V. Van Speybroeck

Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions

A.E.J. Hoffman, I. Senkovska, J. Wieme, A. Krylov, S. Kaskel, V. Van Speybroeck
Journal of Materials Chemistry A
2022
A1

Abstract 

Phase transitions in exible metal-organic frameworks or soft porous crystals are mediated by low-frequency phonons or rigid-unit modes. The alteration of specic building blocks may change the lattice dynamics of these frameworks, which can inuence the phase transition mechanism. In this work, the impact of building block substitution on the rigid-unit modes in exible MIL-53 analogs with a winerack topology will be investigated via ab initio lattice dynamics calculations. First, the accuracy of the theoretical simulations is veried via experimental Raman measurements, which provide unique ngerprint vibrations in the terahertz range to characterize the phase transition. Following analysis of the low-frequency vibrations shows that there exists a set of universal rigid-unit modes inducing translations and/or rotations of the building blocks. The theoretical results demonstrate that linker substitutions have a large eect on the rigid-unit mode frequencies, whereas this is less so for inorganic chain substitutions. These ndings may help to rationally tune the phonon frequencies in soft porous crystals.

How Reproducible are Surface Areas Calculated from the BET Equation?

J.W.M. Osterrieth, J. Rampersad, D. Madden, N. Rampal, L. Skoric, B. Connolly, M.D. Allendorf, V. Stavila, J.L Snider, R. Ameloot, J. Marreiros, C. Ania, D. Azevedo, E. Vilarrasa-Garcia, B.F. Santos, X.-H. Bu, Z. Chang, H. Bunzen, N.R. Champness, S.L. Griffin, B. Cheng, R.-B. Lin, B. Coasne, S. Cohen, J.C. Moreton, Y.J. Colón, L. Chen, R. Clowes, F.-X. Coudert, Y. Cui, B. Hou, D.M. D'Alessandro, P.W. Doheny, M. Dincă, C. Sun, C. Doonan, M.T. Huxley, J.D. Evans, P. Falcaro, R. Ricco, O. Farha, K.B. Idrees, T. Islamoglu, P. Feng, H. Yang, R.S. Forgan, D. Bara, S. Furukawa, E. Sanchez, J. Gascon, S. Telalović, S.K. Ghosh, S. Mukherjee, M.R. Hill, M.M. Sadiq, P. Horcajada, P. Salcedo-Abraira, K. Kaneko, R. Kukobat, J. Kenvin, S. Keskin, S. Kitagawa, K.-i. Otake, R.P. Lively, S.J.A. DeWitt, P.L. Llewellyn, B.V. Lotsch, S.T. Emmerling, A.M. Pütz, C. Martí-Gastaldo, N.M. Padial, J. García-Martínez, N. Linares, D. Maspoch, J.A. Suárez del Pino, P.Z. Moghadam, R. Oktavian, R.E. Morris, P.S. Wheatley, J. Navarro, C. Petit, D. Danaci, M.J. Rosseinsky, A.P. Katsoulidis, M. Schroeder, X. Han, S. Yang, C. Serre, G. Mouchaham, D.S. Sholl, R. Thyagarajan, D. Siderius, R.Q. Snurr, R.B. Goncalves, S. Telfer, S.J. Lee, V.P. Ting, J.L. Rowlandson, T. Uemura, T. Iiyuka, M.A. van der Veen, D. Rega, V. Van Speybroeck, S.M.J. Rogge, A. Lamaire, K.S. Walton, L.W. Bingel, S. Wuttke, J. Andreo, O. Yaghi, B. Zhang, C.T. Yavuz, T.S. Nguyen, F. Zamora, C. Montoro, H. Zhou, A. Kirchon, D. Fairen-Jimenez
Advanced Materials
2022
A1

Abstract 

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Gold Open Access

Stable Amorphous Solid Dispersion of Flubendazole with High Drug Loading via Solvent Electrospinning

J. Becelaere, E. Van den Broeck, E. Schoolaert, V. Vanhoorne, J. F.R. Van Guyse, M. Vergaelen, S. Borgmans, K. Creemers, V. Van Speybroeck, C. Vervaet, R. Hoogenboom, K. De Clerck
Journal of controlled release
2022
A1

Abstract 

In this work, an important step is taken towards the bioavailability improvement of poorly water-soluble drugs, such as flubendazole (Flu), posing a challenge in the current development of many novel oral-administrable therapeutics. Solvent electrospinning of a solution of the drug and poly(2-ethyl-2-oxazoline) is demonstrated to be a viable strategy to produce stable nanofibrous amorphous solid dispersions (ASDs) with ultrahigh drug-loadings (up to 55 wt% Flu) and long-term stability (at least one year). Importantly, at such high drug loadings, the concentration of the polymer in the electrospinning solution has to be lowered below the concentration where it can be spun in absence of the drug as the interactions between the polymer and the drug result in increased solution viscosity. A combination of experimental analysis and molecular dynamics simulations revealed that this formulation strategy provides strong, dominant and highly stable hydrogen bonds between the polymer and the drug, which is crucial to obtain the high drug-loadings and to preserve the long-term amorphous character of the ASDs upon storage. In vitro drug release studies confirm the remarkable potential of this electrospinning formulation strategy by significantly increased drug solubility values and dissolution rates (respectively tripled and quadrupled compared to the crystalline drug), even after storing the formulation for one year.

A general synthesis of azetidines by copper-catalysed photoinduced anti-Baldwin radical cyclization of ynamides

C. Jacob, H. Baguia, A. Dubart, S. Oger, P. Thilmany, J. Beaudelot, C. Deldaele, S. Peruško, Y. Landrain, B. Michelet, S. Neale, E. Romero, C. Moucheron, V. Van Speybroeck, C. Theunissen, G. Evano
Nature Communications
13, 560
2022
A1

Abstract 

A general anti-Baldwin radical 4-exo-dig cyclization from nitrogen-substituted alkynes is reported. Upon reaction with a heteroleptic copper complex in the presence of an amine and under visible light irradiation, a range of ynamides were shown to smoothly cyclize to the corresponding azetidines, useful building blocks in natural product synthesis and medicinal chemistry, with full control of the regioselectivity of the cyclization resulting from a unique and underrated radical 4-exo-dig pathway.

Gold Open Access

Mechanistic characterization of zeolite-catalyzed aromatic electrophilic substitution at realistic operating conditions

M. Bocus, L. Vanduyfhuys, F. De Proft, B.M. Weckhuysen, V. Van Speybroeck
JACS Au (Journal of the American Chemical Society)
2, 2, 502-514
2022
A1

Abstract 

Zeolite-catalyzed benzene ethylation is an important industrial reaction, as it is the first step in the production of styrene for polymer manufacturing. Furthermore, it is a prototypical example of aromatic electrophilic substitution, a key reaction in the synthesis of many bulk and fine chemicals. Despite extensive research, the reaction mechanism and the nature of elusive intermediates at realistic operating conditions is not properly understood. More in detail, the existence of the elusive arenium ion (better known as Wheland complex) formed upon electrophilic attack on the aromatic ring is still a matter of debate. Temperature effects and the presence of protic guest molecules such as water are expected to impact the reaction mechanism and lifetime of the reaction intermediates. Herein, we used enhanced sampling ab initio molecular dynamics simulations to investigate the complete mechanism of benzene ethylation with ethene and ethanol in the H-ZSM-5 zeolite. We show that both the stepwise and concerted mechanisms are active at reaction conditions and that the Wheland intermediate spontaneously appears as a shallow minimum in the free energy surface after the electrophilic attack on the benzene ring. Addition of water enhances the protonation kinetics by about 1 order of magnitude at coverages of one water molecule per Brønsted acidic site. In the fully solvated regime, an overstabilization of the BAS as hydronium ion occurs and the rate enhancement disappears. The obtained results give critical atomistic insights in the role of water to selectively tune the kinetics of protonation reactions in zeolites.

Gold Open Access

Acidity effect on benzene methylation kinetics over substituted H-MeAlPO-5 catalysts

M. Morten, T. Cordero-Lanzac, P. Cnudde, E. A. Redekop, S. Svelle, V. Van Speybroeck, U. Olsbye
Journal of Catalysis
404, 594-606
2021
A1

Abstract 

Methylation of aromatic compounds is a key reaction step in various industrial processes such as the aromatic cycle of methanol-to-hydrocarbons chemistry. The study of isolated methylation reactions and of the influence of catalyst acidity on their kinetics is a challenging task. Herein, we have studied unidirectional metal-substituted H-MeAlPO-5 materials to evaluate the effect of acid strength on the kinetics of benzene methylation with DME. First-principle simulations showed a direct correlation between the methylation barrier and acid site strength, which depends on the metal substituent. Three H-MeAlPO-5 catalysts with high (Me = Mg), moderate (Me = Si) and low acidity (Me = Zr) were experimentally tested, confirming a linear relationship between the methylation activation energy and acid strength. The effects of temperature and reactant partial pressure were evaluated, showing significant differences in the byproduct distribution between H-MgAlPO-5 and H-SAPO-5. Comparison with propene methylation suggested that the Mg substituted catalyst is also the most active for the selective methylation of alkenes.

Gold Open Access

A comparative theoretical study on the solvent dependency of anthocyanin extraction profiles

K.T. Phan, E. Van den Broeck, K. Raes, K. De Clerck, V. Van Speybroeck, S. De Meester
Journal of Molecular Liquids
351
2022
A1

Abstract 

Anthocyanidins and anthocyanins are flavonoids with nutritional, antioxidative and color properties that are present in various food products and biomass, such as food waste. The large chemical diversity amongst these molecules potentially leads to different affinities or activities in food and non-food applications. In order to characterize the extraction profile, advanced analytical techniques along with optimized separation procedures are required. Alternatively, theoretical tools can be applied for predicting the solubility or binding affinity of molecules in various reaction media. In this paper, the solubility of anthocyanidins and anthocyanins was analyzed by various theoretical tools such as group contribution methods (e.g., Hansen solubility parameters and Flory-Huggins interaction parameter (χ12)) and molecular modeling (e.g., static calculations based on Density Functional Theory (DFT) and COSMO-RS). It was found that COSMO-RS was able to give quantitative information on the solubility behavior within various pure solvents and it is able to describe the main intermolecular interactions between colorant and solvent, while Hansen solubility parameters were most appropriate to find the most optimal organic solvent-water mixture ratio. In general, solvents with electron-rich aromatic rings and/or containing electron donors, acting as hydrogen bond acceptors, showed the highest solubilizing power for anthocyanidins and anthocyanins.

Gold Open Access

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