Abstract: We report high-frequency (up to 219 GHz) electron paramagnetic resonance (EPR) spectra and X-ray crystal structure of [Co₄O₄(pyridine)₄(acetate)₄]⁺ ([Co₄O₄(py)₄(OAc)₄]⁺) that serves as a structural and spectroscopic model of cobalt-oxide films that are capable of oxidizing water. These results are, in large part, consistent with those from our earlier, lower-frequency study and serve to benchmark future high-field studies on paramagnetic states of the catalyst film.

Stitch, Troy A.;[1] Krzytek, Jurek;[2] Mercado, Brandon Q.;[1] McAlpin, J. Gregory;[1] Ohlin, C. André;[3] Olmstead, Marilyn;[1] Casey, William H.;[1,4] Britt, R. David [1] Structural insights into [Co₄O₄(C₅H₅N)₄(CH₃CO₂)₄]⁺ -- a Rare Co(IV)-Containing Cuboidal Complex Polyhedron 2013, 64, 304-307. Link.

1. Department of Chemistry, University of California, Davis, California 95616, USA.
2. National High Magnetic Field Laboratory, Florida State University, Tallahassee. 3. School of Chemistry, Monash University, Victoria, Australia
4. Department of Geology, University of California, Davis, California, USA.

Abstract: The discovery of a family of large uranyl peroxo clusters dramatically affected the ideas about the environmental chemistry of actinide elements. To date over 40 structures have been isolated, and have proven to make up a heterogeneous class in terms of size, structural motifs, solution stability and speciation. In spite of their likely importance as environmentally relevant species little is known about the solution dynamics of these clusters, such as dissociation mechanisms, and pH and electrochemical stabilities. An added challenge has been in isolating large quantities of pure compound with NMR-active nuclei in the structure. Here we probe the solution chemistry of a class of uranyl-peroxo clusters which contains 24 uranyl moieties linked by 12 pyrophosphate units.

Johnson, Rene L.;[1] Ohlin, C André[*,2]; Pellegrini, Kristi;[3] Burns, Peter C.;[3,4] Casey, William H.[*,1,5] Dynamics of a Nanometer-size Uranyl Cluster in Solution Angew. Chemie Int. Ed. 2013, 52(29), 7464-7467. Link

1. Department of Chemistry, University of California, Davis, California 95616, USA.
2. School of Chemistry, Monash University, Vic 3800, Australia.
3. Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, IN 46556, USA.
4. Department of Chemistry and Biochemistry, University of Notre Dame, IN 46556, USA.
5. Department of Geology, University of California, Davis, California, USA.

Abstract: The putative applications of poly-, oligo- and mono-oxometalates in biochemistry, biology, pharmacology and medicine are rapidly attracting interest. In particular, these compounds may act as potent ion pump inhibitors and have the potential to play a role in the treatment of e.g. ulcers, cancer and ischemic heart disease. However, the mechanism of action is not completely understood in most cases, and even remains largely unknown in other cases. In the present review we discuss the most recent insights into the interaction between mono- and polyoxometalate ions with ion pumps, with a particular focus on the interaction of decavanadate with Ca²⁺- ATPase. We also compare the proposed mode of action with those of established ion pump inhibitors which are currently in therapeutic use. Of the 18 classes of compounds which are known to act as ion pump inhibitors, the complete mechanism of inhibition is only known for a handful. It has, however, been established that most ion pump inhibitors bind mainly to the E2 ion pump conformation within the membrane domain from the extracellular side and block the cation release. Polyoxometalates such as decavanadate, in contrast, interact with Ca²⁺- ATPase near the nucleotide binding site domain or at a pocket involving several cytoplasmic domains, and therefore needs to cross through the membrane bilayer. In contrast to monomeric vanadate, which only binds to the E2 conformation, decavanadate binds to all protein conformations, i.e. E1, E1P, E2 and E2P. Moreover, the specific interaction of decavanadate with sarcoplasmic reticulum Ca²⁺- ATPase has been shown to be non-competitive with respect to ATP and induces protein cysteine oxidation with concomitant vanadium reduction which might explain the high inhibitory capacity of V10, (IC₅₀=15 μM) which is quite similar to the majority of the established therapeutic drugs.

Aureliano, Manuel;[1,2] Fraqueza, Gil;[2,3] Ohlin, C. André[4] Ion pumps as biological targets for decavanadate Dalton Trans. 2013, 42, 11770-11777.

1. DCBB, FCT, University of Algarve, 8005-139 Faro, Portugal.
2. CCMar, University of Algarve, 8005-139 Faro, Portugal.
3. Department of Food Engineering, IST, University of Algarve, 8005-139 Faro, Portugal.
4. School of Chemistry, Monash University, Vic 3800, Australia

Abstract: Iron- and nickel-substituted decaniobates, [H₂Fe^IIINb₉O₂₈]^6- and [H₃Ni^IINb₉O₂₈]^6- were hydrothermally synthesized as tetramethylammonium salts and the structures were determined by X-ray crystallography. The highly soluble title compounds were characterized by ESI-MS, FT-IR and UV-Vis titration.

Son, Jungho;[1] Ohlin, C. André;[2] Casey, William H.;[1] Dalton Trans. 2013, 42, 7529-7533. Link

1. Department of Chemistry, University of California, Davis, California 95616, USA.
2. School of Chemistry, Monash University, Vic 3800, Australia

Abstract: We have isolated a water-soluble tetramethylammonium salt of a novel Keggin-type polyoxoniobate which contains a central phosphorous site and two capping vanadium sites. The [PV₂Nb₁₂O₄₂]^9- cluster is stable over a wide pH range, as evident by ³¹P and ⁵¹V NMR, UV-Vis and ESI-MS spectrometry. The ease of substitution of phosphate into the central tetrahedral position suggests that other oxoanions can be similarly substituted, promising a richer set of structures in this class.

Son, Jungho;[1] Ohlin, C. André;[2] Johnson, Rene L. ;[1] Yu, Ping;[1] Casey, William H.;[1] A Soluble Phosphorous-Centered Keggin Polyoxoniobate with Bicapping Vanadium sites Chem. Eur. J. ,2013, 19(16), 5191-5197. Link

1. Department of Chemistry, University of California, Davis, California 95616, USA.
2. School of Chemistry, Monash University, Vic 3800, Australia

Abstract: The vanadium-containing heteropolyoxoniobate (TMA)₉[V₃Nb₁₂O₄₂]^.18H₂O was synthesized by hydrothermal reaction of V₂O₅ and hydrous niobium oxide in tetramethylammonium hydroxide solution. The cluster has an α- Keggin structure with a central VO₄ and two trans-bicapped VO₅. The water-soluble product was characterised by X-ray crystallography, ESI-MS and both liquid- and solid-state ⁵¹V NMR. The solid- and solution-phase ⁵¹V NMR spectra indicate two major peaks corresponding to the one VO₄ and two VO₅ sites.

Son, Jungho;[1] Ohlin, C. André;[2] Larsson, Emma C.;[1] Yu, Ping;[1] Casey, William H.;[1] Synthesis and characterization of a soluble vanadium-containing Keggin polyoxoniobate via ESI-MS and ⁵¹V NMR : (TMA) ₉[V₃Nb₁₂O₄₂]·18H₂O. Eur. J. Inorg. Chem., 2013, 10-11, 1748-1753. Link

1. Department of Chemistry, University of California, Davis, California 95616, USA.
2. School of Chemistry, Monash University, Vic 3800, Australia