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1.
J Am Chem Soc ; 145(17): 9700-9707, 2023 May 03.
Article in English | MEDLINE | ID: mdl-37075271

ABSTRACT

The physical properties of many modern multi-component materials are determined by their internal microstructure. Tools capable of characterizing complex nanoscale architectures in composite materials are, therefore, essential to design materials with targeted properties. Depending on the morphology and the composition, structures may be measured by laser diffraction, scattering methods, or by electron microscopy. However, it can be difficult to obtain contrast in materials where all the components are organic, which is typically the case for formulated pharmaceuticals, or multi-domain polymers. In nuclear magnetic resonance (NMR) spectroscopy, chemical shifts allow a clear distinction between organic components and can in principle provide the required chemical contrast. Here, we introduce a method to obtain radial images of the internal structure of multi-component particles from NMR measurements of the relay of nuclear hyperpolarization obtained from dynamic nuclear polarization. The method is demonstrated on two samples of hybrid core-shell particles composed of a core of polystyrene with a shell of mesostructured silica filled with the templating agent CTAB and is shown to yield accurate images of the core-shell structures with a nanometer resolution.

2.
J Am Chem Soc ; 144(33): 15236-15251, 2022 08 24.
Article in English | MEDLINE | ID: mdl-35971919

ABSTRACT

Calcium carbonate (CaCO3) is one of the most significant biominerals in nature. Living organisms are able to control its biomineralization by means of an organic matrix to tailor a myriad of hybrid functional materials. The soluble organic components are often proteins rich in acidic amino-acids such as l-aspartic acid. While several studies have demonstrated the influence of amino acids on the crystallization of calcium carbonate, nanoscopic insight of their impact on CaCO3 mineralization, in particular at the early stages, is still lacking. Herein, we implement liquid phase-transmission electron microscopy (LP-TEM) in order to visualize in real-time and at the nanoscale the prenucleation stages of CaCO3 formation. We observe that l-aspartic acid favors the formation of individual and aggregated prenucleation clusters which are found stable for several minutes before the transformation into amorphous nanoparticles. Combination with hyperpolarized solid state nuclear magnetic resonance (DNP NMR) and density functional theory (DFT) calculations allow shedding light on the underlying mechanism at the prenucleation stage. The promoting nature of l-aspartic acid with respect to prenucleation clusters is explained by specific interactions with both Ca2+ and carbonates and the stabilization of the Ca2+-CO32-/HCO3- ion pairs favoring the formation and stabilization of the CaCO3 transient precursors. The study of prenucleation stages of mineral formation by the combination of in situ LP-TEM, advanced analytical techniques (including hyperpolarized solid-state NMR), and numerical modeling allows the real-time monitoring of prenucleation species formation and evolution and the comprehension of their relative stability.


Subject(s)
Aspartic Acid , Calcium Carbonate , Calcium Carbonate/chemistry , Carbonates , Magnetic Resonance Spectroscopy , Microscopy, Electron, Transmission
3.
Adv Mater ; 34(36): e2204489, 2022 Sep.
Article in English | MEDLINE | ID: mdl-35797893

ABSTRACT

Solution-processed inorganic nanoporous films are key components for the vast spectrum of applications ranging from dew harvesting to solar cells. Shaping them into complex architectures required for advanced functionality often needs time-consuming or expensive fabrication. In this work, crack formation is harnessed to pattern porous inorganic films in a single step and without using lithography. Aqueous inks, containing inorganic precursors and polymeric latexes enable evaporation-induced, defect-free periodic arrays of cracks with tunable dimensions over several centimeters. The ink formulation strategy is generalized to more than ten inorganic materials including simple and binary porous oxide and metallic films covering a whole spectrum of properties including insulating, photocatalytic, electrocatalytic, conductive, or electrochromic materials. Notably, this approach enables 3D self-assembly of cracks by stacking several layers of different compositions, yielding periodic assemblies of polygonal shapes and Janus-type patterns. The crack patterned periodic arrays of nanoporous TiO2 diffract light, and are used as temperature-responsive diffraction grating sensors. More broadly, this method represents a unique example of a self-assembly process leading to long-range order (over several centimeters) in a robust and controlled way.

4.
Nanoscale ; 14(30): 10950-10957, 2022 Aug 04.
Article in English | MEDLINE | ID: mdl-35860928

ABSTRACT

We have investigated the early stages of the formation of iron oxide nanoparticles from iron stearate precursors in the presence of sodium stearate in an organic solvent by in situ liquid phase transmission electron microscopy (IL-TEM). Before nucleation, we have evidenced the spontaneous formation of vesicular assemblies made of iron polycation-based precursors sandwiched between stearate layers. Nucleation of iron oxide nanoparticles occurs within the walls of the vesicles, which subsequently collapse upon the consumption of the iron precursors and the growth of the nanoparticles. We then evidenced that fine control of the electron dose, and therefore of the local concentration of reactive iron species in the vicinity of the nuclei, enables controlling crystal growth and selecting the morphology of the resulting iron oxide nanoparticles. Such a direct observation of the nucleation process templated by vesicular assemblies in a hydrophobic organic solvent sheds new light on the formation process of metal oxide nanoparticles and therefore opens ways for the synthesis of inorganic colloidal systems with tunable shape and size.

5.
Small ; 18(20): e2200414, 2022 05.
Article in English | MEDLINE | ID: mdl-35426247

ABSTRACT

Thermal decomposition is a very efficient synthesis strategy to obtain nanosized metal oxides with controlled structures and properties. For the iron oxide nanoparticle synthesis, it allows an easy tuning of the nanoparticle's size, shape, and composition, which is often explained by the LaMer theory involving a clear separation between nucleation and growth steps. Here, the events before the nucleation of iron oxide nanocrystals are investigated by combining different complementary in situ characterization techniques. These characterizations are carried out not only on powdered iron stearate precursors but also on a preheated liquid reaction mixture. They reveal a new nucleation mechanism for the thermal decomposition method: instead of a homogeneous nucleation, the nucleation occurs within vesicle-like-nanoreactors confining the reactants. The different steps are: 1) the melting and coalescence of iron stearate particles, leading to "droplet-shaped nanostructures" acting as nanoreactors; 2) the formation of a hitherto unobserved iron stearate crystalline phase within the nucleation temperature range, simultaneously with stearate chains loss and Fe(III) to Fe(II) reduction; 3) the formation of iron oxide nuclei inside the nanoreactors, which are then ejected from them. This mechanism paves the way toward a better mastering of the metal oxide nanoparticles synthesis and the control of their properties.


Subject(s)
Metal Nanoparticles , Oxides , Culture Media , Ferric Compounds/chemistry , Iron , Metal Nanoparticles/chemistry , Oxides/chemistry , Stearates
6.
Acc Chem Res ; 55(2): 171-185, 2022 Jan 18.
Article in English | MEDLINE | ID: mdl-34979086

ABSTRACT

ConspectusThe properties of a material depend upon its physical characteristics, one of these being its crystalline state. Next generation solid-state technologies will integrate crystalline oxides into thermal sensitive processes and composite materials. Crystallization of amorphous phases of metal oxides in the solid state typically requires substantial energy input to induce the amorphous to crystalline phase transformation. In the case of silica, the transformation to α-quartz in a furnace occurs above 1300 °C and that of titania, above 400 °C. These calcination processes are costly in energy but also often degrade complex material architectures or compositions.Thus, low temperature crystallization techniques are required that preserve macro- and mesostructures and complex elemental composition (e.g., organic-, metal-, and semiconductor-metal oxide hybrids/composites). Some solution-based techniques exist to directly fabricate crystalline metal oxides. However, these are not always compatible with the specificities of the system or industrial constraints. A postsynthetic, solid-state approach that reduces crystallization temperature in metal oxides is metal-induced crystallization (MIC).MIC is the introduction of catalytic amounts of a cation, which can be an s-block, p-block, or d-block cation, that migrates through the solid metal oxide lattice. The cation is thought to temporarily break metal oxide bonds, allowing [MOx] polyhedra to rotate and reform bonds with neighboring [MOx] groups in a lower energy crystalline phase. Depending on the system, the cation can favor or defavor the formation of a particular crystalline phase, providing a means to tune the purity and crystalline phase ratios. An advantage of MIC is that, although the crystallization occurs in the solid state, the crystallization process can be accomplished for particle suspensions in liquid media. In this case, the energy required to induce the crystallization can come from, for example, a microwave or an ultrasound bath. The crystallization of particles in suspension avoids aggregation from particle-particle sintering. In the case of thin films, the energy for crystallization typically comes from a laser or calcination.MIC is only recently being used as a low temperature metal oxide crystallization technique, despite being widely used in the semiconductor industry. Here, the mechanism and previous studies in MIC are presented for titania, silica, and other oxides. The beauty of this technique is that it is extremely easy to employ: cations can be incorporated into the system postsynthetically and then are often expelled from the lattice upon phase conversion. We expect MIC to enrich materials for photochromic, optoelectronic, catalyst, biological, and other applications.

7.
Small ; 18(4): e2104091, 2022 Jan.
Article in English | MEDLINE | ID: mdl-34766719

ABSTRACT

Incorporating boride nanocrystals could significantly impact the mechanical properties of aluminum alloys. Molten salts synthesis offers opportunities to fabricate superhard boride nanoparticles, which can sustain the harsh conditions during the liquid-phase design of metallic nanocomposites. Here hafnium diboride-aluminum nanocomposites are unveiled from molten salt-derived HfB2 nanoparticles sequentially dispersed in aluminum by ultrasound treatment. The structure and size of the nanocrystals are retained in the final nanocomposites, supporting their high chemical stability. Semicoherent interfaces between the nanoparticles and the matrix are then evidenced by TEM, suggesting that the nanocrystals could promote heterogeneous nucleation of Al and then limit the Al grain size to ≈20 µm. Nanoindentation measurements reveal significant grain boundary strengthening and grain refinement effects. It is finally shown that HfB2 nanoparticles also enable a decrease in matrix grain size and an increase in the hardness of the AlSi7 Cu0.5 Mg0.3 alloy. These proof-of-concept materials are paving the way to light-weight Al matrix nanocomposites doped by molten-salt synthesized nanoparticles.

8.
Org Biomol Chem ; 19(31): 6771-6775, 2021 08 21.
Article in English | MEDLINE | ID: mdl-34292288

ABSTRACT

Enantiopure α-Tfm-proline and α-Tfm-pipecolic acid were synthesized starting from commercially available diesters and ethyl trifluoroacetate. A Strecker type reaction on intermediate chiral Tfm-oxazolo-pyrrolidine and -piperidine provided the corresponding nitrile precursor of enantiopure (R) and (S) α-Tfm-proline and α-Tfm-pipecolic acid. The C-terminal peptide coupling reaction of α-Tfm-pipecolic acid has been successfully achieved.

9.
Nat Commun ; 12(1): 3935, 2021 Jun 24.
Article in English | MEDLINE | ID: mdl-34168129

ABSTRACT

Combining high activity and stability, iridium oxide remains the gold standard material for the oxygen evolution reaction in acidic medium for green hydrogen production. The reasons for the higher electroactivity of amorphous iridium oxides compared to their crystalline counterpart is still the matter of an intense debate in the literature and, a comprehensive understanding is needed to optimize its use and allow for the development of water electrolysis. By producing iridium-based mixed oxides using aerosol, we are able to decouple the electronic processes from the structural transformation, i.e. Ir oxidation from IrO2 crystallization, occurring upon calcination. Full characterization using in situ and ex situ X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy allows to unambiguously attribute their high electrochemical activity to structural features and rules out the iridium oxidation state as a critical parameter. This study indicates that short-range ordering, corresponding to sub-2nm crystal size for our samples, drives the activity independently of the initial oxidation state and composition of the calcined iridium oxides.

10.
Org Lett ; 23(2): 382-387, 2021 01 15.
Article in English | MEDLINE | ID: mdl-33369434

ABSTRACT

The straightforward synthesis of enantiopure 5-(R)-and 5-(S)-trifluoromethylproline is reported. The key steps are a Ruppert-Prakash reagent addition on l-pyroglutamic esters followed by an elimination reaction and a selective reduction. The solution-phase and solid-phase incorporation of this unprotected enantiopure fluorinated amino acid in a short peptide chain was demonstrated. Compared to proline, the CF3 group provides a decrease of the trans to cis amide bond isomerization energy and an increase of the cis conformer population.


Subject(s)
Amides/chemistry , Amino Acids/chemistry , Peptides/chemistry , Proline/chemistry , Indicators and Reagents/chemistry , Isomerism , Molecular Structure
11.
ACS Catal ; 11(24): 15026-15039, 2021 Dec 17.
Article in English | MEDLINE | ID: mdl-34976431

ABSTRACT

A family of iron-doped manganese-related hollandites, K x Mn1-y Fe y O2-δ (0 ≤ y ≤ 0.15), with high performance in CO oxidation have been prepared. Among them, the most active catalyst, K0.11Mn0.876Fe0.123O1.80(OH)0.09, is able to oxidize more than 50% of CO at room temperature. Detailed compositional and structural characterization studies, using a wide battery of thermogravimetric, spectroscopic, and diffractometric techniques, both at macroscopic and microscopic levels, have provided essential information about this never-reported behavior, which relates to the oxidation state of manganese. Neutron diffraction studies evidence that the above compound stabilizes hydroxyl groups at the midpoints of the tunnel edges as in isostructural ß-FeOOH. The presence of oxygen and hydroxyl species at the anion sublattice and Mn3+, confirmed by electron energy loss spectroscopy, appears to play a key role in the catalytic activity of this doped hollandite oxide. The analysis of these detailed structural features has allowed us to point out the key role of both OH groups and Mn3+ content in these materials, which are able to effectively transform CO without involving any critical, noble metal in the catalyst formulation.

12.
J Phys Chem Lett ; 11(21): 9117-9122, 2020 Nov 05.
Article in English | MEDLINE | ID: mdl-33147972

ABSTRACT

Here, we present a correlative microscopic analysis of electrodeposited films from catechol solutions in aqueous electrolytes. The films were prepared in a miniaturized electrochemical cell and were analyzed by identical location transmission electron microscopy, scanning transmission X-ray microscopy, and atomic force microscopy. Thanks to this combined approach, we have shown that the electrodeposited films are constituted of ultrathin graphite oxide nanosheets. Detailed information about the electronic structure of the films was obtained by X-ray absorption near edge structure spectroscopy. These results show the large potential of soft electrochemical conditions for the bottom-up production of ultrathin graphite oxide nanosheet films via a one-pot green chemistry approach from simple organic building blocks.

13.
Nanoscale ; 12(28): 15209-15213, 2020 Jul 23.
Article in English | MEDLINE | ID: mdl-32638791

ABSTRACT

We report phase selective synthesis of intermetallic nickel silicide nanocrystals in inorganic molten salts. NiSi and Ni2Si nanocrystals are obtained by reacting a nickel(ii) salt and sodium silicide Na4Si4 in the molten LiI-KI inorganic eutectic salt mixture. We report that nickel silicide nanocrystals are precursors to active electrocatalysts in the oxygen evolution reaction (OER) and may be low-cost alternatives to iridium-based electrocatalysts.

14.
Proc Natl Acad Sci U S A ; 117(22): 11947-11953, 2020 06 02.
Article in English | MEDLINE | ID: mdl-32424103

ABSTRACT

Living tissues, heterogeneous at the microscale, usually scatter light. Strong scattering is responsible for the whiteness of bones, teeth, and brain and is known to limit severely the performances of biomedical optical imaging. Transparency is also found within collagen-based extracellular tissues such as decalcified ivory, fish scales, or cornea. However, its physical origin is still poorly understood. Here, we unveil the presence of a gap of transparency in scattering fibrillar collagen matrices within a narrow range of concentration in the phase diagram. This precholesteric phase presents a three-dimensional (3D) orientational order biomimetic of that in natural tissues. By quantitatively studying the relation between the 3D fibrillar network and the optical and mechanical properties of the macroscopic matrices, we show that transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The striking similarities between synthetic and natural materials provide insights for better understanding the occurring transparency.


Subject(s)
Biomimetic Materials , Fibrillar Collagens , Animals , Biomimetic Materials/chemical synthesis , Biomimetic Materials/chemistry , Biomimetics/methods , Cornea/chemistry , Fibrillar Collagens/chemical synthesis , Fibrillar Collagens/chemistry
15.
Chem Commun (Camb) ; 56(35): 4812-4815, 2020 Apr 30.
Article in English | MEDLINE | ID: mdl-32236210

ABSTRACT

New insights into the chemical and structural features of iron or titanium-doped KxMnO2 hollandites are reported. Neutron diffraction and atomically resolved transmission electron microscopy elucidate the localization of the dopant cations that could be one of the key factors governing the functional activity of these nanomaterials.

16.
ACS Appl Mater Interfaces ; 12(12): 13598-13612, 2020 Mar 25.
Article in English | MEDLINE | ID: mdl-32077678

ABSTRACT

Mesoporous silica nanoparticles (MSNs) have seen a fast development as drug delivery carriers thanks to their tunable porosity and high loading capacity. The employ of MSNs in biomedical applications requires a good understanding of their degradation behavior both to control drug release and to assess possible toxicity issues on human health. In this work, we study mesoporous silica degradation in biologically relevant conditions through in situ ellipsometry on model mesoporous nanoparticle or continuous thin films, in buffer solution and in media containing proteins. In order to shed light on the structure/dissolution relationship, we performed dissolution experiments far from soluble silicate species saturation. Via a complete decorrelation of dissolution and diffusion contributions, we proved unambiguously that surface area of silica vectors is the main parameter influencing dissolution kinetics, while thermal treatment and open mesoporous network architecture have a minor impact. As a logical consequence of our dissolution model, we proved that the dissolution lag-time can be promoted by selective blocking of the mesopores that limits the access to the mesoporous internal surface. This study was broadened by studying the impact of the organosilanes in the silica structure, of the presence of residual structuring agents, and of the chemical composition of the dissolution medium. The presence of albumin at blood concentration was found affecting drastically the dissolution kinetics of the mesoporous structure, acting as a diffusion barrier. Globally, we could identify the main factors affecting mesoporous silica materials degradation and proved that we can tune their structure and composition for adjusting dissolution kinetics in order to achieve efficient drug delivery.


Subject(s)
Drug Delivery Systems , Nanoparticles/chemistry , Proteins/chemistry , Silicon Dioxide/chemistry , Drug Carriers/chemistry , Drug Liberation , Humans , Kinetics , Nanoparticles/therapeutic use , Porosity
17.
Natl Sci Rev ; 7(11): 1624-1625, 2020 Nov.
Article in English | MEDLINE | ID: mdl-34691494
18.
Small ; 16(4): e1902224, 2020 01.
Article in English | MEDLINE | ID: mdl-31880410

ABSTRACT

Extracellular matrices (ECM) rich in type I collagen exhibit characteristic anisotropic ultrastructures. Nevertheless, working in vitro with this biomacromolecule remains challenging. When processed, denaturation of the collagen molecule is easily induced in vitro avoiding proper fibril self-assembly and further hierarchical order. Here, an innovative approach enables the production of highly concentrated injectable collagen microparticles, based on collagen molecules self-assembly, thanks to the use of spray-drying process. The versatility of the process is shown by performing encapsulation of secretion products of gingival mesenchymal stem cells (gMSCs), which are chosen as a bioactive therapeutic product for their potential efficiency in stimulating the regeneration of a damaged ECM. The injection of collagen microparticles in a cell culture medium results in a locally organized fibrillar matrix. The efficiency of this approach for making easily handleable collagen microparticles for encapsulation and injection opens perspectives in active tissue regeneration and 3D bioprinted scaffolds.


Subject(s)
Aerosols , Collagen , Mesenchymal Stem Cells , Cells, Cultured , Extracellular Matrix/chemistry , Gingiva/cytology , Humans , Mesenchymal Stem Cells/cytology , Mesenchymal Stem Cells/metabolism , Tissue Scaffolds/chemistry
19.
ACS Nano ; 13(10): 11372-11381, 2019 Oct 22.
Article in English | MEDLINE | ID: mdl-31584800

ABSTRACT

Unveiling the mechanism of electrocatalytic processes is fundamental for the search of more efficient and stable electrode materials for clean energy conversion devices. Although several in situ techniques are now available to track structural changes during electrocatalysis, especially of water oxidation, a direct observation, in real space, of morphological changes of nanostructured electrocatalysts is missing. Herein, we implement an in situ electrochemical Transmission Electron Microscopy (in situ EC-TEM) methodology for studying electrocatalysts of the oxygen evolution reaction (OER) during operation, by using model cobalt oxide Co3O4 nanoparticles. The observation conditions were optimized to mimic standard electrochemistry experiments in a regular electrochemical cell, allowing cyclic voltammetry and chronopotentiometry to be performed in similar conditions in situ and ex situ. This in situ EC-TEM method enables us to observe the chemical, morphological, and structural evolutions occurring in the initial nanoparticle-based electrode exposed to different aqueous electrolytes and under OER conditions. The results show that surface amorphization occurs, yielding a nanometric cobalt (oxyhydr)oxide-like phase during OER. This process is irreversible and occurs to an extent that has not been described before. Furthermore, we show that the pH and counterions of the electrolytes impact this restructuration, shedding light on the materials properties in neutral phosphate electrolytes. In addition to the structural changes followed in situ during the electrochemical measurements, this study demonstrates that it is possible to rely on in situ electrochemical TEM to reveal processes in electrocatalysts while preserving a good correlation with ex situ regular electrochemistry.

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