Percorrer por autor "Almeida, Ayssata Patrícia da Costa Leocádia Vaz"
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- Chemical Routes for the Transformation of Bio‐monomers into PolymersPublication . Gomes, Catarina P.; Bzainia, Amir; Almeida, Ayssata Patrícia da Costa Leocádia Vaz; Martins, Cláudia D.; Dias, Rolando; Costa, Mário RuiThis chapter is devoted to the analysis of the main polymerization techniques used to transform monomers derived from plant biomass into polymers. Some of these polymers,or close related macromolecules,are naturally synthesized(e.g.by bacteria) and also produced via biotechnological processes (e.g. the polyhydrox-yalkanoate P(3HP)). The goal of the analysis here presented is the description of chemical synthesis routes eventually leading to a more widespread use of these biobased and renewable polymers. Lower production prices, opportunities for functional/structural tailoring, and production scalability are potential benefits of this approach compared to the biotechnological route (when available). Given their huge volumes, environmental and economic importance as well as Worldwide expression, the exploitation of olive-tree/-oilby-products and winemak-Ing waste streams to generate biopolymers comprises two sections of this work.
- Competitive Adsorption of Phenolic Acids, Secoiridoids, and Flavonoids in Quercetin Molecularly Imprinted Polymers and Application for Fractionation of Olive Leaf ExtractsPublication . Almeida, Ayssata Patrícia da Costa Leocádia Vaz; Martins, Ana Filipa; Dias, Rolando; Costa, Mário RuiThe competitive adsorption of phenolic acids, secoiridoids, and flavonoids in a molecularly imprinted polymer (MIP) functionalized with 4-vinylpiridine (4VP) moieties is analyzed here considering vanillic acid, oleuropein, and quercetin as reference molecules. Measured adsorption isotherms highlight a much stronger binding capacity of the quercetin-MIP particles toward quercetin as compared with vanillic acid and oleuropein. The acquired data were used to design and scale-up sorption/desorption processes aiming at the fractionation of olive leaf extracts. We show that a simple adsorption process, avoiding many pre-preparation steps, is possible when working at a high extract concentration due to the strong binding capacity of the MIP for flavonoids, even when using aqueous mixtures with a large alcoholic content. Solvent-gradient/temperature-swing desorption led to a sequence of fractions with enrichment of non-flavonoids at low alcoholic content while glycosylated flavonoids were enriched in fractions with 40% < alcohol content < 80%. Enrichment factors of 13 and 12 were measured for luteolin-7-O-glucoside and apigenin-7-O-glucoside, respectively. Flavonoid aglycones were enriched in fractions with alcohol content >80% (enrichment factors >20 for luteolin and quercetin). The findings reported here demonstrate the usefulness of the developed materials and sorption/desorption conditions for agricultural residue valorization and circular bioeconomy.
- Design and synthesis of molecularly imprinted polymers to target olive leaf secoiridoidsPublication . Almeida, Ayssata Patrícia da Costa Leocádia Vaz; Dias, RolandoThe purification and concentration of bioactive compounds have become more relevant over time, as these compounds have applicability both at laboratory and industrial scale. Despite their importance, our knowledge of techniques to efficiently isolate these bioactive compounds is impecunious. At this juncture, molecularly imprinted polymeric materials (MIPs) capable of selective recognition and capture of secoiridoids present in olive leaves were synthesized. The combination of different monomers and polymerisation techniques has given rise to twenty-one molecularly imprinted materials comprising different morphologies. These materials were characterized and applied as adsorbents in solid phase extraction (SPE) cartridges, tests performed also included the commercial resins REILLEX402, REILLEX425, XAD4, XAD7HP, and DAX8, where preliminary adsorption studies corroborated the reported high-performance of materials containing the functional monomer 4-vinylpyridine (4VP) in both organic solvents and hydroalcoholic mixtures. In addition to oleuropein, tyrosol, vanillin, quercetin, verbascoside, vanillic acid, and caffeic acid were also considered as template molecules, as they tend to appear in olive leaf extracts. By using an olive leaf extract in adsorption/desorption cycles, fractionation and concentration of phenolic compounds present in the initial extract were achieved, thus luteolin-enriched fractions were obtained. The obtained results indicate that although different MIPs have been successfully synthesized, for the desired purpose the adsorbents MIP3 and MIP7 are the most adequate and they can be used in sequence with Reillex402 to optimize the purification/concentration process of the compounds present in the extracts.
- Pyridyl-functionalized and surface molecularly imprinted cellulose particles to target bioactive compounds in olive leafPublication . Almeida, Ayssata Patrícia da Costa Leocádia Vaz; Gaspar, Rita M.; Ferreira-Dias, Suzana; Costa, Mário Rui; Dias, RolandoHybrid particles consisting of a cellulose core and a 4-vinylpyridine-based cross-linked shell were synthesized inthe presence of the quercetin imprinting template by surface initiated atom transfer radical polymerization (ATRP). The modification of cellulose with the introduction of pyridyl moieties was demonstrated by FTIR, SEM, surface area measurement and quantification of nitrogen in the hybrid particles by elemental analysis. The hybrid materials were assessed for their sorption capacity for standard polyphenols under competitive binding and considering different solvents. It was demonstrated that they exhibited a strong binding capacity for these types of molecules due to favorable interactions with the pyridyl nitrogen, even when loading hydro- alcoholic solvents with high alcohol content (e.g. ethanol/water 80/20 v/v) was employed. Adsorbent particles synthesized at the gram scale were packed into HPLC columns, demonstrating their ability to be used in continuous separation processes and the reusability of the materials. Cycling of the packed column with a solvent gradient was performed without observation of a too high backpressure (maximum value observed ~15 bar). Two different industrial olive leaf extracts, characterized by their high polyphenol and triterpene content, were purified by sorption/desorption using the hybrid adsorbent particles. The present study demonstrates that hybrid particles allow the separation of target compounds in olive leaf. Using simple sorption/desorption steps, enrichment factors of about 20 for glycosylated flavonoids and 6 for luteolin were measured with the two olive leaf extracts.