Comprehensive Analysis of the Chemical and Structural Transformations of Mg-Al-CO3 Layered Double Hydroxides with Different Mg/Al Ratios at Elevated Temperatures.

Mg-Al layered double hydroxides (LDHs) with CO32- interlayer anions are promising CO2 adsorbents. Here, we analyzed the quantitative gas evolution behaviors of Mg-Al LDH particles with different Mg/Al ratios during the multistep chemical/structural transformations at elevated temperatures. The Mg/Al molar ratio strongly affects the behavior: the transformation changes from two apparent steps to three steps depending on the Mg/Al ratio. The transformation occurs in essentially the same way as that observed for large Mg-Al LDH crystals: (1) release of the interlayer water, (2) partial dehydroxylation of the hydroxyl layers followed by coordination of carbonate ions to the metals, and (3) collapse of the layered structure. We provide a molecular/atomic level picture of the structure in each step of the transformation by first-principles density functional theory (DFT) calculation. The structurally optimized model and reexamination of experimental data showed that step (1) results in a large decrease in the interlayer distance of the LDH from ∼7.6 to ∼6.7 Å (a decrease of ∼0.9 Å) and the possible explanation is the waving of the metal hydroxide layers. This study provides a comprehensive understanding of the structural changes of LDHs with various Mg/Al ratios to resolve the various interpretations in the literature.

Thermal self-reduction of metal hydroxide acrylate monolayer nanoparticles leads formation of nanoparticulate and porous structured alloys.

Chemical and physical designs of alloy nanomaterials have attracted considerable attention for the development of highly functional materials. Although polyol processes using ionic precursors are widely used to synthesise alloy nanoparticles, the reduction potential of polyols limits their chemical composition, making it difficult to obtain 3d transition metals. In this study, we employed pre-synthesized metal hydroxide salt monolayer nanoparticles as precursors to obtain alloy nanoparticles. Simultaneous dehydroxylation of the hydroxide moiety and decomposition of the organic moiety allowed the formation of stable face-centred cubic metals passing through the metal carbide and metastable hexagonal close-packed metal phases. This self-reduction process enabled the formation of nanoparticulate bimetallic alloys and macroporous/mesoporous-structured bimetallic alloys by compositing hard/soft templates with pre-synthesized metal hydroxide salt nanoparticles. We believe that the strategy presented in this study can be used to design nanostructures and chemical compositions of multimetallic alloy nanoparticles as well as bimetallic systems.

Thermal Conversion of Nanocrystalline Metal Hydroxide Salts to Metal Carbides, Pnictides, Chalcogenides, and Halides.

A general procedure for synthesizing various inorganic compounds in a similar manner is required in the field of material chemistry. The use of solid-state reactive agents with inorganic precursors is a successful approach in this direction. In this study, organic-inorganic hybrid metal hydroxide salts (MHSs) were utilized to synthesize various inorganic compounds by a simple heat treatment method because they can be assumed to be "premixed" inorganic precursors and solid-state reactive agents. Comparative studies revealed that the nanocrystalline characteristics and coordination of the carboxylate of the synthesized MHSs enabled simultaneous dehydration of hydroxides and decomposition of carboxylates and subsequent formation of metals and metal sulfides. Manganese, iron, cobalt, nickel, and zinc sulfides, as well as nickel carbides, pnictides, chalcogenides, and halides were obtained using the same procedure. We believe that using nanocrystalline organic-inorganic hybrid MHSs as both inorganic precursors and organic reactive agents will be a simple and versatile way to prepare a wide variety of inorganic complex compounds.

Phospholipid-Coated Boronic Oxide Nanoparticles as Boron Agents for Boron Neutron Capture Therapy.

Minimally invasive boron neutron capture therapy (BNCT) is an elegant approach for cancer treatment. The highly selective and efficient deliverability of boron agents to cancer cells is the key to maximizing the therapeutic benefits of BNCT. In addition, enhancement of the frequencies to achieve boron neutron capture reaction is also significant in improving therapeutic efficacy by providing a highly concentrated boron agent in each boron nanoparticle. As the density of the thermal neutron beam remains low, it is unable to induce high-efficiency cell destruction. Herein, we report phospholipid-coated boronic oxide nanoparticles as agents for BNCT that can provide a highly concentrated boron atom in each nanoparticle. The current system exhibited in vitro BNCT activity seven times higher than that of commercial boron agents. Furthermore, the system could penetrate cancer spheroids deeply, efficiently suppressing thermal neutron irradiation-induced growth.

Carborane bearing pullulan nanogel-boron oxide nanoparticle hybrid for boron neutron capture therapy.

Boron neutron capture therapy shows is a promising approach to cancer therapy, but the delivery of effective boron agents is challenging. To address the requirements for efficient boron delivery, we used a hybrid nanoparticle comprising a carborane = bearing pullulan nanogel and hydrophobized boron oxide nanoparticle (HBNGs) enabling the preparation of highly concentrated boron agents for efficient delivery. The HBNGs showed better anti-cancer effects on Colon26 cells than a clinically boron agent, L-BPA/fructose complex, by enhancing the accumulation and retention amount of the boron agent within cells in vitro. The accumulation of HBNGs in tumors, due to the enhanced permeation and retention effect, enabled the delivery of boron agents with high tumor selectivity, meeting clinical demands. Intravenous injection of boron neutron capture therapy (BNCT) using HBNGs decreased tumor volume without significant body weight loss, and no regrowth of tumor was observed three months after complete regression. The therapeutic efficacy of HBNGs was better than that of L-BPA/fructose complex. BNCT with HBNGs is a promising approach to cancer therapeutics.

Reversible conjugation of biomembrane vesicles with magnetic nanoparticles using a self-assembled nanogel interface: single particle analysis using imaging flow cytometry.

Nanoscale biomembrane vesicles such as liposomes and extracellular vesicles are promising materials for therapeutic delivery applications. However, modification processes that disrupt the biomembrane affect the performance of these systems. Non-covalent functionalization approaches that are facile and easily reversed by environmental triggers are therefore being widely investigated. In this study, liposomes were successfully hybridized with magnetic iron oxide particles using a cholesterol-modified pullulan nanogel interface. Both the magnetic nanoparticles and the hydrophobic core of the lipid bilayer interacted with the hydrophobic cholesteryl moieties, resulting in stable hybrids after simple mixing. Single particle analysis by imaging flow cytometry showed that the hybrid particles interacted in solution. Calcein loaded liposomes were not disrupted by the hybridization, showing that conjugation did not affect membrane stability. The hybrids could be magnetically separated and showed significantly enhanced uptake by HeLa cells when a magnetic field was applied. Differential scanning calorimetry revealed that the hybridization mechanism involved hydrophobic cholesteryl inserting into the biomembrane. Furthermore, exposure of the hybrids to fetal bovine serum proteins reversed the hybridization in a concentration dependent manner, indicating that the interaction was both reversible and controllable. This is the first example of reversible inorganic material conjugation with a biomembrane that has been confirmed by single particle analysis. Both the magnetic nanogel/liposome hybrids and the imaging flow cytometry analysis method have the potential to significantly contribute to therapeutic delivery and nanomaterial development.

High Heat Resistance of the Structural Coloration of Colloidal Arrays with Inorganic Black Additives.

Structurally colored materials consisting of arrays of submicrometer-sized particles have drawn a great deal of attention because of their advantages, including low cost, low impact on human health as well as the environment, and resistance to fading. However, their low thermal stability is considered to be a critical issue for their practical use as colorants. Black-colored substances that can absorb the white color are added to colloidal array-type structurally colored materials to enhance their chromaticity. The poor thermal stability of commonly used black coloring additives, carbon black and Fe3O4 nanoparticles, is a main factor that reduces the heat resistance of structural coloration. Here, we demonstrate the preparation of structurally colored materials with extraordinarily high heat resistance of coloration, up to 900 °C. Several metal oxides, i.e., calcium manganese-based oxide (CCMO), chromium-iron-cobalt-nickel oxide (CFCNO), and lanthanum manganite (LMO), are synthesized and employed as black additives for structurally colored coatings prepared by the electrophoretic deposition of spherical silica particles. When CCMO is used as a black additive, the coloration heat resistance of the film is stable up to 700 °C. On the other hand, the films maintain vivid structural colors after exposure to 900 °C temperatures when CFCNO and LMO are employed as black additives. On the basis of this finding, high heat resistance of structural colors requires both heat resistance of the black additives and nonreactivity with the components of the spherical particles used for colloidal arrays.

Theranostic Agent Combining Fullerene Nanocrystals and Gold Nanoparticles for Photoacoustic Imaging and Photothermal Therapy.

Developing photoactivatable theranostic platforms with integrated functionalities of biocompatibility, targeting, imaging contrast, and therapy is a promising approach for cancer diagnosis and therapy. Here, we report a theranostic agent based on a hybrid nanoparticle comprising fullerene nanocrystals and gold nanoparticles (FGNPs) for photoacoustic imaging and photothermal therapy. Compared to gold nanoparticles and fullerene crystals, FGNPs exhibited stronger photoacoustic signals and photothermal heating characteristics by irradiating light with an optimal wavelength. Our studies demonstrated that FGNPs could kill cancer cells due to their photothermal heating characteristics in vitro. Moreover, FGNPs that are accumulated in tumor tissue via the enhanced permeation and retention effect can visualize tumor tissue due to their photoacoustic signal in tumor xenograft model mice. The theranostic agent with FGNPs shows promise for cancer therapy.

Understanding the Electrophoretic Deposition Accompanied by Electrochemical Reactions Toward Structurally Colored Bilayer Films.

Safe, low-cost structurally colored materials are alternative colorants to toxic inorganic pigments and organic dyes. Colloidal amorphous arrays are promising structurally colored materials because of their angle-independent colors. In this study, we focused on precise tuning of the chromaticity by preparing bilayer colloidal amorphous arrays through electrophoretic deposition (EPD). Systematic investigations with various EPD conditions clarified the contributions of each condition to the EPD process and the competing electrochemical reactions, which enabled us to prepare well-colored coatings. EPD films composed of colloidal amorphous array bilayers were successfully synthesized with controlled film thickness. Chromaticity of the films was found to be precisely controlled by the EPD duration. We believe that this understanding of the EPD process and its application to synthesis of structurally colored bilayer films will bring structurally colored materials closer to practical industrial use.

Interconnection of organic-inorganic hybrid nano-building blocks towards thermally robust mesoporous structures.

The use of organic-inorganic hybrid nanoparticles will enable a control of the characteristics of both the nanoparticles and constructed fine structures. In this study, we report the synthesis of acrylate-intercalated layered manganese, cobalt, and nickel hydroxide nanoparticles and their assembly into ordered mesoporous structures. Polymerization of the intercalated acrylates takes place by means of a radical initiator. The formed organic network improved the thermal stability of the layered hydroxides, which results in thermally robust mesoporous structures. Additionally, it is found that the polymerization can be initiated and progressed at 200 °C without any initiators for the layered nickel hydroxide system. This allows for the scalable solid-state thermal polymerization of intercalated acrylates and the formation of thermally robust hierarchically ordered meso/macroporous powders as well as mesoporous films. The electrochemical characterization reveals that the thermally robust mesoporous films having regulated mesopores allow for the effective diffusion of molecules/solvent compared with the films having collapsed mesoporous structures.

Size Effect of Hydroxide Nanobuilding Blocks and Nonionic Block Copolymer Templates on the Formation of Ordered Mesoporous Structures.

The use of precrystallized nanoparticles as nanobuilding blocks (NBBs) is a promising way to obtain mesoporous materials with crystalline walls. In this study, the size effects of both hydroxide NBBs and nonionic block copolymer (BCP) templates on the formation of ordered mesostructures are investigated. The diameter of layered nickel hydroxide NBBs was controlled at the sub-2 nm scale by an epoxide-mediated alkalinization process. Commercially available nonionic BCPs (gyration radii in the range of 11.9-43.9 Å) were used. Mesoperiodic structures were formed by the evaporation-induced self-assembly process. A proper size combination of hydroxide NBBs, smaller than 12.5 Å, and BCPs, larger than 19.9 Å, is shown to be necessary to form ordered mesostructures.

Magnetically Navigated Protein Transduction In Vivo using Iron Oxide-Nanogel Chaperone Hybrid.

Systems for "protein transduction," intracellular delivery of functional proteins, are needed to address deliverability challenges of protein therapeutics. However, in vivo protein transduction remains challenging because of instability in serum, extracellular protease digestion and rapid excretion from the bloodstream. Here, a magnetically guided in vivo protein transduction using magnetic nanogel chaperone (MC) composed of iron oxide nanoparticles and a polysaccharide nanogel, a protein carrier inspired by "catch and release" mechanisms of molecular chaperones is demonstrated. The MC system enables efficient delivery of anti-cancer proteins, saporin and RNaseA, into cultured tumor lines and inhibits cell proliferation, mainly via apoptosis. Magnetic in vivo protein transduction via intravenous whole body administration is demonstrated in a fibrosarcoma model. By in vivo optical imaging, MC accumulated in tumor tissues under magnetic field three times more than without irradiation. With subcutaneous injection, saporin is delivered by MC to the cytoplasm in magnetically targeted tissues. In an oral cancer model, MC-delivered magnetically targeted saporin decreased tumor volume without significant body weight changes and no regrowth of tumor at 3 months after complete regression. Protein transduction with MC shows promise for cancer therapeutics and, potentially, for regenerative medicine and other biomedical applications.

Environmentally Benign Synthesis and Color Tuning of Strontium-Tantalum Perovskite Oxynitride and Its Solid Solutions.

A facile method was successfully developed to prepare strontium-tantalum perovskite oxynitride, SrTaO2N, and its solid solutions. Urea was employed as a solid nitriding agent to eliminate the use of toxic NH3 gas. In addition, utilization of sol-gel-derived Ta2O5 gel as a Ta precursor allowed for completion of nitridation within a shorter period and at a lower calcination temperature compared with the conventional ammonolysis process. Optimization of the reaction conditions, such as the urea content, allowed for the production of solid solutions of SrTaO2N and Sr1.4Ta0.6O2.9. The products exhibited optical absorption and chromatic colors because of the narrower band gaps of oxynitrides compared with those of oxides. The O/N ratios of the solid solutions were easily adjusted by varying the amount of urea in the mixture of precursors. As a result, the colors of the products ranged from yellow to brown. The nitridation process and products developed in this study are interesting environmentally benign alternatives to conventional inorganic pigments.

Robust Structurally Colored Coatings Composed of Colloidal Arrays Prepared by the Cathodic Electrophoretic Deposition Method with Metal Cation Additives.

Structurally colored coatings composed of colloidal arrays of monodisperse spherical particles have attracted great attention owing to their versatile advantages, such as low cost, resistance to fading, and low impacts on the environment and human health. However, the weak mechanical stability is considered to be a major obstacle for their practical applications as colorants. Although several approaches based on the addition of polymer additives to enhance the adhesion of particles have been reported, the challenge remains to develop a strategy for the preparation of structurally colored coatings with extremely high robustness using a simple process. Here, we have developed a novel approach to fabricate robust structurally colored coatings by cathodic electrophoretic deposition. The addition of a metal salt, i.e., Mg(NO3)2, to the coating dispersion allows SiO2 particles to have a positive charge, which enables the electrophoresis of SiO2 particles toward the cathode. At the cathode, Mg(OH)2 codeposits with SiO2 particles because OH- ions are generated by the decomposition of dissolved oxygen and NO3- ions. The mechanical stability of the colloidal arrays obtained by this process is remarkably improved because Mg(OH)2 facilitates the adhesion of the particles and substrates. The brilliant structural color is maintained even after several cycles of the sandpaper abrasion test. We have also demonstrated the coating on a stainless steel fork. This demonstration reveals that our approach enables a homogeneous coating on a complicated surface. Furthermore, the high durability of the coating is clarified because the coating did not peel off even when the fork was stuck into a plastic eraser. Therefore, the coating technique developed here will provide an effective method for the pervasive application of the structural color as a colorant.

Magnetically Navigated Intracellular Delivery of Extracellular Vesicles Using Amphiphilic Nanogels.

Various cells in vivo secrete exosomes consisting of lipid bilayers. They carry mRNAs and miRNAs capable of controlling cellular functions and can be used as drug delivery system nanocarriers. There is the current need to further improve the efficiency of exosome uptake into target cells. In this study, we prepared a hybrid of exosomes and magnetic nanoparticles, which could be guided to target cells by a magnetic field for efficient uptake. Magnetic nanogels were prepared and hybridized to fluorescently labeled exosomes isolated from PC12 cells. By applying a magnetic field to a hybrid with magnetic nanogel, exosomes were efficiently transferred into target cells as confirmed by confocal laser microscopy. Finally, we found that differentiation of adipose-derived stem cells to neuron-like cells was enhanced by magnetic induction of the exosome-magnetic nanogel hybrid, indicating maintenance of the intrinsic functions of the exosomes in the differentiation of adipose-derived stem cells.

Mechanistic Insight on the Formation of GaN:ZnO Solid Solution from Zn-Ga Layered Double Hydroxide Using Urea as the Nitriding Agent.

A solid solution of GaN and ZnO (GaN:ZnO) is promising as a photocatalyst for visible-light-driven overall water splitting to produce H2. However, several obstacles still exist in the conventional preparation procedure of GaN:ZnO. For example, the atomic distributions of Zn and Ga are nonuniform in GaN:ZnO when a mixture of the metal oxides, i.e. Ga2O3 and ZnO, is used as a precursor. In addition, GaN:ZnO is generally prepared under a harmful NH3 flow for long durations at high temperatures. Here, a facile synthesis of GaN:ZnO with homogeneous atomic composition via a simple and safe procedure is reported. A layered double hydroxide (LDH) containing Zn2+ and Ga3+ was used to increase the uniformity of the atomic distributions of Zn and Ga in GaN:ZnO. We employed urea as a nitriding agent instead of gaseous NH3 to increase the safety of the reaction. Through the optimization of reaction conditions such as heat treatment temperature and content of urea, single-phase GaN:ZnO was successfully obtained. In addition, the nitridation mechanism using urea was investigated in detail. NH3 released from the thermal decomposition of urea did not directly nitride the LDH precursor. X-ray absorption and infrared  spectroscopies revealed that Zn(CN2)-like intermediate species were generated at the middle temperature range and Ga-N bonds formed at high temperature along with dissociation of CO and CO2.

Preparation of pH-Responsive Hollow Capsules via Layer-by-Layer Assembly of Exfoliated Layered Double Hydroxide Nanosheets and Polyelectrolytes.

pH-Responsive smart capsules were developed by the layer-by-layer assembly with a colloidtemplating technique. Polystyrene (PS) particles were employed as core templates. Acid-soluble inorganic nanosheets were prepared from Mg-Al layered double hydroxide (LDH) by an exfoliation technique. LDH nanosheets and anionic polyelectrolytes were alternatively deposited on PS core particles by the layer-by-layer assembly using electrostatic interaction. Hollow capsules were obtained by the removal of the PS core particles. The hollow capsules obtained thus were collapsed at acidic conditions by dissolution of LDH nanosheets in the hollow shells. The dissolution rate, i.e., the responsiveness of capsule, is tunable according to the strength of acids.

Structurally colored coating films with tunable iridescence fabricated via cathodic electrophoretic deposition of silica particles.

In recent years, colloidal arrays of submicrometer-sized monodisperse particles used as structurally colored coatings have drawn great attention due to their non-bleaching properties and low impact on human health and the environment. In this paper, structurally colored coating films were fabricated using monodisperse SiO2 particles via the cathodic electrophoretic deposition (EPD) technique. The addition of a strong polycation, poly(diallyldimethylammonium chloride) (PDDA), enables the cathodic EPD of SiO2 particles and carbon black (CB) additives. Optimizing the quantities of PDDA and CB results in the appearance of vivid structural color from the coating films. The arrangement of the particle array is controllable by varying the pH of the water added to the coating sols for EPD. Structurally colored coating films with and without iridescence, i.e., angular dependence, can be fabricated on demand by a simple operation of the EPD process. In addition, the coating film prepared by cathodic EPD displayed high abrasion resistance because PDDA acts not only as a charge control agent but also as a binder.

ZrO2 Nanocrystals As Catalyst for Synthesis of Dimethylcarbonate from Methanol and Carbon Dioxide: Catalytic Activity and Elucidation of Active Sites.

The catalytic activity of zirconium oxide (ZrO2) nanocrystals for the reaction of carbon dioxide (CO2) with methanol to form dimethylcarbonate (DMC) was investigated. ZrO2 nanocrystals prepared by hydrothermal synthesis at various temperatures were compared. The size of the ZrO2 nanocrystals monotonically increased with the hydrothermal temperature, according to specific surface area, transmission electron microscope measurements, and their X-ray diffraction peak widths. The ZrO2 nanocrystals prepared by hydrothermal synthesis were found to exhibit high catalytic activity owing to their high surface area and catalytically active surfaces arising from their high crystallinity. Next, adsorbed species generated from CO2 on the ZrO2 surfaces were measured using CO2 temperature-programmed desorption (TPD) and in situ FT-IR spectroscopy. The results confirmed the presence of several kinds of adsorbed species including bidentate bicarbonate (b-HCO3-), bidentate carbonate (b-CO32-), and monodentate carbonate (m-CO32-). The relationship between the amounts of these surface species and the catalytic activity of the ZrO2 was investigated for the first time. The amount of the bidentate species (b-HCO3- and b-CO32-) was found to correlate well with the catalytic activity, demonstrating that the surface sites that afford these species contribute to the catalytic activity for this reaction.

Magnetically Guided Protein Transduction by Hybrid Nanogel Chaperones with Iron Oxide Nanoparticles.

Protein pharmaceuticals show great therapeutic promise, but effective intracellular delivery remains challenging. To address the need for efficient protein transduction systems, we used a magnetic nanogel chaperone (MC): a hybrid of a polysaccharide nanogel, a protein carrier with molecular chaperone-like properties, and iron oxide nanoparticles, enabling magnetically guided delivery. The MC complexed with model proteins, such as BSA and insulin, and was not cytotoxic. Cargo proteins were delivered to the target HeLa cell cytosol using a magnetic field to promote movement of the protein complex toward the cells. Delivery was confirmed by fluorescence microscopy and flow cytometry. Delivered ß-galactosidase, inactive within the MC complex, became enzymatically active within cells to convert a prodrug. Thus, cargo proteins were released from MC complexes through exchange interactions with cytosolic proteins. The MC is a promising tool for realizing the therapeutic potential of proteins.