Conspectus Although there has been for the past 20 years great interest in the synthesis and use of metal nanoparticles, little attention has been paid to the complexity of the surface of these ...species. In particular, the different aspects concerning the ligands present, their location, their mode of binding, and their dynamics have been little studied. Our group has started in the early 1990s an investigation of the surface coordination chemistry of ruthenium and platinum nanoparticles but at that time with a lack of adequate techniques to fulfill our ambition. Over 10 years later, we went back to this problem and could obtain a more precise vision of the surface species. This Account is centered on ruthenium chemistry. This metal has been the most studied in our group, first thanks to the availability of a precursor, Ru(cyclooctadiene)(cyclooctatriene) (Ru(COD)(COT)), which possesses the ability to decompose in very mild conditions without leaving residues on the resulting nanoparticles and second because of the absence of magnetic perturbations (Knight shift, paramagnetism, ferromagnetism, etc.), which has allowed the use of solution and solid state NMR. In this respect, it has been possible to evidence the presence of a high concentration of hydrides on the surface of these particles, to study their dynamics, and to show that since the polarity of the Ru–H bond is similar to that of the C–H bond, a Ru/H NP would behave as a big lipophilic entity. The second point was to characterize the coordination of ancillary ligands. This has been achieved for different ligands, in particular phosphines and carbenes, which made possible the study of the modification of NP reactivity induced by surface ligands. This led to the conclusion that the presence of surface ligands can benefit both the activity of NP catalysts and their selectivity. If it was expected that the selectivity could be modulated, the promoting effect from the presence of ligands on, for example, arene or CO hydrogenation was totally unexpected. Playing with poison atoms (Sn, Fe, etc.) or ligands (CO) may allow us to play with the reactivity of the NPs to make them more selective for selected reactions. Finally, the search for specific ligands for nanoparticles is still in its infancy, but some examples have been found as have specific reactions of nanoparticles. Obviously arene hydrogenation and CO hydrogenation were well-known in heterogeneous catalysis, but we could demonstrate that they can be carried out in very mild conditions on ligand stabilized RuNPs. On the other hand, the enantiospecific C–H activation leading to enantioselective labeling of large organic or biomolecules or the C–C bond cleavage in mild conditions were both unexpected. There is still much work to perform for reaching the degree of control on nanoparticles that is presently achieved in organometallic molecular chemistry, but this work shows that it is possible.
The COVID-19 pandemic has caused a massive disruption in the way traditional higher education institutions deliver their courses. Unlike transitions from face-to-face teaching to blended, online or ...flipped classroom in the past, changes in emergency remote teaching –a temporary shift of instructional delivery to an alternate remote delivery mode due to crisis circumstances– happen suddenly and in an unplanned way. This study analyzes the move to emergency remote teaching at the School of Telecommunication Engineering (Universidad Politécnica de Madrid), and the impact of organizational aspects related to unplanned change, instruction-related variables –class size, synchronous/asynchronous delivery– and use of digital supporting technologies, on students' academic performance. Using quantitative data of academic records across all (N = 43) courses of a bachelor's degree programme in Telecommunication Engineering and qualitative data from a questionnaire delivered to all (N = 43) course coordinators, the research also compares the academic results of students during the COVID-19 pandemic with those of previous years. The results of this case study show an increase in students' academic performance in emergency remote teaching, and support the idea that organizational factors may contribute to successful implementation of emergency remote teaching; the analysis does not find differences across courses with different class sizes or delivery modes. The study further explores possible explanations for the results of the analysis, considering organizational, individual and instruction-related aspects.
This study investigates the intricate interplay between social class, sex, and self-reported health (SRH) using data from the European Health Survey of Spain 2020 (EESE2020). Employing a ...cross-sectional design and a representative sample of 22,072 individuals, the analysis explores the persistence of disparities after adjusting for covariates, focusing on health-related variables. The study employs logistic regression models and directed acyclic graphs (DAGs) to delineate the direct effects of social class and sex on SRH, identifying a minimum adjustment set to control for confounding variables. Results reveal a gradient effect of social class on SRH, emphasizing the enduring impact of socioeconomic factors. Sex-based disparities in SRH diminish after considering additional health-related variables, highlighting the importance of a holistic approach. DAGs serve as transparent tools in disentangling complex relationships, guiding the identification of essential covariates. The study concludes that addressing health inequalities requires comprehensive strategies considering both individual health behaviours and socio-economic contexts. While recognizing limitations, such as the cross-sectional design, the findings contribute to a nuanced understanding of health disparities, informing evidence-based interventions and policies for a more equitable healthcare system.
In response to a variety of cancer-inducing stresses, cells may engage a stable cell cycle arrest mechanism, termed cellular senescence, to suppress the proliferation of preneoplastic cells. Despite ...this cell intrinsic tumor suppression, senescent cells have also been implicated as active contributors to tumorigenesis by extrinsically promoting many hallmarks of cancer, including evasion of the immune system. Here, we discuss these dual, and seemingly contradictory, roles of senescence during tumorigenesis. Furthermore, we highlight findings of how senescent cells can influence the immune system and discuss the possibility that immune cells themselves may be acquiring senescence-associated alterations. Lastly, we discuss how senescent cell avoidance or clearance may impact pathology.
The development of energetically efficient processes for the aqueous reduction of biomass-derived compounds into chemicals is key for the optimal transformation of biomass. Herein we report an early ...example of the reduction of biomass-derived oxygenated compounds in water by magnetically induced catalysis. Non-coated and carbon-coated core–shell FeCo@Ni magnetic nanoparticles were used as the heating agent and the catalyst simultaneously. In this way it was possible to control the product distribution by adjusting the field amplitude applied during the magnetic catalysis, opening a precedent for this type of catalysis. Finally, the encapsulation of the magnetic nanoparticles in carbon (FeCo@Ni@C) strongly improved the stability of the magnetic catalyst in solution, making its reuse possible up to at least eight times in dioxane and four times in water.
Display omitted
•N-doped graphene supported Ru NPs (Ru/NH2-rGO) are used for the hydrogenation of fatty acids.•A notable selectivity for the carbonyl reduction is observed (93% of the aliphatic ...alcohol at 99% conversion).•Ru/NH2-rGO can be reused up to 4 times without any loss of activity/selectivity.•The presence of basic centres next to the Ru atoms facilitates the hydrogenation of aliphatic acids.•Mechanistic studies points to a heterolytic/homolytic dual mechanism for H2 dissociation.
Ruthenium nanoparticles (Ru NPs) supported on reduced-graphene oxide doped with N (NH2-rGO) was synthesized and used for the selective hydrogenation of fatty acids to alcohols, being the hydrogenation of palmitic acid selected as model. Ru was stabilized forming uniform nanometer size particles on N-doped graphene (Ru/NH2-rGO). The resultant catalyst was very selective for the carbonyl reduction giving 93% of the aliphatic alcohol at 99% conversion. The Ru/NH2-rGO catalysts was more active and selective than the corresponding Ru on non-doped graphene (Ru/rGO) or Ru on carbon (Ru/C). Mechanistic studies points to a dual mechanism for H2 dissociation, i.e. homolytic and heterolytic cleavage exists on the Ru/NH2-rGO, while only the homolytic H2 dissociation occurs on Ru/rGO. This heterolytic splitting, which activates the carbonyl groups and facilitates the hydrogenation of aliphatic acids, is due to the presence of basic centres next to the Ru atoms. The presence of N atoms also increases the stability of the catalyst, allowing a reuse up to four times.
Soluble platinum nanoparticles (Pt NPs) ligated by two different long‐chain N‐heterocyclic carbenes (LC‐IPr and LC‐IMe) were synthesized and fully characterized by TEM, high‐resolution TEM, ...wide‐angle X‐ray scattering (WAXS), X‐ray photoelectron spectroscopy (XPS), and solution NMR. The surface chemistry of these NPs (Pt@LC‐IPr and Pt@LC‐IMe) was investigated by FT‐IR and solid state NMR using CO as a probe molecule. A clear influence of the bulkiness of the N‐substituents on the size, surface state, and catalytic activity of these Pt NPs was observed. While Pt@LC‐IMe showed no activity in the hydroboration of phenylacetylene, Pt@LC‐IPr revealed good selectivity for the trans‐isomer, which may be supported by a homogeneous species. This is the first example of hydroboration of acetylenes catalyzed by non‐supported Pt NPs.
Telling a tall tail: soluble platinum nanoparticles ligated by two different long‐chain N‐heterocyclic carbenes (Pt@LC‐IPr and Pt@LC‐IMe) show marked differences in their catalytic activity depending on the bulkiness of the N‐substituents. While Pt@LC‐IMe behaves similarly to heterogeneous catalysts, the catalytic activity of Pt@LC‐IPr parallels that of molecular complexes in the hydroboration of phenylacetylene.
Formation of stable carbides during CO bond dissociation on small ruthenium nanoparticles (RuNPs) is demonstrated, both by means of DFT calculations and by solid state
13
C NMR techniques. ...Theoretical calculations of chemical shifts in several model clusters are employed in order to secure experimental spectroscopic assignations for surface ruthenium carbides. Mechanistic DFT investigations, carried out on a realistic Ru
55
nanoparticle model (∼1 nm) in terms of size, structure and surface composition, reveal that ruthenium carbides are obtained during CO hydrogenation. Calculations also indicate that carbide formation
via
hydrogen-assisted hydroxymethylidyne (COH) pathways is exothermic and occurs at reasonable kinetic cost on standard sites of the RuNPs, such as 4-fold ones on flat terraces, and not only in steps as previously suggested. Another novel outcome of the DFT mechanistic study consists of the possible formation of μ
6
ruthenium carbides in the tip-B
5
site, similar examples being known only for molecular ruthenium clusters. Moreover, based on DFT energies, the possible rearrangement of the surface metal atoms around the same tip-site results in a μ-Ru atom coordinated to the remaining RuNP moiety, reminiscent of a pseudo-octahedral metal center on the NP surface.
According to advanced
13
C MAS NMR experiments and DFT investigations of multi-step pathways as well as DFT-based NMR assignment of experimental spectra, it is shown that carbide formation can occur on ruthenium NPs during CO bond cleavage.
The article involves a study along the line of performance analysis of tourist destinations, yet taking the regions as territorial units and cultural tourism as a tourist flow to be explored. The aim ...of this study is therefore to evaluate the technical efficiency of regions in attracting greater flows of cultural tourism considering their own cultural resources available in the medium term. The analysis will be carried out at a regional disaggregation level in Spain, and one hypothetical production function will be designed to link cultural resources and demand. We adopt a two-stage procedure to evaluate regional efficiency as cultural destinations: first, measuring performance by non-parametric methods; and second, analysing how other external variables might determine these efficiency ratios. In this case, we consider indicators representing reputation, accessibility, the omnivorous nature of cultural tourism as well as the scope to the regional cultural sector. The findings of this research have implications for economic development and regional disparity analysis and may also prove to be of potential interest vis-à-vis economic policy.
A specific secondary phosphine oxide (SPO) ligand (tert‐butyl(phenyl)phosphine oxide) was employed to generate two iridium catalysts, an Ir–SPO complex and IrNPs (iridium nanoparticles) ligated with ...SPO ligands, which were compared mutually and with several supported iridium catalysts with the aim to establish the differences in their catalytic properties. The Ir–SPO‐based catalysts showed totally different activities and selectivities in the hydrogenation of various substituted aldehydes, in which H2 is likely cleaved by a metal–ligand cooperation, that is, the SPO ligand and a neighboring metal centre operate in tandem to activate the hydrogen molecule. In addition, the supported IrNPs behave very differently from both Ir–SPO catalysts. This study exemplifies perfectly the advantages and disadvantages related to the use of the main types of catalysts, and thus the dissimilarities between them.
Complex–particle duality: Three catalysts were compared: an Ir–SPO complex (secondary phosphine oxide), an Ir nanoparticle ligated with the same SPO, and supported Ir metallic catalysts. They show a completely different behavior in the hydrogenation of functionalised aldehydes.
PDF
