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Capacitance response in an aqueous electrolyte of Nb2O5 nanochannel layers anodically grown in pure molten o-H3PO4

Publication . Upadhyay, Kush; Cha, Gihoon; Hildebrand, Helga; Schmuki, Patrik; Moura E Silva, Teresa; MONTEMOR, FATIMA; Altomare, Marco

Vertically aligned Nb2O5 nanochannel layers are grown on Nb metal substrates by self-organizing electrochemical anodization in a pure molten o-H3PO4 electrolyte. The capacitive behavior of these structures when used as negative electrodes is investigated in aqueous 1 M Na2SO4 electrolyte, in a potential range from −0.2 to −1.25 V vs. SCE. Surface chemistry, morphology and crystallographic features of the Nb2O5 nanochannel electrodes are tailored by adjusting the synthesis parameters, namely anodization time and crystallization temperature, which have a significant effect on the electrode performance. 8 μm thick Nb2O5 nanochannel layers that are converted into orthorhombic phase by crystallization at 450 °C, display a maximized areal capacitance of ∼100 mF cm-2 at a current density of 1 mA cm−2. These electrodes retain 63% of the initial capacitance at 10 mA cm−2 and 81% after 1500 charge-discharge cycles at a current density of 1.3 mA cm−2. Kinetic analysis of the electrochemical results reveals the occurrence of pseudocapacitive and diffusion-controlled processes. Electrochemical impedance spectroscopy evidences for these structures a low resistance across the electrode and at the electrode/substrate interface. These results are associated with the nanochannel morphology (high active area) of the Nb2O5 layers, and are ascribed to their crystalline nature, which provides an “oriented porosity” for ion diffusion and directional pathways for charge transport and collection.

2018-08-10Journal article

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A sustainable synthesis of asymmetric phenazines and phenoxazinones mediated by CotA-Laccase

Publication . Sousa, Ana Catarina; Oliveira, Maria Conceição; Martins, Lígia O.; Robalo, Maria Paula

An efficient and sustainable one-step procedure for the synthesis of new asymmetric phenazines and phenoxazinones from commercially available ortho-substituted diamines and ortho-substituted hydroxyamines is reported. In this study we have expanded the substrate scope of CotA-laccase-catalyzed aerobic oxidations through the use of aromatic amines presenting variable functional groups, including N-substitution, contributing to the rational synthesis of different heterocyclic scaffolds. The transformations proceed smoothly through a cascade of oxidative reactions to the benzoquinonediimine intermediates followed by nucleophilic addition, intramolecular cyclization and aromatization, all performed in mild conditions.

2018-02-01Journal article

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Pseudocapacitive response of hydrothermally grown MoS2 crumpled nanosheet on carbon fiber

Publication . Upadhyay, Kush; Nguyen, Tuyen; Moura E Silva, Teresa; Carmezim, Maria; MONTEMOR, FATIMA

Crumpled MoS2 nanosheets were synthesized directly on carbon fiber paper (CFP) through hydrothermal procedure. Molybdenum sulfide precursor was first produced in the solution and then introduced into the autoclave. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirmed the uniform growth of crumpled nanosheets on the CFP that were assigned to MoS2 according to X-ray photo electron spectroscopy (XPS) and Raman spectroscopy results. Electrochemical measurements of the as deposited MoS2 crumpled nanosheets performed in 1 M Na2SO4 evidenced a specific capacitance of 249 F g−1 at 2 A g−1 and the good rate capability by retaining 41.3% of initial capacitance at 10 A g−1. Electrochemical Impedance spectroscopy measurements showed very low charge transfer resistance and very short relaxation time accounting for the pseudocapacitive rectangular cyclic voltammetry (CV) and high rate capability.

2018-09-01Journal article

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Engineering a bacterial DyP-Type peroxidase for enhanced oxidation of lignin-related phenolics at alkaline pH

Publication . Brissos, Vânia; Tavares, Diogo; Sousa, Ana Catarina; Robalo, Maria Paula; Martins, Lígia O.

Dye-decolorizing peroxidases (DyPs) are a family of microbial heme-containing peroxidases that show important properties for lignocellulose biorefineries due to their ability to oxidize lignin-related compounds. Directed evolution was used to improve the efficiency of the bacterial PpDyP from Pseudomonas putida MET94 for phenolic compounds. Three rounds of random mutagenesis by error prone PCR of the ppDyP gene followed by high-throughput screening allow identification of the 6E10 variant showing a 100-fold enhanced catalytic efficiency (k(ca)t/K-m) for 2,6-dimethoxyphenol (DMP), similar to that exhibited by fungal lignin peroxidases (similar to 10(5) M-1 s(-1)). The evolved variant showed additional improved efficiency for a number of syringyl-type phenolics, guaiacol, aromatic amines, Kraft lignin, and the lignin phenolic model dimer guaiacylglycerol-beta-guaiacyl ether. Importantly, variant 6E10 displayed optimal pH at 8.5, an upshift of 4 units in comparison to the wild type, showed resistance to hydrogen peroxide inactivation, and was produced at 2-fold higher yields. The acquired mutations in the course of the evolution affected three amino acid residues (E188K, A142V, and H125Y) situated at the surface of the enzyme, in the second shell of the heme cavity. Biochemical analysis of hit variants from the laboratory evolution, and single variants constructed using site-directed mutagenesis, unveiled the critical role of acquired mutations from the catalytic, stability, and structural viewpoints. We show that epistasis between A142V and E188K mutations is crucial to determine the substrate specificity of 6E10. Evidence suggests that ABTS and DMP oxidation occurs at the heme access channel. Details of the catalytic cycle of 6E10 were elucidated through transient kinetics, providing evidence for the formation of a reversible enzyme hydrogen peroxide complex (Compound 0) barely detected in the majority of heme peroxidases studied to date.

2017-05Journal article

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Half-sandwich Ru(p-cymene) compounds with diphosphanes: In Vitro and In Vivo evaluation as potential anticancer metallodrugs

Publication . Lenis Rojas, Oscar; Robalo, M. Paula; Tomaz, Ana Isabel; Fernandes, Alexandra; Roma-Rodrigues, Catarina; Gonçalves Teixeira, Ricardo; Marques, Fernanda; FOLGUEIRA, MONICA; Yáñez, Julián; Alba-González, Anabel; Salamini-Montemurri, Martin; Pech-Puch, Dawrin; Vázquez-García, Digna; López-Torres, Margarita; Fernandez, Alberto; Fernandez, Jesus J.

Ruthenium(II) complexes are currently considered attractive alternatives to the widely used platinum-based drugs. We present herein the synthesis and characterization of half-sandwich ruthenium compounds formulated as [Ru(p-cymene)(L)Cl]-[CF3SO3] (L = 1,1-bis(methylenediphenylphosphano)ethylene, 1; L = 1,1-bis(diphenylphosphano)ethylene, 2), which were characterized by elemental analysis, mass spectrometry, H-1 and P-31{H-1} NMR, UV-vis and IR spectroscopy, conductivity measurements and cyclic voltammetry. The molecular structures for both complexes were determined by single-crystal X-ray diffraction. Their cytotoxic activity was evaluated using the MTT assay against human tumor cells, namely ovarian (A2780) and breast (MCF7 and MDA-MB-231). Both complexes were active against breast adenocarcinoma cells, with complex 1 exhibiting a quite remarkable cytotoxicity in the submicromolar range. Interestingly, at concentrations equivalent to the IC50 values in the MCF7 cancer cells, complexes 1 and 2 presented lower cytotoxicity in normal human primary fibroblasts. The antiproliferative effects of 1 and 2 in MCF7 cells might be associated with the induction of reactive oxygen species (ROS), leading to a combined cell death mechanism via apoptosis and autophagy. Despite the fact that in vitro a partial intercalation between complexes and DNA was observed, no MCF7 cell cycle delay or arrest was observed, indicating that DNA might not be a direct target. Complexes 1 and 2 both exhibited a moderate to strong interaction with human serum albumin, suggesting that protein targets may be involved in their mode of action. Their acute toxicity was evaluated in the zebrafish model. Complex 1 (the most toxic of the two) exhibited a lethal toxicity LC50 value about 1 order of magnitude higher than any IC50 concentrations found for the cancer cell models used, highlighting its therapeutic relevance as a drug candidate in cancer chemotherapy.

2021-02-11Journal article

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