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

[EN] In this work we show the use of high-resolution H-1 MAS NMR to distinguish between two kinds of aggregation states of (1R,2S)-ephedrine, a chiral organic structure directing agent, occluded within AFI-type microporous aluminophosphates. We investigate in particular the supramolecular assembly of the molecules through pi MIDLINE HORIZONTAL ELLIPSIS pi 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.This work has been financed by the Spanish State Research Agency (Agencia Espanola de Investigacion, AEI) through the project PID2019-107968RB-I00. BBM acknowledges the Spanish Ministry of Economy and Competitivity for a predoctoral (BES-2013-064605) contract. Secretaria General Adjunta de Informatica-CSIC is acknowledged for running the calculations, and BIOVIA for providing the computational software. We acknowledge the support of the Label of Excellence for the Centre for zeolites and nanoporous materials by the Region of Normandy (CLEAR). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Insight on MWW siliceous zeolites: From 2D precursors toward 3D structure

ITQ-1 layered zeolites, with MWW framework, were prepared using different synthesis and calcination procedures and fully characterized by means of X-ray diffraction, scanning electron microscopy, N2 sorption and vibrational and nuclear magnetic resonance spectroscopies. Exploring different compositions of the precursor gel, the role of the Organic Structure Directing Agent (OSDA) was definitely disclosed. We proved that the concentration of OSDA in the synthesis gel affects the short-range crystalline order of zeolite crystals. In particular, diluted precursor gels led to the formation of low-density materials in the form of hollow spheres, with partially disordered layers, thinner crystals and high defectivity. In general, all ITQ-1 samples had the same crystalline structure but different morphology, either rose-like or hollow spheres. Moreover, the calcination procedure had an impact on the structural defects of the ITQ-1 zeolite: the higher the removal rate of the OSDA, the higher the defectivity degree of the zeolite

Research Trends in Evidence-Based Medicine: A Joinpoint Regression Analysis of More than 50 Years of Publication Data

Background Evidence-based medicine (EBM) has developed as the dominant paradigm of assessment of evidence that is used in clinical practice. Since its development, EBM has been applied to integrate the best available research into diagnosis and treatment with the purpose of improving patient care. In the EBM era, a hierarchy of evidence has been proposed, including various types of research methods, such as meta-analysis (MA), systematic review (SRV), randomized controlled trial (RCT), case report (CR), practice guideline (PGL), and so on. Although there are numerous studies examining the impact and importance of specific cases of EBM in clinical practice, there is a lack of research quantitatively measuring publication trends in the growth and development of EBM. Therefore, a bibliometric analysis was constructed to determine the scientific productivity of EBM research over decades. Methods NCBI PubMed database was used to search, retrieve and classify publications according to research method and year of publication. Joinpoint regression analysis was undertaken to analyze trends in research productivity and the prevalence of individual research methods. Findings Analysis indicates that MA and SRV, which are classified as the highest ranking of evidence in the EBM, accounted for a relatively small but auspicious number of publications. For most research methods, the annual percent change (APC) indicates a consistent increase in publication frequency. MA, SRV and RCT show the highest rate of publication growth in the past twenty years. Only controlled clinical trials (CCT) shows a non-significant reduction in publications over the past ten years. Conclusions Higher quality research methods, such as MA, SRV and RCT, are showing continuous publication growth, which suggests an acknowledgement of the value of these methods. This study provides the first quantitative assessment of research method publication trends in EBM

Local order in zeolites by 14N NMR : a combination of experimental and theoretical approaches.

Nous avons exploré les potentialités de la RMN 14N à l'état solide pour étudier l'ordre et le désordre local dans les zéolithes structurées à l'aide des cations de tétraalkylkammoniums. Cette étude est effectuée en combinant les approches expérimentales et théoriques. Les halogénures de tétraalkylkammonium CnH2n+1+X- (n : 1–4 ; X : Br, I) considérés comme des cristaux modèles, sont étudiés dans une première partie. Nous avons pu corréler des aspects structuraux spécifiques (distorsion des angles CNC, répartition spatiale des anions) aux paramètres spectroscopiques de l'interaction quadripolaire 14N.Dans une deuxième partie, nous décrivons l'ordre local dans la silicalite-1 (MFI), en nous basant notamment sur les paramètres de l'interaction quadripolaire 14N. Des variations chimiques au niveau des agents minéralisateurs ou structurants ont des effets mesurés sur ces paramètres qui peuvent être corrélés à l'ordre local au niveau de l'agent structurant et de la charpente minérale. Des modélisations théoriques effectuées à T = 0 et 300 K ont permis de mieux comprendre ces systèmes.Enfin, dans une troisième partie nous avons démontré la sensibilité des paramètres RMN de l'azote-14 à la distribution des sites actifs (Al, B) dans la zéolithe ZSM-5 en utilisant une large palette d'expériences RMN et de calculs théoriques.Ce travail a permis pour la première fois d'établir l'intérêt de la RMN 14N pour l'étude de l'ordre local dans les zéolithes et de montrer les principales informations qui peuvent en être tirées.We explored the 14N solid state NMR potential to study the local order and disorder in zeolites structured using tetraalkylkammonium cations. This study is performed by combining experimental and theoretical approaches.Tetraalkylkammonium halides CnH2n+1+X- (n: 1-4, X: Br, I) considered as crystal models are studied in the first part. We were able to correlate specific structural aspects (CNC angles distortions, anions spatial distribution) to the 14N NMR parameters. In the second part, we describe the local order in the silicalite-1 (MFI), based in particular on the 14N quadrupolar parameters. Chemical variations in mineralizing or structure directing agents have effects on these measured parameters which can be correlated to the organic and inorganic local orders. Theoretical modeling carried out at T = 0 and 300 K led to a better understanding of these systems. Finally, in the third part we have demonstrated the sensitivity of 14N NMR parameters to the distribution of active sites (Al, B) in ZSM-5 zeolites using a wide range of NMR experiments and theoretical calculations.This work allowed to establish for the first time the interests of 14N NMR to study the local order in zeolites and display key information that can be extracted

On the Recrystallization of Hierarchical Zeolites using Pore Directing Agents

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Is nmr a suitable tools to study defects in zeolites?

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Is nmr a suitable tools to study defects in zeolites?

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Flexibility in zeolites: origin, limits, and evaluation

International audienceNumerous evidences in the literature suggest that zeolitic materials exhibit significant intrinsic flexibility as a consequence of the spring-like behavior of Si-O and Al-O bonds and the distortion ability of Si-O-Si and Al-O-Si angles. Understanding the origin of flexibility and how it may be tuned to afford high adsorption selectivity in zeolites is a big challenge. Zeolite flexibility may be triggered by changes in temperature, pressure, or chemical composition of the framework and extra-framework compounds, as well as by the presence of guest molecules. Therefore, zeolite flexibility can be classified into three categories: (i) temperature and pressure-induced flexibility; (ii) guest-induced flexibility; and (iii) compositionally-induced flexibility. An outlook on zeolite flexibility and the challenges met during the precise experimental evaluations of zeolites will be discussed. Overcoming these challenges will provide an important tool to design novel selective adsorbents

Recent advances in 14N solid state NMR

International audienceThis chapter is devoted to the recent advances in 14N solid-state NMR related to both theoretical and practical aspects. First, the last NMR methods developed to facilitate the direct or indirect detection of 14N signals are presented in a succinct and comprehensive way. Further, the theoretical approaches that have been applied to model the 14N NMR quadrupolar parameters are explained and discussed regarding their ability to yield pertinent information on structures and dynamics of nitrogen containing solids. Last, most of the results obtained by 14N NMR characterization on inorganic, hybrid organic–inorganic, organic, or biological materials are presented, and the related NMR parameters are compiled in tables