GPU accelerated implementation of NCI calculations using promolecular density

IGMPlot: A program to identify, characterize, and quantify molecular interactions

We describe the development and features of a program called IGMPlot, which is based on the independent gradient model (IGM) and its local descriptor δ g $$ \delta g $$ . The IGM approach analyzes the gradient of the electron density (ED) in a molecular system to identify regions of space where chemical interactions take place. IGMPlot is intended for use by both experimental scientists and theoretical chemists. It is standalone software written in C++, with versions available for multiple platforms. Some key features are: probing and quantifying interactions between two given molecular fragments, determining bond strength (IBSI), estimating the atomic contributions to an intermolecular interaction and preparing data to build 2D and 3D representations of interaction regions. The software has been updated to include new features: critical point analysis of the ED, assessing ED asymmetry of a given bond (PDA) and a new descriptor called q g $$ qg $$ designed to enhance the IGM- δ g $$ \delta g $$ analysis. The program can be found at: http://igmplot.univ-reims.fr.

Chiral Counteranion-Directed Catalytic Asymmetric Methylene Migration Reaction of Ene-Aldimines

A catalytic asymmetric methylene migration reaction of ene-aldimines directed by chiral counteranions is developed, with the optimal catalyst identified as phenanthryl-substituted (R)-BINOL phosphate. Control experiments and density functional theory computations reveal the importance of the 2-hydroxy group of the ene-aldimine and attractive (e.g., OH···O, CH···O, CH···π, and π···π) interactions for high enantioselectivity (up to 74% ee). The results contribute to the design of asymmetric catalysis for the rearrangement of highly reactive iminium intermediates.

Sila-Ibuprofen

The synthesis, characterization, biological activity, and toxicology of sila-ibuprofen, a silicon derivative of the most common nonsteroidal anti-inflammatory drug, is reported. The key improvements compared with ibuprofen are a four times higher solubility in physiological media and a lower melting enthalpy, which are attributed to the carbon-silicon switch. The improved solubility is of interest for postsurgical intravenous administration. A potential for pain relief is rationalized via inhibition experiments of cyclooxygenases I and II (COX-I and COX-II) as well as via a set of newly developed methods that combine molecular dynamics, quantum chemistry, and quantum crystallography. The binding affinity of sila-ibuprofen to COX-I and COX-II is quantified in terms of London dispersion and electrostatic interactions in the active receptor site. This study not only shows the potential of sila-ibuprofen for medicinal application but also improves our understanding of the mechanism of action of the inhibition process.

New Way for Probing Bond Strength

The covalent chemical bond is intimately linked to electron sharing between atoms. The recent independent gradient model (IGM) and its δg descriptor provide a way to quantify locally this electron density interpenetration from wavefunction calculations. Each bond has its own IGM-δg^pair signature. The present work establishes for the first time a strong link between this bond signature and the physically grounded bond force constant concept. Analyzing a large set of compounds and bonds, the intrinsic bond strength index (IBSI) emerges from the IGM formulation. Our study shows that the IBSI does not belong to the class of conventional bond orders (like Mulliken, Wiberg, Mayer, delocalization index, or electron localization function-ELF), but is rather a new complementary index, related to the bond strength. A fundamental outcome of this research is a novel index allowing to range all two-center chemical bonds by their intrinsic strength in molecular situation. We believe that the IBSI is a powerful and robust tool for interpretation accessible to a wide community of chemists (organic, inorganic chemistry, including transition-metal complexes and reaction mechanisms).

Accurately extracting the signature of intermolecular interactions present in the NCI plot of the reduced density gradient versus electron density

An electron density (ED)-based methodology is developed for the automatic identification of intermolecular interactions using pro-molecular density. The expression of the ED gradient in terms of atomic components furnishes the basis for the Independent Gradient Model (IGM). This model leads to a density reference for non interacting atoms/fragments where the atomic densities are added whilst their interaction turns off. Founded on this ED reference function that features an exponential decay also in interference regions, IGM model provides a way to identify and quantify the net ED gradient attenuation due to interactions. Using an intra/inter uncoupling scheme, a descriptor (δg^inter) is then derived that uniquely defines intermolecular interaction regions. An attractive feature of the IGM methodology is to provide a workflow that automatically generates data composed solely of intermolecular interactions for drawing the corresponding 3D isosurface representations.