Browsing by Author "Sadoyan, Gayane"
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- Development of amphiphilic adsorbents for the stimulated uptake and release of polyphenolsPublication . Sadoyan, Gayane; Dias, Rolando; Hovhannisyan, NellyThis work was devoted to the development of amphiphilic molecularly imprinted polymers (MIPs) to target the stimulated uptake and release of polyphenols. MIP particles were synthetized through a free radical precipitation polymerization process with a hydrophobic crosslinker and different hydrophilic functional monomers. Polydatin was selected as the template polyphenol and anionic, cationic and neutral adsorbent particles were thus produced The formation of microparticles e g with size in the order of 1 μm was evidenced by SEM. The incorporation of crosslinker and functional monomer in the final polymer networks was observed using FTIR. The adsorption capabilities of the materials synthetized were evaluated using solid phase extraction (SPE) with solvents of different amphiphilic character. Besides the individual retention, the competitive adsorption of a mixture of polydatin + resveratrol + gallic acid was also studied through HPLC (an Ascentis® C18 column was used). Some selectivity of the materials towards the different molecules was observed but the most relevant result obtained was the ability of the produced cationic networks to retain huge amounts of gallic acid. MIPs were also packed in HPLC columns and a continuous process with recycling was conceived through the use of an HPLC pump. Dynamics for the saturation and the release processes were thus measured and the role of the hydrophobic interactions in the different polyphenols adsorption/desorption was highlighted. These issues were further enhanced through the analysis of the retention and release of phenolic compounds in a sequence of two MIPs. A solvent gradient scheme was used and these ideas were applied to a created mixture containing gallic acid, tannic acid, polydatin and resveratrol. Portuguese Douro Region red wine was considered as a source of phenolic compounds and an extract from chestnut shell was also evaluated. The extract from chestnut shell was obtained through supercritical extraction with CO2, using Bragança region fruits. Supercritical extraction with CO2 was performed at T=50 °C and P=150 bar Results obtained evidenced that optimized MIPs can be undoubtedly used to separate and concentrate polyphenols present in red wine, such as resveratrol or polydatin. These findings were further enhanced through the adsorption and release of the gallic acid + tannic acid + polydatin + resveratrol in the series of MIPs. Measurements for the shell chestnut extract obtained with supercritical conditions showed that phenolic compounds should not be present in an appreciable amount (in contrast with the red wine extract). Different extraction techniques (e.g. extraction at alkaline supercritical conditions) and chestnut plant components (leaves, burs, stalks, etc) should be considered in future researches to light this issue. At last, the synthesis of improved amphiphilic adsorbents through the RAFT grafting of functional brushes in the MIP particles surface was addressed. Preliminary results obtained seem to show that the grafted hydrophilic polymer brushes modify the pH/temperature triggered retention/release of polyphenols. However, future studies are needed to clarify these complex issues.
- Development of molecularly imprinted polymers to target polyphenols present in plant extractsPublication . Gomes, Catarina; Sadoyan, Gayane; Dias, Rolando; Costa, Mário RuiThe development of molecularly imprinted polymers (MIPs) to target polyphenols present in vegetable extracts was here addressed. Polydatin was selected as a template polyphenol due to its relatively high size and amphiphilic character. Different MIPs were synthesized to explore preferential interactions between the functional monomers and the template molecule. The effect of solvent polarity on the molecular imprinting efficiency, namely owing to hydrophobic interactions, was also assessed. Precipitation and suspension polymerization were examined as a possible way to change MIPs morphology and performance. Solid phase extraction and batch/continuous sorption processes were used to evaluate the polyphenols uptake/release in individual/competitive assays. Among the prepared MIPs, a suspension polymerization synthesized material, with 4-vinylpyridine as the functional monomer and water/methanol as solvent, showed a superior performance. The underlying cause of such a significant outcome is the likely surface imprinting process caused by the amphiphilic properties of polydatin. The uptake and subsequent selective release of polyphenols present in natural extracts was successfully demonstrated, considering a red wine solution as a case study. However, hydrophilic/hydrophobic interactions are inevitable (especially with complex natural extracts) and the tuning of the polarity of the solvents is an important issue for the isolation of the different polyphenols.
- Engineered polymer particles for the valorization of phenolic compounds present in mixtures obtained through supercritical extractionPublication . Gomes, Catarina; Sadoyan, Gayane; Dias, Rolando; Costa, Mário RuiMolecularly imprinted polymer (MIP) particles are here developed to target phenolic compounds present in mixtures resulting from supercritical extraction processes. Engineered MIP particles are synthetized considering different polymerization processes to tailor products morphology (e.g. precipitation or inverse-suspension polymerization to obtain micro-particles [1]) and also diverse functional monomers to explore preferential interactions with the template polyphenols (e.g. polydatin, resveratrol, etc). Moreover, MIP particles with surface grafted functional polymer chains (e.g. using RAFT polymerization [2,3]) are produced to assess the improvement of the selectivity of MIPs towards the target polyphenols, namely through the tuning of the hydrophilic/hydrophobic effects (amphiphilic materials are generated). The produced MIP particles are applied for the identification, separation and concentration of phenolic compounds present in vegetable extracts. Different plants abundant in the Trás-os-Montes and Alto Douro region (e.g. vineyard, chestnut tree, olive tree, cherry tree, etc) are considered as potential sources of phenolic compounds. Supercritical extraction with CO2 is used to obtain the vegetable extracts (see Figure 1) and the effects of the operation conditions (temperature, pressure, vegetable used, etc) on extract composition is also assessed. Molecular recognition capabilities of the MIPs synthetized towards the polyphenols are evidenced (e.g. packing the particles for chromatography) but hydrophilic/hydrophobic interactions are unavoidable and a solvent gradient is needed.