The cell surface receptor Tartan is a potential in vivo substrate for the receptor tyrosine phosphatase Ptp52F

Receptor-linked protein-tyrosine phosphatases (RPTPs) are essential regulators of axon guidance and synaptogenesis in Drosophila, but the signaling pathways in which they function are poorly defined. We identified the cell surface receptor Tartan (Trn) as a candidate substrate for the neuronal RPTP Ptp52F by using a modified two-hybrid screen with a substrate-trapping mutant of Ptp52F as "bait." Trn can bind to the Ptp52F substrate-trapping mutant in transfected Drosophila S2 cells if v-Src kinase, which phosphorylates Trn, is also expressed. Coexpression of wild-type Ptp52F causes dephosphorylation of v-Src-phosphorylated Trn. To examine the specificity of the interaction in vitro, we incubated Ptp52F-glutathione S-transferase (GST) fusion proteins with pervanadate-treated S2 cell lysates. Wild-type Ptp52F dephosphorylated Trn, as well as most other bands in the lysate. GST "pulldown" experiments demonstrated that the Ptp52F substrate-trapping mutant binds exclusively to phospho-Trn. Wild-type Ptp52F pulled down dephosphorylated Trn, suggesting that it forms a stable Ptp52F-Trn complex that persists after substrate dephosphorylation. To evaluate whether Trn and Ptp52F are part of the same pathway in vivo, we examined motor axon guidance in mutant embryos. trn and Ptp52F mutations produce identical phenotypes affecting the SNa motor nerve. The genes also display dosage-dependent interactions, suggesting that Ptp52F regulates Trn signaling in SNa motor neurons

Metal chloride cathode for a battery

A method of fabricating a rechargeable battery is disclosed which includes a positive electrode which contains a chloride of a selected metal when the electrode is in its active state. The improvement comprises fabricating the positive electrode by: providing a porous matrix composed of a metal; providing a solution of the chloride of the selected metal; and impregnating the matrix with the chloride from the solution

A rapid and convergent synthesis of the integrastatin core

The tetracyclic core of the integrastatin natural products has been prepared in a convergent and rapidmanner. Our strategy relies upon a palladium(II)-catalyzed oxidative cyclization to form the central [3.3.1]-dioxabicycle of the natural product core. Overall, the core has been completed in only 4 linear steps from known compounds

Copper chloride cathode for a secondary battery

Higher energy and power densities are achieved in a secondary battery based on molten sodium and a solid, ceramic separator such as a beta alumina and a molten catholyte such as sodium tetrachloroaluminate and a copper chloride cathode. The higher cell voltage of copper chloride provides higher energy densities and the higher power density results from increased conductivity resulting from formation of copper as discharge proceeds

Development of P-OP Ligands with New Structural Motifs for Rhodium- and Iridium- Mediated Asymmetric Hydrogenations

S’han dut a terme la síntesi de lligands enantiopurs fosfina-fosfit (P-OP) amb nous fragments fosfit i els corresponents estudis de coordinació amb precursors de rodi i iridi per hidrogenacions asimètriques. El complexes de tipus P-OP-rodi i iridi es van utilitzar eficientment a hidrogenacions asimètriques d’una sèrie diversa de substrats. Els lligands P-OP dissenyats es van sintetitzar mitjançant una ruta sintètica ben establerta pel grup d’investigació, que consisteix en l’apertura d’un epoxi-èter enantiopur de Sharpless amb un nucleòfil de fòsfor i la O-fosforilació del fosfino-alcohol resultant amb els electròfils de fòsfor corresponents (derivats de tipus clorofosfit). La ruta sintètica pels pre-catalitzadors més efectius a les transformacions hidrogenatives mediades per rodi es va optimitzar, desenvolupant una síntesi sense separacions cromatogràfiques, que implicava la cristal·lització dels pre-catalitzadors [Rh(P-OP)] desitjats com a mètode de purificació. Estudis sobre les hidrogenacions asimètriques utilitzant complexes [Ir(P-OP)] d’un conjunt de sistemes heterocíclics de set membres contenint la funció C=N va revelar que aquests complexes d’iridi són excel·lents catalitzadors (donant conversions completes i excessos enantiomèrics de fins el 97%). La enantioselectivitat d’aquest procés s’ha racionalitzat mitjançant càlculs teòrics DFT, que han identificat la posició del lligand-Cl a estructures catalíticament rellevants dels complexes d’iridi, així com també una sèrie d’interaccions no-covalents (per exemple interaccions N-H···Cl, C-H···π i C-H···H-Ir), que són els trets clau a l’hora de racionalitzar el resultat estereoquímic de les reaccions. Pel que fa a la hidrogenació d’alquens funcionalitzats, es van preparar pre-catalitzadors [Rh(P-OP)] que incorporen nous fragments fosfit. Es va assolir una alta activitat catalítica (conversió >99%) i enantioselectivitat excel·lent (fins a >97%) a les hidrogenacions asimètriques d’un conjunt d’alquens funcionalitzats amb lligands P-OP que incorporaven grups derivats del 3,3’-difenil-[1,1’-biaril]-2,2’-diol.Se ha estudiado la síntesis de ligandos enantiopuros fosfina-fosfito (P-OP) con nuevos fragmentos fosfito, así como sus propiedades de coordinación con precursores de rodio e iridio para hidrogenación asimétrica. Dichos complejos de rodio e iridio se han utilizado satisfactoriamente en hidrogenaciones enantioselectivas de un conjunto de sustratos con estructuras diversas. Los ligandos P-OP diseñados se sintetizaron mediante una ruta sintética establecida por el grupo de investigación, que consiste en la apertura de un epoxi-éter enantiopuro de tipo Sharpless con un nucleófilo de fósforo, y posterior O-fosforilación del fosfino-alcohol resultante con los correspondientes electrófilos de fósforo (derivados de tipo clorofosfito). La ruta sintética de los pre-catalizadores de rodio más eficientes para transformaciones hidrogenativas se optimizó a través de una síntesis sin separaciones cromatográficas, mediante la cristalización de los correspondientes pre-catalizadores como método de purificación. Estudios realizados en hidrogenación asimétrica sobre una variedad de heterociclos de siete miembros con enlaces C=N en su estructura revelaron que complejos de iridio derivados de ligandos P-OP son catalizadores excelentes, proporcionando conversiones completas y enantioselectividades elevadas (hasta 97% ee). La enantioselectividad de la reacción fue racionalizada mediante cálculos DFT, los cuales identificaron la posición del ligando cloro, así como una serie de interacciones no covalentes (por ejemplo N-H···Cl, C-H···π y C-H···H-Ir) en intermedios de iridio catalíticamente relevantes, como factores clave en la racionalización de los resultados. En lo que respecta a la hidrogenación de alquenos funcionalizados, pre-catalizadores de rodio incorporando nuevos fragmentos fosfito fueron evaluados, de los cuales aquellos derivados del grupo 3,3’-difenil-[1,1'-biaril]-2,2'-diol proporcionaron resultados excelentes tanto en términos de actividad catalítica (conversión >99%) como de enantioselectividad (>99% ee).he synthesis of enantiopure phosphine-phosphite (P-OP) ligands with new phosphite fragments and coordination studies with rhodium and iridium precursors for asymmetric hydrogenations have been performed. The resulting P-OP-rhodium and iridium complexes were efficiently employed in asymmetric hydrogenations of an array of structurally diverse substrates. The designed P-OP ligands were synthesized by a well-established synthetic route developed in the group, which comprised the ring-opening of an enantiopure Sharpless epoxy ether with a phosphorus nucleophile and the O-phosphorylation of the resulting phosphino alcohol with the corresponding phosphorus electrophiles (chlorophosphite derivatives). The synthetic route towards the highest performing pre-catalysts in rhodium-mediated hydrogenative transformations has been optimized by developing a chromatography-free synthesis involving the crystallization of the target [Rh(P-OP)] pre-catalysts as the purification method. Studies on [Ir(P-OP)]-mediated asymmetric hydrogenations of a variety of seven-membered heterocycles that contain C=N bonds have revealed that these iridium complexes are excellent catalysts (up to full conversion; up to 97% ee). The enantioselectivity has been rationalized by means of DFT calculations, which have identified the position of the Cl-ligand in catalytically relevant iridium structures and a number of non-covalent interactions (i.e. N-H···Cl, C-H…π and C-H···H-Ir interactions) as key features in the rationalization of the stereochemical outcome of the reactions. As regards the hydrogenation of functionalized alkenes, [Rh(P-OP)] pre-catalysts incorporating new phosphite fragments have been prepared. High catalytic activity (> 99% conversion) and excellent enantioselectivity (up to >99%) were achieved in asymmetric hydrogenations of a variety of functionalized alkenes by P-OP ligands incorporating 3,3’-diphenyl-[1,1'-biaryl]-2,2'-diol-derived phosphite groups

Organic cathode for a secondary battery

A liquid catholyte for a battery based on liquid metal such as sodium anode and a solid, ceramic separator such as beta alumina (BASE) comprises a mixture of a Group I-III metal salt such as sodium tetrachloroaluminate and a minor amount of an organic carbonitrile depolarizer having at least one adjacent ethylenic band such as 1 to 40 percent by weight of tetracyanoethylene. The tetracyanoethylene forms an adduct with the molten metal salt

Optimized Carbonate and Ester-Based Li-Ion Electrolytes

To maintain high conductivity in low temperatures, electrolyte co-solvents have been designed to have a high dielectric constant, low viscosity, adequate coordination behavior, and appropriate liquid ranges and salt solubilities. Electrolytes that contain ester-based co-solvents in large proportion (greater than 50 percent) and ethylene carbonate (EC) in small proportion (less than 20 percent) improve low-temperature performance in MCMB carbon-LiNiCoO2 lithium-ion cells. These co-solvents have been demonstrated to enhance performance, especially at temperatures down to 70 C. Low-viscosity, ester-based co-solvents were incorporated into multi-component electrolytes of the following composition: 1.0 M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + X (1:1:8 volume percent) [where X = methyl butyrate (MB), ethyl butyrate EB, methyl propionate (MP), or ethyl valerate (EV)]. These electrolyte formulations result in improved low-temperature performance of lithium-ion cells, with dramatic results at temperatures below 40 C

Improved Control of Charging Voltage for Li-Ion Battery

The protocol for charging a lithium-ion battery would be modified, according to a proposal, to compensate for the internal voltage drop (charging current internal resistance of the battery). The essence of the modification is to provide for measurement of the internal voltage drop and to increase the terminal-voltage setting by the amount of the internal voltage drop. Ordinarily, a lithium-ion battery is charged at constant current until its terminal voltage attains a set value equal to the nominal full-charge potential. The set value is chosen carefully so as not to exceed the lithium-plating potential, because plated lithium in metallic form constitutes a hazard. When the battery is charged at low temperature, the internal voltage drop is considerable because the electrical conductivity of the battery electrolyte is low at low temperature. Charging the battery at high current at any temperature also gives rise to a high internal voltage drop. In some cases, the internal voltage drop can be as high as 1 volt per cell. Because the voltage available for charging is less than the terminal voltage by the amount of the internal voltage drop, the battery is not fully charged (see figure), even when the terminal voltage reaches the set value. In the modified protocol, the charging current would be periodically interrupted so that the zero-current battery-terminal voltage indicative of the state of charge could be measured. The terminal voltage would also be measured at full charging current. The difference between the full-current and zero-current voltages would equal the internal voltage drop. The set value of terminal voltage would then be increased beyond the nominal full-charge potential by the amount of the internal voltage drop. This adjustment would be performed repeatedly, in real time, so that the voltage setting would track variations in the internal voltage drop to afford full charge without risk of lithium plating. If the charging current and voltage settings were controlled by a computer, then this method of charge control could readily be implemented in software

Ester-Based Electrolytes for Low-Temperature Li-Ion Cells

Electrolytes comprising LiPF6 dissolved at a concentration of 1.0 M in five different solvent mixtures of alkyl carbonates have been found to afford improved performance in rechargeable lithium-ion electrochemical cells at temperatures as low as -70 C. These and other electrolytes have been investigated in continuing research directed toward extending the lower limit of practical operating temperatures of Li-ion cells. This research at earlier stages, and the underlying physical and chemical principles, were reported in numerous previous NASA Tech Briefs articles, the most recent being Low-EC-Content Electrolytes for Low-Temperature Li-Ion Cells (NPO-30226), NASA Tech Briefs, Vol. 27, No. 1 (January 2003), page 46. The ingredients of the present solvent mixtures are ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl butyrate (MB), methyl propionate (MP), ethyl propionate (EP), ethyl butyrate (EB), and ethyl valerate (EV). In terms of volume proportions of these ingredients, the present solvent mixtures are 1EC + 1EMC + 8MB, 1EC + 1EMC + 8EB, 1EC + 1EMC + 8MP, 1EC + 1EMC + 8EV, and 1EC + 9EMC. These electrolytes were placed in Liion cells containing carbon anodes and LiNi0.8Co0.2O2 cathodes, and the low-temperature electrical performances of the cells were measured. The cells containing the MB and MP mixtures performed best

4-Vinyl-1,3-Dioxolane-2-One as an Additive for Li-Ion Cells

Electrolyte additive 4-vinyl-1,3-dioxolane-2-one has been found to be promising for rechargeable lithium-ion electrochemical cells. This and other additives, along with advanced electrolytes comprising solutions of LiPF6 in various mixtures of carbonate solvents, have been investigated in a continuing effort to improve the performances of rechargeable lithium-ion electrochemical cells, especially at low temperatures. In contrast to work by other researchers who have investigated the use of this additive to improve the high-temperature resilience of Li-ion cells, the current work involves the incorporation of 4-vinyl-1,3-dioxolane-2-one into quaternary carbonate electrolyte mixtures, previously optimized for low-temperature applications, resulting in improved low-temperature performance. The benefit afforded by 4-vinyl-1,3- dioxolane-2-one can be better understood in the light of relevant information from a number of prior NASA Tech Briefs articles about electrolytes and additives for such cells. To recapitulate: The loss of performance with decreasing temperature is attributable largely to a decrease of ionic conductivity and the increase in viscosity of the electrolyte. What is needed to extend the lower limit of operating temperature is a stable electrolyte solution with relatively small lowtemperature viscosity, a large electric permittivity, adequate coordination behavior, and appropriate ranges of solubilities of liquid and salt constituents. Whether the anode is made of graphitic or non-graphitic carbon, a film on the surface of the anode acts as a solid/electrolyte interface (SEI), the nature of which is critical to low-temperature performance. Desirably, the surface film should exert a chemically protective (passivating) effect on both the anode and the electrolyte, yet should remain conductive to lithium ions to facilitate intercalation and de-intercalation of the ions into and out of the carbon during discharging and charging, respectively. The additives investigated previously include alkyl pyrocarbonates. Those additives help to improve low-temperature performances by giving rise to the formation of SEIs having desired properties. The formation of the SEIs is believed to be facilitated by products (e.g., CO2) of the decomposition of these additives. These decomposition products are believed to react to form Li2CO3-based films on the carbon electrodes. The present additive, 4-vinyl-1,3-dioxolane-2-one, also helps to improve lowtemperature performance by contributing to the formation of SEIs having desired properties, but probably in a different manner: It is believed that, as part of the decomposition process, the compound polymerizes on the surfaces of carbon electrodes