A comparative study on the nature and strength of O–O, S–S, and Se–Se bond

Heterometathesis of diphosphanes (R2P–PR2) with dichalcogenides (R'E–ER', E = O, S, Se, Te)

The reactions of R2P–PR2 with R'E–ER', (where E = Se, S, O, Te) to give R2P–ER' have been explored experimentally and computationally. The reaction of Ph2P–PPh2 with PhSe–SePh gives Ph2P–SePh...

Exploring the potential energy surface of novel [H, S, Se, Br] species: a high level first principle study

The characterization of the seleno-sulfide-bromo systems and the isomerization process on the [H, S, Se, Br] potential energy surface were investigated using state-of-the-art theoretical methods. The CCSD(T) and the MP2 levels of theory were employed along with the series of correlation consistent basis sets extrapolated to the complete basis set (CBS) limit in the optimization of the geometrical parameters and computation of electronic energies. The relative stability, in kcal mol^-1, at the CCSD(T)/CBS follows the trend: HSSeBr (0) > HSeSBr (9.51) > SSeHBr (24.02) > SeSHBr (25.42). This order was observed in the previous study of the [H, S, Se, Cl] species. The structural parameters and vibrational frequencies of the [H, S, Se, Br] species are reported. This research work should be helpful to experimentalists in order to gain insights into these novel heteroatom molecules. Graphical abstract Relative energy profile (in kcal mol^-1) using the CCSD(T)/CBS and MP2/CBS (in parentheses) method of the stationary states on the [H, S, Se, Br] PES.

C2-Symmetric P,N Ligands Derived from Carborane-Based Diphosphetanes: Synthesis and Coordination Chemistry

Racemic carborane-based bisphosphanes were obtained by dismutation reactions between a carborane-based diphosphetane and diaryl dichalogenides. NMR spectroscopic and theoretical studies revealed a two-step mechanism explaining the high stereoselectivity of these reactions. The coordination chemistry of the multidentate P,N ligands 6c and 6d in copper(I) and silver(I) complexes was studied. While 6d acted exclusively as tetradentate ligand, 6c showed either tridentate or tetradentate coordination depending on the metal and the counterion.

Energy Matrix of Structurally Important Side-Chain/Side-Chain Interactions in Proteins

The interactions between amino acid side chains in proteins are generally considered to be the most important stabilizing factor controlling the precise arrangement of the polypeptide chain into a well-defined spatial structure. We used the RI-DFT-D method to calculate the full 20 × 20 matrix of interaction energies between all pairs of amino acid side chains. For each pair, we used a representative 3D conformation extracted from an analysis of known protein structures from Protein Data Bank (PDB). The representative comes from the largest cluster of relative orientations of the two side chains. We find that all of the calculated interaction energies between selected pairs of amino acids are attractive in the gas phase with the exception of side chain pairs having the same total charge. We compared these data with those calculated by the parm03 and OPLS-AA/L force fields to investigate the reliability of simple methods in modeling biomolecules and their behavior. The force fields yield good overall interaction energies for our set but have problems in evaluation of some particular interactions which could be of principal importance for protein stability. We then looked in detail at the 20 side chain interactions involving tryptophan. The histograms of interaction energies showed that the distributions of the interaction energies are neither normal nor Boltzmann-like and that our representative geometries correspond mostly to the minimum energy geometry which is rather poorly populated in the whole pairwise energy distribution. We concluded that cluster representatives obtained by the clusterization algorithm based on geometry criteria cannot be considered as a typical interaction for the whole side chain/side chain interaction distribution. They seem to epitomize the strongest interactions in a protein and are often functionally or structurally important.