Bahadir Keskin

Influence of alkyl chain length on the surface activity of antibacterial polymers derived from ROMP

The purpose of this study is to understand the antibacterial properties of cationic polymers on solid surfaces by investigating the structure-activity relationships. The polymer synthesis was carried via ring opening metathesis polymerization (ROMP) of oxanorbornene derivatives. Modulation of molecular weights and alkyl chain lengths of the polymers were studied to investigate the antibacterial properties on the glass surface. Fluorescein (Na salt) staining contact angle measurements were used to characterize the positive charge density and hydrophobicity on the polymer coated surfaces. Positive charge density for the surface coated polymers with molecular weights of 3000 and 10,000 g mol(-1) is observed to be in the range of 2.3-28.5 nmol cm(-2). The ROMP based cationic pyridinium polymer with hexyl unit exhibited the highest bactericidal efficiency against Escherichia coli on solid surface killing 99% of the bacteria in 5 min. However, phenyl and octyl functionalized quaternary pyridinium groups exhibited lower biocidal properties on the solid surfaces compared to their solution phase biocidal properties. Studying the effect of threshold polymer concentrations on the antibacterial properties indicated that changing the concentrations of polymer coatings on the solid surface dramatically influences antibacterial efficiency.

Synthesis and characterization of soluble seco-porphyrazines with bulky substituents

By cyclotetramerization of 3,4-bis(4-tert-butylphenyl)pyrroline-2,5-diimine in the presence of magnesium butanolate, magnesium porphyrazinate with eight (4-tert-butylphenyl) units on the periphery has been synthesized. Its demetalation by the treatment with trifluoroacetic acid resulted in a partially oxidized product, namely, octakis(4-tert-butylphenyl)-2-seco-porphyrazine-2,3-dione. Further reaction of this product with copper(II) acetate, zinc(II) acetate, and cobalt(II) acetate led to the metallo derivatives, [octakis(4-tert-butylphenyl)-2-seco-2, 3-dioxoporphyrazinato]M(II) (M = Cu, Zn, Co). These soluble complexes have been characterized by elemental analysis, FT-IR, 1H NMR, UV-Vis, and mass spectral data.

Radical scavenging and in vitro antifungal activities of Cu(II) and Co(II) complexes of the t-butylphenyl derivative of porphyrazine

Co(II) and Cu(II) complexes and metal-free t-butylphenyl peripherally substituted porphyrazine (Pz) have been screened for in vitro antifungal (Aspergillus niger) and antioxidant (free radical scavenging, superoxide radical scavenging, and reducing power) activities. The results were compared with synthetic antioxidants, e.g., butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), trolox, or α-tocopherol. The free radical scavenging activity of H2Pz was higher than the CuPz complex. However, CuPz complex showed higher superoxide radical scavenging activity than BHA, BHT, and trolox while H2Pz and CoPz showed weaker activity than BHA, BHT, and trolox. The reducing power of all complexes was similar to that of BHT and α-tocopherol on a per molar basis. The ligand and complexes have antifungal activity against A. niger. The compounds have significant superoxide radical scavenging activity against various antioxidant systems in vitro.

Novel indium(III) phthalocyanines; synthesis, photophysical and humidity sensing properties

Three new 3,4-(dimethoxyphenylthio) (4), 4-(thiophen-3yl)phenoxy (5), 3,4-(methylendioxy)phenoxy (6) substituted chloroindium(III) phthalocyanines were synthesized and characterized. The indium(III) phthalocyanine derivatives were characterized by using spectroscopy methods, FT-IR, 1H-NMR spectroscopy, electronic spectroscopy and mass spectra as well as elemental analysis. The photophysical properties (fluorescence quantum yields and fluorescence behavior) of their peripherally tetra-substituted new complexes (4 to 6) have been examined. General trends focus on fluorescence behavior, photophysical and electronic properties as well as the humidity sensing ability of these compounds in dimethylsulfoxide (DMSO), dimethylformamide (DMF) and tetrahydrofuran (THF). Complexes (4 to 6) showed reasonably higher fluorescence quantum yields ranging from 0.050 to 0.092 in DMF, 0.029 to 0.084 in DMSO and 0.023 to 0.060 in THF compared to other indium derivatives in the literature. The nature of the substituent and solvent effects on the electronic and photophysical parameters of the three different substituted indium(III) phthalocyanines (4–6) are also reported. The humidity detection capabilities of the 4–6 films have also been investigated. Comparing humidity-sensing properties of the Pcs, it was found that the humidity sensitivity of 4 is higher than 5 and 6.

Metal-free polymer/MWCNT composite fiber as an efficient counter electrode in fiber shape dye-sensitized solar cells.

UNLABELLED Highly aligned multiwall carbon nanotubes (MWCNT) as fiber were modified with a conducting polymer via a simple dip coating method. Modified MWCNT exhibited admirable improvement in electrocatalytic activity for the reduction of tri-iodide in dye sensitized solar cells. Scanning electron microscopy images confirm the successful deposition of polymer on MWCNT. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy studies were carried out to investigate the inner mechanism for the charge transfer behaviour. Results from bare and modified electrodes revealed that the MWCNT/(poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate) ( PEDOT PSS) composite electrode is much better at catalysing the [Formula: see text] redox couple compared to the pristine fiber electrode. The photoelectric conversion efficiency of 5.03% for the modified MWCNT electrodes was comparable with that of the conventional Pt-based electrode. The scientific results of this study reveal that MWCNT/PEDOT:PSS may be a better choice for the replacement of cost intensive electrode materials such as platinum. Good performance even after bending up to 90° and in-series connection to enhance the output voltage were also successfully achieved, highlighting the practical application of this novel device.

A.c. and d.c. conduction processes in octakis((4-tert-butylbenzylthio)- porphyrazinato)Cu(II) thin films with gold electrodes

The d.c. and a.c. electrical transport properties of Au/Pz/Au devices with various thickness of Pz(octakis[(4-tert-butylbenzylthio)-porphyrazinato]Cu(II)) layer have been investigated. Measurements revealed that, in contrast to previously investigated Au/Pc/Au structures, low voltage d.c. behaviour of the films can be described by the field-lowering mechanisms with a log(J) ∝ V1/2 current density-voltage characteristics under forward and reverse bias. For high reverse voltages, the observed ln(J/V2) – 1/V characteristics indicated that the origin of conduction mechanism is Fowler–Nordheim tunnelling (FNT). On the other hand, the voltage dependence of current density at the higher forward-voltage region indicates that the mechanism of conduction in Au/Pz/Au devices is space charge limited conduction dominated by exponential trap distribution. A thickness independent barrier height was observed for tunnelling, while the total trap concentration show a general tendency to decrease with increasing film thickness. The a.c. conductivity showed two regions in the ln(σa.c.) – ln( f ) plots having different slopes, leading to the conclusion that for low frequency region, the dominant conduction mechanism is a small polaron tunnelling at all temperatures, whereas for high frequency region, correlated barrier hopping model is the dominant mechanism in the investigated devices.

Synthesis, characterization and electrochemical properties of new phthalocyanines

Abstract The chemical synthesis and characterization with spectroscopic and electrochemical properties of [bis(4-fluorophenyl)-methoxy]-substituted metallo-phthalocyanines were reported for the first time. The new phthalocyanines have been characterized by elemental analysis, UV-Vis, FT-IR, and mass spectroscopies. The aggregation behavior of the phthalocyanine compounds was investigated in different solvents and concentrations. It is found that the fluoro substituents of peripherally Co and Cu complexes are examined and induce a shift to the redox processes toward the negative potentials and formed more reversible processes. Metal-based reduction and oxidation reactions were obtained for the Co(II) complex, whereas Cu(II) complexes exhibited Pc-ring-based electron-transfer reactions. The voltammetric measurements supported the proposed structure of the complexes.

Optical characterization of spin-coated cobalt porphyrazine thin films: effect of annealing temperature

Cobalt porphyrazine thin films were prepared by the spin-coating technique. The coated substrates were annealed at different temperatures (373, 423 and 523 K). The optical properties of the films were investigated by measuring the transmittance and reflectance spectra. The refractive index, extinction coefficient, optical band gap, dielectric constant values and thickness of the films were determined. Results showed that the refractive index, the extinction coefficient and the dielectric constants increased on annealing the films at 373 K in comparison with films annealed at other temperatures. On the other hand, the values of the band gap energy and thickness of the annealed film at 373 K were found to be the lowest in comparison with films annealed at different temperatures.

Synthesis and EPR studies of soluble vanadyl octakis(4-tert-butylbenzylthio) porphyrazine

Magnesium porphyrazinate substituted with eight 4-tert-butylphenylthio-groups on peripheral positions has been synthesized by cyclotetramerization of 1,2-bis(4-t-butylphenylthio)maleonitrile in the presence of magnesium butanolate. The metal-free derivative was obtained by treatment with trifluoroacetic acid and further reaction of this product with vanadyl(IV) sulfate led to the vanadyl porphyrazinate. These new compounds have been characterized by elemental analysis, together with FTIR, and UV–vis spectral data. The magnetic properties of the complex have been investigated by electron paramagnetic resonance spectroscopy.

Influence of Heat Treatment on Structure and Charge Capacity of Sol–Gel Produced TiO2 Films

Titanium dioxide thin films were synthesized by sol–gel route from titanium isopropoxide (TIP) with acetic acid. Prior to the heat treatment, the films were amorphous phase. Above 400 °C, phase transition took place from amorphous into anatase phase. Electrochromic properties of each phase indicated reversible coloration upon Li+ ion intercalation in cyclic voltammetric measurements. Nevertheless, both charge capacity and energy band gap of films begun to decrease with increase in annealing temperature due to the crystallization.