Molecular catalyst coordinatively bonded to organic semiconductors for selective light-driven CO reduction in water.

The selective photoreduction of CO in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber.

Trapping an Elusive Fe(IV)-Superoxo Intermediate Inside a Self-Assembled Nanocage in Water at Room Temperature.

Molecular cavities that mimic natural metalloenzymes have shown the potential to trap elusive reaction intermediates. Here, we demonstrate the formation of a rare yet stable Fe(IV)-superoxo intermediate at room temperature subsequent to dioxygen binding at the Fe(III) site of a (EtN)[Fe(Cl)(bTAML)] complex confined inside the hydrophobic interior of a water-soluble PdL nanocage. Using a combination of electron paramagnetic resonance, Mössbauer, Raman/IR vibrational, X-ray absorption, and emission spectroscopies, we demonstrate that the cage-encapsulated complex has a Fe(IV) oxidation state characterized by a stable S = 1/2 spin state and a short Fe-O bond distance of ∼1.

Spectroscopic characterization and reactivity studies of a copper(II) iminoxyl radical complex.

A Cu complex (1) of a bis-pyridine-dioxime ligand and its one-electron oxidized analog (1-ox) were thoroughly characterized by various spectroscopic techniques, including X-ray absorption spectroscopy. 1-ox was found to be a Cu complex of a ligand iminoxyl radical and represents the first example of such a type. Reorganization energy () of 2.

Functional Model of Compound II of Cytochrome P450: Spectroscopic Characterization and Reactivity Studies of a Fe-OH Complex.

Herein, we show that the reaction of a mononuclear Fe(OH) complex () with -tosyliminobenzyliodinane (PhINTs) resulted in the formation of a Fe(OH) species (). The obtained complex was characterized by an array of spectroscopic techniques and represented a rare example of a synthetic Fe(OH) complex. The reaction of with the one-electron oxidizing agent was reported to form a ligand-oxidized Fe(OH) complex ().

Mapping the Ultrafast Mechanistic Pathways of Co Photocatalysts in Pure Water through Time-Resolved X-ray Spectroscopy.

Nanosecond time-resolved X-ray (tr-XAS) and optical transient absorption spectroscopy (OTA) are applied to study 3 multimolecular photocatalytic systems with [Ru(bpy) ] photoabsorber, ascorbic acid electron donor and Co catalysts with methylene (1), hydroxomethylene (2) and methyl (3) amine substituents in pure water. OTA and tr-XAS of 1 and 2 show that the favored catalytic pathway involves reductive quenching of the excited photosensitizer and electron transfer to the catalyst to form a Co square pyramidal intermediate with a bonded aqua molecule followed by a Co square planar derivative that decays within ≈8 μs. By contrast, a Co square pyramidal intermediate with a longer decay lifetime of ≈35 μs is formed from an analogous Co geometry for 3 in H O.

Comparing the reactivity of an oxoiron(IV) cation radical and its oxoiron(V) tautomer towards C-H bonds.

An oxoiron(IV) cation radical is generated upon two-electron oxidation of an iron(III) complex bearing an electron-rich methoxy substituted bTAML framework and thoroughly characterized multiple spectroscopic techniques and density functional theory (DFT). Reactivity studies demonstrate faster rates for oxidation of strong aliphatic sp C-H bonds than for its corresponding oxoiron(V) valence tautomer.

Surface-Promoted Evolution of Ru-bda Coordination Oligomers Boosts the Efficiency of Water Oxidation Molecular Anodes.

A new Ru oligomer of formula {[Ru(bda-κ-NO)(4,4'-bpy)](4,4'-bpy)}, (bda is [2,2'-bipyridine]-6,6'-dicarboxylate and 4,4'-bpy is 4,4'-bipyridine), was synthesized and thoroughly characterized with spectroscopic, X-ray, and electrochemical techniques. This oligomer exhibits strong affinity for graphitic materials through CH-π interactions and thus easily anchors on multiwalled carbon nanotubes (CNT), generating the molecular hybrid material . The latter acts as a water oxidation catalyst and converts to a new species, , during the electrochemical oxygen evolution process involving solvation and ligand reorganization facilitated by the interactions of molecular Ru catalyst and the surface.

Characterization and reactivity study of non-heme high-valent iron-hydroxo complexes.

A terminal FeOH complex, [Fe(L)(OH)] (), has been synthesized and structurally characterized (HL = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). The oxidation reaction of with one equiv. of (4-bromophenyl)ammoniumyl hexachloroantimonate (TBAH) or ceric ammonium nitrate (CAN) in acetonitrile at -45 °C results in the formation of a FeOH ligand radical complex, [Fe(L˙)(OH)] (), which is hereby characterized by UV-visible, H nuclear magnetic resonance, electron paramagnetic resonance, and X-ray absorption spectroscopy techniques.

Structure and excited-state dynamics of dimeric copper(i) photosensitizers investigated by time-resolved X-ray and optical transient absorption spectroscopy.

Time-resolved X-ray (tr-XAS) and optical transient absorption (OTA) spectroscopy in the picosecond time scale coupled with Density Functional theory (DFT) and X-ray absorption near-edge structure (XANES) calculations are applied to study three homoleptic Cu(i) dimeric chromophores with ethyl and longer propyl spacers, denoted as [Cu(mphenet)]Cl (C1), [Cu(mphenet)](ClO) (C2) and [Cu(mphenpr)](ClO) (C3) (where mphenet = 1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane and mphenpr = 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane). Tr-XAS analysis after light illumination at ∼ 100 ps illustrate the formation of a flattened triplet excited state in all 3 complexes. Optical transient absorption (OTA) analysis for C1 monitored in water and C2 and C3 measured in acetonitrile reveals distinct excited-state lifetimes of 169 ps, 670 ps and 1600 ps respectively.

Role of β-adrenoceptors, cAMP phosphodiesterase and external Ca2+ on polyamine-induced relaxation in isolated bovine tracheal strips.

Polyamines relax several smooth muscles and elicit cardiotonic effects in the rat heart via interactions with β-adrenoceptors. The aim of this work was to establish whether β(2)-adrenoceptors were involved in polyamine-relaxation of bovine tracheal strips. Endogenous polyamines displaced the specific radioligand, [(3)H]dihydroalprenolol, but spermine was the most potent.

Modulatory role of endogenous androgens on airway smooth muscle tone in isolated guinea-pig and bovine trachea; involvement of beta2-adrenoceptors, the polyamine system and external calcium.

Androgens relax several smooth muscles, including the airways. They also contract ileum and myocardium via nongenomic mechanisms. To find out whether androgens modulate airway smooth muscles in different species and further assess their mechanism of action, regarding the role of beta-adrenoceptors, polyamines and extracellular Ca(2+), and the modulation of contraction, 5 alpha-dihydrotestosterone, testosterone and 5 beta-dihydrotestosterone were used.

Putrescine modulation of acute activation of the beta-adrenergic system in the left atrium of rat.

Endogenous polyamines mediate acute metabolic effects and cardiac hypertrophy associated to beta-adrenoceptor stimulation. The aim of this study is to characterize the role of polyamines on beta-adrenoceptor system mediated responses. To this end, the functional interaction of polyamine modifying drugs on isoproterenol-elicited cardiotonic effect, in isolated left atria of male Wistar rats, and their effects on [(3)H]dihydroalprenolol (DHA) binding on beta-adrenoceptors and on adenylyl cyclase activity of membrane heart were studied.

Role of putrescine on androgen-elicited positive inotropism in the left atrium of rats.

Functional and biochemical studies were performed in isolated left atria of male Wistar rats to study whether endogenous polyamines may mediate androgen-elicited positive inotropism and their relationship with a rise in cAMP during the cardiotonic effect. 5 alpha-Dihydrotestosterone (100 microM) exposure increased intracellular putrescine as determined by HPLC, but it did not increase spermidine and spermine. This effect was antagonized by an inhibitor of ornithine decarboxylase, alpha-difluoromethylornithine (10 mM), suggesting enzyme activation.

Interaction of androgens with cardiotonic drugs in isolated left atrium of rat.

Pharmacological concentrations of androgens are known to elicit a rapid positive inotropism in isolated left atrium of male rats. Upon short-term exposure to androgens, an increase in intracellular cAMP levels has been observed, though delayed with respect to the time course of contraction, suggesting that other mechanisms may participate in initiating the contraction. Therefore, the interaction of positive inotropism elicited by ouabain, an inhibitor of Na(+)-K(+)-ATPase, and androgens was studied in isolated left atrium of rat.

Identification of a new class of inhibitors of the voltage-gated potassium channel, Kv1.3, with immunosuppressant properties.

The voltage-gated potassium channel, K(v)1.3, is a novel target for development of immunosuppressants. Using a functional (86)Rb(+) efflux assay, a new class of high-affinity K(v)1.

Intracellular cAMP increases during the positive inotropism induced by androgens in isolated left atrium of rat.

Molecular interactions of androgens with the plasma membrane may produce rapid cardiovascular effects that cannot be explained by the classic genomic mechanisms. In this sense, 5 alpha- and 5 beta-dihydrotestosterone-induced an acute positive inotropic effect in isolated left atrium of rat, an effect which may be due to cAMP-dependent mechanisms. To prove this, intracellular levels of cAMP, after exposure to androgens in the organ bath, and binding to beta(1)-adrenoceptors were evaluated.