The reactions of the "clamshell" 1,2-bis(imino)acenaphthene (BIAN) ligand with decamethyleuropocene, boron triiodide, phosphorus triiodide, and tellurium tetraiodide have been investigated. The "clamshell" ligand undergoes one-electron reduction with decamethyleuropocene while treatment of this ligand with boron triiodide generates a BIAN-supported boron monoiodide via two-electron reduction. The reaction of the "clamshell" ligand with phosphorus triiodide involves a two-electron reduction of the BIAN backbone while that with tellurium tetraiodide yields a TeI2 complex without intermolecular charge transfer. / text

Selenium is a required trace element which was originally discovered by the Swedish chemist Jons Jacob Berzelius in 1817. It was initially believed to be a toxin as it was identified as being the cause of hoof maladies and excessive hair loss in horses that feed upon plants with high selenium content. It wasn’t until 1957 that the potential contributions of selenium to physiology were first demonstrated. Selenium is now known to play a critical role in the maintenance of human health. Interestingly, unlike other trace metals/semi-metals, selenium is directly incorporated into proteins in the form of the amino acid selenocysteine (Sec) in a very complicated and energetically costly fashion. Though rare, being found in only 25 human proteins, Sec proteins are involved in numerous vital biological processes including maintenance of redox homeostasis and anti-oxidant defense. Even though Sec is essential, the reason that Sec replaces its structural analog cysteine (Cys) in only 25 proteins is not widely agreed upon. A previous model suggests that the replacement of Cys with Sec provides enzymes with a type of catalytic advantage. The presence of Cys-containing orthologs of mammalian Sec-enzymes in other eukaryotes argues against this model. A newer model to explain the use of Sec is that the gain of function imparted to an enzyme by replacing Cys with Sec is the ability of Sec to impart chemical reversibility. Building on previous results from our lab demonstrating the ability of Sec to confer proteins with the ability to resist over oxidation we have elucidated the mechanism by which Sec containing thioredoxin reductase (TrxR) resists over oxidation. The ability of Sec-TrxR to resist oxidative inactivation is due to the greater electrophilicity of Sec relative to Cys. This allows for quicker resolution and prevents over oxidation. Based on these findings we also investigate the utility of the alkylating agent dimedone to probe the oxidation state of Sec. Interestingly, it was discovered that dimedone will react with seleneninic acid with the resulting adduct being labile. Additonally it was discovered that dimedone will also react with seleninic acid, resulting in the formation of a dimedone dimer. These results call into question the usefulness of dimedone in deteremining the oxidation state of Sec. Finally, we provide evidence that Sec-TrxR enzymes are able to catalyze single electron reductions. This is most likely due to the formation of a stable Sec radical intermediate. As a whole this project provides support for the theory that Sec was selected for due to its ability to convey chemical reversiablity to proteins.

Conventional primary Li/CFx batteries employ graphite and polyvinylidene fluoride additives in the cathodes. These additives usher in some un-desired side-effects, such as lower battery capacities (mAh/g) and smaller current densities (mA/g). An innovative pretreatment was developed in this research in which CFx was subject to a “solvated electron” reduction to obtain a thin layer graphitic carbon coating on the CFx particle surfaces. Resistivity tests revealed that these partially reduced CFx particles have a higher conductivity at comparable graphitic carbon contents. Electrochemical discharge reactions demonstrated that batteries made from the reduced CFx were superior to the conventional batteries with higher current densities and higher capacities achieved. Impedance spectroscopy (EIS) studies found out that the reduced CFx particles have smaller cell reaction resistances, smaller double layer/intercalation capacitances and smaller mass transport resistances. It appears that use of reduced CFx has the potential to replace the conventional CFx plus additives as a cathode material in Li/CFx batteries.

Yes / The first use of a dinuclear UIII/UIII complex in the activation of small molecules is reported. The octadentate Schiff-base pyrrole, anthracene-hinged ‘Pacman’ ligand LA combines two strongly reducing UIII centres and three borohydride ligands in [M(THF)4][{U(BH4)}2(m-BH4)(LA)(THF)2] 1-M, (M ¼ Li, Na, K). The two borohydride ligands bound to uranium outside the macrocyclic cleft are readily substituted by aryloxide ligands, resulting in a single, weakly-bound, encapsulated endo group 1 metal borohydride bridging the two UIII centres in [{U(OAr)}2(m-MBH4)(LA)(THF)2] 2-M (OAr ¼ OC6H2tBu3-2,4,6, M ¼ Na, K). X-ray crystallographic analysis shows that, for 2-K, in addition to the endo-BH4 ligand the potassium countercation is also incorporated into the cleft through h5-interactions with the pyrrolides instead of extraneous donor solvent. As such, 2-K has a significantly higher solubility in non-polar solvents and a wider U–U separation compared to the ‘ate’ complex 1. The cooperative reducing capability of the two UIII centres now enforced by the large and relatively flexible macrocycle is compared for the two complexes, recognising that the borohydrides can provide additional reducing capability, and that the aryloxide-capped 2-K is constrained to reactions within the cleft. The reaction between 1-Na and S8 affords an insoluble, presumably polymeric paramagnetic complex with bridging uranium sulfides, while that with CS2 results in oxidation of each UIII to the notably high UV oxidation state, forming the unusual trithiocarbonate (CS3)2 as a ligand in [{U(CS3)}2(m-k2:k2-CS3)(LA)] (4). The reaction between 2-K and S8 results in quantitative substitution of the endo-KBH4 by a bridging persulfido (S2)2 group and oxidation of each UIII to UIV, yielding [{U(OAr)}2(m-k2:k2-S2)(LA)] (5). The reaction of 2-K with CS2 affords a thermally unstable adduct which is tentatively assigned as containing a carbon disulfido (CS2)2 ligand bridging the two U centres (6a), but only the mono-bridged sulfido (S)2 complex [{U(OAr)}2(m-S (LA)] (6) is isolated. The persulfido complex (5) can also be synthesised from the mono-bridged sulfido complex (6) by the addition of another equivalent of sulfur. / EPSRC, European COST network