Solid state NMR study of the adsorption of organic molecules on zeolite NaX, CaX and CaCoX

In polymerisation processes, the olefin feeds need to have a high purity. Zeolite NaX successively exchanged with calcium- and cobalt ions, is a highly selective adsorbent for the removal of cyclopentadiene impurities from 1-octene. The good performance of this material can be attributed to the accessibility of the transition metal ions, and the structure-stabilizing effect of the calcium ions. In the present work, the adsorption of dicyclopentadiene (DCPD), cyclopentadiene (CPD), 1-octene and n-octane on zeolite X, exchanged with calcium- and/or cobalt ions, has been investigated via proton MAS NMR spectroscopy. The liquid adsorbate was dosed under inert atmosphere in an MAS rotor filled with dry adsorbent, at a pore filling degree of 70 %. Next, the time evolution was recorded of the proton MAS NMR spectrum and the proton spin-lattice and spin-spin relaxation times of the adsorbed components. In the first part of the work, a theoretical study is performed of the proton NMR relaxation behaviour of an adsorbed substrate. The characteristics of a resonance line, i.e. its width, height and intensity, are determined by the effective transverse relaxation time of the spin system. In the analysis it is taken into account that the adsorbate molecules can be subject to random exchange of position. It is shown that the spin-lattice relaxation time of a uniform proton ensemble is a function of the distances between a proton and the nearest neighbouring paramagnetic ions. Therefore, this parameter can be considered as a measure for the strength of the interaction with the paramagnetic ions. The spin-spin relaxation time and the absorption line characteristics are a function of (Contents List of symbols Samenvatting Abstract Chapter I. Introduction Chapter II. Theoretical analysis of the 1H relaxation behaviour of an adsorbed substrate II.1 Introduction II.2 Derivation of a model for the 1H relaxation behaviour of an adsorbed substrate II.2.1 Analysis of the relaxation behaviour of a uniform proton ensemble II.2.1.a Analysis of the relaxation behaviour in absence of exchange II.2.1.b Analysis of the relaxation behaviour in presence of exchange II.2.2 Analysis of the relaxation behaviour of a global proton spin system II.2.3 Description of a model for the 1H relaxation behaviour of an adsorbed substrate II.3 Discussion II.3.1 Discussion of the relaxation behaviour and the absorption line characteristics of a uniform proton ensemble II.3.1.a Influence of its approach towards paramagnetic ions, and of its exchange II.3.1.b Calculation of the critical distance for extinction II.3.1.c Influence of the nature of the adsorbent II.3.2 Implications for the experimental methodology II.4 Conclusion Chapter III. Experimental methodology and results III.1 Experimental methodology III.2 Results III.2.1 Spectral data III.2.2 Relaxometric data Chapter IV. Discussion of Relaxation Data IV.1 Analysis of the chemical shifts of adsorbate in the initial spectra IV.2 Influence of adsorbent/adsorbate nature on line width, spin-lattice (T1) and spin-spin (T2d) relaxation times IV.3 Diffusivity aspects of adsorbate molecules in zeolites derived from line intensities IV.4 Calculation of the diffusional time constants and diffusion coefficients from T1 values IV.5 Average distance between the adsorbate molecules and the paramagnetic ions from T1 values IV.6 Relaxation behaviour of adsorbates from T1 values IV.7 Relaxation behaviour of adsorbates from T2d values IV.8 Chemical transformations occurring during adsorption Chapter V. General conclusions Appendix Appendix I: Derivation of a theoretical expression for the absorption line of a uniform proton spin system Appendix II: Experimental methods for the determination of the spin-lattice and spin-spin relaxation time Appendix III: Values for the intensity, width and height of the resonance lines, and for the total spectral intensity Appendix IV: Calculated 1H NMR spectrum of 1-octene transformation products Referencesstatus: publishe

Dissolution enhancement of the anti-HIV drug UC 781 by formulation in a ternary solid dispersion with TPGS 1000 and Eudragit E100

The present research deals with the improvement of the dissolution properties of the anti-HIV drug UC 781. A ternary solid dispersion consisting of a high amount of TPGS 1000 and exhibiting good powder properties with respect to flowability was developed. Eudragit E100 was selected as a polymer based on supersaturation studies. DSC analysis of solid dispersions containing drug doses from 0 to 80% w/w revealed eutectic phase behaviour of the ternary TPGS 100-Eudragit E100-UC 781 mixture. The release of UC 781 in a medium simulating the gastrointestinal lumen was markedly enhanced, reaching a release of 70% w/w after 4h. XRD results pointed to the presence of crystalline drug in the solid dispersion. The presence of UC 781 in the dispersion had an influence on the TPGS 1000-Eudragit E100 carrier, favoring folding of the polyethylene glycol chains in TPGS 1000. Moreover, the addition of UC 781 to the binary polymer-surfactant mixture was physically expressed by an increase in fluidity of the samples up to a drug load of 50% w/w. NMR was used to investigate this phenomenon, revealing a shielding and/or deshielding effect of the carrier on aromatic C atoms and methyl groups in UC 781. Polyethylene glycol chains present in TPGS 1000 seemed to play a role in this process. In addition, combining UC 781 with the TPGS 1000-Eudragit E100 mixture led to the appearance of TPGS 1000 clusters with a glass transition temperature well below the T(g)'s of the pure compounds.status: publishe

Post-synthesis Snß: An exploration of synthesis parameters and catalysis

© 2015 Elsevier Inc. All rights reserved. Snβ is probably one of the best water tolerating heterogeneous Lewis acids for liquid phase catalysis. Instead of applying the usual lengthy hydrothermal synthesis to prepare Snβ, this contribution uses a more hands-on two-step synthesis method, involving the grafting of Sn precursors in isopropanol under reflux conditions on a commercial β zeolite that was dealuminated in acid. Among several reference synthesis procedures, this Sn introduction method resulted in active Sn catalytic sites. Taking advantage of this practical method, several synthesis parameters were explored and their impact on the catalytic activity in four different Lewis acid catalyzed reactions is discussed. The adsorption isotherm of SnIV in isopropanol over a broad range of Sn salt concentrations at reflux temperature is presented and discussed in relation with FTIR spectroscopy, UV-vis absorption characteristics and the porosity of the materials. The study reveals a selective Sn uptake, up to 2 wt% Sn loading, into silanol nests of the dealuminated precursor, forming a diversity of mononuclear SnIV. Higher Sn loadings result in less active Sn (hydrous) extraframework oxide phases, which also cause partial blockage of the zeolite micropores. Depending on the reaction type under study, space time yield may increase with increasing Sn loading, but the activity per Sn is always lower. Therefore it is concluded that a preferred synthesis should form high contents of isolated Sn active sites, especially for sugar isomerization and intermolecular Meerwein-Ponndorf-Verley, while the other reaction types like Baeyer-Villiger is also sufficiently catalyzed by the small Sn oxide clusters, albeit less actively.publisher: Elsevier articletitle: Post-synthesis Snβ: An exploration of synthesis parameters and catalysis journaltitle: Journal of Catalysis articlelink: http://dx.doi.org/10.1016/j.jcat.2015.06.023 content_type: article copyright: Copyright © 2015 Elsevier Inc. All rights reserved.status: publishe

Enhanced Acidity and Accessibility in Al-MCM-41 through Aluminum Activation

© 2016 American Chemical Society. Incorporating aluminum is the most widely applied and industrially relevant method to functionalize amorphous silica. However, established protocols yield predominately poorly distributed and inaccessible Al species, and as a result only ∼10-15% of the present aluminum gives rise to the acid sites, hampering the overall catalytic potential. Herein, the influence of alkaline activations with aqueous NaOH and NH4OH on the porosity, acidity, and catalytic properties of Al-MCM-41 is studied. By performing room temperature activations in 0.01-0.1 M NaOH or 0.5 M NH4OH, the Ostwald ripening of silica in alkaline media is exploited, which results in high mass retention yields (100-74%) and a controlled transformation of the 3.6 nm mesopores of the parent material to a broad pore range from 3 to ∼12 nm. Electron microscopy indicates the presence of additional interconnected intraparticle porosity, whereas no significant change in the shape and size of the original particles is observed. Elemental analysis reveals that the optimal alkaline activation with 0.05 M NaOH leads to a decrease in the Si/Al ratio at the surface, despite an increase in the bulk Si/Al ratio. 27Al magic angle spinning nuclear magnetic resonance spectroscopy demonstrates a large conversion of octahedral Al into tetrahedral Al, doubling the purely tetrahedral fraction from 30 to 60%. Pyridine-probed Fourier transformed infrared spectroscopy shows a doubling of the Brønsted and Lewis acidity after activation. The compositional and spectroscopic results are ratified by monitoring the relative accessibility of the acid sites, i.e., effective acidity (mol acid sites per mol Al). The alkaline activation enhances the effective acidity by increasing access to the Al sites trapped inside the pore wall and by reincorporation of the octahedral Al as accessible tetrahedral sites. As a result, an unprecedented effective acidity is obtained after the Al incorporation, which is substantiated using a novel accessibility concept. The catalytic potential of the activation protocol is demonstrated by quadrupling the catalytic activity for the acid-catalyzed alkylation of toluene with benzyl alcohol, an over-50% activity gain, a slightly enhanced selectivity, and a strongly reduced coking in the acid-catalyzed coupling of furfural with sylvan.status: publishe

An improved design to capture magnetic microparticles for capillary electrophoresis based immobilized microenzyme reactors

In this paper, we demonstrate the effectiveness of a new 3D printed magnet holder that enables capture of magnetic microparticles in commercially available capillary electrophoresis equipment with a liquid or air based coolant system. The design as well as the method to capture magnetic microparticles inside the capillary are discussed. This setup was tested at temperature and pH values suitable for performing enzymatic reactions. To demonstrate its applicability in CE- immobilized microenzyme reactors (IMER) development, human flavin-containing monooxygenase 3 and bovine serum albumin were immobilized on amino functionalized magnetic microparticles using glutaraldehyde. These microparticles were subsequently used to perform in-line capillary electrophoresis with clozapine as a model substrate. This setup could be used further to establish CE-IMERs of other drug metabolic enzymes in a commercially available liquid based capillary coolant system. The CE-IMER setup was successful, although a subsequent decrease in enzyme activity was observed on repeated runs. This article is protected by copyright. All rights reserved.status: publishe