Maria Honciuc

Field Effect in a Mixture of Cholesteryl Chloride and Cholesteryl Crotonate (75: 25% by weight)

Abstract The cholesteric-nematic phase transition in cholesteryl chloride and cholesteryl crotonate (75:25% by weight) is investigated. The dependence of the critical field on temperature is determined either by microscopical examination under polarized light or by following a DLI technique under electric field. Agreement between these methods has been obtained.

Electrical Properties of Some Fatty Acids‐Cholesterol Mixtures

Abstract Some electric properties of some fatty acids(arachidic, arachidonic, elaidic and lauric) and fatty acid-cholesterol mixtures were determined. The I = I(U) plots revealed a hysteresis behaviour, the hysteresis area being dependent on the choleaterol content. From the I = I(t) plots, the relaxation time τ and the space charge Qsp were determined and it was shown that in case of arachidic acid-cholesterol mixtures 1+1 molar, τ and Qsp reached maxima. The results are explained by considering a hopping mechanism for conduction.

New nonlinear optical materials from living matter

There is current interest in organic materials for use in optoelectronics. The dielectric properties of these materials have proved compatible with low biasing powers, and some methods to improve them have been proposed. We discuss some fatty acids and mixtures of fatty acids, as well as fatty acid–cholesterol, all of them having an important role in biological membranes. They have smectic liquid-crystalline properties in some temperature ranges, this state being involved in the mechanisms determining health and illness. They can be used also in optoelectronic applications, because of the huge optical nonlinearity in the mesomorphic domain. The external self-focusing of a laser beam and nonlinear optical activity have been observed experimentally; by studying the modification of laser pulses in such media, the cholesterol percentage could be estimated. Also the interaction, at different wavelengths, with coherent and noncoherent light was studied.

Nonlinear Optical Properties of Some Fatty Acids‐Cholesterol Mixtures

Abstract It is shown that fatty acids such as the arrachidic and the lauric acids and their mixtures with cholesterol exhibit nonlinear optical properties. The effects of a 20 mW He-Ne laser (λ= 6328 A) on such mixtures exhibiting smectogenic mesomorphism were examined and the optical activity dependence on the cholesterol percentage was determined.

Growth kinetics of cholesteric spherulites under electric fields

Abstract The growth kinetics of cholesteric spherulites of cholesteryl laurate-cholesteryl caprilate mixture (50: 50% by weight) is investigated. It is show that the nucleation is bidimensional and the growth is determined by the orientational relaxation of the molecules near the interface. The same growth mechanism holds when the nucleation was followed under d.c. electric fields; in this case the growth rates were lower. The electric field effects on growth kinetics can be explained by considering both changes in critical supersaturation and changes in some coefficients associated with dissipative effects during relaxation.

BEHAVIOR IN ELECTRIC FIELDS OF SIMPLE BIOLOGICAL MEMBRANES

The latest studies in biophysics and biochemistry have revealed the major role that liquid crystals (LC) and related phenomena play in biological processes. To account for a number of membrane mechanisms in view of the theoretical model developed by S. J. Singer, studies were carried out on mixtures of fatty acids (arachidic, lauric, butyric) and cholesterol in different weight percentages. Such mixtures may help one understand some mechanisms on which the operation of biological membranes relies. To this end, the way these mixtures behave in an electric field was studied. Electric measurements were conducted from which the average time of electric relaxation (τ) and average electric permittivity (er) were determined. Depending on cholesterol percentage, changes by more than one order of magnitude were found to occur in the electric relaxation time. The ratio between the various fatty acid components did not influence the average time τ in any significant manner. By contrast, the relative electric permittivity er was seen to decrease by at least one order of magnitude with raising the cholesterol percentage. The electric properties of such systems essentially depend on changing the amount of cholesterol in the system.

Influence of thermal neutrons on fatty acids with mesomorphic behavior

The influence of thermal neutron irradiation on the smectic- liquid-crystal properties of arachidic and elaidic fatty acids is investigated. These fatty acids are either precursors or constituents of biological membrane. Microstructural aspects and electric measurements are presented to determine the external voltage dependence of current intensity through the sample. A thermodynamic model, which is in good agreement with experimental data, is described.

Response of fatty acid systems with mesomorphic behavior to action of external electric field

Dependence on a n applied external electric field of the current intensity through samples of fatty acids with mesomorphic behavior was investigated. The time dependence of intensity for a potential step applied to the sample, was used to determine the specific space charge. Electric conduction was analyzed based on the experimental results.

Liquid Crystal, Synergetical System? New Considerations on the Self-Organization and Structural Stability in LC State

The transitions from the solid crystal to liquid crystal, from isotropic liquid crystal as well as the transitions between different mesomorphic states could be interpreted in terms of synergetic and nonlinear dynamics.

Estimation of the cholesterol percentages in mixtures of arachidonic acid and cholesterol

Arachidonic acid (AA) samples and mixtures of arachidonic acid - cholesterol (AA-C) were manufactured and subjected to external electric cw or pulsatory optical laser fields. The polarizing microscope showed a pseudohomeotropic smectic C texture for AA at 10 degree(s)C and smectic C textures with fibers for mixtures AA-C at room temperature. The dependences I equals I(U) at t degree(s)C equals const. and I equals I(t) at U equals const., t being time, showed that samples are dielectrics with a weak conduction (I approximately equals 10-9 A, U equals 0 - 40V). Pure acid samples present an electric hysteresis which disappears when cholesterol is added. The current occurred when the electric field is applied, decreases in time, and tends to a constant value. When the temperature was 19 degree(s)C, a cw focussed laser radiation from a He-Ne laser ((lambda) equals 632.8 nm, P equals 20 mW) determined a lenselike effect in AA, but no effect in mixtures. At the same temperature, the samples were crossed by some green pulses ((lambda) equals 532 nm, (tau) equals 200 microsecond(s) ) furnished by an experimental setup containing a Nd3+ glass laser and a KDP crystal for the second harmonic generation. The shape and extension of the pulse in the time domain, displayed on a sampling oscilloscope, are some indications of the cholesterol percentage.