Gareth R. Owen

Reversible dioxygen binding in solvent-free liquid myoglobin.

The ensemble of forces that stabilize protein structure and facilitate biological function are intimately linked with the ubiquitous aqueous environment of living systems. As a consequence, biomolecular activity is highly sensitive to the interplay of solvent-protein interactions, and deviation from the native conditions, for example by exposure to increased thermal energy or severe dehydration, results in denaturation and subsequent loss of function. Although certain enzymes can be extracted into non-aqueous solvents without significant loss of activity, there are no known examples of solvent-less (molten) liquids of functional metalloproteins. Here we describe the synthesis and properties of room-temperature solvent-free myoglobin liquids with near-native structure and reversible dioxygen binding ability equivalent to the haem protein under physiological conditions. The realization of room-temperature solvent-free myoglobin liquids with retained function presents novel challenges to existing theories on the role of solvent molecules in structural biology, and should offer new opportunities in protein-based nanoscience and bionanotechnology.

A new family of metallaboratrane complexes based on 7-azaindole: B–H activation mediated by carbon monoxide

The reaction of Ir(COD)(Tai) [where Tai = {HB(7-azaindoyl)(3)}(-)] with carbon monoxide results, via a sequence of hydride migration and insertion steps, in the formation of the first complexes to contain a metal-to-boron dative interaction supported by 7-azaindole units.

Synthesis and characterisation of group nine transition metal complexes containing new mesityl and naphthyl based azaindole scorpionate ligands

Two novel boron-based flexible scorpionate ligands based on 7-azaindole, Li[HB(azaindolyl)(2)(1-naphthyl)] and Li[HB(azaindolyl)(2)(mesityl)] {Li[(Naphth)Bai] and Li[(Mes)Bai] respectively}, have been prepared (mesityl = 2,4,6-trimethylphenyl). These salts have been isolated in two forms, either as dimeric structures which contain bridging hydride interactions with the lithium centres or as crystalline material containing mono nuclear bis-acetonitrile solvates. The newly formed ligands have been utilised to prepare a range of group nine transition metal complexes with the general formula [M(COD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where M = rhodium, iridium; Ar = 1-naphthyl, mesityl; COD = 1,5-cyclooctadiene) and [Rh(NBD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where NBD = 2,5-norbornadiene; Ar = 1-naphthyl, mesityl). These new complexes have been compared to the previously reported compounds which contain the related scorpionate ligands Li[HB(azaindolyl)(2)(phenyl)] and K[HB(azaindolyl)(3)] {Li[(Ph)Bai] and K[Tai] respectively}. Structural characterisation of the complexes [Rh(COD){κ(3)-NNH-HB (azaindolyl)(2)(mesityl)}], [Ir(COD){κ(3)-NNH-HB (azaindolyl)(2)(mesityl)}] and [Rh(NBD){κ(3)-NNH-HB (azaindolyl)(2)(naphthyl)}] confirm the expected κ(3)-NNH coordination mode for these new ligands. Spectroscopic analysis suggests strong interactions of the B-H functional group with the metal centres in all cases.

Synthesis, structural characterisation and catalytic application of dichloro( η 6 - p -cymene){diphenyl(3-methyl-2-indolyl)phosphine}ruthenium(II) in the transfer hydrogenation of ketones

The synthesis and investigation of ruthenium complexes containing the relatively unexplored ligand, diphenyl-2-(3-methyl)indolylphosphine, is presented herein. The complexes [RuCl2{PPh2(C9H8N)}3], [Ru2(μ-Cl)3(Cl)(MeCN){PPh2(C9H8N)}4] and [RuCl2(η6-p-cymeme){PPh2(C9H8N)}] have been studied. Single crystals of the latter two complexes have been prepared and investigated by X-ray crystallography. A detailed examination of [RuCl2(η6-p-cymeme){PPh2(C9H8N)}] has been carried out. This complex was found to be an active catalyst in the catalytic transfer hydrogenation of ketones.Graphical AbstractThe complex, [RuCl2(η6-p-cymeme){PPh2(C9H8N)}], was synthesised and fully characterised by spectroscopic, analytical and structural methods. The complex was also found to be an active catalyst in the transfer hydrogenation of ketones.

Sequential migrations between boron and rhodium centers: A cooperative process between rhodium and a monosubstituted borohydride unit

The sodium salt of a monosubstituted borohydride anion containing a 2-mercaptopyridyl unit (mp) is reported herein. This compound was coordinated to a rhodium(I) center providing the complex [Rh{κ3-H,H,S-H3B(mp)}(NBD)] (1) (where NBD = 2,5-norbornadiene) in which the boron-based ligand is coordinated to the rhodium center via the thione donor and two of the B-H bonds of the BH3 unit. Reaction of complex 1 with carbon monoxide results in the activation of the complex leading to the product of a formal intramolecular hydroboration reaction, where the NBD unit has, in effect, inserted into one of the B-H bonds. Three complexes were prepared in which the newly formed norbornenyl unit (nbe) is located at the boron center, namely, [Rh{κ3-H,H,S-H2B(nbe)(mp)}(CO)2] (2), [Rh{κ3-H,H,S-H2B(nbe)(mp)}(CO)(PCy3)] (3), and [Rh{κ3-H,H,S-H2B(nbe)(mp)}(CO)(PPh3)] (4). The identities of the three complexes were confirmed by spectroscopic and analytical techniques. Further confirmation was obtained via structural characterization of 3. Studies confirmed that the reactivity occurs at the metal center. A metal-ligand cooperative mechanism, involving initial migration of hydride from boron to metal center, was postulated for the formation of the new complexes based on previous investigations. The newly formed norbornenyl unit then migrates from metal center to boron.

Double addition of H-2 to transition metal-borane complexes: a 'hydride shuttle' process between boron and transition metal centres

The addition of H(2) across a transition metal-borane bond is reported for the first time providing a mechanism for recharging borane functional groups to borohydride.