Organometallic derivatives of the transition elements : II. Proton magnetic resonance spectra of substituted bis(arene)chromium(0) complexes

The proton magnetic resonance spectra of a series of bis(arene)chromium(0) complexes have been investigated. Simple first order spectra are obtained in most cases, for which chemical shift assignments are reported. A significant reduction in J(HH)-values, relative to the free ligand, are observed for the complexed arenes; H---H coupling is limited to adjacent hydrogen atoms. In fluorobenzene complexes, H---F coupling is so diminished as not to be observed in the majority of our spectra. Meta disubstituted arenes, in which the substituents are not identical, yield two diastereomeric bis(arene)chromium(0) complexes from the metal atom synthesis which can be distinguished on the basis of their PMR spectra.     

Crystal structure of ethidium monoazide,a photoactive compound that reacts with nucleic acids

The crystal and molecular structure of ethidium monoazide, a photoactive derivative of ethidium, was determined from X-ray diffraction data. Crystals of 8-azidoethidium chloride monohydrate are monoclinic, space groupP2₁/c, witha = 8.336(5),b = 14.778(6),c = 16.873(5) Å, and = 99.90(3) ° The crystals are poorly ordered, weakly diffracting, and unstable in air. Intensity data were collected with an automated diffractometer from a crystal that was sealed in a thin-walled glass capillary. The structure was solved by direct methods and was refined by least squares toR = 0.20 for the complete set of 2126 unique reflections, and toR = 0.11 for 724 reflections with1 > 2(I). The results demonstrate that the photoactive azide moiety is attached to the 8-position of the phenanthridinium moiety. This azide group is almost linear, is nearly in the plane of the phenanthridinium ring, and is oriented away from the phenyl substituent (i.e.,trans to the C(7)-C(8) bond). Possible models for intercalation complexes of 8-azidoethidium with double-helical nucleic acids were examined by modifying published coordinates from crystal structures of ethidium-dinucleotide complexes. When in the conformation observed in this crystal structure, 8-azidoethidium can be substituted for ethidium in the published complexes without suffering any unacceptable steric interactions.     

A new synthesis of perfluoroacyl halides and anhydrides from perfluorocarboxylate salts. A synthetic study

The nucleophilic cleavage of difluorophosphine esters of perfluorocarboxylic acids by halide ions to form acyl halides has not been previously reported. Furthermore, the reactions between halophosphoryldifluorides or the anhydrides, P₂O₅F₂ and P₂O₃F₄, and perfluorocarboxylate salts produce acyl halides or acyl anhydrides, respectively.     

Synthesis of the ABC ring system of Azaspiracid. 2. A systematic study into the effect of C(16) and C(17) substitution on bis-spirocyclization

[reaction: see text] A systematic study into the effect of C(16) and C(17) substitution on the stereochemical outcome of bis-spirocyclization to form the ABC ring system of azaspiracid is disclosed. Successful construction of the natural 10R,13R bis-spirocyclic stereochemistry has been accomplished on the C(16) benzyloxy-containing precursor.     

A Universal Measure

It is shown that for any ring R of sets there is a locally convex Hausdorff topological vector space M(R) and a measure χ : R → M(R) such that for any other locally convex Hausdorff topological vector space W and any measure µ : R → W, there exists a unique continuous linear map µ : M(R) → W such that . Measure is defined in such a way that M(R)′, the space of all continuous linear functionals on M(R), corresponds to all finite, signed measures in the usual sense when R is a σ-ring. The problem of extending measures from R to the σ-ring generated by R is formulted in this setting. Properties of the universal measure χ are described. The topology of M(R) is studied via the pairing <M(R), M(R)′>. For example, the weak compact subsets of M(R)′ are characterized. This characterization gives rise to a simple proof of the Orlicz-Pettis theorem.     

Influence of asymmetric energetic ion distributions on sawtooth stabilization

The effect of energetic asymmetrically distributed ions on the stability of the internal kink mode in tokamaks is analyzed. Circulating ions which intersect the resonant surface due to finite radial excursion contribute to the mode either in the region of favorable or unfavorable curvature depending on the sign of v( parallel ). Internal kink mode stabilization for predominantly cocirculating ion populations is consistent with the observation of long sawteeth using tangential coinjection of neutral beams in JT-60U [Nucl. Fusion 40, 1383 (2000)]]. Off-axis neutral beam heating emerges as a possible means of assisting sawtooth control in future fusion grade experiments.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.