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Publications (7 of 7) Show all publications
Rahman, T., Petrus, E., Segado, M., Martin, N., Palys, L., Rambaran, M., . . . Nyman, M. (2022). Predicting solubility of ion pairs in aqueous inorganic chemistry. Angewandte Chemie International Edition, 61(19), Article ID e202117839.
Open this publication in new window or tab >>Predicting solubility of ion pairs in aqueous inorganic chemistry
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2022 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 61, no 19, article id e202117839Article in journal (Refereed) Published
Abstract [en]

Polyoxometalates (POMs), ranging in size from 1 to 10's of nanometers, resemble building blocks of inorganic materials. Elucidating their complex solubility behavior with alkali-counterions can inform natural and synthetic aqueous processes. In the study of POMs ([Nb24O72H9]15-, Nb24) we discovered an unusual solubility trend (termed anomalous solubility) of alkali-POMs, in which Nb24 is most soluble with the smallest (Li+) and largest (Rb/Cs+) alkalis, and least soluble with Na/K+. Via computation, we define a descriptor (σ-profile) and use an artificial neural network (ANN) to predict all three described alkali-anion solubility trends: amphoteric, normal (Li+>Na+>K+>Rb+>Cs+), and anomalous (Cs+>Rb+>K+>Na+>Li+). Testing predicted amphoteric solubility affirmed the accuracy of the descriptor, provided solution-phase snapshots of alkali-POM interactions, yielded a new POM formulated [Ti6Nb14O54]14-, and provides guidelines to exploit alkali-POM interactions for new POMs discovery.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
Ion-Pairing, Machine Learning, Polyoxometalate, Polyoxoniobate, SAXS, Solubility
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-192470 (URN)10.1002/anie.202117839 (DOI)000760774500001 ()35148455 (PubMedID)2-s2.0-85125208000 (Scopus ID)
Available from: 2022-02-14 Created: 2022-02-14 Last updated: 2022-08-05Bibliographically approved
Rambaran, M. (2022). Tunable surfaces: using polyoxoniobates and -tantalates as molecular building blocks. (Doctoral dissertation). Umeå: Umeå University
Open this publication in new window or tab >>Tunable surfaces: using polyoxoniobates and -tantalates as molecular building blocks
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Avstämbara ytor : användning av polyoxoniobater och -tantalater som molekylära byggstenar
Abstract [en]

This thesis describes and explains the use of aqueous polyoxometalates (POMs), as molecular building blocks in the fabrication of tunable solid-state materials, such as thin films.  Microwave irradiation in the synthesis of Nb10, Nb6 and Ta6 is a rapid and efficient alternative to conventional hydrothermal methods, while offering equal – if not greater yields – of product. Through microwave irradiation, the concept of an activation pH of anhydrous Nb2O5, niobic and tantalic acids has been devised to explain what products are accessible from each oxide and under what conditions.

The controlled deposition of metal oxide thin films is possible via an iterative spin coating and annealing process of POMs. This approach facilitates deposition of alkali-free, metal oxide thin films with varying crystallinity, thickness and roughness. The ability to deposit successive layers of these polyoxometalate films was a new approach to create thicker and layered metal oxide films. This approach offers an efficient and reproducible means of creating tunable metal oxide thin films or other solid-state structures, which exemplifies the use of POMs as molecular building blocks.

Transition metal niobate thin films can be deposited onto silicon wafers via the aqueous deposition of transition metal-hexaniobate mixtures. This facilitates assessment of the electrochemical properties of these materials, without a need for coin cells or inert conditions. This allows for characterisation of the pseudocapacitive properties of these materials, which abodes well for developing electrochemical energy storage devices.

The viability of using aqueous polyoxoniobate-alkali nitrate mixtures was leveraged as a means of depositing alkali niobate (LiNbO3, NaNbO3, KNbO3) thin films, plus Rb and Cs doped Nb2O5 films and powders. Synthesising solid-state niobates that can incorporate all the alkali cations, entirely from aqueous polyoxoniobate solutions, confers the ability to develop lead-free piezoelectric, ferroelectric and antiferroelectric materials without the use of expensive or energy intensive methods.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2022. p. 224
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-198826 (URN)978-91-7855-850-6 (ISBN)978-91-7855-851-3 (ISBN)
Public defence
2022-09-23, Lilla Hörsalen, Department of Chemistry, KBC-Building, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2022-09-02 Created: 2022-08-24 Last updated: 2022-09-02Bibliographically approved
Chaudhary, H., Iashchishyn, I. A., Romanova, N. V., Rambaran, M. A., Musteikyte, G., Smirnovas, V., . . . Morozova-Roche, L. A. (2021). Polyoxometalates as Effective Nano-inhibitors of Amyloid Aggregation of Pro-inflammatory S100A9 Protein Involved in Neurodegenerative Diseases. ACS Applied Materials and Interfaces, 13(23), 26721-26734
Open this publication in new window or tab >>Polyoxometalates as Effective Nano-inhibitors of Amyloid Aggregation of Pro-inflammatory S100A9 Protein Involved in Neurodegenerative Diseases
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2021 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 13, no 23, p. 26721-26734Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021
National Category
Neurosciences
Identifiers
urn:nbn:se:umu:diva-184376 (URN)10.1021/acsami.1c04163 (DOI)000664289800007 ()34080430 (PubMedID)2-s2.0-85108385742 (Scopus ID)
Funder
Swedish Research Council, 2019-04733Swedish Research Council, 2018-07039The Kempe Foundations, 2029.1
Available from: 2021-06-12 Created: 2021-06-12 Last updated: 2023-09-05Bibliographically approved
Rambaran, M., Gorzsás, A., Holmboe, M. & Ohlin, C. A. (2021). Polyoxoniobates as molecular building blocks in thin films. Dalton Transactions, 50(44), 16030-16038
Open this publication in new window or tab >>Polyoxoniobates as molecular building blocks in thin films
2021 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 44, p. 16030-16038Article in journal (Refereed) Published
Abstract [en]

Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb10O28]6−, [TiNb9O28]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 1000 °C, respectively, whereas the [TiNb9O28]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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2021
National Category
Inorganic Chemistry
Research subject
Materials Science; Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-188370 (URN)10.1039/D1DT03116C (DOI)000704490900001 ()34613326 (PubMedID)2-s2.0-85119868258 (Scopus ID)
Available from: 2021-10-06 Created: 2021-10-06 Last updated: 2022-08-25Bibliographically approved
Gumerova, N. I., Prado-Roller, A., Rambaran, M., Ohlin, C. A. & Rompel, A. (2021). The Smallest Polyoxotungstate Retained by TRIS-Stabilization. Inorganic Chemistry, 60(17), 12671-12675
Open this publication in new window or tab >>The Smallest Polyoxotungstate Retained by TRIS-Stabilization
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2021 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 60, no 17, p. 12671-12675Article in journal (Refereed) Published
Abstract [en]

A polycondensation reaction of the orthotungstate anion WO42–, buffered at pH 7.5 in a TRIS-HCl (0.15 M) solution, results in the first example of a discrete polyoxotungstate anion, with just two W ions stabilized with TRIS ligands. It was isolated and characterized as Na2[WVI2O6(C4O3NH10)2]·6H2O by single-crystal and powder X-ray diffraction, FT-IR spectroscopy, thermogravimetrical analysis (TGA), and elemental analysis in solid state and by electro-spray ionization mass spectrometry (ESI-MS), 13C, and 183W NMR, as well as Raman spectroscopy in solution. This synthesis demonstrates the crucial and new role of the added tris-alkoxy ligand in the development of a new hybrid TRIS-isopolytungstate with the lowest known nuclearity (so far) and the terminal oxygens substituted with two nitrogen atoms arising from amines of the TRIS ligands.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-184548 (URN)10.1021/acs.inorgchem.1c01188 (DOI)000695585400007 ()34121393 (PubMedID)2-s2.0-85108596151 (Scopus ID)
Available from: 2021-06-15 Created: 2021-06-15 Last updated: 2021-10-04Bibliographically approved
Rambaran, M. A., Pascual-Borràs, M. & Ohlin, C. A. (2019). Microwave Synthesis of Alkali‐Free Hexaniobate, Decaniobate, and Hexatantalate Polyoxometalate Ions. European Journal of Inorganic Chemistry (35), 3913-3918
Open this publication in new window or tab >>Microwave Synthesis of Alkali‐Free Hexaniobate, Decaniobate, and Hexatantalate Polyoxometalate Ions
2019 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 35, p. 3913-3918Article in journal (Refereed) Published
Abstract [en]

Microwave preparation of polyoxoniobates and ‐tantalates afford a more rapid alternative to conventional hydrothermal methods of synthesis, in addition to allowing for the use of anhydrous niobium pentoxide in lieu of niobic acid, albeit with diminished yields. Limitations associated with the pH at which different oxides can be activated and how this affects the accessibility of different products are also discussed.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2019
Keywords
Niobium, Tantalum, Synthesis design, Polyoxometalates, Microwave synthesis
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-163505 (URN)10.1002/ejic.201900750 (DOI)000485119900001 ()2-s2.0-85072211990 (Scopus ID)
Funder
The Kempe Foundations, JCK‐1719
Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2022-08-25Bibliographically approved
Simonsson, I., Sögaard, C., Rambaran, M. & Abbas, Z. (2018). The specific co-ion effect on gelling and surface charging of silica nanoparticles: Speculation or reality?. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 559, 334-341
Open this publication in new window or tab >>The specific co-ion effect on gelling and surface charging of silica nanoparticles: Speculation or reality?
2018 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 559, p. 334-341Article in journal (Refereed) Published
Abstract [en]

Based on extensive experimental investigations on many different oxide nanoparticles, it is now a well-established view that the counter-ions exhibit ion specific effects due to their high charge density and strong interaction with oppositively charged surfaces. On the other hand, studies regarding co-ion effects are scarcely reported in the literature. In this study we have measured the surface charge densities and gel-times of silica nanoparticles in a number of salts which have the same counter-ions but different co-ions, i.e. anions in this case. Gel-times were measured in LiCl, NaCl, NaNO3, NaClO4, NaClO3 and Na2SO4 as well as in KCl, KNO3, and K2SO4. We have seen clear correlations between the gel-times and the extent of ion pairing in the solutions; salts that have strong ion pairing exhibit longer gel-times than salts having highly dissociated ions. To better understand the mechanisms at work we have determined the surface charging of silica nanoparticles in these salt solutions and we have observed that the surface charging behavior of silica nanoparticles follows the trends seen in the gel-time studies. From our gel-time determinations and potentiometric measurements we can claim that there is a clear co-ion effect on the gelling and surface charging of silica nanoparticles.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Co-ion effect, Silica nanoparticles, Surface charge, Potentiometric titration, Gel-Times, Ion pairing, Activity coefficients, Silica surface chemistry
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-163504 (URN)10.1016/j.colsurfa.2018.09.057 (DOI)000448734600038 ()
Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-26Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1054-221x

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