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- Surfactant-free emulsion polymerization by “Grafting from” polyvinylamine stabilizerPublication . Gomes, Catarina; Dias, Rolando; Leiza, Jose RamonEmulsion polymerization technique is one of the most common techniques employed in industry to synthesize a wide range of polymers due to its versatility, the possibility to control the properties of the final product and because it is an environmentally friendly technique. Nevertheless, large amounts of surfactant are usually required to stabilize the system which can have deleterious effects on water resistance and on the mechanical properties of the polymer. Among the different techniques employed to circumvent this problem, recently, graft copolymerization of a monomer from water-soluble polymers containing amino groups has been employed to synthesize polymer particles with amphiphilic core-shell nanostructures. Applications of these particles include controlled release drugs, water-borne coatings and diagnostic testing. In this project, water-soluble poly (N-vinylformamide) (PNVF) of different molecular weights was synthesized and characterized. Subsequently, the basic hydrolysis of these polymers was accomplished to obtain poly (vinyl amine) (PVAm) in an easy and controlled way. The synthesized poly (vinyl amines) were then employed as stabilizers in the surfactant-free emulsion polymerization of methyl methacrylate (MMA). The MMA monomer polymerizes via two different ways, grafting from polyvinylamine and homopolymerization, leading to a core-shell type particles with polyvinylamine-based shells. The effect of different variables such as initiator type and concentration, the pH of the reaction and the molecular weight of PVAm’s on the conversion, grafting efficiency and morphology of the polymer particles were investigated. Throughout all the work, an extensive characterization of the polymers obtained in each step was performed in order to clarify possible mechanisms involved in this polymerization process. For the characterization of the polymeric particles obtained during this work were used some characterization techniques such as AF4, NMR, DLS, TEM, SEC/GPC and FT-IR.
- Fractionation of flavonols and anthocyanins in winemaking residues using molecularly imprinted cellulose‐synthetic hybrid particles with pyridyl active surfacePublication . Gomes, Catarina P.; Dias, Rolando; Costa, Mário RuiHybrid cellulose-synthetic particles with surface active pyridyl moieties and molecularly imprinted cavities for quercetin were prepared via atom transfer radical polymerization. The functionalization of the materials with pyridyl groups was confirmed by FTIR and the SEM micrographs of the hybrid particles demonstrate a clear surface modification compared with the pristine cellulose. Competitive sorption/desorption testing of the imprinted and non-imprinted particles with standard polyphenols show the achievement of an imprinting factor IF similar to 8. Moreover, it was also confirmed the high retention capability of the hybrid materials for polyphenols, due to their strong binding with the surface pyridyl moieties, even when using hydroalcoholic solvents of high ethanol content (e.g., ethanol/water 80/20 v/v). The sorption capabilities of the synthesized materials for polyphenols were explored with the fractionation of flavonols and anthocyanins in winemaking residues. High concentration and enrichment factors were achieved for high-added value compounds, namely five times for quercetin and 12 for quercetin-3-O-glucuronide with a diatomaceous earth extract and up to 4 for flavonols in a grape pomace (e.g. myricetin and quercetin glucosides). This research demonstrates de feasibility for the combination between the development of engineered materials addressing sustainability with their application to the valorization of agro-industrial wastes.
- Impressão molecular de polifenóis em partículas de polímero sensíveis a estímulosPublication . Gomes, Catarina; Dias, Rolando; Costa, Mário RuiPolifenóis como o frans-resveratrol, catequina, ácido elágico, ete, apresentam aplicações importantes na indústria farmacêutica, cosmética ou em medicina devido às suas propriedades antioxidantes. Estes compostos estSo presentes em diversas fontes vegetais e existe um elevado interesse no desenvolvimento de técnicas e processos de extracção, purificação e concentração que permitam a sua utilização de forma eficiente. Por outro lado, muitos polifenóis (ex. resveratrol) têm baixa bndisponibilidade por administração oral devido a múltiplos factores como a fraca solubilidade em melo aquoso e a sua elevada taxa de metabolizaçâo e excreção pelo organismo. Desta forma, é também vantajoso o desenvolvimento de veículos para a sua retenção e libertação controlada. A técnica de impressão molecular tem como objectivo criar numa rede de polímero cavidades com tamanho molecular que apresentem elevada afinidade e especificidade com uma molécula alvo (T). Idealmente, o material molecularmente impresso deve ser capaz de reconhecer essa molécula em sucessivos ciclos de retençSo/Iibertaçao.
- Preparation of molecularly imprinted adsorbents with improved retention capability of polyphenols and their application in continuous separation processesPublication . Gomes, Catarina; Dias, Rolando; Costa, Mário RuiThis research explores the use of molecularly imprinted polymers (MIPs) in continuous adsorption processes to target polyphenols present in plant extracts. Different kinds of MIPs were prepared and tested in individual and competitive adsorption/ desorption assays. High polyphenol retention was shown to be possible, even when solvents of low water content are used. A lower impact of hydrophobic interactions is observed with MIPs, namely in comparison with commercial synthetic resins, and so, despite the absence of a perfect selectivity, molecular imprinting was congenial in the functionalization and improved binding site accessibility. Moreover, the potential usefulness of the prepared MIPs to improve downstream processing of polyphenols is also demonstrated through their application in chromatographic separation processes. The direct use of plant extracts of high alcoholic content, avoiding the need for solvent change and water addition, the suppression of energetic costs associated to water evaporation and the possibility to work in a wide range of polyphenols solubility are possible advantages of the developed MIP adsorbents in such kinds of biorefining processes. The development of simulation tools to aid the design and optimization of the involved continuous adsorption/desorption is also here addressed. In this work, MIPs were tested with cork and chestnut shell extracts, a supercritical CO2 olive leaf extract and red wine. Results here obtained show the successful isolation of ellagic acid with cork and chestnut shell extracts, oleuropein with the olive leaf extract and the clear simplification of the red wine extract, enabling the identification/quantification of resveratrol, quercetin, kaempferol and other polyphenols.
- Design of RAFT synthesized amphiphilic and stimuli-responsive block copolymers for encapsulation of polyphenols in polymersomesPublication . Gomes, Catarina; Dias, Rolando; Costa, Mário RuiThis research is devoted to the design and synthesis of amphiphilic/stimuli-responsive block copolymers for encapsulation of polyphenols in polymersomes. The Reversible Addition- Fragmentation Chain Transfer (RAFT) polymerization technique is used to get tailored amphiphilic block copolymers. Multiple combinations between hydrophilic/hydrophobic monomers, RAFT agents and initial compositions are the main design variables of the synthesis runs. Experimental studies are guided by modeling tools to aid in the design of the materials (e.g. to specify the sizes of the two blocks, pH sensitivity). Isolated polyphenols (e.g. resveratrol, quercetin) and more complex extracts from different kinds of plants are afterwards encapsulated in polymersomes, aiming at the development of carriers for protection and controlled release of these bioactive compounds. It is shown that the produced aggregates have a long colloidal stability and are promising vehicles for the stimulatedrelease of polyphenols.
- Supercritical CO2 extraction and purification of bioactive compounds in olive leaf with molecularly imprinted polymersPublication . Gomes, Catarina; Ayssata, Almeida; Dias, Rolando; Martins, Cláudia F.D.; Costa, Mário RuiAround 4.5 million tons of leaves are generated each year as a by-product of the olive and olive-oil production. These olive leaves must be removed from the fields and olive-mills. Usually they are burned, or else used as fuels or for animal feed. However, olive leaf is extremely rich in bio-resources, being estimated that around 1 million tons of bioactive compounds, 1 million tons of cellulose and 1.5 million tons of lignin are currently underexploited [1]. In particular, the extraction and isolation of high-added value bioactive compounds in olive leaf (e.g. polyphenols, triterpenoids, essential oils, lipids, lignocellulose) is especially appealing due to their high-market potential in the food, feed, chemical, nutraceutical, cosmetic and pharmaceutical sectors
- Hybrid cellulose-poly(4-vinylpyridine) adsorbents produced via ATRP and their application to target polyphenols in winemaking, olive oil production and almond processing residuesPublication . Gomes, Catarina; Dias, Rolando; Costa, Mário RuiHybrid cellulose-poly(4-vinylpyridine) particles (MCC-P(4VP)) were synthesized via ATRP grafting and used as adsorbents to target polyphenols in residues derived from winemaking, olive oil production and almond processing. These hybrid particles preserve good conditions to be used in continuous sorption/desorption processes and were assessed for the retention of polyphenols in solvent mixtures ranging from 0 to 100% water content. Other seven adsorbents were used in these assays, including three commercial resins and further materials synthesized in this research with 4VP. We show that the 4VP based adsorbents present a much higher average polyphenol retention in a broad range of working conditions, namely concerning the water content of the extract. This behavior stems from the strong binding capacity of the pyridyl functional group towards many polyphenols and excels with MCC-P(4VP) adsorbents when the hydrophobic interactions play a minor role. MCC-P(4VP) adsorbents were also used for purification and fractionation of polyphenols using simple sorption/desorption steps. A fraction enriched with the malvidin-3-O-glucoside anthocyanin was obtained from grape pomace. Fractions with high content of isorhamnetin-3-O-rutinoside were isolated from almond. Fractions enriched in secoiridoids and flavonoids were produced from olive mill wastewater while many phenolic alcohols and acids were removed. These results show the potential of the MCC-P(4VP) adsorbents to improve downstream processing of polyphenols and increase the biorefining efficiency, namely through the direct handling of organic extracts at high polyphenol concentration. This research also has disclosed the formation of a polymer population deviating from the expected homogeneous process in ATRP grafting. The partition of ATRP reactants between two regions in the homogeneous phase could be a source of some potentially interesting issues relevant to monomers presenting strong H-bond capability, such as 4VP. Thus, many future developments are possible for the designing of the functional materials here addressed, including the introduction of molecular recognition features.
- Surface molecularly imprinted cellulose-synthetic hybrid particles prepared via atrp for enrichment of flavonoids in olive leafPublication . Gomes, Catarina; Dias, Rolando; Costa, Mário RuiSurface molecularly imprinted cellulose-synthetic hybrid particles are prepared via atom transfer radical polymerization (ATRP). The two-step process involves the immobilization of alpha-bromoisobutyryl bromide in the pristine microcrystalline cellulose, to generate ATRP macroinitiator particles, and then the creation of a crosslinked-imprinted shell in the particles surface considering ATRP of 4-vinylpyridine (4VP) and ethylene glycoldimethacrylate (EGDMA) with quercetin as imprinting template. Among the polymerization recipes tested, a system with ethanol as solvent preserves a final size of the hybrid particles suitable for application as adsorbent, while also incorporating the 4VP/EGDMA co-monomers. Testing of imprinted/non-imprinted particles for sorption/desorption of standard phenolic compounds shows the modification of the surface of the pristine cellulose and also the achievement of molecular imprinting (imprinting factor approximate to 2.6). Particles are used for the enrichment of flavonoids in olive leaf extracts and the special features of the developed molecularly imprinted adsorbents are again highlighted with this complex mixture of phenolic compounds. It is shown that production of fractions rich in luteolin-7-O-glucoside, apigenin-7-O-glucoside, or quercetin, among other flavonoids is possible (estimated enrichment factors up to 4). These results point up for the usefulness of natural-synthetic materials with processes to get high-added value compounds in the framework of circular bio-economy.
- Effect of stirring and ultrasound-assisted extraction conditions in flavonoids, tannins, antioxidant, antimicrobial activities of the outer skin of chestnuts (Castanea sativa Miller)Publication . Afonso, Maria João A.P.S.; Dias, Rolando; Gomes, Catarina; Pereira, Ermelinda; Guerra, Nelson P.; Ramalhosa, ElsaThis study aimed to evaluate the presence of bioactive antioxidant molecules in chestnut outer shells. For this proposal, several extraction procedures were used, specifically different solvents (water, ethanol:water (80:20) and acetone:water (80:20)) combined with two extraction methods (stirring and ultrasounds (US)) and times of extraction. Several chemical assays were applied to evaluate the flavonoids, hydrolysable and condensed tannins contents, and the antioxidant activity by total reducing capacity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and reducing power. Some individual compounds were identified by HPLC-UV detection. Furthermore, the antimicrobial activity of the obtained extracts was screened using different microorganisms, namely Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Proteus mirabilis, Klebsiella pneumoniae), as well as fungi (Candida albicans). The mixture acetone:water (80:20) was the best solvent to extract condensed tannins and flavonoids. It was with this mixture that the best total reducing capacity, (DPPH) radical scavenging activity and reducing power were determined. The highest extraction yield was also obtained with this mixture. Only for the hydrolysable tannins, the most suitable extraction solution was ethanol:water (80:20). The presence of gallic and tannic acids was detected by HPLC-UV. Concerning the extraction methods, only the extracts obtained by the US exhibited antimicrobial activity. The ethanolic extract showed antimicrobial activity against the Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Enterococcus faecalis) and the extracts with acetone:water (80:20) and water showed antimicrobial activity against Proteus mirabilis. The results of this study demonstrated that the chestnut outer shell is a promising source of bioactive compounds.
- Effect of extraction conditions on flavonoids, tannins, antioxidant and antimicrobial activities of chestnut outer shells (Castanea sativa Miller)Publication . Afonso, Maria João A.P.S.; Dias, Rolando; Gomes, Catarina; Pereira, Ermelinda; Pérez Guerra, Nelson; Ramalhosa, ElsaDuring the chestnut processing, are generated high amounts of by-products such as chestnut outer shells. They are a promising source of bioactive compounds. This study aimed to evaluate the presence of bioactive compounds in chestnut outer shells (Castanea sativa Mill.), to valorize this by-product. Material and methods. Several extraction procedures were used, specifically different solvents (water, ethanol:water (80:20) and acetone:water (80:20)), combined with two extraction methods (stirring (ST) and ultrasounds (US)) and extraction times. Flavonoids, hydrolizable and condensed tannins, antioxidant activity, antimicrobial activity were determined in the extracts. HPLC-PDA analysis was made to identify some phenolic compounds. Results. The acetone:water (80:20) mixture was the best solvent to extract flavonoids and condensed tannins. With this solvent, the highest total reducing capacity, DPPH radical scavenging activity, and reducing power were also obtained. On the contrary, the most suitable extraction solution for hydrolysable tannins was ethanol:water (80:20). Gallic, (+)-catechin, and tannic acids were detected by HPLC-PDA. Only the extracts obtained by the US exhibited antimicrobial activity. Conclusion. It was stated that chestnut outer shells have high amounts of bioactive compounds. In the extractions, the solvent plays a higher role than the method applied.
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