Comparison of Cu(II)-Promoted Leaving Group Stabilization of the Cleavage of a Homologous Set of Phosphate Mono-, Di-, and Triesters in Water,Methanol

Studies of systems incorporating metal ions that provide leaving group assistance (LGA) in the reactions of small molecules is documented in only a few cases. Herein they reported on an expanded study where the reaction medium changes from methanol to both ethanol and water, how these solvents affect the reaction mechanisms, and the acceleration provided by LGA.The cleavage of a set of phosphate mono-, di-, and triesters having a Cu(II)-complexed 2-phenanthrolyl group at the ortho-position of a departing phenoxide was studied in water and ethanol. Experimentally observed pH/rate profiles, solvent deuterium kinetic isotope effects, and activation parameters are compared with those obtained in methanol. The pH/rate profile in each solvent exhibits an extended plateau due to solvent attack on forms designated as [Cu(II):1b/c]⁰ for the monoester, [Cu(II):2b]⁺, for the diester, and [Cu(II):3a]²⁺for the triester. The solvent dkie values (k_H/k_D) for the three complexes are 0.91, 0.95, and 0.83 for decomposition of [Cu(II):1b/c]⁰ in water (W), methanol (M), and ethanol (E), 1.22, 1.09, and 1.29 for [Cu(II):2b]⁺ in W, M, and E, and 1.94, 2.2, and 1.96 for [Cu(II):3a]²⁺ in W, M, and E. Near unit, or slightly inverse values for the monoester are taken as evidence for little involvement of solvent in a highly dissociative TS for P–OAr cleavage, with slightly higher solvent dkie values for the diester signifying the onset of some solvent participation in assisting the nucleophilic displacement. The larger primary dkie for the triester gives evidence for a solvent-assisted delivery of ROH in the cleavage through a more associative mechanism. Activation parameters for each substrate in the solvents are compared, indicating that the transition from methanol to ethanol for each substrate involves a near cancellation of the ΔΔH^‡ and –TΔΔS^‡ values (25 °C) so that the respective rates in both solvents are very similar. The transition from alcohol to water produces variable effects, with ΔΔH^‡ and –TΔΔS^‡ values canceling for cleavage of the triester and being additive for the mono and diester, explaining their 100–500 rate reduction in passing from methanol to water. The rate enhancing effects of the Cu(II)-promoted leaving group assistance in all three solvents are substantial and estimated at 10¹²–10¹⁵ for the monoester, 10¹²–10¹⁴ for the diester, and 10⁵ for the triester relative to their background reactions.

Mark A. R. Raycroft, C. Tony Liu, and R. Stan Brown. Comparison of Cu(II)-Promoted Leaving Group Stabilization of the Cleavage of a Homologous Set of Phosphate Mono-, Di-, and Triesters in Water, Methanol, and Ethanol. Inorganic Chemistry. March 7, 2012 ASAP. http://pubs.acs.org/doi/full/10.1021/ic300059e

Tris(diethylamino)silane-A new precursor compound for obtaining layers of silicon carbonitride

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane ( EtN)SiH (TDEAS) in the temperature region 373-1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300-1300 K and pressure interval P from 1 × 10 to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-SN phase and of carbon inclusions has been found in the layers.

Fainer, N. N., Golubenko, A. A., Rumyantsev, Y. u., Kesler, V. V., Ayupov, B. B., Rakhlin, V. V., & Voronkov, M. M. (2012). Tris(diethylamino)silane-A new precursor compound for obtaining layers of silicon carbonitride. Glass Physics & Chemistry, 38(1), 15-26.

Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging

Chemosensors for selective detection of various biologically and environmentally relevant metal ions have recently attracted great attention. The widespread use of aluminum in food additives, aluminum-based pharmaceuticals, and storage/cooking utensils often exposes people to aluminum ions. In addition, frequent use of aluminum foil, vessels, and trays for convenience results in moderate increases in the Al3+ concentration in food. After absorption, aluminum ions would be distributed to all tissues in humans and animals and eventually accumulate in the bone. The iron binding protein is known to be the main carrier of Al3+ in plasma, and Al3+ can enter the brain and reach the placenta and fetus. Aluminum ions may stay for a very long time in various organs and tissues before being excreted through the urine. In addition, aluminum ions have been implicated as a causative factor of Alzheimer’s disease and associated with damage to the central nervous system in humans. Although trace amounts of aluminum ions are present in the drinking water, low-dose chronic exposure to the ions may cause Alzheimer’s disease possibly due to accumulation of oxidative damage induced by the ions. Sensitive bioimaging of Al3+ in the cell is a prerequisite for understanding the underlying mechanism about how aluminum ions cause aluminum-induced human diseases including Alzheimer’s disease.Thus, detection of Al3+ is important to control the concentration levels in the biosphere and minimize direct affects on human health.

In recent years, fluorescent chemosensors have attracted significant interest because of their potential use in medicinal and environmental research. The most commonly employed method used for chemosensor detection is the development of probe molecules that consist of a photon interaction site as a fluorophore and a metal binding site. In the presence of specific metal ions, the fluorophore–receptor communication gets turned on as a result of the binding of the metal ions at the receptor site. Until recently, only a few fluorescent chemosensors have been developed for detection of Al3+.Most fluorescent sensors for Al3+ have good selectivity, but this approach has several disadvantages including complicated synthetic procedures and poor water solubility. Meanwhile, some Schiff base compounds coordinated to metal ions were reported to have antitumor and antioxidative activities. Although many Schiff base derivatives incorporating a fluorescent moiety have been used to detect various metal ions, Schiff base-type Al3+ chemosensors are very rare and no examples of water-soluble devices as well as sensors that can be used for cell imaging have been developed. Possible utilization of PSI (o-phenolsalicylimine) as intracellular sensors of Al3+ was also examined by confocal fluorescence microscopy.

Kim, S. Young, J. Kim, Ka(et.al.).Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging March 2, 2012. Inorg. Chem,Article ASAP. http://pubs.acs.org/doi/suppl/10.1021/ic2024583

Effects of Surface Heterogeneity on the Adsorption of CO(2) in Microporous Carbons.

Carbon capture combined with utilization and storage has the potential to serve as a near-term option for CO(2) emissions reduction. CO(2) capture by carbon-based sorbents and CO(2) storage in geologic formations such as coal and shale both require a thorough understanding of the CO(2) adsorption properties in microporous carbon-based materials. Complex pore structures for natural organic materials, such as coal and gas shale, in addition to general carbon-based porous materials are modeled as a collection of independent, noninterconnected, functionalized graphitic slit pores with surface heterogeneities. Electronic structure calculations coupled with van der Waals-inclusive corrections have been performed to investigate the electronic properties of functionalized graphitic surfaces. With Bader charge analysis, electronic structure calculations can provide the initial framework comprising both the geometry and corresponding charge information required to carry out statistical modeling. Grand canonical Monte Carlo simulations were carried out to determine the adsorption isotherms for a given adsorbent-adsorbate interaction at temperature/pressure conditions relevant to carbon capture applications to focus on the effect of the surface functionalities. On the basis of the current work, oxygen-containing functional groups were predicted to enhance CO(2) adsorption in microporous carbon materials in the absence of water vapor, and the hydrated graphite was found to hinder CO(2) adsorption.

Como podemos leer en este artículo cada vez estamos mas cerca de la remediación ambiental, no obstante aun quedan muchos retos políticos, culturales y tecnológicos pero de granito en granito se podrá lograr un cambio.

Liu Y, Wilcox J. SourceDepartment of Energy Resources Engineering, School of Earth Sciences, Stanford University , Green Earth Sciences 065, 367 Panama Street, Stanford, California 94305, United States.

Una mirada al futuro desde el pasado.

Por lo visto, de las tantas fuentes renovables y eficientes de energía. El hidrógeno esta ganando campo para las producción energética casera. En Japón,Matsushita Electronic, el fabricante de Panasonic ha podido producir una celda de combustible de hidrogeno muy eficiente.

"El sistema de Matsushita está basado en una tecnología de electrolitos polímeros que, según el Nikkei, es más eficiente que los modelos existentes. De esta manera, por medio de una reacción química, el nuevo sistema es capaz de convertir más del 39% para generar un máximo de 750 vatios de energía hasta un 37% menos de emisiones contaminantes que los generadores tradicionales."

Por lo visto, iban a hacer pruebas de eficiencia(2009) y si todo quedaba dentro de los estándares de producción y eficiencia las iban a sacar al mercado.Ya han pasado tres años, y tal parece que el poder de tomar la abundancia del elemento mas simple a nuestro favor y en nuestras casas aun esta lejos. Aunque a veces pareciera que no tanto.

Desde el lado de vista económico-gubernamental hay una disruptiva entre eficiencia e interés. Si todos los hogares tuvieran celdas de hidrogeno u otra fuente de energia renovable entonces serian eficientes y no se desperdiciarian recursos. Pero por otro lado el gobienro no tendria las recaudaciones de impuestos de compañias paraestatales o privadas energéticas. No se puede tener a todos contentos.

Para el paper original consulten:

http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid=f9e6ae45-6b45-4e2c-99bc-9c151fbe415e%40sessionmgr4&vid=2&hid=17

ADN,"CREAN UNA BATERÍA DE HIDRÓGENO CAPAZ DE SUMINISTRAR EL 60% DE LA

ENERGÍA DE UNA CASA", ADYN, Mayo 2008, pps.N85

Amazing renewable hydrogen and natural gas using: sun + CO2 +H20

Amazing renewable hydrogen and natural gas using: sun + CO2 +H20

The technology HyperSolar is developing is extraordinary -- using the sun and carbon dioxide and water to create renewable hydrogen and natural gas. How does the technology work?

HyperSolar, Inc. with the University of California, Santa Barbara describes its process as inspired by photosynthesis where by plants use the sun's energy for fuel. To replicate this, the Santa Barbara-based company is "developing a novel solar-powered nanoparticle system that mimics photosynthesis to separate hydrogen from water. The free hydrogen can then be reacted with carbon dioxide to produce methane."

Something like this:

2H20-->2H2 + O2

2H2 + CO2 --> CH4 + O2

And then.. burn it!

CH4 + 2O2 + heat --> CO2 + 2H20 + energy

"If this were not enough "the company is developing a process to use wastewater in place of pure water. In this case, not only will the water come at no cost but it will also leave the process clean"

“UCSB is world renown for its scientific accomplishments. “We are very excited about this opportunity to gain access to the talents and state-of-the-art facilities of one of the world’s top universities for scientific impact,” he said.

Natural gas is becoming an increasingly hot topic in the U.S. As the country debates the environmental impact of extracting the fuel from beneath the earth's surface, President Obama is throwing his support at expanding the natural gas infrastructure."

I hope that here in Mexico could pay more attention to environmental issues and sustainable energy. So, little by little, become less dependent on oil

Find more information on this work in the UCSB website: http://www.nanotech.ucsb.edu/index.php?option=com_content&view=article&id=95:rie-2-methane-hydrogen-based-system

Notice source: http://www.energyboom.com/biofuels/hypersolar-teams-ucsb-develop-renewable-hydrogen-natural-gas-technology

Crystallization Pathway in the Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10Be22.5

A new family of multicomponent metallic alloys exhibits an excellent glass forming ability at moderate cooling rates of about 10K/s and a wide supercooled liquid region. These glasses are eutectic or nearly eutectic, thus far away from the compositions of competing crystalline phases. The nucleation of crystals from the homogeneous amorphous phase requires large thermally activated composition fluctuations for which the time scale is relatively long, even in the supercooled liquid.

In the Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 alloy therefore a different pathway to crystallization is observed. The initially homogeneous alloy separates into two amorphous phases. In the decomposed regions, crystallization probability increases and finally polymorphic crystallization occurs.


Reference
S. Schneider, P. Thiyagarajan, U. Geyer and W. L. Johnson (1996). Crystallization Pathway in the Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10Be22.5. MRS Proceedings, 455 , 295 doi:10.1557/PROC-455-295