Nanocomposite Polymer Electrolytes for Zinc and Magnesium Batteries: From Synthetic to Biopolymers

The diversification of current forms of energy storage and the reduction of fossil fuel consumption are issues of high importance for reducing environmental pollution. Zinc and magnesium are multivalent ions suitable for the development of environmentally friendly rechargeable batteries. Nanocomposite polymer electrolytes (NCPEs) are currently being researched as part of electrochemical devices because of the advantages of dispersed fillers. This article aims to review and compile the trends of different types of the latest NCPEs. It briefly summarizes the desirable properties the electrolytes should possess to be considered for later uses. The first section is devoted to NCPEs composed of poly(vinylidene Fluoride-co-Hexafluoropropylene). The second section centers its attention on discussing the electrolytes composed of poly(ethylene oxide). The third section reviews the studies of NCPEs based on different synthetic polymers. The fourth section discusses the results of electrolytes based on biopolymers. The addition of nanofillers improves both the mechanical performance and the ionic conductivity; key points to be explored in the production of batteries. These results set an essential path for upcoming studies in the field. These attempts need to be further developed to get practical applications for industry in large-scale polymer-based electrolyte batteries

Chitosan-Carboxymethylcellulose Hydrogels as Electrolytes for Zinc–Air Batteries: An Approach to the Transition towards Renewable Energy Storage Devices

Biopolymers are promising materials as electrolytes with high flexibility, good performance, cost effectiveness, high compatibility with solvents, and film-forming ability. Chitosan (CS) and carboxymethylcellulose (CMC) can form an intermolecular complex, giving rise to hydrogels capable of absorbing ionic solutions. Citric acid (CA) is an effective biological chemical crosslinker that assists the formation of amide and ester bonds between CMC and CS, resulting in a structure with high ionic conductivity and good structural integrity. In this study, a chemical crosslinking strategy is used to synthesize electrolyte hydrogels for zinc–air batteries. The effects of crosslinking are studied on the structural and electrochemical performance of the membranes. The results show an improvement in the ionic conductivity with respect to the homologous electrolyte hydrogel systems reported, with a maximum of 0.19 S∙cm−1 at 30 °C. In addition, the cyclic voltammetry studies showed a current intensity increase at higher CA content, reaching values of 360 mA∙cm−2. Structural characterization suggests a higher thermal stability and a decrease in the degree of crystallinity caused by the polymers’ crosslinking. Finally, these membranes were tested in Zn–air batteries, obtaining power densities of 85 mW∙cm−2. The proposed hydrogels show to be appropriate for energy zinc–air battery applications and present an alternative to support the sustainable energy transition

Contribución al mecanismo de formación de poros de sticholisina I, una proteína formadora de poros de la anémona Stichodactyla helianthus, mediante el empleo de mutantes de Cys en zonas funcionalmente relevantes de la proteína

Sticholisina I (St I) es una citolisina producida por la anémona marina Stichodactyla helianthus, que se caracteriza por formar poros oligoméricos en membranas naturales y artificiales. En este trabajo se describe la obtención por vía recombinante en Escherichia coli (E. coli) de una variante recombinante de St I (St Ir), así como su caracterización conformacional y funcional. Estos trabajos permitieron reducir el impacto ecológico que provoca la obtención de St I a partir de las anémonas como fuente natural y además realizar mutagénesis sitio-específica para su caracterización funcional. La ausencia de Cys en St I facilitó la introducción de este residuo aminoacídico, por mutagénesis dirigida, en zonas funcionalmente importantes de la toxina. En el trabajo se sustituyeron por Cys en St Ir de forma independiente, los aminoácidos Glu2 y Phe15 (localizados en el segmento de los primeros treinta aminoácidos que participan en la formación del canal) y la Arg52, Pro80 y Trp111 (en la región de interacción con las membranas). Así, se obtuvieron y purificaron de E. coli cinco proteínas mutadas: StI E2C, StI F15C, StI R52C, StI P80C y StI W111C. Los estudios de caracterización espectroscópicos permitieron establecer que las sustituciones aminoacídicas no provocaron cambios conformacionales en los mutantes con respecto a St Ir. Los monómeros de StI E2C, StI R52C y StI P80C mostraron capacidades similares de unión a las membranas en comparación con la variante recombinante. StI F15C mostró un ligero incremento en su capacidad de interacción con las membranas mientras que StI W111C resultó la de menor capacidad de unión. La capacidad formadora de poros de los monómeros, medida en vesículas liposomales y membrana eritrocitaria, resultó similar entre StI E2C, StI F15C y St Ir. Sin embargo, la actividad lítica de StI R52C, StI P80C y StI W111C disminuyó con respecto a St Ir. Los agregados diméricos por enlace disulfuro en StI R52C y StI W111C disminuyeron la actividad biológica de las proteínas. Una de las novedades científicas más importante del presente trabajo radica en que se demuestra que la presencia de agregados diméricos estabilizados por enlace disulfuro, en StI E2C, incrementa la actividad biológica formadora de poros tanto en vesículas liposomales como en eritrocitos. Estos resultados demuestran, por primera vez, que la unión covalente de los extremos aminos de St I potencia la formación de poros funcionales por un mecanismo hasta ahora desconocido. En la investigación se aportan nuevos elementos sobre la importancia de los residuos Glu2, Phe15, Arg52, Pro80 y Trp111 en las etapas de unión inicial a las membranas y de formación de poros durante el mecanismo lítico. Por último, la obtención de los mutantes de Cys abre las posibilidades para el marcaje de St I con sondas de espín o sondas fluorescentes para estudiar el mecanismo de formación de poros mediante las espectroscopias de resonancia paramagnética electrónica (EPR) y de fluorescencia, y sustentan otras aplicaciones nanobiotecnológicas actualmente en desarrollo en nuestro grupo de trabajo.Sticholisin I (St I) is a cytolysin produced by the sea anemone Stichodactyla helianthus, which is characterized by forming oligomeric pores in natural and artificial membranes. This work describes the recombinant production in Escherichia coli (E. coli) of a recombinant variant of St I (St Ir), as well as its conformational and functional characterization. These works allowed us to reduce the ecological impact caused by obtaining St I from anemones as a natural source and also perform site-specific mutagenesis for its functional characterization. The absence of Cys in St I facilitated the introduction of this amino acid residue, by directed mutagenesis, into functionally important areas of the toxin. In the work, the amino acids Glu2 and Phe15 (located in the segment of the first thirty amino acids that participate in the formation of the channel) and Arg52, Pro80 and Trp111 (in the interaction region) were independently replaced by Cys in St Ir. with the membranes). Thus, five mutated proteins were obtained and purified from E. coli: StI E2C, StI F15C, StI R52C, StI P80C and StI W111C. Spectroscopic characterization studies allowed us to establish that amino acid substitutions did not cause conformational changes in the mutants with respect to St Ir. The monomers of StI E2C, StI R52C and StI P80C showed similar binding capacities to membranes compared to the recombinant variant. StI F15C showed a slight increase in its interaction capacity with membranes while StI W111C had the lowest binding capacity. The pore-forming capacity of the monomers, measured in liposomal vesicles and erythrocyte membrane, was similar between StI E2C, StI F15C and St Ir. However, the lytic activity of StI R52C, StI P80C and StI W111C decreased with respect to St Ir The dimeric aggregates by disulfide bond in StI R52C and StI W111C decreased the biological activity of the proteins. One of the most important scientific novelties of the present work is that it is demonstrated that the presence of dimeric aggregates stabilized by disulfide bond, in StI E2C, increases the pore-forming biological activity in both liposomal vesicles and erythrocytes. These results demonstrate, for the first time, that covalent attachment of the amino termini of St I enhances the formation of functional pores by a previously unknown mechanism. The research provides new elements on the importance of residues Glu2, Phe15, Arg52, Pro80 and Trp111 in the stages of initial binding to membranes and pore formation during the lytic mechanism. Finally, obtaining the Cys mutants opens the possibilities for labeling St I with spin probes or fluorescent probes to study the mechanism of pore formation through electron paramagnetic resonance (EPR) and fluorescence spectroscopies, and support other nanobiotechnological applications currently under development in our working group.Universidad Nacional, Costa RicaAcademia de Ciencias de Cuba, CubaEscuela de Ciencias Biológica