What can tell the quantum chemical topology on carbon–astatine bonds?

International audienceThe nature of carbon-astatine bonds involved in some model species that mimic 211 At-labelled biomolecules, was investigated by means of ELF and QTAIM analyzes in a context of two-component relativistic computations. The nature of the bonded carbon atom proved to be decisive. When At is bonded to an ethynyl group, some charge delocalization with the vicinal triple CC bond strengthens the At-C bond and gives it a multiple bond character. However, At displays also a large positive charge which may alter the in vivo stability of such At-C bonds. In the case of an isopropyl group, the At-C bond is less polarized but also much weaker. In contrast, the bond remains strong whilst retaining a small At positive charge when At is bonded to an sp 2 carbon atom. Hence, these latter results rationalize why aromatic or aryl groups appear reasonably suited for a priori stable radiolabelling of biomolecules with 211 At in the context of alpha therapy

Diabolus in Chemistry?

This article explores the possible presence of a pentacle valence bond structure in C$_5$ cyclic molecules. At this end, we have used quantum chemistry tools to elucidate the possible arrangement and the nature of chemical bonds within linear, cyclic, and three-dimensional structures only formed by five carbon atoms. While the linear structure is clearly the most stable one, local minima were obtained for both bi- and three-dimensional structures. Beyond the historical satanic symbol, the pentacle arrangement corresponds to an unusual formal structure with five crossing between C-C bonds. Our calculations show that this diabolic cyclic C$_5$ scheme is a relevant resonant structure and, furthermore, it is also present in the more known cyclo-pentadienyl molecule

Advancing beyond charge analysis using the electronic localization function: Chemically intuitive distribution of electrostatic moments

International audienc

Comments on the nature of the bonding in oxygenated dinuclear copper enzyme models

International audienc

New insights in chemical reactivity from quantum chemical topology

International audienceBased on the quantum chemical topology of the modified electron localization function ELFx, an efficient and robust mechanistic methodology designed to identify the favorable reaction pathway between two reactants is proposed. We first recall and reshape how the supermolecular interaction energy can be evaluated from only three distinct terms, namely the intermolecular coulomb energy, the intermolecular exchange‐correlation energy and the intramolecular energies of reactants. Thereafter, we show that the reactivity between the reactants is driven by the first‐order variation in the coulomb intermolecular energy defined in terms of the response to changes in the number of electrons. Illustrative examples with the formation of the dative bond B‐N involved in the BH3NH3 molecule and the typical formation of the hydrogen bond in the canonical water dimer are presented. For these selected systems, our approach unveils a noticeable mimicking of Edual onto the DFT intermolecular interaction energy surface calculated between the both reactants. An automated reaction‐path algorithm aimed to determine the most favorable relative orientations when the two molecules approach each other is also outlined

Using the unusual weak N…CO bond as a solvation probe

International audienceMost chemical (or biochemical) reactions take place in a liquid solvent. Water is the natural solvent of biochemical reactions, and is increasingly used for organic synthesis. As water is not an inert solvent, modelling such a complex environment and evaluating the solvation effects on the electronic structure of the solute is a challenge. The unusual weak bond is used here as a probe of the solvation effects. Several solvation models were tested: a continuum, 1027 TIP3P water molecules and a microsolvation model complemented by a continuum or by TIP3P molecules. First, we show that the combination of the topological analysis of the electron localisation function (ELF) and the theory of atoms in molecules (AIM) is a robust way to evaluate and rationalise the strength and the accuracy of a given solvation model. These analyses demonstrate that a polarisable continuum model (PCM) is less accurate than a quantum mechanics/molecular mechanics (QM/MM) calculation where only the probe molecule is included in the QM region. We also show that solvating the solute and its first solvation shell embedded in a PCM leads to the same polarisation effect as a costly QM/MM calculation with 30 H2O included in the QM part and approximately 1000 classical water molecules. Finally, beyond this work, we show here that the combined ELF and AIM analyses can open up new opportunities for the electronic description of environment effects, for example in dynamical calculations

The Topological Analysis of the ELFx Localization Function: Quantitative Prediction of Hydrogen Bonds in the Guanine–Cytosine Pair

International audienceIn this contribution, we recall and test a new methodology designed to identify the favorable reaction pathway between two reactants. Applied to the formation of the DNA guanine (G) –cytosine (C) pair, we successfully predict the best orientation between the base pairs held together by hydrogen bonds and leading to the formation of the typical Watson Crick structure of the GC pair. Beyond the global minimum, some local stationary points of the targeted pair are also clearly identified

Regioselective N-alkylation of imidazo[4,5-b]pyridine-4-oxide derivatives: an experimental and DFT study

International audienc

On the Interplay between Charge‐Shift Bonding and Halogen Bonding

International audienceThe nature of halogen-bond interactions has been analysed from the perspective of the astatine element, which is potentially the strongest halogen-bond donor. Relativistic quantum calculations on complexes formed between halide anions and a series of Y3C-X (Y = F to X, X = I, At) halogen-bond donors disclosed unexpected trends, e.g., At3C-At revealing a weaker donating ability than I3C-I despite a stronger polarizability. All the observed peculiarities have their origin in a specific component of C-Y bonds: the charge-shift bonding. Descriptors of the Quantum Chemical Topology show that the halogen-bond strength can be quantitatively anticipated from the magnitude of charge-shift bonding operating in Y3C-X. The charge-shift mechanism weakens the ability of the halogen atom X to engage in halogen bonds. This outcome provides rationales for outlier halogen-bond complexes, which are at variance with the consensus that the halogen-bond strength scales with the polarizability of the halogen atom