Electrochemical and Photoelectrochemical Investigation of Water Oxidation with Hematite Electrodes

Atomic layer deposition (ALD) was utilized to deposit uniform thin films of hematite (α-Fe2O3) on transparent conductive substrates for photocatalytic water oxidation studies. Comparison of the oxidation of water to the oxidation of a fast redox shuttle allowed for new insight in determining the rate limiting processes of water oxidation at hematite electrodes. It was found that an additional overpotential is needed to initiate water oxidation compared to the fast redox shuttle. A combination of electrochemical impedance spectroscopy, photoelectrochemical and electrochemical measurements were employed to determine the cause of the additional overpotential. It was found that photogenerated holes initially oxidize the electrode surface under water oxidation conditions, which is attributed to the first step in water oxidation. A critical number of these surface intermediates need to be generated in order for the subsequent hole-transfer steps to proceed. At higher applied potentials, the behavior of the electrode is virtually identical while oxidizing either water or the fast redox shuttle; the slight discrepancy is attributed to a shift in potential associated with Fermi level pinning by the surface states in the absence of a redox shuttle. A water oxidation mechanism is proposed to interpret these results

Activation of sodium-potassium pump contributes to insulin-induced vasodilation in humans

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Plasma lipoproteins, apolipoproteins, and triglyceride metabolism in familial hypertriglyceridemia.

Several parameters of lipoprotein metabolism were examined in 38 men with primary hypertriglyceridemia (phenotype IV). Family investigation showed that 17 men had familial combined hyperlipidemia (FCH), seven had familial hypertriglyceridemia (FHT), and 14 had unclassified hypertriglyceridemia (UNC). In all three groups, plasma high density lipoprotein (HDL) cholesterol and the concentrations of apolipoprotein A-I and A-II were decreased, and apolipoprotein B was increased, each to the same extent. These results are compatible with an increased risk of cardiovascular disease in both FCH and FHT patients. The mean concentration of LDL cholesterol and the ratio of LDL to HDL cholesterol were significantly higher in FCH subjects, which could explain their increased risk. Postheparin lipoprotein lipase and hepatic lipase were the same in both groups. Determination of apolipoprotein C composition, which may modulate lipoprotein lipase activity, did not reveal any abnormalities in the different groups. In both FCH and FHT, the mean turnover rate of plasma triglycerides was almost twice normal, indicating that overproduction of plasma triglyceride plays an important role in both disorders. However, there was an overlap with normal controls, indicating impaired triglyceride removal in some subjects. The underlying mechanism of hypertriglyceridemia in FCH and FHT therefore seems to be heterogeneous.</jats:p

Insight into the Photoinduced Ligand Exchange Reaction Pathway of <i>cis</i>-[Rh₂(μ-O₂CCH₃)₂(CH₃CN)₆]²⁺ with a DNA Model Chelate

We previously showed that [Rh2(O2CCH3)2(CH3CN)6]2+ binds to dsDNA only upon irradiation with visible light and that photolysis results in a 34-fold enhancement of its cytotoxicity toward Hs-27 human skin fibroblasts, making it potentially useful for photodynamic therapy (PDT). With the goal of gaining further insight on the photoinduced binding of DNA to the complex, we investigated by NMR spectroscopy the mechanism by which 2,2′-bipyridine (bpy), a model for biologically relevant bidentate nitrogen donor ligands, binds to [Rh2(O2CCH3)2(CH3CN)6]2+ upon irradiation in D2O. The photochemical results are compared to the reactivity in the dark in D2O and CD3CN. The photolysis of [Rh2(O2CCH3)2(CH3CN)6]2+ with equimolar bpy solutions in D2O with visible light affords [Rh2(O2CCH3)2(eq/eq-bpy)(CH3CN)2(D2Oax)2]2+ (eq/eq) with the reaction reaching completion in ∼8 h. Only vestiges of eq/eq are observed at the same time in the dark, however, and the reaction is ∼20 times slower. Conversely, the dark reaction of [Rh2(O2CCH3)2(CH3CN)6]2+ with an equimolar amount of bpy in CD3CN affords [Rh2(O2CCH3)2(η1-bpyax)(CH3CN)5]2+ (η1-bpyax), which remains present even after 5 days of reaction. The photolysis results in D2O are consistent with the exchange of one equiv CH3CNeq for solvent, and the resulting species quickly reacting with bpy to generate eq/eq; the initial eq ligand dissociation is assisted by absorption of a photon, thus greatly enhancing the reaction rate. The photolytic reaction of [Rh2(O2CCH3)2(CH3CN)6]2+:bpy in a 1:2 ratio in D2O affords the eq/eq and (eq/eq)2 adducts. The observed differences in the reactivity in D2O vs CD3CN are explained by the relative ease of substitution of eq D2O vs CD3CN by the incoming bpy molecule. These results clearly highlight the importance of dissociation of an eq CH3CN molecule from the dirhodium core to attain high reactivity and underscore the importance of light for the reactivity of these compounds, which is essential for PDT agents