V. Van Speybroeck

Carbon Capture Turned Upside Down: High-Temperature Adsorption & Low-Temperature Desorption (HALD)

L. Joos, K. Lejaeghere, J. Huck, V. Van Speybroeck, B. Smit
Energy & Environmental Science
8, 2480-2491
2015
A1

Abstract 

Carbon Capture & Sequestration (CCS) could reduce CO2 emissions from large fossil-fuel power plants in the short term, but the high energy penalty of the process hinders its industrial deployment. Moreover, the utility of nanoporous materials, known to be selective for the CO2/N2 separation, is drastically reduced due to the competitive adsorption with H2O. Taking advantage of the power plant's waste heat to perform CCS while at the same time surmounting the negative effect of H2O is therefore an attractive idea. We propose an upside-down approach for CCS in nanoporous materials, High-temperature Adsorption & Low-temperature Desorption (HALD), that exploits the temperature-dependent competitive adsorption of CO2 and H2O. First, we provide a theoretical background for this entropy-driven behavior and demonstrate under what conditions competitive adsorption can be in favor of CO2 at high temperature and in favor of H2O at low temperature. Then, molecular simulations in all-silica MFI provide a proof of concept. The International Zeolite Association database is subsequently screened for potential candidates and finally, the most promising materials are selected using a post-Pareto search algorithm. The proposed post-Pareto approach is able to select the material that shows an optimal combination of multiple criteria, such as CO2/H2O selectivity, CO2/N2 selectivity, CO2 uptake and H2O uptake. As a conclusion, this work provides new perspectives to reduce the energy requirement for CCS and to overcome the competitive adsorption of H2O.

Open Access version available at UGent repository

Synthesis of poly(2-oxazoline)s with side chain methyl ester functionalities: Detailed understanding of copolymerization behavior of methyl ester containing monomers with 2-alkyl-2-oxazolines

P. Bouten, D. Hertsen, M. Vergaelen, B. Monnery, S. Catak, J. van Hest, V. Van Speybroeck, R. Hoogenboom
Polymer Chemistry
7 (17), 2711-2719
2015
A1

Abstract 

Poly(2-oxazoline)s with methyl ester functionalized side chains are interesting as they can undergo a direct amidation reaction or can be hydrolyzed to the carboxylic acid, making them versatile functional polymers for conjugation. In this work, detailed studies on the homo- and copolymerization kinetics of two methyl ester functionalized 2-oxazoline monomers with 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, and 2-n-propyl-2-oxazoline are reported. The homopolymerization of the methyl ester functionalized monomers is found to be faster compared to the alkyl monomers, while copolymerization unexpectedly reveals that the methyl ester containing monomers significantly accelerate the polymerization. A computational study confirms that methyl ester groups increase the electrophilicity of the living chain end, even if they are not directly attached to the terminal residue. Moreover, the electrophilicity of the living chain end is found to be more important than the nucleophilicity of the monomer in determining the rate of propagation. However, the monomer nucleophilicity can be correlated with the different rates of incorporation when two monomers compete for the same chain end, that is, in copolymerizations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015

Beyond the diketopiperazine family with alternatively bridged brevianamide F analogues

I. Wauters, H. Goossens, E. Delbeke, K. Muylaert, B.I. Roman, K. Van Hecke, V. Van Speybroeck, C.V. Stevens
Chemistry - A European Journal
80 (16), 8046-8054
2015
A1

Abstract 

A method for the preparation of 3,5-bridged piperazin-2-ones from a tryptophan–proline-based diketopiperazine is described using diphosgene to induce the ring closure. Density functional theory calculations were conducted to study the mechanism of this C–C bond formation. Several derivatives of the thus obtained α-chloroamine were synthesized by substitution of the chlorine atom using a range of O-, N-, S-, and C-nucleophiles. This novel class of brevianamide F analogues possess interesting breast cancer resistance protein inhibitory activity.

On the convergence of atomic charges with the size of the enzymatic environment

D.E.P. Vanpoucke, J. Olah, F. De Proft, V. Van Speybroeck, G. Roos
Journal of Chemical Information and Modeling (JCIM)
Volume 55 Issue 3 page 564–571
2015
A1

Abstract 

Atomic charges are a key concept to give more insight into the electronic structure and chemical reactivity. The Hirshfeld-I partitioning scheme applied to the model protein human 2-cysteine peroxiredoxin thioredoxin peroxidase B is used to investigate how large a protein fragment needs to be in order to achieve convergence of the atomic charge of both, neutral and negatively charged residues. Convergence in atomic charges is rapidly reached for neutral residues, but not for negatively charged ones. This study pinpoints difficulties on the road towards accurate modeling of negatively charged residues of large biomolecular systems in a multiscale approach.

Semi-Analytical mean-field model for predicting breathing in Metal-Organic Frameworks

L. Vanduyfhuys, A. Ghysels, S.M.J. Rogge, R. Demuynck, V. Van Speybroeck
Molecular Simulation
41, 16-17, 1311-1328
2015
A1

Abstract 

A new semi-analytical model is proposed to rationalize breathing of MIL-53 type materials. The model is applied on two case studies, the guest-induced breathing of MIL-53(Cr) with CO 2 and CH 4 , and the phase transformations for MIL-53(Al) upon xenon adsorption. Experimentally, MIL-53(Cr) breathes upon CO 2 adsorption, which was not observed for CH 4 . This result could be ascribed to the stronger interaction of carbon dioxide with the host matrix. For MIL-53(Al) a phase transition from the large pore phase could be enforced to an intermediate phase with volumes of about 1160 − 1300 A, which corresponds well to the phase observed experimentally upon xenon adsorption. Our thermodynamic model correlates nicely with the adsorption pressure model proposed by Coudert et al. Furthermore the model can predict breathing behavior of other flexible materials, if the user can determine the free energy of the empty host, the interaction energy between a guest molecule and the host matrix and the pore volume accessible to the guest molecules. This will allow to generate the osmotic potential from which the equilibria can be deduced and the anticipated experimentally observed phase may be predicted.

Open Access version available at UGent repository

QuickFF: A program for a quick and easy derivation of force fields for Metal-Organic Frameworks from ab initio input

L. Vanduyfhuys, S. Vandenbrande, T. Verstraelen, R. Schmid, M. Waroquier, V. Van Speybroeck
Journal of Computational Chemistry
36, 13, 1015–1027
2015
A1

Abstract 

QuickFF is a software package to derive accurate force fields for isolated and complex molecular systems in a quick and easy manner. Apart from its general applicability, the program has been designed to generate force fields for metal-organic frameworks in an automated fashion. The force field parameters for the covalent interaction are derived from ab initio data. The mathematical expression of the covalent energy is kept simple to ensure robustness and to avoid fitting deficiencies as much as possible. The user needs to produce an equilibrium structure and a Hessian matrix for one or more building units. Afterward, a force field is generated for the system using a three-step method implemented in QuickFF. The first two steps of the methodology are designed to minimize correlations among the force field parameters. In the last step, the parameters are refined by imposing the force field parameters to reproduce the ab initio Hessian matrix in Cartesian coordinate space as accurate as possible. The method is applied on a set of 1000 organic molecules to show the easiness of the software protocol. To illustrate its application to metal-organic frameworks (MOFs), QuickFF is used to determine force fields for MIL-53(Al) and MOF-5. For both materials, accurate force fields were already generated in literature but they requested a lot of manual interventions. QuickFF is a tool that can easily be used by anyone with a basic knowledge of performing ab initio calculations. As a result, accurate force fields are generated with minimal effort.

Open Access version available at UGent repository

Advances in theory and their application within the field of zeolite chemistry

V. Van Speybroeck, K. Hemelsoet, L. Joos, M. Waroquier, R.G. Bell, C.R.A. Catlow
Chemical Society Reviews
Vol. 44 , 7044-7111
2015
A1

Abstract 

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functionalities to obtain the best material for a given application. Over the last decades, theoretical modeling has matured to a level that model guided design has become within reach. Major hurdles have been overcome to reach this point and almost all contemporary methods in computational materials chemistry are actively used in the field of modeling zeolite chemistry and applications. Integration of complementary modeling approaches is necessary to obtain reliable predictions and rationalizations from theory. A close synergy between experimentalists and theoreticians has led to a deep understanding of the complexity of the system at hand, but also allowed the identification of shortcomings in current theoretical approaches. Inspired by the importance of zeolite characterization which can now be performed at the single atom and single molecule level from experiment, computational spectroscopy has grown in importance in the last decade. In this review most of the currently available modeling tools are introduced and illustrated on the most challenging problems in zeolite science. Directions for future model developments will be given.

Open Access version available at UGent repository

On the Possibility of [1,5] Sigmatropic Shifts in Bicyclo[4.2.0]octa-2,4-dienes

H. Goossens, J.M. Winne, S. Wouters, L. Hermosilla, P. J. De Clercq, M. Waroquier, V. Van Speybroeck, S. Catak
Journal of Organic Chemistry
80 (5) 2609-2620
2015
A1

Abstract 

The thermal equilibration of the methyl esters of endiandric acids D and E was subject to a computational study. An electrocyclic pathway via an electrocyclic ring opening followed by a ring flip and a subsequent electrocyclization proposed by Nicolaou [Chem. Soc. Rev. 2009], was computationally explored. The free energy barrier for this electrocyclic route was shown to be very close to the bicyclo[4.2.0]octa-2,4-diene reported by Huisgen [Tet. Lett. 1968]. Furthermore, the possibility of a [1,5] sigmatropic alkyl group shift of bicyclo[4.2.0]octa-2,4-diene systems at high temperatures was explored in a combined computational and experimental study. Calculated reaction barriers for a biradical-mediated stepwise [1,5] sigmatropic alkyl group shift were shown to be comparable with the reaction barriers for the bicyclo[4.1.0]hepta-2,4-diene (norcaradiene) walk rearrangement, whereas calculated reaction barriers for a concerted [1,5] sigmatropic alkyl group shift were found to be higher in energy. However, the stepwise pathway is suggested to only be feasible for appropriately substituted compounds. Experiments conducted on a deuterated analogous diol derivative confirmed the calculated (large) differences in barriers between electrocyclic and sigmatropic pathways.

Elucidating the Structural Isomerism of Fluorescent Strigolactone Analogue CISA-1

H. Goossens, T.S.A Heugebaert, B. Dereli, M. Van Overtveldt, O. Karahan, I. Doğan, M. Waroquier, V. Van Speybroeck, V. Aviyente, S. Catak, C.V. Stevens
European Journal of Organic Chemistry
2015 (6), 1211–1217
2015
A1

Abstract 

The synthesis of a new potent strigolactone analogue (CISA-1), resulting in the formation of two interconverting structural isomers, which could not be identified, was recently reported by Rasmussen et al [Molecular Plant, 2013, 6, 100]. In the present study, a combined computational and experimental approach is used to identify the exact nature of these structural isomers. While standard experimental techniques were not able to determine the identity of the isomers, chromatographic methods excluded E/Z isomerisation. Computational 1H NMR chemical shift values and DFT calculations on interconversion barriers strongly suggest that the CISA-1 isomers were interconverting (Z)-configured atropisomers.

Accelerated living cationic ring-opening polymerization of a methyl ester functionalized 2-oxazoline monomer

P.J.M. Bouten, D. Hertsen, M. Vergaelen, B. Monnery, M.A. Boerman, H. Goossens, S. Catak, J.C.M. van Hest, V. Van Speybroeck, R. Hoogenboom
Polymer Chemistry
6, 514-518
2015
A1

Abstract 

Kinetic studies on the homo- and copolymerization of 2-methoxycarboxyethyl-2-oxazoline (MestOx) with 2-methyl-2-oxazoline (MeOx) and 2-ethyl-2-oxazoline (EtOx) were performed. For the homopolymerisation of MestOx an increased propagation rate constant was observed compared to MeOx and EtOx while the copolymerization of MestOx with MeOx or EtOx unexpectedly revealed slower incorporation of MestOx. Density functional theory (DFT) calculations show that nearby MestOx residues in the living chain can activate both the oxazolinium chain end and the attacking monomer, stabilizing the propagation transition state, leading to faster homopolymerisation of MestOx. These effects also accelerate incorporation of both monomers in the copolymerisations. However, since MeOx is shown to be more nucleophilic than MestOx, the incorporation order is reversed in the copolymerisations.

Open Access version available at UGent repository

Pages

Subscribe to RSS - V. Van Speybroeck