Protic ionic liquids as recyclable solvents for the acid catalysed synthesis of diphenylmethyl thioethers

The acid catalysed formation of diphenylmethyl (DPM) thioethers was successfully achieved using the protic ionic liquid (pIL) triethylamine:methanesulfonic acid (TeaMs) as the reaction solvent under microwave irradiation. A slight excess of methanesulfonic acid (10% v/v) was required to facilitate the reaction, which was applied to a variety of thiols. Aliphatic, aromatic and heterocyclic aromatic thiols were converted to their corresponding DPM thioethers in high yields (63–99%), in short reaction times (5–20 min) and using mild temperatures (80–100 °C). Finally, the pIL (TeaMS) was recycled five times without loss of yield.     

Conversion of fatty aldehydes to alka(e)nes and formate by a cyanobacterial aldehyde decarbonylase: cryptic redox by an unusual dimetal oxygenase

Cyanobacterial aldehyde decarbonylase (AD) catalyzes conversion of fatty aldehydes (R-CHO) to alka(e)nes (R-H) and formate. Curiously, although this reaction appears to be redox-neutral and formally hydrolytic, AD has a ferritin-like protein architecture and a carboxylate-bridged dimetal cofactor that are both structurally similar to those found in di-iron oxidases and oxygenases. In addition, the in vitro activity of the AD from Nostoc punctiforme (Np) was shown to require a reducing system similar to the systems employed by these O(2)-utilizing di-iron enzymes. Here, we resolve this conundrum by showing that aldehyde cleavage by the Np AD also requires dioxygen and results in incorporation of (18)O from (18)O(2) into the formate product. AD thus oxygenates, without oxidizing, its substrate. We posit that (i) O(2) adds to the reduced cofactor to generate a metal-bound peroxide nucleophile that attacks the substrate carbonyl and initiates a radical scission of the C1-C2 bond, and (ii) the reducing system delivers two electrons during aldehyde cleavage, ensuring a redox-neutral outcome, and two additional electrons to return an oxidized form of the cofactor back to the reduced, O(2)-reactive form.     

Inner–outer interactions in rough-wall turbulence

Here we revisit the inner–outer interaction model (IOIM) of Marusic et al. (Science, vol. 329, 2010, pp. 193–196) that enables the prediction of statistics of the fluctuating streamwise velocity in the inner region of wall-bounded turbulent flows from a large-scale velocity signature measured in the outer region of the flow. The model is characterised by two empirically observed inner–outer interactions: superposition of energy from outer region large-scale motions; and amplitude modulation by these large-scale motions of a small-scale ‘universal’ signal (u^*), which in smooth-wall flows is Reynolds number invariant. In the present study, the inner–outer interactions in rough-wall turbulent boundary layers are examined within the framework of the IOIM. Simultaneous two-point hot-wire anemometry measurements enable quantification, via the model parameters, of the strengths of superposition and amplitude modulation effects in a rough-wall flow, and these are compared to a smooth-wall flow. It is shown that the present rough-wall significantly reduces the effects of superposition, while increasing the amplitude modulation effect. The former is true even in flows that exhibit outer region similarity. Using the model parameters obtained from the two-point measurements, predictions of inner region streamwise velocity statistics and spectra are compared to measurements over a range of friction and roughness Reynolds numbers. These results indicate that the u^* signal does depend on roughness Reynolds number (k⁺_s), but is robust to changes in friction Reynolds number (δ⁺). Additionally, the superposition strength is shown to be relatively independent of both roughness and friction Reynolds number. The implications of the present results on the suitability of the IOIM as a predictive tool in rough-wall turbulence are discussed.     

A unified theory of turbulent flow

Summary A general theory of turbulent flow is applied to incompressible flow in a circular pipe. The theoretical mean velocity distribution is found to be in good agreement with experiment, but there is some discrepancy in the normal stress distribution. The available pressure drop data are used to estimate the value of the apparent wall velocity as a function of Reynolds number and roughness. It is found that the results can be represented by simple expressions which in turn imply simple expressions for the pressure drop as a function of Reynolds number and roughness. However, it has not been possible to derive these results from fundamental considerations. The basis of Reynolds analogy and the application of the theory to channel flow are also discussed.     

Synthesis of block copolymers by sequential carbenium ion polymerization

The sequential carbenium ion block copolymerization of ethyl vinyl ether (EVE) and isobutyl vinyl ether (IBVE) with N-vinylcarbazole (NVC) is described. Requisite conditions for the successful application of the sequential synthesis technique to these systems were established: (1) the use of stable carbocation initiator salts (e.g., Ph₃CSbCl₆) which lead to essentially terminationless polymerizations; (2) low solvent-to-monomer ratios in order to suppress any possible chain transfer to methylene dichloride molecules; (3) high ratios of initiator to monomer which create a pseudo-“living” system. The block products (PEVE-b-PNVC and PIBVE-b-PNVC) were isolated by precipitation and extraction. The intrinsic viscosities of these products displayed minima at 30°C.     

Mechanistic investigations of lipoic acid biosynthesis in Escherichia coli: both sulfur atoms in lipoic acid are contributed by the same lipoyl synthase polypeptide

Lipoyl synthase catalyzes the final step in the de novo biosynthesis of the lipoyl cofactor, which is the insertion of two sulfur atoms into an octanoyl chain that is bound in an amide linkage to a conserved lysine on a lipoyl-accepting protein. We show herein that the sulfur atoms in the lipoyl cofactor are derived from lipoyl synthase itself, and that each lipoyl synthase polypeptide contributes both of the sulfur atoms to the intact cofactor.     

Bestimmung von Schwefel in organischen Verbindungen

Ohne Zusammenfassung     

Calculation of hydrodynamic parameters of random coil polymers from size exclusion chromatography and comparison with parameters by conventional methods

A new method of treating data from size exclusion chromatography, originally evaluated for native proteins, has been extended to random coil polymers using data from dextran and polyethylene glycol as specific examples. Columns are calibrated with globular proteins of known molecular weight. Multiplication by a constant transforms the abscissa to molecular radii. The constants in the equation r = gM^Z are then evaluated directly from the size exclusion chromatographic data and compared with the corresponding constants obtained from viscometry, sedimentation velocity and light scattering, relating Stokes radius, root mean square end-to-end distance and radius of gyration to molecular weight.