Tuncer Çaykara

UV degradation of poly(methyl methacrylate) and its vinyltriethoxysilane containing copolymers

Abstract The photodegradation of poly(methyl methacrylate) (PMMA) and vinyltriethoxysilane (VTES)–methyl methacrylate (MMA) copolymer films was studied by UV irradation (λ=259 nm). Evidence for the photodegradation of PMMA and copolymers was found in the different FT–IR and UV–VIS spectra. The scission of ester side-groups of PMMA were determined by using FT–IR and UV–VIS difference spectra. However, in the same process of the copolymers, both scission of the ester side-groups and crosslinking occur simultaneously. It is observed that UV irradation causes changes of the mechanical properties of PMMA and copolymers.

Effect of pH, ionic strength, and temperature on uranyl ion adsorption by poly(N‐vinyl 2‐pyrrolidone‐g‐tartaric acid) hydrogels

Poly-electrolyte N-vinyl 2-pyrrolidone-g-tartaric acid (PVP-g-TA) hydrogels with varying compositions were prepared in the form of rods from ternary mixtures of N-vinyl 2-pyrrolidone/tartaric acid/water. The effect of external stimuli, such as the solution pH, ionic strength, and temperature, on uranyl adsorption by these hydrogels was investigated. Uranyl adsorption capacities of the hydrogels were determined to be 53.2–72.2 (mg UO/g dry gel) at pH 1.8, and 35.3–60.7 (mg UO/g dry gel) at pH 3.8, depending on the amount of TA in the hydrogel. The adsorption studies have shown that the temperature and the ionic strength of the swelling solution also influence uranyl ion adsorption by PVP-g-TA hydrogels.

Equilibrium swelling behavior of pH- and temperature-sensitive poly(N-vinyl 2-pyrrolidone-g-citric acid) polyelectrolyte hydrogels

Hydrogels containing triprotic acid moieties sensitive to pH and ionic strength changes of the swelling medium were prepared from the ternary systems N-vinyl 2-pyrrolidone/citric acid/water by irradiation with g rays at ambient tempera- ture. Equilibrium swelling behavior of these hydrogels was studied using an equation, based on the phantom network theory of James-Guth and the approaches of Peppas et al., which was modified by the authors for determination of Mc and x parameter. The Mc and x parameters were related to equilibrium swelling behavior of the charged poly- meric network, pH, temperature, and ionic strength of the surrounding medium. The degree of swelling of these hydrogels decreases with these variables in accordance with expectation.

A SERS-Based Sandwich Assay for Ultrasensitive and Selective Detection of Alzheimer’s Tau Protein

In this study, a simple and highly selective homogeneous sandwich assay was developed for fast and ultrasensitive detection of the tau protein using a combination of monoclonal antitau functionalized hybrid magnetic nanoparticles and polyclonal antitau immobilized gold nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) component, respectively. The magnetic silica particles were first coated with poly(2-hydroxyethyl methacrylate) via surface-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization and then biofunctionalized with monoclonal antitau, which are both specific for tau and can be collected via a simple magnet. After separating tau from the sample matrix, they were sandwiched with the SERS substrate composed of polyclonal antitau and 5,5-dithiobis(2-dinitrobenzoic acid) on gold nanoparticles. The correlation between the tau concentration and SERS signal was found to be linear within the range of 25 fM to 500 nM. The limit of detection for the sandwich assay is less than 25 fM. Moreover, the sandwich assay was also evaluated for investigating the tau specificity on bovine serum albumin and immunoglobulin G.

Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate

Blend films of poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. This blend films were characterized by tensile strength test, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The miscibility in the blends of PVA and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition‐dependent glass transition temperatures (Tgs), indicating that the blends are miscible. FT‐IR studies indicate that there is the intermolecular hydrogen bonding interactions, i.e. –OH…−OOC– in PVA/NaAlg blends. The blend films also exhibited the higher thermal stability and their mechanical properties improved compared to those of homopolymers.

Construction of myoglobin imprinted polymer films by grafting from silicon surface

Molecularly imprinted polymer (MIP) films on silicon wafers were prepared by surface-initiated atom transfer polymerization (ATRP). 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate were used as the functional monomer and the cross-linking agent, respectively. Myoglobin (Mb) was selected as the template molecule to form the MIP films. Various characterization techniques including ellipsometry, contact-angle goniometer, atomic force microscopy, grazing angle-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, were used to characterize the films. Ellipsometry was also used to quantify and compare the binding capacity of the MIP and nonimprinted polymer (NIP) films. The MIP films exhibited higher rebinding capacity than the NIP films at all solution concentrations of Mb. A selectivity coefficient of 3.15 was achieved for the MIP films prepared against the Mb template molecule.

Hemoglobin recognition of molecularly imprinted hydrogels prepared at different pHs.

The hemoglobin-imprinted hydrogels were fabricated by using N-t-butylacrylamide (TBA) acrylamide (AAm) and itaconic acid (IA) monomers and hemoglobin (Hb, MW 65 kDa) imprinted molecule in pH buffer solutions (pH 4.0, 6.8 and 8.0). The nonimprinted hydrogels were also prepared at same conditions without Hb imprinting molecule. The effects of pH, initial concentration and adsorption time over the Hb adsorption capacity of both imprinted and nonimprinted hydrogels were analyzed and found to be strongly dependent on the preparation pH (pH(prep)). The maximum Hb adsorption for the imprinted hydrogel prepared at pH 4.0 was found to be 12.4 mg protein g(-1) dry gel in pH 4.0 buffer solution. This behavior was attributed to the formation of more accessible adsorption sites (imprints) because of the non-covalent interactions between the template and network during formation in pH 4.0 buffer solution which is below of the isoelectric point (pI 6.8) of Hb. Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherm. Langmuir analysis showed that an equal class of adsorption was formed in the hydrogels. Moreover, batch adsorption equilibrium and selectivity studies were also performed by using two reference molecules as fibrinogen (Fb, MW 340 kDa) and myoglobin (Mb, MW 17 kDa). The imprinted hydrogels have 1.5-2.2 times higher adsorption capacity for Hb than the nonimprinted hydrogels prepared at the same pHs, and also have 2.0-3.1 times higher selectivity for the imprinted molecule.

Dependence of Protein Recognition of Temperature-Sensitive Imprinted Hydrogels on Preparation Temperature

Temperature-sensitive imprinted and non-imprinted hydrogels composed of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-propanosulfonic acid (AMPS) have been prepared by free-radical crosslinking copolymerization in aqueous solution at three different temperatures: 10 degrees C (below the lower critical solution temperature, LCST), 33 degrees C (at the LCST), and 40 degrees C (above the LCST). Myoglobin (Mb, MW 17 kDa) is used as the template biomolecule. The effects of the initial concentration and adsorption time over the Mb adsorption capacity of the hydrogels have been analyzed and found to be strongly dependent on the preparation temperature (T(prep)). The maximum Mb adsorption for the imprinted hydrogel prepared at 10 degrees C is 97.40 +/- 2.35 mg Mb x g(-1) dry gel in 0.32 mg x mL(-1) Mb solution at 22 degrees C. Moreover, batch adsorption equilibrium and selectivity studies have been performed using a reference molecule, hemoglobin (Hb, MW 65 kDa). The imprinted hydrogels have a 2.8-3.3 times higher adsorption capacity for Mb than the non-imprinted hydrogels prepared at the same T(prep)s, and also have a 1.8-2.7 times higher selectivity for the imprinted molecule.

Thermal, Spectroscopic, and Mechanical Properties of Blend Films of Poly(N-Vinyl-2-Pyrrolidone) and Sodium Alginate

Blends of poly(N-vinyl-2-pyrrolidone) (PVP) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. These blends were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile strength test. The miscibility in the blends of PVP and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition-dependent glass transition temperatures (T g s), indicating that the blends are miscible in amorphous state. FT-IR studies indicate that there are the intermolecular hydrogen bonding interactions, i.e., –OH·····O=C in PVP/NaAlg blends. This blend films also exhibited the higher thermal stability and improved the elongation at break in dry states.

Extremely sensitive sandwich assay of kanamycin using surface-enhanced Raman scattering of 2-mercaptobenzothiazole labeled gold@silver nanoparticles

Herein, we report the development of extremely sensitive sandwich assay of kanamycin using a combination of anti-kanamycin functionalized hybrid magnetic (Fe3O4) nanoparticles (MNPs) and 2-mercaptobenzothiazole labeled Au-core@Ag-shell nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) substrate, respectively. The hybrid MNPs were first prepared via surface-mediated RAFT polymerization of N-acryloyl-L-glutamic acid in the presence of 2-(butylsulfanylcarbonylthiolsulfanyl) propionic acid-modified MNPs as a RAFT agent and then biofunctionalized with anti-kanamycin, which are both specific for kanamycin and can be collected via a simple magnet. After separating kanamycin from the sample matrix, they were sandwiched with the SERS substrate. According to our experimental results, the limit of detection (LOD) was determined to be 2pg mL(-1), this value being about 3-7 times more than sensitive than the LOD of previously reported results, which can be explained by the higher SERS activity of silver coated gold nanoparticles. The analysis time took less than 10min, including washing and optical detection steps. Furthermore, the sandwich assay was evaluated for investigating the kanamycin specificity on neomycin, gentamycin and streptomycin and detecting kanamycin in artificially contaminated milk.