Determination of trace amounts of iron by catalytic-adsorptive stripping voltammetry

A highly sensitive and selective voltammetric procedure is described for the determination of trace amounts of iron. The procedure is based on the adsorptive collection of an iron-thiocyanate-nitric oxide complex on a hanging mercury drop electrode. The adsorbed complex catalyzes the reduction of nitrite in solution, which gives a detection limit of 40 ppt iron (30 s accumulation). The stripping current increases linearly with iron concentration up to 80 ppb. The relative standard deviations are 4.2% and 1.6% at 0.5 ppb and 40 ppb respectively. Most of the common ions, except cobalt, do not interfere with the determination of iron. The procedure is applied to determine iron in biological samples, natural waters and analytical-grade chemicals.     

Adsorptive stripping voltammetric determination of traces of molybdenum in natural water in the presence ofα-benzoinoxime

The electrochemical behavior of the molybdenum complex of -benzoinoxime was investigated using cyclic voltammetry and linear scan voltammetry, after adsorptive accumulation of the complex onto a hanging mercury drop electrode (HMDE). The signal corresponds to the reduction of molybdenum in the complex adsorbed at the HMDE surface. Under optimal conditions, the adsorptive stripping voltammetric procedure gave an extremely low detection limit of 0.1 nM (9.6ng/l) Mo(VI) following stirred accumulation for 5 min at 0.0 V (vs. Ag/AgCl). The reduction cur rent-[Mo(VI)] relationships were linear up to 25 and 100 nM. Repetitive determinations of 10 nM solutions gave relative standard deviations of 2.2 and 3.5%, for 1 and 5-min accumulation periods, respectively. Most of the ions investigated did not interfere with the determination of molybdenum, except for tungsten. Excellent selectivity against copper was observed. The proposed procedure was applied to the direct determination of molybdenum in natural water.     

Effect of intra- and extra-liposomal distribution of sodium chloride on the stability of large unilamellar vesicles

Three groups of 1,2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) large unilamellar vesicle (LUV) dispersions were studied: LUV (A) dispersions with only extraliposomal sodium chloride (NaCl), LUV (B) dispersions with intra- and extraliposomal NaCl, and LUV (C) dispersions with only intraliposomal NaCl. The NaCl concentrations ranged from 0 to 150 mM. An abrupt increase in leakage was observed around -10 degree C for all the three groups of LUV, which coincided with the temperature of extraliposomal ice formation. Within the three groups, leakage of LUV (C) was significantly higher than the other groups. Extraliposomal ice formation and the resulting freeze-concentration of LUV may be the major cause of the leakage. Intraliposomal ice formation observed at -43 degree C seemed to stop leakage of LUV when LUV were frozen below -43 degree C. An exotherm of eutectic crystallization of NaCl was occasionally observed at -37 degree C, with a higher probability of formation at 150 mM extraliposomal NaCl than at 50 mM. The eutectic crystals were thought to cause additional leakage from the LUV (B).     

A two-phase model for laminar film condensation from steam-air mixtures in vertical parallel-plate channels

Detailed results are presented for laminar film condensation from steam-air mixtures flowing downward in vertical flat-plate channels. The mixture flow is laminar and saturation conditions prevail at the inlet. A fully coupled implicit numerical approach is used that achieves excellent convergence behavior, even for high inlet gas mass fractions. The detailed results include velocity, temperature, and gas mass fraction profiles, as well as axial variations of film thickness, pressure gradient and Nusselt number. The effects of a wide range of changes in the four independent variables (the inlet-to-wall temperature difference and the inlet values of gas concentration, Reynolds number, and pressure) on the film thickness, axial pressure gradient, and the local and average Nusselt numbers are carefully examined. It was found that increases in inlet concentration of noncondensable gas caused significant decreases in the film thickness, local Nusselt number, and axial pressure gradient. An analytical solution for the film thickness and velocity field at the end of condensation path was developed and shown to be the asymptotic value of the numerical results for large distances along the channel.     

Miscibility of some poly(neopentyl glycol adipate)/chlorinated polymer blends

Poly(neopentyl glycol adipate), PDPA, was found to be miscible with poly(epichlorohydrin-co-ethylene oxide). PDPA also formed miscible blends with chlorinated polyethylene samples containing 48 and 42% by weight of chlorine. Chlorinated polyethylene with a lower chlorine content was not miscible with PDPA.     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry

A novel method is described for the determination of cobalt(II) by differential pulse voltammetry, based on accumulation of a cobalt complex, [CoSCNNO]⁺, on a hanging mercury drop electrode, followed by measurement of the catalytic current of the adsorbed complex. The effects of various experimental parameters on the catalytic current were investigated. The current was found to be linear for 0.3 nM to 100 nM Co, with a detection limit of 70 pM (4.1 ng l⁻¹) and a relative standard deviation of 1.6% for 50 nM Co (n = 25). The developed method showed considerable selectivity against nickel and zinc. A possible mechanism of the reduction process is proposed.     

On centripetal flows of entities in scale‐free networks with nodes of finite capability

We examine the transmission of entities from the peripheries of scale‐free networks toward their centers when the nodes of the network have finite processing capabilities. We look at varying network utilization, U and find that clogging of the network sets in after a threshold value has been exceeded, and that the congestion sets in at the downstream nodes (those nearer to the collector) having large numbers of upstream neighbors. Investigation of the question of the degree of correlation of several characteristics of scale‐free networks (such as the average path length to the collector <l_(min)> and the average clustering coefficient ) with the dynamics of centripetal flow in them reveals a negative answer: any correlation is indirect and will manifest in the number of producer nodes (which dictate the effective heaviness of the flow) and the interconnectedness of the feeder nodes, those nodes which are immediate neighbors of the collector node. An examination of reinforcement strategies shows dramatic improvements in both the finishing rate, and the average total transmission time, when the more centrally‐placed nodes are reinforced first, showing that the entities spend a large amount of their lifetime waiting in line at those nodes (which constitute the bottlenecks in the network) compared to the nodes in the periphery. Our results reinforce the importance of a network's hubs and their immediate environs, and suggest strategies for prioritizing elements of a network for optimization. © 2014 Wiley Periodicals, Inc. Complexity 21: 283–295, 2015     

Copolymerization of methacrylonitrile with p-methylstyrene

Methacrylonitrile was copolymerized with p-methylstyrene in methyl ethyl ketone at 80°C initiated by azobisisobutyronitrile. Monomer reactivity ratios of methacrylonitrile and p-methylstyrene were found to be 0.205 and 0.377, respectively, using the Kelen-Tüdos method. Triad fractions and monomer sequence lengths of three copolymers were determined from ¹³C-NMR spectra and were found to be in good agreement with those calculated from reactivity ratios. © 1994 John Wiley & Sons, Inc.     

Polymerization of styrene with ionic comonomer,nonionic comonomer,or both

Nanosized polystyrene latexes with high polymer contents were obtained from an emulsifier-free process by the polymerization of styrene with ionic comonomer, nonionic comonomer, or both. After seeding particles were generated in an initial emulsion system consisting of styrene, water, an ionic comonomer [sodium styrenesulfonate (NaSS)] or nonionic comonomer [2-hydroxyethyl methacrylate (HEMA)], and potassium persulfate, most of the styrene monomer or a mixture of styrene and HEMA was added dropwise to the polymerizing emulsion over 6 h. Stable latexes with high polystyrene contents (≤25%) were obtained. The latex particle weight-average diameters were largely reduced (41 nm) by the continuous addition of monomer(s) compared with those (117 nm) obtained by the one-pot polymerization method. Latex particles varied from about 30 to 250 nm in diameters, whereas their molar masses were within 10⁴ to 10⁵ g/mol. The effect of the comonomer concentration on the number of polystyrene particles per milliliter of latex and the weight-average molar masses of the copolymers during the polymerization are discussed. The surface compositions of the latex particles were analyzed by X-ray photoelectron spectroscopy, which indicated that the surface of the latex particles was significantly enriched in NaSS, HEMA, or both. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1634–1645, 2001     

Artomandin, a new xanthone from Artocarpus kemando (Moraceae)

A new furanodihydrobenzoxanthone, artomandin (1), together with three other flavonoid derivatives, artoindonesianin C, artonol B, and artochamin A, as well as β-sitosterol were isolated from the stem bark of Artocarpus kemando. The structures of these compounds were determined on the basis of spectral evidence. All of these compounds displayed inhibition effects to a very susceptible degree in cancer cell line tests. Compound 1 also exhibited significant antioxidant capacity in the free radical 1,1-diphenyl-2-picrylhydrazyl tests.