31 research outputs found
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. Molecular simulations showed that the para-xylene dication displays a cylindrical shape suitable for confining in zeolite pores, while the meta-xylene derivative has an angular shape that shifts from the typical dimensions required for 12MR zeolite channels. Despite enantio-purity of the para-xylene dication with (S, S, S, S) configuration, no enrichment in polymorph A of the zeolite beta samples obtained was observed by Transmission Electron Microscopy. With the aid of molecular simulations, the failure in transferring chirality to the zeolite is explained by the loose fit of this SDA in the large-pores of zeolite beta, and a lack of close geometrical fit with the chiral element of polymorph A, as evidenced by the very similar interaction of the cation with the two enantiomorphic space groups of polymorph A. Nevertheless, the molecular-level knowledge gained in this work can provide insights for the future design of more efficient SDAs towards the synthesis of chiral zeolites
Intervenci贸n nutricional en el paciente oncohematol贸gico
Background: Oncohematological diseases such as
lymphoma or leukaemia affect an increasing number of
newly diagnosed patients in Spain and other countries.
Both disease and treatment may have a negatively impact
in the nutritional status of the patient. Malnutrition is not
uncommon among oncohematological patients. This
situation can compromised the course of the disease, the
clinical response of the treatment and the patient鈥檚
quality of life.
Method: The implementation of a multidisciplinary
approach and a systematic and protocolled nutritional
assessment would be useful when dealing with haematological
malignancies.
Results: We present a proposal of protocol for nutritional
intervention in oncohematological patients. This
proposal is been developed from the analysis of the
published literature as well as clinical practice of a multidisciplinary
team specialized in the management of
patients with haematological malignanciesObjetivos: Las enfermedades oncohematol贸gicas como
el Linfoma o la Leucemia afectan a un n煤mero importante
y creciente de personas en Espa帽a. Tanto la enfermedad
como las distintas modalidades de tratamiento
que puede llegar a precisar el paciente a lo largo del curso
de la misma impactan negativamente en el estado nutricional
del paciente, no siendo infrecuente el desarrollo de
desnutrici贸n, situaci贸n que compromete la evoluci贸n, la
respuesta al tratamiento y la calidad de vida del paciente.
M茅todo: La implementaci贸n de una estrategia multidisciplinar,
sistematizada y protocolizada de valoraci贸n
nutricional puede resultar de utilidad a la hora de abordar
a los pacientes con enfermedades oncohematol贸gicas.
Resultados: Se presenta una propuesta de protocolo de
evaluaci贸n y soporte nutricional en el paciente oncohematol贸gico
elaborada a partir del an谩lisis de la literatura
publicada al respecto, as铆 como de la pr谩ctica cl铆nica habitual
de un equipo sanitario multidisciplinar especialmente
implicado en el manejo de los pacientes con enfermedades
oncohematol贸gica
GTM-3, an extra-large pore enantioselective chiral zeolitic catalyst
The development of chiral zeolitic catalysts possessing extra-large pores and endowed with the capability of enantioselectively processing bulky products represents one of the greatest challenges in chemistry. Here, we report the discovery of GTM-3, an enantio-enriched extra-large pore chiral zeolite material with -ITV framework structure, obtained using a simple enantiopure organic cation derived from the chiral pool, N,N-ethyl-methyl-pseudoephedrinium, as the chiral-inductor agent. We demonstrate the enantio-enrichment of GTM-3 in one of the two enantiomorphic polymorphs using the two enantiomers of the organic cation. Interestingly, we prove the ability of this zeolitic material to perform enantioselective catalytic operations with very large substrates, here exemplified by the catalytic epoxide aperture of the bulky trans-stilbene oxide with alcohols, yielding unprecedented product enantiomeric excesses up to 30%. Our discovery opens the way for the use of accessible chiral zeolitic materials for the catalytic asymmetric synthesis of chiral pharmaceutical compounds
Impact of Controlling the Site Distribution of Al Atoms on Catalytic Properties in Ferrierite-Type Zeolites
Zeolites with the ferrierite (FER) topology are synthesized using a combination of tetramethylammonium
(TMA) cations with differently sized cyclic amines (pyrrolidine (Pyr), hexamethyleneimine (HMI), and 1,4-
diazabicyclo[2.2.2]octane (DAB)). Using these organic structure-directing agents (SDAs), low Si/Al ratios
and concentrated synthesis mixtures favor the crystallization of FER materials. Increasing the size of the
cyclic amine or decreasing the aluminum content leads to the crystallization of other phases or the creation
of excessive amounts of connectivity defects. TMA cations play a decisive role in the synthesis of the FER
materials, and their presence allows the use of HMI to synthesize FER. Proton MAS NMR is used to quantify
the accessibility of pyridine to acid sites in these FER samples, where it is found that the FER + HMI + TMA
sample contains only 27% acid sites in the 8-MR channels, whereas FER + Pyr and FER + Pyr + TMA
contain 89% and 84%, respectively. The constraint index (CI) test and the carbonylation of dimethyl ether
(DME) with carbon monoxide are used as probe reactions to evaluate how changes in the aluminum distribution
in these FER samples affect their catalytic behavior. Results show that the use of Pyr as an SDA results in
the selective population of acid sites in the 8-MR channels, whereas the use of HMI generates FER zeolites
with an increased concentration of acid sites in the 10-MR channels