Showing: 10 from total: 69 publications
1. A simpler and greener alternative route for anchoring carbohydrates with structural integrity on silica and glass supports
Kadhirvel, P ; Azenha, M ; Ivanova, G ; Pereira, C ; Silva, AF
in JOURNAL OF CARBOHYDRATE CHEMISTRY, 2022, ISSN: 0732-8303,  Volume: 41, 
Article,  Indexed in: scopus, wos 
Abstract A novel, straightforward, and environmentally friendly direct coupling procedure to immobilize carbohydrates on solid supports is presented. A characterization study showed that all amino groups on solid supports participated in the linkage with a carbohydrate unit, implicating that the surface load can be easily adjusted by tuning the amination coverage of the surface. Most importantly, the integrity of the cyclic conformation of the linked sugar unit was demonstrated, a feature that is critical for most of the possible applications of carbohydrate-functionalized surfaces. Furthermore, carbohydrate-immobilized submicron particles synthesized by the direct coupling method, on which lectin profiling experiments were conducted, validated the successfulness of our simplistic approach.

2. Crystallization of hollow TiO2 into anatase at mild conditions, for improved surface recognition in selective photocatalysis
Ferreira, VRA ; Azenha, MA ; Pereira, CM ; Silva, AF
in APPLIED CATALYSIS A-GENERAL, 2022, ISSN: 0926-860X,  Volume: 648, 
Article,  Indexed in: scopus, wos 
Abstract The objective of this work was the exploration of low calcination temperature ranges (< 350 degrees C) to obtain molecularly imprinted microspheres (MIM) with a high crystallinity as anatase, in cooperation of an acidic pretreatment aiming at the preservation of the hollow shape and also of the selective binding sites. It was confirmed the possibility of obtaining bilirubin-imprinted crystalline TiO2 microspheres (highly crystalline anatase, as confirmed by XRD) exhibiting higher photocatalytic efficiency associated especially with the hollow shape and calcination at lower temperatures (200 degrees C or 250 degrees C). It was with the calcination temperature of 250 degrees C that the highest photocatalytic efficiency was obtained, under UV irradiation, associated with the highest adsorption selectivity (alpha(K) = 19) and degradation selectivity (alpha(k) = 2.7) observed for the degradation of the template against a closely related analogue compound.

3. Improved Metal Cation Optosensing Membranes through the Incorporation of Sulphated Polysaccharides
Santos, PRM ; Johny, A ; Silva, CQ ; Azenha, MA ; Vazquez, JA ; Valcarcel, J ; Pereira, CM ; Silva, AF
in MOLECULES, 2022, Volume: 27, 
Article,  Indexed in: wos 
Abstract Optosensing chitosan-based membranes have been applied for the detection of heavy metals, especially in drinking water. The novelty of this study is based on the use of sulphated polysaccharides, in such optosensing membranes, aiming at an improved analytical performance. The sulphated polysaccharides, such as ulvan, fucoidan and chondroitin sulfate, were extracted from by-products and wastes of marine-related activities. The membranes were developed for the analysis of aluminum. The variation in the visible absorbance of the sensor membranes after the contact between the chromophore and the aluminum cation was studied. The membranes containing sulphated polysaccharides showed improved signals when compared to the chitosan-only membrane. As for the detection limits for the membranes containing ulvan, fucoidan and chondroitin sulfate, 0.17 mg L-1, 0.21 mg L-1 and 0.36 mg L-1 were obtained, respectively. The values were much lower than that obtained for the chitosan-only membrane, 0.52 mg L-1, which shows the improvement obtained from the sulphated polysaccharides. The results were obtained with the presence of CTAB in analysis solution, which forms a ternary complex with the aluminum cation and the chromophore. This resulted in an hyperchromic and batochromic shift in the absorption band. When in the presence of this surfactant, the membranes showed lower detection limits and higher selectivity.

4. Molecularly Imprinted Methyl-Modified Hollow TiO2 Microspheres
Ferreira, VRA ; Azenha, MA ; Pereira, CM ; Silva, AF
in MOLECULES, 2022, ISSN: 1420-3049,  Volume: 27, 
Article,  Indexed in: crossref, scopus, unpaywall, wos 
Abstract The possibility of generating organically modified hollow TiO2 microspheres via a simple sol-gel synthesis was demonstrated for the first time in this work. A mixture of titania precursors, including an organically modified precursor, was used to obtain methyl-modified hollow TiO2 microspheres selective for bilirubin by the molecular imprinting technique (Methyl-HTM-MIM). Methyl-HTM-MIM were prepared by a sol-gel method using titanium (IV) isopropoxide (TTIP), and methyltitanium triisopropoxide (MTTIP) as precursors. Two ratios of titania precursors were tested (1/6 and 1/30 mol(MTTIP)/mol(TTIP)). With the characterization results obtained by the SEM and ATR-FTIR techniques, it was possible to establish that only the 1/30 mol(MTTIP)/mol(TTIP) ratio allowed for the preparation of hollow spheres with a reasonably homogeneous methylated-TiO2 shell. It was possible to obtain a certain degree of organization of the hybrid network, which increased with calcination temperatures. By adjusting isothermal adsorption models, imprinting parameters were determined, indicating that the new methylated microspheres presented greater selectivity for bilirubin than the totally inorganic hollow TiO2 microspheres. The effectiveness of the molecular imprinting technique was proven for the first time in an organically modified titania material, with imprinting factor values greater than 1.4, corresponding to a significant increase in the maximum adsorption capacity of the template represented by the molecularly imprinted microspheres. In summary, the results obtained with the new methyl-HTM-MIM open the possibility of exploring the application of these microspheres for selective sorption (separation or sensing, for example) or perhaps even for selective photocatalysis, particularly for the degradation of organic compounds.

5. Impact of Combined Heat and Salt Stresses on Tomato Plants-Insights into Nutrient Uptake and Redox Homeostasis
Sousa, B ; Rodrigues, F ; Soares, C ; Martins, M ; Azenha, M ; Lino Neto, T ; Santos, C ; Cunha, A ; Fidalgo, F
in ANTIOXIDANTS, 2022, Volume: 11, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Currently, salinity and heat are two critical threats to crop production and food security which are being aggravated by the global climatic instability. In this scenario, it is imperative to understand plant responses to simultaneous exposure to different stressors and the cross-talk between underlying functional mechanisms. Thus, in this study, the physiological and biochemical responses of tomato plants (Solanum lycopersicum L.) to the combination of salinity (100 mM NaCl) and heat (42 degrees C; 4 h/day) stress were evaluated. After 21 days of co-exposure, the accumulation of Na+ in plant tissues was superior when salt-treated plants were also exposed to high temperatures compared to the individual saline treatment, leading to the depletion of other nutrients and a harsher negative effect on plant growth. Despite that, neither oxidative damage nor a major accumulation of reactive oxygen species took place under stress conditions, mostly due to the accumulation of antioxidant (AOX) metabolites alongside the activation of several AOX enzymes. Nonetheless, the plausible allocation of resources towards the defense pathways related to oxidative and osmotic stress, along with severe Na toxicity, heavily compromised the ability of plants to grow properly when the combination of salinity and heat was imposed.

6. Subcellular compartmentalization of aluminum reduced its hazardous impact on rye photosynthesis
De Sousa, A ; AbdElgawad, H ; Fidalgo, F ; Teixeira, J ; Matos, M ; Tamagnini, P ; Fernandes, R ; Figueiredo, F ; Azenha, M ; Teles, LO ; Korany, SM ; Alsherif, EA ; Selim, S ; Beemster, GTS ; Asard, H
in ENVIRONMENTAL POLLUTION, 2022, ISSN: 0269-7491,  Volume: 315, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Aluminum (Al) toxicity limits crops growth and production in acidic soils. Compared to roots, less is known about the toxic effects of Al in leaves. Al subcellular compartmentalization is also largely unknown. Using rye (Secale cereale L.) Beira (more tolerant) and RioDeva (more sensitive to Al) genotypes, we evaluated the patterns of Al accumulation in leaf cell organelles and the photosynthetic and metabolic changes to cope with Al toxicity. The tolerant genotype accumulated less Al in all organelles, except the vacuoles. This suggests that Al compartmentalization plays a role in Al tolerance of Beira genotype. PSII efficiency, stomatal conductance, pigment biosynthesis, and photosynthesis metabolism were less affected in the tolerant genotype. In the Calvin cycle, carboxylation was compromised by Al exposure in the tolerant genotype. Other Calvin cycle-related enzymes, phoshoglycerate kinase (PGK), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), triose-phosphate isomerase (TPI), and fructose 1,6-bisphosphatase (FBPase) activities decreased in the sensitive line after 48 h of Al exposure. Consequentially, carbohydrate and organic acid metabolism were affected in a genotype-specific manner, where sugar levels increased only in the tolerant genotype. In conclusion, Al transport to the leaf and compartmentalization in the vacuoles tolerant genotype's leaf cells provide complementary mechanisms of Al tolerance, protecting the photosynthetic apparatus and thereby sustaining growth.

7. Recent advances in multivariate analysis coupled with chemical analysis for soil surveys: a review
Milinovic, J ; Vale, C ; Azenha, M
Review,  Indexed in: scopus, wos 
Abstract Purpose Soil is a complex open system covering various physical and chemical attributes. In soil testing, multivariate analysis (MVA) has an important application because it allows the interpretation of a large amount of data for the design of relevant environmental scenarios. The purpose of this research is to summarize recent applications of MVA for identifying soil types or characteristics and for predicting soil attributes with a critical evaluation. Methods Based on a comprehensive search of the available database, in this review, we have provided updated information on the most representative classification and regression MVA applied in the past decade in soil surveys. Regression MVA were compared in terms of applicability, efficiency, and predictive power of different soil attributes. Results Principal component analysis (PCA) allows the grouping of soils into independent clusters according to their differences in texture or physicochemical composition, which may mirror local or regional environmental signatures. PCA is also used to reduce the dimensionality of spectral data before their application in regression MVA. Partial least square regression (PLSR) is the most commonly applied regression MVA for predicting soil attributes after the correlation of spectra (e.g., Vis-NIR) vs. conventional analysis results. The resulting PLSR models, evaluated by correlation coefficient (R-2) and root mean squared error (RMSE), can be valid for the estimation of several soil attributes (e.g., organic carbon, clay). Conclusions Application of regression MVA may have limitations in predicting some soil attributes. Objective interpretation of the dynamic nature of soils requires the selection of representative samples as well as appropriate MVA, which can have significant potential in an effective soil survey.

8. Wrack Composed by Fucus spp, Ascophyllum nodosum and Pelvetia canaliculata Limits Metal Uptake and Restores the Redox Homeostasis of Barley Plants Grown in Cu-Contaminated Soils
Sousa, F ; Martins, M ; Sousa, B ; Soares, C ; Azenha, M ; Pereira, R ; Fidalgo, F
in JOURNAL OF PLANT GROWTH REGULATION, 2022, ISSN: 0721-7595,  Volume: 41, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Since metal contamination compromises crop growth and food safety, eco-friendly responses to prevent this are needed. This study provided an integrative evaluation of the potential of wrack (macroalgae debris) to increase the tolerance of Hordeum vulgare L. (barley plant) to copper (Cu).Plants were grown in a soil mixed with 219 mg Cu kg(-1) with/without 2% (m/m) wrack for 14 days. Copper impaired all growth-related parameters. Wrack application counteracted most of these negative impacts and lowered metal accumulation in roots. Metal exposure increased reactive oxygen species content [superoxide anion (O-2(center dot-)) and hydrogen peroxide [H2O2]) and lipid peroxidation degree, which was evaluated through the quantification of malondialdehyde, while co-treatment with wrack partially reverted some of these effects. The non-enzymatic antioxidant (AOX) system was mainly activated by Cu, with accumulated glutathione (GSH), ascorbate (AsA) and phenols, mostly in roots, while proline content was reduced. Wrack protective action was through a modulation of GSH and AsA redox state and enhanced ascorbate peroxidase. The results suggest wrack's potential to alleviate Cu-induced phytotoxicity, which probably relies on the reduction of Cu-induced oxidative stress through a more efficient activity of AOX metabolites and by limiting Cu absorption and bioaccumulation, especially in roots of barley plants.

9. The potential of beach wrack as plant biostimulant to mitigate metal toxicity: mineral composition, antioxidant properties and effects against Cu-induced stress
Sousa, F ; Martins, M ; Sousa, B ; Soares, C ; Azenha, M ; Pereira, R ; Fidalgo, F
in JOURNAL OF APPLIED PHYCOLOGY, 2022, ISSN: 0921-8971,  Volume: 34, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Plant biostimulants such as seaweed extracts, present a sustainable alternative to agrochemicals. Moreover, the accumulation of beach-cast seaweed (wrack), due to climate change and anthropic pressures, is expected to increase in the coming decades. Thus, from a perspective of circular economy, based on the valorisation of an organic residue, this study aimed at achieving an elemental and biochemical characterisation of beach wrack and understanding the effects of an aqueous extract prepared from this residue on the mitigation of metal-induced stress, using barley (Hordeum vulgare L.) as a model. The quantification of wrack's macro- and micronutrients showed that K, Ca and Na were the most abundant elements, being this composition similar to that of other organic fertilisers. Furthermore, despite the studied wrack having lower values of photosynthetic pigments, amino acids and sugars, higher amounts of phenols and flavonoids (8.35 +/- 0.24 and 3.95 +/- 1.22 mg g(-1) dry matter respectively) were detected when compared to freshly collected seaweeds. This work highlighted that wrack showed potential as a fertiliser-through increasing root biomass (63%) and leaf biometry (up to 45%) in plants treated with 5.0 and 7.5 g L-1 wrack extract alone-also being a possible cost-effective, eco-friendly and sustainable biostimulant to mitigate the phytotoxic effects of Cu, since plants treated with 7.5 g wrack L-1 showed an increase of 34% in leaf length, when compared to seedlings exposed only to Cu.

10. Early Activation of Antioxidant Responses in Ni-Stressed Tomato Cultivars Determines Their Resilience Under Co-exposure to Drought
Spormann, S ; Soares, C ; Martins, V ; Azenha, M ; Geros, H ; Fidalgo, F
Article in Press,  Indexed in: crossref, scopus, wos 
Abstract Throughout their life cycle, plants are subjected to a variety of environmental constraints, including abiotic stresses. The present study aimed at characterizing the responses of the two tomato cultivars Gold Nugget (GN) and Purple Calabash (PC) exposed to a combination of nickel (Ni) and drought. The following hypotheses were pursued: (i) the activation of responses to one stressor eases further adjustments to a second stressor; and (ii) the two tomato cultivars are differentially susceptible to drought and heavy metal-stress. Besides biometrical evaluations, the distribution of Ni in tissues and the redox homeostasis in both cultivars were compared in response to Ni-stress, polyethylene glycol (PEG)-induced drought, and to their combination. Regarding single stresses, Ni caused more harmful effects to plants than PEG-induced drought, in terms of growth inhibition and production of reactive oxygen species. Ni was mostly accumulated in the roots. The GN cultivar promptly activated antioxidant defenses under Ni-stress, while, in PC, such antioxidants were more strongly induced under combined stress. Stress co-exposure led to a drastic proline accumulation, resembling a signal of stress sensitivity. Overall, the GN cultivar seemed to be less susceptible to the combined stress than PC, as it could activate stronger antioxidant defenses under single Ni toxicity, possibly easing further adjustments demanded by the later co-exposure to drought. This study showed that the two cultivars of the same species had different levels of perception and responsiveness to Ni-induced stress, which translated into different susceptibilities to the combined exposure to PEG-induced drought. [GRAPHICS] .