Nonplanar porphyrins: synthesis, properties, and unique functionalities.

Porphyrins are variously substituted tetrapyrrolic macrocycles, with wide-ranging biological and chemical applications derived from metal chelation in the core and the 18π aromatic surface. Under suitable conditions, the porphyrin framework can deform significantly from regular planar shape, owing to steric overload on the porphyrin periphery or steric repulsion in the core, among other structure modulation strategies. Adopting this nonplanar porphyrin architecture allows guest molecules to interact directly with an exposed core, with guest-responsive and photoactive electronic states of the porphyrin allowing energy, information, atom and electron transfer within and between these species.

Photocatalytic hydrogen evolution using a Ru(ii)-bound heteroaromatic ligand as a reactive site.

A Ru complex, [Ru(tpphz)(bpy)] (1) (tpphz = tetrapyridophenazine, bpy = 2,2'-bipyridine), whose tpphz ligand has a pyrazine moiety, is converted efficiently to [Ru(tpphz-HH)(bpy)] (2) having a dihydropyrazine moiety upon photoirradiation of a water-methanol mixed solvent solution of 1 in the presence of an electron donor. In this reaction, the triplet metal-to-ligand charge-transfer excited state (MLCT*) of 1 is firstly formed upon photoirradiation and the MLCT* state is reductively quenched with an electron donor to afford [Ru(tpphz˙)(bpy)], which is converted to 2 without the observation of detectable reduced intermediates by nano-second laser flash photolysis. The inverse kinetic isotope effect (KIE) was observed to be 0.

Mechanistic Insight into Concerted Proton-Electron Transfer of a Ru(IV)-Oxo Complex: A Possible Oxidative Asynchronicity.

We have thoroughly investigated the oxidation of benzyl alcohol (BA) derivatives by a Ru(O) complex () in the absence or presence of Brønsted acids in order to elucidate the proton-coupled electron-transfer (PCET) mechanisms in C-H oxidation on the basis of a kinetic analysis. Oxidation of BA derivatives by without acids proceeded through concerted proton-electron transfer (CPET) with a large kinetic isotope effect (KIE). In contrast, the oxidation of 3,4,5-trimethoxy-BA ((MeO)-BA) by was accelerated by the addition of acids, in which the KIE value reached 1.

Fundamental electron-transfer and proton-coupled electron-transfer properties of Ru(iv)-oxo complexes.

Isolation and characterisation of Ru(O) complexes were accomplished to investigate their fundamental electron transfer (ET) and proton-coupled ET (PCET) properties. Reorganisation energies (λ) in electron transfer (ET) and proton-coupled ET (PCET) from electron donors to the isolated Ru(O) complexes have been determined for the first time to be in the range of 1.70-1.

Efficient photocatalytic proton-coupled electron-transfer reduction of O using a saddle-distorted porphyrin as a photocatalyst.

Photocatalytic O2 reduction reactions proceeded to produce H2O2 using a diprotonated saddle-distorted dodecaphenylporphyrin as a photocatalyst. The quantum yield (12%), the turnover number (3000 for 6 h), and the turnover frequency (500 h-1) are achieved in photocatalytic systems based on free-base porphyrins for the first time. The photocatalytic reaction mechanism has been revealed by ns-laser flash photolysis and kinetic analysis.

Dioxygen/Hydrogen Peroxide Interconversion Using Redox Couples of Saddle-Distorted Porphyrins and Isophlorins.

Interconversion between dioxygen (O) and hydrogen peroxide (HO) has attracted much interest because of the growing importance of HO as an energy source. There are many reports on O conversions to HO; however, no example has been reported on O/HO interconversion. Herein, we describe successful achievement of a reversible O/HO conversion based on an N21, N23-dimethylated saddle-distorted porphyrin and the corresponding two-electron-reduced porphyrin (isophlorin) for the first time.

Formation of supramolecular hetero-triads by controlling the hydrogen bonding of conjugate bases with a diprotonated porphyrin based on electrostatic interaction.

The thermodynamic stability of diprotonated saddle-distorted dodecaphenylporphyrin (HDPP(X)) was controlled by the hydrogen-bonding strength of conjugate bases (X) of strong acids (HX) or acids (R-COOH) having positively charged moieties. The thermodynamic control of HDPP(X) made it possible to achieve selective formation of supramolecular hetero-triads, HDPP(X)(Cl).

Visible-Light-Driven Photocatalytic CO Reduction by a Ni(II) Complex Bearing a Bioinspired Tetradentate Ligand for Selective CO Production.

A Ni(II) complex bearing an SN-type tetradentate ligand inspired by the active site of carbon monoxide dehydrogenase was found to selectively catalyze CO reduction to produce CO in a photocatalytic system using [Ru(bpy)] (bpy = 2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. The Ni(II) complex shows a high turnover number over 700 with high CO selectivity of >99% and quantum yield of 1.42% in the photocatalytic system.

Thermodynamics and Photodynamics of a Monoprotonated Porphyrin Directly Stabilized by Hydrogen Bonding with Polar Protic Solvents.

Addition of 1 equiv of TFA to an acetone solution containing dodecaphenylporphyrin (H DPP) in the presence of 10 % MeOH (v/v) resulted in selective formation of a monoprotonated form (H DPP ), in sharp contrast to protonation of H DPP directly affording a diprotonated form (H DPP ) in acetone in the absence of MeOH. The crucial role of MeOH for selective H DPP formation was interpreted as hydrogen-bonding stabilization of H DPP , since a MeOH molecule was found to form hydrogen bonds with an NH proton of H DPP in the crystal. The selectivity of H DPP formation was evaluated by the formation yield of H DPP , which increased when elevating the portion of MeOH (0-10 %) in acetone with saturation behavior, suggesting that H DPP is stabilized by hydrogen bonding with MeOH even in solution, together with the thermodynamic parameters determined from a van't Hoff plot based on the spectroscopic titration.

Increased cell surface expression of C-terminal truncated erythropoietin receptors in polycythemia.

Primary familial and congenital polycythemia (PFCP) is a disorder characterized by an increased number of erythrocytes despite normal blood oxygen pressure and a normal serum erythropoietin (EPO) level. Recent studies revealed that erythroid progenitor cells from certain individuals with PFCP express various forms of EPO receptor (EPOR) truncated at the terminal carboxyl site (EPOR-TTC(PFCP)). EPOR-TTC(PFCP) can transmit EPO-mediated proliferative signals more efficiently than can full-length EPOR (EPOR-F), at least partly because of defective recruitment of SHP-1 phosphatase to these receptors.

Quantitative assessment of the stem cell self-renewal capacity.

Little is known about the manner in which hematopoietic stem cells (HSCs) self-renew. To address this issue, we used a serum-free single-cell culture, followed by transplantation of cultured cells into lethally irradiated mice. CD34-negative or low, c-Kit-positive, Sca-1-positive, lineage marker-negative (CD34-KSL) cells are highly enriched for murine bone marrow HSCs.

Expansion of hematopoietic stem cells in the developing liver of a mouse embryo.

The activity of hematopoietic stem cells in the developing liver of a C57BL/6 mouse embryo was quantified by a competitive repopulation assay. Different doses of fetal liver cells at days 11 to 18 of gestation were transplanted into irradiated mice together with 2 x 10(5) adult bone marrow cells. A long-term repopulation in myeloid-, B-cell, and T-cell lineage by fetal liver cells was evaluated at 20 weeks after transplantation.

Comparison of hematopoietic activities of human bone marrow and umbilical cord blood CD34 positive and negative cells.

Although the hematopoietic activities of human CD34+ bone marrow (BM) and cord blood (CB) cells have been well characterized, the phenotype of nonobese-diabetic severe combined immunodeficient (NOD/SCID) mice repopulating cells (SRCs) in CB and BM has not yet been fully examined. To address this issue, various hematopoietic activities were compared in terms of total and CD34+ CB and BM cells. Clonal culture of fluorescence-activated cell sorter (FACS) CD34+ CB and BM cells revealed a higher incidence of colony-forming cells with greater proliferation capacity in CB over BM CD34+ cells.