Silica Functionalized by Bifunctional Dendrimers: Hybrid Nanomaterials for Trapping CO2

A water-soluble polyphosphorhydrazone Janus dendrimer built by "click" chemistry as support for Ru-complexes in catalysis

The field of supported catalysis has experienced increased attention with respect to the development of novel architectures for immobilizing catalytic species, aiming to maintain or enhance their activity while facilitating the easy recovery and reuse of the active moiety. Dendrimers have been identified as promising candidates capable of imparting such properties to catalysts through selective functionalization. The present study details the synthesis of two polyphosphorhydrazone (PPH) dendrons, each incorporating azide or acetylene groups at the core for subsequent coupling through "click" triazole chemistry. Employing this methodology, a novel PPH Janus dendrimer was successfully synthesized, featuring ten polyethylene glycol (PEG) chains on one side of the structure and ten Ru(p-cymene) derivatives on the other. This design was intended to confer dual properties, influencing solubility modulation, and allowing the presence of active catalytic moieties. The synthesized dendrimer underwent testing in the isomerization of allyl alcohols in organic solvents and biphasic solvent mixtures. The results demonstrated a positive dendritic effect compared with model monometallic and bimetallic species, providing a proof-of-concept for the first PPH Janus dendrimer with tested applications in catalysis.

Strategies for the Preparation of Phosphorus Janus Dendrimers and Their Properties

Dendrimers, being highly branched monodispersed macromolecules, predominantly exhibit identical terminal functionalities within their structural framework. Nonetheless, there are instances where the presence of two distinct surface functionalities becomes advantageous for the fulfilment of specific properties. To achieve this objective, one approach involves implementing Janus dendrimers, consisting of two dendrimeric wedges terminated by dissimilar functionalities. The prevalent method for creating these structures involves the synthesis of dendrons that possess a core functionality that complements that of a second dendron, facilitating their coupling to generate the desired dendrimers. In this comprehensive review, various techniques employed in the fabrication of phosphorus-based Janus dendrimers are elucidated, displaying the different coupling methodologies employed between the two units. The advantages of phosphorus dendrimers over classic dendrimers will be shown, as the presence of at least one phosphorus atom in each generation allows for the easy monitoring of reactions and the confirmation of purity through a simple technique such as ³¹P NMR, as these structures typically exhibit easily interpretable patterns.

Properties and Bioapplications of Amphiphilic Janus Dendrimers: A Review

Amphiphilic Janus dendrimers are arrangements containing both hydrophilic and hydrophobic units, capable of forming ordered aggregates by intermolecular noncovalent interactions between the dendrimer units. Compared to conventional dendrimers, these molecular self-assemblies possess particular and effective attributes i.e., the presence of different terminal groups, essential to design new elaborated materials. The present review will focus on the pharmaceutical and biomedical application of amphiphilic Janus dendrimers. Important information for the development of novel optimized pharmaceutical formulations, such as structural classification, synthetic pathways, properties and applications, will offer the complete characterization of this type of Janus dendrimers. This work will constitute an up-to-date background for dendrimer specialists involved in designing amphiphilic Janus dendrimer-based nanomaterials for future innovations in this promising field.

Specific Bifunctionalization on the Surface of Phosphorus Dendrimers Syntheses and Properties

Dendrimers are highly branched macromolecules possessing, in most cases, identical terminal functions. However, it is sometimes desirable to have two types of surface functions in order to fulfil specific properties. The stochastic functionalization is frequently used for such purposes, but the presence of an uncontrolled number of each type of terminal function, albeit acceptable for research purposes, has no practical use. Thus, it is highly desirable to find strategies suitable for the precise grafting of two different functional groups on the surface of dendrimers. The easiest way, and the most widely used, consists in using a bifunctional monomer to be grafted to all of the surface functions of the dendrimers. Two other strategies are known but are rarely used: the modification of an existing function, to generate two functions, and the sequential grafting of one function then of a second function. The three methods are illustrated in this review with polyphosphorhydrazone (PPH) dendrimers, together with their properties as catalysts, for materials, and as biological tools.

AB5 Derivatives of Cyclotriphosphazene for the Synthesis of Dendrons and Their Applications

AB5 compounds issued from the reactivity of hexachlorocyclotriphosphazene are relatively easy to obtain using two ways: either first the reaction of one chloride with one reagent, followed by the reaction of the five remaining Cl with another reagent, or first the reaction of five chlorides with one reagent, followed by the reaction of the single remaining Cl with another reagent. This particular property led to the use of such compounds as core for the synthesis of dendrons (dendritic wedges), using the five functions for growing the dendritic branches. The single function can be used for the synthesis of diverse types of dendrimers (onion peel, dumbbell-shape, Janus), for covalent or non-covalent grafting to solid surfaces, providing nanomaterials, for grafting a fluorophore, especially for studying biological mechanisms, or for self-associations to get micelles. All these properties are reviewed in this paper.

Hybrid phosphorus–viologen dendrimers as new soft nanoparticles: design and properties

Design of new families of dendritic soft nanoparticles constituted of phosphorus, viologen and carbosilane fragments and their properties as nanomaterials and applications in biology.

Dendritic Polymers as Promising Additives for the Manufacturing of Hybrid Organoceramic Nanocomposites with Ameliorated Properties Suitable for an Extensive Diversity of Applications

As the field of nanoscience is rapidly evolving, interest in novel, upgraded nanomaterials with combinatory features is also inevitably increasing. Hybrid composites, offer simple, budget-conscious and environmental-friendly solutions that can cater multiple needs at the same time and be applicable in many nanotechnology-related and interdisciplinary studies. The physicochemical idiocrasies of dendritic polymers have inspired their implementation as sorbents, active ingredient carriers and templates for complex composites. Ceramics are distinguished for their mechanical superiority and absorption potential that render them ideal substrates for separation and catalysis technologies. The integration of dendritic compounds to these inorganic hosts can be achieved through chemical attachment of the organic moiety onto functionalized surfaces, impregnation and absorption inside the pores, conventional sol-gel reactions or via biomimetic mediation of dendritic matrices, inducing the formation of usually spherical hybrid nanoparticles. Alternatively, dendritic polymers can propagate from ceramic scaffolds. All these variants are covered in detail. Optimization techniques as well as established and prospected applications are also presented.

Improved carbon dioxide storage over clay-supported perhydroxylated glucodendrimer

Low-cost biosourced hybrid microporous adsorbents with improved affinity towards carbon dioxyde (CO2) were prepared through the incorporation of various amounts of glucosylated dendrimer into bentonite- and montmorillonite-rich composite materials. Characterization by nitrogen adsorption–desorption isotherms, surface specific and pore size analyses (BET and BJH), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed changes in the interlayer spacing and textural structure of the materials. Thermal programmed desorption measurements (TPD) showed significant improvements of the retention capacity of CO2 (CRC) and water (WRC). This was explained in terms of enhancement of both surface basicity and hydrophilic character due to the incorporation of terminal polyhydroxyl groups. The CRC was found to vary according to the previous saturation time with CO2 and the carrier gas throughput. CO2 was totally released upon temperature not exceeding 80 °C or even at room temperature upon strong carrier gas stream, thus providing evidence that CO2 capture involves almost exclusively physical interaction with the OH groups of the dendrimer. This result opens promising prospects for the reversible capture of carbon dioxide with easy release without thermal regeneration, more particularly when extending this concept to biosourced dendrimers.

Cyclotriphosphazene, an old compound applied to the synthesis of smart dendrimers with tailored properties

The versatile reactivity of hexachlorocyclotriphosphazene (N3P3Cl6) has been developed for the synthesis of specifically engineered dendrimers. Dendrimers are hyperbranched macromolecules built by concentric layers constituted of associated monomeric units. Many of the properties of dendrimers depend on the type of their surface (terminal) functions, which are generally all identical. For some specific purposes, it is desirable to have one function that is different at the level of the core. Hexachlorocyclotriphosphazene offers the possibility to differentiate the reactivity of one (or more) Cl from the others, for producing specifically engineered dendritic tools. These specific reactions on N3P3Cl6 have produced highly dense dendrimers, Janus dendrimers (two faces), tools for functionalizing materials, with uses as catalysts, as chemical sensors, for trapping CO2, for the culture of cells, or for imaging biological events. These properties will be emphasized in this review.