Propellanes. Part LXXX. Baeyer-Villiger Oxidation of [4.3.3]Propellane-8,11-dione

Oxidation of the title compound with m-chloroperbenzoic acid affords a keto-lactone, two bis-lactones and a bis-spirolactone, in varying amounts depending upon the reaction conditions. The structures were established by means of X-ray diffraction, ¹H- and ¹³C-NMR spectroscopy.     

The chemistry of polycyclic arene imines. II. Photochemistry of phenanthrene 9,10-imine and of its N-butyl derivative

The uv irradiation of phenanthrene 9, 10-imine has been shown to give 9H-tetrabenzo[a, c, g, i]carbazole as the major photo-product both in argon purged acetone and in dichloromethane. Phenanthrazine, N-9-phenanthrenyl-9-phenanthrenamine and phenanthrene were formed in smaller quantities. 9-Phenanthrenamine was found to be a minor by-product. N-Butylphenanthrene 9, 10-imine yielded under similar conditions phenanthrene and N-butyl-9-phenanthrenamine as the only isolable polycyclic compounds. In the presence of air the substituted imine gave mainly 2-propylphenanthro[9, 10-d]oxazole.     

Polyimides derived from cyclooctadiene dianhydrides

1,5-Cyclooctadiene-1,2,5,6-tetracarboxylic dianhydride reacts with diamines in m-cresol at 110°C to give high molecular weight polymides soluble in m-cresol and tetrachloroethane. Films can be cast from solution and fibers drawn by dry and wet spinning. These polyimides showed rather low thermal stability, but high hydrolytic stability and good mechanical properties. The polyamic acid intermediates cannot be isolated due to spontaneous cyclization even at room temperature. This is discussed in terms of the strain in the cyclooctadiene ring.     

An analysis of the vanishing interfacial tension technique for determination of minimum miscibility pressure

Observations of interfacial tensions for mixtures of a gas and oil have been proposed as a way to measure the minimum miscibility pressure for displacement of a multicomponent oil by a gas mixture in a porous medium. The experimental approach known as the “vanishing interfacial tension technique” (VIT) is to measure interfacial tensions for a gas–oil mixture at a sequence of pressures. The estimate of the minimum miscibility pressure (MMP) is taken to be the pressure at which the interfacial tension extrapolates to zero when plotted against pressure. In this paper, the behavior observed in the VIT experiment is analyzed by performing phase equilibrium calculations with an equation of state and calculations of interfacial tensions using a parachor approach. The analysis shows that the VIT estimate of the MMP depends strongly on the overall composition of the gas–oil mixture used in the VIT experiment. Comparison of the estimates obtained for systems with three and four components and for a multicomponent crude oil system with MMPs calculated from solutions of the differential equations that describe the interactions of flow and phase equilibria indicates that the VIT approach can give estimates of the MMP that differ substantially from the MMP that would be observed in a displacement experiment. For some choices of the composition of the fluid mixture in the cell and the compositions of the oil and gas, however, it can also give estimates that are reasonably close to the value that would be obtained in a slim tube displacement experiment. However, the overall composition that gives the smallest error in the MMP estimate and the magnitude of the error cannot be determined from the VIT experiment alone. The uncertainty in the VIT estimate of the MMP arises from a fundamental limitation of the experiment: it investigates mixture compositions that are linear combinations of the initial oil and injection gas that are quite different from the critical mixture that forms at the MMP in a gas–oil displacement in a porous medium. The results indicate that the VIT approach to determine the MMP for multicomponent gas–oil displacements should be used with caution given the potential for significant errors in the resulting estimate of the MMP.     

A queueing network with a single cyclically roving server

A queueingnetwork that is served by asingle server in a cyclic order is analyzed in this paper. Customers arrive at the queues from outside the network according to independent Poisson processes. Upon completion of his service, a customer mayleave the network, berouted to another queue in the network orrejoin the same queue for another portion of service. The single server moves through the different queues of the network in a cyclic manner. Whenever the server arrives at a queue (polls the queue), he serves the waiting customers in that queue according to some service discipline. Both the gated and the exhaustive disciplines are considered. When moving from one queue to the next queue, the server incurs a switch-over period. This queueing network model has many applications in communication, computer, robotics and manufacturing systems. Examples include token rings, single-processor multi-task systems and others. For this model, we derive the generating function and the expected number of customers present in the network queues at arbitrary epochs, and compute the expected values of the delays observed by the customers. In addition, we derive the expected delay of customers that follow a specific route in the network, and we introduce pseudo-conservation laws for this network of queues.Summary of notation B_i, B _i ^* (s) service time of a customer at queue i and its LST - b_i, b_i ⁽²⁾ mean and second moment of B_i - R_i, R _i ^* (s) duration of switch-over period from queue i and its LST - r_i, r_i mean and second moment of R_i - r, r⁽²⁾ mean and second moment of _i ^N =₁R_i - _i external arrival rate of type-i customers - _i total arrival rate into queue i - _i utilization of queue i; _i=_i - system utilization _i ^N =_1i - c=E[C] the expected cycle length - X _i ^j number of customers in queue j when queue i is polled - X_i=X _i ⁱ number of customers residing in queue i when it is polled - f_i(j) - X _i ^* number of customers residing in queue i at an arbitrary moment - Y_i the duration of a service period of queue i - W_i,T_i the waiting time and sojourn time of an arbitary customer at queue i - F^*(z₁, z₂,..., z_N) GF of number of customers present at the queues at arbitrary moments - F_i(z₁, z₂,..., z_N) GF of number of customers present at the queues at polling instants of queue i - ¯F_i(z₁, z₂,...,z_N) GF of number of customers present at the queues at switching instants of queue i - V_i(z₁, z₂,..., z_N) GF of number of customers present at the queues at service initiation instants at queue i - ¯V_i(z₁,z₂,...,z_N) GF of number of customers present at the queues at service completion instants at queue i The work of this author was supported by the Bernstein Fund for the Promotion of Research and by the Fund for the Promotion of Research at the Technion.Part of this work was done while H. Levy was with AT&T Bell Laboratories.     

Control of redox transitions and oxygen species binding in Mn centers by biologically significant ligands; model studies with [Mn]-bacteriochlorophyll a

Mn-superoxide dismutase (Mn-SOD), which protects the cell from the toxic potential of superoxide radicals (O(2)(-*)), is the only type of SOD which resides in eukaryotic mitochondria. Up-to-date, the exact catalytic mechanism of the enzyme and the relationship between substrate moieties and the ligands within the active site microenvironment are still not resolved. Here, we set out to explore the possible involvement of hydroperoxyl radicals ((*)OOH) in the catalytic dismutaion by following the interplay of Mn(III)/Mn(II) redox transitions, ligands binding, and evolution or consumption of superoxide radical, using a new model system. The model system encompassed an Mn atom chelated by a bacteriochlorophyll allomer macrocycle (BChl) in aerated aprotic media that contain residual water. The redox states of the Mn ion were monitored by the Q(y) electronic transitions at 774 and 825 nm for [Mn(II)]- and [Mn(III)]-BChl, respectively (Geskes, C.; Hartwich, G.; Scheer, H.; Mantele, W.; Heinze, J. J. Am. Chem. Soc. 1995, 117, 7776) and confirmed by electron spin resonance spectroscopy. Evolution of (*)OOH radicals was monitored by the ESR spin-trap technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The experimental data suggest that the [Mn]-BChl forms a (HO(-))[Mn(III)]-BChl(OOH) complex upon solvation. Spectrophotometeric titrations with tetrabutylamonnium acetate (TBAA) and 1-methylimidazole (1-MeIm) together with ESI-MS measurements indicated the formation of a 1:1 complex with [Mn]-BChl for both ligands. The coordination of ligands at low concentrations to [Mn(III)]-BChl induced a release of a (*)OOH radical and a [Mn(III)]-BChl --> [Mn(II)]-BChl transition at higher concentrations. The estimated equilibrium constants for the total redox reaction ( )()are 1.9 x 10(4) +/- 1 x 10(3) M(-)(1) and 12.3 +/- 0.6 M(-)(1) for TBAA and 1-MeIm, respectively. The profound difference between the equilibrium constants agrees with the suggested key role of the ligand's basicity in the process. A direct interaction of superoxide radicals with [Mn(III)]-BChl in a KO(2) acetonitrile (AN) solution also resulted in [Mn(III)]-BChl --> [Mn(II)]-BChl transition. Cumulatively, our data show that the Mn(III) center encourages the protonation of the O(2)(-)(*) radical in an aprotic environment containing residual water molecules, while promoting its oxidation in the presence of basic ligands. Similar coordination and stabilization of the (*)OOH radical by the Mn center may be key steps in the enzymatic dismutation of superoxide radicals by Mn-SOD.     

Formation of hypervalent complexes of PhCCSiF3 with pyridine through intermolecular silicon...nitrogen interaction

We report here the synthesis of trifluoro-phenylethynyl-silane (1) that forms with pyridine (Py), through intermolecular Si...N interaction, the pentacoordinate 1.Py complex and at low temperatures also the hexacoordinate 1.Py2 complex. 1H, 19F, 29Si, and 15N NMR spectra, as well as the first report for an intermolecular 29Si...15N one-bond spin-spin coupling, are presented for the two complexes. Quantum mechanical ab initio calculations (MP2/6-31G*) suggest a distorted trigonal bipyramid structure for the 1.Py complex and a nearly ideal octahedral structure for the 1.Py2 complex. The hypervalent complexes of 1 with Py described here imply a possible application of such Si...N intermolecular interactions in supramolecular chemistry.     

Investigation of micelle formation by fluorescence correlation spectroscopy

We show that noncovalently bound dye molecules can be used as labels in single-molecule fluorescence experiments for the determination of aggregate formation in standard surfactant systems. Aqueous solutions of sulfosuccinic acid bis(2-ethylhexyl) ester sodium salt, hexadecyltrimethylammonium chloride, and pentaethylene glycol monododecyl ether have been studied by fluorescence correlation spectroscopy using commercially available dyes. The translational diffusion coefficient and the critical micelle concentrations have been determined and compare well to values reported in the literature. The respective charges of the surfactant and of the dye molecule are crucial for the effectiveness of the presented method.