Asymmetric structure analysis of active surface-sites by in situ polarized total-reflection fluorescence EXAFS

An in situ polarization-dependent total reflection fluorescence yield EXAFS system has been developed to analyze the asymmetric structures of catalytically active metal sites on single crystal surfaces. This technique separately reveals the bonding feature parallel and perpendicular to the support surface. The systems of Cu ion on -quartz(0001), Co oxide on -alumina(0001), and Pt₄ on -alumina(0001) were investigated as model surfaces of supported catalytic systems. The location of Cu sites on -quartz(0001), the epitaxial growth mode of Co₃O₄ on -alumina(0001), and the Pt raft structure with metal-support interaction in Pt₄ / -alumina(0001) were observed.     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Synthesis and properties of aromatic polyesters and brominated polyesters derived from α,α′-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene

The interfacial polycondensation technique was used for the preparation of polyarylates and brominated polyarylates. Polyarylates and brominated polyarylates were prepared by mixing a solution of diacid chloride such as terephthaloyl chloride, isophthaloyl chloride, or their mixture in dichloromethane with an aqueous alkaline solution of ,-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene or ,-bis(4-hydroxy-3,5-dibromophenyl)-1,4(or 1,3)-diisopropylbenzene using triethylbenzylammonium chloride as the phase transfer agent. Moderate to high molecular weight polyarylates with _inh up to 1.27 dL/g were obtained, and most of them could be cast into tough and flexible films depending on the polymer composition. In general, polymers containing more 1,3-isomer or isophthaloyl chloride moieties gave transparent and flexible films and had lower glass transition temperatures and higher solubility. Although these polymers have two isopropylidene linkages in their repeating units, they still exhibit moderately high thermal stability and show no obvious weight loss before 400 °C. The introduction of bromine on the polymer backbone caused a decrease of inherent viscosity, crystallinity, and thermal stability of the polyarylates, while causing an increase in glass transition temperature and a great enhancement of fire retardancy.     

Kinetics and Mechanism of Copolymerization of α-terpineol with Methylmethacrylate in Presence of Azobisisobutyronitrile as an Initiator

The radical copolymerization of -terpineol with methyl-methacrylate in xylene at 80±0.1C for 50 minutes in the presence of azobisisobutyronitrile (AIBN) follows ideal kinetics and results in the formation of a functional and random copolymer. The activation energy is 33 KJ/mole. The IR spectrum and NMR spectra of the copolymer(s) shows the bands at 1750 and 3400 cm^–1 for ester group of methylmethacrylate and alcoholic group of -terpineol and peaks at 3 to 4 for methoxy group and at 6.5 to 7.5 due to alcoholic group of methylmethacrylate and -terpineol repectively. The values of reactivity ratios, calculated by Kelen–Tüdos method, are r ₁ (MMA) = 0.18 and r ₂ (-terpineol) = 0.046. The Alfrey-Price; Q–e parameters for -terpineol has been calculated as 0.149 and 2.486. The mechanism of copolymerization has been elucidated and it is concluded that the double bond present in the monocyclic ring of -terpineol is an active site for copolymerization and the alcoholic group of -terpineol remain to give functional copolymer.     

Factors governing the electrochemical synthesis of α-nickel (ii) hydroxide

The electrodeposition of -nickel hydroxide is promoted by the simultaneous chemical corrosion of the electrode by an acidic nitrate bath. Chemical corrosion results in the formation of a poorly ordered layered phase which is structurally similar to -nickel hydroxide and provides nucleation sites for the deposition of the latter. Therefore under conditions which enhance corrosion rates such as low current density (<1.3 mA cm–2), high temperature (60 C), high nickel nitrate concentration ( 1M) and the resultant low pH (1.7), -nickel hydroxide electrodeposition is observed, while -nickel hydroxide forms under other conditions. Further, -nickel hydroxide deposition is more facile on an iron electrode compared to nickel or platinum.     

Isolation and identification of male medfly attractive components inLitchi chinensis stems andFicus spp. stem exudates

Short-range attraction/feeding stimulation of male Mediterranean fruit flies [Ceratitis capitata (Wiedemann), (Diptera: Tephritidae)] to a stem extract of a host plant,Litchi chinensis Sonn. (Sapindaceae), and to milky exudates from stems of nonhost plants,Ficus retusa L. andF. benjamina L. (Moraceae), were attributed to the presence of the sesquiterpene -copaene. The presence of -copaene in the milky exudate from stems ofF. benghalensis L. is also suggested as eliciting similar behavioral responses in male medflies. The presence of minor quantities of -ylangene in the plants and its contributory effects to the behavioral response of male medflies is discussed. Short-range attraction/feeding stimulation of male medflies to equal amounts of -ylangene-free -copaene samples (94.5%+), prepared from -copaene-enriched angelica seed oil and copaiba oil, respectively, showed no difference in intensity of response. -Ylangene elicited a slightly less intense response for male medflies than -copaene.Names of products in this paper are included for the benefit of the reader and do not imply endorsement or preferential treatment by USDA.     

Suppression of the α → β-nickel hydroxide transformation in concentrated alkali: Role of dissolved cations

The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the -nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the -phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases.     

Additional male mediterranean fruitfly (Ceratitis capitata wied.) Attractants from Angelica seed oil (Angelica archangelica L.)

Two sesquiterpene hydrocarbons, -copaene and -ylangene, were isolated from bioactive fractions of angelica seed oil and were shown by field bioassays to be attractive to the male Mediterranean fruit fly. Their relative attractiveness, compared with the(+)-and (–)--copaene enantiomers, are: (+)--copaene>angelica -copaene>angelica -ylangene>(–)--copaene. The enantiomer ratios for the two compounds are: -copaene, 61.4% (+), 38.6% (–); -ylangene, 91.9% (+), 8.1% (–).trans--Bergamotene was also isolated from the same fractions, but in sufficient quantity for bioassay [enantiomer ratio: 95.7% (+), 4.3% (–)].     

α-Copaene, A Potential Rendezvous Cue for the Mediterranean Fruit Fly, Ceratitis Capitata?

-Copaene, a potent attractant for male Mediterranean fruit flies, Ceratitis capitata, is found as a minor component in the essential oils of various plant species, including its hosts such as orange, guava, and mango. Despite the specific attraction of male flies and the wide distribution of the compound in host plants, the biological significance of -copaene remains unknown. In a laboratory test, leklike behavior of C. capitata was induced artificially by using a plastic leaf model treated with (+)--copaene. It was also found that (+)--copaene affected virgin females, provoking "pseudomale" courtship behavior in the short-range bioassay. Mating occurred exclusively on the artificial leaves treated with -copaene, suggesting the compound potentially serves as a chemical cue to facilitate orientation of flies to the rendezvous site.     

Enantioselective hydrogenation of α-ketoesters over Pt/alumina modified with cinchonidine: theoretical investigation of the substrate-modifier interaction

Enantio-differentiation in the asymmetric hydrogenation of -ketoesters to -hydroxyesters over platinum catalysts modified with cinchona-alkaloid modifiers occurs through interaction of the ketoester with the cinchona modifier. The structure of the probable transition complex has been calculated for the system methyl pyruvate (substrate) cinchonidine (modifier) using molecular mechanics and quantum chemistry techniques at both ab initio and semiempirical levels. The calculations suggest that protonated cinchonidine is energetically more likely to interact with the substrate and that the crucial interaction occurs via hydrogen bonding of the quinuclidine nitrogen and the oxygen of the -carbonyl moiety of methyl pyruvate. In this complex the methyl pyruvate is transformed into a half-hydrogenated species which is adsorbed on the platinum surface and on hydrogenation yields the product methyll actate. Theoretical studies indicate that adsorption of the complex leading to (R) -methyl lactate is energetically more favourable than that of the corresponding complex which yields (S) -methyl lactate, which may be the key for the enantio-differentiation.     

Phase transitions and dimensional and morphological changes in an “Aluminum Hydroxide-Alumina” system under a shock-wave action

A method is proposed to study the sequence of phase transitions in powdered materials under a shock-wave action. It is shown that the aluminum hydroxide-alumina system has the following sequence of phase transformations under a shock-wave action: bayerite boehmite -Al₂O₃ -Al₂O₃. It is found that there are no transitional high-temperature modifications of alumina. A method is developed for obtaining a submicron alumina powder, which allows obtaining materials with a controlled phase composition, including a thermodynamically stable -modification of Al₂O₃. The specific features of the morphological structure and the phase and structural characteristics of powders after a shock-wave action are considered.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 110–119, January–February, 2005.     

Chiral specificity in responses by the bark beetleDendroctonus valens to host kairomones

The attraction of the red turpentine beetle,Dendroctonus valens, to the resin volatiles of its host,Pinus ponderosa, is elicited by three chiral monoterpenes. In field assays response was greatest to (S)-(–)--pinene; 92% (S)-(–)--pinene found inP ponderosa resin was not attractive. However, 75% (R)-(+)--pinene, which occurs inPinus lambertiana, a sympatric host ofD. valens, was attractive. (S)-(–)--Pinene interrupted response to (R)-(+)--pinene. (S)-(+)-3-Carene from both hosts was attractive at the (R)-(+)--pinene level. Three sympatric coniferous nonhosts each have the same attractive monoterpenes but produce less resin. These studies demonstrate the importance of chirality of host compounds in the host finding behavior of this bark beetle.     

Both Ovarian Fluid and Female Urine Increase Sex Steroid Hormone Levels in Mature Atlantic Salmon (Salmo salar) Male Parr

We compared the ability of urine and ovarian fluid from female Atlantic salmon (Salmo salar) to stimulate increase in plasma concentrations of sex steroid hormones in mature conspecific male parr (priming effect of the stimuli). We also tested the hypothesis that prostaglandin F₂ (PGF₂) may act as a priming pheromone in the tested stimulants. Individual males of salmon parr were exposed to female urine, ovarian fluid, urine–ovarian fluid mix, or PGF₂. Plasma concentrations of the sex steroids of 17,20-dihydroxy-4-pregnen-3-one (17,20-P) were higher in males exposed to urine, ovarian fluids, and PGF₂ compared to control males. PGF₂ and a mixture of urine and ovarian fluid also gave increased concentrations of 11-ketotestosterone (11-KT). Concentrations of PGF₂ were higher in ovarian fluids than in urine. A behavior test with mature male parr in a fluviarium showed neither attraction to nor avoidance of 0.1 nM PGF₂, but plasma levels of 17,20-P were significantly higher in exposed males compared to controls.     

Electrosynthesis of 4,4′-dinitroazobenzene on PbO2 electrodes

Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO₂ electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO₂ electrode. It was found that the electrocatalytic activity of a PbO₂ electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.     

Alpha-acaridial a female sex pheromone from an alarm pheromone emilting mite Rhizoglyphus robini

The female sex pheromone of Rhizoglyphus robini Claparède (Astigmata: Acaridae) was identified as -acaridial [2(E)-(4-methyl-3-pentenyl)- butenedial], which stimulated males sexually and enhanced the frequency of male mounting behavior. Although a hexane extract of females manifested alarm pheromone activity against tested males due to the presence of the alarm pheromone neryl formate, silica gel column fractions containing -acaridial evoked increased mounting behavior by males at a dose of 0.1 female equivalent. Synthetic -acaridial at a dose of 10 ng showed a peak of activity as a sex pheromone, with a convex dose–response relationship. Its content was determined to be 388 ± 244 ng per female and 163 ± 97 ng per male by GC. This is the first time that two pheromones (the alarm pheromone neryl formate, and the sex pheromone -acaridial) have been demonstrated to be components of the same opisthonotal gland secretion in astigmatid mites. A mechanism for the appropriate expression of the two pheromones by the mites under different conditions is proposed.     

Synergistic Effect of Ethanol to α-Pinene in Primary Attraction of the Larger Pine Shoot Beetle, Tomicus piniperda

-Pinene and ethanol were released in the approximate proportions 1:0.1, 1:0.9 and 1:9 (at 21°C). Ethanol, released in the range of 3–279 mg/day, generally synergized the attraction of T. piniperda to -pinene (30 mg/day at 21°C), although attraction to the mixtures varied within and between years. The low release rate of ethanol together with -pinene attracted a significantly higher number of beetles than -pinene alone in 1995, April of 1996, and in 1997. Lures with the medium release rate of ethanol were the most attractive only in March of 1996. The high dose of ethanol significantly synergized attraction to -pinene in 1995 and 1997. The variable attraction of T. pinipeda to ethanol and -pinene at various release rates and proportions may be due to the temperature dependent nature of beetle antennal sensitivity. At ambient temperatures of 10–13°C. T. piniperda was most attracted to the lures with -pinene and high release rates of ethanol, at 14–17°C it was most attracted to those with medium release rates of ethanol, and at 18°C and higher it was most attraacted to those with low release rates of ethanol.     

Dose and enantiospecific responses of white pine cone beetles,Conophthorus coniperda,to alpha-Pinene in an eastern white pine seed orchard

The white pine cone beetle, Conophthorus coniperda, exhibited dose and enantiospecific responses to -pinene in stands of mature eastern white pine, Pinus strobus, in a seed orchard near Murphy, North Carolina, USA. (–)--Pinene significantly increased catches of cone beetles to traps baited with (± )-trans-pityol. (+)--Pinene did not increase catches of beetles to pityol-baited traps and interrupted the response of beetles to traps baited with (±)-trans-pityol and (–)--pinene. Maximal attraction of cone beetles to pityol-baited traps was obtained with lures releasing (–)--pinene at a rate of 103 mg/day at 23^°C. Lures releasing (–)--pinene at rates lower or higher than 103 mg/day resulted in reduced catches to traps baited with (±)-trans-pityol. The sex ratio in all catches was heavily male biased. Attraction of the clerid predator, Thanasimus dubius, to traps baited with (±)-trans-pityol increased significantly with the presence of -pinene, irrespective of enantiomeric composition. Maximal attraction of T. dubius to pityol-baited traps occurred with devices releasing (–)--pinene at the highest rate tested, 579 mg/d at 23^°C, a sub optimal rate for cone beetles.     

Preparation and properties of <Emphasis Type="Italic">α</Emphasis>-phenylcinnamylideneacetylated poly(2-hydroxyethyl methacrylate)

A photosensitive polymer, -phenylcinnamylideneacetylated poly(2-hydroxyethyl methacrylate) (poly(HEMA)), was synthesized and characterized. Light irradiation upon the photosensitive poly(HEMA) film induced gel formation via dimerization between the pendent -phenylcinnamylideneacetylates of the polymer. The gel content of the crosslinked polymer increased with increasing irradiation time and reached 60% when irradiated for 30 minutes. Correspondingly, the water content decreased from 27% to 18% with irradiation time increasing from 0 to 30 minutes. The solute permeability of the -phenylcinnamylideneacetylated poly(HEMA) without irradiation is about the same as that of the poly(HEMA) film. The crosslinked -phenylcinnamylideneacetylated poly(HEMA) film prepared by light irradiation had much lower permeability as compared with the non-crosslinked film. More specifically, the photocrosslinked film had the permeability of 5.37 × 10^–7 cm/s, 1.32 × 10^–7 cm/s and 0.53 × 10^–7 cm/s for p-nitrophenol, tryptophan and flurbiprofen, respectively. This photosensitive -phenylcinnamylideneacetylated poly(HEMA) provides a new base material for fabricating poly(HEMA) hydrogel.     

Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/-Al₂O₃ catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/-Al₂O₃ composite oxides and Pd-La/-Al₂O₃ catalysts show that Pd catalyzes the solid state reaction between A1₂O₃ and Al₂O₃ to form LaAlO₃. TPRd studies conducted on Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaAlO₃, and Pd-La/-Al₂O₃ catalysts suggest that Pd in the Pd-La/-Al₂O₃ catalyst interacts more strongly with LaAlO₃ than with -Al₂O₃. Reaction studies were conducted to investigate the activity of Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaA10₃, and Pd-La/-Al₂O₃ catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO₃ catalysts are most active for NO removal at stoichiometric and under net reducing conditions.     

Synergistic interaction between potato glycoalkaloidsα-solanine andα-chaconine in relation to destabilization of cell membranes: Ecological implications

In studies of the lysis of rabbit erythrocytes, red beet cells, andPenicillium notatum protoplasts by the potato glycoalkaloids -solanine and -chaconine, the latter was consistently the more membrane-disruptive compound and erythrocytes the more susceptible cell type. A 11 mixture of solanine and chaconine produced pronounced synergistic effects in all three test systems. In beet cells, such effects were apparent from an early stage of treatment and persisted over a period of several hours. With erythrocytes and fungal protoplasts, the synergism was maximal with mixtures containing approximately 70% chaconine, whereas with beet cells it peaked at approximately 40% chaconine. Synergistic interactions between solanine and chaconine also occurred with regard to cholesterol binding in vitro, with a maximum response corresponding to the 50% mixture. The implications of these findings for the nature and efficacy of chemical defense systems in plants are discussed.