Ana B. García

Modification of the surface chemistry of active carbons by means of microwave-induced treatments

The surface chemistry of two active carbons was modified using a microwave device as a heat source. When microwave treatments are conducted in a nitrogen flow, most oxygen-containing groups are removed from the surface of the carbons. This in turn gives rise to a significant increase in the pH of the carbons. Microwave treatment is less time-consuming than conventional heating. Only a few minutes are required to transform an acidic carbon into a basic carbon with a relatively low oxygen content. On the other hand, microwave-treated carbons undergo re-oxidation, to a greater or lesser extent, upon atmospheric exposure. It was observed that atmospheric re-oxidation of microwave-treated carbons tends to restore more acidic groups when the treatment is carried out on an acidic precursor than when the carbon is of a basic character. Nevertheless, carbons exposed to the atmosphere for up to 2 months still showed higher pHs than those of the corresponding precursors.

Update 1 of: α,β-Diamino Acids: Biological Significance and Synthetic Approaches

The discovery of nonproteinogenic amino acids among natural products, either in native state or as fragments of complex molecules, has increased the level of interest in this family of molecules from different scientific standpoints. Compounds with valuable biological properties can be found among these atypical amino acids. In addition, they have served as building blocks for the synthesis of new molecules or as surrogates of native amino acids in known peptidic entities to modulate their biological behavior. In this context, R, -diamino acids and their derivatives esters and amides, have attracted a great deal of attention among organic chemists and biochemists through the years. This interest has been due to the ubiquitous nature of R, -diamino acids as key structural fragments of biologically active compounds. Beyond this focus, the simplest compound, 2,3-diaminopropionic acid, has recently found application in the environmentally safe production of hydrogen for fuel cells, as a selective carrier of CO2 through gel membranes.1a Also, it has served to assemble a molecular device that produces propelling motion upon IR irradiation1b and, lately, in the context of food chemistry, 2,3-diaminopropionic acid has been identified as an inhibitor of polyphenol oxidase, the enzyme responsible for the browning of fruits and vegetables1c and as an enhancer of Maillard browning.1d In spite of the incidence of these molecules in an increasing number of areas, this review will deal with the biological significance, the therapeutic uses, and other interesting applications of R, -diamino acids and their derivatives found in the existing literature. Additionally, aside from the above considerations, the structural complexity of these molecules, having two vicinal chiral centers has also represented a challenge for synthetic organic chemists, especially the synthesis of enantiopure materials. Therefore, the aim of this article will also be to provide a deep and general view of the existing methodology for the synthesis of aliphatic R, or 2,3-diamino acids and their simple derivatives, esters, * To whom correspondence should be addressed. E-mail: iqov379@ iqog.csic.es. Alma Viso was born in Madrid (Spain) in 1964. She obtained a B.S. degree in Chemistry in 1987 and a Ph.D. in 1992 from Universidad Complutense de Madrid (UCM). In 1992, she moved to Massachusetts Institute of Technology (MIT) as a Fulbright fellow to work with Stephen L. Buchwald for 18 months. She joined the faculty at UCM (Madrid) in 1993 as an Assistant Professor and was promoted to Associate Professor in May 2002. In December 2002, she joined Instituto de Quı́mica Orgánica General, CSIC, as a Staff Researcher (Cientı́fico Titular) and was promoted to Senior Staff Researcher (Investigador Cientı́fico) in 2007. Her current research interests are focused in two main areas, the development of new methodologies in asymmetric synthesis using sulfoxides and sulfinamides and the application of these novel methods to efficient syntheses of therapeutically valuable products. Chem. Rev. PR1

Coal recovery from coal fines cleaning wastes by agglomeration with vegetable oils : effects of oil type and concentration

The aim of this work was to obtain high calorific value products from coal fines cleaning wastes by agglomeration with vegetable oils. These residues are mainly being disposed of in dumps, causing important economic and environmental problems. Three Spanish coal fines wastes from different coal cleaning plants were agglomerated with crude and refined sunflower and soybean oils over a wide range of oil concentrations. The response of these fines wastes to agglomeration with the oils, was evaluated by the percentages of coal matter recovery, ash rejection and efficiency index. Speaking in terms of products quality, the best results were attained at the lowest oil concentrations, especially when the refined ones were used. In these cases, the agglomeration with vegetable oils allowed the recovery from coal fines wastes of a ready to burn fine coal fuel.

Modification of the surface properties of an activated carbon by oxygen plasma treatment

Samples of a commercial activated carbon exposed to an oxygen plasma under identical conditions (150 W power, 0.1 kPa) for different times to attain 3–41 wt% burnoff of carbonaceous matter were characterized with emphasis on texture and surface chemistry. A 100% burnoff sample consisting of the inorganic matter of the starting material was also prepared and characterized to account for its contribution to the surface properties of the plasma-modified carbons. SEM-EDX and XRD showed that the major inorganic constituents of the activated carbons tested were calcium carbonate and silica. The structure of the carbonaceous matter changed little during the plasma treatment, and only a certain selective attack on more disordered material at high burnoff could be inferred. Adsorption of N2 at 77 K and CO2 at 273 K revealed a moderate decrease in surface area and porosity as a consequence of the plasma treatment (with allowance made for the diluent effect of inorganic matter). Plasma treatment resulted in a more well-defined plateau in the zeta potential-pH curve, appearing at a lower pH than for the untreated carbon, indicating that the negative charge brought about by the plasma treatment was due to dissociation of newly formed acidic groups. The isoelectric point disappeared even at low burnoff and the surface acidity increased up to 10–20 wt% burnoff and then remained constant. The hydrophilicity of plasma-treated carbons, measured by contact angle with water, did not change significantly. It is concluded that the plasma treatment offers potential advantages for the surface modification of activated carbons, as no substantial change in texture takes place whereas the surface chemistry can be modified to tailor specific properties. The oxygen plasma appeared not to reach the smallest micropores of the carbon, indicating that the reaction took place only near the external surfaces of the particles.

Cleaning of Spanish high-rank coals by agglomeration with vegetable oils

The aim of this work was to study the feasibility of using vegetable oils for coal agglomeration. Three Spanish anthracites were agglomerated with refined sunflower and soybean oils. The response of coals to agglomeration with these oils was evaluated by measuring the percentages of organic matter recovery and ash and pyritic sulfur rejections. The influence of oil type and concentration on agglomeration results was investigated. In addition, results were compared with those previously obtained in the agglomeration of these coals with n-heptane. It can be concluded that refined sunflower and soybean oils are suitable for use as agglomerants for these high-rank coals, especially to clean those coals with a high content of mineral matter.

Efficient microwave-assisted production of furfural from C5 sugars in aqueous media catalysed by Brönsted acidic ionic liquids

Small amounts of SO3H-functionalised room temperature synthesized ionic liquids efficiently dehydrate aqueous xylose to furfural under microwave heating at mild reaction conditions. The RT-ionic liquid catalysts were also found to be effective catalysts for the two step one-pot simultaneous hydrolysis and dehydration of a lignocellulosic waste biorefinery-derived syrup enriched in C5 sugar oligomers.

Effects of oxygen plasma treatment on the surface of graphitized carbon black

Sterling FT carbon black was oxidized in a cool oxygen plasma to various burn-off degrees ranging between 6 and 84%. Plasma-treated samples were characterized by nitrogen and carbon dioxide adsorption, scanning electron microscopy and contact angle measurements. Following the oxygen plasma treatment no changes in BET surface area or porosity were detected. SEM examinations evidenced an absence of fractures or other changes in the morphology of the particles, suggesting that carbon black oxidation by an oxygen plasma takes place through smooth, progressive etching of successive layers of the material. Some heterogeneity in the consumption of spheres was clear at high burn-offs. The contact angles with water decreased at low burn-offs and then remained approximately constant. The oxygen plasma treatment can be tentatively proposed as a suitable method to change carbon black surfaces from hydrophobic to hydrophilic.

Luminescent one- and two-dimensional extended structures and a loosely associated dimer based on platinum(II)-thallium(I) backbones.

Neutralization reactions between (NBu4)2[ trans-Pt(C 6F5)2(CN)2] 1 and (NBu4)2[cis-Pt(C6F5)2(CN)2] 2 with TlPF 6 have been carried out, and the resulting structures of [trans,trans,trans-Tl2{Pt(C6F5)2(CN)2}.(CH3COCH3) ] n [4.(CH3COCH3)2] n and {Tl[Tl{cis-Pt(C6F5)2(CN)2}].(H2O)} n [5.(H2O)] n have been determined by X-ray crystallography. Remarkably, the change from trans to cis geometry on the platinum substrate causes a significant decrease in the Pt(II)...Tl(I) metallophilic interaction. Thus, the platinum center in the trans fragment easily connects with two Tl(I) ions forming a distorted pseudo-octahedron PtTl2, which generates a final two-dimensional layered structure by secondary additional intermolecular Tl(I)...N(CN) interactions. However, the [cis-Pt(C6F5)2(CN)2] (2-) fragment interacts strongly with just one Tl center leading to an extended helical [-Pt-Tl-Pt-Tl-] n(n-) chain. In this case, the second thallium center neutralizes the anionic chain mainly through Tl...N(CN) ( intra) and Tl...F(C 6F 5) (intra and inter)actions. The reaction of TlPF 6 with the monoanionic fragment (NBu4)[cis-Pt(C6F5)2(CN)(PPh2C[triple bond]CPh)] 3 yields the discrete associated dimer [Tl{cis-Pt(C6F5)2(CN)(PPh2C[triple bond]CPh)}] 2 [ 6] 2. Dimer [ 6] 2 could be described as two square pyramids with the thallium atoms in the apical positions, connected through Tl...N(cyano) interactions. The final heteropolynuclear Pt-Tl complexes, except 4 at room temperature, show bright emission in the solid state when irradiated with UV-vis radiation, in contrast to the precursors 1 and 3, which are not luminescent. This difference indicates that the emissions in 4- 6 are presumably related to the interaction between the metal centers. The Pt-Tl bonding interactions and, consequently, the emissive properties are lost in solution at room temperature, as shown by the conductivity and NMR measurements. However, variable-concentration luminescence measurements in glassy acetonitrile solutions indicate the formation of different aggregates with different degrees of Pt...Tl interactions for 4 and 5 and a dimeric structure similar to that observed in solid state for 6.

Effects of oil concentration and particle size on the cleaning of Spanish high-rank coals by agglomeration with n-heptane

The response of three high-ash Spanish anthracites to agglomeration with n-heptane was evaluated by measuring the organic matter recovery, ash rejection and pyritic sulfur rejection. The influence of oil concentration and coal particle size on the agglomeration results was investigated. The combustible recoveries of these coals increased to a maximum as the n-heptane concentration is raised, and then decreased. Ash rejection fell as the coal recovery increased. The effect of oil concentration on pyritic sulfur rejection was comparable with that on ash rejection. Regarding ash, pyritic sulfur was removed from one coal with noticeable selectivity. Ash rejection and organic matter recovery were improved by grinding one coal to <45 μm. Coal particle size had a more pronounced effect than n-heptane concentration on selectivity of oil agglomeration for cleaning this coal.

Coal recovery from fines cleaning wastes by agglomeration with colza oil: a contribution to the environment and energy preservation

The objectives of this work were to recover high-calorific value/low-ash content coals from coal fines cleaning wastes by agglomeration with colza oil and to decrease the risk of spontaneous combustion of the dump where the coal wastes are disposed of. Three Spanish coal fines wastes from different coal cleaning plants were agglomerated with refined colza oil over a wide range of oil concentration. The results were evaluated by the percentages of organic matter recovery and ash rejection as well as the ash content of the recovered coal and the amount of organic matter remaining in the dump after oil agglomeration. It was concluded that the agglomeration of coal fines wastes with colza oil allows the recovery of significant amounts of energy that is currently wasted and reduces the risk of spontaneous combustion of coal dumps as well as the amount of coal fines wastes to be handled and disposed of.