Controlling the action of chlorine radical: from lab to environment.

The strength of Bz-Cl˙ complexation has been explored using density functional theory (DFT) calculations, including dispersion-corrected (DFT-D) calculations. Of the methods tested, the ωB97X-D method seems the best performing, along with the previously tested MPW1K method. The effect of substituent (X = NO(2), F, Cl, Br, H, CH(3), OCH(3), OH, NH(2) and N(CH(3))(2)) on the stabilities of the Ar-Cl˙π-like intermediates show a good correlation with the linear free energy relationships used experimentally, but this is not the case for Ar-Cl˙σ-complexes, suggesting the transition state of abstraction as being π-like in nature. The role of PAH and lignin derivatives in mediating chlorination reactions in nature is explored. Stable π-complexes were identified for lignin derivatives, indicating humic substances may mediate chlorine atom reactivity at the marine boundary layer, in addition to forming chlorolignins.

Proline-rich proteins--deriving a basis for residue-based selectivity in polyphenolic binding.

(1)H NMR titration experiments have been used to establish that minimal proline-based models show enhanced binding selectivity towards phenol in CDCl(3), relative to other similarly protected amino acid residues. Cooperative binding effects appear to play a role, with sarcosine models affording binding constants to phenol intermediate to those obtained from proline models and other amino acid models. The mechanism for binding, based on DFT calculations and the application of Hunter's molecular recognition toolbox model, cannot be solely attributed to hydrogen bond strength, and appears to be mediated through C-H-pi bonds and the rotational freedom of the amide substrate.

Chlorine--benzene complexes--the reliability of density functionals for non-covalent radical complexes.

The structure of the chlorine atom-benzene complex has been a topic of significant controversy for more than 50 years. We have reexamined the structure of this complex with new density functional methods especially designed for non-covalent complexes, and compared the structures and energetics to those obtained using standard DFT and high accuracy composite methods. We find that the popular B3LYP functional fails to identify stationary points revealed by other functionals, and that the eta(1)-sigma complex appears to be more stable than the eta(1)-pi complex, contrary to other recent work, highlighting the careful selection of methods required in non-covalent radical systems.