Kinked Silicon Nanowires: Superstructures by Metal-Assisted Chemical Etching.

We report on metal-assisted chemical etching of Si for the synthesis of mechanically stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle, and location of the kinks via successive etch-quench sequences. We analyzed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine-tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be incorporated in biological cells without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physicochemical events at the Si/Au-electrolyte interface and offers guidelines for the development of finite-element modeling of metal-assisted Si chemical etching.

Tailored Synthesis of N -Substituted peri-Xanthenoxanthene Diimide (PXXDI) and Monoimide (PXXMI) Scaffolds.

The tailored synthesis of homo (A2) and hetero (AB) N-substituted peri-xanthenoxanthene diimides (PXXDIs) and peri-functionalized PXX monoimides (PXXMIs) from 3-hydroxy naphthalic anhydride is described. As A2-type PXXDIs could be synthesized in one step, AB-type PXXDIs and PXXMIs were prepared through a modular approach capitalizing on sequential Suzuki coupling, imidation, and Pummerer reactions with very high yields. In view of their potential applications as organic semiconductors, self-organization studies were performed through liquid deposition on surfaces, depicting the formation of islands, needles, and rods.

Kinked silicon nanowires-enabled interweaving electrode configuration for lithium-ion batteries.

A tri-dimensional interweaving kinked silicon nanowires (k-SiNWs) assembly, with a Ni current collector co-integrated, is evaluated as electrode configuration for lithium ion batteries. The large-scale fabrication of k-SiNWs is based on a procedure for continuous metal assisted chemical etching of Si, supported by a chemical peeling step that enables the reuse of the Si substrate. The kinks are triggered by a simple, repetitive etch-quench sequence in a HF and H2O2-based etchant. We find that the inter-locking frameworks of k-SiNWs and multi-walled carbon nanotubes exhibit beneficial mechanical properties with a foam-like behavior amplified by the kinks and a suitable porosity for a minimal electrode deformation upon Li insertion. In addition, ionic liquid electrolyte systems associated with the integrated Ni current collector repress the detrimental effects related to the Si-Li alloying reaction, enabling high cycling stability with 80% capacity retention (1695 mAh/gSi) after 100 cycles. Areal capacities of 2.42 mAh/cm2 (1276 mAh/gelectrode) can be achieved at the maximum evaluated thickness (corresponding to 1.3 mgSi/cm2). This work emphasizes the versatility of the metal assisted chemical etching for the synthesis of advanced Si nanostructures for high performance lithium ion battery electrodes.

Stereospecific Winding of Polycyclic Aromatic Hydrocarbons into Trinacria Propellers.

The stereospecific trimerization of enantiomerically pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically pure molecular propellers, in which three binaphthyl rings are held together with dioxecine rings. X-ray diffraction analysis revealed that three out the six naphthyl moieties are folded in a (EF)3 -type arrangement held by three intramolecular C-H⋅⋅⋅π interactions. This slips outward the three remaining naphthyl rings in a blade-like fashion, just like in three-folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name "trinacria propeller" derives. The propeller conformation is also preserved in chlorinated solutions, as displayed by the presence of a peak at 4.7 ppm typical of an aromatic proton resonance engaged in a C-H⋅⋅⋅π interaction. The denaturation of the propeller-like conformation is obtained at high temperature, corresponding to activation energy for the ring inversion of ca. 18.2 kcal mol-1 . Notably, halide-functionalized molecular propellers exposing I-atoms at the leading and trailing edges could be prepared stereo- and regiospecifically by choosing the relevant iodo-bearing BINOL derivative.

Biotechnological promises of Fe-filled CNTs for cell shepherding and magnetic fluid hyperthermia applications.

Fe-filled carbon nanotubes (Fe@CNTs) recently emerged as an effective class of hybrid nanoparticles for biotechnological applications, such as magnetic cell sorting and magnetic fluid hyperthermia. Aiming at studying the effects of both the Fe loading and the magnetocrystalline characteristics in these applications, we describe herein the preparation of Fe@CNTs containing different Fe phases that, upon functionalization with the antibody Cetuximab (Ctxb), allow the targeting of cancer cells. Our experimental findings reveal that an optimal Ctxb/Fe weight ratio of 1.2 is needed for efficient magnetic cell shepherding, whereas enhanced MFH-induced mortality (70 vs. 15%) can be reached with hybrids enriched in the coercive Fe(3)C phase. These results suggest that a synergistic effect between the Ab loading and the Fe distribution in each nanotube exists, for which the maximum shepherding and hyperthermia effects are observed when higher densities of Fe@CNTs featuring the more coercive phase are interfaced with the cells.

Carboxylated, Fe-filled multiwalled carbon nanotubes as versatile catalysts for O2 reduction and H2 evolution reactions at physiological pH.

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl-functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O2 and H2 O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching.

Magnetically Active Carbon Nanotubes at Work.

Endohedral and exohedral assembly of magnetic nanoparticles (MNPs) and carbon nanotubes (CNTs) recently gave birth to a large body of new hybrid nanomaterials (MNPs-CNTs) featuring properties that are otherwise not in reach with only the graphitic or metallic cores themselves. These materials feature enhanced magnetically guided motions (rotation and translation), magnetic saturation and coercivity, large surface area, and thermal stability. By guiding the reader through the most significant examples in this Concept paper, we describe how researchers in the field engineered and exploited the synergistic combination of these two types of nanoparticles in a large variety of current and potential applications, such as magnetic fluid hyperthermia therapeutics and in magnetic resonance imaging to name a few.

Photoinduced and thermal denitrogenation of bulky triazoline crystals: insights into solid-to-solid transformation.

The photoinduced and thermal denitrogenation of crystalline triazolines with bulky substituents leads to the quantitative formation of aziridines in clean solid-to-solid reactions despite very large structural changes in the transition from reactant to product. Analysis of the reaction progress by powder X-ray diffraction, solid-state (13)C CPMAS NMR, solid-state FTIR spectroscopy, and thermal analysis has revealed that solid-to-solid reactions proceed either through metastable phases susceptible to amorphization or by mechanisms that involve a reconstructive phase transition that culminates in the formation of the stable phase of the product. While the key for a solid-to-solid transformation is that the reaction occurs below the eutectic temperature of the reactant and product two-component system, experimental evidence suggests that those reactions will undergo a reconstructive phase transition when they take place above the glass transition temperature.

Cell uptake of a biosensor detected by hyperpolarized 129Xe NMR: the transferrin case.

For detection of biological events in vitro, sensors using hyperpolarized (129)Xe NMR can become a powerful tool, provided the approach can bridge the gap in sensitivity. Here we propose constructs based on the non-selective grafting of cryptophane precursors on holo-transferrin. This biological system was chosen because there are many receptors on the cell surface, and endocytosis further increases this density. The study of these biosensors with K562 cell suspensions via fluorescence microscopy and (129)Xe NMR indicates a strong interaction, as well as interesting features such as the capacity of xenon to enter the cryptophane even when the biosensor is endocytosed, while keeping a high level of polarization. Despite a lack of specificity for transferrin receptors, undoubtedly due to the hydrophobic character of the cryptophane moiety that attracts the biosensor into the cell membrane, these biosensors allow the first in-cell probing of biological events using hyperpolarized xenon.

Effect of pH and counterions on the encapsulation properties of xenon in water-soluble cryptophanes.

In the (129)Xe NMR-based biosensing approach in which the hyperpolarized noble gas is transported to biological receptors for a sensitive molecular imaging, cryptophanes are excellent xenon host systems. However to avoid formation of self-organized systems, these hydrophobic cage molecules can be rendered water soluble by introduction of ionic groups. We show that the sensitivity of xenon to its local environment and the presence of these ionic functions can lead to interesting properties. For a first water-soluble cryptophane derivative, we show that a precise monitoring of the local pH can be performed. For a second cryptophane, the presence of ionic groups close to the cryptophane cavity modifies the xenon binding constant and in-out exchange rate. The latter allows the tuning of physical properties of xenon-cryptophane interactions without resorting to a change of the cavity size. These results open new perspectives on the influence of chemical modifications of cryptophanes for optimizing the biosensor properties.