Dendritic, nanosized building block for siloxane-based materials: a spherosilicate dendrimer

A spherosilicate dendrimer ( DMS‐1 ) with closely spaced reaction sites (Si? H groups) on the dendrimer surface has been synthesized by stepwise silylation of double‐four‐ring silicate with chlorotriethoxysilane (ClSi(OEt)₃) and subsequently with chlorodimethylsilane (ClSiHMe₂). DMS‐1 consists of a maximum of 40 Si atoms in the interior frameworks and 24 reactive Si? H groups on the surface. Because DMS‐1 is spherical and about 1.5 nm in diameter, it can be regarded as the smallest well‐defined silica‐based nanoparticle. DMS‐1 also forms molecular crystals and is soluble in typical organic solvents. A molecularly ordered silica‐based hybrid can be prepared by heating a cast film of DMS‐1 at 180 °C for 5 days. The surface of DMS‐1 can be modified by hydrosilylation with 1‐hexadecene, triethoxyvinylsilane, and allylic‐terminated tetraethylene glycol monomethyl ether. More than 20 Si? H groups out of 24 react with these reagents. The solubilities of the products depend on the modification. DMS‐1 is not only a building block for nanohybrids, but also the smallest and most precisely designed siloxane‐based nanoparticle.     

Optical imaging with dynamic contrast agents

Biological imaging applications often employ molecular probes or nanoparticles for enhanced contrast. However, resolution and detection are still often limited by the intrinsic heterogeneity of the sample, which can produce high levels of background that obscure the signals of interest. Herein, we describe approaches to overcome this obstacle based on the concept of dynamic contrast: a strategy for elucidating signals by the suppression or removal of background noise. Dynamic contrast mechanisms can greatly reduce the loading requirement of contrast agents, and may be especially useful for single-probe imaging. Dynamic contrast modalities are also platform-independent, and can enhance the performance of sophisticated biomedical imaging systems or simple optical microscopes alike. Dynamic contrast is performed in two stages: 1) a signal modulation scheme to introduce time-dependent changes in amplitude or phase, and 2) a demodulation step for signal recovery. Optical signals can be coupled with magnetic nanoparticles, photoswitchable probes, or plasmon-resonant nanostructures for modulation by magnetomotive, photonic, or photothermal mechanisms, respectively. With respect to image demodulation, many of the strategies developed for signal processing in electronics and communication technologies can also be applied toward the editing of digital images. The image-processing step can be as simple as differential imaging, or may involve multiple reference points for deconvolution by using cross-correlation algorithms. Periodic signals are particularly amenable to image demodulation strategies based on Fourier transform; the contrast of the demodulated signal increases with acquisition time, and modulation frequencies in the kHz range are possible. Dynamic contrast is an emerging topic with considerable room for development, both with respect to molecular or nanoscale probes for signal modulation, and also to methods for more efficient image processing and editing.     

Supramolecular hybrid of metal nanoparticles and semiconducting single-walled carbon nanotubes wrapped by a fluorene-carbazole copolymer

The first approach for the preparation of metal nanoparticle/semiconducting single-walled carbon nanotube (SWNT) hybrids with specified chirality is described. For this purpose, a copolymer of a fluorene derivative with two long-chain alkyl substituents and a carbazole derivative carrying a thiol group was used. The copolymer was found to selectively dissolve (7,6)- and (8,7)SWNTs, as determined by UV/Vis/NIR absorption and Raman spectroscopy and 2D photoluminescence mapping. Gold and silver nanoparticles with diameters of about 3.8 and about 3.2 nm, respectively, were readily attached along the SWNTs by means of coordination bonds between the nanoparticles and the thiol moieties on the copolymer, as revealed by atomic force and electron microscopy studies. The study provides a novel way to design and fabricate metal nanoparticle/semiconducting SWNT hybrids with specific nanotube chirality.     

Triple-layer (au@perylene)@polyaniline nanocomposite: unconventional growth of faceted organic nanocrystals on polycrystalline au

Unconventional crystal growth: Core/shell nanocrystals were obtained by growth of a dominant single-crystalline phase of perylene over polycrystalline Au nanoparticle seeds and isolated by coating with polyaniline (PANI) shells. Perylene is released in the presence of sodium dodecyl sulfate (SDS) micelles. The TEM images show (Au@perylene)@PANI nanocomposites before and after complete release of perylene leaving Au@PANI (inset).     

Nanosized vanadium, tungsten and molybdenum oxide clusters grown in porous chitosan microspheres as promising hybrid materials for selective alcohol oxidation

The ability of chitosan biopolymer to coordinate vanadium, tungsten and molybdenum metallic species and to control their mineralisation growth provides a new family of surface-reactive organic-inorganic hybrid microspheres. Drying the resulting materials under supercritical conditions allowed the gel network dispersion to be retained, thereby leading to a macroporous catalyst with surface areas ranging from 253 to 278 m(2) g(-1). On account of the open framework structure of these microspheres, the redox species entangled within the fibrillar network of the polysaccharide aerogels were found to be active, selective and reusable catalysts for cinamylalcohol oxidations.     

Both spacer length and parity influence the thermal and light-induced properties of iron(II) alpha,omega-bis(tetrazole-1-yl)alkane coordination polymers

A new series of [mu-tris-{1,n-bis(tetrazol-1-yl)alkane-N4,N4'}iron(II)] bis(perchlorate) spin-crossover coordination polymers ([Fe(nditz)3](ClO4)2]; n = 4-9) has been synthesised and characterised. The ditetrazole bridging ligands provide octahedral symmetry at the iron(II) centres while allowing the distance between iron(II) centres to be varied. These polymers have therefore been investigated to determine the effects of spacer length on their thermal and light-induced spin-transition behaviour. An increase in the number of carbon atoms in the spacer (n) raises the thermal spin-crossover temperature, while decreasing the stability of the light-induced metastable state generated through the light-induced excited spin state trapping (LIESST) effect by irradiating the sample at 530 nm. Remarkably, however, the parity of the spacer also has an effect, enabling the series of complexes to be divided into two sub-series depending on whether the bridging ligand possesses an even or an odd number of carbon atoms. An explanation at the molecular level using the single configurational coordinate (SCC) model is presented.     

High-relaxivity MRI contrast agents: where coordination chemistry meets medical imaging

The desire to improve and expand the scope of clinical magnetic resonance imaging (MRI) has prompted the search for contrast agents of higher efficiency. The development of better agents requires consideration of the fundamental coordination chemistry of the gadolinium(III) ion and the parameters that affect its efficacy as a proton relaxation agent. In optimizing each parameter, other practical issues, such as solubility and in vivo toxicity, must also be addressed, making the attainment of safe, high-relaxivity agents a challenging goal. This Minireview presents recent advances in the field, with an emphasis on gadolinium(III) hydroxypyridinone chelate complexes.     

Organic-inorganic nanohybrids through the direct tailoring of semiconductor nanocrystals with conjugated polymers

Two main synthetic strategies are used to prepare conjugated oligomer- or polymer-nanocrystal nanohybrids. In the first strategy ligand exchange is invoked to either replace with a bifunctional ligand, which contains a second functional group for coupling with conjugated oligomers or polymers (COs or CPs), or exchange for the functionalized COs or CPs in a "grafting-onto" process. Alternatively, in the second strategy the nanocrystal (NC) is passivated with functional ligands from which COs or CPs are directly grown in the absence of ligand exchange. The well-defined interface between the COs or CPs and NCs facilitates an efficient charge-transfer between them.     

Rational synthesis of covalently bonded organic-inorganic hybrids

Hybrid materials based on covalently linked inorganic polyoxometalates (POMs) and organic species containing a delocalized pi system have drawn increasing attention. These hybrids, traditionally prepared by cluster assembly approaches that lack predictability and controllability, can now be synthesized through common organic reactions by using organically functionalized POM clusters as building blocks. This minireview highlights some of the most recent advances on a particular type of hybrids where the organic and inorganic components are connected by an imido linkage.