Mustafa Arık

Molecular excitons of Pyronin B and Pyronin Y in colloidal silica suspension

Abstract The electrostatic interactions of the cationic dyes Pyronin B (PyB) and Pyronin Y (PyY) with the negatively charged colloidal silica was investigated by molecular absorption and steady state fluorescence spectroscopy. Both dyes indicated changes in the absorption and emission spectra upon interaction with colloidal silica. A blue shift was observed in the absorption spectra for both dyes with increased dye concentration when the colloidal silica concentration was kept constant. These new bands observed that are higher energy than monomer bands are due to H-aggregates and they were analyzed by using exciton theory and monomer–dimer equilibrium.

Solvent effect on nonradiative process of pyronin B in protic and aprotic solvent systems

Abstract Absorption and emission spectra of pyronin B were taken in acetonitrile and acetonitrile-benzene solvent mixtures. Fluorescence lifetime (τf) and quantum yield (Φf) were determined as a function of temperature and nonradiative rate constant (knr) was calculated from τf and Φf. Activation energies of nonradiative process were obtained from Arrhenius plots of knr. Solvent effects on knr were discussed in terms of proposed models. The results were compared to those previously obtained for pyronin B in n-alcohols and alcohol–water mixtures. Solvent polarity and specific solute–solvent interactions were the main parameters controlling the internal conversion process for pyronin B in protic and aprotic solvent systems.

The investigation of the interaction between orientin and bovine serum albumin by spectroscopic analysis

In this paper, the interaction between orientin and bovine serum albumin (BSA) was examined using fluorescence and absorbance spectroscopy. The analysis of the quenching mechanism was done using Stern-Volmer plots which exhibit upward (positive) deviation. A linear response to orientin was shown in the concentration range between 3 and 50 μM. The experimental results showed the presence of a static quenching process between orientin and BSA. The thermodynamic parameters ΔH, ΔS and ΔG were also calculated and suggested that the hydrophobic and electrostatic interactions played an important role in the interaction between orientin and BSA. Furthermore, the distances between BSA and orientin were determined according to Förster non-radiation energy transfer theory. In addition, the results of the synchronous fluorescence obtained indicated that the binding of orientin with BSA could affect conformation in BSA.

Cytotoxicity of 1-Aryl-3-buthylamino-1-propanone Hydrochlorides against Jurkat and L6 Cells

1-Aryl-3-buthylamino-1-propanone hydrochloride type mono Mannich bases were synthesized and their cytotoxicity was tested against transformed human T-lymphocytes (Jurkat cells) and rat skeletal muscle derived myoblasts (L6 cells). Aryl part was changed as phenyl in 1, 4-methylphenyl in 2, 4-chlorophenyl in 3, 4-fluorophenyl in 4, 4-bromophenyl in 5, 4-hydroxyphenyl in 6, 2-acethylthiophene in 7. Of the compounds synthesized, 2, 5, 6, and 7 are reported for the first time. Compounds 1-7 had 3.16, 3.13, 3.35, 2.87, 4.17, 2.60, and 3.04 times higher cytotoxic potency than the reference compound 5-fluorouracil (CAS 51-21-8) against Jurkat cells, respectively. Compounds 1, 3, 4, 5, 6, and 7 had 1.22, 1.46, 1.59, 2.18, 1.24, and 1.45 times higher cytotoxic potency than the reference compound 5-fluorouracil against L6 cells, respectively. Among the compounds tested, only compound 5 had almost equal cytotoxic potency with the reference compound melphalan (CAS 148-82-3) against Jurkat and L6 cells. All compounds synthesized showed higher cytotoxic activity against Jurkat cells compared with L6 cells. Specifically, compounds 1-7 had 2.05, 2.68, 1.82, 1.43, 1.51, 1.66, and 1.66 times higher cytotoxicity against Jurkat cells compared with L6 cells. In Jurkat cells, there was a significant negative correlation between Log P and IC50 values (correlation coefficient: -0.955, p = 0.03), which actually means a positive correlation between the Log P and the cytotoxic activity of the compounds. These results suggest that the most potent compound 5 (a 4-bromo derivative) against both cell lines may serve as a model compound to develop new cytotoxic agents for further studies.

Synthesis and Characterization of Reduced Graphene Oxide/Rhodamine 101 (rGO-Rh101) Nanocomposites and Their Heterojunction Performance in rGO-Rh101/p-Si Device Configuration

Reduced graphene oxide (rGO)-rhodamine 101 (Rh101) nanocomposites with different ratios of rGO have been synthesized in aqueous medium by ultrasonic homogenization. The fluorescence of Rh101 as measured using a laser dye with high fluorescence quantum yield was substantially quenched with increasing amount of rGO in the nanocomposite. Formation of rGO-Rh101 nanocomposites was confirmed by x-ray diffraction analysis, scanning electron microscopy, ultraviolet–visible (UV–Vis) spectroscopy, and fluorescence microscopy. Furthermore, rGO-Rh101 nanocomposite/p-Si heterojunctions were synthesized, all of which showed good rectifying behavior. The electrical characteristics of these devices were analyzed using current–voltage (I–V) measurements to determine the ideality factor and barrier height. The experimental results confirmed the presence of lateral inhomogeneity in the effective barrier height of the rGO-Rh101 nanocomposite/p-Si heterojunctions. In addition to I–V measurements, one device was analyzed in more detail using frequency-dependent capacitance–voltage measurements. All electrical measurements were carried out at room temperature and in the dark.

Optical and morphological characterizations of pyronin dye-poly (vinyl alcohol) thin films formed on glass substrates

Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared by using spin-coating technique. The optical and morphological properties of the thin films were studied by UV-Vis., steady-state fluorescence spectroscopies and atomic force microscopy (AFM). The thin films on glass substrate were fabricated at various [PVA]/[dye] (P/D) ratios. Hence, the monomeric and H-aggregates thin films of pyronin dye mixed with PVA were formed as a function of the dye and PVA concentration. It was determined that while the monomeric thin films showed strong fluorescence, the formation of H-aggregates in the thin film caused to decreasing the fluorescence intensity. AFM studies demonstrated that the morphology of the thin film was drastically varied with changing the optical property of the thin film such as monomeric and H-aggregates thin films.