No abstract

Solid materials with uniform micropores, such as zeolites, can act as selective catalysts and adsorbents for molecular mixtures by separating those molecules small enough to enter their pores while leaving the larger molecules behind. Zeolite A is a microporous material with a high void volume. Despite its widespread industrial use in, for example, molecular separations and in detergency, its capability as a petroleum-refining material is limited owing to its poor acid-catalytic activity and hydrothermal stability, and its low hydrophobicity. These characteristics are ultimately a consequence of the low framework Si/Al ratio (normally around one) and the resulting high cationic fraction within the pores and cavities. Researchers have modified the properties of type-A zeolites by increasing the Si/Al compositions up to a ratio of three. Here we describe the synthesis of zeolite A structures exhibiting high Si/Al ratios up to infinity (pure silica). We synthesize these materials, named ITQ-29, using a supramolecular organic structure-directing agent obtained by the self-assembly, through pi-pi type interactions, of two identical organic cationic moieties. The highly hydrophobic pure-silica zeolite A can be used for hydrocarbon separations that avoid oligomerization reactions, whereas materials with high Si/Al ratios give excellent shape-selective cracking additives for increasing propylene yield in fluid catalytic cracking operations. We have also extended the use of our supramolecular structure-directing agents to the synthesis of a range of other zeolites.

Crude oil is an important feedstock for the petrochemical industry and the dominant energy source driving the world economy, but known oil reserves will cover demand for no more than 50 years at the current rate of consumption. This situation calls for more efficient strategies for converting crude oil into fuel and petrochemical products. At present, more than 40% of oil conversion is achieved using catalysts based on faujasite; this zeolite requires extensive post-synthesis treatment to produce an ultrastable form, and has a large cavity accessible through four 0.74-nm-wide windows and thus limits the access of oil molecules to the catalytically active sites. The use of zeolites with better accessibility to their active sites should result in improved catalyst efficiency. To date, two zeolites with effective pore diameters exceeding that of faujasite have been reported, but their one-dimensional pore topology excludes use in oil refining. Similarly, zeolites with large pores and a three-dimensional pore topology have been reported, but in all these materials the pore openings are smaller than in faujasite. Here we report the synthesis of ITQ-21, a zeolite with a three-dimensional pore network containing 1.18-nm-wide cavities, each of which is accessible through six circular and 0.74-nm-wide windows. As expected for a zeolite with this structure, ITQ-21 exhibits high catalytic activity and selectivity for valuable products in preliminary oil refining tests.

Ischemia exists in many diseased tissues, including arthritic joints, atherosclerotic plaques, and malignant tumors. Macrophages accumulate in these sites and up-regulate hypoxia-inducible transcription factors (HIFs) 1 and 2 in response to the hypoxia present. Here we show that the gene expression profile in primary human and murine macrophages changes markedly when they are exposed to hypoxia for 18 hours.

Some symmetrical Ar3C and unsymmetrical (C6C15)3-xAr,C radicals with different chlorine substitution patterns (x = 1, 2; Ar: 2H-C6HC14, 3H,5H-C6H2C14, 4H-C6HC14, C6H5) are prepared. X-ray crystal structures for most of them have been obtained at room temperature. The general conformations are conditioned by the great volume of the chlorine atoms in the ortho positions resulting in unsymmetrical, propellerlike conformations. Experimental evidence of the steric shielding of the trivalent carbon atom, as well as the practical nonexistence of the so-called buttressing effect, is given. The steric shielding is in correlation with the observed stabilities. The magnetic susceptibilities of the radicals are discussed and related to molecular packing and spin densities in terms of McConnell's theory, when antiferromagnetism is observed. The g-factors, hyperfine coupling constants (hcc) of IH and I3C nuclei, and line widths of the radicals are determined at several temperatures by ESR experiments in solid-state and isotropic solutions. Different conformational dynamic behaviors are traced to the number of chlorine atoms in ortho positions. Temperature-dependent line widths are explained by the relative contribution of the modulation of the dipolar hyperfine interaction through molecular tumbling and chlorine nuclear quadrupolar relaxation mechanism. The hcc values have been calculated according to the INDO method with the experimental X-ray geometries and compared with the experimental values; a g o d agreement is obtained. The assignment of the I3C satellites to bridgehead and ortho positions is confirmed IntroductionIn the course of our studies on derivatives of perchlorotri-