Ángel Cantín

The ITQ-37 mesoporous chiral zeolite

The synthesis of crystalline molecular sieves with pore dimensions that fill the gap between microporous and mesoporous materials is a matter of fundamental and industrial interest. The preparation of zeolitic materials with extralarge pores and chiral frameworks would permit many new applications. Two important steps in this direction include the synthesis of ITQ-33, a stable zeolite with 18 × 10 × 10 ring windows, and the synthesis of SU-32, which has an intrinsically chiral zeolite structure and where each crystal exhibits only one handedness. Here we present a germanosilicate zeolite (ITQ-37) with extralarge 30-ring windows. Its structure was determined by combining selected area electron diffraction (SAED) and powder X-ray diffraction (PXRD) in a charge-flipping algorithm. The framework follows the SrSi2 (srs) minimal net and forms two unique cavities, each of which is connected to three other cavities to form a gyroidal channel system. These cavities comprise the enantiomorphous srs net of the framework. ITQ-37 is the first chiral zeolite with one single gyroidal channel. It has the lowest framework density (10.3 T atoms per 1,000 Å3) of all existing 4-coordinated crystalline oxide frameworks, and the pore volume of the corresponding silica polymorph would be 0.38 cm3 g-1.

Modular Organic Structure-Directing Agents for the Synthesis of Zeolites

Routes to Rare Zeolites Zeolites are microporous crystalline solids with well-defined structures. Although many naturally occurring ones have been obtained in laboratory synthesis, some have remained elusive. One of these, boggsite, is of interest for catalytic reactions because it has large channels defined by rings of 10 or 12 atoms that intersect within its crystalline lattice. Simancas et al. (p. 1219) report the synthesis of boggsite by using phosphazenes as the organic groups that directed the formation of rings during synthesis. These reagents can be readily modified—a feature that should allow greater flexibility in synthesis routes. Phosphazene molecules enable the synthesis of a rare naturally occurring zeolite. Organic structure-directing agents (OSDAs) are used to guide the formation of particular types of pores and channels during the synthesis of zeolites. We report that the use of highly versatile OSDAs based on phosphazenes has been successfully introduced for the synthesis of zeolites. This approach has made possible the synthesis of the elusive boggsite zeolite, which is formed by 10- and 12-ring intersecting channels. This topology and these pore dimensions present interesting opportunities for catalysis in reactions of industrial relevance.

A New Microporous Zeolitic Silicoborate (ITQ-52) with Interconnected Small and Medium Pores

A new zeolite (named as ITQ-52) having large cavities and small and medium channels has been synthesized. This was achieved by using a new family of amino-phosphonium cations as organic structure directing agents (OSDA). These cations contain P-C and P-N bonds, and therefore they lie between previously reported P-containing OSDA, such as tetraalkylphosphonium and phosphazenes. In this study, it has been found that 1,4-butanediylbis[tris(dimethylamino)]phosphonium dication is a very efficient OSDA for crystallization of several zeolites, and in some particular conditions, the new zeolite ITQ-52 was synthesized as a pure phase. The structure of ITQ-52 has been solved using high-resolution synchrotron X-ray powder diffraction data of the calcined solid. This new zeolite crystallizes in the space group I2/m, with cell parameters a = 17.511 Å, b = 17.907 Å, c = 12.367 Å, and β = 90.22°. The topology of ITQ-52 can be described as a replication of a composite building unit with ring notation [4(3)5(4)6(1)] that gives rise to the formation of an interconnected 8R and 10R channel system.

Isolation and Synthesis of N-(2-Methyl-3-oxodec-8-enoyl)-2-pyrroline and 2-(Hept-5-enyl)-3-methyl-4-oxo-6,7,8,8a-tetrahydro-4H-pyrrolo[2,1-b]1,3-oxazine – Two New Fungal Metabolites with in vivo Anti-Juvenile-Hormone and Insecticidal Activity

Two new natural products, N-(2-methyl-3-oxodec-8-enoyl)-2-pyrroline (2) and 2-(hept-5-enyl)-3-methyl-4-oxo-6,7,8,8a-tetrahydro-4H-pyrrolo[2,1-b]-1,3-oxazine (3), have been isolated from Penicillium brevicompactum Dierckx. Compound 2 has shown an important in vivo anti-juvenile-hormone (anti-JH) activity while compound 3 has exhibited insecticidal activity against Oncopeltus fasciatus Dallas. Both products have been synthesized starting from 1,4-hexadiene, by means of a sequence of reactions which includes the preparation of 6-octenoic acid and its transformation into the corresponding acid chloride, in order to acylate Meldrums acid. Subsequent aminolysis with pyrrolidine, followed by methylation at the activated position of the β-oxo amide with iodomethane, introduction of a methoxy group at the pyrrolidine ring by anodic oxidation and final elimination of methanol on SiO2 led to 2 and 3. The fact that both metabolites can be prepared by the same sequence indicates that they must be biogenetically related. Based on structural similarities, compounds 2 and 3 are also closely related to the recently discovered brevioxime (1).

Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene

Purifying ethylene with flexible zeolites Ethylene is a key feedstock for many chemicals and polymers, but its production requires cryogenic separation from ethane, an energy-consuming step. In theory, pure silica zeolites are well suited to separate olefins from paraffins. Bereciartua et al. synthesized a pure silica zeolite with very small pores, which, if static, would not adsorb either of these hydrocarbons. However, molecular dynamics suggested that the pores should be flexible. Indeed, in competitive adsorption experiments, the zeolite preferentially adsorbed ethylene from a mixed stream of ethylene and ethane. Science, this issue p. 1068 A pure silica zeolite has small, flexible pores that preferentially adsorb ethylene over ethane. The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

Isolation, structural assignment and insecticidal activity of (−)-(1S,2R,3R,4S)-1,2-epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate, a natural product from Minthostachys tomentosa

Abstract (−)-(1 S ,2 R ,3 R ,4 S )-1,2-Epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate has previously been identified as the active compound of Minthostachys tomentosa responsible for the insecticidal activity against Oncopeltus fasciatus . Its structure was initially assigned on the basis of spectral data. In order to confirm the structure and to define the stereochemistry, stereoselective synthesis of its enantiomer, (+)-(1 R ,2 S ,3 S ,4 R )-1,2-epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate, starting from ( R )-(−)-piperitone, was carried out using a Sharpless reaction as the key step. The natural product is dextro -rotatory while the synthetic product is levo -rotatory. Measurements of insecticidal activities of the different steroisomers revealed that only the natural product is active.

Charge matching between the occluded organic cations and zeolite framework as structure directing effect in zeolite synthesis

Abstract The charge matching effect has been found to be an important parameter driving the synthesis towards particular zeolite frameworks. This has been evidenced by isomorphous incorporation of Aluminium into the zeolite synthesis as well as by incorporation of fluoride anions at zeolite interstices. In both cases, negatively zeolite frameworks are developed and the resulting structure must provide enough space to locate the compensating organic cations. Therefore, this can be used by combining with the appropriate selection of organic polycations to direct the synthesis towards a particular structure, such as the formation of Ge-ITQ-24 materials.

Layered hybrid materials with nanotechnological applications: use of disilane precursors as pillaring agents

Abstract A new family of layered organic-inorganic hybrid materials was synthesized using bridged silsesquioxane compounds (disilanes) as pillars which are intercalated between magadiite layers. The organic-inorganic precursors react with the surface silanol groups of the inorganic layers of silicate, bonding covalently with them. The preparation process was followed by DRX and the presence of organic linkers was confirmed by chemical and thermogravimetrical analyses, 13 C and 29 Si NMR spectroscopy. Micro and mesoporosity were also generated due to the existence of interlayer galleries. The layered hybrid materials exhibited thermally stable networks. The resultant materials can be of interest as acid or basic catalysts, sensors and for non linear optics.

New Insight into the Transcarbamylase Family: The Structure of Putrescine Transcarbamylase, a Key Catalyst for Fermentative Utilization of Agmatine

Transcarbamylases reversibly transfer a carbamyl group from carbamylphosphate (CP) to an amine. Although aspartate transcarbamylase and ornithine transcarbamylase (OTC) are well characterized, little was known about putrescine transcarbamylase (PTC), the enzyme that generates CP for ATP production in the fermentative catabolism of agmatine. We demonstrate that PTC (from Enterococcus faecalis), in addition to using putrescine, can utilize L-ornithine as a poor substrate. Crystal structures at 2.5 Å and 2.0 Å resolutions of PTC bound to its respective bisubstrate analog inhibitors for putrescine and ornithine use, N-(phosphonoacetyl)-putrescine and δ-N-(phosphonoacetyl)-L-ornithine, shed light on PTC preference for putrescine. Except for a highly prominent C-terminal helix that projects away and embraces an adjacent subunit, PTC closely resembles OTCs, suggesting recent divergence of the two enzymes. Since differences between the respective 230 and SMG loops of PTC and OTC appeared to account for the differential preference of these enzymes for putrescine and ornithine, we engineered the 230-loop of PTC to make it to resemble the SMG loop of OTCs, increasing the activity with ornithine and greatly decreasing the activity with putrescine. We also examined the role of the C-terminal helix that appears a constant and exclusive PTC trait. The enzyme lacking this helix remained active but the PTC trimer stability appeared decreased, since some of the enzyme eluted as monomers from a gel filtration column. In addition, truncated PTC tended to aggregate to hexamers, as shown both chromatographically and by X-ray crystallography. Therefore, the extra C-terminal helix plays a dual role: it stabilizes the PTC trimer and, by shielding helix 1 of an adjacent subunit, it prevents the supratrimeric oligomerizations of obscure significance observed with some OTCs. Guided by the structural data we identify signature traits that permit easy and unambiguous annotation of PTC sequences.

A new synthesis route of the tridirectional 12 ring channel zeolite ITQ-7

Abstract A new synthesis procedure for the synthesis of ITQ-7 zeolites is reported that has been afforded by combining theoretical and experimental approaches. This new synthesis method is specially relevant since the earlier procedure reported in the literature [1] is not any longer applicable because the principal precursor of the structure directing agent (SDA) employed in that route is not commercially available. Here, we present a convenient method for synthesising ITQ-7 zeolites using a family of new SDAs that can be easily prepared from α-terpinene and maleimide as main reactants. The appropriate fitting of the new SDAs within in pores of ITQ-7 structure is highlighted by studying the synthesis in the presence of the non-substituted SDA which leads to closely related structure of polymorph C of the Beta zeolite (BEC code). Finally, the differences and similarities between the two synthetic routes described for preparing ITQ-7 zeolites are discussed in this work.