İNŞaat mühendiSLİĞİ anabiLİm dali

Utilization Of New Materials In Specific Separation and Determination Of Phenolic Compounds
Molecular imprinted polymers (MIPs) are solid polymeric materials containing templates which have recognizing abilities chemically of specific molecules (or their derivatives). MIPs offer distinct advantages such as ease of preparation, low cost, tolerance to extreme thermal and chemical conditions, long shelf life, and enhanced versatility in experimental design compared to natural proteinaceuous receptors.
Quercetin is the most active compound in flavone family, widely occurring in leaves, fruits, and flowers of many plants. Quercetin has become the topic of increasing interest based on its antioxidant, antiviral and antitumor properties. So, the isolation of quercetin from various plant matrices is becoming an important research area. Moreover, preconcentration and/or separation is a required stage for determining quercetin in complex multicomponent food products as well as in biological objects. Caffeic acid is a hydroxycinnamic acid derivative which is present in many plants and beverages. It accounts for up to 70% of the total hydroxycinnamic acid content in fruits. Caffeic acid can slow down the process of inflammation, thereby providing protection from the hazardous effects of free radicals and against endothelial damage, etc.
In this work, because of the above mentioned reasons, imprinted polymers for the isolation and preconcentration of quercetin and caffeic acid were synthesized separately. Quercetin imprinted polymers in different molar ratios (template:monomer:cross-linker: 1:4:20, 1:5:30, 1:8:40, 1:10:50) were prepared by using quercetin as the template molecule, 4-vinylpyridine (4VP), methacrylic acid (MAA), acrylamide (AA) as the functional monomers, ethylene glycol dimethacrylate (EDMA) as the cross-linker and 2,2’-azobisisobutyronitrile (AIBN) as initiator in the porogen of acetone. Non-imprinted polymers (NIPs) were also synthesized without template. Their recognition and selectivity properties were investigated by equilibrium binding experiments with QC solutions in different proportions of acetonitrile (ACN)-dimethylsulfoxide (DMSO) mixtures and methanol (MeOH) monitoring the absorbances at 370 nm. The MIP with 1:4:20 molar ratio of quercetin-4VP-EDMA was established as the most suitable for recognition of quercetin. The mentioned MIP was found to be highly selective for quercetin according to the other structurally related compounds (rutin, catechin, etc). Sorption parameters of the MIP and the NIP were calculated by using Freundlich and Langmuir isotherms with quercetin solutions in ACN: DMSO (98:2, v/v).
Also in this study, a series with different molar ratios of caffeic acid imprinted polymers (1:4:12, 1:4:16, 1:4:20, 1:5:30, 1:6:30, 1:8:40) were prepared in tetrahydrofuran as porogen. Caffeic acid as template molecule, 4-vinylpyridine (4VP), methacrylic acid (MAA), acrylamide (AA), 1-vinylimidazole as functional monomers, ethylene glycol dimethacrylate (EDMA) as cross-linking agent and 2,2’-azobisisobutyronitrile (AIBN) as initiator were used for the preparation of caffeic acid-MIPs. Non-imprinted polymers (NIPs) were also synthesized without template. Their recognition and selectivity properties were investigated by equilibrium binding experiments monitoring the absorbances at 320 nm. The MIP with 1:4:16 molar ratio of caffeic acid-4VP-EDMA was established as the most suitable for recognition of caffeic acid. The mentioned MIP was found to be highly selective for caffeic acid according to the other structurally related compounds (gallic acid, chlorogenic acid, etc). Sorption parameters of the MIPs and the NIPs were calculated by using Freundlich and Langmuir isotherms with caffeic acid solutions in ACN.
Structure analysis of caffeic acid and quercetin imprinted polymers was carried out by using fourier transform infrared (FTIR)- attenuated total reflection (ATR) spectrum. Morphologies of these polymers were investigated with scanning electron microscopy (SEM).
Molecularly imprinted solid phase extraction (MISPE) applications were performed by using prepared imprinted polymers. Thus, recoveries of caffeic acid (anad/or caffeic acid derivative chlorogenic acid) and quercetin (and/or quercetin derivative kaempferol, miricetin, rutin) were carried out from synthetic mixtures and natural products (nettle extract hydrolizate, red onion peel extract and extract hydrolizate, and black tea extract hydrolizate for quercetin; green coffee bean extract for both quercetin and chlorogenic acid).