Polyoxoniobates as molecular building blocks in thin films

in Dalton Transactions, 2021, 50, 16030-16038. Link

Mark Rambaran, András Gorzsás, Michael Holmboe, CA Ohlin.

Abstract: Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb₁₀O₂₈]^6- , [TiNb₁₀O₂₈]^7- and [Ti₂Nb₈O₂₈]^8- onto silicon wafers, and annealing them. The [Nb₁₀O₂₈]^6- cluster yields films of Nb₂O₅ in the orthorhombic and monoclinic crystal phases when annealed at 800 °C and 1,000 °C, respectively, whereas the [TiNb₁₀O₂₈]^7-  and [Ti₂Nb₈O₂₈]^8- clusters yield the monoclinic crystal phases of Ti₂Nb₁₂O₂₉ and TiNb₂O₇ (titanium-niobium oxides) in different ratios. We also demonstrate a protocol for depositing successive layers of metal oxide films. Finally, we explore factors affecting the roughness of the films.

Computational exploration of heterometal substitution into the decaniobate framework, [Nb₁₀O₂₈]^6-

in Phys. Chem. Chem. Phys., 2021, 23, 10402-10408. Link

C. A. Ohlin

Abstract: The factors governing the substitution of group 4B–12B metals into the decaniobate framework are explored using density functional theory in order to ascertain whether (1) recently isolated [MNb9O28]x− clusters are kinetic or thermodynamic products, (2) density functional theory is a sufficient level of theory to accurately predict substitution patterns in polyoxometalates where ion pairing and other effects may operate, and (3) it can be used to guide future synthetic efforts. Computations using restricted, unrestricted and open-shell density functional theory at PBE0/def2-tzvp were found to correctly predict substitution patterns in known clusters, and were subsequently used to calculate the relative energies of a large series of [MNb9O28]x− clusters, to reveal trends and suggest potential synthetic approaches. OPBE/def2-tzvp correctly predicted favoured spin states of known substituted decametalates.

Polyoxometalates as Effective Nano-inhibitors of Amyloid Aggregation of Pro-inflammatory S100A9 Protein Involved in Neurodegenerative Diseases

in ACS Appl. Mater. Interfaces, 2021, 13(23), 26721-26734.

Chaudhary, Himanshi; Iaschishyn, Igor A.; Romanova, Nina V.; Rambaran, Mark A.; Musteikyte, Greta; Smirnovas, Vytautas; Holmboe, Michael; Ohlin, C. André; Svedruzić, Zelsko M.; Morozova-Roche, Ludmilla A.

Abstract: Pro-inflammatory and amyloidogenic S100A9 protein is central to the amyloid-neuroinflammatory cascade in neurodegenerative diseases. Polyoxometalates (POMs) constitute a diverse group of nanomaterials, which showed potency in amyloid inhibition. Here, we have demonstrated that two selected nanosized niobium POMs, Nb10 and TiNb9, can act as potent inhibitors of S100A9 amyloid assembly. Kinetics analysis based on ThT fluorescence experiments showed that addition of either Nb10 or TiNb9 reduces the S100A9 amyloid formation rate and amyloid quantity. Atomic force microscopy imaging demonstrated the complete absence of long S100A9 amyloid fibrils at increasing concentrations of either POM and the presence of only round-shaped and slightly elongated aggregates. Molecular dynamics simulation revealed that both Nb10 and TiNb9 bind to native S100A9 homo-dimer by forming ionic interactions with the positively charged Lys residue-rich patches on the protein surface. The acrylamide quenching of intrinsic fluorescence showed that POM binding does not perturb the Trp 88 environment. The far and near UV circular dichroism revealed no large-scale perturbation of S100A9 secondary and tertiary structures upon POM binding. These indicate that POM binding involves only local conformational changes in the binding sites. By using intrinsic and 8-anilino-1-naphthalene sulfonate fluorescence titration experiments, we found that POMs bind to S100A9 with a Kd of ca. 2.5 μM. We suggest that the region, including Lys 50 to Lys 54 and characterized by high amyloid propensity, could be the key sequences involved in S1009 amyloid self-assembly. The inhibition and complete hindering of S100A9 amyloid pathways may be used in the therapeutic applications targeting the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

Energetics of paramagnetic oxide clusters: the Fe(III) oxyhydroxy Keggin ion

Phys. Chem. Chem. Phys., 2020, DOI: 10.1039/C9CP05795A. Link

C. A. Ohlin

Abstract: The energetics of the different spin states of the five Baker-Figgis isomers of the iron(III) Keggin ion, [Fe(O₄)(Fe(OH)₂ (OH₂))₁₂]⁷⁺, has been investigated using density functional theory in order to demonstrate how the energy landscape of medium-to-large discrete paramagnetic transition metal oxide clusters with large numbers of antiferromagnetically coupled centres can be resolved. Antiferromagnetic coupling causes the energies to span a surprisingly large range of 30 kcal/mol, as determined by calculating the energies of all 664 unique spin configurations based on determination of the antiferromagnetic coupling constants by density functional theory. A program which simplifies the resolution of the energetics of this type of systems is also provided.

Hydrocarbon-soluble, hexaanionic fulleride complexes of magnesium
Chem. Sci., 2019, 10, 10755-10764. Link
Samuel R. Lawrence,  C. André Ohlin, David B. Cordes,  Alexandra M. Z. Slawin, Andreas Stasch

Abstract: The reaction of the magnesium(I) complexes [{( ^Arnacnac)Mg}₂], ( ^Arnacnac = HC(MeCNAr)₂ , Ar =Dip (2,6-iPr₂C₆H₃), Dep (2,6-Et₂C₆H₃), Mes (2,4,6-Me₃C₆H₂), Xyl (2,6-Me₂C₆H₃ )) with fullerene C₆₀ afforded a series of hydrocarbon-soluble fulleride complexes [{(^Arnacnac)Mg}_nC₆₀], predominantly with n = 6, 4 and 2. ¹³C{¹H} NMR spectroscopic studies show both similarities (n = 6) and differences (n = 4, 2) to previously characterised examples of fulleride complexes and materials with electropositive metal ions. The molecular structures of[{(^Arnacnac)Mg}_nC₆₀] with n = 6, 4 and 2 can be described as inverse  coordination complexes of n [(^Arnacnac)Mg]⁺ ions with C₆₀^n- anions showing predominantly ionic metal-ligand interactions, and include the first well-defined and soluble complexes of the C₆₀^6- ion. Experimental studies show the flexible ionic nature of the {(^Arnacnac)Mg}⁺····C₆₀^6-  coordination bonds. DFT calculations on the model complex [{(^Menacnac)Mg}₆C₆₀] (^Menacnac = HC(MeCNMe)₂) support the formulation as an ionic complex with a centralC₆₀^6- anion and comparable frontier orbitals toC₆₀^6- with a small HOMO-LUMO gap. The reduction of C₆₀ to its hexaanion gives an indication about the reducing strength of dimagnesium(I) complexes.

Microwave Synthesis of Alkali-Free Hexaniobate, Decaniobate, and Hexatantalate Polyoxometalate Ions
in Eur. J. Inorg. Chem., 2019, 35, 3913-3918.   Link
M. A. Rambaran, M. Pascual-Borràs and C. A. Ohlin

Abstract: Microwave synthesis of polyoxoniobates and -tantalates circumvents the prolonged heating required by conventional hydrothermal methods, while providing comparable or greater yields. Microwave irradiation allows synthesis of polyoxoniobates from anhydrous niobium pentoxide, in lieu of niobic acid and sets the precedent for the discovery of new polyoxoniobates and -tantalates.

A postdoctoral fellowship in spectroscopic studies of mercury interactions with bacterial surfaces is available in Erik Björn’s group. See https://www.umu.se/en/work-with-us/fellowships-and-grants/6-1298-19/

“Direct Single- and Double-Side Triol-Functionalization of the Mixed Type Anderson Polyoxotungstate [Cr(OH)₃W₆O₂₁]^6–”

in Inorganic Chemistry, 2019, 58(1), 106-113. Link

Nadiia I. Gumerova, Tania Caldera Fraile, Alexander Roller, Gerald Giester, Magda Pascual-Borràs, C. André Ohlin, and Annette Rompel

Abstract: Since the first successful triol-functionalization of the Anderson polyoxometalates, the protons of the central octahedron X(OH)₆ (X—heteroatom) have been considered as a prerequisite for their functionalization and therefore the functionalization of Anderson structures from the unprotonated sides have never been reported. Herein, for the first time, we organically functionalized the mixed-type Anderson polyoxometalate with real-time observation of hybrid anion formation.

Dr Hussein Kanbar has joined the group of A/Prof. Michael Holmboe and will  be working on the molecular mechanisms behind the immobilization and preservation of sedimentary and ancient DNA (aDNA) by clay minerals.