Interplay of chloride levels and palladium(ii)-catalyzed O-deallenylation bioorthogonal uncaging reactions.

The palladium-mediated uncaging reaction of allene substrates remains a promising yet often overlooked strategy in the realm of bioorthogonal chemistry. This method exhibits high kinetic rates, rivaling those of the widely employed allylic and propargylic protecting groups. In this study, we investigate into the mechanistic aspects of the C-O bond-cleavage deallenylation reaction, examining how chloride levels influence the kinetics when triggered by Pd(ii) complexes. Focusing on the deallenylation of 1,2-allenyl protected 4-methylumbelliferone promoted by Allyl2Pd2Cl2, our findings reveal that reaction rates are higher in environments with lower chloride concentrations, mirroring intracellular conditions, compared to elevated chloride concentrations typical of extracellular conditions. Through kinetic and spectroscopic experiments, combined with DFT calculations, we uncover a detailed mechanism that identifies AllylPd(H2O)2 as the predominant active species. These insights provide the basis for the design of π-allylpalladium catalysts suited for selective uncaging within specific cellular environments, potentially enhancing targeted therapeutic applications.

Ready-to-use room temperature one-pot synthesis of surface-decorated gold nanoparticles with targeting attributes.

Gold nanoparticles (AuNPs) can be used in diagnostic and therapeutic applications. The development of facile and fast synthetic approaches is accordingly desirable towards ready-to-use biomedical materials. We report a practical one-pot method for the synthesis in aqueous media and room temperature of surface-decorated AuNPs with enhanced biological responses. The gold ions could be reduced using only polyethyleneimine (PEI) derivatives containing sugar and-or alkyl chains acting simultaneously as reducing and stabilizing agent, without the aid of any other mediator. The process is possibly potentialized by the presence of the amino groups in the polymer chains which further confer colloidal stability. The kinetics of AuNPs nucleation and growth depends on the chemical nature of the polymer chains. Particularly, the presence of lactose moieties conjugated to the PEI chains conducted to surface-decorated AuNPs with low cytotoxicity that are remarkably faster uptaken by HepG2 cells. These cells overexpress asialoglycoprotein (ASGP-R), a galactose receptor. These findings may kick off significant advances towards the practical and ready-to-use manufacturing of functionalized AuNPs towards cell-targeting since the methodology is applicable for a large variety of other ligands that can be conjugated to the same polymer chains.

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

Core-shell PdCu nanoparticles with different metal proportions were synthesized using a one-pot methodology and characterized by STEM, HRTEM, XANES and EXAFS analysis. The bimetallic nanoparticles were applied as catalysts in the Sonogashira cross-coupling reaction to investigate the mode of action of the PdCu in the reaction. The copper content directly influenced the generation of the cross-coupling product, shaping the performance of the catalyst. A quasi-homogeneous reaction pathway was evidenced by kinetics and poisoning experiments as well as XAS, HRTEM and HRMS analysis. These findings help to elucidate the mode of action of the PdCu nanocatalysts in the, as yet, unrevealed Sonogashira mechanism and the potential development of new nanocatalysts.

Ruthenium Trichloride Catalyst in Water: Ru Colloids versus Ru Dimer Characterization Investigations.

An easy-to-prepare ruthenium catalyst obtained from ruthenium(III) trichloride in water demonstrates efficient performances in the oxidation of several cycloalkanes with high selectivity toward the ketone. In this work, several physicochemical techniques were used to demonstrate the real nature of the ruthenium salt still unknown in water and to define the active species for this Csp3-H bond functionalization. From transmission electron microscopy analyses corroborated by SAXS analyses, spherical nanoobjects were observed with an average diameter of 1.75 nm, thus being in favor of the formation of reduced species. However, further investigations, based on X-ray scattering and absorption analyses, showed no evidence of the presence of a metallic Ru-Ru bond, proof of zerovalent nanoparticles, but the existence of Ru-O and Ru-Cl bonds, and thus the formation of a water-soluble complex. The EXAFS (extended X-ray absorption fine structure) spectra revealed the presence of an oxygen-bridged diruthenium complex [Ru(OH) xCl3- x]2(µ-O) with a high oxidation state in agreement with catalytic results. This study constitutes a significant advance to determine the true nature of the RuCl3·3H2O salt in water and proves once again the invasive nature of the electron beam in microscopy experiments, routinely used in nanochemistry.

Antimicrobial activity of nano-sized silver colloids stabilized by nitrogen-containing polymers: the key influence of the polymer capping.

Synthesis of stable silver colloids was achieved using nitrogen-containing polymers acting simultaneously as a reducing and stabilizer agent. The polymers polyethyleneimine (PEI), polyvinylpyrrolidone (PVP) and poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PEO-b-P2VP) were used in the procedures. The influence of the surface chemistry and chemical nature of the stabilizer on the cytotoxicity and antimicrobial properties have been evaluated. The produced nanomaterials were found to be non-toxic up to the highest evaluated concentration (1.00 ppm). Nevertheless, at this very low concentration, the AgNPs stabilized by PVP and PEO-b-P2VP were found to be remarkable biocides against bacteria and fungus. On the other hand, we have surprisingly evidenced negligible antimicrobial activity of AgNPs stabilized by positively charged PEI although both (AgNPs and PEI) materials separately are known for their antimicrobial activity as also evidenced in the current investigation. The evidence is claimed to be related to the blocking of Ag+ kinetic release. Accordingly, the antimicrobial effect of nano-sized silver colloids largely depends on the chemical nature of the polymer coating. Possibly, the outstanding colloid stabilization provided by polyethyleneimine slows down Ag+ release thereby hampering its biological activity whereas the poorer stabilization and good ionic transport property of PVP and PEO-b-P2VP allows much faster ion release and cell damage.

Kinetic investigation into the chemoselective hydrogenation of α,ß-unsaturated carbonyl compounds catalyzed by Ni(0) nanoparticles.

A series of Ni(0) nanocatalysts was prepared from a Ni(COD)2 complex in the presence of different stabilizers (hexadecylamine, polyvinylpyrrolidone (PVP), PVP/triphenylphosphine, octanoic acid and stearic acid) for their evaluation in the selective hydrogenation reaction of α,ß-unsaturated carbonyl compounds by H2 under mild reaction conditions, i.e., low H2 pressure, temperature and catalyst loading. All nanocatalysts were active in reducing only the C[double bond, length as m-dash]C bond and this chemoselectivity was attributed to the reduced nature of the Ni-NPs surface. Moreover, the hydrogenation reaction rate appeared to be sensitive to ligand type, with the carboxylic acid-stabilized systems showing the best performances. A full kinetic investigation into the t-chalcone chemoselective reduction of the C[double bond, length as m-dash]C bond, with the best catalyst (Ni-octanoic acid) revealed that the rate-determining step is the hydrogenation of the adsorbed substrate on the NPs surface, following a Horiuti-Polanyi type of mechanism. Regarding sustainable chemistry concerns, the best catalyst could be reused up to 10 times without significant loss of activity.

Synthesis of silver glyconanoparticles from new sugar-based amphiphiles and their catalytic application.

Oligosaccharide-based amphiphiles were readily prepared by click chemistry from ω-azido-hexanoic or dodecanoic acids with propargyl-functionalized maltoheptaose or xyloglucanoligosaccharides. These amphiphilic compounds were used as capping/stabilizer agents in order to obtain highly stable catalytic silver glyconanoparticles (Ag-GNPs) through the in situ reduction of silver nitrate with NaBH4. With a view to long-term storage, the stabilization was optimized using a multivariate approach, and the nanoparticles were characterized by UV-vis, TEM, SAXS, and DLS. In order to explore the functionality of the Ag-GNPs in catalysis, a full kinetic analysis of the reduction of p-nitrophenol by NaBH4 in water and in water/ethanol mixtures was performed under semi-heterogeneous and quasi-homogeneous conditions. A pseudomonomolecular surface reaction was performed, and the kinetic data obtained were treated according to the Langmuir model. The Ag-GNPs were very active, and both substrates adsorbed onto the surface of the nanoparticles. For comparison purposes, the reaction was also performed in the presence of silver-sodium dodecanoate nanoparticles, which showed catalytic activity similar to that of the glyconanoparticles, supporting the choice of the carboxyl group as the stabilizing agent, although it provided much lower temporal stability. Finally, by combining kinetic and water/ethanol surface tension data it was possible to observe the effect of the addition of the less polar solvent (ethanol) to the reaction medium.

Formation of catalytic silver nanoparticles supported on branched polyethyleneimine derivatives.

A new and straightforward method for screening highly catalytically active silver nanoparticle-polymer composites derived from branched polyethyleneimine (PEI) is reported. The one-step systematic derivatization of the PEI scaffold with alkyl (butyl or octyl) and ethanolic groups led to a structural diversity correlated to the stabilization of silver nanoparticles and catalysis. Analysis of PEI derivative libraries identified a silver nanoparticle-polymer composite that was able to efficiently catalyze the p-nitrophenol reduction by NaBH(4) in water with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 0.57 s(-1) m(-2) L. Carried out in the presence of excess NaBH(4), the catalytic reaction was observed to follow pseudo-first-order kinetics and the apparent rate constant was linearly dependent on the total surface area of the silver nanoparticles (Ag-NPs), indicating that catalysis takes place on the surface of the nanoparticles. All reaction kinetics presented induction periods, which were dependent on the concentration of substrates, the total surface of the nanoparticles, and the polymer composition. All data indicated that this induction time is related to the resistance to substrate diffusion through the polymer support. Hydrophobic effects are also assumed to play an important role in the catalysis, through an increase in the local substrate concentration.