Electro-osmotic flow in coated nanocapillaries: a theoretical investigation

Motivated by recent experiments, we present a theoretical investigation of how the electro-osmotic flow occurring in a capillary is modified when its charged surfaces are coated by charged polymers. The theoretical treatment is based on a three dimensional model consisting of a ternary fluid-mixture, representing the solvent and two species for the ions, confined between two parallel charged plates decorated by a fixed array of scatterers representing the polymer coating. The electro-osmotic flow, generated by a constant electric field applied in a direction parallel to the plates, is studied numerically by means of Lattice Boltzmann simulations. In order to gain further understanding we performed a simple theoretical analysis by extending the Stokes-Smoluchowski equation to take into account the porosity induced by the polymers in the region adjacent the walls. We discuss the nature of the velocity profiles by focusing on the competing effects of the polymer charges and the frictional forces they exert. We show evidence of the flow reduction and of the flow inversion phenomenon when the polymer charge is opposite to the surface charge. By using the density of polymers and the surface charge as control variables, we propose a phase diagram that discriminates the direct and the reversed flow regimes and determine its dependence on the ionic concentration.Comment: 15 pages, 6 figures in Physical Chemistry Chemical Physics, 201

Synthesis and study of novel zwitterionic transition metal complexes and their application as olefin polymerisation catalysts

The synthesis, characterization and coordination chemistry of novel zwitterionic late transition metal complexes has been carried out, and an investigation of their ability to act as olefin polymerisation catalysts has been conducted. These systems are based on 6- aminofulvene-2-aldiminate ligands (R2AFA¯) which are capable of binding metal centres via two nitrogen donors, delocalising the negative charge into their cyclopentadienyl moiety, thus resulting in the formation of neutral zwitterionic complexes. Preparation and characterisation of mono- and di-substituted complexes such as Ph2AFACuPPh3, (Ph2AFA)2Zn, (Ph2AFA)2Co, (Ph2AFA)2Ni and (Ph2AFA)2Pd have revealed that this type of ligand has enough flexibility to distort upon coordination to the metal depending on geometrical or steric restrictions. As a result, when the ligand coordination involves narrow binding angle of the metal chelate, as it happens in the square-planar species, a severe loss of planarity of the ligand framework is observed, in contrast with the tetrahedral structures where such binding angles are wider. Although the coordination of the ligand primarily occurs through the nitrogen donors, once they have been occupied by the metal centre, it is possible to exploit the aromatic Cp ring for coordination to a Cp*Ru+ unit. In this way, the synthesis and characterisation of two- and tri-metallic complexes [(Cp*Ru)(Ph’2AFA)Pd(η3-C3H5)][BF4] (where Ph’= 2,4,6-trimethylphenyl) and [(Cp*Ru)2(Ph2AFA)2Pd][BF4]2 has been achieved, featuring the R2AFA¯ molecule acting as an ambidentate ligand, binding the palladium atom in a diimine fashion and the ruthenium centres by means of the C5 ring. The synthesis of the complex Cp*RuPh2AFA where the two N atoms are vacant was also achieved and it was found that this compound acts as a proton sponge in the presence of protic solvents. In an effort to prepare AFA-metal complexes which could be of potential use in olefin polymerisation catalysis, two novel species, [(Ph2AFA)Pd(Me)PPh3] and [(Ph’2AFA)Pd(C3H5)] (where Ph’= 2,4,6-trimethylphenyl) have been synthesised and characterised, and polymerisation tests with ethylene have been carried out. Some preliminary screening of other molecules as monomers for polymerisation catalysis has also been conducted

Wire Up on Carbon Nanostructures! How To Play a Winning Game

Carbon nanotubes and graphene possess a unique extended \u3c0-system that makes them stand out among carbon nanostructures. The resulting electronic properties enable electron or charge flow along one or two directions, respectively, thus offering the opportunity to connect electronically different entities that come into contact, be they living cells or catalytic systems. Using these carbon nanostructures thus holds great promise in providing innovative solutions to address key challenges in the fields of medicine and energy. Here, we discuss how chemical functionalization of these carbon nanostructures is a crucial tool to master their properties and deliver innovation

Into the carbon: A matter of core and shell in advanced electrocatalysis

Electrocatalysis, particularly related to fuel cell applications or other processes related to sustainability, has been steadily advanced by the design of new hierarchical materials involving two or more phases. One particularly appealing type of structure features metal species confined within carbon layers. These materials combine the benefits of the two components, which often work in synergy. However, given the intrinsic catalytic activity of carbon and the fact that the metal may be chemically inaccessible, in many cases, which of the two phases is the truly active site is not fully clear. Particularly for pure core–shell systems, where the metal is completely covered by carbon, the identification of the specific task of each component is not trivial. Many reported works on this type of bi-component catalyst are speculative in this regard. It is important for catalyst development that future studies on these systems will include a thorough cross-check of the reactivity aspects by means of combination of suitable techniques or experiments to unravel probable mechanisms and that assumptions are avoided.Electrocatalysis, particularly related to fuel cell applications or other processes related to sustainability, has been steadily advanced by the design of new hierarchical materials involving two or more phases. One particularly appealing type of structure features metal species confined within carbon layers. These materials combine the benefits of the two components, which often work in synergy. However, given the intrinsic catalytic activity of carbon and the fact that the metal may be chemically inaccessible, in many cases, which of the two phases is the truly active site is not fully clear. Particularly for pure core–shell systems, where the metal is completely covered by carbon, the identification of the specific task of each component is not trivial. Many reported works on this type of bi-component catalyst are speculative in this regard. It is important for catalyst development that future studies on these systems will include a thorough cross-check of the reactivity aspects by means of combination..

The Unexpected Advantages of Using D-Amino Acids for Peptide Self- Assembly into Nanostructured Hydrogels for Medicine

Self-assembled peptide hydrogels have brought innovation to the medicinal field, not only as responsive biomaterials but also as nanostructured therapeutic agents or as smart drug delivery systems. D-amino acids are typically introduced to increase the peptide enzymatic stability. However, there are several reports of unexpected effects on peptide conformation, self-assembly behavior, cytotoxicity and even therapeutic activity. This mini-review discusses all the surprising twists of heterochiral self-assembled peptide hydrogels, and delineates emerging key findings to exploit all the benefits of D-amino acids in this novel medicinal area

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

4Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.Part of the described research was funded by the University of Trieste (FRA2021 to M.M.).openopenRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, SilviaRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, Silvi

The Covalent Functionalization of Graphene on Substrates

The utilization of grown or deposited graphene on solid substrates offers key benefits for functionalization processes, but especially to attain structures with a high level of control for electronics and \u201csmart\u201d materials. In this review, we will initially focus on the nature and properties of graphene on substrates, based on the method of preparation. We will then analyze the most relevant literature on the functionalization of graphene on substrates. In particular, we will comparatively discuss radical reactions, cycloadditions, halogenations, hydrogenations, and oxidations. We will especially address the question of how the reactivity of graphene is affected by its morphology (i.e., number of layers, defects, substrate, curvature, etc.)

Design of dye-sensitized TiO2 materials for photocatalytic hydrogen production: light and shadow

Visible light-driven production of fuels and value-added chemicals is currently one of the most intensely investigated research topics across various scientific disciplines, due to its potential to ease the World\u2019s dependence on fossil fuels. In this perspective, we recapitulate some of the main features of dyesensitized photocatalytic systems aimed at solar H2 production, focusing in particular on TiO2-based threecomponent assemblies with organic sensitizers. Relevant aspects include the structural and electronic properties of the sensitizers, the nature of the semiconductor and the hydrogen evolution catalysts, the role of the sacrificial donor and the effect of the reaction parameters on H2 production rate and stability. Besides presenting the most significant recent developments of the field, we also analyse some of its common practices in terms of experimental design, laboratory procedures and data presentation, trying to highlight their weaknesses and suggesting possible improvements. We then conclude with a short paragraph discussing the possible future development of this exciting research area

Lattice Boltzmann Method for mixtures at variable Schmidt number

When simulating multicomponent mixtures via the Lattice Boltzmann Method, it is desirable to control the mutual diffusivity between species while maintaining the viscosity of the solution fixed. This goal is herein achieved by a modification of the multicomponent Bhatnagar-Gross-Krook (BGK) evolution equations by introducing two different timescales for mass and momentum diffusion. Diffusivity is thus controlled by an effective drag force acting between species. Numerical simulations confirm the accuracy of the method for neutral binary and charged ternary mixtures in bulk conditions. The simulation of a charged mixture in a charged slit channel show that the conductivity and electro-osmotic mobility exhibit a departure from the Helmholtz-Smoluchowski prediction at high diffusivity.Comment: 18 pages, 6 figure

The Glitter of Carbon Nanostructures in Hybrid/Composite Hydrogels for Medicinal Use

In recent years, we have witnessed to fast developments in the medicinal field of hydrogels containing various forms of integrated nanostructured carbon that adds interesting mechanical, thermal, and electronic properties. Besides key advances in tissue engineering (especially for conductive tissue, such as for the brain and the heart), there has been innovation also in the area of drug delivery on-demand, with engineered hydrogels capable of repeated response to light, thermal, or electric stimuli. This mini-review focusses on the most promising developments as applied to the gelation of protein/ peptide (including self-assembling amino acids and low-molecular-weight gelators), polysaccharide, and/or synthetic polymer components in medicine. The emerging field of graphene-only hydrogels is also briefly discussed, to give the reader a full flavor of the rising new paradigms in medicine that are made possible through the integration of nanostructured carbon (e.g., carbon nanotubes, nanohorns, nanodiamonds, fullerene, etc.). Nanocarbons are offering great opportunities to bring on a revolution in therapy that the modern medicinal chemist needs to master, to realise their full potential into powerful therapeutic solutions for the patient