RESUMO
Capacity retention is a critical property to enhance in electrochemical storage systems applied to renewable energy. In lithium-sulfur (Li-S) batteries, the capacity fade resulting from the shuttle effect of polysulfides is a major obstacle to their practical application. Sepiolite, an eco-friendly earth-abundant clay with suitable surface chemistry for anchoring and retaining various molecules and structures, was studied as a cathode additive to mitigate the shuttle effect using experimental and theoretical approaches. Electrochemical measurements, spectroscopy, and ab initio calculations were performed to describe the mechanism and interfaces involved in polysulfide retention using 2 wt% of sepiolite as an additive in Li-S batteries. The results showed that the addition of sepiolite significantly improved the capacity retention during battery cycling. Spectroscopic analysis revealed that the effective sepiolite-polysulfide interface was governed by oxidized sulfur species. Additionally, ab initio studies showed a highly exothermic adsorption both inside and outside the sepiolite pore. This study demonstrates the potential use of eco-friendly, low-cost, non-toxic, natural, and abundant materials as additives to increase capacity retention.
RESUMO
At the present, no secreted phospholipase A2 (sPLA2) from soybean (Glycine max) was investigated in detail. In this work we identified five sequences of putative secreted sPLA2 from soybean after a BLAST search in G. max database. Sequence analysis showed a conserved PA2c domain bearing the Ca²âº binding loop and the active site motif. All the five mature proteins contain 12 cysteine residues, which are commonly conserved in plant sPLA2s. We propose a phylogenetic tree based on sequence alignment of reported plant sPLA2s including the novel enzymes from G. max. According to PLA2 superfamily, two of G. max sPLA2s are grouped as XIA and the rest of sequences as XIB, on the basis of differences found in their molecular weights and deviating sequences especially in the N- and C-terminal regions of the isoenzymes. Furthermore, we report the cloning, expression and purification of one of the putative isoenzyme denoted as GmsPLA2-XIA-1. We demonstrate that this mature sPLA2 of 114 residues had PLA2 activity on Triton:phospholipid mixed micelles and determine the kinetic parameters for this system. We generate a model based on the known crystal structure of sPLA2 from rice (isoform II), giving first insights into the three-dimensional structure of folded GmsPLA2-XIA-1. Besides describing the spatial arrangement of highly conserved pair HIS-49/ASP-50 and the Ca⺲ loop domains, we propose the putative amino acids involved in the interfacial recognition surface. Additionally, molecular dynamics simulations indicate that calcium ion, besides its key function in the catalytic cycle, plays an important role in the overall stability of GmsPLA2-XIA-1 structure.
Assuntos
Glycine max/enzimologia , Glycine max/genética , Fosfolipases A2/genética , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Biocatálise , Cálcio/química , Cálcio/metabolismo , Clonagem Molecular , Simulação por Computador , Eletroforese em Gel de Poliacrilamida , Eritrócitos/metabolismo , Hemólise , Humanos , Isoenzimas/classificação , Isoenzimas/genética , Isoenzimas/metabolismo , Cinética , Modelos Moleculares , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Fosfolipases A2/química , Fosfolipases A2/metabolismo , Filogenia , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Homologia de Sequência de Aminoácidos , Espectrometria de FluorescênciaRESUMO
Nanoripple structures spontaneously formed at room temperature during chemical and electrochemical deposition of metals, semiconductors, and alloys on gold and copper templates, patterned with nanocavities, have been studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Annealing the templates at approximately equal to 373 K also results in ripple formation. Both experimental results and modeling, including anisotropic surface diffusion, demonstrate that nanocavity size in the template determines the ripple wavelength and amplitude, prior to a final stage of coarsening. Therefore, an ordered array of "nanodefects" introduced in the substrate is able to guide the self-organization of these nanofeatures during their growth, creating the possibility for nanofabrication of parallel interconnections with adjustable periodicity. Ripples are robust nanostructures that can in turn be used as templates for the preparation of hybrid nanostructured surfaces with specific physical properties.