Preparation, structure, and dynamics of a nickel π-allyl cyanide complex

The complex (dippe)Ni(η³-allyl)(CN) has been prepared and fully characterized (dippe=bis-(diisopropylphosphino)ethane), including X-ray diffraction studies, as a square pyramidal structure. The complex shows dynamic ¹H-NMR behavior consistent with substantial structural rearrangements upon π to σ allyl interconversion. A comparison is made with (dippe)Ni(η³-allyl)Br, which also displays a square pyramidal structure.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Cleavage of carbon-carbon bonds in aromatic nitriles using nickel(0)

The nickel(0) fragment [(dippe)Ni] has been found to react with a variety of aromatic nitriles. Initial pi-coordination to the C=C and Ctbd1;N bonds of 2-cyanoquinoline is found to lead ultimately to C-CN oxidative addition. 3-Cyanoquinoline reacts similarly, although no eta(2)-CN complex is observed. 2-, 3-, And 4-cyanopyridines react initially to give eta(2)-nitrile complexes that then lead to quantitative formation of C-CN oxidative addition products. Benzonitrile reacts similarly but undergoes reversible insertion into the Ph-CN bond to give an equilibrium mixture of Ni(II) and Ni(0) adducts. A series of para-substituted benzonitriles has been studied in terms of both the position of the equilibrium between (dippe)Ni(eta(2)-arylnitrile) right harpoon over left harpoon (dippe)Ni(CN)(aryl) and the rate of approach to equilibrium, and the Hammett plots indicate a buildup of negative charge at the ipso carbon both in the transition state and the Ni(II) product. Terephthalonitrile gives both eta(2)-nitrile and oxidative addition adducts, as well as dimetalated products. No C-C or C-N cleavage of the aromatic ring is seen with quinoline or acridine; only eta(2)-arene complexes are formed. The structures of many of these compounds are supported by X-ray data.     

Correlation between biological activity and energies of electronic transitions in benzodiazepines. Negative ion mass spectrometry and ultraviolet absorption spectroscopy study of some derivatives

A correlation between the energies of electronic singlet transitions in benzodiazepines and their biological activity, which was revealed earlier by means of negative ion mass spectrometry with resonance electron capture, has been verified with a UV absorption spectroscopy investigation. Also, it has been noted that the energies of electronic singlet transitions in benzodiazepines are close in value to the ionization energies of atoms Cs, Rb, K, Na, Li and Tl, the cations of which are known to play an important role in nerve cell excitation processes. Copyright 1999 John Wiley & Sons, Ltd.     

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.     

Purification and Characterization of Agarase from Marine Bacteria <Emphasis Type="Italic">Acinetobacter</Emphasis> sp. PS12B and Its Use for Preparing Bioactive Hydrolysate from Agarophyte Red Seaweed <Emphasis Type="Italic">Gracilaria verrucosa</Emphasis>

Acinetobacter strain PS12B was isolated from marine sediment and was found to be a good candidate to degrade agar and produce agarase enzyme. The extracellular agarase enzyme from strain PS12B was purified by ammonium sulfate precipitation followed by DEAE-cellulose ion-exchange chromatography. The specific activity of the crude enzyme which was 1.52 U increased to 45.76 U, after two-stage purification, with an enzyme yield of 9.76%. Purified enzyme had a molecular mass of 24 kDa. The optimum pH and temperature for activity of purified agarase were found to be 8.0 and 40 °C, respectively. The K_m and V_max values for agarase were 4.69 mg/ml and 0.5 μmol/min, respectively. Treatment with EDTA reduced the agarase activity by 58% at 5 mM concentration. The enzyme activity was stimulated by the presence of Fe²⁺, Mn²⁺, and Ca2⁺ ions while reducing reagents (β-mercaptoethanol and dithiothreitol, DTT) enhanced its activity by 30–40%. The purified agarase exhibited tolerance to both detergents and organic solvents. Major hydrolysis products of agar were DP4 and also a mixture of longer oligosaccharides DP6 and DP7. The enzyme hydrolysed seaweed (Gracilaria verrucosa) exhibited strong antioxidant activity in vitro. Successful hydrolysis of seaweed indicates the potential use of the enzyme to produce seaweed hydrolysate having health benefits as well as the industrial application like the production of biofuels.     

Platinum(II) Complexes with Constructive and Destructive Interaction of Diphosphane and Binaphthol Ligands

Eight molecules with different conformations are present in the unit cell of the Pt^II complex 1 , which contains a mismatched arrangement of the chiral ligands Chiraphos and Binol (i.e., (S,S)-Chiraphos prefers the δ conformation, whereas (R)-Binol tends to induce the λ conformation in the diphosphane). The observed flexibility of these bidentate ligands should not be disregarded in stereochemical models for explaining the selectivity in asymmetric catalysis.