Toward Nanodevices:  Synthesis and Characterization of the Nanoporous Surfactant-Encapsulated Keplerate (DODA)₄₀(NH₄)₂[(H₂O)_n⊂Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]

Abstract

We describe the spontaneous self-assembly and the superstructure of a discrete surfactant-encapsulated cluster, (DODA) 40 (NH 4 ) 2 [(H 2 O) n ⊂Mo 132 O 372 (CH 3 COO) 30 (H 2 O) 72 ] (2, n ≈ 50), which consists of a hollow giant isopolyoxomolybdate core covered by a hydrophobic shell of dimethyldioctadecylammonium (DODA) cations. The structural characterization of these nanoporous core-shell particles is based on small-angle X-ray scattering (SAXS) data on solutions of the encapsulated clusters, TEM investigations, FT-IR and UV-vis spectroscopy, as well as determination of the molecular area of 2 by Langmuir film investigations. Computer modeling of the solvent-accessible surface of the encapsulated cluster yields a central cavity with a volume of 1.5 nm 3 that is occupied by approximately 50 H 2 O molecules. The cluster bears (Mo-O) 9-ring openings with an average diameter of 0.43 nm. The covered surface area of 84 Å 2 /DODA indicates a rather tight packing of the amphiphile at the cluster surface. Due to the unique supramolecular architecture of 2 as well as its high solubility in common organic solvents, this compound shows promising perspectives for future applications in host-guest chemistry and homogeneous size-selective catalysis.

Modeling the Interface between Biological and SyntheticComponents in Hybrid Nanosystems

“…Our simulations confirmed that DODA molecules, starting from a random distribution, would aggregate to form a steady-state hydrophobic spheroid. In accord to previous modeling work [133] on a porous CH 3 COO-linker nanocapsule (the total charge of which is −42e), the concentration of DODA was observed to decrease with the radial distance from the capsule's surface. In our case, the total charge of the capsule-DODA spheroid varied from −2 to −10e in the steady state.…”

“…It was previously shown that such porous nanocapsules can be encapsulated with dimethyldioctadecylammonium (DODA) surfactants, amphiphilic cations consisting of a cationic ammonium group attached to two long nonpolar tails [133,127].…”

From molecular modules to modular materials

“…This preparation scheme permits characterization of the materials brought into use at each step. Besides alkylammonium compounds, this approach has also been successfully used to encapsulate POMs with dendritically branching amphiphiles [73][74][75][76]. These results show that surfactant-encapsulation is widely applicable to different POM clusters and amphiphilic systems.…”

“…7) [74,75]. Based on elemental analysis, 40 DODA molecules encapsulate the cluster, leading to a discrete, nearly spherical particle with a molecular mass of approximately 43.900 g/mol.…”

Self-assembled materials for catalysis

“…The POMs can also self-assemble into ordered patterns at the nanometer scale, and thus have multilevel ordered structures [120,121]. The great diversity in composition and structure of POMs make them attractive materials in many fields [122].…”