Nadide Kazanci

Tamoxifen increases membrane fluidity at high concentrations.

There are contradictory results in the literature relating to the effect oftamoxifen on membrane fluidity. The present work investigates the effect oftamoxifen on membrane dynamics to find out whether the concentration oftamoxifen can be one of the factors in this discrepancy. Turbidity(absorbance at 440 nm) and Fourier transform infrared spectroscopicstudies reveal that tamoxifen causes opposite effects on membranefluidity at low (1 mol.%) and high (30 mol.%) tamoxifen concentrations. Lowtamoxifen concentrations increase the absorbance in the gel and liquidcrystalline phase, whereas high tamoxifen concentrations decrease theabsorbance in gel and liquid crystalline phase, whereas tamoxifenconcentrations decrease the absorbance. Observations on both phasesshow that the bandwidth of the CH2 stretching bands decreases with1 mol.% tamoxifen and increases with 30 mol.% tamoxifen present, indicatinga decrease in membrane fluidity at low tamoxifen concentrations and anincrease in fluidity at high tamoxifen concentrations. It is seen that theapparent discrepancy in the literature on the effect of tamoxifen onmembrane fluidity mainly arises from the tamoxifen concentration used andthe confusion on the concept of lipid fluidity and lipid order.

Vitamin D2 at high and low concentrations exert opposing effects on molecular order and dynamics of dipalmitoyl phosphatidylcholine membranes

Fourier Transform Infrared spectroscopic studies show that low concentrations of vitamin D2 (1 and 3m ol %) does not induce significant change in the overall shape of the thermotropic profile of dipalmitoyl phosphatidylcholine (DPPC) membrane. In contrast, at higher concentrations of vitamin D2 (9 and 12 mol %), the phase transition shifts to lower temperatures and a significant broadening in the phase transition curve is also observed. Low concentration of vitamin D 2 decreases the frequency of the CH2 stretching mode, implying an ordering effect, whilst high concentration of vitamin D 2 disorders the system. Furthermore, at low and high concentrations, vitamin D2 causes opposing effect on membrane dynamics. It decreases the bandwidth of the CH2 stretching modes at low concentrations while increasing it at high concentrations. We have also observed different actions of vitamin D2 at low and high concentrations in the deep interior and interfacial region of the membrane, by monitoring the frequency of the CH3 stretching band and C=O stretching bands, respectively.

Lyotropic nematic mesophases: investigations of mesomorphic and thermo-optical properties

Abstract Investigations of mesomorphic and thermo-optical properties of lyotropic nematic-calamitic (N c ) and nematic-discotic (N d ) mesophases are described. The peculiarities of microscopic textures and the temperature and concentration changes of the refractive index and birefringence have been studied. The nematic-isotropic liquid phase transition temperatures and the temperature widths of heterophase regions of the phase transitions from the N c and N d mesophases to the isotropic phase have been determined with a high accuracy. Thermic hysteresis in the width of heterophase regions of the phase transitions between nematic mesophases and isotropic liquid have been found.

Refracting and birefringent properties of lyotropic nematic mesophases

Abstract In this work, we investigated refracting, birefringent and thermotropic properties of lyotropic nematic mesophases. In particular, the morphological properties of nematic–calamitic and nematic–discotic lyotropic mesophases have been investigated in the heterophase regions at lyotropic nematic–isotropic liquid phase transitions. The changes in isotropic, mean refractive index, and anisotropic, birefringence, optical properties of the nematic mesophases by the changes in temperature have been observed to have fluctuational character in the heterophase regions of lyotropic nematic–isotropic liquid phase transitions. This character reflects the character of changes in shapes and sizes of micelles and in symmetries of the mesophases in the heterophase region.

IR AND TURBIDITY STUDIES OF VITAMIN E-CHOLESTEROL-PHOSPHOLIPID MEMBRANE INTERACTIONS

Binary and tertiary mixture of α-tocophenol, cholesterol and dimyristoylphosphatidylcholine in the form of multilamellar liposomes were investigated by Fourier Transform Infrared and visible spectroscopy. Results of the FTIR and turbidity experiments indicate that α T decreases or diminishes the effect of cholesterol on the frequency and the bandwidth of the C-H stretching, CH2 scissoring and C=O stretching bands in FTIR spectra and the turbidity measurements (recorded as absorbance values at 440 nm) in phospholipid model membranes.

Interactions of tamoxifen with distearoyl phosphatidylcholine multilamellar vesicles: FTIR and DSC studies

Interactions of a non-steroidal antiestrogen drug, tamoxifen (TAM), with distearoyl-sn-glycero-3-phosphatidylcholine (DSPC) multilamellar liposomes (MLVs) were investigated as a function of drug concentration (1-15 mol%) by using two noninvasive techniques, namely Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). FTIR spectroscopy results show that increasing TAM concentrations (except 1 mol%) increased the wavenumbers of the CH2 stretching modes, implying an disordering effect for DSPC MLVs both in the gel and liquid crystalline phases. The bandwidth values of the CH2 stretchings except for 1 mol% increased when TAM concentrations increased for DSPC liposomes, indicating an increase in the dynamics of liposomes. The CO stretching and PO2- antisymmetric double bond stretching bands were analyzed to study interactions of TAM with head groups of lipids. As the concentrations of TAM increased, dehydration occurred around these functional groups in the polar part of the lipids. The DSC studies on thermal properties of DSPC lipids indicate that TAM eliminated the pre transition, shifted the main phase transition to lower temperatures and broadened the phase transition curve of the liposomes.

Surface-induced textures in lyotropic liquid crystalline mesophases

In the present work the investigation of the effect of YBa2Cu3O7−x complex compounds thin films on the mesomorphic, morphologic and orientational properties of lyotropic nematics have been carried out. The thin films of YBa2Cu3O7−x lead to an increase in number of morphologies of investigated nematics and promote the obtaining of tilted oriented and homeotropic textures of these nematics. The coating of YBa2Cu3O7−x thin films by inverted cylindrical DC magnetron sputtering system has been shown in this work to be a useful method for obtaining oriented textures of lyotropic nematics.

Some peculiarities of nematic–isotropic liquid phase transitions in monomorphic and polymorphic mesogens

In this study, the dynamics of the changes of the morphological properties in the nematic mesophase and in the heterophase regions of the phase transitions between the nematic mesophase and the isotropic liquid for the thermotropic mesogens have been investigated. Experimentally, we have obtained the thermal hysteresis for the investigated phase transitions. For the analysis of the phase transition temperatures and the peculiarities of the heterophase regions, the mean field theory has been used.

Morphology, surface-induced orientational properties and phase transition peculiarities of lyotropic nematic mesophases in pentadecane solutions of tetranuclear platinum mesogens

Abstract We have investigated the surface-induced orientational properties and peculiarities of the phase transitions of a lyotropic system, composed of a sheet-shaped tetranuclear platinum organyl in pentadecane, and exhibiting two different lyotropic nematic mesophases (N 1 and N 2 ). Corrugated YBa 2 Cu 3 O 7− x surfaces with a sinusoidal profile have been used to induce planar orientation of these two nematic lyomesophases, which differ significantly with their orientational behavior. We have also measured the birefringence of these nematic mesophases. Based on high-accuracy determinations of the transition temperatures, we are discussing some peculiarities of the phase transitions between the two nematic mesophases and between N 2 mesophase and isotropic liquid, in particular, the width of the heterophase regions between them.

Effect of YBa2Cu3O7-x thin films on the textures and orientational properties of liquid crystals

Abstract.In the present work, the effect of thin films of YBa2Cu3O7-x complex compound on the mesomorphic and orientational properties of thermotropic nematic liquid crystals has been studied. Homogeneous, stable and reproducible homeotropic and tilted oriented textures of nematic liquid crystals were obtained. The effect of YBa2Cu3O7-x thin films on the morphologic, orientational and optical properties of thermotropic nematic liquid crystals are discussed.