Synthesis of FeCoMnAPO-5 molecular sieve and catalytic activity in cyclohexane oxidation by oxygen

A new FeCoMnAPO-5 with AFI structure was synthesized under hydrothermal conditions and characterized by XRD, FT-IR, X-ray fluorescence, nitrogen adsorption and SEM. The oxidation of cyclohexane with molecular oxygen was studied over the catalyst at 403 K. It show d higher activity compared to FeAPO-5, CoAPO-5 and MnAPO-5. The FeCoMnAPO-5 catalyst was recycled twice without loss of activity or selectivity.

New route for light olefins production from chloromethane over HSAPO-34 molecular sieve

HSAPO-34 molecular sieve was employed in chloromethane conversion and showed high performance in activity and selectivity in production of light olefins. Our detailed IR investigation allowed the identification of the active sites and the adsorbed species and demonstrated that the conversion started from 350 degrees C with alkoxy group as the intermediate. The fixed-bed catalytic testing evidenced that in the range of 350-500 degrees C, 70-80% of chloromethane was transferred to ethylene, propylene and butenes. Increasing reaction temperature favors the conversion and enhances the yield of lighter olefins. A very important reversible phenomenon, the breaking of Al-O-P bonds upon adsorption of HCl, a main product of reaction to generate a large amount of P-OH groups and the recovery of Al-O-P upon removal of HCI was revealed. (c) 2005 Elsevier B.V. All rights reserved.

Stabilization of Ti-molecular sieve catalysts used in selective sulfoxidation reactions by ionic liquids

Sulfoxidation reactions of 4,6-dimethyl-2-methylthiopyrimidine have been performed using titanosilicate catalysts in ionic liquids, dioxane and ethanol. The ionic liquid reactions showed superior reactivity compared with molecular solvents. Moreover, on examination of the recycling of the catalyst, a significant increase in the stability of catalyst was found both in terms of recycling activity and leaching of the titanium from the catalyst. The mechanism by which the ionic liquid reduces the solubilisation of the catalysts is explored.

Tuning mesoporous molecular sieve SBA-15 for the immobilization of α-amylase

The present work describes the immobilization of α-amylase over well ordered mesoporous molecular sieve SBA-15 with different pore diameters synthesized by post synthesis treatment (PST) hydrothermally after reaction at 40°C. The materials were characterized by N 2 adsorption–desorption studies, small angle X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. Since α-amylase obtained from Bacillus subtilis has dimensions of 35 × 40 × 70 Å it is expected that the protein have access to the pore of SBA-15 (PST-120°C) with diameter 74 Å. The pore dimension is appropriate to prevent considerable leaching. The rate of adsorption of the enzyme on silica of various pore sizes revealed the influence of morphology, pore diameter, pore volume and pH.

Can sieve-element plastids in Panicum maximum (Poaceae) leaves act in the blockage of injured sieve-tube elements?

The ultrastructural features and the plastid changes caused by sample preparation were studied in sieve elements of Panicum maximum leaves. Samples of expanded leaves, taken near the ligule region, were fixed and processed by common light and transmission electron microscopy methods. In mature sieve-tube elements, the protoplast is electron-translucent and plastids are the most frequent organelles. Mitochondria and smooth endoplasmic reticulum segments are also visible and occupy a parietal position within the cell. The plastids are globular and show electron-dense proteinaceous inclusions in the stroma. The protein crystals are predominantly cuneate, but thin crystalloids and amorphous and/or filamentous proteins also occur. The presence of intact plastids plus others in different phases of plastid envelope rupture were interpreted as evidence that this rupture is a normal event in response to injury. This plastid envelope rupture is possibly activated by the release of pressure in the sieve-tube element. After plastid membrane vesiculation, the stroma and the protein crystals are dispersed within the sieve-element ground cytoplasm. The vesicles originating from the plastid envelope move to one cell pole, while protein crystalloids move to the opposite pole and agglomerate in the sieve-plate region. Our findings indicate that these protein crystalloids, which deposit in the sieve plate, may act in sieve-plate pores occlusion, preventing the release of phloem sap, similar to the role of P-protein in dicotyledons. (c) 2008 Elsevier GmbH. All rights reserved.

Occurrence of form PIIcf sieve-element plastids in Xyris species (Xyridaceae)

Mature leaf fragments from eight species of Xyris from the Serra do Cipo, State of Minas Gerais, Brazil, were prepared by the usual methods for electron microscopy. Ultrastructural analysis of phloem shows the occurrence of nacreous walls with a polylamellate structure in the sieve-elements of X. tortilis and plastids similar to P-plastids, form PIIcf in the sieve-elements of all investigated species.

Planktic foraminiferal sieve size specific d13C and d18O values and maximum test diameter from ODP sites 171-1051 and 120-748

Many genera of modern planktic foraminifera are adapted to nutrient-poor (oligotrophic) surface waters by hosting photosynthetic symbionts, but it is unknown how they will respond to future changes in ocean temperature and acidity. Here we show that ca. 40 Ma, some fossil photosymbiont-bearing planktic foraminifera were temporarily 'bleached' of their symbionts coincident with transient global warming during the Middle Eocene Climatic Optimum (MECO). At Ocean Drilling Program (ODP) Sites 748 and 1051 (Southern Ocean and mid-latitude North Atlantic, respectively), the typically positive relationship between the size of photosymbiont-bearing planktic foraminifer tests and their carbon isotope ratios (d13C) was temporarily reduced for ~100 k.y. during the peak of the MECO. At the same time, the typically photosymbiont-bearing planktic foraminifera Acarinina suffered transient reductions in test size and relative abundance, indicating ecological stress. The coincidence of minimum d18O values and reduction in test size-d13C gradients suggests a link between increased sea-surface temperatures and bleaching during the MECO, although changes in pH and nutrient availability may also have played a role. Our findings show that host-photosymbiont interactions are not constant through geological time, with implications for both the evolution of trophic strategies in marine plankton and the reliability of geochemical proxy records generated from symbiont-bearing planktic foraminifera.