On the Origin of Enantioselectivity in Chiral Zeolite Asymmetric Catalyst GTM-3: Host-Guest Transfer of Chirality.

Knowledge of how extra-large-pore chiral zeolite asymmetric catalysts based on the -ITV framework imprint their chirality during a catalytic reaction is crucial in order to spread the scope for the catalytic enantioselective production of chiral compounds of interest. In this work, we have carried out a combined experimental and computational study on the catalytic activity of antipode GTM-3 catalysts during the ring-opening of -stilbene oxide with 1-butanol. Identification of the enantiomers of all the chiral species unraveled a surprising catalytic behavior: these chiral catalysts promote the transformation of one enantiomer of -stilbene oxide in the corresponding product (with inversion of configuration of the attacked C) via an S2 mechanism, and at the same time, the transformation of the other enantiomer of -stilbene oxide via an S1-like mechanism into the (with retention of configuration) and secondary products (diphenylacetaldehyde via rearrangement and derived products).

Confinement of a Styryl Dye into Nanoporous Aluminophosphates: Channels vs. Cavities.

Styryl dyes are generally poor fluorescent molecules inherited from their flexible molecular structures. However, their emissive properties can be boosted by restricting their molecular motions. A tight confinement into inorganic molecular sieves is a good strategy to yield highly fluorescent hybrid systems.

Exploiting the photophysical features of DMAN template in ITQ-51 zeotype in the search for FRET energy transfer.

The combination between photoactive molecules and inorganic structures is of great interest for the development of advanced materials in the field of optics. Particularly, zeotypes with extra-large pore size are attractive because they allow the encapsulation of bulky dyes. The microporous aluminophoshate Mg-ITQ-51 (IFO-type structure) represents an ideal candidate because of the synergic combination of two crucial features: the IFO framework itself, which is composed of non-interconnected one-dimensional extra-large elliptical channels with a diameter up to 11 Å able to host bulky guest species, and the particular organic structure-directing agent used for the synthesis (1,8-bis(dimethylamino)naphthalene, DMAN), which efficiently fills the IFO pores, and is itself a photoactive molecule with interesting fluorescence properties in the blue range of the visible spectrum, thus providing a densely-incorporated donor species for FRET processes.

Inversion of chirality in GTM-4 enantio-enriched zeolite driven by a minor change of the structure-directing agent.

A surprising inversion of chirality of the -ITV zeolite framework is observed when the ethyl group of the enantiopure ,-ethyl-methyl-pseudoephedrinium organic structure-directing agent is replaced by a benzyl or 2-methylbenzyl group, keeping the same molecular absolute configuration. Interestingly, chiral zeolite materials obtained with these new benzyl-containing cations reach unprecedentedly high enantiomeric excesses up to 55%.

Driving the Active Site Incorporation in Zeolitic Materials via the Organic Structure-Directing Agent Through Development of H-Bonds with Hydroxyl Groups.

(1S,2S)-N-methyl-pseudoephedrine (MPS) was used as organic structure-directing agent (OSDA) for the synthesis of Mg-doped nanoporous aluminophosphates. This molecule displays a particular conformational behavior, where the presence of H-bond donor and acceptor groups provide a rigid conformational space with one asymmetric conformation preferentially occurring. MPS drives the crystallization of Mg-containing AFI materials.

A combination of proton spin diffusion NMR and molecular simulations to probe supramolecular assemblies of organic molecules in nanoporous materials.

In this work we show the use of high-resolution H MAS NMR to distinguish between two kinds of aggregation states of (1,2)-ephedrine, a chiral organic structure directing agent, occluded within AFI-type microporous aluminophosphates. We investigate in particular the supramolecular assembly of the molecules through π⋯π type interactions of their aromatic rings when confined within the one-dimensional AFI channels. A series of high-resolution two-dimensional spin diffusion spectra combined with molecular simulations and DFT calculations allowed us to distinguish different aggregation states of ephedrine molecules and precisely estimate the distances between the aromatic rings and their closest protons inside the zeolite channels as a consequence of distinct proton spin diffusion profiles.

Modulation of the Activity of Gold Clusters Immobilized on Functionalized Mesoporous Materials in the Oxidation of Cyclohexene via the Functional Group. The Case of Aminopropyl Moiety.

Gold nanoclusters and isolated gold atoms have been produced in a two-liquid phase procedure that involves a solution of gold in aqua regia and rosemary essential oil as organic layer. These gold entities have been immobilized on the ordered mesoporous silica material SBA-15 functionalized with different amounts of aminopropyl groups. The resulting materials have been characterized by XRD, N adsorption, chemical analysis, TGA, Si MAS NMR, C CP/MAS NMR, UV-vis spectroscopy, XPS, and STEM.

Synthesis of large-pore zeolites from chiral structure-directing agents with two l-prolinol units.

In this work, we perform an in-depth experimental and computational study about the structure-directing effect of two new chiral organic quaternary ammonium dications bearing two N-methyl-prolinol units linked by a xylene spacer in para or meta relative orientation, displaying four enantiopure stereogenic centers in (S) configuration. Synthesis results show that the para-xylene derivative is an efficient structure-directing agent, promoting the crystallization of ZSM-12 (in pure-silica composition), beta zeolite (as pure-silica, or in the presence of Al or Ge), and a mixture of polymorphs C, A and B of zeolite beta (in the presence of Ge). In contrast, the meta-xylene derivative showed a much poorer structure-directing activity, yielding only amorphous materials unless Ge is present in the gel, where beta and polymorph C (together with A and B) zeolites crystallized.

White Light Emission by Simultaneous One Pot Encapsulation of Dyes into One-Dimensional Channelled Aluminophosphate.

By simultaneous occlusion of rationally chosen dyes, emitting in the blue, green and red region of the electromagnetic spectrum, into the one-dimensional channels of a magnesium-aluminophosphate with AEL-zeolitic type structure, MgAPO-11, a solid-state system with efficient white light emission under UV excitation, was achieved. The dyes herein selected-acridine (AC), pyronin Y (PY), and hemicyanine LDS722-ensure overall a good match between their molecular sizes and the MgAPO-11 channel dimensions. The occlusion was carried out via the crystallization inclusion method, in a suitable proportion of the three dyes to render efficient white fluorescence systems by means of fine-tuned FRET (fluorescence resonance energy transfer) energy transfer processes.

One-Directional Antenna Systems: Energy Transfer from Monomers to J-Aggregates within 1D Nanoporous Aluminophosphates.

A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mg-containing aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å × 7.

Self-assembly of chiral (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine into low-dimensional aluminophosphate materials driven by their amphiphilic nature.

In an attempt to promote the crystallization of chiral inorganic frameworks, we explore the ability of chiral (1R,2S)-ephedrine and its diastereoisomer (1S,2S)-pseudoephedrine to act as organic building blocks for the crystallization of hybrid organo-inorganic aluminophosphate frameworks in the presence of fluoride. These molecules were selected because of their particular molecular asymmetric structure, which enables a rich supramolecular chemistry and a potential chiral recognition phenomenon during crystallization. Up to four new low-dimensional materials have been produced, wherein the organic molecules form an organic bilayer in-between the inorganic networks.

The Alchemical Manuscripts of David Lindsay (1587-1641), Lord Lindsay of Balcarres.

The private book collection of David Lindsay, First Lord Lindsay of Balcarres (1587-1641), was one of the largest in early modern Scotland. Despite being dispersed during the following three centuries, this collection still provides evidence for Lindsay's scientific interests and approach to the study of alchemy. In this paper we seek to partially reconstruct his library by describing and, where possible, identifying the sources of Lindsay's own transcriptions of alchemical texts, as well as works mentioned in a book-list written in his hand.

Formation of a Nonlinear Optical Host-Guest Hybrid Material by Tight Confinement of LDS 722 into Aluminophosphate 1D Nanochannels.

In this work, hemicyanine dye LDS 722 is encapsulated into the 1D elliptical nanochannels of MgAPO-11 aluminophosphate by a crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20 μm×30 μm) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations.

Towards chiral distributions of dopants in microporous frameworks: helicoidal supramolecular arrangement of (1R,2S)-ephedrine and transfer of chirality.

A molecular-mechanics computational study is performed in order to analyze the arrangement of (1R,2S)-(-)-ephedrine molecules within the 12-MR channels of the AFI aluminophosphate microporous framework and the influence on the spatial distribution of dopants embedded in the tetrahedral network. Results showed that ephedrine molecules arrange exclusively as dimers by π-π stacking of the aromatic rings within the AFI channels. Interestingly, the asymmetric nature of ephedrine and the presence of H-bond-forming groups (NH2 and OH) involve a preferential orientation where consecutive dimers within the channels are rotated by an angle of +30°; this is driven by the establishment of inter-dimer H-bonds.

Modulating dye aggregation by incorporation into 1D-MgAPO nanochannels.

The fluorescing dye Pyronine Y has been incorporated by crystallization inclusion into three different one-dimensional microporous aluminophosphate host materials. A computer-aided rational choice of the framework of the host material made it possible to modulate the aggregation state of the guest dye molecules. Undesirable H-type dimers of Pyronine Y are included within the large channels of the AFI structure, which allow the inclusion of any of the aggregated species of the dye.

Stripping voltammetric determination of pyridine-2-aldoxime methochloride at the iron(III) doped zeolite modified glassy carbon electrode.

An iron(III) doped zeolite modified glassy carbon electrode was constructed for the determination of pyridine-2-aldoxime methochloride. X-ray diffraction and chemical analysis were utilized to determine the optimum pH and chemical content for doping zeolite. Cyclic voltammetry was used to characterize the modified electrode and study the kinetics of the acid treated and untreated modified electrode.

Control of CO2 adsorption heats by the Al distribution in FER zeolites.

Proper combination of template and optimized reaction conditions provides zeolite FER with homogeneous distribution of Al in the framework; this results in a new zeolite adsorbent exhibiting a constant heat of CO(2) adsorption.

Synthesis of Zn-containing microporous aluminophosphate with the STA-1 structure.

Zn atoms have been incorporated into the STA-1 microporous framework (SAO framework type) for the first time. Pure Zn-containing STA-1 aluminophosphate has been obtained in the presence of either (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) or benzylpyrrolidine (BP) as structure-directing agent. Characterisation results have demonstrated that the organic molecules remain intact within the microporous framework after the hydrothermal treatment.

Dopant-siting selectivity in nanoporous catalysts: control of proton accessibility in zeolite catalysts through the rational use of templates.

A computational study is performed to rationalize the effect of the organic template molecules used in the synthesis of zeolites on their catalytic behaviour. Apart from being structure-directing, these molecules influence the location of heteroatoms. Molecules bearing acidic protons susceptible to forming H-bonds with framework oxygens show the strongest dopant-siting direction.

Molecular insights into the self-aggregation of aromatic molecules in the synthesis of nanoporous aluminophosphates: a multilevel approach.

Fluorescence spectroscopy and a range of computer simulation techniques are used to study the structure directing effect of benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of nanoporous aluminophosphate frameworks with AFI (one-dimensional channels) and SAO (three-dimensional interconnected channels) topologies. We study the supramolecular chemistry of BP and BPM molecules in aqueous solution and compare it with the aggregation state of the molecules found when they are inside the AlPO nanopores after crystallization. The aggregation of the molecules within the structures can be explained by a combination of thermodynamic and kinetic effects.

Insights into structure direction of microporous aluminophosphates: competition between organic molecules and water.

A combination of experimental characterisation techniques and computational modelling has allowed us to gain insight into the molecular features governing structure direction in the synthesis of microporous aluminophosphates. The occlusion of three different structure-directing agents (SDAs), triethylamine (TEA), benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM), within the AFI structure during its crystallisation, together with the simultaneous incorporation of water, has been experimentally measured. We found a higher incorporation of organic molecules in the structure obtained with BPM, while a higher water (and lower organic) content is found for the ones obtained with TEA and BP as SDAs.

Supramolecular chemistry in the structure direction of microporous materials from aromatic structure-directing agents.

A combination of fluorescence spectroscopy, thermogravimetric analysis, and molecular mechanics calculations has been used to study the structure-directing effect of the aromatic benzylpyrrolidine (BP) molecule (and its monofluorinated derivatives), and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of the microporous AFI structure. The results clearly show that, while all molecules form supramolecular aggregates in concentrated water solution, BPM molecules have a much more pronounced trend to aggregate as dimers within the AFI structure due to the development of interdimer H-bond interactions. Instead, BP (and its ortho- and meta-fluorinated derivatives) SDAs tend to incorporate in the AFI structure as monomers but with the simultaneous occlusion of water molecules, while para-fluorinated BP derivatives do not form compact dimers able to be accommodated in the AFI structure.

Structure-directing role of molecules containing benzyl rings in the synthesis of a large-pore aluminophosphate molecular sieve: an experimental and computational study.

We describe the synthesis of AlPO-5 and SAPO-5 materials (AFI topology) using five different tertiary amines or quaternary ammonium ions containing one or two benzyl rings as structure-directing agents (SDAs). All of the molecules successfully direct the crystallization of AlPO-5; however, only the most efficient templates are able to crystallize SAPO-5. The observed differences in template efficiency can be rationalized in terms of the interaction energy between these molecules and the AFI framework.

Computational study of a chiral supramolecular arrangement of organic structure directing molecules for the AFI structure.

Molecular mechanics computational methods have been employed to study the structure directing effect of S-(-)-1-benzyl-2-pyrrolidiniummethanol molecules towards microporous aluminophosphate materials with the AFI structure. These chiral molecules form dimers inside the one-dimensional AFI channel, which are the active structure-directing agents in the synthesis. Four different conformers of the S-(-)-1-benzyl-2-pyrrolidiniummethanol molecule are in principle available; of these, the S,S-trans shows a marked stability in dimeric form.