Tetrabromoethane as σ-Hole Donor toward Bromide Ligands: Halogen Bonding between C2H2Br4 and Bromide Dialkylcyanamide Platinum(II) Complexes

The complexes trans-[PtBr2(NCNR2)2] (R2 = Me21, (CH2)52) were cocrystallized with 1,1,2,2-tetrabromoethane (tbe) in CH2Cl2 forming solvates 1·tbe and 2·tbe, respectively. In both solvates, tbe involved halogen bonding, viz. the C–Br···Br–Pt interactions, were detected by single-crystal X-ray diffractions experiments. Appropriate density functional theory calculations (M06/def2-TZVP) performed for isolated molecules and complex-tbe clusters, where the existence of the interactions and their noncovalent nature were confirmed by electrostatic potential surfaces (ρ = 0.001 a.u.) for isolated molecules, topology analysis of electron density, electron localization function and HOMO-LUMO overlap projections for clusters.

Pharmaceutical Values of Calycosin: One Type of Flavonoid Isolated from Astragalus

Astragalus is a popular Materia Medica in China, and it could be applied in the treatment of various diseases. It contains a variety of chemically active ingredients, such as saponins, flavonoids, and polysaccharides. Plant-derived bioactive chemicals are considered natural, safe, and beneficial. Among the infinite plant-identified and isolated molecules, flavonoids have been reported to have positive effects on human health. Calycosin is the most important active flavonoid substance identified predominantly within this medicinal plant. In recent years, calycosin has been reported to have anticancer, antioxidative, immune-modulatory, and estrogenic-like properties. This review collected recent relevant literatures on calycosin and summarized its potential pharmaceutical properties and working mechanism involved, which provided solid basis for future clinical research.

Theoretical modeling of defects in the molecular crystal of 2-(2'-hydroxyphenyl)benzothiazole

2-(2'-hydroxyphenyl)benzothiazole is a photoreactive compound that exhibits excited state intramolecular proton transfer in the structure with an OH...N hydrogen bond. Energy of various structures is calculated for isolated molecules, clusters and periodic structures of 2-(2'-hydroxyphenyl)benzothiazole by density-functional based tight-binding methods. It is shown that the most stable conformation of the isolated molecule is a planar structure with an OH...N hydrogen bond. Other conformations have significantly larger energy in comparison with the average room temperature heat energy that implies a low equilibrium number of those structures in non-polar solvents. In crystal the defect with lowest energy is non-hydrogen-bonded conformation formed by rotation of the OH bond. The energy of this defect is close to the energy difference for corresponding conformations of the isolated molecule. For other conformations, the energy values of the defects are larger than the energy differences for isolated molecules. In contrast to the crystal of 2-(2'-hydroxyphenyl)benzoxazole, energy of the defect caused by the entire molecule reorientation is comparable with the energy of defects caused by different conformations.