A generalised model for dynamic photocurrent responses at dye-sensitised liquid|liquid interfaces

The heterogeneous photoinduced electron transfer involving dyes adsorbed at the interface between two immiscible electrolyte solutions and redox molecules located in the adjacent phase manifests itself as photocurrent responses under potentiostatic conditions. Photocurrent transients as functions of the light intensity and bias potential allow the extraction of insightful information on the kinetics of the various processes associated with the photoinduced reaction. Previous analyses of this type of responses were based on phenomenological models that did not consider mass transport. In the present paper, we develop a generalised model for photocurrent transients taking into account the diffusion of reacting species to the interface. Comparison with the experimental data confirms that the responses can be described adequately by applying stationary conditions to the surface concentration of the photoactive species. Mechanistic aspects associated with the nature of the photocurrent relaxation on the microsecond time scale are examined. In particular, the dependence of the transient response on the light intensity indicates that charge recombination proceeds mainly as a first order reaction from an interfacial geminate ion pair. Coupled ion transfer reactions involving the photoproducts can also contribute to the photocurrent, depending on the formal ion transfer potential of the corresponding species

Pseudo-single crystal electrochemistry on polycrystalline electrodes : visualizing activity at grains and grain boundaries on platinum for the Fe2+/Fe3+ redox reaction

The influence of electrode surface structure on electrochemical reaction rates and mechanisms is a major theme in electrochemical research, especially as electrodes with inherent structural heterogeneities are used ubiquitously. Yet, probing local electrochemistry and surface structure at complex surfaces is challenging. In this paper, high spatial resolution scanning electrochemical cell microscopy (SECCM) complemented with electron backscatter diffraction (EBSD) is demonstrated as a means of performing ‘pseudo-single-crystal’ electrochemical measurements at individual grains of a polycrystalline platinum electrode, while also allowing grain boundaries to be probed. Using the Fe2+/3+ couple as an illustrative case, a strong correlation is found between local surface structure and electrochemical activity. Variations in electrochemical activity for individual high index grains, visualized in a weakly adsorbing perchlorate medium, show that there is higher activity on grains with a significant (101) orientation contribution, compared to those with (001) and (111) contribution, consistent with findings on single-crystal electrodes. Interestingly, for Fe2+ oxidation in a sulfate medium a different pattern of activity emerges. Here, SECCM reveals only minor variations in activity between individual grains, again consistent with single-crystal studies, with a greatly enhanced activity at grain boundaries. This suggests that these sites may contribute significantly to the overall electrochemical behavior measured on the macroscale

35 años de análisis de isótopos estables en la arqueología Argentina: conceptos, fundamentos, metodología y aplicaciones

El objetivo de este trabajo es celebrar más de tres décadas de la integración de los análisis de isótopos estables en investigaciones arqueológicas en nuestro país. Se presenta una síntesis sobre los conceptos,fundamentos teóricos y metodológicos y las aplicaciones, principalmente en tres grandes temas: paleodieta, paleomovilidad y paleoambiente. A su vez, brindamos ejemplos de abordajes isotópicos sobre problemáticas de paleodietas en sociedades cazadoras recolectoras y agricultoras; movilidad de grupos humanos; estrategias de pastoreo; preparación y cocción de alimentos; estudios paleoambientales y paleoclimáticos. Este compendio puede resultar una referencia útil para estudiantes e investigadores que decidan adentrarse en este campo de investigación. Los casos mencionados no agotan el estado de la cuestión, ni abarcan todas las regiones donde fueron desarrollados estos estudios, sino que el propósito es mostrar la diversidad temática y el modo en que los isótopos estables permiten ampliar el conocimiento sobre las sociedades en el pasado.The main goal of this work is to celebrate more than three decades of the application of stable isotope analyses in Argentinian archaeology. We present a synthesis of the concepts, theoretical and methodological aspects and applications covering three main topics: paleodiet, paleomobility and paleoenvironment. At the same time, we provide examples of isotopic approaches to study problems such as paleodiets in hunter-gatherer and agricultural societies, human mobility, herding strategies, food preparation and cooking, and paleoenvironmental and paleoclimatic studies. This compendium will be a useful reference for students and researchers inclined to enter this field of research. However, the cases mentioned here do not represent the state of art nor do they cover all the Argentinian regions where these studies were carried out, but rather show the thematic diversity and the way in which stable isotope analyses allow to broaden our knowledge about societies in the past.Introducción - Conceptos básicos, fundamentación y notación de los análisis de isótopos estables - Espectrometría de masas - Relaciones isotópicas mayormente utilizadas en arqueología -- Isótopos estables del carbono -- Isótopos estables del nitrógeno -- Isótopos estables del oxígeno e hidrógeno -- Otras relaciones isotópicas de interés: azufre y estroncio - Tejidos y materiales -- Tejidos biológicos -- Residuos orgánicos -- Carbonatos biogénicos -- Sedimentos - Conservación, contaminación y diagénesis -- Fracción orgánica o colágeno -- Fracción Mineral o Bioapatita - Discriminación y fraccionamiento isotópico - Interpretación paleodietaria y ecología isotópica - Abordajes isotópicos de problemáticas en arqueología argentina - Consideraciones finales y perspectivas futura

Electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH) : Comparison of highly oriented pyrolytic graphite (HOPG) and polycrystalline boron-doped diamond (pBDD) electrodes

The electro-oxidation of nicotinamide adenine dinucleotide (NADH) is studied at bare surfaces of highly oriented pyrolytic graphite (HOPG) and semi-metallic polycrystalline boron-doped diamond (pBDD). A comparison of these two carbon electrode materials is interesting because they possess broadly similar densities of electronic states that are much lower than most metal electrodes, but graphite has carbon sp2-hybridization, while in diamond the carbon is sp3-hybridised, with resulting major differences in bulk structure and surface termination. Using cyclic voltammetry (CV), it is shown that NADH oxidation is facile at HOPG surfaces but the reaction products tend to strongly adsorb, which causes rapid deactivation of the electrode activity. This is an important factor that needs to be taken into account when assessing HOPG and its intrinsic activity. It is also shown that NADH itself adsorbs at HOPG, a fact that has not been recognized previously, but has implications for understanding the mechanism of the electro-oxidation process. Although pBDD was found to be less susceptible to surface fouling, pBDD is not immune to deterioration of the electrode response, and the reaction showed more sluggish kinetics on this electrode. Scanning electrochemical cell microscopy (SECCM) highlights a significant voltammetric variation in electroactivity between different crystal surface facets that are presented to solution with a pBDD electrode. The electroactivity of different grains correlates with the local dopant level, as visualized by field emission-scanning electron microscopy. SECCM measurements further prove that the basal plane of HOPG has high activity towards NADH electro-oxidation. These new insights on NADH voltammetry are useful for the design of optimal carbon-based electrodes for NADH electroanalysis

Activation and Deactivation of a Robust Immobilized Cp*Ir-Transfer Hydrogenation Catalyst: A Multielement in Situ X-ray Absorption Spectroscopy Study

A highly robust immobilized [Cp*IrCl2]2 precatalyst on Wang resin for transfer hydrogenation, which can be recycled up to 30 times, was studied using a novel combination of X-ray absorption spectroscopy (XAS) at Ir L3-edge, Cl K-edge, and K K-edge. These culminate in in situ XAS experiments that link structural changes of the Ir complex with its catalytic activity and its deactivation. Mercury poisoning and “hot filtration” experiments ruled out leached Ir as the active catalyst. Spectroscopic evidence indicates the exchange of one chloride ligand with an alkoxide to generate the active precatalyst. The exchange of the second chloride ligand, however, leads to a potassium alkoxide–iridate species as the deactivated form of this immobilized catalyst. These findings could be widely applicable to the many homogeneous transfer hydrogenation catalysts with Cp*IrCl substructure

Solvation free energy profile of the SCN- ion across the water-1,2-dichloroethane liquid/liquid interface. A computer simulation study

The solvation free energy profile of a single SCN- ion is calculated across the water-1,2-dichloroethane liquid/liquid interface at 298 K by the constraint force method. The obtained results show that the free energy cost of transferring the ion from the aqueous to the organic phase is about 70 kJ/mol, The free energy profile shows a small but clear well at the aqueous side of the interface, in the subsurface region of the water phase, indicating the ability of the SCN- ion to be adsorbed in the close vicinity of the interface. Upon entrance of the SCN- ion to the organic phase a coextraction of the water molecules of its first hydration shell occurs. Accordingly, when it is located at the boundary of the two phases the SCN- ion prefers orientations in which its bulky S atom is located at the aqueous side, and the small N atom, together with its first hydration shell, at the organic side of the interface

Caution, "normal" BMI: health risks associated with potentially masked individual underweight - EPMA position paper 2021

An increasing interest in a healthy lifestyle raises questions about optimal body weight. Evidently, it should be clearly discriminated between the standardised "normal" body weight and individually optimal weight. To this end, the basic principle of personalised medicine "one size does not fit all" has to be applied. Contextually, "normal" but e.g. borderline body mass index might be optimal for one person but apparently suboptimal for another one strongly depending on the individual genetic predisposition, geographic origin, cultural and nutritional habits and relevant lifestyle parameters - all included into comprehensive individual patient profile. Even if only slightly deviant, both overweight and underweight are acknowledged risk factors for a shifted metabolism which, if being not optimised, may strongly contribute to the development and progression of severe pathologies. Development of innovative screening programmes is essential to promote population health by application of health risks assessment, individualised patient profiling and multi-parametric analysis, further used for cost-effective targeted prevention and treatments tailored to the person. The following healthcare areas are considered to be potentially strongly benefiting from the above proposed measures: suboptimal health conditions, sports medicine, stress overload and associated complications, planned pregnancies, periodontal health and dentistry, sleep medicine, eye health and disorders, inflammatory disorders, healing and pain management, metabolic disorders, cardiovascular disease, cancers, psychiatric and neurologic disorders, stroke of known and unknown aetiology, improved individual and population outcomes under pandemic conditions such as COVID-19. In a long-term way, a significantly improved healthcare economy is one of benefits of the proposed paradigm shift from reactive to Predictive, Preventive and Personalised Medicine (PPPM/3PM). A tight collaboration between all stakeholders including scientific community, healthcare givers, patient organisations, policy-makers and educators is essential for the smooth implementation of 3PM concepts in daily practice