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Important efforts are currently under way in order to develop further the nascent field of plasmonic photocatalysis, striving for improved efficiencies and selectivities. A significant fraction of such efforts has been focused on distinguishing, understanding, and enhancing specific energy-transfer mechanisms from plasmonic nanostructures to their environment. Herein, we report a synthetic strategy that combines two of the main physical mechanisms driving plasmonic photocatalysis into an engineered system by rationally combining the photochemical features of energetic charge carriers and the electromagnetic field enhancement inherent to the plasmonic excitation. We do so by creating hybrid photocatalysts that integrate multiple plasmonic resonators in a single entity, controlling their joint contribution through spectral separation and differential surface functionalization. This strategy allows us to create complex hybrids with improved photosensitization capabilities, thanks to the synergistic combination of two photosensitization mechanisms. Our results show that the hot electron injection can be combined with an energy-transfer process mediated by the near-field interaction, leading to a significant increase in the final photocatalytic response of the material and moving the field of plasmonic photocatalysis closer to energy-efficient applications. Furthermore, our multimodal hybrids offer a test system to probe the properties of the two targeted mechanisms in energy-related applications such as the photocatalytic generation of hydrogen and open the door to wavelength-selective photocatalysis and novel tandem reactions.

Over the years, porphyrins have arisen as exceptional photosensitizers given their ability to act as chlorophyll-mimicking dyes, thus, transferring energy from the light-collecting areas to the reaction centers, as it happens in natural photosynthesis. For this reason, porphyrin-sensitized TiO2-based nanocomposites have been widely exploited in the field of photovoltaics and photocatalysis in order to overcome the well-known limitations of these semiconductors. However, even though both areas of application share some common working principles, the development of solar cells has led the way in what is referred to the continuous improvement of these architectures, particularly regarding the molecular design of these photosynthetic pigments. Yet, those innovations have not been efficiently translated to the field of dye-sensitized photocatalysis. This review aims at filling this gap by performing an in-depth exploration of the most recent advances in the understanding of the role played by the different structural motifs of porphyrins as sensitizers in light-driven TiO2-mediated catalysis. With this goal in mind, the chemical transformations, as well as the reaction conditions under which these dyes must operate, are taken in consideration. The conclusions drawn from this comprehensive analysis offer valuable hints for the implementation of novel porphyrin–TiO2 composites, which may pave the way toward the fabrication of more efficient photocatalysts. Ministerio de Ciencia e Innovación | Ref. PID2020-113704RB-I00 Xunta de Galicia | Ref. ED431G 2019/06 Xunta de Galicia | Ref. ED431C 2022/24 Xunta de Galicia | Ref. ED431C 2021/45

Tear analysis has become an invaluable asset in clinical research in order to identify and quantify novel biomarkers for a wide array of conditions. The present work is intended to take this area of study one step further by implementing an innovative sensing platform through which exploration of low-molecular-weight compounds is conducted outperforming traditional analytical technologies. With this aim, carefully engineered plasmonic nanoassemblies have been synergistically combined with molecular-sieving materials giving rise to size-selective samplers with SERS detection capabilities. These architectures have been then integrated onto hydrogel-based contact lenses and tested in simulated tear fluids in order to evidence their operational features. Through this approach, a prolonged analyte accumulation can be realized, thus providing a competitive advantage in those scenarios where concentration of biomarkers is typically low or minimum sample volumes are not met. Additionally, quenching of metabolic flux and analyte extraction protocols can be circumvented, hence preventing the intrinsic physical and chemical interferences stemming from these procedures. The obtained results render these sensing platforms as promising medical devices, and constitute a great opportunity in order to expand the clinical toolkit in tear analysis.

Important efforts are currently under way in order to implement plasmonic phenomena in the growing field of photocatalysis, striving for improved efficiency and reaction selectivity. A significant fraction of such efforts has been focused on distinguishing, understanding and enhancing specific energy transfer mechanisms from plasmonic nanostructures to their environment. Herein we report a synthetic strategy that brings together two of the main physical mechanisms driving plasmonic photocatalysis into an engineered system by rationally combining the photochemical features of energetic charge carriers and the electromagnetic field enhancement inherent to the plasmonic excitation. We do so by creating hybrid photocatalysts that integrate multiple plasmonic resonators in a single entity, controlling their joint contribution through spectral separation and differential surface functionalization. This strategy allows us to study the combination of different photosensitization mechanisms when activated simultaneously. Our results show that hot electron injection can be combined with an energy transfer process mediated by near-field interaction, leading to a significant increase of the final photocatalytic response of the material. In this manner, we overcome the limitations that hinder photocatalysis driven only by a single energy transfer mechanism, and move the field of plasmonic photocatalysis closer to energy-efficient applications. Furthermore, our multimodal hybrids offer a test system to probe the properties of the two targeted mechanisms in energy-related applications such as the photocatalytic generation of hydrogen and open the door to wavelength-selective photocatalysis and novel tandem reactions.

The synthesis of a hydrogel-based soft contact lens featuring laser shielding capabilities is reported. These light-protective properties are accomplished through the integration of gold-based plasmonic nanoresonators into the lens polymer network, which provides the hydrogel with a high optical density while preserving visible light transmittance. The implementation of these hybrid materials shows great potential in the eye care setting in terms of applications. Along these lines, the ability of the Au nanocomposites to act as efficient light concentrators renders this approach a cost-effective alternative to other less absorbing formulations which may also be toxic or degradable upon light irradiation. Furthermore, the use of these hybrid lenses would provide the wearer with an all day long protection and a minimal obstruction to perform common tasks in those scenarios where high powered light sources are operated.

International audience; Plasmonic materials are intensively used to extend the photoactivity of large bandgap semiconductors into the visible light region. In this framework, the present study examines the joint role played by the morphology and composition of plasmonic nano-particles in their photosensitizing capabilities. The critical influence of these parameters is evidenced by the effect of Au and core−shell Au@Ag nanorods on a TiO 2-driven photochemical probe reaction. In this case, the use of the bimetallic composites leads to a remarkable increase in the photocatalytic activity of the semiconductor compared to that found for the monometallic Au sensitizers. The mechanism behind this observation has then been computed theoretically concluding that, in terms of hot electron injection, the contribution of the transversal modes of the Au@Ag NRs and the low damping of these nanostructures are responsible for the photocatalytic properties reported herein. The great potential of these architectures is confirmed by their notable performance toward photocatalytic hydrogen generation, rendering this approach an appealing strategy in the search for efficient solar-driven energy systems. N oble metal nanoparticles (NPs) present outstanding optical properties given their strong interaction with light in the visible and near-infrared (NIR) ranges of the electromagnetic spectrum. 1 This coupling arises because of the coherent oscillation of conduction electrons of the metallic objects in resonance with the incoming electromagnetic field, an effect known as localized surface plasmon resonance (LSPR). 2 As a result, a short-lived population of charge carriers ("hot" electrons) is created, being thermalized within the crystalline lattice of the metal on the femtosecond time scale. 3,4 Recent reports have shown that the combination of plasmonic objects with acceptor species such as organic molecules or semiconductors can lead to the exchange of charge carriers and hence to the possibility of using such species to drive chemical processes of interest. 5 Along these lines, plasmonic photosensitization has been identified as a promising interaction between a noble metal and a large bandgap semiconductor toward the formation of hybrid photocatalysts with improved efficiencies and broadband activity. 6,7 In this manner, the Schottky barrier created between both materials extends the lifetime of the hot carriers, thus leading to an accumulation of electrons at the conduction band

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An alternative model to the well-established paradigm of the externally switchable drug delivery systems is herein proposed. In contrast to the on–off archetype, here the amount of released drug is pre-set by the application of an external stimulus, and is gradually released after the withdrawal of the exogenous signal. These attributes are achieved through an innovative approach featuring the integration of plasmonic nanovehicles in a polymer-based film. Such a platform is provided with optically responsive capabilities together with multiple diffusional barriers, allowing for an “on-demand” time-limited release where light acts as a therapeutic “starting shot”. These nanoarchitectured depots have great potential as implantable drug delivery systems in clinical scenarios where a recurrent, sustained, and yet, on–off administration of medication is required. The application of these hybrid materials may extend the implementation of nanomedicine strategies beyond the point-of-care setting.

Metal&ndash, semiconductor nanocomposites have become interesting materials for the development of new photocatalytic hybrids. Along these lines, plasmonic nanoparticles have proven to be particularly efficient photosensitizers due to their ability to transfer plasmonic hot electrons onto large bandgap semiconductors such as TiO2, thus extending the activity of the latter into a broader range of the electromagnetic spectrum. The extent of this photosensitization process can be substantially enhanced in those geometries in which high electromagnetic fields are created at the metal&ndash, semiconductor interface. In this manner, the formation of plasmonic hot spots can be used as a versatile tool to engineer the photosensitization process in this family of hybrid materials. Herein, we introduce the use of titanate nanowires as ideal substrates for the assembly of Au nanorods and TiO2 nanoparticles, leading to the formation of robust hybrids with improved photocatalytic properties. Our approach shows that the correct choice of the individual units together with their rational assembly are of paramount importance in the development of complex nanostructures with advanced functionalities.

Nanostructures with concave shapes made from continuous segments of plasmonic metals are known to dramatically enhance Raman scattering. Their synthesis in solutions is hindered, however, by their thermodynamic instability due to large surface area and high curvature of refracted geometries with nanoscale dimensions. Herein, we show that nanostructures with concave geometries can spontaneously form via self-organization of gold nanoparticles (NPs) at the air-water interface. The weakly bound surface ligands on the particle surface make possible their spontaneous accumulation and self-assembly at the air-water interface, forming monoparticulate films. Upon heating to 80 °C, the NPs further assemble into concave nanostructures where NPs are cold-welded to each other. Furthermore, the nanoassemblies effectively adsorb molecular analytes during their migration from the bulk solution to the surface where they can be probed by laser spectroscopies. We demonstrate that these films with local concentration of analytes increased by orders of magnitude and favorable plasmonic shapes can be exploited for surface-enhanced Raman scattering for high-sensitivity analysis of aliphatic molecules.

The use of plasmonic metal nanoparticles as photosensitizers has undergone a strong development in the past few years given their ability to increase the activity of semiconductors into the visible and near-infrared regions. The present work reports an experimental and theoretical study on the critical influence that shape anisotropy of gold nanoparticles exerts on the photocatalytic performance of Au–TiO2 nanoarchitectures. The obtained results show that for a given amount of metallic material, Au nanostars endow titania with a strongly enhanced catalytic efficiency compared to that found in the presence of Au nanospheres or nanorods. This is ascribed to the ability of nanostars to locally create extremely large electromagnetic field enhancements around their spikes, which ensures an increased population of hot electrons close to the interface between the metal and the semiconductor. Therefore, these nanostructures exhibit a novel regime of photocatalytic activity that could be described as plasmonic hot...

Hollow inorganic nanostructures have attracted much interest in the last few years due to their many applications in different areas of science and technology. In this Feature Article, we overview part of our current work concerning the collective use of plasmonic and magnetic nanoparticles located in voided nanostructures and explore the more specific operational issues that should be taken into account in the design of inorganic nanocapsules. Along these lines, we focus our attention on the applications of silica-based submicrometer capsules aiming to stress the importance of creating nanocavities in order to further exploit the great potential of these functional nanomaterials. Additionally, we will examine some of the recent research on this topic and try to establish a perspective for future developments in this area.

A Pt seed-mediated growth method for the synthesis of Ni/NiO and Ni/Ni(OH)2 nanocomposites has been designed so that the morphology and composition of the final materials can be kinetically tailored by a rational choice of the type of seed. Spherical and dendritic Pt nanoparticles provide rather different architectures depending on the different catalytic activity they can exert. Thus, the Pt nanoparticle's initial morphology establishes the conditions for the initial nickel deposition and consequently determines the subsequent autocatalytic growth of the magnetic nanocomposite. Pt seed morphology and reaction conditions reveal the autocatalytic nickel deposition kinetics as a critical factor in the tunability of morphology and composition of nickel-based nanostructures, offering a great opportunity to modulate the final properties of these materials.

Elena González-Domínguez,1,* Nerea Iturrioz-Rodríguez,2,* Esperanza Padín-González,2 Juan Villegas,2 Lorena García-Hevia,2 Moisés Pérez-Lorenzo,1 Wolfgang J Parak,3 Miguel A Correa-Duarte,1,* Mónica L Fanarraga2,* 1Department of Physical Chemistry, Biomedical Research Center (CINBIO), Southern Galicia Institute of Health Research (IISSG), Biomedical Research Networking Center for Mental Health (CIBERSAM), Universidade de Vigo, Vigo, Spain; 2Nanomedicine Group, Universidad de Cantabria-IDIVAL, Santander, Spain; 3Department of Physics, Philipps Universität Marburg, Marburg, Germany *These authors contributed equally to this work Abstract: Carbon nanotubes (CNTs) are likely to transform the therapeutic and diagnostic fields in biomedicine during the coming years. However, the fragmented vision of their side effects and toxicity in humans has proscribed their use as nanomedicines. Most studies agree that biocompatibility depends on the state of aggregation/dispersion of CNTs under physiological conditions, but conclusions are confusing so far. This study designs an experimental setup to investigate the cytotoxic effect of individualized multiwalled CNTs compared to that of identical nanotubes assembled on submicrometric structures. Our results demonstrate how CNT cytotoxicity is directly dependent on the nanotube dispersion at a given dosage. When CNTs are gathered onto silica templates, they do not interfere with cell proliferation or survival becoming highly compatible. These results support the hypothesis that CNT cytotoxicity is due to the biomimetics of these nanomaterials with the intracellular nanofilaments. These findings provide major clues for the development of innocuous CNT-containing nanodevices and nanomedicines. Keywords: MWCNTs, biomimetics, cytoskeleton, microtubules, apoptosis, migration, proliferation

A solar heat shield coating featuring the combination of plasmonic nanostructures in silica-based insulating materials has been developed and tested under conditions resembling natural sunlight exposure. Our results when implementing this coating on standard glazing reveal a blocking efficiency higher than 40%, compatible with a notable preservation of visible light transmittance above 75%. This strategy is (i) cost-effective, as only requires minute amounts of absorbent material in order to obtain the desired effect; (ii) straightforward, because no particular ordering of the plasmon resonators is needed onto the glass substrate; (iii) eco-friendly, as no metal leaching is observed once the gold is encapsulated; and (iv) retrofit-capable, given the fact that these nanostructures can be easily incorporated onto pre-installed glazing. All of these features emphasize the great potential of this approach in the search of more sustainable technologies for the fenestration industry.

The translocation of nanomaterials or complex delivery systems into the cytosol is a main challenge in nanobiotechnology. After receptor-mediated endocytosis, most nanomaterials are sequestered undergoing degradation, therapy inactivation or exocytosis. Here we explore a novel surface particle-coating made of adsorbed carbon nanotubes that provides coated materials with new properties that reproduce the viral cell invasive mechanisms, namely: receptor mediated endocytosis, endo-lysosomal escape and cytosolic particle release preserving intact cell viability. This novel biomimetic coating design will enable the intracytoplasmic delivery of many different functional materials endowed with therapeutic, magnetic, optical or catalytic functionalities thus, opening the door to a wide array of chemical and physical processes within the cytosolic or nuclear domains, and supporting the generation of new developments in the biotechnological, pharmaceutical and biomedical industries.

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.

A study on the effect of sodium bis(2-ethylhexyl)sulfosuccinate-based metallomicroemulsions on the Lewis acid-catalyzed hydrolysis of the ester 2,4-dinitrophenylpicolinate is reported. For a given amount of metal (Ni2+), the presence of these colloidal systems increases the catalytic efficiency of the Lewis acid approximately 1000% over that found in bulk water. This finding is justified on the basis of the highly localized confinement of the catalyst at the aqueous interface of the microemulsion. In addition, the obtained results indicate that the encounter of the ester with the metal catalyst is significantly favored in the presence of this metallo-functionalized microreactor. The mathematical model developed herein also allows an accurate determination and prediction of the influence of the metallomicroemulsion composition on the catalytic effect on the reaction rate. The results obtained lead to the development of similar reaction systems involving the application of metal Lewis acid catalysts such as carbon-carbon bond-forming reactions. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this Perspective, we discuss some of the most significant aspects in the development of nanosized catalysts for Suzuki cross-coupling reactions. Thus, the effect of the size and shape of Pd nanoparticles on the catalytic activity, together with their stability, recycling ability, and the influence of different reaction parameters, will be brought up for consideration. Furthermore, a comprehensive discussion on the homogeneous or heterogeneous nature of the mechanism for Pd-catalyzed carbon–carbon bond-forming reactions will be conducted. Understanding where the active sites are and how the reaction takes place at those sites is the key for the design of new and more effective nanocatalysts.

An experiment is described to introduce advanced undergraduate students to an exciting area of nanotechnology that incorporates nanoparticles onto carbon nanotubes to produce systems that have valuable technological applications. The synthesis of such material has been easily achieved through a simple three-step procedure. Students explore cutting-edge research and gain knowledge in nanoscience.

This work calls for a paradigm shift in order to change the operational patterns of self-regulated membranes in response to chemical signals. To this end, the fabrication of a retrofitting material is introduced aimed at developing an innovative generation of porous substrates endowed with symbiotic but fully independent sensing and actuating capabilities. This is accomplished by transferring carefully engineered plasmonic architectures onto commercial microfiltration membranes lacking of such features. The integration of these materials leads to the formation of a coating surface proficient for ultrasensitive detection and "on-command" gating. Both functionalities can be synergistically modulated by the spatial and temporal distribution of an impinging light beam offering an unprecedented control over the membrane performance in terms of permeability. The implementation of these hybrid nanocomposites in conventional polymeric porous materials holds great potential in applications ranging from intelligent fluid management to advanced filtration technologies and controlled release.

Enols are one of the most Important types of ambident nucleophiles being widely used as reagents in organic chemistry, The relevance of enols has led to considerable interest in developing methods to determine the reactivity of their nucleophilic centers, In this sense, the mainstream, literature works on this topic make use of a. combination of overall rate constants together with the analysis of the reaction products, By knowing the product ratio it is possible to determine the ratio between the reaction rates on each site, Thus, the reactivity for each, nucleophilic position can be obtained, This is a reliable approach as long as the isolation or in situ characterization of the reaction products can be carried out, In the case of unstable and/or interconvertible products where the use of identification techniques is not possible, an alternative methodology must be found, For that: reason, our research group has developed a model that allows us to study and quantify separately the reaction rates of enol nucleophilic centers even if only one final reaction product is obtained, This model is based on the fact: that nitrosation of enols shows well-differentiated behavior depending on whether the reaction proceeds through the carbon or the oxygen atom, The present study provides insights into the ambident nature of enols as well as a methodology for determining the chemical reactivity of their nucleophilic centers. © 2009 Wiley-VCH Verlag GmbH & Co, KGaA.

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.

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. © Science Reviews.

A kinetic study of the reactions of thiolate ions with three Fischer-type [aryloxy(phenyl)carbene]pentacarbonyl chromium(0) complexes in 50% MeCN-50% water (v/v) is reported. Brønsted plots of the second-order rate constants are biphasic with an initial steep rise for weakly basic thiolate ions (beta(nuc) approximately equal to 1.0) followed by a slightly descending leg with a negative slope (beta(nuc) approximately equal to -0.2) for strongly basic thiolate ions. This indicates a change from rate-limiting leaving group departure at low pK(RSH)(a) to rate-limiting nucleophilic attachment at high pK(RSH)(a). The negative beta(nuc) values result from a combination of minimal progress of C-S bond formation at the transition state and the requirement for partial desolvation of the nucleophile before it enters the transition state. Possible factors that may affect the degree of bond formation in reactions of Fischer carbene complexes as well as reactions of other unsaturated electrophiles with thiolate ions are discussed.

A kinetic study of the reversible deprotonation of methylnitroacetate (4H) by primary aliphatic amines, secondary alicyclic amines, hydroxide ion, and water in water at 25 degrees C and in 50% DMSO/50% water (v/v) at 20 degrees C is reported. Intrinsic rate constants, k0, determined by extrapolation or interpolation of Brønsted plots have been determined. In comparison to proton transfers involving other nitroalkanes, the intrinsic rate constants for 4H are exceptionally high; for example, log k0 for the reaction of 4H with secondary alicyclic amines in water (1.22) is 1.81 log units higher than log k0 for nitromethane (-0.59), while in 50% DMSO/50% water, log k0 for 4H (2.44) is 1.71 log units higher than that for nitromethane (0.73). A general discussion of the factors affecting intrinsic rate constants of proton transfer from nitroalkanes is presented; it provides the context for an understanding as to why k0 is so high for the proton transfers from 4H. The correlation between intrinsic rate constants for the addition of nucleophiles to alkenes of the type R'R' 'C=CXY and the intrinsic rate constants of proton transfers from carbon acids of the type H2CXY is also discussed as a general proposition as well as with specific reference to the Ph(SMe)C=C(NO2)CO2Me/H2C(NO2)CO2Me pair.

The effect of AOT-based microemulsions on the reaction between crystal violet and sulphite ion has been studied. On addition of a crystal violet–sulphite (colourless) mixture to AOT-microemulsions, the equilibrium is completely displaced to the reagents (deep blue) while the reaction of crystal violet and sulphite to form a colourless compound is completely inhibited in this medium. This behaviour is an irrefutable evidence of the existence of three well-differentiated microenvironments in the AOT-based microemulsions, even at very low water contents.

A kinetic study of the reversible deprotonation of benzofuran-3(2H)-one (3H-O) and benzothiophene-3(2H)-one (3H-S) by amines and hydroxide ion in water at 25 degrees C is reported. The respective conjugate bases, 3--O and 3--S, represent benzofuran and benzothiophene derivatives, respectively, and thus are aromatic. The main question addressed in this paper is whether this aromaticity has the effect of enhancing or lowering intrinsic barriers to proton transfer. These intrinsic barriers were either determined from Brønsted plots for the reactions with amines or calculated on the basis of the Marcus equation for the reaction with OH-; they were found to be lower for the more highly aromatic benzothiophene derivative, indicating that aromaticity lowers the intrinsic barrier. It is shown that the reduction in the intrinsic barrier is not an artifact of other factors such as inductive, steric, resonance, polarizability, and pi-donor effects, although these factors affect the intrinsic barriers in a major way. Our results imply that aromatic stabilization of the transition state is ahead of proton transfer; this contrasts with simple resonance effects, which typically lag behind proton transfer at the transition state, thereby increasing intrinsic barriers.

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.

A synthetic strategy for the microencapsulation of ultra-small gold nanoparticles toward the development of a novel nanoreactor is reported. In this case, it is shown that the catalytic activity of Au nanoclusters as small as 0.8 nm remains unaffected after a thermal treatment up to 800 °C in air. This is accomplished through the deposition and further coating of the gold nanoparticles in a void/silica/Au/silica configuration where the nature of the alternate shells can be tuned regardless of each other's porosity and the size of the embedded metal nanoparticles. Such spatial confinement suppresses the growth of the gold nanoclusters and thus preserves their catalytic properties. In this way, a remarkable compromise between the immobilization and the accessibility to the metal nanocatalyst can be met. Furthermore, these nanoreactors are found to be colloidally stable in simulated body fluids which also makes them suitable for biomedical applications. The implementation of hollow nanoreactors containing highly dispersed and immobilized but accessible ultra-small metal nanoparticles constitutes a promising alternative in the search for model catalysts stable under realistic technical conditions.

The influence of micellar media upon the transnitrosation reaction between N-methyl-N-nitroso-p-toluensulfonamide (MNTS) and three linear alkylamines (n-octylamine (OA), N-methyl-n-octylamine (MOA) and N,N-dimethyl-n-octylamine (DMOA)) in micelles of Cetyltrimethylammonium Chloride (CTACl) has been studied. The rate constants were obtained and the pseudophase model allowed us to obtain the intrinsic reactivity constants in the aqueous pseudophase and in the micellar pseudophase (ki2 and kw2) and the binding constant of the amines to the micellar phase (Ka).

A kinetic study was carried out on the aminolysis of p-nitrophenyl acetate (NPA) by glycine (GLY) in AOT/isooctane/water (w/o) microemulsions. The experimental results show that the reaction by GLY occurs mostly in the aqueous microdroplet. On the basis of the analysis of the kinetic data, we have calculated the rate constants in the aqueous microdroplet, k2 w, and it can be observed that these increase as the water content of the system decreases. In the aqueous microdroplet, the predominant interaction Na+⋯OH2 causes a decrease in the strength of the hydrogen bonds and therefore facilitates the desolvation of the reagents as W decreases. This desolvation of the reagents causes the increase of k2w as W decreases. © 2005 Elsevier B.V. All rights reserved.

A study was carried out on the influence of different polyethylene glycol dimethyl ethers (glymes) on the conductance percolation of AOT/isooctane/water microemulsions. The glymes used were chosen on the basis of this chain length (the number of polymeric units). In all cases we observed a decrease in the percolation threshold on increasing the amount of a glyme added to the microemulsion. We observed a correlation between the effect exerted by the glyme and its chain length, which shows the importance of including them in the interface for the percolative phenomenon. Such inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets.

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.

The bioaccumulation of polycyclic aromatic compounds originating from textile processing industries is nowadays a major environmental problem worldwide. In order to tackle this situation, several inorganic semiconductors have been tested as photocatalysts for the degradation of these harmful pollutants in the search of sustainable and cost-effective solutions. Nevertheless, these semiconductor materials often involve important limitations, such as poor efficiency and selectivity, which, in the end, substantially restrict their implementation at the industrial scale. As an alternative, we herein report the fabrication and application of Au-decorated titanate nanotubes (TNTs) as high-performance architectures for the selective degradation of organic contaminants. This synthetic strategy is intended to establish a synergetic integration of the physicochemical and photocatalytic features of these hybrid nanostructures, by combining the remarkable adsorption capabilities of TNTs with the enhanced light-harvesting efficiency provided by the incorporation of a noble metal component. The obtained results evidence the great potential that rationally designed plasmonic composites may have for the development of selective environmental remediation technologies and in particular on the current challenges faced by the wastewater treatment sector.

The performance of a Pt(II) diazapyrenium-based metallacycle as a reusable substoichiometric catalyst for the SNAr reaction between halodinitrobenzenes and sodium azide at rt in aqueous media is reported. The results suggest that the catalytic effect is promoted by the association of the azide to the diazapyrenium cationic subunits of the catalyst. The findings demonstrate that the formation of an inclusion complex between pyrene and the metallacycle has a regulatory effect over the system, resulting in allosteric-like inhibition of the SNAr reaction.

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.

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.

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.

A multitechnique investigation on the self-assembly behavior of a biocompatible polymer in the high dilution regime is reported herein. The obtained results unambiguously reveal the existence of premicellar structures that may further extend the efficiency of traditional polymeric micelles as drug-delivery vehicles. Such an expansion in the excipient capacity arises from (i) the increased drug retention of submicellar assemblies due to their higher resistance to dilution and therefore to their improved circulation time and (ii) the superior carrier permeability of these premicellar aggregates as a result of their smaller size, which makes these drug vehicles more effectively targeted to the tumors through the so-called enhanced permeability and retention effect. The uptake ability of the polymeric premicelles described in this work has been tested through the use of Nile Red as drug model given its intermediate lipophilicity (log P ≈ 3-5) similar to that of potent chemotherapy agents and its microenvironment-sensitive fluorescence properties relevant for localization purposes. Thus, it has been found that an efficient drug encapsulation can be achieved under conditions well below the normally required critical micelle concentration. These results may constitute a promising strategy in order to develop new and more efficient polymeric formulations in drug delivery technology. © 2013 American Chemical Society.

Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (III), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.

Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (III), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.

In this Perspective, we discuss some of the most significant aspects in the development of nanosized catalysts for Suzuki cross-coupling reactions. Thus, the effect of the size and shape of Pd nanoparticles on the catalytic activity, together with their stability, recycling ability, and the influence of different reaction parameters, will be brought up for consideration. Furthermore, a comprehensive discussion on the homogeneous or heterogeneous nature of the mechanism for Pd-catalyzed carbon–carbon bond-forming reactions will be conducted. Understanding where the active sites are and how the reaction takes place at those sites is the key for the design of new and more effective nanocatalysts.

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.

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.

The catalytic effect of triethylene glycol dimethyl ether (glyme) on the butylaminolysis of 4-nitrophenylcaprate (NPC) in water/AOT/chlorobenzene microemulsions has been studied. Experimental results show the existence of four simultaneous reaction pathways. One of them takes place at the microemulsion interphase where the rate-determining step of butylaminolysis is the formation of the addition intermediate, T±. The locus of the other three pathways is the continuous medium of the microemulsion. These three pathways consist of the decomposition of the addition intermediate catalyzed by butylamine, by glyme, and by both of them. The kinetic model allows us to obtain the value of every rate and distribution constant involved in the overall reaction mechanism. We must emphasize that the reactions located in the continuous medium exhibit a kinetic behavior similar to the corresponding one found in pure chlorobenzene. On the basis of the pseudophase model, the percentage of reaction in each of the microdomains of the microemulsion has been calculated. Likewise, changes in the loci of reaction from the interphase to the continuous medium as a function of catalyst concentration have been proved. © 2007 American Chemical Society.