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- On the development of selective chelators for Cadmium: Synthesis, structure and chelating properties of 3-((5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl)amino)benzo[d]isothiazole 1,1-dioxide, a novel Thiadiazolyl SaccharinatePublication . Leal, Joana F.; Guerreiro, Bruno; Amado, Patrícia; Fernandes, André L.; Barreira, Luísa; Paixão, José A.; Lurdes S. Cristiano, M.Aquatic contamination by heavy metals is a major concern for the serious negative consequences it has for plants, animals, and humans. Among the most toxic metals, Cd(II) stands out since selective and truly efficient methodologies for its removal are not known. We report a novel multidentate chelating agent comprising the heterocycles thiadiazole and benzisothiazole. 3-((5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl)amino)benzo[d]isothiazole 1,1-dioxide (AL14) was synthesized from cheap saccharin and characterized by different techniques, including single crystal X-ray crystallography. Our studies revealed the efficiency and selectivity of AL14 for the chelation of dissolved Cd(II) (as compared to Cu(II) and Fe(II)). Different spectral changes were observed upon the addition of Cd(II) and Cu(II) during UV-Vis titrations, suggesting different complexation interactions with both metals.
- The potential of Chitosan-Based composites for adsorption of diarrheic shellfish toxinsPublication . Leal, Joana F.; Amado, Patrícia; P. Lourenço, J.; Lurdes Santos Cristiano, MariaOkadaic acid (OA) is one of the most potent marine biotoxins, causing diarrheal shellfish poisoning (DSP). The proliferation of microalgae that produce OA and its analogues is frequent, threatening human health and socioeconomic development. Several methods have been tested to remove this biotoxin from aquatic systems, yet none has proven enough efficacy to solve the problem. In this work, we synthesized and characterized low-cost composites and tested their efficacy for OA adsorption in saltwater. For the synthesis of the composites, the following starting materials were considered: chitosan of low and medium molecular weight (CH-LW and CH-MW, respectively), activated carbon (AC), and montmorillonite (MMT). Characterization by vibrational spectroscopy (FTIR), X-ray diffraction (XRD), and microscopy revealed differences in the mode of interaction of CH-LW and CH-MW with AC and MMT, suggesting that the interaction of CH-MW with MMT has mainly occurred on the surface of the clay particles and no sufficient intercalation of CH-MW into the MMT interlayers took place. Among the composites tested (CH-LW/AC, CH-MW/AC, CH-MW/AC/MMT, and CH-MW/MMT), CH-MW/MMT was the one that revealed lower OA adsorption efficiency, given the findings evidenced by the structural characterization. On the contrary, the CH-MW/AC composite revealed the highest average percentage of OA adsorption (53 ± 11%). Although preliminary, the results obtained in this work open up good perspectives for the use of this type of composite material as an adsorbent in the removal of OA from marine environments.
- TiO2-rGO nanocomposite as an efficient catalyst to photodegrade formalin in aquaculture's waters, under solar lightPublication . Leal, Joana F.; Cruz, Sandra M. A.; Almeida, Bernardo T. A.; Esteves, Valdemar, I; Marques, Paula A. A. P.; Santos, Eduarda B. H.Formalin or hydrate of formaldehyde, a common disinfectant used in aquaculture, is not able to absorb sunlight, therefore its photodegradation must be catalyzed. To take advantage of sunlight for its photodegradation, TiO2-reduced graphene oxide (TiO2-rGO) nanocomposites with different GO contents (0.25-3.0 wt%) were synthesized and characterized by scanning electron microscopy (SEM), UV-vis and ATR-FTIR spectroscopies. Additionally, their specific surface areas (S-BET), pore volume and size were determined. The photocatalysts efficiency for formaldehyde (FM) degradation under simulated sunlight was assessed in aqueous solution. Among the nanocomposites considered, TiO2-rGO 0.5 wt% was the most efficient, achieving 93.8 +/- 4.6% of FM photodegradation in 90 min. The same irradiation conditions were applied in natural water matrices (aquaculture's freshwater and saltwater) to evaluate the influence of natural water constituents on photocatalysis. The photodegradation percentages obtained were 63.7 +/- 0.6% and 16.0 +/- 1.4% in aquaculture's freshwater and saltwater, respectively. This lower efficiency to photodegrade FM in natural aqueous matrices is attributed to the inhibition of photocatalytic oxidation of organic compounds caused by dissolved organic matter (DOM) and inorganic ions existing in the aquatic environment. Nevertheless, the results obtained for photocatalytic efficiency in natural waters are promising, suggesting a great potential of application in green photocatalysis to remove FM from contaminated freshwater.
- Cation-exchange resin applied to paralytic Shellfish toxins depuration from Bivalves exposed to Gymnodinium catenatumPublication . Leal, Joana F.; Bombo, Gabriel; Amado, Patrícia; Pereira, Hugo; Lurdes S. Cristiano, M.The accumulation of marine biotoxins in shellfish and their consumption causes serious food safety problems, threatening human health and compromising the availability of protein-based food. It is thus urgent to develop methodologies for the detoxification of live bivalves, avoiding their economic and nutritional devaluation. In this context, we tested an adsorption mechanism of paralytic shellfish toxins (PST) based on a cation-exchange resin. The first studies using cultures of Gymnodinium catenatum (natural producers of PST) showed a decrease of about 80% in overall toxicity after 48 h. Interestingly, we found that the toxins are adsorbed differently, with toxins’ structural features playing a part in the adsorption capacity via steric hindrance, electronic effects, or the extent of positive charge density (e.g., dcSTX). The positive effect of the resin in accelerating PST clearance from live mussels (Mytilus edulis) is not evident when compared to resin-free clearance; nevertheless, relevant information could be gathered that will facilitate further in vivo studies. Several factors appear to be at play, namely the competition of natural substances (e.g., salts, organic matter) for the same binding sites, the blocking of pores due to interactions between molecules, and/or difficulties in resin absorption by mussels. Additionally, the present work revealed the ability of mussels to neutralize pH and proposes bioconversion reactions among the PST molecules.
- Marine paralytic shellfish toxins: chemical properties, mode of action, newer analogues, and structure–toxicity relationshipPublication . Leal, Joana F.; Cristiano, Maria De LurdesUp to the end of 2020 Every year, the appearance of marine biotoxins causes enormous socio-economic damage worldwide. Among the major groups of biotoxins, paralytic shellfish toxins, comprising saxitoxin and its analogues (STXs), are the ones that cause the most severe effects on humans, including death. However, the knowledge that currently exists on their chemistry, properties and mode of toxicological action is disperse and partially outdated. This review intends to systematically compile the dispersed information, updating and complementing it. With this purpose, it addresses several aspects related to the molecular structure of these toxins. Special focus is given to the bioconversion reactions that may occur in the different organisms (dinoflagellates, bivalves, and humans) and the possible mediators involved. A critical review of the most recently discovered analogues, the M-series toxins, is presented. Finally, a deep discussion about the relationship between the molecular structure (e.g., effect of the substituting groups and the net charge of the molecules) and the toxic activity of these molecules is performed, proposing the concept of "toxicological traffic light" based on the toxicity equivalency factors (TEFs).
- Revisiting the HPLC-FLD method to quantify paralytic shellfish toxins: C3,4 quantification and the first steps towards validationPublication . Leal, Joana F.; Cristiano, Maria De LurdesParalytic shellfish toxins (PSTs) are a large group of biotoxins that cause paralytic shellfish poisoning. Their appearance in natural waters and their ingestion by aquatic species have a huge socio-economic impact, whereby their monitoring is of the upmost relevance to minimize the consequences. For earlier detection and faster response/action by stakeholders, validation of adjusted analytical methods, particularly for lower concentration levels, is important. This work proposes a derived High-Performance Liquid Chromatography method, with fluorescence detection (HPLC-FLD). The main differences from the official method are the size of the HPLC column and the gradient elution conditions. It covers the current eleven certified reference materials (CRM) available on the market, including the most recent—C3,4. This first calibration report for C3,4 suggests limits of detection (LOD) and limits of quantification (LOQ) of 6 nM and 19 nM (~5 µg STX.2HCl eqv./kg and 17 µg STX.2HCl eqv./kg), respectively. For the remaining CRM, LODs ranged between 3 and 28 nM (~0.9 and 127 µg STX.2HCl eqv./kg), while LOQs varied between 11 and 94 nM (~3 and 409 µg STX.2HCl eqv./kg, considering toxicity equivalency factors (TEFs) reported by EFSA).
- Why are bivalves not detoxified?Publication . Leal, Joana F.; Cristiano, Maria de LurdesParalytic (PSP), diarrheic (DSP), and amnesic shellfish poisonings are among the most prominent foodborne diseases threatening the food security. Because of the absence of legal methods capable of eliminating these biotoxins, the option is to rely on natural detoxification, compromising the availability of protein-based food and imposing severe socioeconomic impacts. In vivo detoxification methodologies have focused on the use of adsorbents (mainly applied to PSP), some of which are combined with nontoxic algae. Alternative methodologies for DSP have emerged, but they are based on absorption inhibition, which may be unfeasible in real situations. It is thus imperative to optimize existing proposals or develop novel, safe, and cost-effective methods so that the solution is seen as an attractive financial investment.
- Toxin profile of two Gymnodinium catenatum strains from Iberian Coastal WatersPublication . Leal, Joana F.; Bombo, Gabriel; Pereira, Hugo; Vicente, Bernardo; Amorim, Ana; Cristiano, Maria L. S.Gymnodinium catenatum has been the main species responsible for paralytic shellfish poisoning events along the Portuguese coast (Iberian Peninsula), causing bans on bivalve harvesting that result in huge economic losses. This work presents the characterization of two novel isolates of G. catenatum regarding their growth and toxin profiles. Laboratory growth experiments revealed that, although low growth rates were obtained during cultivation, the cell yields were high compared to those reported in the literature. Evaluation of the toxin profiles, by HPLC-FLD, essentially confirmed the typical composition of toxins of this regional population (Iberian Peninsula), namely, the absence or low representation of the toxins dcNEO, GTX1,4 and NEO and a higher ratio of the toxins C1,2, GTX6 and GTX5. However, the percentage of the identified toxins varied among the strains of this study (under the same isolation, growth, and analysis conditions), and also differed from that of other strains described in the literature. Interestingly, we found a comparatively high abundance of dcSTX in both strains, relative to the other toxins, and an unquantifiable amount of C3,4 toxins. In addition to the geographic relationship between toxin profiles, chemical conversions among toxins may explain some differences encountered in the toxin profiles of G. catenatum strains.