Dataset Information

Photocatalytic aerobic oxidation by a bis-porphyrin-ruthenium(IV) mu-oxo dimer: observation of a putative porphyrin-ruthenium(V)-oxo intermediate.

ABSTRACT: The title complexes catalyze the aerobic oxidations of hydrocarbons using visible light and atmospheric oxygen as oxygen source in sequences employing photodisproportionation reactions. The putative oxidants, ruthenium(V)-oxo porphyrin species, can be detected and studied in real time via laser flash photolysis methods.

SUBMITTER: Vanover E

PROVIDER: S-EPMC2877504 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Photocatalytic aerobic oxidation by a bis-porphyrin-ruthenium(IV) mu-oxo dimer: observation of a putative porphyrin-ruthenium(V)-oxo intermediate.

Vanover Eric E Huang Yan Y Xu Libin L Newcomb Martin M Zhang Rui R

Organic letters 20100501 10

The title complexes catalyze the aerobic oxidations of hydrocarbons using visible light and atmospheric oxygen as oxygen source in sequences employing photodisproportionation reactions. The putative oxidants, ruthenium(V)-oxo porphyrin species, can be detected and studied in real time via laser flash photolysis methods. ...[more]

PMID: 20394434

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Project description:Metal-free porphyrin-dendrimers provide a convenient platform for the construction of membrane-impermeable ratiometric probes for pH measurements in compartmentalized biological systems. In all previously reported molecules, electrostatic stabilization (shielding) of the core porphyrin by peripheral negative charges (carboxylates) was required to shift the intrinsically low porphyrin protonation pK(a)'s into the physiological pH range (pH 6-8). However, binding of metal cations (e.g., K(+), Na(+), Ca(2+), Mg(2+)) by the carboxylate groups on the dendrimer could affect the protonation behavior of such probes in biological environments. Here we present a dendritic pH nanoprobe based on a highly non-planar tetraaryltetracyclohexenoporphyrin (Ar(4)TCHP), whose intrinsic protonation pK(a)'s are significantly higher than those of regular tetraarylporphyrins, thereby eliminating the need for electrostatic core shielding. The porphyrin was modified with eight Newkome-type dendrons and PEGylated at the periphery, rendering a neutral water-soluble probe (TCHpH), suitable for measurements in the physiological pH range. The protonation of TCHpH could be followed by absorption (e.g., ?(Soret)(dication)?270,000 M(-1) cm(-1)) or by fluorescence. Unlike most tetraarylporphyrins, TCHpH is protonated in two distinct steps (pK(a)'s 7.8 and 6.0). In the region between the pK(a)'s, an intermediate species with a well-defined spectroscopic signature, presumably a TCHpH monocation, could be observed in the mixture. The performance of TCHpH was evaluated by pH gradient measurements in large unilamellar vesicles. The probe was retained inside the vesicles and did not pass through and/or interact with vesicle membranes, proving useful for quantification of proton transport across phospholipid bilayers. To interpret the protonation behavior of TCHpH we developed a model relating structural changes on the porphyrin macrocycle upon protonation to its basicity. The model was validated by density functional theory (DFT) calculations performed on a planar and non-planar porphyrin, making it possible to rationalize higher protonation pK(a)'s of non-planar porphyrins as well as the easier observation of their monocations.

Dataset Information

Photocatalytic aerobic oxidation by a bis-porphyrin-ruthenium(IV) mu-oxo dimer: observation of a putative porphyrin-ruthenium(V)-oxo intermediate.

Publications

Photocatalytic aerobic oxidation by a bis-porphyrin-ruthenium(IV) mu-oxo dimer: observation of a putative porphyrin-ruthenium(V)-oxo intermediate.

Similar Datasets

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