Ionospheric ion upwelling in the wake of flux transfer events at the dayside magnetopause

The effects of flux transfer events (FTE) on the dayside auroral ionosphere are studied, using a simple twin-vortex model of induced ionospheric plasma flow. It is shown that the predicted and observed velocities of these flows are sufficient to drive nonthermal plasma in the F region, not only within the newly opened flux tube of the FTE, but also on the closed, or "old" open, field lines around it. In fact, with the expected poleward neutral wind, the plasma is more highly nonthermal on the flanks of, but outside, the open flux tube: EISCAT observations indicate that plasma is indeed driven into nonthermal distributions in these regions. The nonthermal plasma is thereby subject to additional upforce due to the resulting ion temperature anisotropy and transient expansion due to Joule heating and also to ion accelerations associated with the FTE field aligned current system. Any upflows produced on closed field lines in the vicinity of the FTE are effectively bunched-up in the "wake" of the FTE. Observations from the AMPTE-UKS satellite at the magnetopause reveal ion upflows of energy ∼100 eV flowing out from the ionosphere on closed field lines which are only found in the wake of the FTE. Such flows are also only found shortly after two, out of all the FTEs observed by AMPTE-UKS. The outflow from the ionosphere is two orders of magnitude greater than predicted for the "classical" polar wind. It is shown that such ionospheric ion flows are only expected in association with FTEs on the magnetopause which are well removed from the sub-solar point-either towards dusk or, as in the UKS example discussed here, towards dawn. It is suggested that such ionospheric ions will only be observed if the center of the FTE open flux tube passes very close to the satellite. Consequently, we conclude the ion upflows presented here are probably driven by the second of two possible source FTEs and are observed at the satellite with a lag after the FTE which is less than their time-of-flight.

An imaginary potential with universal normalization for dissipative processes in heavy-ion reactions

In this work we present new coupled channel calculations with the Sao Paulo potential (SPP) as the bare interaction, and an imaginary potential with system and energy independent normalization that has been developed to take into account dissipative processes in heavy-ion reactions. This imaginary potential is based on high-energy nucleon interaction in nuclear medium. Our theoretical predictions for energies up to approximate to 100 MeV/nucleon agree very well with the experimental data for the p, n + nucleus, (16)O + (27)Al, (16)O + (60)Ni, (58)Ni + (124)Sn, and weakly bound projectile (7)Li + (120)Sn systems. (C) 2008 Elsevier B.V. All rights reserved.

The sensitization of the ligand-field state of the hexaammineruthenium(II) complex ion by organic compounds

The sensitized photolysis of [Ru(NH3)(6)](2+) by the organic dye rhodamine B and biacetyl was studied under conditions in which only the sensitizer absorbs. The reaction products resulting from ammonia aquation and Ru(II) to Ru(III) oxidation are the same for direct and sensitized photolysis. The energy transfer rate constant, calculated from the fluorescence quenching of rhodamine B, is similar to that estimated from the limiting quantum yield of the photosensitized photoaquation of the complex. Both reactions originate from a common reactive low-lying ligand-field (LF) state, which is also responsible for the direct photolysis reactions. This state, which leads directly to photoaquation, seems to have a certain charge transfer to solvent (CTTS) character, which is responsible for the photo-oxidation products. Sensitization is effective with rhodamine B (17 450 cm(-1)) and biacetyl (19 000 cm(-1)), whereas no reaction is observed with neutral red (16 900 cm(-1)). These results show that the excited state responsible for the photochemical reactions lies in the energy range between 16 900 cm(-1) and 17 700 cm(-1) and possesses spin-orbit character.

Ligand-rare-earth ion energy transfer in coordination compounds. A theoretical approach

A theoretical approach to the energy transfer process that occurs between a ligand and a rare-earth ion in luminescent complexes is presented. A discussion on the energy transfer mechanisms involved and on the associated selection rules is made. Numerical estimates are also presented.

Kinetic aspects of ion exchange in KhFek[Fe(CN)(6)](l)center dot mH(2)O compounds: A combined electrical and mass transfer functions approach

The present paper quantifies and develops the kinetic aspects involved in the mechanism of interplay between electron and ions presented elsewhere(1) for KhFek[Fe(CN)(6)](l)center dot mH(2)O (Prussian Blue) host materials. Accordingly, there are three different electrochemical processes involved in the PB host materials: H3O+, K+, and H+ insertion/extraction mechanisms which here were fully kinetically studied by means of the use of combined electronic and mass transfer functions as a tool to separate all the processes. The use of combined electronic and mass transfer functions was very important to validate and confirm the proposed mechanism. This mechanism allows the electrochemical and chemical processes involved in the KhFek[Fe(CN)(6)](l)center dot mH(2)O host and Prussian Blue derivatives to be understood. In addition, a formalism was also developed to consider superficial oxygen reduction. From the analysis of the kinetic processes involved in the model, it was possible to demonstrate that the processes associated with K+ and H+ exchanges are reversible whereas the H3O+ insertion process was shown not to present a reversible pattern. This irreversible pattern is very peculiar and was shown to be related to the catalytic proton reduction reaction. Furthermore, from the model, it was possible to calculate the number density of available sites for each intercalation/deintercalation processes and infer that they are very similar for K+ and H+. Hence, the high prominence of the K+ exchange observed in the voltammetric responses has a kinetic origin and is not related to the amount of sites available for intercalation/deintercalation of the ions.

Low-weight coordination polymers derived from the self-assembly reactions of Pd(II) pyrazolyl compounds and azide ion

The low-weight Pd(II) coordination polymers [(N(3))(HL)Pd {Pd(3)(mu-N(3))(mu-L)(5)}10(mu-L)(2)Pd(L)(HL)]{L = Pz(-) (1); mPz(-) (2), IPz(-)(3)} and [(N(3))(HPz)Pd{Pd(6)(mu-N(3))(2)(mu-PZ)(5)(mu-L)(5)}(10)(mu-L)(2)Pd(Pz)(HPz)] {L = mPz(-) (4), dmPz(-) (5); IPz(-) (6)} {L = pyrazolate (Pz(-)), 4-methylpyrazolate(mPz(-)), 4-iodopyrazo late (IPz(-)), 3,5-dimethylpyrazolate (dmPz(-))} have been prepared in this work. IR spectra clearly indicated the exobidentate nature of pyrazolato ligands as well the end-on coordination mode of the azido group. The molecular weight determinations by osmometry indicated that the species have a low degree of polymerization (n = 10). NMR experiments showed two pyrazolate environments in a 2:1 ratio, being assigned to the six-membered ring Pd(mu-L)(2)Pd and the Pd(mu-N(3))(mu-L)Pd metallocycle, respectively. UV-visible spectroscopy gave further evidences for the oligomeric structures of 1-6. Some alternative structures for the isostructural polymers have been suggested. (c) 2005 Elsevier Ltd. All rights reserved.

New insights on reaction pathway selectivity promoted by crown ether phase-transfer catalysis: Model ab initio calculations of nucleophilic fluorination

Crown ethers have the ability of solubilizing inorganic salts in apolar solvents and to promote chemical reactions by phase-transfer catalysis. However, details on how crown ethers catalyze ionic S(N)2 reactions and control selectivity are not well understood. In this work, we have used high level theoretical calculations to shed light on the details of phase-transfer catalysis mechanism of KF reaction with alkyl halides promoted by 18-crown-6. A complete analysis of the of the model reaction between KF(18-crown-6) and ethyl bromide reveals that the calculations can accurately predict the product ratio and the overall kinetics. Our results point out the importance of the K* ion and of the crown ether ring in determining product selectivity. While the K* ion favors the S(N)2 over the E2 anti pathway, the crown ether ring favors the S(N)2 over E2 syn route. The combination effects lead to a predicted 94% for the S(N)2 pathway in excellent agreement with the experimental value of 92%. A detailed analysis of the overall mechanism of the reaction under phase-transfer conditions also reveals that the KBr product generated in the nucleophilic fluorination acts as an inhibitor of the 18-crown-6 catalyst and it is responsible for the observed slow reaction rate. (C) 2012 Elsevier B.V. All rights reserved.

Developments in target-ion source chemistry for ISOL facilities

This work investigates the influence of chemical reactions on the release of elements from target-ion source units for ISOL facilities. Methods employed are thermochromatography, yield and hold-up time measurements; adsorption enthalpies have been determined for Ag and In. The results obtained with these methods are consistent. Elements exhibit reversible or irreversible reactions on different surfaces (Tantalum, quartz, sapphire). The interactions with surfaces inside the target-ion source unit can be used to improve the quality of radioactive ion beams. Spectroscopic data obtained at CERN-ISOLDE using a medium-temperature quartz transfer line show the effectivity of selective adsorption for beam purification. New gamma lines of 131Cd have been observed and a tentative decay scheme is presented.

Beyond simple proton transfer processes: domino reactions between 4-substituted indoles and nitroethene as a new gateway to ergot alkaloids

The multimodal biology activity of ergot alkaloids is known by humankind since middle ages. Synthetically modified ergot alkaloids are used for the treatment of various medical conditions. Despite the great progress in organic syntheses, the total synthesis of ergot alkaloids remains a great challenge due to the complexity of their polycyclic structure with multiple stereogenic centres. This project has developed a new domino reaction between indoles bearing a Michael acceptor at the 4 position and nitroethene, leading to potential ergot alkaloid precursors in highly enantioenriched form. The reaction was optimised and applied to a large variety of substrate with good results. Even if unfortunately all attempts to further modify the obtained polycyclic structure failed, it was found a reaction able to produce the diastereoisomer of the polycyclic product in excellent yields. The compounds synthetized were characterized by NMR and ESIMS analysis confirming the structure and their enantiomeric excess was determined by chiral stationary phase HPLC. The mechanism of the reaction was evaluated by DFT calculations, showing the formation of a key bicoordinated nitronate intermediate, and fully accounting for the results observed with all substrates. The relative and absolute configuration of the adducts were determined by a combination of NMR, ECD and computational methods.

Doubly charged ion mass spectra of alkyl-substituted furans and pyrroles

Doubly charged ion mass spectra of alkyl-substituted furans and pyrroles were obtained using a double-focusing magnetic mass spectrometer operated at 3.2 kV accelerating voltage. Molecular ions were the dominant species found in doubly charged spectra of lower molecular weight heterocydic compounds, whereas the spectra of the higher weight homologues were typified by abundant fragment ions from extensive decomposition. Measured doubly charged ionization and appearance energies ranged from 22.8 to 47.9 eV. Ionization energies were correlated with values calculated using self-consistent field–molecular orbital techniques. A multichannel diabatic curve-crossing model was developed to investigate the fundamental organic ion reactions responsible for development of doubly charged ion mass spectra. Probabilities for Landau–Zener type transitions between reactant and product curves were determined and used in the collision model to predict charge-transfer cross-sections, which compared favorably with experimental cross-sections obtained using time-of-flight techniques.

The Synthesis of Macrocyclic Polystyrene by Sequential Atom Transfer Radical Reactions

A method for the production of macrocyclic polystyrene via ring closing of a linear !,"-dibrominated polystyrene by an Atom Transfer Radical Coupling (ATRC) reaction is described. The dibrominated polystyrene chain was produced from two simultaneous atom transfer radical polymerizations (ATRPs) originating from a dibrominated benzal bromide initiator. To ensure the retention of the halogen end groups polymerization was allowed to proceed to less than 50% conversion. Using this precursor in an intramolecular ATRC (ring closing) reaction was found to yield in excess of 90% cyclic product based on refractive index-gel permeation chromatography (GPC) analysis. The cyclic architecture of the polymer was verified by GPC, Nuclear Magnetic Resonance (NMR), and mass spectrometry analysis. The utility of this method has been expanded by the addition of 2-methyl-2-nitrosopropane to the coupling reaction, which allows for the coupling to proceed at a faster rate and to yield macrocycles with incorporated alkoxyamine functionality. The alkoxyamine functionality allows for degradation of the cycles at high temperatures (>125° C) and we hypothesize that it may allow the macrocycles to act as a macroinitiator for a ring expansion polymerization in future studies.

Gold Phosphonates as Transfer Agents in Palladium Catalyzed Hirao Reactions

Through a cross-coupling reaction, aryl phosphonates are produced in high yields when the corresponding aryl bromides are reacted with a gold phosphorylating agent in the presence of a palladium catalyst and an appropriate ligand. To the best of our knowledge, this transformation is the first example involving the transfer of a phosphonate functional group from a gold complex to palladium that has been reported. Throughout the investigation, three gold phosphorylating agents were screened for activity towards the phosphorylation of aryl bromides. Aryl bromides with electrondonating and electron-withdrawing groups were successfully employed in the crosscoupling reactions. All cross-coupling reactions were carried out in THF at room temperature (25ºC) or in a microwave reactor (CEM Discover) at 60ºC for 30 or 60 minutes. The effects of changing reaction parameters such as time, temperature, catalyst and free ligand loading have been investigated. All aryl bromide substrates tested in the cross-coupling reactions produced phosphorylated products.

Electrogenic light reactions in photosystem I: resolution of electron-transfer rates between the iron-sulfur centers.

Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 micros to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and acceptors, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 micros) increase, ascribed to electron transfer from the primary electron donor P700 to the iron-sulfur electron acceptor FB, was followed by a slower, biphasic increase with time constants of 30 and 200 micros. The 30-micros phase is assigned to electron transfer from FB to the iron-sulfur center FA. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from FA to P700. Upon chemical prereduction of FA and FB the 30- and 200-micros phases disappeared and the decay time constant was accelerated to 330 micros, assigned to charge recombination from the phylloquinone electron acceptor (A1) or the iron-sulfur center FX to P700.

The chemistry of British bituminous coals : an assessment of phase transfer catalysed reactions in the determination of coal structure

Three British bituminous coals, (Gedling, Cresswell, and Cortonwood Silkstone) were selected for study. Procedures were developed, using phase transfer catalysts (PTC's), to degrade the solvent insoluble fractions of the coals. PTC's are of interest because they have the potential to bring about selective high conversion reactions, under mild conditions, (often in the past, severe reaction conditions have had to be used to degrade the coals, this in turn resulted in the loss of much of the structural information). We have applied a variety of physical and chemical techniques to maximise the amount of structural information, these include, elemental analysis, 1H-NMR, 13C-CPMAS-NMR, GPC, GC-MS, FTIR spectroscopy, DRIFT spectroscopy, and gas adsorption measurements. The main conclusions from the work are listed below:- ( 1 ) PTC O-methylation; This reaction removes hydrogen bonds within the coal matrix by 'capping' the phenolic groups. It was found that the polymer-like matrix could be made more flexible, but not significantly more soluble, by O-methylation. I.E. the trapped or 'mobile' phase of the coals could be removed at a faster rate after this reaction had been carried out. ( 2 ) PTC Reductive and Acidic Ether Cleavage; The three coals were found to contain insignificant amounts of dialkyl and alkyl aryl ethers. The number of diaryl ethers could not be estimated, by reductive ether cleavage, (even though a high proportion of all three coals was solublised). The majority of the ethers present in the coals were inert to both cleavage methods, and are therefore assumed to be heterocyclic ethers. ( 3 ) Trif!uoroperacetic Acid Oxidation; This oxidant was used to study the aliphatic portions of the polymer-like macromolecular matrix of the coals. Normally this reagent will only solublise low rank coals, we however have developed a method whereby trifluoroperacetic acid can be used to degrade high rank bituminous coals. ( 4 ) PTC/Permanganate Oxidation; This reagent has been found to be much more selective than the traditional alkaline permanganate oxidation, with a lot more structural information being retained within the various fractions. This degradative method therefore has the potential of yielding new information about the molecular structure of coals.