Moisés Pérez-Lorenzo

Hollow‐Shelled Nanoreactors Endowed with High Catalytic Activity

Hollow-shelled nanoreactors have emerged as efficient structures to maximize the potential of nanoparticles in the field of catalysis. In this Concept article, we underline the importance of both the morphology of the active nanoparticles as well as the composition and porosity of the shell for the catalytic performance of the overall nanocomposite. Different configurations are discussed, with a focus on preparative methods and applications in organic synthesis. Perspectives on future designs that may offer new opportunities to improve the selectivity of the catalyzed transformations and add additional features are also addressed, in order to illustrate the potential of these unique nanostructures.

Highly Active Nanoreactors: Nanomaterial Encapsulation Based on Confined Catalysis**

It happens inside: highly active nanoreactors are prepared by encapsulating dendritic Pt nanoparticles (NPs) grown on a polystyrene template inside hollow porous silica capsules. The catalytic activity of these Pt NPs is preserved after encapsulation and template removal. Different metals, such as Ni, can thus be reduced inside the capsules, thereby leading to the formation of composites with tunable magnetic properties.

Nanoreactors for simultaneous remote thermal activation and optical monitoring of chemical reactions.

We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress.

Microemulsions as microreactors in physical organic chemistry

Microemulsions are very versatile reaction media which nowadays find many applications, ranging from nanoparticle templating to preparative organic chemistry. The thermodynamically stable and microheterogeneous nature of microemulsions, used as reaction media, induces drastic changes in the reagent concentrations, and this can be specifically used for tuning the reaction rates. In particular, amphiphilic organic molecules can accumulate and orient at the oil-water interface, inducing regiospecificity in organic reactions. In this review, we will show the recent tendencies of the use of microemulsions as organic reaction media.

Modification of reactivity by changing microemulsion composition. Basic hydrolysis of nitrophenyl acetate in AOT/isooctane/water systems

A study was carried out on the basic hydrolysis of p-nitrophenyl acetate (NPA) in AOT/isooctane/water microemulsions keeping constant the hydroxide ion concentration referred to the droplet water. The obtained results show that the pseudofirst order rate constant, kobs, is approximately 100 times lower than the corresponding value in bulk water and increases together with the [AOT], keeping constant the molar ratio W, W = [H2O]/[AOT]. On experiments varying W, keeping constant [AOT], it can be observed that kobs decreases from W = 2 to W = 10 as W increases, reaching a minimum value for W ≅ 10, and then increasing again. The observed behavior is a consequence of two factors: the variation of hydroxide ion concentration referred to the total volume of the system, and the association of the NPA to the interface of the microemulsion. The experimental results can be explained quantitatively considering that the NPA is distributed throughout the three pseudophases of the system and that the reaction takes place solely in the aqueous microdroplet. The second order rate constant in the aqueous microdroplet of the microemulsion, kw2, increase as W decreases, showing a parallelism with the behavior observed in aqueous DMSO. The values of kw2 increase approximately 35 times from W = 40 to W = 2 due fundamentally to the partial desolvation of the hydroxide ions as the water content of the microemulsion decreases.

Organic Reactivity in Aot-Stabilized Microemulsions

Microemulsions are highly versatile reaction media, which currently find many applications. In this review, we shall describe recent trends in the use of microemulsions as organic reaction media, and present models for their functioning, in particular the pseudophase model. This model allows a quantitative explanation of organic reactivity in these microheterogeneous media.

Ostwald ripening of platinum nanoparticles confined in a carbon nanotube/silica-templated cylindrical space

Sintering of nanoparticles mediated by an Ostwald ripening mechanism is generally assessed examining the final particle size distributions. Based on this methodology, a general approach for depositing platinum nanoparticles onto carbon nanotubes in solution has been employed in order to evaluate the sintering process of these metallic nanoparticles at increasing temperatures in a carbon nanotube/silica-templated confined space.

Denitrosation of N-Nitrososulfonamide as Chemical Probe for Determination of Binding Constants to Cyclodextrins

The influence of β-CD concentration on the acid hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) has been studied in the presence and absence of different alcohol concentrations. The rate of the denitrosation reaction in bulk water decrease as the β-CD concentration increases due to MNTS complexation in the CD cavity and the reaction taking place exclusively outside the cyclodextrin. Changes in this inhibition due to the presence of β-CD allow us to obtain the binding constants of different alcohols to the cyclodextrin. These binding constants are in very good agreement with those determined in the bibliography by other methods.

First kinetic discrimination between carbon and oxygen reactivity of enols.

Nitrosation of enols shows a well-differentiated behavior depending on whether the reaction proceeds through the carbon (nucleophilic catalysis is observed) or the oxygen atom (general acid-base catalysis is observed). This is due to the different operating mechanisms for C- and O-nitrosation. Nitrosation of acetylacetone (AcAc) shows a simultaneous nucleophilic and acid-base catalysis. This simultaneous catalysis constitutes the first kinetic evidence of two independent reactions on the carbon and oxygen atom of an enol. The following kinetic study allows us to determine the rate constants for both reaction pathways. A similar reactivity of the nucleophilic centers with the nitrosonium ion is observed.

Hierarchical Nanoplatforms for High‐Performance Enzyme Biocatalysis under Denaturing Conditions

A hierarchically structured nanoplatform comprising the integration of enzymes into a hybrid carbon‐nanotube‐based magnetic nanocomposite was developed. By means of this complex support, laccases are endowed with exceptional performance even in fully denaturing environments. In this regard, up to 10‐fold enhancements in the biocatalytic activity of the enzymes can be attained at different temperatures and pH conditions. Furthermore, these platforms are found to provide laccases with unprecedented recycling potential. In this line, these composites allow straightforward recovery and reuse of the biocatalysts with no loss of efficiency even after 10 successive runs. These outstanding operational capabilities make these nanocarriers a promising material to tackle the challenges associated with the implementation of enzymes in industrial biotechnology.