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Self-assembly in aqueous solution of wheel-shaped Mo154 oxide clusters into vesicles

Abstract

Surfactants and membrane lipids readily assemble into complex structures1 such as micelles, liposomes or hollow vesicles owing to their amphiphilic character—the fact that part of their structure is attracted to polar environments while another part is attracted to non-polar environments. The self-assembly of complex structures also occurs in polyoxometallate chemistry, as exemplified by the molybdenum blue solutions known for centuries. But while the presence of nanometre-sized metal oxide aggregates in these solutions has long been recognized, unravelling the composition and formation process of these aggregates proved difficult. Recent work has indicated that discrete, wheel-shaped mixed-valence polyoxomolybdate clusters of the type {Mo154} (refs 2–4) assemble into well-defined nanometre-sized aggregates, including spherical structures5. Here we report light-scattering data and transmission electron microscopy images of hollow spherical structures with an average, almost monodisperse radius of about 45 nm and composed of approximately 1,165 {Mo154} wheel-shaped clusters. The clusters appear to lie flat and homogeneously distributed on the vesicle surface. Unlike conventional lipid vesicles, the structures we observe are not stabilized by hydrophobic interactions. Instead, we believe the polyoxomolybdate-based vesicles form owing to a subtle interplay between short-range van der Waals attraction and long-range electrostatic repulsion, with important further stabilization arising from hydrogen bonding involving water molecules encapsulated between the wheel-shaped clusters and in the vesicles’ interior.

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References

  1. 1

    Evans, D. F. & Wennerström, H. The Colloidal Domain: Where Physics, Chemistry, Biology, and Technology Meet 2nd edn (Wiley, Chichester, 1999)

  2. 2

    Müller, A. et al. Rapid and simple isolation of the crystalline molybdenum-blue compounds with discrete and linked nanosized ring-shaped anions: Na15[MoVI126MoV28O462H14(H2O)70]0.5 [MoVI124MoV28O457H14(H2O)68]0.5·ca.400H2O and Na22[MoVI118MoV28O442H14(H2O)58]·ca.250H2O. Z. Anorg. Allg. Chem 625, 1187–1192 (1999)

  3. 3

    Cronin, L., Diemann, E. & Müller, A. in Inorganic Experiments 2nd edn (ed. Woollins, J. D.) 340–346 (Wiley-VCH, Weinheim, 2003)

  4. 4

    Müller, A. & Serain, C. Soluble molybdenum blues—“des Pudels Kern”. Acc. Chem. Res. 33, 2–10 (2000)

  5. 5

    Müller, A. et al. Hierarchic patterning: architectures far beyond “giant molecular wheels”. Chem. Commun. 1928–1929 (2001)

  6. 6

    Scheele, C. W. in Sämtliche Physische und Chemische Werke (ed. Hermbstädt, D. S. F.) Vol. 1, 185–200 (Martin Sändig oHG, Niederwalluf/Wiesbaden, 1971) [reprint from 1793 original]

  7. 7

    Berzelius, J. J. Beitrag zur näheren Kenntniss des Molybdäns. Poggend. Ann. Phys. Chem. 6, 369–392 (1826)

  8. 8

    Müller, A., Kögerler, P. & Kuhlmann, C. A variety of combinatorially linkable units as disposition: from a giant icosahedral Keplerate to multi-functional metal-oxide based network structures. Chem. Commun. 1347–1358 (1999)

  9. 9

    Rösler, H. J. Lehrbuch der Mineralogie 418 (Deutscher Verlag für Grundstoffindustrie, Leipzig, 1991)

  10. 10

    Provencher, S. W. CONTIN: A general purpose constrained regularization program for inverting noisy linear algebraic and integral equations. Comput. Phys. Commun. 27, 229–242 (1982)

  11. 11

    Hiemenz, P. C. & Rajagopalan, R. Principles of Colloid and Surface Chemistry Ch. 5 (Marcel Dekker, New York, 1997)

  12. 12

    Zhou, S. et al. Spherical bilayer vesicles of fullerene-based surfactants in water: a laser light scattering study. Science 291, 1944–1947 (2001)

  13. 13

    Polarz, S., Smarsly, B. & Antonietti, M. Colloidal organization and clusters: self-assembly of polyoxometalate-surfactant complexes towards three-dimensional organized structures. ChemPhysChem 2, 457–461 (2001)

  14. 14

    Müller, A. et al. Generation of cluster capsules (Ih) from decomposition products of a smaller cluster (Keggin - Td) while surviving ones get encapsulated: species with core-shell topology formed by a fundamental symmetry-driven reaction. Chem. Commun. 657–658 (2001)

  15. 15

    Müller, A. The beauty of symmetry. Science 300, 749–750 (2003)

  16. 16

    Caspar, D. & Klug, A. Physical principles in construction of regular viruses. Cold Spring Harb. Symp. Quant. Biol. 27, 1–24 (1962)

  17. 17

    Kurth, D. G., Volkmer, D., Ruttorf, M., Richter, B. & Müller, A. Ultrathin composite films incorporating the nanoporous isopolyoxomolybdate “Keplerate” (NH4)42[Mo132O372(CH3COO)30(H2O)72]. Chem. Mater. 12, 2829–2831 (2000)

  18. 18

    Polarz, S., Smarsly, B., Göltner, C. & Antonietti, M. The interplay of colloidal organization and oxo-cluster chemistry: polyoxometalate-silica hybrids—materials with a nanochemical function. Adv. Mater. 12, 1503–1507 (2000)

  19. 19

    Müller, A., Shah, S. Q. N., Bögge, H. & Schmidtmann, M. Molecular growth from a Mo176 to a Mo248 cluster. Nature 397, 48–50 (1999)

  20. 20

    Müller, A., Toma, L., Bögge, H., Schmidtmann, M. & Kögerler, P. Synergetic activation of “silent receptor” sites leading to a new type of inclusion complex: integration of a 64-membered ring comprising K+ and SO42- ions into a molybdenum oxide-based nanoobject. Chem. Commun. 2000–2001 (2003)

  21. 21

    Liu, T. B. Supramolecular structures of polyoxomolybdate-based giant molecules in aqueous solution. J. Am. Chem. Soc. 124, 10942–10943 (2002)

  22. 22

    Liu, T. B. An unusually slow self-assembly of inorganic ions in dilute aqueous solution. J. Am. Chem. Soc. 125, 312–313 (2003)

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Acknowledgements

We thank M. Schmidtmann for the generation of Fig. 1d. T.L. acknowledges support of this work by the US Department of Energy, Division of Materials Science, and A.M. correspondingly, the Deutsche Forschungsgemeinschaft, the European Union, the Fonds der Chemischen Industrie, and the Volkswagen-Stiftung. H.L. acknowledges the support of the LDRD fund from BNL.

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Correspondence to Tianbo Liu or Achim Müller.

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Further reading

Figure 1: Structure of the 3.6 mm size {Mo154}-type nanowheel with a hydrophilic surface and nanosized central cavity.
Figure 2: Zimm plot based on SLS measurements.
Figure 3: Transmission electron microscopy studies of wheel-type vesicles on carbon film.

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