Keplerate {Mo132}-Stearic Acid Conjugates: Supramolecular Synthons for the Design of Dye-Loaded Nanovesicles, Langmuir-Schaefer Films, and Infochemical Applications.

Self-assembly gives rise to the versatile strategies of smart material design but requires precise control on the supramolecular level. Here, inorganic-organic synthons (conjugates) are produced by covalently grafting stearic acid tails to giant polyoxometalate (POM) Keplerate-type {Mo132} through an organosilicon linker (3-aminopropyltrimethoxysilane, APTMS). Using the liposome production approach, the synthons self-assemble to form hollow nanosized vesicles (100-200 nm in diameter), which can be loaded with organic dyes─eriochrome black T (ErChB) and fluorescein (FL)─where the POM layer serves as a membrane with subnanopores for cell-like communication. The dye structure plays an essential role in embedding dyes into the vesicle's shell, which opens the way to control the colloidal stability of the system. The produced vesicles are moved by an electric field and used for the creation of an infochemistry scheme with three types of logic gates (AND, OR, and IMP). To design 2D materials, synthons can form spread films, from simple addition on the water-air interface to lateral compression in the Langmuir bath, and highly ordered structures appear, demonstrating electron diffraction in Langmuir-Schaefer (LS) films. These results show the significant potential of POM-based synthons and nanosized vesicles to supramolecular design the diversity of smart materials.

Gigantic supramolecular assemblies built from dynamic hierarchical organization between inorganic nanospheres and porphyrins.

Noncovalent ionic interactions between nanosized Keplerate-type capsules {Mo132} and tetra-cationic porphyrins have been investigated in aqueous solution using small-angle X-ray scattering, 1H NMR and photophysical methods. These complementary multiscale methods reveal the formation of large hybrid oligomers built from a short-range organization in which the cationic porphyrin is glued onto the large POM surface. The local structuring appears to be strongly dependent on the dye : {Mo132} ratio changing the morphology of the oligomers from linear to dense aggregates.

Tetrahedral Keggin Core Tunes the Visible Light-Assisted Catalase-Like Activity of Icosahedral Keplerate Shell.

In this work, the effect of Keggin polyoxometalates encapsulated in Keplerate {Mo72Fe30} shell (K shell) on the visible light-assisted catalase-like activity (H2O2 dismutation) of the resulting core-shell clusters PMo12@K, SiMo12@K, and BW12@K was investigated. Superior photodismutation activity of PMo12@K compared to that of K shell and two other core-shell clusters was discovered. The homogeneity of PMo12@K and its improved oxidative stability, increased redox potential, and reduced band gap caused by a synergistic effect between the Keplerate shell and Keggin core seem reasonable to explain such a superiority. The light-dependent photocatalytic performance of PMo12@K evaluated by action spectra revealed a maximum apparent quantum efficiency (AQY) at 400 nm, demonstrating the visible light-driven photocatalytic reaction. A first-order rate constant of 2 × 10-4 s-1 and activation energy of 108.8 kJ mol-1 alongside a turnover frequency of 0.036 s-1 and a total turnover number of up to ∼3800 approved the effective photocatalytic activity and improved the oxidative stability of PMo12@K. A nonradical photocatalytic mechanism through a Fe-OOH intermediate was proposed. Thus, the structure, optical activity, and oxidative stability of a host Keplerate-type nanocluster can be tuned significantly by encapsulation of a guest, like "cluster-in-cluster" structures, which opens the scope for introducing new visible light-sensitive hierarchical nanostructures.

The cooperative effect of the sorption of volatile molecules into metal-oxide frameworks as a function of the dielectric constant.

The separation of volatile molecules into metal-oxide frameworks (MOxF) is possible with the combination of two approaches: spatial confinement and sorption-desorption equilibria. We have shown that nanoporous MOxF, namely giant POMs with Keplerate or toroidal structures, have a specific sorption behaviour towards different volatile substances that can be generalized through the dependence of the limit sorption on the dielectric constant and molecular polarizability. Assisted by the Hildebrand and Hansen solubility parameters and the Snyder polarity index, an analysis of sorption behaviour shows that the contributions of hydrogen bonding, hydrophobic forces and polar and dispersion interactions can be expressed through a cooperative phenomenon (the formation of a quasi-liquid layer) correlated with dielectric constant as a major parameter. The obtained data can be used to predict the separation of volatile substances using MOxF-embedded hybrid materials, such as selective membranes.

A top-down design for easy gram scale synthesis of melem nano rectangular prisms with improved surface area.

An unprecedented top-down design for the preparation of melem by 1 h stirring of melamine-based g-C3N4 in 80 °C concentrated sulfuric acid (95-98%) was discovered. The melem product was formed selectively as a monomer on the gram scale without the need for controlled conditions, inert atmosphere, and a special purification technique. The as-prepared air-stable melem showed a distinctive nano rectangular prism morphology that possesses a larger surface area than the melems achieved by traditional bottom-up designs making it a promising candidate for catalysis and adsorption processes.

DDAO Controlled Synthesis of Organo-Modified Silica Nanoparticles with Encapsulated Fluorescent Boron Dipyrrins and Study of Their Uptake by Cancerous Cells.

The design of cargo carriers with high biocompatibility, unique morphological characteristics, and capability of strong bonding of fluorescent dye is highly important for the development of a platform for smart imaging and diagnostics. In this paper, BODIPY-doped silica nanoparticles were prepared through a "one-pot" soft-template method using a sol-gel process. Several sol-gel precursors have been used in sol-gel synthesis in the presence of soft-template to obtain the silica-based materials with the most appropriate morphological features for the immobilization of BODIPY molecules. Obtained silica particles have been shown to be non-cytotoxic and can be effectively internalized into the cervical cancer cell line (HeLa). The described method of synthesis allows us to obtain silica-based carriers with an immobilized fluorescent dye that provide the possibility for real-time imaging and detection of these carriers.

Fundamental Aspects of Xanthene Dye Aggregation on the Surfaces of Nanocluster Polyoxometalates: H- to J-Aggregate Switching.

The induced aggregation of the xanthene dye rhodamine B (RhB) on metal oxide centers belonging to the highly symmetric surfaces of precise nanoscale templates with Keplerate (Mo132 ) or toroidal (Mo138 ) structures has been studied. With the joint use of the Langmuir isotherm and full Stern-Volmer models, the thermodynamic reasons for dye adsorption on the nanocluster surface, such as a mixture of monomer, H-aggregate (H-dimer), and J-aggregate forms (which can coexist or switch one into another under the exact conditions), were established: this was shown through UV/Vis and fluorescence spectroscopies. By using the framework of the exciton model, it is shown that the angle (α) between the transition dipole moments of RhB is very sensitive to surface strain inside the dye sub-monolayer. As a result, it is possible to switch from H- to J-aggregates by the post-functionalization of polyoxometalate (POM)-RhB associates by the surfactant bilayer shell, which allows the surface strain to grow. Recommendations are provided for managing the appearance of H- or J-aggregates on metal oxide (or polyelectrolyte) surfaces during photovoltaic or bioimaging applications.

Highly luminescent Zn-Cu-In-S/ZnS core/gradient shell quantum dots prepared from indium sulfide by cation exchange for cell labeling and polymer composites.

Gradient core-shell Zn-Cu-In-S/ZnS quantum dots (QDs) of small size and with highly efficient photoluminescence were synthesized via a multi-step high-temperature method involving cation exchange. The procedure starts with the preparation of indium sulfide nanoparticles followed by the addition of Cu and Zn precursors. At this stage, Zn replaces Cu atoms and as a result the concentration of Cu ions in the final QDs is only about 5% of the total In content in a QD. Zn incorporation and the formation of a gradient ZnS shell dramatically increases the photoluminescence quantum yield. Furthermore, the formation of the ZnS shell improves the chemical stability of Cu-In-S QDs, as demonstrated by the preparation of polystyrene-QD composites and labeling of glioma cells. This work provides an effective strategy for obtaining efficient and stable fluorophores free of heavy metals.

Coordinative interaction between nitrogen oxides and iron-molybdenum POM Mo72Fe30.

The process of adsorption of nitrogen monoxide and dioxide by the giant Keplerate nanocluster Mo72Fe30 was studied in detail under ambient conditions and air/argon atmosphere. The obtained Raman and IR spectra showed that the coordination of NOx to the Mo72Fe30 leads to the formation of nitrate ions by sharing the bridged or terminal oxygen in FeO6 polyhedra with the adsorbed NO2 molecules. In accordance with elemental analysis and X-ray photoelectron spectroscopy, the composition of the produced complex was found to be [POM-(NO2)x]·(NO2)y (where x = 6, y = 14 ± 3). The carried out thermal analysis revealed the significant influence of NOx coordination in the release of water molecules and decomposition of the constitutional acetate ligands for Mo72Fe30. Furthermore, the performed measurements of the temperature dependency of the electron paramagnetic resonance spectra for the pure nanocluster and that treated with NO2 allowed us to draw up a conclusion about the delocalization of weak-bonded NO2 molecules in the pores of the Mo72Fe30 crystal at 25 °C. The opposite situation was observed under cryogenic temperatures. The localization of NO2 molecules occurs resulting in the distortion of FeO6 octahedra towards tetrahedral symmetry accompanied with the appearance of the signal at g-factor 4.3. The produced complex compound [POM-(NO2)x]·(NO2)y possesses sufficient NO2 capacity, water solubility and pH-dependant decomposition; these are important properties of a potential NOx donor, which can be hypothetically applied in biomedicine.

Colloidal branched CdSe/CdS 'nanospiders' with 2D/1D heterostructure.

In this paper we report the synthesis of colloidal CdSe/CdS core-shell heteronanoplatelets with epitaxially grown wurtzite (WZ) 1D CdS branches or legs by using cadmium diethyldithiocarbamate as a single-source precursor. The growth of WZ branches was achieved by exploiting zinc blende-wurtzite polytypism of cadmium chalcogenides induced by oleylamine. Synthesized 'nanospiders' exhibit enhanced absorption in the UV-blue region and narrow and relatively intense red photoluminescence depending on the amount of CdS in the heteronanostructure.