Design of Mononuclear Ruthenium Catalysts for Low‐Overpotential Water Oxidation

Water oxidation is a key reaction in natural photosynthesis and in many schemes for artificial photosynthesis. Inspired by energy challenges and the emerging understanding of photosystem II, the development of artificial molecular catalysts for water oxidation has become a highly active area of research in recent years. In this Focus Review, we describe recent achievements in the development of single‐site ruthenium catalysts for water oxidation with a particular focus on the overpotential of water oxidation. First, we introduce the general scheme to access the high‐valent ruthenium–oxo species, the key species of the water‐oxidation reaction. Next, the mechanisms of the O? O bond formation from the active ruthenium–oxo species are described. We then discuss strategies to decrease the onset potentials of the water‐oxidation reaction. We hope this Focus Review will contribute to the further development of efficient catalysts toward sustainable energy‐conversion systems.     

Acid/base-regulated reversible electron transfer disproportionation of N–N linked bicarbazole and biacridine derivatives

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt₃, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials.     

Protein labeling with red squarylium dyes for analysis by capillary electrophoresis with laser-induced fluorescence detection

Two new red luminescent asymmetric squarylium dyes (designated "Red-1c and Red-3") have been shown to exhibit absorbance shifts to longer wavelengths upon the addition of protein, along with a concomitant increase in fluorescence emission. Specifically, the absorbance maxima for Red-1c and Red-3 dyes are 607 and 622 nm, respectively, in the absence of HSA, and 642 and 640 nm in the presence of HSA, making the excitation of their protein complexes feasible with inexpensive and robust diode lasers. Fluorescence emission maxima, in the presence of HSA, are 656 and 644 nm for Red-1c and Red-3, respectively. Because of the inherently low fluorescence of the dyes in their free state, Red-1c and Red-3 were used as on-column labels (that is, with the dye incorporated into the separation buffer), thus eliminating the need for sample derivatization prior to injection and separation. A comparison of precolumn and on-column labeling of proteins with these squarylium dyes revealed higher efficiencies and greater sensitivities for on-column labeling, which, when conducted with a basic, high-salt content buffer, permitted baseline resolution of a mixture of five model proteins. LOD for model proteins, such as transferrin, alpha-lactalbumin, BSA, and beta-lactoglobulin A and B, labeled with these dyes and analyzed by CE with LIF detection (CE-LIF) were found to be dependent upon dye concentration and solution pH, and are as low as 5 nM for BSA. Satisfactory linear relationships between peak height (or peak area) and protein concentration were obtained by CE-LIF for this on-column labeling method with Red-3 and Red-1c.     

Novel synthesis of (Z)-difluoroacrylates via a highly stereoselective addition-elimination reaction

[STRUCTURE: SEE TEXT] On treating readily prepared benzyl 2,3,3-trifluoroacrylate with various Grignard reagents, e.g., aryl-, alkyl-, or alkenylmagnesium halide, in the presence of a catalytic amount of copper(I) salt in THF at -78 degrees C for 1 h, the corresponding alpha,beta-difluoroacrylates were obtained in 54-98% yields with high Z-selectivity.     

Generators for the tautological algebra of the moduli space of curves

In this paper, we prove that the tautological algebra in cohomology of the moduli space M_g of smooth projective curves of genus g is generated by the first [g/3] Mumford-Morita-Miller classes. This solves a part of Faber's conjecture (Moduli of Curves and Abelian Varieties Vieweg, Braunschweig, 1999) concerning the structure of the tautological algebra affirmatively. More precisely, for any k we express the kth Mumford-Morita-Miller class e_k as an explicit polynomial in the lower classes for all genera g=3k−1,3k−2,…,2.     

O $$(\bar \Lambda /m_c )$$ effects in tests of factorization hypothesis for heavy-hadron nonleptonic decays

In the framework of the heavy-quark effective theory, theO ( O(_QCD)) corrections are estimated in the test of factorization hypothesis forB-meson nonleptonic decays proposed by Bjorken. Similar calculations are also carried out for _b nonleptonic decays. The effects of these corrections on the estimate of theD _s -meson decay constant are discussed.     

The compound Cr2TiO5 in the system Cr2O3TiO2

The compound Cr₂TiO₅ could be synthesized as a stoichiometric single phase above 1660°C in air. Application of selected area electron diffraction, high resolution electron microscopy and powder X-ray diffraction studies showed that Cr₂TiO₅ is isomorphous with CrFeTiO₅, with V₃O₅ type structure. It is monoclinic, a = 7.020(1)Å, b = 5.025(1)Å, c = 9.945(2)Å and β = 111.43(2)°. It was found that Cr₂TiO₅ is unstable relative to a mixture of Cr₂O₃ (ss) and a so-called “E” phase, below 1660°C.     

Phase transfer catalysis of modified dextran anion exchangers

Dextran anion exchangers with lipophilic substituents have been synthesized, which were found to be useful as phase transfer catalysts for displacement and hydrogenation reactions under triphase conditions.     

Enantiospecific total synthesis of (-)-megaphone by a highly controlled consecutive 1,4- and 1,3-asymmetric induction

Enantiospecific total synthesis of (-)-megaphone (1) is reported. The key synthetic tactic is the use of (4$\text{S}$)-2$\text{Z}$-ethylidene-4-trityloxymethyl-butan-4-olide (6) to both establish the relative and absolute stereochemistry of the contiguous tertiary and quaternary carbon centers by a highly controlled 1,4- and 1,3-asymmetric induction and construct the 4-methoxy-6,6-dialkyl-cyclohexenone portion of 1.     

Total synthesis of (+--oudemansin

($\text{+}\text{-}$)-Oudemansin has been synthesized starting from $\text{trans}$-cinnamaldehyde by a route involving the stereoselective Zn(BH₄)₂ reduction of β-keto ester.