Water-soluble anionic POSS-core dendrimer: synthesis and copper(II) complexes in aqueous solution

Fabrication of highly ordered Cu2+/Fe3+ decorated polyhedral oligomeric silsesquioxane hybrids: How metal coordination influences structure

Incorporation of isolated metal centers into well-organized nanostructures is a promising route in the development of the next generation of chemical, magnetic and electronic devices. In this work, a layer-by-layer protocol to grow highly ordered thin films of metal-decorated organic-inorganic cage-like polyhedral oligomeric silsesquioxane (POSS) is introduced. The key strategy is to use metal ions (Cu²⁺ or Fe³⁺) as linker for the amino-functionalized cage-like POSS, which are self-assembled between arachidic acid layers during Langmuir-Schaefer deposition. The Langmuir-Schaefer films are examined by X-ray photoelectron spectroscopy, X-ray diffraction, grazing incidence wide-angle X-ray scattering and extended X-ray absorption fine structure in order to understand how the coordination of metal ions influences the structure in the course of the layer-by-layer formation of the films.

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

N-Oxide polymer-cupric ion nanogels potentiate disulfiram for cancer therapy

Disulfiram (DSF) exerts potent anticancer activity via the formation of chelates with copper or zinc ions in tumor tissues, but the low abundance of these ions in the tumor cannot sustain its antitumor activity. Herein, we show that a zwitterionic water-soluble N-oxide polymer, poly[2-(N-oxide-N,N-dimethylamino)ethyl methacrylate] (OPDMA), can complex cupric ions and form nanogels (OPDMA/Cu), which efficiently deliver copper ions to tumor tissue to potentiate DSF significantly for effective antitumor therapy.

On eccentricity-based topological descriptors of water-soluble dendrimers

Previous studies show that certain physical and chemical properties of chemical compounds are closely related with their molecular structure. As a theoretical basis, it provides a new way of thinking by analyzing the molecular structure of the compounds to understand their physical and chemical properties. The molecular topological indices are numerical invariants of a molecular graph and are useful to predict their bioactivity. Among these topological indices, the eccentric-connectivity index has a prominent place, because of its high degree of predictability of pharmaceutical properties. In this article, we compute the closed formulae of eccentric-connectivity-based indices and its corresponding polynomial for water-soluble perylenediimides-cored polyglycerol dendrimers. Furthermore, the edge version of eccentric-connectivity index for a new class of dendrimers is determined. The conclusions we obtained in this article illustrate the promising application prospects in the field of bioinformatics and nanomaterial engineering.

Syntheses and catalytic activities of new metallodendritic catalysts

Metallodendritic catalysts showed high selectivity in the epoxidation of olefins even after being used for at least five cycles.

Synthesis of a bi-functional terminal polyhedral octasilicate-core dendrimer containing carbazole and 1,8-naphthalimide, and its photoluminescence properties, film formability, and glass transition behavior

The bi-functional terminal polyhedral octasilicate (OS)-core dendrimer containing carbazole and 1,8-naphthalimide on its peripheries was synthesized and studied its photoluminescence properties, film formability, and glass transition behavior.

Bendable, free-standing calcite thin films

Since the hardness and toughness of natural nacre are determined by hierarchical microstructures with organic matters, it is of great importance to control the microstructures of artificial free-standing CaCO3 thin films. However, the fabrication of such films has so far been quite limited, to the extent that their mechanical properties have not been reported. To address this, free-standing calcite thin films were prepared through repeated cycles of layer-by-layer deposition of vaterite precursor composite particles with organic polymers, followed by a phase transition to calcite. In this way, two distinct calcite thin film types were produced based on either 3.2 or 1.0 wt % organic material, with subsequent three-point bending tests revealing that both exhibit elastic bending prior to fracture. More importantly, by increasing the organic content from 1.0 to 3.2 wt %, the bending strength increased from 0.95 ± 0.26 MPa to 1.90 ± 0.21 MPa.

The design and synthesis of an innovative octacarboxy-silsesquioxane building block

An octacarboxy-silsesquioxane was designed and synthesised through a multiple-step regioselective reaction. This novel hybrid inorganic-organic compound presents highly attractive features for application as a building block, as it has a robust, rigid structure and a high number of carboxylic coordination sites organised in a cubic symmetry.

Star-shaped molecules with polyhedral oligomeric silsesquioxane core and azobenzene dye arms

We synthesized a series of hybrid nanomaterials combining organic dyes with polyhedral oligomeric silsesquioxanes (POSS) based on three different azobenzenes: monoazobenzene (4-phenylazophenol), bis-azobenzene (Disperse Yellow 7 and Fast Garnet derivative), and push-pull azobenzene (Disperse Red 1) via hydrosilylation coupling. The azo-functionalized POSS compounds possess high thermal stability, and their branched architecture resulted in effective suppression of molecular aggregation and allowed for direct imaging of individual dye-POSS structures with expected molecular dimensions. Stable, uniform, smooth, and ultrathin nanocomposite films with mixed silica-organic composition and relatively low refractive indices can be fabricated from all azo-POSS branched conjugates. Finally, the photoisomerization behavior of POSS-conjugated 4-phenylazophenol was investigated in solution as well as in ultrathin nanocomposite film. We found that conjugation to POSS core did not affect the kinetics of trans-cis photoisomerization and thermal cis-trans relaxation. Furthermore, rapid and reversible photoisomerization was observed in azo-POSS nanocomposite films. We suggest that the highly stable branched azo-POSS conjugates with high dye grafting density described here can be considered for nanometer-sized photoswitches, active layer material with optical-limiting properties, and a medium with photoinduced anisotropy for optical storage.

Size-controlled vaterite composite particles with a POSS-core dendrimer for the fabrication of calcite thin films by phase transition

Vaterite composite particles with a size-controlled sphere were obtained by a carbonate controlled-addition method by using a carboxylate-terminated poly(amidoamine) (PAMAM)-type polyhedral oligomeric silsesquioxane (POSS)-core dendrimer. An aqueous ammonium carbonate solution was added to an aqueous solution of the dendrimer and CaCl2 at different times (3 min, 30 min, and 1 h) and stirred for 1 h at 30 °C. When the complexation time of the POSS-core dendrimer-CaCl2 solution was increased from 3 min to 1 h, the average particle sizes of the spheres increased from 0.71 ± 0.08 to 1.86 ± 0.22 μm, respectively. However, the average particle sizes decreased with decreasing temperature. Particles with minimum sizes of 70 ± 6 nm were obtained when COONa to calcium ion molar ratio was 16 and the complexation time was 3 min at 20 °C. Incubation of the vaterite composite particles in distilled water for 3 days led to complete phase transition to calcite. Negative zeta potential values, ranging from -30 to -10 mV, were detected for the vaterite particles, indicating that the POSS-core dendrimers were exposed on the CaCO3 particles. The CaCO3 particle surfaces were successfully coated with poly(diallyldimethylammonium chloride) (PDDA) in aqueous dispersions by adding a controlled concentration of the polymer. Alternate vaterite composite particles and polyelectroyte multilayer films were prepared by a layer-by-layer method. The obtained (PDDA/vaterite)10(PDDA) multilayer films were incubated in distilled water at 30 °C. Incubation for 5 days led to complete phase transition to calcite, as estimated by Fourier transform infrared (FTIR) spectroscopic and XRD analyses. The SEM observation of the sample after 5 days of incubation showed a granular network structure of irregularly shaped calcite particles. Although some patches and pores were present in the films, the SEM image clearly demonstrated that large-area and continuous CaCO3 films were formed.

Synthesis, characterization, and thermal behavior of carboranyl-styrene decorated octasilsesquioxanes: influence of the carborane clusters on photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl-styrene fragments attached to each corner are described. These compounds have been synthesized by olefin-metathesis reactions between octavinylsilsesquioxane and carboranyl-styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl-POSS compounds exhibit a mass loss lower than 10%. The UV/Vis absorption data of these carboranyl-POSS compounds shows a slight bathochromic shift with respect to the carboranyl-styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl-POSS compounds with regard to their carboranyl-styrene precursors are observed; the phenyl-o-carborane-containing POSS compound exhibits the highest fluorescence intensity (Φ(F)=44%), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o-carborane clusters, the fluorescence intensity is much lower (Φ(F)=9 and 2%, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o-carboranyl-styrene compound exhibits the highest Φ(F), and a quenching of the fluorescence is observed in the phenyl-o-carboranyl-styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time-dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.

Anionic sulfonated and carboxylated PPI dendrimers with the EDA core: synthesis and characterization of selective metal complexing agents

Herein we describe the synthesis and characterization of new sulfonated and carboxylated poly(propyleneimino) (PPI) dendrimers with the ethylenediamino (EDA) core, at generations 1, 2 and 3. By means of UV-Vis and EPR spectroscopy, using Cu(2+) as a probe, we concluded that these dendrimers show a specific pattern in the coordination of metal ions. In agreement with the UV-Vis studies, EPR spectra of carboxylated compounds are constituted by 3 different signals which appear and then disappear with increasing copper concentration, corresponding to the saturation of different copper complexation sites. At the lowest copper concentration up to a 1:1 molar ratio between Cu(II) and the dendrimer, the spectrum is characteristic of a CuN2O2 coordination at the core of the dendrimer. The spectrum appearing at higher Cu(II) concentrations indicates a peripheral location of the ions coordinating one nitrogen and 3 oxygen atoms in a square planar geometry in restricted mobility conditions. For the highest concentrations tested, copper ions are confined at the external dendrimer surface with CuO4 coordination. For sulfonate systems, the EPR results are in line with a weaker interaction of Cu(II) with the nitrogen sites and a stronger interaction with the oxygen (SO3(-)) groups with respect to the interactions measured by EPR for carboxylate systems.

Synthesis and reactivity of nitrogen nucleophiles-induced cage-rearrangement silsesquioxanes

Novel phthalimide and o-sulfobenzimide-functionalized silsesquioxanes were successfully synthesized via nucleophilic substitution reactions from octakis(3-chloropropyl)octasilsesquioxane. Surprisingly, the formation of deca- and dodecasilsesquioxanes cages was discovered during substitution with phthalimide, but only octasilsesquioxane maintained a cage in the o-sulfobenzimide substitution reaction. Moreover, we report the electronic effect of nitrogen nucleophiles to promote cage-rearrangement of inorganic silsesquioxane core for the first time. Structures of products were confirmed by (1)H, (13)C, and (29)Si NMR spectroscopy, ESI-MS analysis, and single-crystal X-ray diffraction.