Search

Abstract: We describe a simple and versatile method for the catalytic epoxidation of a broad range of olefins (e.g., ketones, esters, and alkyl halides) with aqueous H2O2 using manganese salophen catalysts. Low catalyst loading, short reaction times, and a simple reaction setup (e.g., no pH buffer is required) are salient features of the system, which unites the benefits of H2O2 as an oxidant with the versatility and modularity of salen-based catalysts. [Copyright &y& Elsevier]

Abstract: The conversion of N,N′-dilithiobis(alkylamido)phenylboranes [RN–BPh–NR]Li2 (R= t Bu (1), i Pr (2)) to the equivalent dithallium(I) bisamides proceeds readily through the reaction with two molar equivalents of thallous chloride. The thallium amides [RN–BPh–NR]Tl2 (R= t Bu (3), i Pr (4)) have been prepared and characterized by 1H and 11B{1H} NMR. Single crystal X-ray structures of 2–4 reveal the formation of aggregates in the solid state. [Copyright &y& Elsevier]

Abstract: A modular ligand macrocycle is composed from two phenolic groups linked to a cyclohexane bridge through an amide bond and an imine bond. The stability of the asymmetric linkers to metathesis permits a macrocyclic platform to be assembled from the condensation of two different phenolic groups in a single-step, high yield, reaction. The primary coordination sphere may be tuned with functional groups on one phenolic group. The other phenolic group may be modified with a scaffold possessing a proton transfer group. In this way, control over the secondary coordination sphere of the macrocycle is achieved. Manganese complexes of the amido-imine linked macrocycle catalytically epoxidizes 1,2-dihydronapthalene using sodium hypochlorite as the oxidant. The amido-imine macrocycles represent a new metal active site capable of supporting high oxidation states and attendant atom transfer chemistry while at the same time permitting control over the primary and secondary sphere of the metal center. [Copyright &y& Elsevier]

Ribonucleotide reductases (RNRs) are essential enzymes producing de novo deoxynucleotide (dNTP) building blocks for DNA replication and repair and regulating dNTP pools important for fidelity of these processes. A new study reveals that the class Ia Escherichia coli RNR is regulated by dATP via stabilization of an inactive α4β4 quaternary structure, slowing formation of the active α2β2 structure. The results support the importance of the regulatory α4β4 complex providing insight in design of experiments to understand RNR regulation in vivo. [ABSTRACT FROM AUTHOR]

Abstract: Time-resolved absorption spectroscopy has been employed to study the directionality and rate of charge transfer in W–Y and Ac-W–Y dipeptides as a function of pH. Excitation with 266-nm nanosecond laser pulses produces both W⋅ (or [⋅WH]+, depending on pH) and Y⋅. Between pH 6 and 10, W⋅ to was found to oxidize Y with kX⋅=9.0×104 s−1 and 1.8×104 s−1 for the W–Y and Ac-W–Y dipeptide systems, respectively. The intramolecular charge transfer rate increases as the pH is lowered over the range 6>pH>2. For 10

A solar chemical and fuels industry demands CO 2 reduction products beyond one-carbon molecules. We have shown that a hybrid biological | inorganic (HBI) system can use the hydrogen produced from water splitting catalysts to reduce CO 2 into multi-carbon products with high energy efficiency. Here we report the integration of the HBI device with triple-junction solar cells to complete a solar-powered water splitting | CO 2 fixation cycle driven by the HBI. Solar-to-chemical efficiency ( ŋ solar ) of 6% averaged over 24 h are experimentally achieved with little sophisticated engineering or reactor design. We show that the limiting factor of ŋ solar in the integrated HBI system is the voltage mismatch between the output of solar cell and the input of hybrid CO 2 -fixing device. With a better voltage match, ŋ solar exceeding 10% can be expected. [ABSTRACT FROM AUTHOR]

An expanding renewable energy market to supplant petrochemicals has motivated synthesis technologies that use renewable feedstocks, such as CO 2 . Hybrid biological-inorganic systems provide a sustainable, efficient, versatile, and inexpensive chemical synthesis platform. These systems comprise biocompatible electrodes that transduce electrical energy either directly or indirectly into bioavailable energy, such as H 2 and NAD(P)H. In combination, specific bacteria use these energetic reducing equivalents to fix CO 2 into multi-carbon organic compounds. As hybrid biological-inorganic technologies have developed, the focus has shifted from phenomenological and proof-of-concept discovery towards enhanced energy efficiency, production rate, product scope, and industrial robustness. In this review, we highlight the progress and the state-of-the-art of this field and describe the advantages and challenges involved in designing bio- and chemo- compatible systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metalloporphyrin synthesis and structural characterization. • Ultrafast excited state dynamics. • Nonradiative decay kinetics and mechanisms. The Mn(III)Cl and Pd(II) meso -(4-fluoro-2,6-dimethyl-phenyl) porphyrins have been synthesized and structurally characterized by X-ray crystallography. Together with its Zn(II) congener, this homologous series of porphyrins show the manifestation of d–d states and spin–orbit coupling on the excited state dynamics of metalloporphyrins. [ABSTRACT FROM AUTHOR]

Redox-driven proton pumps, radical initiation and propagation in biology, and small-molecule activation processes all involve the coupling of electron transfer to proton transport. A mechanistic framework in which to interpret these processes is being developed by examining proton-coupled electron transfer (PCET) in model and natural systems. Specifically, PCET investigations are underway on the following three fronts: (1) the elucidation of the PCET reaction mechanism by time-resolved laser spectroscopy of electron donors and acceptors juxtaposed by a proton transfer interface; (2) the role of amino acid radicals in biological catalysis with the radical initiation and transport processes of E. coli ribonucleotide reductase (RNR) as a focal point; and (3) the application of PCET towards small–molecule activation with emphasis on biologically relevant bond-breaking and bond-making processes involving oxygen and water. A review of recent developments in each of these areas is discussed. [Copyright &y& Elsevier]

The preserved dσ* character preserved across the different d-electron counts of a homologous binuclear complex series allows for M–X bond activation upon ligand-to-metal charge transfer excitation. Such photoactivation of the M–X bond is crucial to achieving an efficient HX-splitting photocycle, which provides an alternative to solar energy storage by water splitting. [Display omitted] The photogeneration of X 2 is the key to achieving an efficient HX-splitting photocycle, as it is more thermodynamically and kinetically challenging than its H 2 half reaction counterpart. Here we report a strategy that enables Cl 2 photoelimination from low-valent binuclear d9–d9 and d9–d10 Ni complexes. We demonstrate the importance a of metal–metal bond interaction for M–X bond photoactivation with a combination of TD-DFT computations together with spectroscopy and photocrystallography, exemplifying a design principle for future developments of 3d metal complexes for HX photocatalysis. [ABSTRACT FROM AUTHOR]