Highly stable layered double hydroxide colloids: a direct aqueous synthesis route from hybrid polyion complex micelles

Vapor-Induced Assembly of a Platinum(II) Complex Loaded on Layered Double Hydroxide Nanoparticles

Controlled self-assembly of PtII complexes is key to the development of optical and stimuli-responsive materials, but designing and precisely controlling them is still difficult owing to weak intermolecular interactions. Herein, we report the successful water-vapor-induced assembly of an anionic PtII complex [Pt(CN)2 (ppy)]- (Hppy=2-phenylpyridine) electrostatically loaded onto cationically charged layered double hydroxide (LDH) nanoparticles consisting of Mg2+ and Al3+ ions. When the PtII complexes were densely loaded onto the LDH nanoparticles, the assembly was maintained, even in dilute aqueous media. In the case of sparse loading, the PtII complexes were loaded discretely in the dry state; however, when water vapor was adsorbed, the increased mobility of the PtII complexes led to their assembly on the LDH nanoparticles. The presence of water vapor led to a drastic change in luminescence from green to orange.

Advanced nanopesticides: Advantage and action mechanisms

The use of various chemical substances to control pests, diseases, and weeds in the field is a necessary part of the agricultural development process in every country. While the application of pesticides can improve the quality and yield of crops, plant resistance and the harm caused by pesticide residues to the environment and humans have led to the search for greener and safer pesticide formulations to improve the current situation. In recent years, nanopesticides (NPts) have shown great potential in agriculture due to their high efficiency, low toxicity, targeting, resistance, and controlled slow release demonstrated in the experimental stage. Commonly used approaches to prepare NPts include the use of nanoscale metal materials as active ingredients (AI) (ingredients that can play a role in insecticide, sterilization and weeding) or the construction of carriers based on commonly used pesticides to make them stable in nano-sized form. This paper systematically summarizes the advantages and effects of NPts over conventional pesticides, analyzes the formation and functions of NPts in terms of structure, AI, and additives, and describes the mechanism of action of NPts. Despite the feasibility of NPts use, there is not enough comprehensive research on NPts, which must be supplemented by more experiments in terms of biotoxicology and ecological effects to provide strong support for NPts application.

Iron-based hybrid polyionic complexes as chemical reservoirs for the pH-triggered synthesis of Prussian blue nanoparticles

HYPOTHESIS

Hybrid polyion complexes (HPICs) obtained from the complexation in aqueous solution of a double hydrophilic block copolymer and metal ions can act as efficient precursors for the controlled synthesis of nanoparticles. In particular, the possibility to control the availability of metal ions by playing on the pH conditions is of special interest to obtain nanoparticles with controlled size and composition.

EXPERIMENTS

HPICs based on Fe³⁺ ions were used to initiate the formation of Prussian blue (PB) nanoparticles in presence of potassium ferrocyanide in reaction media with varying pH values.

FINDINGS

Complexed Fe³⁺ ions within HPICs can be easily released by adjusting the pH value either through the addition of a base/acid or by using a merocyanine photoacid. This allows to modulate the reactivity of Fe³⁺ ions with potassium ferrocyanide present in solution. As a result, PB nanoparticles with different structures (core, core-shell), composition and controlled size are obtained.

Double-hydrophilic block copolymer-metal ion associations: Structures, properties and applications

Hybrid polyionic complexes (HPICs), constructed from double-hydrophilic block copolymers and metal ions, have been largely developed with increasing interest in the past decade in the fields of catalysis, materials science and biological applications. The chemical natures of both blocks are very versatile, but one block should be able to interact with ions, and the second one should be neutral. Many metals have been used to form HPICs, which have, in their simplest architectural form, a core-shell structure of a few tens of nanometers in radius with an external shell made of the neutral block of the copolymer. In this review, we focus our discussion on the stability, shape, size and inner structure of these hybrid micelles. We then describe the most recent applications of HPICs, as reported in the literature, and point out the current challenges, missing structural information and future perspectives for this class of organized structures.

Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH

In the United Kingdom, decommissioning of legacy spent fuel storage facilities involves the retrieval of radioactive sludges that have formed as a result of corrosion of Magnox nuclear fuel. Retrieval of sludges may re-suspend a colloidal fraction of the sludge, thereby potentially enhancing the mobility of radionuclides including uranium. The colloidal properties of the layered double hydroxide (LDH) phase hydrotalcite, a key product of Magnox fuel corrosion, and its interactions with U(VI) are of interest. This is because colloidal hydrotalcite is a potential transport vector for U(VI) under the neutral-to-alkaline conditions characteristic of the legacy storage facilities and other nuclear decommissioning scenarios. Here, a multi-technique approach was used to investigate the colloidal stability of hydrotalcite and the U(VI) sorption mechanism(s) across pH 7-11.5 and with variable U(VI) surface loadings (0.01-1 wt %). Overall, hydrotalcite was found to form stable colloidal suspensions between pH 7 and 11.5, with some evidence for Mg²⁺ leaching from hydrotalcite colloids at pH ≤ 9. For systems with U present, >98% of U(VI) was removed from the solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentrations. Under alkaline conditions, U(VI) surface precipitates formed on the colloidal hydrotalcite nanoparticle surface. Under more circumneutral conditions, Mg²⁺ leaching from hydrotalcite and more facile exchange of interlayer carbonate with the surrounding solution led to the formation of uranyl carbonate species (e.g., Mg(UO₂(CO₃)₃)^2-_(aq)). Both X-ray absorption spectroscopy (XAS) and luminescence analysis confirmed that these negatively charged species sorbed as both outer- and inner-sphere tertiary complexes on the hydrotalcite surface. These results demonstrate that hydrotalcite can form pseudo-colloids with U(VI) under a wide range of pH conditions and have clear implications for understanding the uranium behavior in environments where hydrotalcite and other LDHs may be present.

Autofluorescence-Free In Vivo Imaging Using Polymer-Stabilized Nd3+-Doped YAG Nanocrystals

Neodymium-doped yttrium aluminum garnet (YAG:Nd³⁺) has been widely developed during roughly the past 60 years and has been an outstanding fluorescent material. It has been considered as the gold standard among multipurpose solid-state lasers. Yet, the successful downsizing of this system into the nanoregimen has been elusive, so far. Indeed, the synthesis of a garnet structure at the nanoscale, with enough crystalline quality for optical applications, was found to be quite challenging. Here, we present an improved solvothermal synthesis method producing YAG:Nd³⁺ nanocrystals of remarkably good structural quality. Adequate surface functionalization using asymmetric double-hydrophilic block copolymers, constituted of a metal-binding block and a neutral water-soluble block, provides stabilized YAG:Nd³⁺ nanocrystals with long-term colloidal stability in aqueous suspensions. These newly stabilized nanoprobes offer spectroscopic quality (long lifetimes, narrow emission lines, and large Stokes shifts) close to that of bulk YAG:Nd³⁺. The narrow emission lines of YAG:Nd³⁺ nanocrystals are exploited by differential infrared fluorescence imaging, thus achieving an autofluorescence-free in vivo readout. In addition, nanothermometry measurements, based on the ratiometric fluorescence of the stabilized YAG:Nd³⁺ nanocrystals, are demonstrated. The progress here reported paves the way for the implementation of this new stabilized YAG:Nd³⁺ system in the preclinical arena.

On Complex Coacervate Core Micelles: Structure-Function Perspectives

The co-assembly of ionic-neutral block copolymers with oppositely charged species produces nanometric colloidal complexes, known, among other names, as complex coacervates core micelles (C3Ms). C3Ms are of widespread interest in nanomedicine for controlled delivery and release, whilst research activity into other application areas, such as gelation, catalysis, nanoparticle synthesis, and sensing, is increasing. In this review, we discuss recent studies on the functional roles that C3Ms can fulfil in these and other fields, focusing on emerging structure-function relations and remaining knowledge gaps.

A Facile Way of Modifying Layered Double Hydroxide Nanoparticles with Targeting Ligand-Conjugated Albumin for Enhanced Delivery to Brain Tumour Cells

Active targeting of nanoparticles (NPs) for cancer treatment has attracted increasing interest in the past decades. Various ligand modification strategies have been used to enhance the targeting of NPs to the tumor site. However, how to reproducibly fabricate diverse targeting NPs with narrowly changeable biophysiochemical properties remains as a major challenge. In this study, layered double hydroxide (LDH) NPs were modified as a target delivery system. Two brain tumor targeting ligands, i.e., angiopep-2 and rabies virus glycoprotein, were conjugated to the LDH NPs via an intermatrix protein moiety, bovine serum albumin (BSA), simultaneously endowing the LDHs with excellent colloidal stability and targeting capability. The ligands were first covalently linked with BSA through the heterobifunctional cross-linker sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate. Then, the ligand-linked BSA and pristine BSA were together coated onto the surface of LDHs through electrostatic interaction, followed by cross-linking with the cross-linker glutaraldehyde to immobilize these BSAs on the LDH surface. In this way, we are able to readily prepare colloidally stabilized tumor-targeted LDH NPs. The targeting efficacy of the ligand-conjugated LDH delivery system has been evidenced in the uptake by two neutral cells (U87 and N2a) compared to unmodified LDHs. This new approach provides a promising strategy for rational design and preparation of target nanoparticles as a selective and effective therapeutic treatment for brain tumors.

Design of latex-layered double hydroxide composites by tuning the aggregation in suspensions

Colloidal stability of polymeric latex particles was studied in the presence of oppositely charged layered double hydroxide (LDH) platelets of different interlayer anions. Adsorption of the LDH particles led to charge neutralization and to overcharging of the latex at appropriate concentrations. Mixing stable colloidal suspensions of individual particles results in rapid aggregation once the LDH adsorption neutralizes the negative charges of the polymer spheres, while stable suspensions were observed at high and low LDH doses. The governing interparticle interactions included repulsive electrical double layer forces as well as van der Waals and patch-charge attractions, whose strength depended on the amount of LDH particles adsorbed on the latex surface. The type of the LDH interlayer anions did not affect the colloidal stability of the samples. Structural investigation of the obtained latex-LDH composites revealed that the polymer spheres were completely coated with the inorganic platelets once their concentration was sufficiently high. These results are especially important for designing synthetic routes for hybrid systems in suspensions, where stable colloids are required for uniform film-formation and for the homogeneous distribution of the inorganic filler within the composite materials.

Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry

Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

First double hydrophilic graft copolymer bearing a poly(2-hydroxylethyl acrylate) backbone synthesized by sequential RAFT polymerization and SET-LRP

This article reports the first synthesis of well-defined double hydrophilic graft copolymers with a PHEA backbone, by the combination of RAFT polymerization, SET-LRP, and a grafting-from strategy.

Layered double hydroxide nanoparticles to enhance organ-specific targeting and the anti-proliferative effect of cisplatin

The role of nanoparticle charge in biodistribution is evaluated by modifying the external surface of layered double hydroxides with various charges and a fluorescent dye (Cy5.5) is doped to assess the biodistribution.