Fenton reactions in lipid phases

Metal catalysis of membrane lipid oxidation has been thought to occur only at cell surfaces. However, conflicting observations of the pro-oxidant activity of ferric (Fe³⁺) vs ferrous (Fe²⁺) forms of various chelates have raised questions regarding this dogma. This paper suggests that the solubilities of iron complexes in lipid phases and the corresponding abilities to initiate lipid oxidation there, either directly or via Fenton-like production of reactive hydroxyl radicals, are critical determinants of initial catalytic effectiveness. Partitioning of Fe³⁺ and Fe²⁺ complexes and chelates into bulk phases of purified lipids was quantified by atomic absorption spectroscopy. mM solutions of iron salts partitioned into oleic acid at levels of about micromolar. Ethylenediamine tetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) chelates were somewhat less soluble, while adenosine diphosphate (ADP) chelates, and ferrioxamine were soluble as chelates at greater than 10⁻⁵ M. Solubilities of all iron compounds in methyl linoleate were 10- to 100-fold lower. To determine whether Fenton-like reactions occur in lipid phases, H₂O₂ and either Fe²⁺ or Fe³⁺ and a reducing agent were partitioned into the lipid along with the spintrap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and free radical adducts were recorded by electron paramagnetic resonance (EPR). Hydroxyl radicals (OH^.) adducts were observed in oleic acid, but in lipid esters secondary peroxyl radicals predominated, and the presence of OH^. adducts was uncertain. Presented at the symposium “Free Radicals, Antioxidants, Skin Cancer and Related Diseases” at the 78th AOCS Annual Meeting in New Orleans, LA, May 1987     

The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al₂O₃ and Co–Re/γ-Al₂O₃ was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H₂/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H₂/CO ratios in the feed, the CO conversion and the CH₄ selectivity decreased, while the C₅₊ selectivity and olefin/paraffin ratio for C₂–C₄ increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H₂/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H₂/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H₂/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C₅₊, lower selectivity to CH₄, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.     

Progressive ratio schedules of reinforcement.

[Correction Notice: An erratum for this article was reported in Vol 35(2) of Journal of Experimental Psychology: Animal Behavior Processes (see record 2009-05154-003). The URL provided for the supplemental material was incomplete. The complete URL is http://dx.doi.org/10.1037/a0012497.supp] Pigeons' pecks produced grain under progressive ratio (PR) schedules, whose response requirements increased systematically within sessions. Experiment 1 compared arithmetic (AP) and geometric (GP) progressions. Response rates increased as a function of the component ratio requirement, then decreased linearly (AP) or asymptotically (GP). Experiment 2 found the linear decrease in AP rates to be relatively independent of step size. Experiment 3 showed pausing to be controlled by the prior component length, which predicted the differences between PR and regressive ratio schedules found in Experiment 4. When the longest component ratios were signaled by different key colors, rates at moderate ratios increased, demonstrating control by forthcoming context. Models for response rate and pause duration based on Bizo and Killeen (1997) described performance on AP schedules; GP schedules required an additional parameter representing the contextual reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Possible Role of Circulating Bone Marrow Mesenchymal Progenitors in Modulating Inflammation and Promoting Wound Repair

Circulating bone marrow mesenchymal progenitors (BMMPs) are known to be potent antigen-presenting cells that migrate to damaged tissue to secrete cytokines and growth factors. An altered or dysregulated inflammatory cascade leads to a poor healing outcome. A skin model developed in our previous study was used to observe the immuno-modulatory properties of circulating BMMP cells in inflammatory chronic wounds in a scenario of low skin perfusion. BMMPs were analysed exclusively and in conjunction with recombinant tumour necrosis factor alpha (TNFα) and recombinant hepatocyte growth factor (HGF) supplementation. We analysed the expression levels of interleukin-8 (IL-8) and ecto-5′-nucleotidase (CD73), together with protein levels for IL-8, stem cell factor (SCF), and fibroblast growth factor 1 (FGF-1). The successfully isolated BMMPs were positive for both hemopoietic and mesenchymal markers and showed the ability to differentiate into adipocytes, chondrocytes, and osteocytes. Significant differences were found in IL-8 and CD73 expressions and IL-8 and SCF concentrations, for all conditions studied over the three time points taken into consideration. Our data suggests that BMMPs may modulate the inflammatory response by regulating IL-8 and CD73 and influencing IL-8 and SCF protein secretions. In conclusion, we suggest that BMMPs play a role in wound repair and that their induced application might be suitable for scenarios with a low skin perfusion.     

Coal as an option for power generation in U.S. territories of the Pacific

General considerations relating to the use of coal in U.S. territories and trust territories of the Pacific suggest that coal is a viable option for power generation. Future coal supplies, principally from Australia and the west coast of America, promise to be more than adequate, but the large bulk carriers (100,000–200,000 dwt) expected to serve Far Eastern markets will probably not be able to land coal directly in the territories because of inadequate port facilities. Hence, smaller than Panamax-class vessels (60,000 dwt) or some arrangement utilizing self-loading barges or lighters would have to be used. Except for Guam, with peak power requirements on the order of 175 MW_e, most territories have current, albeit inadequate, installations of 1–25 MW_e. Turnkey, conventional-coal-fired, electrical-power generating systems are available in that size range. Fluidized bed combustion is another option currently being commercialized. Its use has clear environmental advantages and a variety of fuels (e.g. coal, heavy oils, biomass, etc.) may be employed without interruption of power generation. U.S. environmental laws, such as the Clean Air Act, are now applicable to Guam and American Samoa; the trust territories are exempt. When United Nations trusteeship terminates, the current unclear position of the Commonwealth of the Northern Marianas will cease and the laws will probably apply. Nonetheless, the small power requirements of many small islands will qualify for exemption from the New Source Performance Standards called for in the Clean Air Act.The principal problems with coal use in the territories, apart from the shallow draft of most harbors, are the limited amount of land available and the high capital costs associated with conversion. Ocean dumping of ash and sludge can be permitted under existing Environmental Protection Agency regulations, and barge-mounted power installations are not out of the question. The feasibility of converting from oil-fired to coal-fired electrical-power generating systems must be determined with site-specific information.     

Integrated fuel-cycle models for fast breeder reactors

Breeder-reactor fuel-cycle analysis can be divided into four different areas or categories. The first category concerns questions about the spatial variation of the fuel composition for single loading intervals. Questions of the variations in the fuel composition over several cycles represent a second category. Third, there is a need for a determination of the breeding capability of the reactor. The fourth category concerns the investigation of breeding and long-term fuel logistics. Two fuel-cycle models used to answer questions in the third and fourth area are presented.The space- and time-dependent actinide balance, coupled with criticality and fuel-management constraints, is the basis for both the Discontinuous Integrated Fuel-Cycle Model and the Continuous Integrated Fuel-Cycle Model. These models are derived by formally condensing the base equations through spatial integration. Cycle-average isotopic microscopic reaction rate and reactivity-worth coefficients, based on equilibrium behavior, complete the derivation of the discontinuous model. Approximating the discontinuous reload with continuous charge and discharge currents transforms the discontinuous model into the more mathematically elegant continuous model.The results of the continuous model are compared with results obtained from detailed two-dimensional space and multigroup depletion calculations. The continuous model yields nearly the same results as the detailed calculation, and this is with a comparatively insignificant fraction of the computational effort needed for the detailed calculation. Thus, the integrated model presented is an accurate tool for answering questions concerning reactor breeding capability and long-term fuel logistics.