Yasemin Arslan Udum

Electrochemically controlled solid-phase microextraction (EC-SPME) based on overoxidized sulfonated polypyrrole

A method for the extraction and selective determination of cations is proposed using electro-synthesized overoxidized sulfonated polypyrrole film. The polymer film is used for the selective extraction of trace levels of nickel and cadmium ions by solid-phase microextraction (SPME). The cation uptake and release properties of the overoxidized sulfonated polypyrrole film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction. Increased extraction efficiency and selectivity toward cations were achieved in high saline content of water. Simple preparation of film coatings on a platinum wire was possible using a constant potential method. Applied positive and negative potentials facilitated the extraction and desorption of cations, respectively. Nickel and cadmium ions were desorbed into sample aliquot and determined by electrothermal atomic absorption spectrometry (ETAAS). The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate moiety on the film and the altered solution pH occurring at the counter electrode caused by the applied potential. The method was validated using a standard reference material and tested for the determination of cadmium ion in commercial table salt samples.

Synthesis and characterization of conducting polymers containing polypeptide and ferrocene side chains as ethanol biosensors

A novel approach for the fabrication of a biosensor from a conducting polymer bearing polypeptide segments and ferrocene moieties is reported. The approach involves the electrochemical copolymerization of the electroactive polypeptide macromonomer and independently prepared ferrocene imidazole derivative of dithiophene, on the electrode surface. The polypeptide macromonomer was synthesized by the simultaneous formation of N-carboxyanhydride (NCA) and ring opening polymerization of N-Boc-L-lysine (α-amino acid of the corresponding NCA) using an amino functional bis-EDOT derivative (BEDOA-6) as an initiator. Alcohol oxidase was then covalently immobilized onto the copolymer coated electrode using glutaraldehyde as the crosslinking agent. The intermediates and final conducting copolymer before and after enzyme immobilization were fully characterized by FT-IR, 1H-NMR, GPC, cyclic voltammetry, SEM and EIS analyses. The newly designed biosensor which combined the advantages of each component was tested as an ethanol sensing system offering fast response time (9 s), wide linear range (0.17 mM and 4.25 mM) and low detection limit (0.28 mM) with a high sensitivity (12.52 μA mM−1 cm−2). Kinetic parameters KappM and Imax were 2.67 mM and 2.98 μA, respectively. The capability of the biosensor in determining ethanol content in alcoholic beverages was also demonstrated.

A sepiolite modified conducting polymer based biosensor.

A conducting polymer modified with sepiolite was utilized in the construction of a highly sensitive and fast amperometric cholesterol biosensor. In this study a monomer; (10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine (PHED)) was synthesized and then its polymer was coated on a graphite electrode by electropolymerization to obtain a matrix for enzyme immobilization. Cholesterol oxidase was immobilized onto polymer coated electrode by adsorption technique. Sepiolite was introduced for a successful immobilization of the cholesterol oxidase. Immobilized enzyme kinetic parameters (KM(app), Imax) were evaluated by Michaelis-Menten kinetics and calculated as 0.031 mM and 6.06 μA, respectively. LOD and sensitivity were estimated as 0.36 μM and 1.64 mA/mMcm(2). Characterization of designed biosensor was done to examine the effect of various factors such as enzyme amount, optimum pH and shelf-life. A novel accurate and inexpensive cholesterol biosensor was developed for the determination of total cholesterol in food samples.

Electrochemical Properties of Perylene Diimide (PDI) and Benzotriazole (Btz) Bearing Conjugated Polymers to Investigate the Effect of π-Bridge on Electrochemical Properties

In this study, a series of benzotriazole (BTZ) and perylene diimide (PDI) based copolymers; CoP1 and CoP2 were synthesized via Stille coupling. The effect of perylene diimide (PDI) unit on electrochemical properties of BTZ bearing polymers was investigated. In addition, two different π-bridges: thiophene and dithienopyrrole (DTP) were incorporated into polymer backbone to explore their effects on electrochemical and spectroelectrochemical properties of corresponding polymers; CoP1 and CoP2. Electrochemical and spectral results showed that while CoP1 has only n-type doping property CoP2 has an ambipolar character although p-type doping property is rare for PDI based polymers. Owing to the DTP group, CoP2 showed the lowest band gap reported up to now between perylene diimide derivatives. The effect of different π–bridges and perylene diimide (PDI) unit on the HOMO and LUMO energy levels, optical band gaps, switching time, and optical contrast were presented.

Synthesis of a benzotriazole bearing alternating copolymer for organic photovoltaic applications

A low band gap donor–acceptor (D–A) copolymer PTBTBDT, namely, poly(2-dodecyl-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole-alt-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene), was designed and synthesized via a Pd-catalyzed Stille polycondensation reaction. The polymer was characterized using 1H NMR spectroscopy, UV-vis absorption spectroscopy, cyclic voltammetry, and gel permeation chromatography (GPC). PTBTBDT has good solubility in common organic solvents, good thermal stability, broad absorption, low band gap and exhibits not only high hole mobility but also moderate photovoltaic properties. PTBTBDT displays broad absorption in the wavelength range from 300 nm to 630 nm, and its HOMO and LUMO energy levels were calculated to be −4.98 eV and −3.34 eV, respectively. Bulk heterojunction solar cells were fabricated using PTBTBDT as the electron donor and PC70BM as the acceptor. The device exhibits a power conversion efficiency of 2.12% with a current density of 5.45 mA cm−2, an open-circuit voltage of 0.72 V, and a fill factor of 54% under the illumination of AM 1.5 G, 100 mW cm−2. Under similar device fabrication conditions, the PTBTBDT based device showed considerably improved efficiency among its previously synthesized counterparts, i.e. PBDTDTBTz and PBDTBTz based devices, which have 1.7% and 1.4% efficiencies, respectively. The hole mobility of the PTBTBDT : PC70BM (1 : 2 w/w) blend reached up to 1.47 × 10−3 cm2 V−1 s−1 as calculated by the space-charge-limited current (SCLC) method. By side-chain engineering, this study demonstrates a good example of tuning the absorption range, energy level, charge transport, and photovoltaic properties of polymers.

Polymerization and biosensor application of water soluble peptide-SNS type monomer conjugates

A simple and efficient approach for the preparation of a biosensing platform was developed based on newly designed peptide-SNS type monomer conjugates. The approach involves the electrochemical polymerization of the peptide-SNS type monomer on the electrode surface. To synthesize the peptide bearing monomers, the SNS-type monomer having a carboxylic acid functional group was anchored to the C-terminal of the peptide by solid phase peptide synthesis via coupling reagents. Utilization of peptides to increase the solubility of the monomers was first investigated in this report. The obtained monomers, soluble in water, were fully characterized by spectral analyses and utilized as matrices for biomolecule attachment. Polymerization of monomers in water has the potential to provide an alternative process for the electrochemical preparation of the polymers in aqueous media, without using any organic solvent. Under the optimized conditions, the biosensor responded to the target analyte, glucose, in a strikingly selective and sensitive manner, and showed promising feasibility for the quantitative analysis of glucose in beverages.

Synthesis and optical properties of fused aromatic thienopyrazine based π-conjugated polymers

Two new polythieno[3,4-b]pyrazine derivatives, poly-10,12-bis(4-hexylthiophen-2-yl)dibenzo[f,h] thieno[3,4-b]quinoxaline (PDBTQ) and poly-8,10-bis(4-hexylthiophen-2-yl)acenaphtho[1,2-b]thieno[3,4-e]pyrazine (PATP) were synthesized by electrochemical polymerization and their electrochemical properties reported. Electroactivity of the monomer and electrochemical redox behavior of its polymers were investigated by cyclic voltammetry. Spectroelectrochemical analysis was performed and the band gaps of the polymers were determined as 2.0?eV and 1.2?eV from the onset of the ???* transitions of PDBTQ and PATP, respectively. The polymer PDBTQ shows multicolored electrochromic behavior with five distinct states?orange (0.0?V), yellow (+0.30?V), brown (+0.50?V), green (+0.65?V), blue-gray (0.80?V); PATP has two distinct colors?transmissive gray (0.0?V) and green (+0.80?V). The polymers revealed superior optical contrast in the near-infrared (NIR) region with fast switching times of less than 1?s.