Synthesis of ROMP Monomers Containing Metal–Metal Bonds

Methods for the synthesis of cyclic monomers that have both metal–metal bonds and carbon–carbon double bonds are reported. Ring opening metathesis polymerization (ROMP) of these monomers would yield polymers that are photochemically degradable. The first method investigated involved substitution of Cp₂Fe₂(CO)₄ by the bidentate phosphine ligand DPPEN (Ph₂P CH=CH–PPh₂). Cp₂Fe₂(CO)₂( -DPPEN) was synthesized and the X-ray crystal structure is reported but the molecule could not be polymerized by a ROMP method using Grubbs’s catalyst. The inability of this monomer to polymerize (or copolymerize with cyclooctatetraene) was attributed to the bulky phenyl rings being in close proximity to the C=C in the DPPEN ligand, which prevents coordination of the monomer to the catalyst. To decrease the steric interactions, the DPPBN ligand was synthesized (DPPBN=Ph CH CH=CH CH PPh₂). However, the reaction of DPPBN with Cp₂Fe₂(CO)₄ yielded the product Cp₂Fe₂(CO)₂( -1,2,4-triphos), where the 1,2,4-triphos ligand is a tridentate ligand formed by the formal additional of Ph₂PH to DPPBN (1,2,4-triphos=Ph CH CH(PPh₂) CH CH PPh₂). An X-ray structure of the Cp₂Fe₂(CO)₂( -1,2,4-triphos) complex revealed that the 1,2,4-triphos ligand chelates exclusively through the two phosphorus atoms that are bridged by two carbon atoms. It is suggested that this structural feature may simply reflect the increased stability of the 6-membered ring over the 7- and 8-membered rings. The reactions of the Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ dimers with DPPBN were investigated next. Reactions of Cp₂Mo₂(CO)₆ and Cp₂Mo₂(CO)₄ with the DPPEN and DPPBN ligands resulted in the disproportionation of the dimers. The X-ray crystal structure of [CpMo(CO)₂(DPPEN)][CpMo(CO)₃] was determined and is reported. The CpMo(CO)(DPPEN)Cl complex was formed when these same reactions were carried out in the presence of CH₂Cl₂. The X-ray crystal structure of this molecule is also reported.     

Organometallic Coordination Networks Based on \uppi-Bonded Transition Metal Quinonoid Complexes

Hydroquinones -bonded to the transition metal fragments Mn(CO) , Rh(COD)⁺, and Rh[P(OPh)₃]₂⁺ are readily deprotonated to afford anionic -quinone complexes that function as organometalloligands by binding to metal ions through the quinone oxygen atoms. The resulting supramolecular assemblies display a variety of interesting and potentially useful network topologies. An erratum to this article can be found at     

Tapered ZnO Whiskers: {hkil}-Specific Mosaic Twinning VLS Growth from a Partially Molten Bottom Source

Zn particulates overlaid with wurtzite (W)-type ZnO condensates having nearly orthogonal and facets were found to self-catalyze unusual tapered W-ZnO whiskers upon isothermal atmospheric annealing, i.e., thermal oxidation, at 600 °C. Analytical electron microscopic observations indicated that such whiskers formed tapered slabs having mosaic and twinned domains. The tapered whiskers can be rationalized by an alternative vapor–liquid–solid growth, i.e., {hkil}-specific coalescence twinning growth from the ZnO condensates taking advantage of a partially molten bottom source of Zn and the adsorption of atoms at the whisker tips and ledges under the influence of capillarity effect. The tapered whiskers having strong photoluminescence at 391 nm and with a considerable flexibility could have potential applications.     

Electrochemical redox reactions of chromium and iron ions in molten NaCl–2CsCl eutectic for pyro-reprocessing of nuclear fuels

Basic electrochemical and spectroscopic properties of Cr³⁺, Cr²⁺, Fe³⁺, and Fe²⁺ were studied to analyze the cyclic redox reactions of Cr and Fe, which may decrease the current efficiency of the electro-winning method using NaCl–2CsCl melts. The formal redox potentials of the and couples, and , in NaCl–2CsCl melts at 923 K were spectroelectrochemically determined to be −0.648 ± 0.005 V and , respectively. These values were determined by measuring electromotive force and UV–VIS absorption spectra at varying concentration ratios of trivalent and divalent ions. Cyclic voltammetry was also carried out to examine the characteristics of the voltammograms for the and couples in NaCl–2CsCl melts. The determined by the spectroelectrochemical method was close to that determined by cyclic voltammetry . The effect of temperature on the in NaCl–2CsCl melts was studied by cyclic voltammetry in the range from 823 to 1,023 K . Diffusion coefficients of Cr³⁺ and Cr²⁺, and , were determined between 823 and 1,023 K to be and , respectively. Molar absorptivities of Cr³⁺ and Cr²⁺ in NaCl–2CsCl melts at 923 K were determined to be 77.8 ± 2.4 M⁻¹ cm⁻¹ at 17,670 cm⁻¹ and 48.0 ± 1.4 M⁻¹ cm⁻¹ at 9,170 cm⁻¹, respectively. In addition, the effects of these ions on the cyclic redox reaction of the pyro-reprocessing process were discussed.     

Ferrocenyl Monomers and Polymers of <Emphasis Type="Italic">N</Emphasis>-Allyl and <Emphasis Type="Italic">N</Emphasis>-Acrylatenaphthalimides

A series of N-allyl, N-ethylmethacrylate and N-phenylmethacrylatenaphthalimide monomers have been prepared with –C=CFc, –C≡CFc and –C≡CSiMe₃ substituents at the 4-position of the naphthalimide ring. All have been characterised by elemental analysis and spectroscopy; the X-ray structure of N-allyl-4-ethenylferrocenylnapththalimide is also reported. Free-radical polymerisation of these monomers gave homopolymers, random co- and terpolymers with polydispersities ranging from 1.7 to 3.2. Incorporation into a polymer matrix has no effect on the spectroscopic and electrochemical properties of the naphthalimide or ferrocenyl components. The ferrocenyl polymers are electrochromic and when oxidised give naphthalimide charge-transfer bands in the NIR; this electrochromism was examined by OTTLE techniques.     

Controlling Reaction Pathways for Alcohol Dehydration and Dehydrogenation over FeSBA-15 Catalysts

The iron location in FeSBA-15 strongly influences the selectivity to dehydrogenation and dehydration in ethanol conversion. At low iron loading, Fe is present as isolated $\hbox{Fe}^{3+}The iron location in FeSBA-15 strongly influences the selectivity to dehydrogenation and dehydration in ethanol conversion. At low iron loading, Fe is present as isolated species in the amorphous silica phase. At higher loading additional aggregated forms of iron oxide exist. Isolated species in the silica matrix imply Br?nsted acidity resulting in selective formation of ethylene, whereas clusters catalyze formation of ethylene and aldehyde.     

Ceramic Precursor Aluminum-Containing Polycarbosilane: Preparation and Structure

The aluminum-containing polycarbosilane (Al-PCS) with various quantities of aluminum was obtained by adding aluminium acetylacetonate (Al(AcAc)₃) as an aluminum source to polysilacarbosilane (PSCS). Subsequently, thermal decomposition and condensation at various conditions were carried out. The molecular weight distribution, yield and softening point of the resulting Al-PCS differ with the Al(AcAc)₃:PSCS weight ratio, the thermolysis temperature and the reaction time. The larger the Al(AcAc)₃:PSCS weight ratio, the higher the thermolysis temperature and the longer the reaction time, the greater the yield and softening point of Al-PCS. In addition, the oxygen and aluminum contents of Al-PCS increase at higher Al(AcAc)₃:PSCS weight ratios. As the mixing weight ratio of Al(AcAc)₃:PSCS increased, additional oxygen was introduced into Al-PCS with the increased Al content. The structure of Al-PCS was characterized by the FT-IR. These results show that Al-PCS is very similar to polycarbosilane in structure.     

Electrochemical behavior of AZ91D magnesium alloy in phosphate medium: Part II. Induced passivation

Induced passivation of AZ91D magnesium alloy in phosphate solution was carried out both chemically, using various inorganic oxidants, namely, molybdate, vanadate and iodate, as well as electrochemically by anodizing the alloy under various controlled overpotentials within the range 0.1–3.4 V. In acidic phosphate (pH 4.5), molybdate and vanadate anions exhibit similar behavior, as they show a dissolution effect at lower concentrations and passivation at higher concentrations. On the other hand, iodate anions shows critical behavior with a passivation effect up to 0.1 mM and depassivation for higher concentrations. Generally, over the concentration domain (0.01–1.0 mM) the results reveal small inhibitive effects with maximum values of 19.7% for and 24–25% for and manifesting weak propensities for these inorganic species to enhance the corrosion resistance of AZ91D alloy in acidic phosphate medium. The effect of anodic potential on the characteristics of surface films formed on the alloy in alkaline phosphate solution (pH 11.9) indicates that higher forming overpotential induces better passivation due to the formation of rather thicker and more resistive anodic films. The stability of the films is greater in alkaline as compared to acidic phosphate solutions.     

Effects of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles on the electrodeposition of Zn,Co and ZnCo. I. Electrodeposition in the absence of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electrodeposition of Zn, Co and ZnCo from acid sulfate solutions onto steel was investigated in this first part of a study of the effects of SiC or Al₂O₃ particles on these processes and the formation of ZnCo–SiC and ZnCo–Al₂O₃ electrocomposites. Zn electrodeposition shows a well-defined pre-bulk region, where the hydrogen evolution reaction (HER) and Zn underpotential deposition (upd) compete. Zn bulk electrodeposition begins with primary nucleation and diffusion-controlled growth, strongly dependent on conditions favoring previous Zn upd against HER. It is assumed that this first bulk process takes place over the upd Zn. Zn bulk electrodeposition is followed by secondary nucleation and growth. Co electrodeposition begins with a slow reduction in parallel with HER, followed by a faster reduction. strongly hinders the initial reduction. The ZnCo and Zn electrodeposition curves are initially similar, retaining features of pre-bulk and bulk Zn electrodeposition.     

Differentiation of Competitive vs. Non-competitive Mechanisms Mediating Disruption of Moth Sexual Communication by Point Sources of Sex Pheromone (Part 2): Case Studies

Eleven out of 13 disruption profiles (plots of dispenser density vs. male catch) from moth sex pheromone literature were consistent with a competitive-attraction mechanism, in which dispensers attract males and thereby divert them from females. Mean dispenser activity (D _a) across all competitive-attraction cases was 0.04 ± 0.06 (SD); values ranged from 0.0005 for a tiny laminated flake dispenser of racemic disparlure targeting gypsy moth to 0.2 for polyethylene tube dispensers used against lightbrown apple moth. A dispenser application activity () can be calculated by multiplying D _a by the number of such dispensers applied per hectare of crop. The highest dispenser application activity () values approached 200 and corresponded to >99% inhibition of catches of male moths in monitoring traps. Relative to the scale, % inhibition of catches of male moths compressed and obscured large differences in when % disruption exceeded 90%. For cases of competitive attraction, these two efficacy scales can be interconverted by using the formula: . When disruptive point sources of pheromone were directly observed, male moths were seen approaching pheromone dispensers whose disruption profiles matched competitive attraction. Two cases fit non-competitive disruption mechanisms, which include camouflage, desensitization (adaptation and/or habituation), and sensory imbalance. In these cases, pheromone was released at rates higher than for cases of disruption by competitive attraction. Practical ramifications of the finding that competitive attraction appears to be the prevalent mechanism for moth mating disruption by pheromone point sources are listed. We believe that the congruence of diverse sets of mating disruption field data with explicit a priori predictions validates competitive-attraction theory. The analytical tools and principles governing competitive attraction that were uncovered during this study of mating disruption of moths should be generally applicable to competitive-attraction phenomena.     

N2O and NO emissions from different N sources and under a range of soil water contents

Emissions of nitrous oxide (N₂O) and nitric oxide (NO) have been identified as one of the most important sources of atmospheric pollution from grasslands. Soils are major sources for the production of N₂O and NO, which are by-products or intermediate products of microbial nitrification and denitrification processes. Some studies have tried to evaluate the importance of denitrification or nitrification in the formation of N₂O or NO but there are few that have considered emissions of both gases as affected by a wide range of different factors. In this study, the importance of a number of factors (soil moisture, fertiliser type and temperature) was determined for N₂O and NO emissions. Nitrous oxide and NO evolution in time and the possibility of using the ratio NO:N₂O as an indicator for the processes involved were also explored. Dinitrogen (N₂) and ammonia (NH₃) emissions were estimated and a mass balance for N fluxes was performed. Nitrous oxide and NO were produced by nitrification and denitrification in soils fertilised with and by denitrification in soils fertilised with . Water content in the soil was the most important factor affecting N₂O and NO emissions. Our N₂O and NO data were fitted to quadratic (r=0.8) and negative exponential (r=0.7) equations, respectively. A long lag phase was observed for the N₂O emitted from soils fertilised with (denitrification), which was not observed for the soils fertilised with (nitrification) and was possibly due to a greater inhibiting effect of low temperatures on microbial activity controlling denitrification rather than on nitrification. The use of the NO:N₂O ratio as a possible indicator of denitrification or nitrification in the formation of N₂O and NO was discounted for soils fertilised with . The N mass balance indicated that about 50 kg N ha⁻¹ was immobilised by microorganisms and/or taken up by plant roots, and that most of the losses ocurred in wet soils (WFPS >60%) as N₂ and NH₃ losses (>55%).     

Thermodynamic and kinetic aspects of the electron transfer reaction of bovine cytochrome c immobilized on 4-mercaptopyridine and 11-mercapto-1-undecanoic acid films

Bovine cytochrome c (cyt c) was adsorbed on a polycrystalline gold electrode coated with 4-mercaptopyridine and 11-mercapto-1-undecanoic acid self-assembled monolayers (SAMs) and the thermodynamics and kinetics of the heterogeneous protein-electrode electron transfer (ET) reaction were determined by cyclic voltammetry. The E°′ values for the immobilized protein were found to be lower than those for the corresponding diffusing species. The thermodynamic parameters for protein reduction ( and ) indicate that the stabilization of the ferric state due to protein–SAM interaction is enthalpic in origin. The kinetic data suggest that a tunneling mechanism is involved in the ET reaction: the distance between the redox center of the protein and the electrode surface can be efficiently evaluated using the Marcus equation.     

Some applications of viscometry from studies on the absorption of vegetable oils and solvents by paper substrates

In previous studies on the drying performance of oleoresinous and solvent-based offset lithographic printing inks, a test was devised to determine the rate of absorption of drops of vegetable oils and solvents deposited on the surface of a paper substrate. The influence of viscosity on the rate of horizontal capillary absorption indicated a potential use of the absorption data to predict viscosity in the oxidative polymerization of polyunsaturated vegetable oils. Volumes as low as 1.0 mL could be used in thermal oxidative polymerization studies and tested by the Drop Deposition method. The stain radii R _s of absorbed drops of the oil, e.g., on blotting paper or filter paper substrates, follow a linear relationship with the square root of time (  s) and the slopes m of the R _s vs graphs are converted to dynamic viscosity in dPa.s units using a modified form of the Lucas Washburn equation from which . The study has implications for assessing the stability of vegetable oils used in frying operations. The test method may also be used in the study of room temperature oxidative polymerization of polyunsaturated vegetable oils to evaluate drier catalysts used in surface coatings. An erratum to this article can be found at     

Molecular weight averages as criteria for quality assessment of heated oils and fats

A simple method for quality assessment of heated oils and fats is described. The proposed method involves precise determination of molecular weight averages (MWA)viz., the weight average molecular weight ( ), the number average molecular weight ( ) and the Z-average molecular weight ( ) by high performance size exclusion chromatography (HPSEC) and their quantitative correlation to percent polar material obtained by column chromatography (CC). Change in MWA on heat treatment of fourteen different edible oils and fats at 180° ± 2°C for eight 8-hr days is studied. Relative standard deviations and regression coefficients of correlation between MWA and their ratios ( , { }, { }, { }, { } and { )vs percent polar material have been reported. Probable discard time was predicted for all the oils based on the above-mentioned correlations and also from the percent of high molecular weight (H. Mwt) species formed. It was observed that the oils which are generally recommended for coronary patients deteriorated faster. A possibility of extending this methodology to the frying oils is suggested. Part of the work was presented at “40th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy” at Georgia World Congress Centre, USA, 1989. IICT Communication No. 2630.     

Electrocatalytic activity of copper alloys for \hbox{NO}_{3}^{-} reduction in a weakly alkaline solution Part 1: Copper–zinc

A comparative study of the influence of an addition of Zn to Cu as the basic cathode material on electrocatalytic activity for reduction was performed. Potentiodynamic measurements using a rotating ring-disk electrode were carried out in an artificial solution simulating solution after regeneration of the ion-exchange column for removal in drinking water treatment. The results were verified by batch electrolysis experiments. An enhancement of the electrocatalytic activity was observed. Unfortunately, NH₃ was found to be the main reduction product. The highest electrocatalytic activity was obtained using an electrode containing 41 wt.% Zn.     

Stimulus Responsive Poly(ferrocenylsilanes): Redox Chemistry of Iron in the Main Chain

Redox chemistry of organometallic poly(ferrocenylsilane) polymers (soluble in organic or aqueous environment) is discussed. Poly(ferrocenyldimethylsilane) (PFDMS) was oxidized in CH₂Cl₂ solution with different oxidants. Oxidation was accomplished with stepwise increasing amounts of ferric chloride (FeCl₃), iodine (I₂) and tris(4-bromophenyl)ammoniumyl hexachloroantimonate ( ). The process was followed by UV–visible spectroscopy. Mixed-valence salts with different Fe(III)/Fe(II) ratios were obtained. The oxidation products were characterized by Mössbauer spectroscopy, which proved to be a very valuable tool to analyze mixed valence ferrocenyl compounds. Mössbauer analysis demonstrated that 100% oxidation could be achieved with TBPA^{· +}. Decamethylferrocene (DMFC) was found to be a suitable reducing agent for the oxidized polymer. The reduction process was monitored by UV–visible spectroscopy. The polymer was characterized by gel permeation chromatography (GPC) following the oxidation/reduction cycle and evidence of some fragmentation of the chains was observed. A water-soluble PFS polycation was successfully oxidized with FeCl₃ for pH values between 4 and 5. Ascorbic acid (vitamin C) was found to completely reduce the oxidized water-soluble polymer.     

Intrinsic viscosity-number average molecular weight relationship for poly (n-Octadecyl acrylate) and poly (N-n-octadecylacrylamide)

Intrinsic viscosity-number average molecular weight relationships have been measured, at 30C in benzene, for poly (n-octadecyl acrylate) as [η]=2.72×10⁻⁴ Mn^0.638 and for poly (N-n-octadecylacrylamide) as [η]=0.82×10⁻⁴ Mn^0.676. Whole polymers of various molecular weights were prepared in benzene solution at 65C with dodecyl mercaptan as primary regulator. By the use of these parameters, the molecular weight of such polymers and their homologs may now be measured by simple solution-viscosity determinations. In the expression { } (relating degrees of polymerization { } to the mercaptan/monomer ratio), intercept { } and apparent transfer constant C_s for n-octadecyl acrylate were 6.28×10⁻³ and 0.68; for N-n-octadecylacrylamide 1.10×10⁻³ and 0.62 respectively. These parameters permit preparation of homopolymers of chosen molecular weight. Presented at the AOCS Meeting, Philadelphia, October 1966 E. Utiliz. Res. Devel. Div., ARS, USDA.     

Lack of increased availability of root-derived C may explain the low N2O emission from low N-urine patches

Urine deposition on grassland causes significant N₂O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in ¹³C- labelled grassland monoliths to investigate the link between N₂O production and carbon mineralization following application of low rates of urine-N. Measurements of N₂O and CO₂ emissions from the monoliths as well as C signal of evolved CO₂ were done on day −4, −1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m⁻² in the first and second experiment, respectively. The C signal was also determined for soil organic matter, dissolved organic C and CO₂ evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day −1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N₂O flux, which was generally low (−8 to g N₂O-N m⁻² h⁻¹). After the second application event, the N₂O emission increased significantly to g N₂O-N m⁻² h⁻¹ and the N₂O emission factor for the added urine-N was 0.18%. However, the associated ¹³C signal of soil respiration was unaffected by urine. Consequently, the increased N₂O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots.     

The titanium/hydrogen system as the solid-state reference in high-temperature proton conductor-based hydrogen sensors

It has been demonstrated that a mixture of the solid solutions of hydrogen in -titanium and -titanium may be applied as a solid-state hydrogen reference electrode in conjunction with the high-temperature proton-conducting solid electrolyte . The design and preparation of a sensor that incorporates this type of reference electrode are described, and coulometric titration experiments as well as cell voltage measurements are presented and discussed. The activity of the residual oxygen in the reference material has been identified as a critical parameter that needs to be controlled in order to ensure reliable and reproducible sensor performance. The impact of other impurities in the reference material is also considered.     

The inhibition of copper–nickel alloy corrosion under controlled hydrodynamic condition in seawater

A comparative study of the corrosion resistance of a bare Cu–10 Ni alloy and a Cu–10 Ni alloy protected by sodium-diethyl-dithiocarbamate (NaEt₂dtc) has been undertaken. The experimental conditions varied from quiescent natural seawater to seawater subjected to jet impingement of different fluid velocities. The mechanism of inhibitor action has been suggested that includes the formation of a surface chelate compound between the dissolving metal ion and the (Et₂dtc)⁻ ligand, as well as formation of a 3-D ternary surface complex. The surface layer that incorporates both the inhibitor and the cuprous oxide, represented by the structure: has shown an excellent protective performance with efficiency > 90% under stagnant and fluid impingement conditions.