Conceptual Density Functional Theory Descriptors Research Articles

Proposal of a Fermi-Dirac-Derived Reactivity Descriptor: Beyond the Frontier MO Model.

In this paper, we derive a reactivity descriptor stemming from the Fermi-Dirac population scheme, applied to density functional calculations on molecular systems. Assuming that molecular orbitals only marginally change when temperature is slightly increased from 0 K, we study the response of electron density to a change in temperature. Connection with usual conceptual density functional theory descriptors is made, and the T-variation of electron density for some representative examples is given and discussed.

Density Functional Treatment on Alkylation of a Functionalized Deltahedral Zintl Cluster.

Density functional theory (DFT) is one of the popular methods to understand the electronic structure of molecular systems based on electronic density. On the basis of this theory, several conceptual DFT descriptors have been developed which can deal with the stability, reactivity, and several other physicochemical properties of molecules. Here, we have taken a nine-atom-functionalized deltahedral Zintl cluster of germanium (Ge) to examine the alkylation reaction mechanism. The study showed that the Zintl cluster having a methyl group as a ligand, [Ge9(CH3)3-], acts as a better nucleophile than the cyanide (-CN)-substituted cluster [Ge9(CN)3-] in terms of different thermodynamic parameters like free energy, enthalpy of activation, reaction energy, etc. A detailed reaction electronic flux analysis reveals the nature of the electronic activity throughout the reaction pathway. The reaction force, Wiberg bond indices, and dual descriptor lend additional support to the reaction mechanism. It has been found that the alkylation reaction between the Zintl ion and the alkyl halide follows a SN2-like mechanism.

Extending the Marcus μ-Scale of Solvent Softness Using Conceptual Density Functional Theory and the Orbital Overlap Distance: Method and Application to Ionic Liquids

The chemical hardness of a solvent can play a decisive role in solubility and reactivity in solution. Several empirical scales quantifying solvent softness have been proposed. We explore whether computed properties of solvent molecules can reproduce these experimental scales. Our “orbital overlap distance” quantifying the size of orbitals at a molecule’s surface effectively reproduces the Marcus μ-scale of solvent softness. The orbital overlap distance predicts that the surface of chemically hard solvent molecules is dominated by compact orbitals possessing a small orbital overlap distance. In contrast, the surface of chemically soft solvent molecules has a larger contribution from diffuse orbitals and a larger orbital overlap distance. Other conceptual density functional theory descriptors, including the global hardness and electronegativity, can also reproduce the Marcus scale. We further introduce a “solvent versatility” RMSD Dsurf scale quantifying variations in the surface orbital overlap distance. “Good” solvents such as DMSO, which combine chemically “hard” and “soft” sites within a single molecule, possess a large RMSD Dsurf. We conclude by applying this approach to predict the Marcus μ-parameters for widely-used ionic liquids and ionic liquid–cosolvent systems.

Relaxation of Kohn–Sham orbitals of organometallic complexes during the approach of a nucleophilic reactant (or an electron approach): the case of [sal(ph)en]2 Zn complexes

In a recent paper, the Lewis acidic character of a series of Zn-Sal(ph)en complexes was reviewed, using conceptual density functional theory descriptors to assess the acidic character. It was shown that the nature of the bridging diamine link in the Schiff base ligand controls this character that is mainly responsible for the coordination of the Zn2+, hence for the geometry of these complexes. However, the usual dual descriptor did exhibit significant weaknesses to retrieve the electrophilic part on the metal cation of the Zn-sal(ph)en complexes. Indeed, it is necessary to include the densities of the electronic excited states through the so-called state-specific dual descriptor. This procedure will allow us to recover successfully the appropriate reactivity of the studied complexes holding diamine bridges differing by flexible to semi-rigid and to rigid ranges. Nevertheless, the selection of the excited state allowing a meaningful description of the Lewis acidic is not a priori obtained from a direct identification of the Kohn–Sham (KS) orbitals involved in the excitation. The present work reports an analysis of the relaxation of the KS orbitals when a fraction of charge is added to a virtual orbital, and when an excitation is considered, while a fractional charge is transferred from an occupied orbital toward a virtual orbital.

On the influence of dynamical effects on reactivity descriptors

In this paper, we investigate the role of structural dynamical effects on reactivity properties of selected Michael acceptors. To this aim, quantum molecular dynamics simulations were performed. Conceptual density functional theory descriptors were then evaluated on selected snapshots, providing statistical indicators suitable to assess the discrepancies between static and dynamical approaches. The implications of these results for building a predictive model correlated to Mayr’s electrophilicity index are then discussed, paving the way towards a more realistic account of experimental results.

Coordination chemistry of Zn2+ with Sal(ph)en ligands: Tetrahedral coordination or penta‐coordination? a DFT analysis

In this article, the Lewis acidic character within a series of Zn‐Sal(ph)en complexes is reviewed and revisited. Besides traditional analyses found in the literature, conceptual density functional theory descriptors are used to assess this acidic character. Using these tools, we highlight how the nature of the bridging diamine linker in the Schiff base ligand controls this feature mainly responsible of the coordination geometry of these complexes. This Lewis acidic behavior is addressed first by application of the usual dual descriptor to a prototypical complex, namely ZnCl42−. However, the usual dual descriptor exhibits significant weaknesses to retrieve the electrophilic part on the metal cation of Zn‐sal(ph)en complexes. The inclusion of the densities of the electronic excited states through the so‐called state‐specific dual descriptor allows us to recover successfully the appropriate reactivity of these chosen complexes with different diamine bridges in flexible to semirigid, and then to rigid ranges. The coordination of the Zn2+ is shown to be dictated by the geometry of the sal(ph)en ligand. © 2018 Wiley Periodicals, Inc.

Perturbed reactivity descriptors: the chemical hardness

A simple framework to study the effects of (small) external perturbations on conceptual density functional theory descriptors is discussed. Based on this, the general expressions recently presented for the perturbed chemical potential are revisited. Additionally, new formulas that take into account the effect of the molecular environment on the chemical hardness are derived. Some consequences of this framework are analyzed in the context of several magnitudes that characterize charge transfer reactions. It is expected that the resulting formulas provide more accurate results when the unperturbed chemical potentials and chemical hardnesses of the reagents are not significantly different between them.

An explicit approach to conceptual density functional theory descriptors of arbitrary order

We present explicit formulas for arbitrary-order derivatives of the energy, grand potential, electron density, and higher-order response functions with respect to the number of electrons, and the chemical potential for any smooth and differentiable model of the energy versus the number of electrons. The resulting expressions for global reactivity descriptors (hyperhardnesses and hypersoftnesses), local reactivity descriptors (hyperFukui functions and local hypersoftnesses), and nonlocal response functions are easy to evaluate computationally. Specifically, the explicit formulas for global/local/nonlocal hypersoftnesses of arbitrary order are derived using Bell polynomials. Explicit expressions for global and local hypersoftness indicators up to fifth order are presented.

Analogue-based approaches in anti-cancer compound modelling: the relevance of QSAR models

QSAR is among the most extensively used computational methodology for analogue-based design. The application of various descriptor classes like quantum chemical, molecular mechanics, conceptual density functional theory (DFT)- and docking-based descriptors for predicting anti-cancer activity is well known. Although in vitro assay for anti-cancer activity is available against many different cell lines, most of the computational studies are carried out targeting insufficient number of cell lines. Hence, statistically robust and extensive QSAR studies against 29 different cancer cell lines and its comparative account, has been carried out. The predictive models were built for 266 compounds with experimental data against 29 different cancer cell lines, employing independent and least number of descriptors. Robust statistical analysis shows a high correlation, cross-validation coefficient values, and provides a range of QSAR equations. Comparative performance of each class of descriptors was carried out and the effect of number of descriptors (1-10) on statistical parameters was tested. Charge-based descriptors were found in 20 out of 39 models (approx. 50%), valency-based descriptor in 14 (approx. 36%) and bond order-based descriptor in 11 (approx. 28%) in comparison to other descriptors. The use of conceptual DFT descriptors does not improve the statistical quality of the models in most cases. Analysis is done with various models where the number of descriptors is increased from 1 to 10; it is interesting to note that in most cases 3 descriptor-based models are adequate. The study reveals that quantum chemical descriptors are the most important class of descriptors in modelling these series of compounds followed by electrostatic, constitutional, geometrical, topological and conceptual DFT descriptors. Cell lines in nasopharyngeal (2) cancer average R2 = 0.90 followed by cell lines in melanoma cancer (4) with average R2 = 0.81 gave the best statistical values.

Structures, Infrared Spectra and Reactivities of (+)-Catechin Metal Complexes

We investigated the structures, infrared spectra, and reactivities of (+)-catechin (Cc, C15H14O6) and its metal complexes (M-Cc, M=Ca, Zn, Cd, Cu, Al, Cr) using density functional theory (DFT) with the B3LYP functional and the 6-311+G(d,p) basis set for non-metallic elements and the LANL2DZ basis set for metals. The results showed that the M-Cc complexes were structurally and spectroscopically different from their precursor (Cc). The frontier molecular orbitals and conceptual density functional theory descriptors imply that some of the M-Cc systems tend to be more active than the Cc monomer. Different metal complexes were found to have different values for the indices. These results are helpful in understanding the studied properties of (+)-catechin and other metallic compounds.

QSPR modeling of thermal stability of nitroaromatic compounds: DFT vs. AM1 calculated descriptors

The quantitative structure-property relationship (QSPR) methodology was applied to predict the decomposition enthalpies of 22 nitroaromatic compounds, used as indicators of thermal stability. An extended series of descriptors (constitutional, topological, geometrical charge related and quantum chemical) was calculated at two different levels of theory: density functional theory (DFT) and semi-empirical AM1 approaches. Reliable models have been developed for each level, leading to similar correlations between calculated and experimental data (R(2) > 0.98). Hence, both of them can be employed as screening tools for the prediction of thermal stability of nitroaromatic compounds. If using the AM1 model presents the advantage to be less time consuming, DFT allows the calculation of more accurate molecular quantum properties, e.g., conceptual DFT descriptors. In this study, our best QSPR model is based on such descriptors, providing more chemical comprehensive relationships with decomposition reactivity, a particularly complex property for the specific class of nitroaromatic compounds.

Can Electrophilicity Act as a Measure of the Redox Potential of First‐Row Transition Metal Ions?

Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car-Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc(3+) | Sc(2+) to Cu(3+) | Cu(2+)) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region.