Polystyrene/clay nanocomposites by atom transfer radical nitroxide coupling chemistry

An efficient protocol, atom transfer radical nitroxide coupling chemistry, for the preparation of polymer/clay nanocomposites via grafting-onto strategy with well-defined polymer, which were synthesized via atom transfer radical polymerization, has been described. The radical coupling, taking place between the clay layers, not only leads to attached polymer chains but also to successful nanocomposite formation with highly exfoliated morphology. Copyright © 2012 Wiley Periodicals, Inc

Towards a quantitative approach to the utilization of magnetic effects as a means of isotopic enrichment

The photolysis of methyldesoxybenzoin in sodium dodecyl sulfate micellar solutions, produces benzaldehyde and styrene as disproportionation products of the triplet geminate radical pair. We have found that both the benzaldehyde and the recovered methyldeoxybenzoin are enriched in 13-C. These results provide the first direct evidence that both recombination and disproportionation are identically selective to the magnetic isotope effect, an important point anticipated by theory, but previously untested. An investigation of the photostereoisomerization of the diasteromers of 2,4-diphenylpentane-3-one in micellar solutions has allowed a quantitative analysis of the probabilities of recombination of the micellized primary geminate radical pair toward formation of different combination products. The results show that within the confidence provided by highly accurate data, the primary geminate radical pairs recombine to regenerate the precursor substrate structure or diastereomer with equal probability

Solution Photoreactivity of Phenanthrenequinone Diimine Complexes of Rhodium and Correlations with DNA Photocleavage and Photooxidation

The transient absorption spectra of Rh(III) complexes containing one or two phi ligands (phi = 9,10-phenanthrenequinone diimine) and various ancillary ligands were measured at pH 5.0 utilizing visible and UV excitation. The spectra were all consistent with a primarily phi ligand-centered (LC) nπ* transition. The spectral profile obtained with visible excitation of the complexes is slightly different and significantly weaker at pH 8.0, where now Rh(phi)2(phen)3+, Rh(phi)2(bpy)3+, and Rh(phen)2(phi)3+ are deprotonated. Irradiation of these complexes in basic media with 308 nm laser excitation leads to irreversible ligand-loss photochemistry. The LC excited states of Rh(phi)2(phen)3+, Rh(phi)2(bpy)3+, and Rh(phen)2(phi)3+ are reductively quenched by the purine DNA bases, A, dA, dAMP, AMP, G, dG, dGMP, and GMP, with rate constants ranging from 1.4 × 109 M-1 s-1 to 4.7 × 109 M-1 s-1 at pH 5.0, but no quenching was observed for dC or dT. Absorbances assigned to the reduced Rh(II) complex and dG· were observed in the transient absorption spectrum. There are some parallels between the observed photochemistry in solution and the DNA photocleavage results, in particular the presence of oxidative damage to the DNA bases

Modeling of diffusion-reaction processes involving geminate radical pairs

A Markovian theory is developed to study the efficiency of diffusion-reaction processes involving geminate radical pairs moving on the surface of a catalyst (e.g. zeolite) support. Results obtained for the simplest (lattice) system are corroborated by Monte Carlo calculations, and these are extended to study the effect of system size. A kinetic model is developed to account for the results obtained and leads to the general conclusion that the photochemical generation of a triplet pair, followed by the subsequent diffusion and eventual recombination of the radicals R↑ and R↓, lengthens the mean reaction time by a factor of ∼2, relative to the case in which R↑ and R↓ are assumed to be present at the very outset.SCOPUS: ar.jinfo:eu-repo/semantics/publishe