Duygu Çimen

Enantioseparation of aromatic amino acids using CEC monolith with novel chiral selector, N-methacryloyl-l-histidine methyl ester

A new type of polymethacrylate‐based monolithic column with chiral stationary phase was prepared for the enantioseparation of aromatic amino acids, namely d,l‐phenylalanine, d,l‐tyrosine, and d,l‐tryptophan by CEC. The monolithic column was prepared by in situ polymerization of butyl methacrylate (BMA), N‐methacryloyl‐l‐histidine methyl ester (MAH), and ethylene dimethacrylate (EDMA) in the presence of porogens. The porogen mixture included DMF and phosphate buffer. MAH was used as a chiral selector. FTIR spectrum of the polymethacrylate‐based monolith showed that MAH was incorporated into the polymeric structure via in situ polymerization. Some experimental parameters including pH, concentration of the mobile phase, and MAH concentration with regard to the chiral CEC separation were investigated. Single enantiomers and enantiomer mixtures of the amino acids were separately injected into the monolithic column. It was observed that l‐enantiomers of aromatic amino acids migrated before d‐enantiomers. The reversal enantiomer migration order for tryptophan was observed upon changing of pH. Using the chiral monolithic column (100 μm id and 375 μm od), the best chiral separation was performed in 35:65% ACN/phosphate buffer (pH 8.0, 10 mM) with an applied voltage of 12 kV in CEC. SEM images showed that the chiral monolithic column has a continuous polymeric skeleton and large through‐pore structure.

Poly-L-Histidine Attached Poly(glycidyl methacrylate) Cryogels for Heavy Metal Removal

Poly-L-histidine immobilized poly(glycidyl methacrylate) (PGMA) cryogel discs were used for the removal of heavy metal ions [Pb(II), Cd(II), Zn(II) and Cu(II)] from aqueous solutions. In the first step, PGMA cryogel discs were synthesized using glycidyl methacrylate (GMA) as a basic monomer and methylene bisacrylamide (MBAAm) as a cross linker in order to introduce active epoxy groups through the polymeric backbone. Then, the metal chelating groups are incorporated to cryogel discs by immobilizing poly-L-histidine (mol wt ≥ 5000) having poly-imidazole ring. The swelling test, fourier transform infrared spectroscopy and scanning electron microscopy were performed to characterize both the PGMA and poly-L-histidine immobilized PGMA [P-His@PGMA] cryogel discs. The effects of the metal ion concentration and pH on the adsorption capacity were studied. These parameters were varied between 3.0–6.0 and 10–800 mg/L for pH and metal ion concentration, respectively. The maximum adsorption capacity of heavy metal ions of P-His@PGMA cryogel discs were 6.9 mg/g for Pb(II), 6.4 mg/g for Cd(II), 5.6 mg/g for Cu(II) and 4.3 mg/g for > Zn(II). Desorption of heavy metal ions was studied with 0.1 M HNO3 solution. It was observed that cryogel discs could be recurrently used without important loss in the adsorption amount after five repetitive adsorption/desorption processes. Adsorption isotherms were fitted to Langmuir model and adsorption kinetics were suited to pseudo-second order model. Thermodynamic parameters (i.e. ΔH° ΔS°, ΔG°) were also calculated at different temperatures.

Poly-(l)-histidine immobilized cryogels for lysozyme purification

Immobilized metal ion affinity chromatography is one of the methods used for the adsorption of proteins. In this study, poly(glycidyl methacrylate) cryogel discs were prepared by free radical polymerization. The metal chelating groups were polymeric chain of poly-(l)-histidine (mol wt ≥ 5000) having poly-imidazole ring sequence. Then, Cu(II), Zn(II), and Ni(II) ions were separately chelated on the poly-(l)-histidine immobilized poly(glycidyl methacrylate) cryogel discs to be used in immobilized metal ion affinity chromatography separation of lysozyme. The swelling test, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller, and scanning electron microscopy were performed to characterize both poly(glycidyl methacrylate) and poly-(l)-histidine immobilized poly(glycidyl methacrylate) cryogel discs. The effects of the pH, lysozyme concentration, adsorption time, and ionic strength on the adsorption capacity were studied. These parameters were varied between 4.0 and 8.0 for pH, 0.0 and 2.0 mg/ml for initial lysozyme concentration, 0 and 120 min for adsorption time, and 0.0 and 1.0 µM for ionic strength. The maximum lysozyme adsorption capacity of the Cu(II), Zn(II), and Ni(II) ions chelated poly-(l)-histidine immobilized poly(glycidyl methacrylate) cryogel discs was 36.4, 26.8, and 17.3 mg/g cryogel, respectively. Desorption of lysozyme from cryogel discs was easily achieved by 1.0 M NaCI solution. Repeated adsorption-elution processes showed that these cryogel discs were suitable for repeatable lysozyme adsorption. Adsorption isotherms fitted to Langmuir model and adsorption kinetics suited to pseudo-second order model. Thermodynamic parameters (i.e. ΔH°, ΔS°, ΔG°) were also calculated from Langmuir isotherms at different temperatures.

Removal of iron by chelation with molecularly imprinted supermacroporous cryogel.

Iron chelation therapy can be used for the selective removal of Fe3+ ions from spiked human plasma by ion imprinting. N-Methacryloyl-(L)-glutamic acid (MAGA) was chosen as the chelating monomer. In the first step, MAGA was complexed with the Fe3+ ions to prepare the precomplex, and then the ion-imprinted poly(hydroxyethyl methacrylate-N-methacryloyl-(L)-glutamic acid) [PHEMAGA-Fe3+] cryogel column was prepared by cryo-polymerization under a semi-frozen temperature of − 12°C for 24 h. Subsequently, the template, of Fe3+ ions was removed from the matrix by using 0.1 M EDTA solution. The values for the specific surface area of the imprinted PHEMAGA-Fe3+ and non-imprinted PHEMAGA cryogel were 45.74 and 7.52 m2/g respectively, with a pore size in the range of 50–200 μm in diameter. The maximum Fe3+ adsorption capacity was 19.8 μmol Fe3+/g cryogel from aqueous solutions and 12.28 μmol Fe3+/g cryogel from spiked human plasma. The relative selectivity coefficients of ion-imprinted cryogel for Fe3+/Ni2+ and Fe3+/Cd2+ were 1.6 and 4.2-fold greater than the non-imprinted matrix, respectively. It means that the PHEMAGA-Fe3+ cryogel possesses high selectivity to Fe3+ ions, and could be used many times without significantly decreasing the adsorption capacity.

Surface plasmon resonance based nanosensors for detection of triazinic pesticides in agricultural foods

Abstract Herein, we have focused on the preparation of triazinic pesticide imprinted SPR nanosensors for detection of herbicides. Triazinic pesticides are weedkillers that are related with possible carcinogenic effects, birth defects, and menstrual problems when uptake by humans. Although there are restrictions and bans on their use in some countries they are still one of the most widely used pesticides in the world. The development of rapid, sensitive, and inexpensive diagnosis tools for environmental and biological monitoring is currently a research area of great interest. Surface plasmon resonance (SPR) nanosensors have been used widely for the detection of triazinic pesticides because of their simplicity, lack of requirement for labeling and ease of miniaturization, low cost, high specificity and sensitivity, and real-time measurement. Molecularly imprinted polymers that have molecular recognition talent, are easy to prepare, less expensive, stable, and can be manufactured with good reproducibility, are used for the creation of biorecognitive surfaces on the SPR nanosensors. Herein, we have focused on the production of triazinic pesticide-imprinted SPR nanosensors.