Mimicking of tunichlorin is of importance to correlate its biological function to the unusally similar structure to chlorophylls but with a nickel cofactor. Benefiting from the facile derivatization of porpholactones, we herein constructed a tunichlorin mimic 6 carrying a β-hydroxyl group ([mesotetrakis(pentafluorophenyl)-3-hydroxy-2-oxaisobacteriochlorinato]nickel-(II)), which exhibits significant hydrogen evolution reaction (HER) rate acceleration of ca. 56-fold compared to its porphyrin analogues. Importantly, in the presence of water, the TOF of 6 is up to 6.1 × 10 4 s −1 with the lowest overpotential, ranking the best among the catalysts described. Coating catalyst 6 on a Ni foam electrode showed good HER performance in a two-electrode alkaline (1 M KOH) electrolyzer (η 20 = 540 mV). The functional roles of the β-hydroxyl group on the acceleration of electron transfer and the formation of the hydrogen bond network with water has been suggested in either chemical or electrochemical reductions and H/D kinetic isotope effects (KIEs), combined with DFT calculations. Interstingly, the DFT model suggested that the formation of the hydrogen bond renders more electron density on the Ni center (ρ Ni = 0.91) in a oneelectron reduced intermediate [6 H 2 O ] − , which helps the stabilization of both one-or two-electron reduced intermediates and dramatically enhances the HER rates.
Oxidative
stress is one of the hallmarks of ischemic stroke. Catalase-based
(CAT) biomimetic complexes are emerging as promising therapeutic candidates
that are expected to act as neuroprotectants for ischemic stroke by
decreasing the damaging effects from H2O2. Unfortunately,
these molecules result in the unwanted production of the harmful hydroxyl
radical, HO•. Here, we report a series of salen-based
tri-manganese (Mn(III)) metallocryptands (1–3) that function as catalase biomimetics. These cage-like
molecules contain a unique “active site” with three
Mn centers in close proximity, an arrangement designed to facilitate
metal cooperativity for the effective dismutation of H2O2 with minimal HO• production. In fact,
significantly greater oxygen production is seen for 1–3 as compared to the monomeric Mn(Salen) complex, 1c. The most promising system, 1, was studied
in further detail and found to confer a greater therapeutic benefit
both in vitro and in vivo than the
monomeric control system, 1c, as evident from inter alia studies involving a rat model of ischemic stroke
damage and supporting histological analyses. We thus believe that
metallocryptand 1 and its analogues represent a new and
seemingly promising strategy for treating oxidative stress related
disorders.
A programmable strategy at the molecular level to modulate the ratio of a catalyst and photosensitizer to maximize the collaborative efficiency of anti-angiogenesis and PDT.
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