₄(Et? Se? C?C? Se? Et)(THF)]: Space group P2₁/n, Z = 4, structure determination with 2942 unique reflections, R = 0.038. Lattice dimensions at 20°C: a = 934.2, b = 1639.5, c = 1189.5 pm, β = 96.497°. [WCl₄(Et? Te? C?C? Te? Et)(THF)]: Space group P2₁/n, Z = 4, structure determination with 4097 unique reflections, R = 0.067, Lattice dimensions at ?70°C: a = 899.2, b = 1691.9, c = 1213.3 pm, β = 96.82°. The complexes have monomeric molecular structures with the oxygen atom of the THF molecules in trans-position to the side-on bound alkyne ligands.