F. De Proft

A Sustainable Way of Recycling Polyamides: Dissolution and Ammonolysis of Polyamides to Diamines and Diamides Using Ammonia and Biosourced Glycerol

W. Stuyck, K. Janssens, M. Denayer, F. De Schouwer, R. Coeck, K.V. Bernaerts, J. Vekeman, F. De Proft
Green Chemistry
24, 6923-6930
2022
A1

Abstract 

In order to make recycling a viable strategy for post-consumer plastics, economically feasible revalorization processes must be developed. The ammonolysis of polyamides can be such a cutting-edge recycling technology; however, due to the rigid structure of these polyamide plastics, operating conditions of current ammonolysis processes are harsh, including high temperatures (>300 °C) and high NH3 pressures. Here, we report a very green and elegant ammonolysis process of the widely abundant polyamide 66 by using a hard Lewis acid catalyst and 1 bar of NH3 in a simple glycol solvent at 200 °C. Computational studies revealed that especially the vicinal diol moiety of these glycol solvents plays a key role in activation of the ammonia nucleophile, with glycerol being the most effective solvent, reaching the depolymerization equilibrium after 20 h even without a catalyst. To our delight, a biosourced glycerol (obtained from the saponification of triglycerides) could also directly serve as a suitable solvent, even outperforming the ammonolysis process in highly purified glycerol.

Synergistic Effects in the Activity of Nano-Transition-Metal clusters Pt12M (M = Ir, Ru or Rh) for NO dissociation

J. Vekeman, Q. Wang, X. Deraet, D. Bazin, F. De Proft, H. Guesmi, F. Tielens
ChemPhysChem
2022
A1

Abstract 

The dissociation of environmentally hazardous NO through dissociative adsorption on metallic clusters supported by oxides, is receiving growing attention. Building on previous research on monometallic M 13  clusters [J. Phys. Chem. C, 2019, 123(33), 20314-20318], this work considers bimetallic Pt 12 M (M = Rh, Ru or Ir) clusters. The adsorption energy and activation energy of NO dissociation on the clusters have been calculated in vacuum using Koh,-Sham DFT, while their trends were rationalized using reactivity indices such as molecular electrostatic potential and global Fermi softness. The results shown that doping of the Pt clusters lowered the adsorption energy as well as the activation energy for NO dissociation. Furthermore, reactivity indices were calculated as a first estimate of the performance of the clusters in realistic amorphous silica pores (MCM-41) through  ab initio  molecular dynamics simulations.

Nanostructured Materials and Heterogeneous Catalysis: A Succint Review Regarding DeNox Catalysis

D. Bazin, J. Vekeman, Q. Wang, X. Deraet, F. De Proft, H. Guesmi, F. Tielens
Comptes Rendus. Chimie
25, S3, 163
2022
A1

Abstract 

In this contribution, we would like to underline the peculiar chemical properties of nanometer scale metallic particles. To attain this goal, we select the case of DeNox catalysis (NOx reduction to nitrogen molecule) for which such nanomaterials play a crucial role. Experimental data as well as recent theoretical calculation through density functional theory are used to assess the relationship between the adsorption mode of NO and the behaviour of nanometre scale metallic particles.

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

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

X. Deraet, J. Turek, M. Alonso, F. Tielens, S. Cottenier, P.W. Ayers, B.M. Weckhuysen, F. De Proft
Chemistry - A European Journal
27, 19 , 6050-6063
2021
A1

Abstract 

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

Towards a Predictive Model for Polymer Solubility Using the Noncovalent Interaction Index: Polyethylene as a Case Study

M. Denayer, J. Vekeman, F. Tielens, F. De Proft
Physical Chemistry Chemical Physics (PCCP)
23, 25374-25387
2021
A1
Published while none of the authors were employed at the CMM

Abstract 

In this work we present the development of a novel, quantitative solubility descriptor based on the non-covalent interaction index. It is presented as a more insightful alternative to Hansen's solubility parameters and the COSMO model to assess and predict polymer solubility in different solvents. To this end, we studied the solvation behaviour as a function of the chain length of a single chain of arguably the most simple polymer, polyethylene, in anisole (solvent) and methanol (poor solvent) via molecular dynamics simulations. It was found that in anisole the solute maximized its interface with the solvent, whereas in methanol the macromolecule formed rod-like structures by folding on itself once the chain length surpassed a certain barrier. We assessed this behaviour – which can be related to solubility – quantitatively and qualitatively via well-known descriptors, namely the solvation free energy, and the solvent accessible surface area. In addition, we propose the non-covalent interaction (NCI) index as a versatile descriptor, providing information on the strength, as well as the nature, of the solute–solvent interactions, the solute's intramolecular interactions and on the solute's conformation, both qualitatively and quantitatively. Finally, as a quantitative measure for solubility, defined in this context as the solute's tendency to maximize its interactions with the solvent, we propose two new NCI-based descriptors: the relative integrated NCI density and the integrated NCI difference. The former represents the quantitative difference in solute–solvent interactions between a fully extended coil and the actual conformation during simulation and the latter the quantitative difference between the intermolecular (solute–solvent) and the intramolecular (in the solute) non-covalent interactions. The easy interpretation and calculation of these novel quantities open up the possibility of fast, reliable and insightful high-throughput screening of different (anti)solvent and solute combinations.

Towards a Predictive Model for Polymer Solubility using the Noncovalent Interaction Index: Polyethylene as a Case Study

M. Denayer, J. Vekeman, F. Tielens, F. De Proft
Physical Chemistry Chemical Physics (PCCP)
2021
A1
Published while none of the authors were employed at the CMM

Abstract 

In this work we present the development of a novel, quantitative solubility descriptor based on the non-covalent interaction index. It is presented as a more insightful alternative to Hansen's solubility parameters and the COSMO model to assess and predict polymer solubility in different solvents. To this end, we studied the solvation behaviour as a function of the chain length of a single chain of arguably the most simple polymer, polyethylene, in anisole (solvent) and methanol (poor solvent) via molecular dynamics simulations. It was found that in anisole the solute maximized its interface with the solvent, whereas in methanol the macromolecule formed rod-like structures by folding on itself once the chain length surpassed a certain barrier. We assessed this behaviour – which can be related to solubility – quantitatively and qualitatively via well-known descriptors, namely the solvation free energy, and the solvent accessible surface area. In addition, we propose the non-covalent interaction (NCI) index as a versatile descriptor, providing information on the strength, as well as the nature, of the solute–solvent interactions, the solute's intramolecular interactions and on the solute's conformation, both qualitatively and quantitatively. Finally, as a quantitative measure for solubility, defined in this context as the solute's tendency to maximize its interactions with the solvent, we propose two new NCI-based descriptors: the relative integrated NCI density and the integrated NCI difference. The former represents the quantitative difference in solute–solvent interactions between a fully extended coil and the actual conformation during simulation and the latter the quantitative difference between the intermolecular (solute–solvent) and the intramolecular (in the solute) non-covalent interactions. The easy interpretation and calculation of these novel quantities open up the possibility of fast, reliable and insightful high-throughput screening of different (anti)solvent and solute combinations.

Towards a Predictive Model for Polymer Solubility Using the Noncovalent Interaction Index: Polyethylene as a Case Study

M. Denayer*, J. Vekeman*, F. Tielens, F. De Proft
Physical Chemistry Chemical Physics (PCCP)
2021
A1
Published while none of the authors were employed at the CMM

Abstract 

In this work we present the development of a novel, quantitative solubility descriptor based on the non-covalent interaction index. It is presented as a more insightful alternative to Hansen's solubility parameters and the COSMO model to assess and predict polymer solubility in different solvents. To this end, we studied the solvation behaviour as a function of the chain length of a single chain of arguably the most simple polymer, polyethylene, in anisole (solvent) and methanol (poor solvent) via molecular dynamics simulations. It was found that in anisole the solute maximized its interface with the solvent, whereas in methanol the macromolecule formed rod-like structures by folding on itself once the chain length surpassed a certain barrier. We assessed this behaviour – which can be related to solubility – quantitatively and qualitatively via well-known descriptors, namely the solvation free energy, and the solvent accessible surface area. In addition, we propose the non-covalent interaction (NCI) index as a versatile descriptor, providing information on the strength, as well as the nature, of the solute–solvent interactions, the solute's intramolecular interactions and on the solute's conformation, both qualitatively and quantitatively. Finally, as a quantitative measure for solubility, defined in this context as the solute's tendency to maximize its interactions with the solvent, we propose two new NCI-based descriptors: the relative integrated NCI density and the integrated NCI difference. The former represents the quantitative difference in solute–solvent interactions between a fully extended coil and the actual conformation during simulation and the latter the quantitative difference between the intermolecular (solute–solvent) and the intramolecular (in the solute) non-covalent interactions. The easy interpretation and calculation of these novel quantities open up the possibility of fast, reliable and insightful high-throughput screening of different (anti)solvent and solute combinations.

Influence of solvation and dynamics on the mechanism and kinetics of nucleophilic aromatic substitution reactions in liquid ammonia

S.L. Moors, B. Brigou, D. Hertsen, P. Balazs, P. Geerlings, V. Van Speybroeck, S. Catak, F. De Proft
Journal of Organic Chemistry
81 (4), 1635-1644
2016
A1

Abstract 

The role of the solvent and the influence of dynamics on the kinetics and mechanism of the SNAr reaction of several halonitrobenzenes in liquid ammonia, using both static calculations and dynamic ab initio molecular dynamics simulations, are investigated. A combination of metadynamics and committor analysis methods reveals how this reaction can change from a concerted, one-step mechanism in gas phase to a stepwise pathway, involving a metastable Meisenheimer complex, in liquid ammonia. This clearly establishes, among others, the important role of the solvent and highlights the fact that accurately treating solvation is of crucial importance to correctly unravel the reaction mechanism. It is indeed shown that H-bond formation of the reacting NH3 with the solvent drastically reduces the barrier of NH3 addition. The halide elimination step, however, is greatly facilitated by proton transfer from the reacting NH3 to the solvent. Furthermore, the free energy surface strongly depends on the halide substituent and the number of electron-withdrawing nitro substituents.

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.

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