Christian R. Goldsmith

A homogeneous gallium(III) compound selectively catalyzes the epoxidation of alkenes.

We demonstrate that a simple gallium(III) complex, [Ga(phen)(2)Cl(2)]Cl (phen = 1,10-phenanthroline), can serve as a homogeneous catalyst for the epoxidation of alkenes. The olefin epoxidations proceed relatively quickly at mild temperatures and, under optimum conditions, are highly selective for the epoxide product.

Observation of a ferric hydroperoxide complex during the non-heme iron catalysed oxidation of alkenes and alkanes by O2

A non-heme iron complex catalyses the oxidation of allylic, benzylic, and aliphatic C-H bonds by O(2). During this reactivity, a ferric hydroperoxide species is observed. The kinetic analysis of this complexs formation may suggest a ferric superoxo species as the initial metal-based oxidant.

A Mononuclear Manganese(II) Complex Demonstrates a Strategy To Simultaneously Image and Treat Oxidative Stress

A manganese(II) complex with a ligand containing an oxidizable quinol group serves as a turn-on sensor for H2O2. Upon oxidation, the relaxivity of the complex in buffered water increases by 0.8 mM(-1) s(-1), providing a signal that can be detected and quantified by magnetic resonance imaging. The complex also serves as a potent antioxidant, suggesting that this and related complexes have the potential to concurrently visualize and alleviate oxidative stress.

Two-photon imaging of Zn2+ dynamics in mossy fiber boutons of adult hippocampal slices

Significance Zinc is essential to various organs, including the liver and brain. In the brain, Zn2+ is present at high concentrations and selectively accumulates in the presynaptic vesicles of glutamatergic neurons. Understanding the roles of zinc in these glutamatergic vesicles has been hampered by the inability to visualize zinc accumulation and release at individual synapses. We report a fluorescent zinc-responsive probe and a technique to selectively image mobile zinc in presynaptic vesicles. Using two-photon laser microscopy, we visualized Zn2+ at the synaptic level in tissues from adult mouse brains and successfully monitored Zn2+ release from individual neurons. Our probe and methodology will allow further studies into how Zn2+ regulates synaptic plasticity and other neurologic functions. Mossy fiber termini in the hippocampus accumulate Zn2+, which is released with glutamate from synaptic vesicles upon neural excitation. Understanding the spatiotemporal regulation of mobile Zn2+ at the synaptic level is challenging owing to the difficulty of visualizing Zn2+ at individual synapses. Here we describe the use of zinc-responsive fluorescent probes together with two-photon microscopy to image Zn2+ dynamics mediated by NMDA receptor-dependent long-term potentiation induction at single mossy fiber termini of dentate gyrus neurons in adult mouse hippocampal slices. The membrane-impermeant fluorescent Zn2+ probe, 6-CO2H-ZAP4, was loaded into presynaptic vesicles in hippocampal mossy fiber termini upon KCl-induced depolarization, which triggers subsequent endocytosis and vesicular restoration. Local tetanic stimulation decreased the Zn2+ signal observed at individual presynaptic sites, indicating release of the Zn2+ from vesicles in synaptic potentiation. This synapse-level two-photon Zn2+ imaging method enables monitoring of presynaptic Zn2+ dynamics for improving the understanding of physiological roles of mobile Zn2+ in regular and aberrant neurologic function.

Synthesis and Characterization of α-Diimine Complexes of Group 13 Metals and Their Catalytic Activity toward the Epoxidation of Alkenes.

Complexes of group 13 metal (Al, Ga, In) ions with neutral α-diimine ligands have been prepared and characterized. The Al(III) and Ga(III) [M(α-diimine)2Cl2][MCl4] complexes catalyze the epoxidation of alkenes by peracetic acid under ambient conditions. The two complexes display nearly identical reactivity, demonstrating that inexpensive and highly abundant aluminum is a viable catalytic metal for these reactions.

Synthesis and Characterization of an Asymmetric, Linear, Trinuclear Manganese(II) Complex

After prolonged heating in acetonitrile, a highly asymmetric, trinuclear manganous complex self-assembles from MnCl(2) and bis(2-pyridylmethyl)-1,2-ethanediamine (bispicen). The central Mn(II) ion is bridged to the terminal metal ions in the molecule by single chloride anions. The organic ligands each bind to a single Mn(II) ion. The central Mn(II) and only one of the terminal Mn(II) ions are six-coordinate and bound to bispicen ligands. The remaining terminal Mn(II) ion is coordinated by a tetrahedral array of chloride anions, endowing the trinuclear cluster with a high degree of asymmetry. Variable temperature magnetic measurements are consistent with an S = 5/2 system, indicating net antiferromagnetic coupling.

Superoxide dismutase activity enabled by a redox-active ligand rather than metal

AbstractReactive oxygen species are integral to many physiological processes. Although their roles are still being elucidated, they seem to be linked to a variety of disorders and may represent promising drug targets. Mimics of superoxide dismutases, which catalyse the decomposition of O2•− to H2O2 and O2, have traditionally used redox-active metals, which are toxic outside of a tightly coordinating ligand. Purely organic antioxidants have also been investigated but generally require stoichiometric, rather than catalytic, doses. Here, we show that a complex of the redox-inactive metal zinc(ii) with a hexadentate ligand containing a redox-active quinol can catalytically degrade superoxide, as demonstrated by both reactivity assays and stopped-flow kinetics studies of direct reactions with O2•− and the zinc(ii) complex. The observed superoxide dismutase catalysis has an important advantage over previously reported work in that it is hastened, rather than impeded, by the presence of phosphate, the concentration of which is high under physiological conditions.Catalytic superoxide dismutase mimics typically involve manganese centres. Now, a complex based on redox-inactive zinc(ii) and a redox-active quinol ligand is found to catalytically degrade superoxide. The reaction, proposed to occur through oxidation of the ligand to a quinoxyl radical, is hastened rather than inhibited by the presence of phosphate.