F. De Proft

Reactivity Indices for Radical Reactions Involving Polyaromatics

K. Hemelsoet, V. Van Speybroeck, G.B. Marin, F. De Proft, P. Geerlings, M. Waroquier
Journal of Physical Chemistry A
108 (35) , 7281-7290
2004
A1

Abstract 

The reactivity of polyaromatics involved in various radical reactions is studied. The reactions under study are hydrogen abstractions by a methyl radical and additions to double bonds both intra- and intermolecular. The chemical reactivity of the involved molecules is described through different properties, which are calculated within the density functional theory (DFT) framework. The softness reactivity index is tested on its usefulness and reliability to provide information about the reactivity of the global molecule or about chemical selectivity. The applicability of the hard and soft acids and bases (HSAB) principle for bimolecular radical reactions is illustrated by comparing the results of the softness-matching criterion with kinetic and thermodynamic data. For large polyaromatic molecules several magnetic indices, in particular, magnetic susceptibilities, chemical shifts, and nucleus independent chemical shifts (NICS), are computed to quantify the aromatic character of the involved species. The applicability of these magnetic indices in the case of radical reactions is validated by comparing with kinetic results obtained from transition state theory.

DOI 

http://dx.doi.org/10.1021/jp048743k

Tentative Structures for the Radiation-Induced Radicals in Crystalline β-d-Fructose Using Density Functional Theory

E. Pauwels, P. Lahorte, G. Vanhaelewyn, F. Callens, F. De Proft, P. Geerlings, M. Waroquier
Journal of Physical Chemistry A
106 (51), 12370-12375
2002
A1

Abstract 

In this study, density functional theory calculations were used to identify the structure of the radiation-induced radicals in solid state β-d-fructose, using a single molecule approach. Four model radicals were proposed, and the electron paramagnetic resonance (EPR) parameters were calculated for the optimized geometries. These calculated parameters were subsequently compared with those of two radical species, observed in an experimental EPR and electron nuclear double resonance study on irradiated fructose (Vanhaelewyn, G.; Lahorte, P.; De Proft, F.; Mondelaers, W.; Geerlings, P.; Callens, F. Phys. Chem. Chem. Phys. 2001, 3, 1729). On the basis of this preliminary comparison, three model structures were rejected. By varying the main degree of freedom of the remaining model, a number of conformations were obtained that yielded isotropic and anisotropic hyperfine tensor components in close agreement with experimental results. To disentangle between these possible conformers, a detailed study was made of the hyperfine tensor eigenvectors. One conformation was found to be in close agreement with the experimental measurement of the hyperfine tensor of the two observed radical species. It was concluded that these experimental species are in fact manifestations of one and the same radical, with a structure conforming to our model but with slightly altered conformations.

DOI 

http://dx.doi.org/10.1021/jp0264174

The Electronegativity Equalization Method I: Parametrization and Validation for Atomic Charge Calculations

P. Bultinck, W. Langenaeker, P. Lahorte, F. De Proft, P. Geerlings, M. Waroquier, J.P. Tollenaere
Journal of Physical Chemistry A
106(34), 7887-7894
2002
A1

Abstract 

The applicability of the electronegativity equalization method (EEM) is investigated for the fast calculation of atomic charges in organic chemistry, with an emphasis on medicinal chemistry. A large training set of molecules was composed, comprising H, C, N, O, and F, covering a wide range of medicinal chemistry. Geometries and atomic charges are calculated at the B3LYP/6-31G* level, and from the calculated charges, effective electronegativity and hardness values are calibrated in a weighted least-squares fashion. The optimized parameter set is compared to other theoretical as well as experimental values and origins of the differences discussed. An approach toward extension of EEM to include new atoms is introduced. The quality of the EEM charges is assessed by comparison with B3LYP/6-31G* charges calculated for a set of medicinal molecules, not contained in the training set. The EEM approach is found to be a very powerful way to obtain ab initio quality charges without the computational cost of the ab initio approach.

DOI 

http://dx.doi.org/10.1021/jp0205463

Validation of DFT-Based Methods for Predicting Qualitative Thermochemistry of Large Polyaromatics

K. Hemelsoet, F. De Vleeschouwer, V. Van Speybroeck, F. De Proft, P. Geerlings, M. Waroquier
ChemPhysChem
12(6), 1100-1108
2011
A1

Abstract 

We present a validation of computationally efficient density functional-based methods for the reproduction of relative bond dissociation energies of large polyaromatic hydrocarbons. Through the calculation of intrinsic radical stabilities and the computation of spin densities, the extent of delocalization of the unpaired electron in the benzylic radicals is examined. We focus on the influence of the level of theory choice applied for the geometry optimization and the role of van der Waals corrections on thermochemical properties. The dispersion effects mainly influence the energetics, causing a small upward shift of the bond dissociation energies. The long-range corrected CAM-B3LYP functional does not improve the traditional B3LYP results for the geometry description of the large delocalized radicals, however a non-negligible influence was encountered when applied for the energetics. It is reported that the f polarization functions present in the 6-311+G(3df,2p) basis set lead to an erroneous trend when combined with the B2PLYP functional for the computation of the single point energies.

DOI 

http://dx.doi.org/10.1002/cphc.201000788

Assessment of atomic charge models for gas-phase computations on polypeptides

T. Verstraelen, E. Pauwels, F. De Proft, V. Van Speybroeck, P. Geerlings, M. Waroquier
Journal of Chemical Theory and Computation (JCTC)
8 (2), 661-676
2012
A1

Abstract 

The concept of the atomic charge is extensively used to model the electrostatic properties of proteins. Atomic charges are not only the basis for the electrostatic energy term in biomolecular force fields but are also derived from quantum mechanical computations on protein fragments to get more insight into their electronic structure. Unfortunately there are many atomic charge schemes which lead to significantly different results, and it is not trivial to determine which scheme is most suitable for biomolecular studies. Therefore, we present an extensive methodological benchmark using a selection of atomic charge schemes [Mulliken, natural, restrained electrostatic potential, Hirshfeld-I, electronegativity equalization method (EEM), and split-charge equilibration (SQE)] applied to two sets of penta-alanine conformers. Our analysis clearly shows that Hirshfeld-I charges offer the best compromise between transferability (robustness with respect to conformational changes) and the ability to reproduce electrostatic properties of the penta-alanine. The benchmark also considers two charge equilibration models (EEM and SQE), which both clearly fail to describe the locally charged moieties in the zwitterionic form of penta-alanine. This issue is analyzed in detail because charge equilibration models are computationally much more attractive than the Hirshfeld-I scheme. Based on the latter analysis, a straightforward extension of the SQE model is proposed, SQE+Q0, that is suitable to describe biological systems bearing many locally charged functional groups.

Open Access version available at UGent repository

DOI 

http://dx.doi.org/10.1021/ct200512e

Reactivity of Activated versus Nonactivated 2-(Bromomethyl)aziridines with respect to Sodium Methoxide: a Combined Computational and Experimental Study

H. Goossens, K. Vervisch, S. Catak, S. Stankovic, M. D'Hooghe, F. De Proft, P. Geerlings, N. De Kimpe, M. Waroquier, V. Van Speybroeck
Journal of Organic Chemistry
76 (21), 8698-8709
2011
A1

Abstract 

The difference in reactivity between the activated 2-bromomethyl-1-tosylaziridine and the non-activated 1-benzyl-2-(bromomethyl)aziridine with respect to sodium methoxide was analyzed by means of DFT calculations within the supermolecule approach, taking into account explicit solvent molecules. In addition, the reactivity of epibromohydrin with regard to sodium methoxide was assessed as well. The barriers for direct displacement of bromide by methoxide in methanol are comparable for all three heterocyclic species under study. However, ring opening was found to be only feasible for the epoxide and the activated aziridine, and not for the non-activated aziridine. According to these computational analyses, the synthesis of chiral 2-substituted 1-tosylaziridines can take place with inversion (through ring opening/ring closure) or retention (through direct bromide displacement) of configuration upon treatment of the corresponding 2-(bromomethyl)aziridines with one equivalent of a nucleophile, whereas chiral 2-substituted 1-benzylaziridines are selectively obtained with retention of configuration (via direct bromide displacement). Furthermore, the computational results showed that explicit accounting for solvent molecules is required to describe the free energy profile correctly. To verify the computational findings experimentally, chiral 1-benzyl-2-(bromomethyl)aziridines and 2-bromomethyl-1-tosylaziridines were treated with sodium methoxide in methanol. The presented work concerning the reactivity of 2-bromomethyl-1-tosylaziridine stands in contrast to the behaviour of the corresponding 1-tosyl-2-(tosyloxymethyl)aziridine with respect to nucleophiles, which undergoes a clean ring-opening/ring-closure process with inversion of configuration at the asymmetric aziridine carbon atom.

DOI 

http://dx.doi.org/10.1021/jo201255z

Cationic ring-opening polymerization of 2-propyl-2-oxazolines: understanding structural effects on polymerization behavior based on molecular modeling

M. Glassner, H. Goossens, S. Catak, V. De La Rosa, B. Monnery, F. De Proft, V. Van Speybroeck, R. Hoogenboom
ISBN/ISSN:
Talk

Conference / event / venue 

248th National Meeting of the American-Chemical-Society (ACS 2014 )
San Francisco, CA
Sunday, 10 August, 2014 to Thursday, 14 August, 2014

Reactivity of Aziridinium Salts in Different Solvents Unraveled by a Combined Theoretical and Experimental Approach

The series Topics in Heterocyclic Chemistry presents critical reviews on present and future trends in the research of heterocyclic compounds. Overall the scope is to cover topics dealing with all areas within heterocyclic chemistry, both experimental and theoretical, of interest to the general heterocyclic chemistry community. The series consists of topic related volumes edited by renowned editors with contributions of experts in the field.
Content Level » Research

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