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.

Dithienylethene-Based Photoswitchable Phosphines for the Palladium-Catalyzed Stille Coupling Reaction.

Homogeneous transition metal catalysis is a constantly developing field in chemical sciences. A growing interest in this area is photoswitchable catalysis, which pursues in situ modulation of catalyst activity through noninvasive light irradiation. Phosphorus ligands are excellent targets to accomplish this goal by introducing photoswitchable moieties; however, only a limited number of examples have been reported so far. In this work, we have developed a series of palladium complexes capable of catalyzing the Stille coupling reaction that contain photoisomerizable phosphine ligands based on dithienylethene switches. Incorporation of electron-withdrawing substituents into these dithienylethene moieties allows variation of the electron density on the phosphorus atom of the ligands upon light irradiation, which in turn leads to a modulation of the catalytic properties of the formed complexes and their activity in a model Stille coupling reaction. These results are supported by theoretical computations, which show that the energy barriers for the rate-determining steps of the catalytic cycle decrease when the photoswitchable phosphine ligands are converted to their closed state.

Amplified photomodulation of a bis(dithienylethene)-substituted phosphine.

Phosphine ligands play a crucial role in homogeneous catalysis, allowing fine-tuning of the catalytic activity of various metals by modifying their structure. An ultimate challenge in this field is to reach controlled modulation of catalysis in situ, for which the development of phosphines capable of photoswitching between states with differential electronic properties has been proposed. To magnify this light-induced behavior, in this work we describe a novel phosphine ligand incorporating two dithienylethene photoswitchable moieties tethered to the same phosphorus atom. Double photoisomerization was observed for this ligand, which remains unhindered upon gold(I) complexation. As a result, the preparation of a fully ring-closed phosphine isomer was accomplished, for which amplified variation of phosphorus electron density was verified both experimentally and by computational calculations. Accordingly, the presented molecular design based on multiphotochromic phosphines could open new ways for preparing enhanced photoswitchable catalytic systems.

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.

Spiropyran-based chromic hydrogels for CO2 absorption and detection.

By enabling rapid, cost-effective, user-friendly and in situ detection of carbon dioxide, colorimetric CO2 sensors are of relevance for a variety of fields. However, it still remains a challenge the development of optical chemosensors for CO2 that combine high sensitivity, selectivity and reusability with facile integration into solid materials. Herein we pursued this goal by preparing hydrogels functionalized with spiropyrans, a well-known class of molecular switches that undergo different color changes upon application of light and acid stimuli. By varying the nature of the substituents of the spiropyran core, different acidochromic responses are obtained in aqueous media that allow discriminating CO2 from other acid gases (e.g., HCl). Interestingly, this behavior can be transferred to functional solid materials by synthesizing polymerizable spiropyran derivatives, which are used to prepare hydrogels. These materials preserve the acidochromic properties of the incorporated spiropyrans, thus leading to selective, reversible and quantifiable color changes upon exposure to different CO2 amounts. In addition, CO2 desorption and, therefore, recovery of the initial state of the chemosensor is favored by irradiation with visible light. This makes spiropyran-based chromic hydrogels promising systems for the colorimetric monitorization of carbon dioxide in a diversity of applications.

Biotinylated Phosphorus Dendrimers as Control Line in Nucleic Acid Lateral Flow Tests.

Lateral flow assays (LFA) are an affordable, easy-to-use, qualitative rapid test for clinical diagnosis in nonlaboratory environments and low-resource facilities. The control line of these tests is very important to provide a valid result, confirming that the platform operates correctly. A clear, nondiffused line is desirable. The number of colored nanoparticles that reach the control line in a positive test can be very small, and they should all be trapped efficiently by the molecules adsorbed there. In this work, we proposed the use of robust biotinylated dendrimers of two different generations as signal amplifiers in control lines of LFA, able to react with streptavidin-modified gold nanoparticles. Besides the synthesis and characterization, the analytical performance as control lines will be studied, and their response will be compared with other commercially available biotinylated molecules. Finally, the utility of the dendrimer implemented in a NALF (Nucleic Acid Lateral Flow) strip was also demonstrated for detection of the amplicons obtained by double-tagging PCR (polymerase chain reaction) for the detection of E. coli as a model of foodborne pathogen.

Triarylmethane Dyes for Artificial Repellent Cotton Fibers.

Families of new hydrophobic and/or oleophobic triarylmethane dyes possessing long hydrocarbon or polyfluorinated chains have been prepared. When covalently grafted on to cotton fabric, these dyes give rise to a new type of colored superhydrophobic fibers.

Supermolecular columnar liquid-crystalline phosphorus dendrimers decorated with sulfonamide derivatives.

A series of supermolecular liquid crystals has been synthesized by combining phosphorus dendrimers of the zero, first, and fourth generations with sulfonamide derivatives, thus generating dendromesogens bearing 6, 12, and 96 mesogenic units on their surfaces. The relevant reactions could be monitored by (1) H, (19) F, and (31) P{(1) H} NMR spectroscopies. The thermal and mesomorphic properties of the products have been studied by optical microscopy, differential scanning calorimetry, and X-ray diffraction. All of the new macromolecules prepared in this work have been found to show mesomorphic properties over a wide temperature range; moreover, for all of the compounds, the columnar mesophases observed were maintained or vitrified at room temperature. On increasing the generation of these dendromesogens, mesophases appear at lower temperatures and remain stable over a wider temperature interval. In all cases, on the basis of X-ray analysis, a cylindrical symmetry of the molecules can be proposed to promote the supramolecular columnar arrangement observed in the mesophases. In this type of model, the height of the dendrimer clearly increases with increasing dendrimer generation, whereas its cross- sectional area increases only slightly, probably due to compression of the highly hyperbranched structures as a consequence of their progressive steric constraints. The mesomorphic arrangement is governed by the peripheral sulfonamide units.

An alternative to the classical α-arylation: the transfer of an intact 2-iodoaryl from ArI(O2CCF3)2.

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

Photochemical activation of extremely weak nucleophiles: highly fluorinated urethanes and polyurethanes from polyfluoro alcohols.

An efficient and environmentally friendly photoreaction between phenyl isocyanate or pentafluorophenyl isocyanate and polyfluorinated alcohols and diols is described for the first time. New highly fluorinated urethanes and diurethanes, derived from aromatic isocyanates, are produced in good yields in a photoreaction that is apparently governed by the acidic properties of the polyfluoro alcohols and diols. The wettability properties of the new polyfluorinated diurethanes have been tested, some of them showing significantly high values of hydrophobicity and oleophobicity. This new photoreaction has also been tested in the production of a model polyfluorinated polyurethane, establishing the influence of the irradiation power in the outcome of the process, and directly achieving a molecular weight distribution corresponding to a number-average DP(n) = 12 and a highest DP(n) = 20 after 4 h of irradiation (DP(n): "number-average degree of polymerization").

Synthesis and structural characterization of a dendrimer model compound based on a cyclotriphosphazene core with TEMPO radicals as substituents.

The synthesis of the 3Gc0T zero generation dendrimer with a cyclotriphosphazene core functionalized with nitroxyl radicals in its six branches has been performed. The radical units have been used as probes to determine the orientation of the six branches in solution experimentally by Electron Paramagnetic Resonance (EPR) spectroscopy compared with the structure obtained in the solid state by X-ray diffraction. The orientation of the dendrimer branches is the same in solution as in the solid state.

Highly hydrophobic polyfluorinated azo dyes grafted on surfaces.

Artificial hydrophobic surfaces have a great potential in a wide range of industrial applications owing to their self-cleaning, anti-fogging and anti-biofouling properties. A family of polyfluorinated reactive azo dyes has been prepared and some of them easily modified and grafted on cotton fabric and glass surfaces obtaining new coloured hydrophobic materials.

Dendritic structures within dendritic structures: dendrimer-induced formation and self-assembly of nanoparticle networks.

15-Membered tri-olefinic azamacrocycles as end-groups of phosphorus-containing dendrimers from generation 1 to 4 are used for obtaining Pt nanoparticles in mild conditions; remarkable and unprecedented branched supramolecular assemblies composed of dendrimers and coalesced Pt nanoparticles are obtained, which become larger for higher dendrimer generations, affording for the first time a very unique organization of organic dendritic structures interweaved with inorganic dendritic structures.

Phosphine-free perfluoro-tagged palladium nanoparticles supported on fluorous silica gel: application to the Heck reaction.

The immobilization of phosphine-free perfluoro-tagged palladium nanoparticles Pd-1 on fluorous silica gel (FSG) and their utilization in the Heck reaction have been investigated. High yields of vinylic substitution products have been obtained. Recycling studies have shown that the solid-supported palladium catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.

Synthesis and photochemical behavior of phosphorus dendrimers containing azobenzene units within the branches and/or on the surface.

We describe the synthesis of three series of phosphorus-containing dendrimers having azobenzene derivatives specifically placed at some generations in the interior and/or on the surface. The largest compound obtained possesses 48 azobenzene groups on the surface. Irradiation at 350 nm induces isomerization of the azobenzene groups from the E form to the Z form, whatever their location. The thermal back-isomerization to the E form in the dark at room temperature was observed in all cases. The kinetics of this Z-->E back-isomerization was studied in several cases; the rate is not dependent on the number of azobenzene units or of the generation, when the azobenzene groups are linked to the surface of the dendrimer. A different behavior was observed when the azobenzene groups were located within the framework of the dendrimer.