Reactions of [NiIII(cyclam)] with aqueous sulfur dioxide: Exhibition of a deuterium isotope effect and catalysis by chloride and bromide

One unit of S(IV) (SO₂ or SHO₃^?) is oxidized per 2 units of [Ni^III(cyclam)] species to obtain sulfate. Kinetic analyses have been done by varying the acidities (0.013 ? [H⁺] ? 1.0 M) and halide concentrations (0.000 ? [X^?] ? 0.012 M; X=Cl and Br) at constant ionic strength (μ = 1.0 M). The rate law that incorporates the [X^?] and [H⁺] dependence is ?d[Ni^III]_T/dt=2k[Ni^III]_T[S(IV)]_T where 2k={k_a[H⁺] + k_bK + kK′_X[H⁺] [X^?] + kK′_XK[X^?]} {[H⁺] + K}^?1 {1 + K′_X[X^?]}^?1, here k_a=87 ± 7 M^?1 s^?1, k_b=(2.5 ± 0.5)×10³ M^?1 s^?1 and pK = 1.8 ± 0.2. Rate constants k_a and k_b are attributed to the reactions of [Ni^III(cyclam) (H₂O)₂]³⁺ with SO₂ and SHO₃^?, respectively. Monohalo species apparent equilibrium constants K′_Cl=(1600 ± 400) M^?1 and K′_Br=(190 ± 20) M^?1 and rate constants k=80 ± 8 M^?1 s^?1 and k = 140 ± 15 M^?1 s^?1 are ascribed to the protonated pathway, involving the [Ni^III(cyclam) (H₂O)X]²⁺ and SO_2(aq) reaction pairs. The other two rate constants of k=(5 ± 1)×10³ M^?1 s^?1 and k=(3.1 ± 0.5)×10⁴ M^?1 s^?1, refer to the deprotonated pathway and are assigned to the [Ni^III(cyclam) (H₂O)X]²⁺ /SHO₃^? redox couple. A deuterium H₂O / D₂O isotope effect of 2.1–2.8 can be attributed partially to an equilibrium isotope effect at low acidity though a small kinetic isotope (2.5 ± 0.5) effect is evident for the dihydrogen sulfito pathway, k_a. The kinetic isotope effect and the absence of sulfite radical scavenging effects are explained by a mechanism entailing migration of a hydride from sulfur to the Ni^III center to produce a Ni^III—H species, which rapidly comproportionates, and S(VI). © 1993 John Wiley & Sons, Inc.     

Comparative preparations of homoleptic hydridic anions of iron and ruthenium using solution-based organometal hydrogenation techniques

A study of the preparations of the complex hydridic anions [MH(6)](4)(-) (M = Fe and Ru) reveals a number of distinctive features. Here a soluble homoleptic ruthenium hydride has been prepared for the first time. For example, both FeX(2) and [Ru(eta(4)-1,5-COD)X(2)], X = Cl and Br, react with PhMgBr solutions under hydrogen to produce the title compounds. The benzene liberated in these reactions is more readily hydrogenated in the case of a homogeneous room temperature ruthenium hydride preparation to both cyclohexane and cyclohexene. The (1)H NMR spectroscopic data show that the two complex anions have hydride absorptions in the low-frequency region, delta -20.3 and -14.7, respectively. Further, (1)H spin-lattice relaxation times (T(1)) for M-H are longer in the case of Ru vs Fe.     

三价铬与丙二酸形成的配合物的热解过程研究

利用热重分析及原位红光谱等方法，定性，定量地研究了三价铬和丙二酸形成的配合物［Ｃｒ（Ｃ３Ｈ２Ｏ４）（Ｈ２Ｏ）４］［Ｃｒ（Ｃ３Ｏ４）２（Ｈ２Ｏ２）］．４Ｈ２Ｏ的热解过程，提出了室温至４００℃下的详细热解途径。基于多种实验结果，分析了螯合物中六员环的化学断裂方式，并由配合物的快原子轰击质谱（ＦＡＢ－ＭＳ）加以佐证。     

Electron paramagnetic resonance study of partially oriented clay platelets intercalated with copper(II) 1,4,8,11-tetraazacyclotetradecane

Electron paramagnetic resonance (EPR) spectra of powder and oriented films of montmorillonite, hectorite, and saponite intercalated with [Cu(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) exhibit three components: an orientation-dependent component without hyperfine features, an orientation-dependent component with hyperfine features, and an orientation-independent component without hyperfine feature. EPR spectra of [Cu(cyclam)](2+)-saponite, which exhibit only two components and the best resolved hyperfine features, were simulated. The spectra indicate that a large portion of the saponite platelets are inclined to the glass surface, although they tend to align with their basal planes parallel to the glass surface. The orientation-dependent spectra could be simulated by introducing a Gaussian distribution with a standard deviation of 20 degrees for the inclination angle. The standard deviation may be used as a disorder parameter for the microcrystals assembled on glass plates. Spectral simulation also shows that the CuN(4) plane of [Cu(cyclam)](2+) is parallel to the clay layers. EPR spectra of some other partially oriented systems are also discussed.     

Speciation of iron and manganese in dam water particles using electron spectroscopy for chemical analysis (ESCA)

The speciation of iron and manganese compounds retained by membrane filtration of dam water samples was studied by use of electron spectroscopy for chemical analysis (ESCA). Samples were taken at various depths and times of year from North Pine Dam near Brisbane, Australia. Both surface and bulk properties of samples representative of the water column profile were investigated. ESCA results showed that iron(III) compounds were found to predominate in the whole water column in any season of the year while the significance of iron(II) species varied in the hypolimnion (the bottom layer). In summer, although various ratios of manganese(II), manganese(III) and manganese(IV) compounds were found to occur down the water column, manganese(IV) compounds were predominant in the epilimnion (the top layer), while both manganese(II) and (IV) compounds predominated in the metalimnion (the middle layer) and the hypolimnion. The majority of Mn(IV) compounds were found throughout the water column after heavy rain and winter season. The ratios of atomic concentrations of iron and manganese as determined by atomic absorption spectrophotometry and ESCA are also discussed.     

Structures and Bioactivities of Steroidal Saponins Isolated from the Genera Dracaena and Sansevieria

The species Dracaena and Sansevieria, that are well-known for different uses in traditional medicines and as indoor ornamental plants with air purifying property, are rich sources of bioactive secondary metabolites. In fact, a wide variety of phytochemical constituents have been isolated so far from about seventeen species. This paper has reviewed the literature of about 180 steroidal saponins, isolated from Dracaena and Sansevieria species, as a basis for further studies. Saponins are among the most characteristic metabolites isolated from the two genera. They show a great variety in structural motifs and a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-proliferative effects and, in most case, remarkable cytotoxic properties.     

High-throughput manual parallel synthesis using SynPhase crowns and lanterns

The high-throughput manual solid-phase parallel synthesis of libraries comprising thousands of discrete samples using pellicular supports (i.e. SynPhase crowns and lanterns) and a suite of novel tools and techniques is described. Key aspects of this approach include the combination of a split-split-split synthesis strategy with spatial encoding to differentiate thousands of crowns, the rapid washing and filtration of up to 48 reaction vessels in parallel, the application of an inexpensive and environmentally friendly technique to remove trifluoroacetic acid from sixteen 96-well plates in parallel, and a high-throughput method for removing cleaved crowns from reusable pin racks. Tens of thousands of discrete samples have been produced in-house using this conceptually and operationally straightforward strategy.     

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