[2.2]Paracyclophane-based coumarins: effective organo-photocatalysts for light-induced desulfonylation processes.

Herein, we demonstrate for the first time that coumarins derived from [2.2]paracyclophane (pCp) can act as effective organo-photocatalysts and promote the reductive cleavage of sulfonamides under light-irradiation. In the presence of these original compounds, photodesulfonylation reactions occur under mild conditions at low catalyst loadings in the presence of Hantzsch ester. Theoretical and experimental investigations are described, which elucidate the reaction mechanism and the nature of the active species involved in the photocatalytic process. This proof-of-concept study paves the way for further application of pCps in the field of photocatalysis.

Tris-benzo[cd]indole Cyanine Enables the NIR-photosensitized Radical and Thiol-ene Polymerizations at 940†nm.

A near-infrared-absorbing heptamethine (HM+ ) incorporating three bulky benzo[cd]indole heterocycles was designed to efficiently prevent self-aggregation of the dye, which results in a strong enhancement of its photoinitiating reactivity as compared to a parent bis-benzo[cd]indole heptamethine (HMCl+ ) used as a reference system. In this context, we highlight an efficient free-radical NIR-polymerization up to a 100 % acrylates C=C bonds conversion even under air conditions. Such an important initiating performance was obtained by incorporating our NIR-sensitizer into a three-component system leading to its self-regeneration. This original photoredox cycle was thoroughly investigated through the identification of each intermediary species using EPR spectroscopy.

Labile iron potentiates ascorbate-dependent reduction and mobilization of ferritin iron.

Ascorbate mobilizes iron from equine spleen ferritin by two separate processes. Ascorbate alone mobilizes ferritin iron with an apparent Km (ascorbate) ≈1.5mM. Labile iron >2µM, complexed with citrate (10mM), synergises ascorbate-dependent iron mobilization by decreasing the apparent Km (ascorbate) to ≈270µM and raising maximal mobilization rate by ≈5-fold. Catalase reduces the apparent Km(ascorbate) for both ascorbate and ascorbate+iron dependent mobilization by ≈80%. Iron mobilization by ascorbate alone has a higher activation energy (Ea=45.0±5.5kJ/mole) than when mediated by ascorbate with labile iron (10µM) (Ea=13.7±2.2kJ/mole); also mobilization by iron-ascorbate has a three-fold higher pH sensitivity (pH range 6.0-8.0) than with ascorbate alone. Hydrogen peroxide inhibits ascorbate's iron mobilizing action. EPR and autochemiluminescence studies show that ascorbate and labile iron within ferritin enhances radical formation, whereas ascorbate alone produces negligible radicals. These findings suggest that iron catalysed single electron transfer reactions from ascorbate, involving ascorbate or superoxide and possibly ferroxidase tyrosine radicals, accelerate iron mobilization from the ferroxidase centre more than EPR silent, bi-dentate two-electron transfers. These differing modes of electron transference from ascorbate mirror the known mono and bidentate oxidation reactions of dioxygen and hydrogen peroxide with di-ferrous iron at the ferroxidase centre. This study implies that labile iron, at physiological pH, complexed with citrate, synergises iron mobilization from ferritin by ascorbate (50-4000µM). This autocatalytic process can exacerbate oxidative stress in ferritin-containing inflamed tissue.