Gelation Mechanism Revealed in Organometallic Gels: Prevalence of van der Waals Interactions on Oligomerization by Coordination Chemistry.

Shaping of nanomaterials is a necessary step for their inclusion in electronic devices and batteries. For this purpose, the formulation of a moldable material including these nanomaterials is desirable. Organomineral gels are a very interesting option, since the components of the nanomaterial itself form a gel without the help of a binder. As a consequence, the properties of the nanomaterial are not diluted by the binder. In this article we studied organometallic gels based on a [ZnCy2 ] organometallic precursor and a primary alkyl amine which together forms spontaneously gels after few hours. We identified the main parameters controlling the gel properties monitored by rheology and NMR measurements The experiments demonstrate that the gelation time depends on the length of the alkyl chain of the amine and that the gelation mechanism derived firstly from the rigidification of the aliphatic chains of the amine, which takes precedence over the oligomerization of the inorganic backbone. This result highlights that the control of the rheological properties of organometallic gels remains mainly governed by the choice of the amine.

Coordination of Ethylamine on Small Silver Clusters: Structural and Topological (ELF, QTAIM) Analyses.

Amine ligands are expected to drive the organization of metallic centers as well as the chemical reactivity of silver clusters early growing during the very first steps of the synthesis of silver nanoparticles via an organometallic route. Density functional theory (DFT) computational studies have been performed to characterize the structure, the atomic charge distribution, and the planar two-dimensional (2D)/three-dimensional (3D) relative stability of small-size silver clusters (Agn, 2 ≤ n ≤ 7), with or without an ethylamine (EA) ligand coordinated to the Ag clusters. The transition from 2D to 3D structures is shifted from n = 7 to 6 in the presence of one EA coordinating ligand, and it is explained from the analysis of the Ag-N and Ag-Ag bond energies. For fully EA saturated silver clusters (Agn-EAn), the effect on the 2D/3D transition is even more pronounced with a shift between n = 4 and 5. Subsequent electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM) topological analyses allow for the fine characterization of the dative Ag-N and metallic Ag-Ag bonds, both in nature and in strength. Electron transfer from ethylamine to the coordinated silver atoms induces an increase of the polarization of the metallic core.

Radiosensitizing Fe-Au nanocapsules (hybridosomes®) increase survival of GL261 brain tumor-bearing mice treated by radiotherapy.

Glioblastoma remains a cancer for which the effectiveness of treatments has shown little improvement over the last decades. For this pathology, multiple therapies combining resection, chemotherapy and radiotherapy remain the norm. In this context, the use of high-Z nanoparticles such as gold or hafnium to potentiate radiotherapy is attracting more and more attention. Here, we evaluate the potentiating effect of hollow shells made of gold and iron oxide nanoparticles (hybridosomes®) on the radiotherapy of glioblastoma, using murine GL261-Luc+ brain tumor model. While iron oxide seems to have no beneficial effect for radiotherapy, we observe a real effect of gold nanoparticles-despite their low amount-with a median survival increase of almost 20% compared to radiotherapy only and even 33% compared to the control group. Cellular and in vivo studies show that a molecule of interest nano-precipitated in the core of the hybridosomes® is released and internalized by the surrounding brain cells. Finally, in vivo studies show that hybridosomes® injected intra-tumorally are still present in the vicinity of the brain tumor more than 5 days after injection (duration of the Stupp protocol's radiation treatment). Interestingly, one mouse treated with radiotherapy in the presence of gold-containing hybridosomes® survived 78 days. Monitoring of the tumoral growth of this long-term survivor using both MRI and bioluminescence revealed a decrease of the tumor size after treatment. These very encouraging results are a proof-of-concept that hybridosomes® are really effective tools for the development of combined therapies (chemo-radiotherapy).

The Hydrogen-Storage Challenge: Nanoparticles for Metal-Catalyzed Ammonia Borane Dehydrogenation.

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H2 production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H2 by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes.

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial.

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopic study including 17 O isotope exchange that for a ZnO-alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.

Topological Analysis of Ag-Ag and Ag-N Interactions in Silver Amidinate Precursor Complexes of Silver Nanoparticles.

A series of silver amidinate complexes has been studied both experimentally and theoretically, in order to investigate the role of the precursor complex in the control of the synthesis of silver nanoparticles via an organometallic route. The replacement of the methyl substituent of the central carbon atom of the amidinate anion by a n-butyl group allows for the crystallization of the tetranuclear silver amidinate complex 3 instead of a mixture of di- and trinuclear silver amidinate complexes 1 and 2, as obtained with a methyl substituent. The relative stabilities and dissociation schemes of various isomeric arrangements of silver atoms in 3 are investigated at the computational DFT level of calculation, depending on the substituents of the amidinate ligand. The tetranuclear silver amidinate complex 4, exhibiting a diamondlike arrangement of the four silver atoms, is also considered. Ag-N bonds and argentophilic Ag-Ag interactions are finely characterized using ELF and QTAIM topological analyses and compared over the series of the related di-, tri-, and tetranuclear silver amidinate complexes 1-4. In contrast to the Ag-N dative bonds very similar over the series, argentophilic Ag-Ag interactions of various strengths and covalence degree are characterized for complexes 1-4. This gives insight into the role of the amidinate substituents on the nuclearity and intramolecular chemical bonding of the silver amidinate precursors, required for the synthesis of dedicated AgNPs with chemically well defined surfaces.

Controlled Growth of Ag Nanocrystals in a H-Bonded Open Framework.

A procedure that enabled rational access to the first example of hybrid material made of NPs grown within a H-bonded framework is reported. To avoid competitive reactions with the framework units, the metal precursor was chemically trapped in the porous structure and subsequently photo-reduced to afford the hybrid material Ag@SPA-2, which consists of Ag NPs of nanometric sizes (<15 nm) homogeneously distributed in the crystals of the host material. In a subsequent step, taking advantage of the porous matrix the silver NPs have been transformed in situ to Ag2 S NP by simple infiltration of H2 S. The supramolecular network is shown to play an important role in stabilizing the inorganic nanomaterials and thus in controlling their growth.

Removable Composite Electrode Made of Silver Nanoparticles on Pyrolyzed Photoresist Film for the Electroreduction of 4-Nitrophenol.

Access to removable nanocomposite electrodes for electrosensing of pollutants is of great importance. However, the preparation of reproducible and reliable carbon electrodes decorated with metallic nanoparticles, a prerequisite for trustworthy devices, remains a challenge. Here we describe an innovative and easy method to prepare such electrodes. These latter are silicon-coated with a thin carbon film on which controlled silver nanostructures are grafted. Different silver nanostructures and surface coverage of the carbon electrode (16, 36, 51, and 67%) can be obtained through a careful control of the time of the hydrogenolysis of the N-N' isopropyl butylamidinate silver organometallic precursor (t = 1, 5, 15, and 60 min, respectively). Importantly, all nanocomposite surfaces are efficient for the electrodetection of 4-nitrophenol with a remarkable decrease of the overpotential of the reduction of such molecule up to 330 mV. The surfaces are characterized by atomic force microscopy, grazing incidence X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy. Furthermore, surface-enhanced Raman scattering effect is also observed. The exaltation of the Raman intensity is proportional to the surface coverage of the electrode; the number of hot spots increases with the surface coverage.

The role of alkylamine in the stabilization of CuO nanoparticles as a determinant of the Al/CuO redox reaction.

We report on a new strategy to synthesize Al/CuO nanothermites from commercial Al and ultra-small chemically synthesized CuO nanoparticles coated with alkylamine ligands. These usual ligands stabilize the CuO nanoparticles and prevent them from aggregating, with the goal to enhance the interfacial contact between Al and CuO particles. Using a variety of characterization techniques, including microscopy, spectroscopy, mass spectrometry and calorimetry (ATG/DSC), the structural and chemical evolution of CuO nanoparticles stabilized with alkylamine ligands is analyzed upon heating. This enables us to describe the main decomposition processes taking place on the CuO surface at low temperature (<500 °C): the ligands fragment into organic species accompanied with H2O and CO2 release, which promotes CuO reduction into Cu2O and further Cu. We quantitatively discuss these chemical processes highlighting for the first time the crucial importance of the synthesis conditions that control the chemical purity of the organic ligands (octylamine molecules and derivatives such as carbamate and ammonium ions) in the nanothermite performance. From these findings, an effective method to overcome the ligand-induced CuO degradation at low temperature is proposed and the Al/CuO nanothermite reaction is analyzed, in terms of onset temperature and energy released. We produce original structures composed of aluminium nanoparticles embedded in CuO grainy matrices exhibiting an onset temperature ∼200 °C below the usual Al/CuO onset temperatures, having specific combustion profiles depending on the synthesis conditions, while preserving the total amount of energy released.

Multinuclear solid-state NMR study: a powerful tool for understanding the structure of ZnO hybrid nanoparticles.

Characterization of hybrid materials is crucial for gaining an in-depth understanding of nano-objects. Here, it is evidenced that the use of multinuclear 1H, 2H, 13C, 15N, 67Zn and 17O MAS NMR spectroscopy is a very powerful approach to acquire both structural and dynamic information on hybrid ZnO nanomaterials prepared from an organometallic approach. Not only is the coordination mode of the organic part onto the inorganic surface evidenced but also important information about the dynamics of the organic capping molecules and some particularities of the nanocrystal structure itself are obtained.

Electro-click construction of hybrid nanocapsule films with triggered delivery properties.

Hollow nanocapsules (named Hybridosomes®) possessing a polymer/nanoparticle shell were used to covalently construct hybrid films in a one-pot fashion. The alkyne bearing organic/inorganic Hybridosomes® were reticulated with azide bearing homobifunctional polyethyleneglycol (PEG) linkers, by using an electro-click reaction on F-SnO2 (FTO) electrodes. The coatings were obtained by promoting the Cu(i)-catalyzed click reaction between alkyne and azide moieties in the vicinity of the electrode by the electrochemical generation of Cu(i) ions. The physicochemical properties of the covalently reticulated hybrid films obtained were studied by SEM, AFM, UV-vis and fluorescence spectroscopy. The one-pot covalent click reaction between the nanocapsules and the PEG linkers in the film did not affect the desirable features of the Hybridosomes® i.e. their hollow nanostructure their chemical versatility and their pH-sensitivity. Consequently, both the composition and the cargo-loading of the Hybridosomes® films could be tuned, demonstrating the versatility of these hybrid coatings. For example, the Hybridosome® films were used to encapsulate and release a bodipy fluorescent probe in response to either a pH drop or the application of an oxidative +1 V potential (vs. Ag/AgCl) at the substrate. By advancing the field of electro-synthesized films a step further toward the design of complex physicochemical interfaces, these results open perspectives for multifunctional coatings where chemical versatility, controllable stability and a hollow nanostructure are required.

Organometallic Synthesis of CuO Nanoparticles: Application in Low-Temperature CO Detection.

A metal-organic approach has been employed for the preparation of anisotropic CuO nanoparticles. These nanostructures have been characterized by transmission and high resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The CuO nanoparticles have been deposited as gas-sensitive layers on miniaturized silicon devices. At an operating temperature of 210 °C, the sensors present an optimum response toward carbon monoxide correlated with a fast response (Rn) and short recovery time. A high sensitivity to CO (Rn≈150 %, 100 ppm CO, RH 50 %) is achieved. These CuO nanoparticles serve as a very promising sensing layer for the fabrication of selective CO gas sensors working at a low temperature.

Evidence for Core Oxygen Dynamics and Exchange in Metal Oxide Nanocrystals from In Situ 17O MAS NMR.

Long-term stability of the properties of nanocrystals (NCs) is of paramount importance for any applicative development. However, these are jeopardized by chemical and structural alterations of the NCs induced by the environment and the working conditions. Among the species that alter the NCs properties, water molecules are of tremendous importance. We used 17O solid-state NMR spectroscopy to follow this process and the dynamics of O atoms in metal oxide NCs. Using ZnO as reference material, different chemical environments for the O atoms are characterized and a dynamic exchange process between the NCs and the O atoms from water is evidenced. The exchange does not involve only surface atoms but also ones located deeper inside the ZnO core of the NCs. Finally, a postsynthesis process based on watering/drying cycles is proposed that may greatly improve the long-term stability of metal oxide NCs.

Importance of the Correlation between Width and Length in the Shape Analysis of Nanorods: Use of a 2D Size Plot To Probe Such a Correlation.

Analysis of nanoparticle size through a simple 2D plot is proposed in order to extract the correlation between length and width in a collection or a mixture of anisotropic particles. Compared to the usual statistics on the length associated with a second and independent statistical analysis of the width, this simple plot easily points out the various types of nanoparticles and their (an)isotropy. For each class of nano-objects, the relationship between width and length (i.e., the strong or weak correlations between these two parameters) may suggest information concerning the nucleation/growth processes. It allows one to follow the effect on the shape and size distribution of physical or chemical processes such as simple ripening. Various electron microscopy pictures from the literature or from the authors' own syntheses are used as examples to demonstrate the efficiency and simplicity of the proposed 2D plot combined with a multivariate analysis.

SnO2 "Russian Doll" Octahedra Prepared by Metalorganic Synthesis: A New Structure for Sub-ppm CO Detection.

Micrometer-sized hierarchical Sn3 O2 (OH)2 octahedra, which are self-assembled one inside the other, resembling "Russian doll" organization, have been obtained by a metalorganic approach. This synthesis is based on the controlled hydrolysis of [Sn(NMe2 )2 ]2 in the presence of an alkylamine ligand in an organic solvent (THF). The water content of the medium proved to be a key parameter for the formation of these multi-walled octahedra. The resultant structures have been used as gas-sensitive layers on micromachined silicon devices. During in situ heating, Sn3 O2 (OH)2 is oxidized to SnO2 while retaining the initial morphology. The sensors present outstanding dynamic responses at very low CO concentrations (7 % and 67 % resistance variation to 0.25 and 20 ppm CO, respectively, at an operating temperature of 500 °C). This superior gas-sensing performance is closely related to the unique microstructure of the SnO2 multi-walled octahedra.

One-Step Synthesis of Hybrid Liquid-Crystal ZnO Nanoparticles: Existence of a Critical Temperature Associated with the Anisotropy of the Nanoparticles.

Zinc oxide nanoparticles were obtained from the hydrolysis of an organometallic precursor in pure hexadecylamine. Interestingly, we demonstrate that the final (anisotropic or isotropic) shape of the nanoparticles is strongly correlated to the existence of a critical temperature. This suggests that the organization of the fatty amines is a paramount parameter in this synthesis. Moreover, the final hybrid ZnO materials systematically exhibit a liquid-crystal smectic phase, whereas no liquid-crystal phase was observed in the pristine reaction media. This simple process is, therefore, a direct and straightforward method to synthesize liquid-crystal hybrid materials.

Improved Transversal Relaxivity for Highly Crystalline Nanoparticles of Pure γ-Fe2O3 Phase.

Pure and highly crystalline γ-Fe2O3 nanocrystals (NCs) are obtained when hydrolysis and oxidation of a Fe(II) organometallic precursor are performed in successive steps. Their synthesis in pure alkylamine leads to NCs of about 6 nm. In aqueous solutions of poly(vinyl)pyrrolidone, such pristine NCs form aggregates of about 150 nm that exhibit a high transversal relaxivity (r2 =466 mM(-1) s(-1)) about four times higher than that of a commercial Feridex magnetic resonance imaging (MRI) contrast agent. Consequently, they provide a significant decrease in the NMR signal at very short echo time (8 ms), which is of paramount importance in clinical practice because of the reduced duration of MRI measurements.

Simple elaboration of drug-SPION nanocapsules (hybridosomes®) by solvent shifting: Effect of the drug molecular structure and concentration.

Drug nanocapsules coated with iron oxide nanoparticles (SPION) were elaborated by the simultaneous nanoprecipitation of the drug and the nanoparticles, through solvent shifting. We examined four drugs: sorafenib, sorafenib tosylate, α-tocopherol and paclitaxel, to cover the cases of molecular solids, ionic solids, and molecular liquids. We first investigated the formation of the drug core in the final mixture of solvents at different concentrations. A Surfactant-Free Micro-Emulsion domain (SFME, thermodynamically stable) was observed at low drug concentration and an Ouzo domain (metastable) at high drug concentration, except for the case of paclitaxel which crystallizes at high concentration without forming an Ouzo domain. When co-nanoprecipitated with the molecular drugs in the Ouzo domain (sorafenib or α-tocopherol), the SPION limited the coalescence of the drug particles to less than 100 nm, forming capsules with a drug encapsulation efficiency of ca 80 %. In contrast, larger capsules were formed from the SFME or when using the ionic form (sorafenib tosylate). Finally, the sorafenib-SPION capsules exhibit a similar chemotherapeutic effect as the free drug on the hepatocellular carcinoma in vitro.

Metal-organic pathways for anisotropic growth of a highly symmetrical crystal structure: example of the fcc Ni.

The control of the metallic nanocrystal shape is of prime importance for a wide variety of applications. We report a detailed research work on metal-organic chemical routes for the synthesis of a highly symmetrical crystal structure. In particular, this study shows the key parameters ensuring the anisotropic growth of nickel nanostructures (fcc crystal). Numerous reaction conditions are investigated (precursors, solvents, temperature, reducing agents, reaction time, and types and ratios of surfactants, such as alkyl amines, carboxylic acids, and phosphine oxides), and their effects on the size and shape of the final product are reported. The role of the growth modifiers and the structuring of the reaction media on the anisotropic growth are demonstrated. This metal-organic approach generates several novel anisotropic nanostructures in a wide size range depending on the reaction conditions. In this way, nanomaterials with reproducible size, shape, and composition are obtained with good yield. Transmission electron microscopy techniques (TEM and HRTEM) are the principal methods for monitoring the morphology.

Secured Nanosynthesis-Deposition Aerosol Process for Composite Thin Films Incorporating Highly Dispersed Nanoparticles.

Application of nanocomposites in daily life requires not only small nanoparticles (NPs) well dispersed in a matrix, but also a manufacturing process that is mindful of the operator and the environment. Avoiding any exposure to NPs is one such way, and direct liquid reaction-injection (DLRI) aims to fulfill this need. DLRI is based on the controlled in situ synthesis of NPs from the decomposition of suitable organometallic precursors in conditions that are compatible with a pulsed injection mode of an aerosol into a downstream process. Coupled with low-pressure plasma, DLRI produces nanocomposite with homogeneously well-dispersed small nanoparticles that in the particular case of ZnO-DLC nanocomposite exhibit unique properties. DLRI favorably compares with the direct liquid injection of ex situ formed NPs. The exothermic hydrolysis reaction of the organometallic precursor at the droplet-gas interface leads to the injection of small and highly dispersed NPs and, consequently, the deposition of fine and controlled distribution in the nanocomposite. The scope of DLRI nanosynthesis has been extended to several metal oxides such as zinc, tin, tungsten, and copper to generalize the concept. Hence, DLRI is an attractive method to synthesize, inject, and deposit nanoparticles and meets the prevention and atom economy requirements of green chemistry.