Ozonide ions on the surface of MgO nanocrystals

The adsorption properties of oxygen radicals on the surface of polycrystalline oxides can provide relevant information about the functionality of specific surface sites in oxidation catalysis. Using electron paramagnetic resonance spectroscopy, we investigated O₂ adsorption at MgO nanocrystal surfaces which were previously enriched with O⁻ radicals i.e. trapped hole centers. On dehydroxylated particle surfaces, two ozonide radical types O ₃ ⁻ were isolated as adsorbates and the related energies for O₂ adsorption were found to be 55 ± 5 kJ mol⁻¹ and 100 ± 5 kJ mol⁻¹. The respective adsorption sites are assigned to hole centers trapped on oxygen terminated corners and cation vancancies, respectively. In addition, O ₃ ⁻ ions were also employed as probes for electron trapping sites on partially hydroxylated sample surfaces. Five types of O⁻ radicals emerge from surface colour centre bleaching with N₂O, but only two of them adsorb O₂ at room temperature. A connection between the well-characterized (H⁺)(e^-) defect – an electron trapped in close vicinity of a nearby proton [Chiesa et al. J. Phys. Chem. B 109 (2005) 7314] – and one ozonide type which exhibits significant magnetic coupling with an adjacent proton, was established on the basis of their production parameter dependence. Although the g tensor of an O₃ ⁻ species reflects the properties of the radical itself rather than the structure of the adsorption site, the related signatures are proposed to serve also as spectroscopic fingerprints for catalytically relevant surface anion environments.     

On-farm estimation of indigenous nitrogen supply for site-specific nitrogen management in the North China plain

Estimating indigenous nitrogen supply (INS) by measurement of crop N uptake in N omission plots for site-specific N management is not feasible on a routine basis because it involves destructive plant sampling and plant tissue analysis, which is time-consuming and expensive. The objective of this study was to determine the amount of INS and develop a method to estimate it using soil testing in the North China plain (NCP). On-farm experiments at 229 sites were conducted from 2003 to 2005 in seven key winter wheat (Triticum aestivum L.)/summer maize (Zea mays L.) production regions of the NCP. The mean INS during the wheat-growing season was129 kg N ha⁻¹ with a range from 62 to 212 kg N ha⁻¹, and it varied from 69 to 202 kg N ha⁻¹ with a mean of 142 kg N ha⁻¹ during the maize-growing season. Considering all sites, the variability of INS was not simulated by initial soil N _min or apparent N mineralization (N _organic) alone, while together they could explain about 38% and 60% of INS during the wheat and maize-growing seasons, respectively. During the wheat-growing season, mean N _organic was 63 kg N ha⁻¹, and 59% and 33% of its variation could be explained by SOM in high-yielding regions (mean yield, 7.6 t ha⁻¹) and low-yielding regions (mean yield, 5.3 t ha⁻¹), respectively. Mean N _organic during the maize-growing season was 109 kg N ha⁻¹, 22% of which could be explained by SOM across all sites. An average of 40% and 42% of INS variation could be explained by both SOM and initial soil N _min content during the wheat and maize-growing seasons, respectively. We conclude that the accuracy of estimating crop N requirement for site-specific N management will be increased by using initial soil N _min and SOM.     

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α-tocopherol in liposomes

The ¹O₂ quenching rate constants (k _Q ) of α-tocopherol (α-Toc) and carotenoids such as β-carotene, astaxanthin, canthaxanthin, and lycopene in liposomes were determined in light of the localization of their active sites in membranes and the micropolarity of the membrane regions, and compared with those in ethanol solution. The activities of α-Toc and carotenoids in inhibiting ¹O₂-dependent lipid peroxidation (reciprocal of the concentration required for 50% inhibition of lipid peroxidation: [IC₅₀]⁻¹) were also measured in liposomes and ethanol solution and compared with their k _Q values. The k _Q and [IC₅₀]⁻¹ values were also compared in two photosensitizing systems containing Rose bengal (RB) and pyrenedodecanoic acid (PDA), respectively, which generate ¹O₂ at different sites in membranes. The k _Q values of α-Toc were 2.9×10⁸M⁻¹s⁻¹ in ethanol solution and 1.4×10⁷ M⁻¹s⁻¹ (RB system) or 2.5×10⁶ M⁻¹s⁻¹ (PDA system) in liposomes. The relative [IC₅₀]⁻¹ value of α-Toc in liposomes was also five times higher in the RB system than in the PDA-system. In consideration of the local concentration of the OH-group of α-Toc in membranes, the k _Q value of α-Toc in liposomes was recalculated as 3.3×10⁶ M⁻¹s⁻¹ in both the RB and PDA systems. The k _Q values of all the carotenoids tested in two photosensitizing systems were almost the same. The k _Q value of α-Toc in liposomes was 88 times less than in ethanol solution, but those of carotenoids in liposomes were 600–1200 times less than those in ethanol solution. The [IC₅₀]⁻¹ value of α-Toc in liposomes was 19 times less than that in ethanol solution, whereas those of carotenoids in liposomes were 60–170 times less those in ethanol solution. There were no great differences (less than twice) in the k _q and [IC₅₀]⁻¹ values of any carotenoids. The k _Q values of all carotenoids were 40–80 times higher than that of α-Toc in ethanol solution but only six times higher that of α-Toc in liposomes. The [IC₅₀]⁻¹ values of carotenoid were also higher than that of α-Toc in ethanol solution than in liposomes, and these correlated well with the k _Q values.     

Caffeine Molecular Imprinted Microgel Spheres by Precipitation Polymerization

Imprinted uniform microgel spheres were prepared by precipitation polymerization. Acetonitrile was used as the dilute solvent with MAA as the monomer, EDMA as the crosslinker and caffeine as the print molecule. Comparison of caffeine adsorption on molecular imprinted and blank microgel spheres was made. Langmuir model was used to fit the adsorption data. It was found that the caffeine imprinted microgel spheres show specific binding sites to the target molecules. A binding study of caffeine on imprinted microgel spheres was made by Scatchard analysis; the dissociation constants (K_D) and the maximum binding capacity were K_D= 1.84×10⁻⁴mol/L,Q _max = 16.98 μmol/g for high affinity binding site and K_D=1.33×l0⁻³ mol/L, Q_max=46.84 μmol/g for lower affinity binding site, respectively This microgel spheres can be useful affinity adsorbents in further applications.     

Preparation and characterization of SO42-/TiO2 and S2O82-/TiO2 catalysts

Nanosized solid superacids SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂, as well as MCM-41-supported SO₄ ²⁻/ZrO₂, were prepared. Their structures, acidities, and catalytic activities were investigated and compared using XRD, N₂ adsorption-desorption, and in situ FTIR-pyridine adsorption, as well as an evaluation reaction with pseudoionone cyclization. The results showed that SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ possess not only nanosized particles with diameters < 7.0 nm, a BET surface greater than 140 cm²/g and relatively regular mesostructures with pores around 4.0 nm, but also a pure anatase phase and strong acidity. Different from the Lewis acid nature of SO₄ ²⁻/ZrO₂/MCM-41, SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ exhibit mainly Bronsted acidities. The strongest Bronsted acid sites were produced on SO₄ ²⁻/TiO₂ promoted with H₂SO₄, while Lewis acid sites on S₂O₈ ²⁻/TiO₂ even stronger than those on SO₄ ²⁻/ZrO₂/MCM-41 were generated when persulfate solution was used as sulfating agent. Because of their distinct acid natures, SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO₄ ²⁻/ZrO₂/MCM-41. It can be concluded that the existence of more Br?nsted acid sites was favorable for proton participation in the cyclization reaction. Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(2): 239–244 [译自: 高校化学工程学报]     

Surface active sites present in the orthorhombic M1 phases: low energy ion scattering study of methanol and allyl alcohol chemisorption over Mo–V–Te–Nb–O and Mo–V–O catalysts

The outermost surface compositions and chemical nature of active surface sites present on the orthorhombic (M1) Mo–V–O and Mo–V–Te–Nb–O phases were determined employing methanol and allyl alcohol chemisorption and surface reaction in combination with low energy ion scattering (LEIS). These orthorhombic phases exhibited vastly different behavior in propane (amm)oxidation reactions and, therefore, represented highly promising model systems for the study of the surface active sites. The LEIS data for the Mo–V–Te–Nb–O catalyst indicated surface depletion for V (−23%) and Mo (−27%), and enrichments for Nb (+55%) and Te (+165%) with respect to its bulk composition. Only minor changes in the topmost surface composition were observed for this catalyst under the conditions of the LEIS experiments at 400 °C, which is a typical temperature employed in these propane transformation reactions. These findings strongly suggested that the bulk orthorhombic Mo–V–Te–Nb–O structure is terminated by a unique active and selective surface layer in propane (amm)oxidation. Moreover, direct evidence was obtained that the topmost surface VO _x sites in the orthorhombic Mo–V–Te–Nb–O catalyst were preferentially covered by chemisorbed allyloxy species, whereas methanol was a significantly less discriminating probe molecule. The surface TeO _x and NbO _x sites on the Mo–V–Te–Nb–O catalyst were unable to chemisorb these probe molecules to the same extent as the VO _x and MoO _x sites. These findings suggested that vastly different catalytic behavior exhibited by the Mo–V–O and Mo–V–Te–Nb–O phases is related to different surface locations of V⁵⁺ ions in the orthorhombic Mo–V–O and Mo–V–Te–Nb–O catalysts. Although the proposed isolated V⁵⁺ pentagonal bipyramidal sites in the orthorhombic Mo–V–O phase may be capable of converting propane to propylene with modest selectivity, the selective 8-electron transformation of propane to acrylic acid and acrylonitrile may require the presence of several surface VO _x redox sites lining the entrances to the hexagonal and heptagonal channels of the orthorhombic Mo–V–Te–Nb–O phase. Finally, the present study strongly indicated that chemical probe chemisorption combined with low energy ion scattering (LEIS) is a novel and highly promising surface characterization technique for the investigation of the active surface sites present in the bulk mixed metal oxides.     

Sulfidation of an aluminum-nickel-molybdenum catalyst and its activity in thiophene hydrodesulfurization

We consider the interaction of H₂S with the molybdenum component of the catalyst using an Mo₇O₂₄H₁₂ cluster as an example. At 200–300°C, SH groups substitute for OH groups of the molybdenum component. Intense reduction of the molybdenum component starts at 300°C. The reaction of hydrogen with the molybdenum component at 300°C generates Mo-H hydride groups, Mo⁵⁺ ions, and anionic vacancies; these vacancies are filled in by sulfur anions produced by the dissociation of hydrosulfuric acid. An NiMoO₄ crystal phase is reduced and completely sulfided at 300°C. Mo₇O₂₄H₁₂ clusters are sulfided only partially; complete substitution by sulfur does not occur in them even at 600–650°C. We consider the thiophene hydrodesulfurization scheme on molybdenum oxysulfide in the presence of nickel, as well as the scheme of this reaction on MoS₂ in the absence of nickel. We conclude that hydrodesulfurization and hydriding occur at the same sites. Catalytically active surface sites in Mo₇O _x S _y + Ni, MoS₂ + Ni, and MoS₂ structures are alike. A common feature of these structures is the existence of Mo-H⁻ and MoSH⁻ basic sites. The difference between them lies in the nature of proton-donor sites: in MoS₂, proton donors are Mo-S-H⁺ groups, whereas in nickel-containing structures, nickel crystallites reacting with hydrogen are generators of protons and hydride ions.     

PC and PE synthesis: mixed micellar analysis of the cholinephosphotransferase and ethanolaminephosphotransferase activities of human choline/ethanolamine phosphotransferase 1 (CEPT1)

The human choline/ethanolamine phosphotransferase 1 (CEPT1) gene codes for a dual-specificity enzyme that catalyzes the de novo synthesis of the two major phospholipids through the transfer of a phosphobase from CDP-choline or CDP-ethanolamine to DAG to form PC and PE. We used an expression system devoid of endogenous cholinephosphotransferase and ethanolaminephosphotransferase activities to assess the diradylglycerol specificity of CEPT1. A mixed micellar assay was used to ensure that the diradylglycerols delivered were not affecting the membrane environment in which CEPT1 resides. The CEPT1 enzyme displayed an apparent K _m of 36 μM for CDP-choline and 4.2 mol% for di-18∶1 DAG with a V _max of 14.3 nmol min⁻¹ mg⁻¹. When CDP-ethanolamine was used as substrate, the apparent K _m was 98 μM for CDP-ethanolamine and 4.3 mol% for di-18∶1 DAG with a V _max of 8.2 nmol min⁻¹ mg⁻¹. The preferred diradylglycerol substrates used by CEPT1 with CDP-choline as the phosphobase donor were di-18∶1 DAG, di-16∶1 DAG, and 16∶0/18∶1 DAG. A major difference between previous emulsion-based assay results and the mixed micelle results was a complete inability to use 16∶0(O)/2∶0 as a substrate for the de novo synthesis of platelet-activating factor when the mixed micelle assay was used. When CDP-ethanolamine was used as the phosphobase donor, 16∶0/18∶1 DAG, di-18∶1 DAG, and di-16∶1 DAG were the preferred substrates. The mixed micelle assay also allowed the lipid activation of CEPT to be measured, and both the cholinephosphotransferase and ethanolaminephosphotransferase activities displayed the unusual property of product activation at 5 mol%, implying that specific lipid activation binding sites exist on CEPT1. The protein kinase C inhibitor chelerythrine and the human DAG kinase inhibitor R59949 both inhibited CEPT1 activity with IC₅₀ values of 40 μM.     

Saturated fatty acid adsorption by acidified rice hull ash

Rice hull ash (RHA) was treated with 1.0 M HNO₃ (RHA-A1) and another batch was treated with 14.0 M HNO₃ (RHA-A14). RHA-A1 and RHA-A14 had a pH of 6.58 and 6.13, respectively. Adsorption of saturated fatty acids (C₈, C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈) was carried out on RHA-A1 and RHA-A14 at 32±1°C. The adsorption data conformed to the Langmuir isotherm. The specific surface area of RHA-A1 was 183.84 m² g⁻¹ while that of RHA-A14 was 174.67 m² g⁻¹. The specific pore volume of RHA-A1 was 0.216 cm³ g⁻¹ while that of RHA-A14 was 0.234 cm³ g⁻¹. The acid-treated ash, RHA-A14 (q _m =0.43±0.03 mmol g⁻¹ where q _m is the amount of adsorbate adsorbed to form a monolayer coverage on the ash particles) showed a twofold increase in the adsorption of fatty acid per gram ash compared to RHA-A1 (q _m =0.25±0.03 mmol g⁻¹). The free energy of adsorption, ΔG° _ads, was determined to be −7.06±0.10 and −6.75±0.11 kcal mol⁻¹ for RHA-A1 and RHA-A14, respectively. The reduced ΔG° _ads values observed for RHA-A14 were attributed to the electrostatic repulsion of the hydrophobic chain of the fatty acid adsorbed on adjacent sites and brought into close proximity of each other. The ΔG° _ads values showed that the process of adsorption took place through physisorption on both RHA.     

Hydrotreating of Heavy Gas Oil Derived from Athabasca Bitumen Over Co–Mo/γ-Al2O3 Catalyst Prepared by Sonochemical Method

Co–Mo/γ-Al₂O₃ oxide containing 9.8 wt% Mo and 2.9 wt% Co was prepared by high-intensity ultrasonic irradiation of Mo(CO)₆, Co₂(CO)₈, and γ-Al₂O₃ in decahydronapthalene under air flow. The oxidic Co–Mo catalyst thus formed was characterized by elemental analysis, BET N₂ adsorption and XRD. The surface sites on the sulfided Co–Mo/γ-Al₂O₃ catalyst were characterized by infrared spectroscopy of CO adsorption. Hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities were evaluated for heavy gas oil derived from Athabasca bitumen in a trickle bed reaction system using the following conditions: temperatures ranging from 370 to 400 °C, a pressure of 8.8 MPa, a liquid hourly space velocity of 1 h⁻¹, and a H₂/feed ratio of 600 ml/ml. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared Co–Mo/γ-Al₂O₃ catalyst containing similar wt% of Mo and Co. The Co–Mo catalyst prepared by sonochemical method has higher HDN and HDS rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

Review of SO2-4/MxOy solid superacid catalysts

Some metal oxides modified with sulfate ions form highly acidic or superacidic catalysts. SO₂₋⁴/M _x O _y solid superacid catalysts, play a vital role in more and more fields such as organic synthesis, fine chemicals, pharmaceuticals, and means for strengthening environmental safeguards. This review highlights the recent development of solid superacid catalysts based on SO₂₋⁴/M _x O _y , including synthesis method, characterization of acid sites and acid strength, and applications.     

Bleaching kinetics of sunflowerseed oil

The bleaching process for sunflowerseed oil follows a rate formula, log (A/A ₀)=−κ , according to absorbance measurements. The dark color of crude oil converts to a light color as the absorbance value decreases. The activation energy E _a was calculated from the Arrhenius equation as 3 kJ, and other activation thermodynamic parameters were determined as ΔS ^⊄=−4.4 J K⁻¹, ΔH ^⊄=−31.2 J mol⁻¹, and ΔG ^⊄=1.6 kJ mol⁻¹. The study showed that the bleaching process was exothermic, presented a decrease of entropy, and was a nonspontaneous process during activation.     

From Electron Density Flow Towards Activation: Benzene Interacting with Cu(I) and Ag(I) Sites in ZSM-5. DFT Modeling

The effects of support pretreatment with nC₁–C₅ alcohols on the performance of Rh–Mn–Li/SiO₂ catalyst in the synthesis of C₂-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H₂, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C₂-oxygenates (STY_C2-oxy) and selectivities towards C₂-oxygenates (S_C2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh⁺/Rh⁰ sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO₂ catalyst.     

Physicochemical characterization of ATP binding to human 5-lipoxygenase

Human 5-lipoxygenase requires ATP as a stimulatory factor. At the two preferred concentrations of the free Ca²⁺, 0.02 μM with a resting cell and 20 μM with a stimulated cell, Scatchard analysis revealed that 5-lipoxygenase has one affinity ATP binding site with aK _d of 4.6 μM at the low Ca²⁺ concentration but has two affinity ATP binding sites with a higherK _d of 4.4 μM and a lowerK _d of 14.5 μM at the high Ca²⁺ concentration. In contrast, in a Tween 20 reaction system, 5-lipoxygenase had similar activation coefficients for ATP at both Ca²⁺ concentrations; these were 12.7 μM at the low Ca²⁺ concentration and 12.0 μM at the high Ca²⁺ concentration. These results showed that 5-lipoxygenase has an ATP binding site and suggest that self-association of 5-lipoxygenase in 20 μM Ca²⁺ may affect ATP binding affinity as measured by Scatchard analysis.     

Reaction between Hydrosulfide and Iron/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N₂) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m²/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS⁻]_t=0^−0.5[A]_t=0[H⁺]_t=0^−0.5 , where k_i represents the apparent rate constants for the oxidation of HS⁻ (k_HS) or the dissolution of Fe(II) (k_Fe), [HS⁻]_{t = 0} is the initial hydrosulfide concentration, [A]_{t = 0} is the initial Fe/Ce (hydr)oxide surface area and [H⁺]_{t = 0} is the initial proton concentration. The rate constant, k_HS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10⁻⁴ mol² L⁻¹ m⁻² min⁻¹, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS⁻ oxidized and Fe(II) produced; k_Fe = (3.9116 ± 0.41) × 10⁻⁵ mol² L⁻¹ m⁻² min⁻¹).     

A DFT study on benzene adsorption over tungsten sulfides: surface model and adsorption geometries

Benzene adsorption on a WS₂(100) surface was studied by ab initio periodic DFT computations. Benzene adsorption is facile on the bridge site of the bare W edge via η² or η³ coordination. Taking into account the stable configuration at the W edge under typical hydrotreating reaction conditions (623 K, H₂S/H₂ = 0.01), benzene adsorption is found to be difficult, even when defective bridge sites are created.     

Biodiesel production by the transesterification of cottonseed oil by solid acid catalysts

Methyl esters (biodiesel) were produced by the transesterification of cottonseed oil with methanol in the presence of solid acids as heterogeneous catalysts. The solid acids were prepared by mounting H₂SO₄ on TiO₂ · nH₂O and Zr(OH)₄, respectively, followed by calcining at 823K. TiO₂-SO₄ ²⁻ and ZrO₂-SO₄ ²⁻ showed high activity for the transesterification. The yield of methyl esters was over 90% under the conditions of 230°C, methanol/oil mole ratio of 12:1, reaction time 8 h and catalyst amount (catalyst/oil) of 2% (w). The solid acid catalysts showed more better adaptability than solid base catalysts when the oil has high acidity. IR spectral analysis of absorbed pyridine on the samples showed that there were Lewis and Br?nsted acid sites on the catalysts. Translated from The Chinese Journal of Process Engineering, 2006, 6(4): 571–575 [译自: 过程工程学报]     

Biosynthesis of hydrocarbons by algae: Decarboxylation of stearic acid to N-heptadecane inAnacystis nidulans determined by13C- and2H-labeling and13C nuclear magnetic resonance

The distribution of isotopic labels inn-heptadecane enriched from [1,2-¹³C] and [2-¹³C, 2-²H₃) acetates byAnacystis nidulans has been determined by¹³C nuclear magnetic resonance (¹³C NMR). Labeling with [1,2-¹³C] acetate is consistent with assembly from¹³C−¹³C units derived from an acetate “starter” group and 8 malonate units, as in fatty acid biosynthesis, followed by production of a methyl group through bond cleavage of the terminal¹³C−¹³C unit. A comparison of the hydrocarbon with palmitic acid (the only fatty acid produced in sufficient amount for NMR analysis) enriched from [2-¹³C,2-²H₃]acetate by the same culture shows that they have retained the same fraction of²H at corresponding sites, and have therefore undergone identical biosynthetic and hydrogen-deuterium exchange processes, as would be expected ifn-heptadecane originates from de novo-synthesized stearic acid. NRCC No. 18251.     

Biological response of guinea pig peritoneal macrophages to platelet-activating factor

We investigated the effects of platelet-activating factor (PAF) on guinea pig peritoneal macrophages. Specific and high-affinity binding sites for PAF were detected on guinea pig peritoneal macrophages. Scatchard analysis of PAF binding revealed high affinity binding sites (7.9×10⁴/cell) with a dissociation constant of 2.3×10⁻¹⁰ M. When treated with 10⁻⁹−10⁻⁵ M PAF, guinea pig peritoneal macrophages released hydrogen peroxide into the medium in a time-dependent manner. The release reaction upon stimulation with 10⁻⁵ M PAF reached a plateau within 30 min and the extent of release was twice as high as that when stimulated byN-formyl-L-methionyl-leucyl-L-phenylalanine (fMLP; 2 μM)-treated cells. Neither lysoPAF nor the PAF enantiomer was effective. PAF-induced H₂O₂ release was inhibited specifically by PAF antagonists, suggesting that PAF activated macrophages through binding to specific sites. Lysosomal enzyme (N-acetyl-β-D-glucosaminidase) was released from guinea pig peritoneal macrophages upon treatment with 10⁻⁵ M PAF for 60 min. Guinea pig peritoneal macrophages were treated with PAF for 8 hr and the conditioned medium was examined for cytokines. The medium exhibited cytocidal activity against mouse fibroblast L929 cells [tumor necrosis factor (TNF) activity], and this activity was comparable to that detected after treatment of cells with the bacterial lipopolysaccharide (LPS). Furthermore, the same conditioned medium also showed colony-stimulating factor (CSF) activity. Generation of these cytokines was stereospecific. Our findings suggest that PAF is a unique macrophage activator that potentiates both respiratory burst/lysosomal enzyme release (early-phase response) and monokine production/glucose consumption (late-phase response). Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

Poly(methylphenylphosphazene)–Graft–Poly(methyl Methacrylate) Copolymers Via Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) was used to graft poly(methyl methacrylate), PMMA, onto poly(methylphenylphosphazene), [(Me)(Ph)PN] _n , PMPP. A two-step process was used to convert a portion of the methyl substituents on [(Me)(Ph)PN] _n to –CH₂C(CH₃)₂OH groups and then to bromoalkyl groups, –CH₂C(CH₃)₂OC(=O)C(CH₃)₂Br, the latter of which served as initiation sites for ATRP of methyl methacrylate (MMA) in the presence of CuCl/bipyridine. Variations in the length of the grafted chains were investigated and the graft copolymers were compared to the parent polymer and blends of similar composition. The new bromoalkyl derivatives of [(Me)(Ph)PN] _n and the PMPP–graft–PMMA copolymers were characterized by elemental analysis, ¹H and ³¹P NMR spectroscopy, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). We dedicate this paper to Professor Harry R. Allcock for consistently maintaining the highest standards in his creative, pioneering work in inorganic rings and polymers.