Catalytically active membrane-like devices: ionic liquid-hybrid organosilicas decorated with palladium nanoparticles

Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8–2.1 nm) Pd nanoparticles (Pd-NPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this “restricted” ionic environment. This suggests that IL-hybrid organosilica/Pd-NPs under multiphase conditions (“dynamic asymmetric mixture”) operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal rate-determining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase

Platinum-Triggered Bond-Cleavage of Pentynoyl Amide and N-Propargyl Handles for Drug-Activation.

The ability to create ways to control drug activation at specific tissues while sparing healthy tissues remains a major challenge. The administration of exogenous target-specific triggers offers the potential for traceless release of active drugs on tumor sites from antibody-drug conjugates (ADCs) and caged prodrugs. We have developed a metal-mediated bond-cleavage reaction that uses platinum complexes [K2PtCl4 or Cisplatin (CisPt)] for drug activation. Key to the success of the reaction is a water-promoted activation process that triggers the reactivity of the platinum complexes. Under these conditions, the decaging of pentynoyl tertiary amides and N-propargyls occurs rapidly in aqueous systems. In cells, the protected analogues of cytotoxic drugs 5-fluorouracil (5-FU) and monomethyl auristatin E (MMAE) are partially activated by nontoxic amounts of platinum salts. Additionally, a noninternalizing ADC built with a pentynoyl traceless linker that features a tertiary amide protected MMAE was also decaged in the presence of platinum salts for extracellular drug release in cancer cells. Finally, CisPt-mediated prodrug activation of a propargyl derivative of 5-FU was shown in a colorectal zebrafish xenograft model that led to significant reductions in tumor size. Overall, our results reveal a new metal-based cleavable reaction that expands the application of platinum complexes beyond those in catalysis and cancer therapy.EPSRC studentship for Benjamin Stenton

Indium-decorated Pd nanocubes degrade nitrate anions rapidly

Indium-decorated palladium nanoparticles (In-on-PdNPs) are active for room-temperature catalytic reduction of aqueous nitrate, where the active sites are metallic In atoms on the Pd surface. The PdNPs are pseudo-spherical in shape, and it is unclear if their faceted nature plays a role in nitrate reduction. We synthesized different-sized, cube-shaped NPs with differing In coverages (sc%), and studied the resultant In-on-Pd-nanocubes (NCs) for nitrate reduction. The NCs exhibited volcano-shape activity dependence on In sc%, with peak activity around 65–75 sc%. When rate constants were normalized to undercoordinated atoms (at edge + corners), the NCs exhibited near-identical maximum activity (20×-higher than In-on-PdNPs) at ρIn/Pd edge+corner ∼0.5 (∼5 In atoms per 10 edge and corner atoms). NCs with a higher In edge + corner density (ρIn/Pd edge+corner ∼1.5) were less active but did not generate NH4+ at nitrate conversions tested up to 36 %. Edge-decorated cubes may be the structural basis of improved bimetallic catalytic denitrification of water

Water soluble polymer–surfactant complexes-stabilized Pd(0) nanocatalysts: Characterization and structure–activity relationships in biphasic hydrogenation of alkenes and α,β-unsaturated ketones

International audienceA suitable approach to stabilize palladium nanoparticles in water as a green reaction medium for catalytic hydrogenation reactions is described. Supramolecular self-assemblies, obtained through the mixture of modified polyethyleneimines as amphiphilic polymers and water-soluble ammonium salts as surfactants, were used as efficient protective agents in the synthesis of Pd(0) nanospecies. The size and dispersion of the nanoparticles prepared with these original self-assemblies were characterized by TEM, SAXS and DLS techniques. The performances of the catalysts according to the polymer–surfactant mixtures were investigated in the hydrogenation of alkenes and α,β-unsaturated ketones in pure biphasic water/substrate medium, under mild conditions (room temperature and 1 bar H2). The nanocatalysts showed efficient catalytic activities and selectivity towards CC bonds. From investigations, the polymer–surfactant complexes act as cooperative protective agents and a pertinent structure–activity relationship was proposed based on the zeta-potential values and the catalytic activity of the resulting colloid

ASSOCIATION OF BRANCHED POLYETHYLENE IMINE WITH SURFACTANTS IN AQUEOUS SOLUTION

Three polymer-surfactant systems comprised of branched polyethylene imine (PEI) with an anionic surfactant (sodium dodecylsulfate; SDS), a cationic surfactant (tetradecyltrimethylammonium bromide; TTAB), and a zwitterionic surfactant (N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate; SB3-14) were studied based on the properties of surface tension, pyrene fluorescence emission, dynamic light scattering, pH, and zeta potential measurements. The critical aggregation concentration (cac) and polymer saturation point (psp) were determined for all three systems. The effect of these surfactants on the physico-chemical characteristics (diameter and surface charge) of the complexes formed was determined. Polymer-surfactant interactions occurred in all of the systems studied, with the strongest interactions, electrostatic in nature, occurring in the SDS-PEI system. After the neutralization of the polymer charges with the addition of the surfactant, the hydrophobic effect started to control the interlacing of the polymer chains. For the PEI-TTAB system, a very dense film was formed at surfactant concentrations above 2.0 mmol L-1. In this case, the bromide counter-ion interacted with both the positively-charged PEI and the head of the surfactant, which is responsible for the formation of double layer coordination complexes. For the system composed of PEI and the zwitterionic surfactant, less cooperative associations occurred in comparison with the other systems.</p

Core-shell PdCu bimetallic colloidal nanoparticles in Sonogashira cross-coupling reaction: mechanistic insights into the catalyst mode of action

Contains fulltext : 216221.pdf (publisher's version ) (Closed access

Controlled In-Cell Generation of Active Palladium(0) Species for Bioorthogonal Decaging.

Owing to their bioorthogonality, transition metals have become very popular in the development of biocompatible bond-cleavage reactions. However, many approaches require design and synthesis of complex ligands or formulation of nanoparticles which often perform poorly in living cells. This work reports on a method for the generation of an active palladium species that triggers bond-cleaving reactions inside living cells. We utilized the water-soluble Na2PdCl4 as a simple source of Pd(II) which can be intracellularly reduced by sodium ascorbate to the active Pd(0) species. Once generated, Pd(0) triggers the cleavage of allyl ether and carbamate caging groups leading to the release of biologically active molecules. These findings do not only expand the toolbox of available bioorthogonal dissociative reactions but also provide an additional strategy for controlling the reactivity of Pd species involved in Pd-mediated bioorthogonal reactions