The redox properties of organotransition-metal complexes IV. The activation of cyclic polyolefiniron tricarbonyl derivatives by one-electron oxidation

Cyclic polyolefiniron tricarbonyl derivatives [Fe(CO)₂L(C_nH_m)] (L = CO or phosphorus donor) and oxidising agents such as Ag⁺ or [NO]⁺ in CH₂Cl₂ give reactive paramagnetic cations [Fe(CO)₂L(C_nH_m]⁺ which can abstract hydrogen from the solvent to give [Fe(CO)₂L(C_nH_{m + 1})]⁺.     

Reversible sequence of intramolecular associative and dissociative electron-transfer reactions in hydrotris(pyrazolylborate) complexes of rhodium

The one-electron chemically reversible oxidation of four neutral [RhLL'(kappa(2)-Tp(Me2))]complexes [Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate], which leads to kappa(3)-Tp(Me2) bonding in the corresponding monocations, has been studied by cyclic voltammetry (CV) and other electrochemical methods. The CV behavior of [Rh(CO)[P(OPh)(3)]Tp(Me2)] (1) and [Rh(CO)(PPh(3))Tp(Me2)] (2) is quasi-nernstian at slow CV scan rates, with heterogeneous charge-transfer rates, k(s), of 0.025 cm s(-1) and 0.015 cm s(-1) (at 273 K), respectively. By contrast, [Rh(CO)(PCy(3))Tp(Me2)] (3, Cy = cyclohexyl) and [Rh(PPh(3))(2)Tp(Me2)] (4) display electrochemically irreversible CV curves that arise from rate-limiting slow electron-transfer reactions. Both the oxidation of 3 (or 4) and the rereduction of 3(+) (or 4(+)) have two-step (EC-type) mechanisms in which the electron transfer (e.t.) process is followed by a separate structural change, leading to an overall square scheme with irreversible charge-transfer kinetics. Homogeneous redox catalysis was used to determine the E(1/2) value of the oxidation of 3 to an intermediate 3C(+) which is postulated to have a pseudo-square pyramidal structure. Digital simulations gave k(s) = 9 x 10(-3) cm s(-1) for the heterogeneous charge-transfer rate of 3/3C(+). The close-to-nernstian CV behavior of 1 is ascribed to the fact that, unlike the sterically constrained derivatives 3 and 4, the third pyrazolyl ring in 1 is already in a configuration which favors formation of the Rh-N(2) bond in 1(+). The overall redox mechanism for this series of compounds involves an associative oxidative e.t. reaction followed by a dissociative reductive e.t. process.     

The electrochemistry of organotransition-metal complexes : II. Formation and reactivity of the radical cations [trans-Fe(CO3(PR3)2]+ and [Fe(CO)3 (Ph2 PCH2 CH2 PPh2)]+

[Fe(CO)₃ L₂] (L = PPh₃, PPh₂Me, P(OPh)₃ or P(NMe₂)₃; L₂ = Ph₂ PCH₂ CH₂ PPh₂⁺) undergo reversible one-electron oxidations to give the radical cations [Fe(CO)₃L₂]⁺ which have been studied by IR and ESR spectroscopy.     

On the weighted Kneser-Poulsen conjecture

Suppose that p = (p1, p2, …, pN) and q = (q1, q2, …, qN) are two configurations in , which are centers of balls B ^d (p _i , r _i ) and B ^d (q _i , r _i ) of radius r _i , for i = 1, …, N. In [9] it was conjectured that if the pairwise distances between ball centers p are contracted in going to the centers q, then the volume of the union of the balls does not increase. For d = 2 this was proved in [1], and for the case when the centers are contracted continuously for all d in [2]. One extension of the Kneser-Poulsen conjecture, suggested in [6], was to consider various Boolean expressions in the unions and intersections of the balls, called flowers, where appropriate pairs of centers are only permitted to increase, and others are only permitted to decrease. Again under these distance constraints, the volume of the flower was conjectured to change in a monotone way. Here we show that these generalized Kneser-Poulsen flower conjectures are equivalent to an inequality between certain integrals of functions (called flower weight functions) over , where the functions in question are constructed from maximum and minimum operations applied to functions each being radially symmetric monotone decreasing and integrable. Research supported in part by NSF Grant No. DMS-0209595.     

Dihedral ‘star’ tensegrity structures

This paper presents conditions for self-equilibrium and super stability of dihedral ‘star’ tensegrity structures, based on their dihedral symmetry. It is demonstrated that the structures are super stable if and only if they have an odd number of struts, and the struts are as close as possible to each other. Numerical investigations show that their prestress stability is sensitive to the geometry realisation.     

Velocity-defect scaling for turbulent boundary layers with a range of relative roughness

Velocity profile measurements in zero pressure gradient, turbulent boundary layer flow were made on a smooth wall and on two types of rough walls with a wide range of roughness heights. The ratio of the boundary layer thickness (δ) to the roughness height (k) was 16≤δ/k≤110 in the present study, while the ratio of δ to the equivalent sand roughness height (k _s) ranged from 6≤δ/k _s≤91. The results show that the mean velocity profiles for all the test surfaces agree within experimental uncertainty in velocity-defect form in the overlap and outer layer when normalized by the friction velocity obtained using two different methods. The velocity-defect profiles also agree when normalized with the velocity scale proposed by Zagarola and Smits (J Fluid Mech 373:33–70, 1998). The results provide evidence that roughness effects on the mean flow are confined to the inner layer, and outer layer similarity of the mean velocity profile applies even for relatively large roughness.     

Distributed-memory parallel computation of a forced,time-dependent,sooting, ethylene/air coflow diffusion flame

Forced, time-varying laminar flames help bridge the gap between laminar and turbulent combustion as they reside in an ever-changing flow environment. A distributed-memory parallel computation of a time-dependent sooting ethylene/air coflow diffusion flame, in which a periodic fluctuation (20 Hz) is imposed on the fuel velocity for four different amplitudes of modulation, is presented. The chemical mechanism involves 66 species, and a soot sectional model is employed with 20 soot sections. The governing equations are discretised using finite differences and solved implicitly using a damped modified Newton's method. The solution proceeds in parallel using strip domain decomposition over 40 central processing units (CPUs) until full periodicity is attained. For forcing amplitudes of 30%, 50%, 70% and 90%, a complete cycle of numerical predictions of the time-resolved soot volume fraction is presented. The 50%, 70% and 90% forcing cases display stretching and pinching off of the sooting region into an isolated oval shape. In the 90% forcing case, a well-defined hollow shell-like structure of the soot volume fraction contours occurs, in which the interior of the isolated sooty region has significantly lower soot concentrations than the shell. Preliminary comparisons are made with experimental measurements of the soot volume fraction for the 50% forcing case. The experimental results are qualitatively consistent with the model predictions.     

Wideband steady-state numerical model of a tensile-strained bulk semiconductor optical amplifier

A wideband steady-state numerical model of a tensile-strained bulk InGaAsP semiconductor optical amplifier (SOA) is presented. The model is based on a set of travelling wave equations that govern the propagation of the amplified signal and spontaneous emission photon rates and a carrier density rate equation. The model is applicable over a wide range of operating regimes and can be used to determine the effects of varying the amplifier geometric and material parameters. Simulations and comparisons with experiment are given which demonstrate the versatility of the model.     

Iodination of triazenide-bridged rhodium and iridium complexes: oxidative addition vs. one-electron oxidation

The triazenide-bridged tetracarbonyls [(OC)(2)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo oxidative addition of iodine across the dimetal centre, giving the [RhM](4+) complexes [I(OC)(2)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)I], structurally characterised for M = Ir. The anionic tricarbonyl iodide [I(OC)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)Rh(CO)(2)](-) forms [I(2)(OC)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)Rh(CO)I](-) by initial one-electron transfer whereas the analogous tricarbonyl phosphine complexes [(OC)(Ph(3)P)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo bridge cleavage, giving mononuclear [Rh(p-MeC(6)H(4)NNNC(6)H(4)Me-p)I(2)(CO)(PPh(3))] and dimeric [I(OC){RNNN(R)C(O)}M(mu-I)(2)M{C(O)N(R)NNR}(CO)I] (M = Rh or Ir, R = C(6)H(4)Me-p) in which CO has been inserted into a metal-nitrogen bond.     

Human pathogenic Cryptosporidium species bioanalytical detection method with single oocyst detection capability

A bioanalytical detection method for specific detection of viable human pathogenic Cryptosporidium species, C. parvum, C. hominis, and C. meleagridis is described. Oocysts were isolated from water samples via immunomagnetic separation, and mRNA was extracted with oligo-dT magnetic beads, amplified using nucleic acid sequence-based amplification (NASBA), and then detected in a nucleic acid hybridization lateral flow assay. The amplified target sequence employed was hsp70 mRNA, production of which is stimulated via a brief heat shock. The described method was capable of detecting one oocyst in 10 μL using flow-cytometer-counted samples. Only viable oocysts were detected, as confirmed using 4′,6-diamidino-2-phenylindole and propidium iodide (DAPI/PI) staining. The detection system was challenged by detecting oocysts in the presence of large numbers of common waterborne microorganisms and packed pellet material filtered from environmental water samples. When the method was compared with EPA Method 1622 for C. parvum detection, highly comparable results were obtained. Since the described detection system yields unambiguous results within 4.5 h, it is an ideal method for monitoring the safety of drinking water.