Reinier Oropesa-Nuñez

Physico-chemical studies of molecular interactions between non-ionic surfactants and bovine serum albumin.

Surfactants, particularly non-ionic types, are often added to prevent and/or minimize protein aggregation during fermentation, purification, freeze-drying, shipping, and/or storage. In this work we have investigated the interactions between two non-ionic surfactants (Tween 20 and Tween 80) and bovine serum albumin (BSA), as model protein, using surface tension, fluorescence measurements and computational analysis. The results showed that, in both cases, the surface tension profile of the surfactants curve is modified upon addition of the protein, and the CMC values of Tween 20 and Tween 80 in the presence of protein are higher than the CMC values of the pure surfactants. The results indicate that although Tween 20 and Tween 80 do not greatly differ in their chemical structures, their interactions with BSA are of different nature, with distinct binding sites. Measurements at different protein concentrations showed that the interactions are also dependent on the protein aggregation state in solution. It was found from fluorescence studies that changes observed in both the intensity and wavelength of the tryptophan emission are probably caused by modifications of tryptophan environment due to surfactant binding, rather than by direct interaction. Based on a computational analysis of a BSA three-dimensional model, we hypothesize about the binding mechanism of non-ionic surfactant to globular protein, which allowed us to explain surface tension profiles and fluorescence results.

Molecular insights into cell toxicity of a novel familial amyloidogenic variant of β2‐microglobulin

The first genetic variant of β2‐microglobulin (b2M) associated with a familial form of systemic amyloidosis has been recently described. The mutated protein, carrying a substitution of Asp at position 76 with an Asn (D76N b2M), exhibits a strongly enhanced amyloidogenic tendency to aggregate with respect to the wild‐type protein. In this study, we characterized the D76N b2M aggregation path and performed an unprecedented analysis of the biochemical mechanisms underlying aggregate cytotoxicity. We showed that, contrarily to what expected from other amyloid studies, early aggregates of the mutant are not the most toxic species, despite their higher surface hydrophobicity. By modulating ganglioside GM1 content in cell membrane or synthetic lipid bilayers, we confirmed the pivotal role of this lipid as aggregate recruiter favouring their cytotoxicity. We finally observed that the aggregates bind to the cell membrane inducing an alteration of its elasticity (with possible functional unbalance and cytotoxicity) in GM1‐enriched domains only, thus establishing a link between aggregate‐membrane contact and cell damage.

Solution-Processed Hybrid Graphene Flake/2H-MoS2 Quantum Dot Heterostructures for Efficient Electrochemical Hydrogen Evolution

We designed solution-processed, flexible hybrid graphene flake/2H-MoS2 quantum dot (QD) heterostructures, showing enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) with respect to their native individual components. The 2H-MoS2 QDs are produced through a scalable, environmentally friendly, one-step solvothermal approach from two-dimensional (2D) 2H-MoS2 flakes obtained by liquid phase exfoliation (LPE) of their bulk counterpart in 2-Propanol. This QDs synthesis avoids the use of high boiling point and/or toxic solvents. Graphene flakes are produced by LPE of graphite in N-Methyl-2-pyrrolidone. The electrochemical properties of 2H-MoS2 QDs and their HER-favorable chemical and electronic coupling with graphene enable to reach current density of 10 mA/cm² at an overpotential of 136 mV, surpassing the performances of graphene flake/2H-MoS2 (1T-MoS2) flake heterostructures. Our approach provides a shortcut, viable and cost-effective method for enhancing the 2D materials electrocataly...

Interaction of toxic and non-toxic HypF-N oligomers with lipid bilayers investigated at high resolution with atomic force microscopy

Protein misfolded oligomers are considered the most toxic species amongst those formed in the process of amyloid formation and the molecular basis of their toxicity, although not completely understood, is thought to originate from the interaction with the cellular membrane. Here, we sought to highlight the molecular determinants of oligomer-membrane interaction by atomic force microscopy. We monitored the interaction between multiphase supported lipid bilayers and two types of HypF-N oligomers displaying different structural features and cytotoxicities. By our approach we imaged with unprecedented resolution the ordered and disordered lipid phases of the bilayer and different oligomer structures interacting with either phase. We identified the oligomers and lipids responsible for toxicity and, more generally, we established the importance of the membrane lipid component in mediating oligomer toxicity. Our findings support the importance of GM1 ganglioside in mediating the oligomer-bilayer interaction and support a mechanism of oligomer cytotoxicity involving bilayer destabilization by globular oligomers within GM1-rich ordered raft regions rather than by annular oligomers in the surrounding disordered membrane domains.

Amyloid and membrane complexity: The toxic interplay revealed by AFM

Lipid membranes play a fundamental role in the pathological development of protein misfolding diseases. Several pieces of evidence suggest that the lipid membrane could act as a catalytic surface for protein aggregation. Furthermore, a leading theory indicates the interaction between the cell membrane and misfolded oligomer species as the responsible for cytotoxicity, hence, for neurodegeneration in disorders such as Alzheimers and Parkinsons disease. The definition of the mechanisms that drive the interaction between pathological protein aggregates and plasma membrane is fundamental for the development of effective therapies for a large class of diseases. Atomic force microscopy (AFM) has been employed to study how amyloid aggregates affect the cell physiological properties. Considerable efforts were spent to characterize the interaction with model systems, i.e., planar supported lipid bilayers, but some works also addressed the problem directly on living cells. Here, an overview of the main works involving the use of the AFM on both model system and living cells will be provided. Different kind of approaches will be presented, as well as the main results derived from the AFM analysis.

Engineered MoSe2‐Based Heterostructures for Efficient Electrochemical Hydrogen Evolution Reaction

Two-dimensional transition metal-dichalcogenides are emerging as efficient and cost-effective electrocatalysts for hydrogen evolution reaction (HER). However, only the edge sites of their trigonal prismatic phase show HER-electrocatalytic properties, while the basal plane, which is absent of defective/unsaturated sites, is inactive. Here, we tackle the key challenge that is increasing the number of electrocatalytic sites by designing and engineering heterostructures composed of single-/few-layer MoSe2 flakes and carbon nanomaterials (graphene or single-wall carbon nanotubes (SWNTs)) produced by solution processing. The electrochemical coupling between the materials that comprise the heterostructure effectively enhances the HER-electrocatalytic activity of the native MoSe2 flakes. The optimization of the mass loading of MoSe2 flakes and their electrode assembly via monolithic heterostructure stacking provided a cathodic current density of 10mAcm-2 at overpotential of 100mV, a Tafel slope of 63mVdec-1 and an exchange current density (j0) of 0.203 Acm-2. In addition, electrode thermal annealing in a hydrogen environment and chemical bathing in n-butyllithium are exploited to texturize the basal planes of the MoSe2 flakes (through Se-vacancies creation) and to achieve in situ semiconducting-to-metallic phase conversion, respectively, thus they activate new HER-electrocatalytic sites. The as-engineered electrodes show a 4.8-fold enhancement of j0 and a decrease in the Tafel slope to 54mVdec-1.

3D porous polyurethanes featured by different mechanical properties: Characterization and interaction with skeletal muscle cells

The fabrication of biomaterials for interaction with muscle cells has attracted significant interest in the last decades. However, 3D porous scaffolds featured by a relatively low stiffness (almost matching the natural muscle one) and highly stable in response to cyclic loadings are not available at present, in this context. This work describes 3D polyurethane-based porous scaffolds featured by different mechanical properties. Biomaterial stiffness was finely tuned by varying the cross-linking degree of the starting foam. Compression tests revealed, for the softest material formulation, stiffness values close to the ones possessed by natural skeletal muscles. The materials were also characterized in terms of local nanoindenting, rheometric properties and long-term stability through cyclic compressions, in a strain range reflecting the contraction extent of natural muscles. Preliminary in vitro tests revealed a preferential adhesion of C2C12 skeletal muscle cells over the softer, rougher and more porous structures. All the material formulations showed low cytotoxicity.

Tunable Friction Behavior of Photochromic Fibrillar Surfaces

Grasslike compliant micro/nano crystals made of diarylethene (DAE) photochromic molecules are spontaneously formed on elastomer films after dipping them in a solution containing the photochromic molecules. The frictional forces of such micro- and nanofibrillar surfaces are reversibly tuned upon ultraviolet (UV) irradiation and dark storage cycles. This behavior is attributed to the Youngs modulus variation of the single fibrils due to the photoisomerization process of the DAE molecules, as measured by advanced atomic force microscopy (AFM) techniques. In fact, a significant yet reversible decrease of the stiffness of the outer part of the fibrils in response to the UV light irradiation is demonstrated. The modification of the molecular structure of the fibrils influences their mechanical properties and affects the frictional behavior of the overall fibrillar surfaces. These findings provide the possibility to develop a system that controllably and accurately generates both low and high friction forces.

ITO nanoparticles break optical transparency/high-areal capacitance trade-off for advanced aqueous supercapacitors

The ever-increasing demand for energy storage in portable electronic devices is driving research on supercapacitor technology. In this context, optical transparency and mechanical robustness of supercapacitors are the key properties for the development of next-generation multifunctional devices, such as head-up displays, high-aesthetic touch screens and monolithic energy conversion/storage integrated systems. Here, we demonstrate that indium tin oxide nanoparticles (ITO NPs) are ideal materials for a facile solution-processed fabrication of transparent/semi-transparent electrodes with high areal capacitance (Careal) in aqueous solutions (1 M Na2SO4), overcoming the crucial trade-off between optical transparency and areal supercapacitor performance. In particular, our ITO NP electrodes exhibit Careal values of 0.40, 0.72 1.53, 3.41, and 6.45 mF cm−2 at 0.2 mA cm−2 for a transmittance (T) of 81.9%, 69.7%, 64.4%, 46.6% and 26.7% at 550 nm, respectively. The Careal values at current densities higher than 1.2 mA cm−2 are record-high (i.e., 0.81, 1.76 and 3.17 mF cm−2 at 10 mA cm−2 for a T of 64.4%, 46.6% and 26.7% at 550 nm). Indium tin oxide nanoparticle electrodes show 94% capacitance retention over 10 000 charge–discharge cycles. Flexible electrodes are also designed on a polyethylene terephthalate substrate, showing operational activity over 100 bending cycles under curvature radii of 1 and 0.5 cm. Finally, the coating of the ITO NP electrode with a photoactive polymer, i.e., rr-poly(3-hexylthiophene), permits the fabrication of a light-powered supercapacitor, as a clear-cut case of an innovative hybrid electric power delivery device, storing an energy density of 17.54 nW h cm−2 under simulated sunlight illumination.

High-yield production of 2D crystals by wet-jet milling

Efficient and scalable production of two-dimensional (2D) materials is required to overcome technological hurdles towards the creation of a 2D-material-based industry. Here, we present a novel approach developed for the exfoliation of layered crystals, i.e., graphite, hexagonal-boron nitride and transition metal dichalcogenides. The process is based on high-pressure wet-jet-milling (WJM), resulting in a 2 L h−1 production of 10 g L−1 of single- and few-layer 2D crystal flakes in dispersion making the scaling-up more affordable. The WJM process enables the production of defect-free and high quality 2D-crystal dispersions on a large scale, opening the way for their full exploitation in different commercial applications, e.g., as anode active material in lithium ion batteries, as reinforcement in polymer–graphene composites, and as conductive inks, as we demonstrate in this report.