Sulphur substituted organotin compounds : VII. Charge transfer interactions of arylthiomethyl(triphenyl)tin compounds with tetracyanoethylene

Thermolysis of η²-benzoyl(phenyl)zirconocene yields the η²-benzophenonzirconocene complex 2, isolated as a dimer. 2 exhibits an ambivalent reactivity pattern. The formation of five-membered metallacycles from 2 and olefinic hydrocarbons possibly proceeds analogous to reactions of “normal” metalolefin π-complexes. However, both reactions with the electron-deficient olefins dimethylfumarate and -maleate and the behavior towards electrophilic and protic reagents as well as aromatic hydrocarbons might be interpreted in terms of a metallaoxirane-character of 2.     

Quantitative analysis of perchlorate in extracts of whole fish homogenates by ion chromatography: comparison of suppressed conductivity detection and electrospray ionization mass spectrometry

The perchlorate anion (ClO ₄ ^– ) is an anthropogenic contaminant of increasing concern in water supplies, and has been shown to disrupt thyroid activity. Most perchlorate analyses are currently carried out by ion chromatography (IC) with suppressed conductivity detection (SCD). While this procedure has been demonstrated to provide acceptable performance for analysis of water samples, the determination of perchlorate in high-conductivity aqueous extracts of plant or animal material is not readily accomplished by IC-SCD unless lengthy cleanup protocols are applied. With the addition of electrospray ionization mass spectrometry (ESI-MS) to IC, it was hypothesized that the interference imposed by various ionic species could be significantly reduced without the need for purification; however, the analysis of perchlorate in relatively unpurified extracts of biologically derived homogenates by IC-ESI-MS has not previously been described in the literature. The research presented here represents a comparison of the capabilities of IC-SCD and IC-ESI-MS to detect perchlorate in reagent water and in crude extracts of perchlorate-exposed fish (threespine stickleback, Gasterosteus aculeatus). ESI-MS was found to compare favorably to SCD for the detection of perchlorate in deionized water, and to exceed SCD performance in perchlorate analysis of fish-derived extracts.     

Electrode processes in the oxidation of tetrahydroisoquinoline derivatives

The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has E_p=0.55 V vs. Ag/Ag⁺. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated.     

Reissert compound studies. Cyclization of N-(ω-chloroalkanoyl)reissert compounds

Treatment of 2-(4-chlorobutanoyl)- and 2-(5-chloropentanoyl)-1, 2-dihydroisoquinaldonitrile with sodium hydride gave rise to tricyclic benzoquinolizone and azepino[1,2-α]isoquinoline derivatives. A similar reaction was observed in the quinoline series. Several reactions of 1,2,3,4-tetrahydro-4-oxo-11bH-benzo[α]quinolizine-11b-carbonitrile are reported.     

Crystal structure and spectroscopic characterization of K8(VO)2O(SO4)6

Red and yellow dichroistic crystals of a vanadium(V) compound, potassium (mu-oxo, di-mu-sulfato)bis(oxodisulfatovanadate), K(8)(VO)(2)O(SO(4))(6), have been obtained from the ternary catalytic model melt system K(2)S(2)O(7)[bond]K(2)SO(4)[bond]V(2)O(5). By slow cooling of the melt from 420 to 355 degrees C, crystal growth occurred, using solid V(2)O(5) crystals present in the melt as nucleation promoter. The compound crystallizes in the monoclinic space group P2(l) with a = 13.60(9) A, b = 13.93(9) A, c = 14.05(9) A, beta = 90.286(10) degrees, and Z = 2. It contains two VO(6) octahedra linked together by a mu-oxo and two mu-sulfato bridges. Furthermore, each octahedron has two monodentate sulfate ligands, making the dimeric entity coordinatively saturated. IR spectroscopy shows bands arising from V[bond]O[bond]V and V[double bond]O stretches as well as splitting of sulfate bands due to the different degrees of freedom present for different conformations of sulfate ligands. The coordination of vanadium in K(8)(VO)(2)O(SO(4))(6) is discussed in relation to the reaction mechanism of SO(2) oxidation catalysis.     

Computerized, comprehensive databases of cellular and secreted proteins from normal human embryonic lung MRC-5 fibroblasts: identification of transformation and/or proliferation sensitive proteins

Databases of protein information from human embryonal lung fibroblasts (MRC-5) have been established using computer analyzed two-dimensional gel electrophoresis. One thousand four hundred and eighty-two cellular proteins (1060 with isoelectric focusing and 422 with nonequilibrium pH gradient electrophoresis, in the first dimension) ranging in molecular mass between 8 and 234 kDa were separated and numbered. Information entered in the database (in most cases for major proteins) includes: protein name, HeLa protein catalog number, mouse protein catalog number, proteins matched in transformed human epithelial amnion cells (AMA) and peripheral blood mononuclear cells (PBMC), transformation and/or proliferation sensitive proteins, synthesis in quiescent cells, cell cycle regulated proteins, mitochondrial and heat shock proteins, cytoskeletal proteins and proteins whose synthesis is affected by interferons. Additional information entered for a few transformation-sensitive proteins that have been selected for future studies includes levels of synthesis and amounts in fetal human tissues. A total of four hundred and seventy-six [35S]methionine labeled polypeptides (258 isoelectric focusing; 218, nonequilibrium pH gradient electrophoresis) secreted by MRC-5 fibroblasts were separated and recorded (J. E. Celis et al., Leukemia 1987, 1, 707-717). Information entered in this database includes molecular weight and transformation sensitive proteins. These databases, as well as those of epithelial and lymphoid cell proteins (J. E. Celis et al., Leukemia 1988, 9, 561-601), represent the initial stages of a systematic effort to establish comprehensive databases of human protein information. In the long run, these databases are expected to offer a useful framework in which to focus the human genome sequencing effort.     

Reactions of Ru3(CO)12 with Diphosphenes — A New Route to 50‐Electron Ru3P2 nido‐Clusters

The reaction of the symmetric diphosphene 2, 4, 6‐(CF₃)₃‐C₆H₂‐P=P‐C₆H₂‐2, 4, 6‐(CF₃)₃ 4 with Ru₃(CO)₁₂ led to the 50‐electron Ru₃P₂ nido‐cluster Ru₃(CO)₉[μ‐P‐C₆H₂‐2, 4, 6‐(CF₃)₃]₂ 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru₃P₂ centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C₆H₂(CF₃)₃ groups is also appreciably distorted. Temperature‐dependent ¹⁹F NMR studies of the [A₃M₃X]₂ spin system (A = M = CF₃, X = ³¹P) of 5 indicated a rotational barrier ΔG^≠ of 82.3 kJ mol^‐1 at 141 °C. The same Ru₃P₂ core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru₃(CO)₁₂; hindered rotation about the C(aryl)—P bonds was also observed, in this case.     

Ion excitation in a linear quadrupole ion trap with an added octopole field

Modeling of ion motion and experimental investigations of ion excitation in a linear quadrupole trap with a 4% added octopole field are described. The results are compared with those obtained with a conventional round rod set. Motion in the effective potential of the rod set can explain many of the observed phenomena. The frequencies of ion oscillation in the x and y directions shift with amplitude in opposite directions as the amplitudes of oscillation increase. Excitation profiles for ion fragmentation become asymmetric and in some cases show bistable behavior where the amplitude of oscillation suddenly jumps between high and low values with very small changes in excitation frequency. Experiments show these effects. Ions are injected into a linear trap, stored, isolated, excited for MS/MS, and then mass analyzed in a time-of-flight mass analyzer. Frequency shifts between the x and y motions are observed, and in some cases asymmetric excitation profiles and bistable behavior are observed. Higher MS/MS efficiencies are expected when an octopole field is added. MS/MS efficiencies (N(2) collision gas) have been measured for a conventional quadrupole rod set and a linear ion trap with a 4% added octopole field. Efficiencies are chemical compound dependent, but when an octopole field is added, efficiencies can be substantially higher than with a conventional rod set, particularly at pressures of 1.4 x 10(-4) torr or less.     

Simulation of 59Co NMR chemical shifts in aqueous solution

59Co chemical shifts were computed at the GIAO-B3LYP level for [Co(CN)6]3-, [Co(H2O)6]3+, [Co(NH3)6]3+, and [Co(CO)4]- in water. The aqueous solutions were modeled by Car-Parrinello molecular dynamics (CPMD) simulations, or by propagation on a hybrid quantum-mechanical/molecular-mechanical Born-Oppenheimer surface (QM/MM-BOMD). Mean absolute deviations from experiment obtained with these methods are on the order of 400 and 600 ppm, respectively, over a total delta(59Co) range of about 18,000 ppm. The effect of the solvent on delta(59Co) is mostly indirect, resulting primarily from substantial metal-ligand bond contractions on going from the gas phase to the bulk. The simulated solvent effects on geometries and delta(59Co) values are well reproduced by using a polarizable continuum model (PCM), based on optimization and perturbational evaluation of quantum-mechanical zero-point corrections.     

Acrylonitrile polymerization by Cy3PCuMe and (Bipy)2FeEt2

Cy(3)PCuMe (1) undergoes reversible ligand redistribution at low temperature in solution to form the tight ion pair [Cu(PCy(3))(2)][CuMe(2)] (3). The structure of 3 was assigned on the basis of (i) the stoichiometry of the 1 = 3 equilibrium, (ii) the observation of a triplet for the PCy(3) C1 (13)C NMR resonance due to virtual coupling to two (31)P nuclei, and (iii) reverse synthesis of 1 by combining separately generated Cu(PCy(3))(2)(+) and CuMe(2)(-) ions. Complex 1 and [Cu(PCy(3))(2)][PF(6)] (5) coordinate additional PCy(3) to form (Cy(3)P)(2)CuMe and [Cu(PCy(3))(3)][PF(6)], respectively, while 3 does not. Complex 1, free PCy(3), and (bipy)(2)FeEt(2) (2) each initiate the polymerization of acrylonitrile. In each case, the polyacrylonitrile contains branches that are characteristic of an anionic polymerization mechanism. The major initiator in acrylonitrile polymerization by 1 is PCy(3), which is liberated from 1. A transient iron hydride complex is proposed to initiate acrylonitrile polymerization by 2.