Redox Active Ligands for Catalyzing the Hydrogen Evolution Reaction.

Boron subphthalocyanines with chloride and fluoride axial ligands and three antimony complexes chelated by corroles that differ in size and electron-richness were examined as electrocatalysts for reduction of protons to hydrogen. Experiment- and computation-based investigations revealed that all redox events are ligand-centered and that the meso-C of the corroles and the peripheral N atoms of the subphthalocyanines are the largely preferred proton-binding sites.

First-row transition metal carbonates catalyze the electrochemical oxygen evolution reaction: iron is master of them all.

In pursuing green hydrogen fuel, electrochemical water-splitting emerges as the optimal method. A critical challenge in advancing this process is identifying a cost-effective electrocatalyst for oxygen evolution on the anode. Recent research has demonstrated the efficacy of first-row transition metal carbonates as catalysts for various oxidation reactions.

Hydrogen adsorption on various transition metal (111) surfaces in water: a DFT forecast.

The hydrogen adsorption and hydrogen evolution at the M(111), (M = Ag, Au Cu, Pt, Pd, Ni & Co) surfaces of various transition metals in aqueous suspensions were studied computationally using the DFT methods. The hydrogens are adsorbed dissociatively on all surfaces except on Ag(111) and Au(111) surfaces. The results are validated by reported experimental and computational studies.

Reaction of Fe with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of Fe and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO, PMS) or peroxydisulfate (SO, PDS) with Fe(HO) (Fe). This paper presents results on the kinetics and mechanisms of reactions between Fe and PMS or PDS in the absence and presence of bicarbonate (HCO) at different pH. In the absence of HCO, Fe, rather than the commonly assumed SO, is the dominant oxidizing species.

Electronic Coupling and Electrocatalysis in Redox Active Fused Iron Corroles.

Conjugated arrays composed of corrole macrocycles are increasingly more common, but their chemistry still lags behind that of their porphyrin counterparts. Here, we report on the insertion of iron(III) into a β,β-fused corrole dimer and on the electronic effects that this redox active metal center has on the already rich coordination chemistry of [Htpfc] COT, where COT = cyclo-octatetraene and tpfc = tris(pentafluorophenyl)corrole. Synthetic manipulations were performed for the isolation and full characterization of both the 5-coordinate [Fetpfc(py)]COT and 6-coordinate [Fetpfc(py)]COT, with one and two axial pyridine ligands per metal, respectively.

Hydrogen evolution catalysis by terminal molybdenum-oxo complexes.

Stable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons to hydrogen gas. The upto 670 mV differences in the [(oxo)Mo(IV)]/[(oxo)Mo(III)] redox potentials of the dissolved complexes came into effect by the catalytic onset potential for proton reduction thereby, significantly earlier than their reduction process in the absence of acids, but the two more promising complexes were not stable at practical conditions.

Dimeric Corrole Analogs of Chlorophyll Special Pairs.

Chlorophyll special pairs in photosynthetic reaction centers function as both exciton acceptors and primary electron donors. Although the macrocyclic natural pigments contain Mg(II), the central metal in most synthetic analogs is Zn(II). Here we report that insertion of either Al(III) or Ga(III) into an imidazole-substituted corrole affords an exceptionally robust photoactive dimer.

Aging and pathological aging signatures of the brain: through the focusing lens of SIRT6.

Brain-specific SIRT6-KO mice present increased DNA damage, learning impairments, and neurodegenerative phenotypes, placing SIRT6 as a key protein in preventing neurodegeneration. In the aging brain, SIRT6 levels/activity decline, which is accentuated in Alzheimer's patients. To understand SIRT6 roles in transcript pattern changes, we analyzed transcriptomes of young WT, old WT and young SIRT6-KO mice brains, and found changes in gene expression related to healthy and pathological aging.

The Role of Carbonate in Catalytic Oxidations.

CO, HCO, and CO are present in all aqueous media at pH > 4 if no major effort is made to remove them. Usually the presence of CO/HCO/CO is either forgotten or considered only as a buffer or proton transfer catalyst. Results obtained in the last decades point out that carbonates are key participants in a variety of oxidation processes.

Axial/Peripheral Chloride/Fluoride-Substituted Boron Subphthalocyanines as Electron Acceptors.

Chloroboron subphthalocyanines (Cl-BsubPc) are robust compounds that can be readily modified at the axial and peripheral positions. Peripherally chlorinated derivatives were recently found to be advantageous regarding integration into organic electronic devices. We now report on the effects of fluorides introduced on both the peripheral and axial positions of BsubPcs.

The Fe(citrate) Fenton reaction under physiological conditions.

The Fenton reaction of Fe(citrate) in the presence and absence of bicarbonate (HCO) is studied. It is found that the rate constant of the Fenton reaction (k) increases with increasing [citrate]. k also increase with increasing [HCO]; this effect is most significant at biological citrate concentrations.

Rhenium(i) sapphyrins: remarkable difference between the CF and CF-substituted derivatives.

Despite sapphyrins being the first ever reported extended porphyrins, their coordination chemistry remains quite limited. The newly gained access to meso-alkyl-substituted sapphyrins encouraged the study of their rhenium chelates in comparison with meso-aryl-substituted derivatives. Both the CF- and CF-substituted sapphyrins act as bidentate/monoanionic ligands, with the coordination sphere of the rhenium(i) ion completed by three carbonyls.

Cobalt Carbonate as an Electrocatalyst for Water Oxidation.

Co salts in the presence of HCO /CO in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E ≈0.71 V (vs.

Tuning Chemical and Physical Properties of Phosphorus Corroles for Advanced Applications.

Although the affinity of metallocorroles to axial ligands is quite low, this is not the case when the chelated element is phosphorus. This work is hence focused on the mechanism of ligand exchange of six-coordinate phosphorus corroles as a tool for affecting their chemical and physical properties. These fundamental investigations allowed for the development of facile methodologies for the synthesis of a large series of complexes and the establishment of several new structure/activity profiles that may be used to understand and predict spectroscopic features and for tailor-made modification of photophysical and electrochemical properties.

Carbonate-radical-anions, and not hydroxyl radicals, are the products of the Fenton reaction in neutral solutions containing bicarbonate.

The Fenton reaction, Fe(HO) + HO → Oxidizing product, is of major importance in biology as the major cause of oxidative stress, and in advanced oxidation processes. It is commonly assumed that ·OH is the product of the Fenton reaction. The results presented herein point out that ·OH is indeed the oxidizing product in acidic solutions for [Fe(HO)] > [HO]; Fe is the active oxidizing product in neutral solutions; in slightly acidic solutions for [HO] > [Fe(HO)] a mixture of ·OH and Fe is formed.

Carbonate and carbonate anion radicals in aqueous solutions exist as CO(HO) and CO(HO)˙ respectively: the crucial role of the inner hydration sphere of anions in explaining their properties.

An effort to reproduce the chemical and physical properties of carbonate and carbonate anion radicals in aqueous solutions by DFT proves that one has to include an inner hydration sphere of six water molecules for both anions. Application of the SMD model to CO3(H2O)62- and CO3(H2O)6˙- enables achievement of the experimental value of the redox potential of the CO3(H2O)6˙-/2- couple. This is a result of the direct inclusion of a considerable charge transfer (CT) from CO32- to its inner hydration sphere in the calculation of the hydration effect.

Reactive Intermediates Involved in Cobalt Corrole Catalyzed Water Oxidation (and Oxygen Reduction).

A detailed investigation of the cobalt corrole Co(tpfc) as molecular catalyst for electrochemical water oxidation uncovered many important mechanism-of-action details that are crucial for the design of optimally performing systems. This includes the identification of the redox states that do and do not participate in catalysis and very significant axial ligand effects on the activity of the doubly oxidized complex. Specifics deduced for the electrocatalysis under homogeneous conditions include the following: the one-electron oxidation of the cobalt(III) corrole is completely unaffected by reaction conditions; catalysis coincides with the second oxidation event; two catalytic waves develop in the presence of OH, and the one at lower overpotential is dominant under more basic conditions.

One-Pot Synthesis of Contracted and Expanded Porphyrins with meso-CF Groups.

Corrole and sapphyrin with the smallest meso-substituents reported so far were prepared in a one-pot synthesis that relies on a non-aldehydic precursor for introducing CF groups. The substantial amounts of products obtained by this facile pathway allowed for the full characterization of 5,10,15-tris(trifluoromethyl)corrole, the access to a variety of stable chelates thereof and investigations that disclose the unique structural and chemical properties induced by the CF substituents. The novel 5,10,15,20-tetra(trifluoromethyl)sapphyrin undergoes only single protonation, which according to its crystal structure is stabilized by favorable non-bonding F/H interaction between the meso-CF and the inverted pyrrolic NH.

Mechanistic Studies on the Role of [Cu (CO ) ] as a Water Oxidation Catalyst: Carbonate as a Non-Innocent Ligand.

Recently it was reported that copper bicarbonate/carbonate complexes are good electro-catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a Cu or a Cu complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that Cu (CO ) complexes are the active intermediates in the electrolysis of Cu (CO ) solution.

Effect of Selective CF Substitution on the Physical and Chemical Properties of Gold Corroles.

Gold corroles are not readily accessible and they display no interesting physical or chemical properties. A facile methodology has now been developed for obtaining selectively CF -substituted gold(III) corroles and the introduction of these groups has been found to have an immense effect on the structures of the complexes, their photophysical and redox properties, and on their ability to participate in catalytic processes.

The Planar Cyclooctatetraene Bridge in Bis-Metallic Macrocycles: Isolating or Conjugating?

A minor modification of the reported procedure for the synthesis of a corrole dimer that is fused by the cyclooctatetraene (COT) unit, (Htpfc)COT, allowed for its isolation in 18% yield. Of the two redox isomers that this interesting macrocycle does form, the current focus is on the reduced form, in which each subunit resembles that of monomeric corroles with a trianionic N coordination core. The corresponding bis-gallium(III) complex was prepared as an entry into the potentially rich coordination chemistry of (Htpfc)COT.

Measured rates of fluoride/metal association correlate with rates of superoxide/metal reactions for Fe(III)EDTA(H2O)- and related complexes.

The effects of 10 paramagnetic metal complexes (Fe(III)EDTA(H2O)-, Fe(III)EDTA(OH)2-, Fe(III)PDTA-, Fe(III)DTPA2-, Fe(III)2O(TTHA)2-, Fe(III)(CN)6(3-), Mn(II)EDTA(H2O)2-, Mn(II)PDTA2-, Mn(II)beta-EDDADP2-, and Mn(II)PO4(-)) on F- ion 19F NMR transverse relaxation rates (R2 = 1/T2) were studied in aqueous solutions as a function of temperature. Consistent with efficient relaxation requiring formation of a metal/F- bond, only the substitution inert complexes Fe(III)(CN)6(3-) and Fe(III)EDTA(OH)2- had no measured effect on T2 relaxation of the F- 19F resonance. For the remaining eight complexes, kinetic parameters (apparent second-order rate constants and activation enthalpies) for metal/F- association were determined from the dependence of the observed relaxation enhancements on complex concentration and temperature.