No abstract

The chalcogen bond, the noncovalent, electrostatic attraction between covalently bonded atoms in group 16 and Lewis bases, is present in protein-ligand interactions based on X-ray structures deposited in the Protein Data Bank (PDB). Discovering protein-ligand chalcogen bonding in the PDB employed a strategy that focused on searching the database for protein complexes of five-membered, heterocyclic ligands containing endocyclic sulfur with endo electron-withdrawing groups (isothiazoles; thiazoles; 1,2,3-, 1,2.4-, 1,2,5-, 1,3,4-thiadiazoles) and thiophenes with exo electron-withdrawing groups, e.g., 2-chloro, 2-bromo, 2-amino, 2-alkylthio. Out of 930 ligands investigated, 33 or 3.5% have protein-ligand S---O interactions of which 31 are chalcogen bonds and two appear to be S---HO hydrogen bonds. The bond angles for some of the chalcogen bonds found in the PDB are less than 90°, and an electrostatic model is proposed to explain this phenomenon.

No abstract

b S Supporting Information C hemiluminescence is light emission from a chemical reaction. Peroxyoxalate chemiluminescence involves the reaction of oxalate diesters with hydrogen peroxide to generate unstable 1,2-dioxetanedione, which decomposes into electronically excited carbon dioxide (Scheme 1). The excited CO 2 transfers energy to a fluorescer or fluorophore, which releases light upon decay to the ground state. 1,2 Cyalume "light sticks" utilize this same chemistry for emergency lighting, fishing lures, and entertainment. The commercially available oxalate diesters, bis(2,4,6-trichlorophenyl)oxalate (TCPO) and bis(2,4-nitrophenyl)oxalate (DNPO), are typically used in both lecture demonstrations and laboratory experiments in chemiluminescence. 3À6 However, the serious environmental toxicities of the products 2,4,6-trichlorophenol 7 and 2,4-dinitrophenol, 8 as well as exposure to potentially hazardous organic solvent vapors in an open air setting, have encouraged us to redesign this demonstration along greener lines. In our demonstration, hazardous solvents such as dichloromethane are replaced with triacetin, a low volatility, nontoxic, and biodegradable compound, 9 and the oxalate diester is divanillyl oxalate 1, 10 which is readily prepared in one step from the artificial flavoring agent vanillin 2 (Scheme 2). In addition to CO 2 , the product of our chemiluminescent reaction is terrestrially nontoxic vanillin 2. 11 ' AUTHOR INFORMATION

No abstract