Dioleyl Phosphate Research Articles

Effect of anesthetics on the self-sustained oscillation in an artificial membrane induced by repetitive conformational change of DOPH molecules between hydrophilic and hydrophobic phases

The mechanism of anesthesia was approached from a study of an artificial excitable membrane that well reproduced the active electrical properties of the nerve membrane. Self-sustained oscillations of the membrane potential in a model membrane in which dioleyl phosphate (DOPH) was infiltrated into the pores of a millipore filter were utilized to investigate the effect of volatile anesthetic agents on the repetitive conformational change of DOPH molecules between hydrophilic multibilayers and hydrophobic oil droplets, while this process was coupled with diffusion of K+ across the membrane placed between KCl aqueous solutions. The period of the self-sustained oscillations increased due to the addition of volatile anesthetics to the aqueous solutions, and there were critical values of concentrations of volatile anesthetics above which the self-sustained oscillations disappeared. The volatile anesthetic agents affected the hydrophobic oil droplets of the DOPH molecules and impeded their repetitive conformational change between the hydrophilic and hydrophobic phases, just as local anesthetics had been reported to do.

Metal Ion-Imprinted Polymer Prepared by the Combination of Surface Template Polymerization with Postirradiation by γ-rays

Zinc ion-imprinted polymers were prepared by the combination of surface template polymerization and irradiation by γ-rays. Dioleyl phosphate, which has two C−C double bonds in the oleyl chains, and divinylbenzene were employed as a functional monomer and a cross-linking agent, respectively. After the surface template polymerization with water-in-oil emulsions, the imprinted resins were irradiated with γ-rays to make the polymer matrices more rigid and also to allow the functional monomer to attach firmly to the matrices. The irradiated imprinted resin exhibits a tremendously high selectivity toward zinc ions over copper ions. Thus it is understood that the postirradiated imprinted polymers are characterized by stable and highly specific recognition sites. The combination of surface template polymerization with irradiation with γ-rays offers a potential technique to construct highly selective molecular-recognizing polymers applicable to the adsorption of various water-soluble substances.

The effects of chain flexibility on the properties of vesicles formed from di‐n‐alkyl phosphates

AbstractThis paper describes a study of the effects of chain flexibility and chain packing on the properties of vesicles formed from sodium di‐n‐alkyl phosphates. Three di‐n‐alkyl phosphates with a constant chain length but with different degrees of unsaturation have been synthesized: dioleyl phosphate (DOP) and dielaidyl phosphate (DEP) having, respectively, a cis and a trans double bond at C‐9 and the saturated distearyl phosphate (DSP). These surfactants form vesicles, as confirmed by transmission electron microscopy (EM). The gel to liquid‐crystalline phase transition was studied using both fluorescence polarization and differential scanning microcalorimetry. According to fluorescence polarization, using trans, trans, trans‐1,6‐diphenyl‐hexa‐1,3,5‐triene (DPH) as a probe, DSP vesicles undergo a cooperative transition from a gel to a liquid‐crystalline state at 72°C. The polarization of the probe captured in DOP or DEP vesicles decreased gradually in the temperature range 0–40°C, indicating a non‐cooperative phase transition. It appears that the vesicle bilayer is in a gel state below 0°C and in a liquid‐crystalline state above 40°C. A temperature‐dependent 31P NMR study failed to identify the exact phase‐transition temperature. The effect of the fusogenic cation Ca2+ was studied qualitatively using EM. Calcium induces fusion of DEP vesicles but, within a short time, tubules are formed which are most probably anhydrous crystals of the calcium salts. For DSP vesicles the latter process is extremely fast and fused vesicles cannot be detected. In contrast, DOP vesicles fuse under the influence of calcium, but no crystallization takes place. The fused DOP vesicles are stable for more than one week in the presence of 4 mM Ca2+ stored at room temperature or at 60°C. Addition of EDTA to DOP vesicles leads to chelation of the calcium ions and to a transition to multilamellar vesicles.

Some Characteristics of Microemulsions in Sodium Dioleyl Phosphate/n-Heptane/Brine System

The behavior of microemulsions in the sodium dioleyl phosphate (SDOLP)/n-heptane system was investigated. This system provided a water-in-oil microemulsion without using a cosurfactant. The phase diagram of the WinsorII was determined. Along the phase boundary between the microemulsion and the excess brine solution, the small angle X-ray scattering, the viscosity, and the electric conductivity of the microemulsions were measured. SDOLP provided the spherical aggregates, which were highly isolated from each other even in the concentrated region of the aggregates. These characteristics were estimated to be attributed to peculiar packing of the hydrocarbon chain tails of SDOLP due tocis-double bonds.

Nonlinear Dynamics in a Theoretical Model of Excitable Lipid Membrane

A theoretical model is presented for reproducing chaotic behaviors observed experimentally in the DOPH (dioleyl phosphate) membrane system with external periodic stimulation. The model describes the self-sustained oscillation of the membrane potential of the DOPH membrane by taking into account the effect of applied AC electric current. The route to chaos was classified as break-down of quasi-periodicity, although it was unclear experimentally. Effects of the change in the phenomenological parameters in the theoretical model on the attractor were also investigated. It was shown that some dynamic bifurcation properties can change much more sensitively than average quantities as the mean frequency. The change of the attractor was discussed in relation to the interaction of DOPH molecules with taste substances by comparing with experimental results.

Dynamics and Mechanism of Self-Sustained Oscillation of Lipid Impregnated in a Single Hole

The mechanism of the oscillatory electric potential of a dioleyl phosphate (DOPH) layer in a single hole sandwiched by two KCl solutions, 100 mM and 5 mM, was investigated using two types of cells for axial and transverse observations. It was discovered that the electrical oscillation was related to a macroscopic behavior of the interfaces between DOPH and KCl solutions caused by a chemically driven surface tension effect.

Cutoff effect of n-alkanols in an excitable model membrane composed of dioleyl phosphate

A series of n-alkanols from ethanol to tridecanol interacted with a negatively charged lipid membrane composed of dioleyl phosphate, which exhibited a

Behavior of a System Composed of Globally Coupled Neuron Models

The patterns of chaotic oscillations of a Millipore membrane infiltrated with dioleyl phosphate are changed by chemical substances or light. We regarded the membrane as a system of globally coupled neuron models and examined the behavior of the system. As a result, the oscillation of each element becomes disordered or ordered according to the changes of parameters of the system. This result suggests that the changes of chaotic oscillation patterns of the membrane can be attributed to the changes of parameters of the system due to chemical substances or light.

Changes of Chaotic Oscillation Patterns of Artificial Lipid Membrane Induced by Light

We have examined chaotic oscillation patterns of a Millipore membrane infiltrated with dioleyl phosphate and an azobenzene derivative under visible or UV irradiation. As a result, the amplitude of the oscillation was larger and the correlation dimension was smaller under UV irradiation. This result suggests that some of many nonlinear oscillators of the membrane could oscillate coherently under UV irradiation. We believe that it is the first experimental result which can be explained by the globally coupled map model.

Estimation of Ca2+-Induced Surface Structural Changes of Artificial Lipid Membrane.

The surface structure of an artificial membrane composed of a Millipore filter and a synthetic lipid analogue, dioleylphosphate (DOPH), changes from a highly reflective hydrophilic state to a poorly reflective hydrophobic state in KCl solution with increasing calcium ion concentration in the solution. Using a microscopic digital image processing system the structural changes can be characterized quantitatively, in a histogram of the brightness level and a binary black-and-white picture. The gross area of hydrophilic domains and the mean diameter of hydrophilic particles were measured by processing the binary picture.

Electrical characteristics in an excitable element of lipid membrane

Electrical characteristics in a membrane constructed from a porous filter adsorbed with a lipid analogue, dioleyl phosphate (DOPH), were investigated in a situation interposed between 100 m M NACl + 3 m M CaCl 2 and 100 m M KCl. Calcium ions affected significantly the membrane characteristics. The membrane potential was negative on the KCl side, which implies the higher permeability to K + than Na +; this tendency was increased by a tiny amount of Ca 2+. While the membrane showed a low electrical resistance of several kΩ. cm 2under K +/Na + gradient, it showed several MΩ · cm 2+ by Ca 2+. The surface structure of the membrane exhibited many voids in the low-resistance state, but the surface was covered by oil droplets in the high-resistance state. Oscillations of the membrane potential appeared spontaneously with application of the electrical current from the KCl side to the NaCl + CaCl 2 side. The frequency was increased with the electrical current. All these results were explained comprehensively using an electrochemical kinetic model taking account of the Ca 2+ binding effect, where DOPH assemblies make a phase transition between oil droplets due to Ca 2+ and multi-bilayers with excess K +. The oscillation arises from coupling of the phase transition to accumulation and release of K + or Ca 2+. This membrane can be used as an excitable element regulated by Ca 2+ in neuro-computer devices.

Static Responses of Artificial Membranes composed of a Mixture of Lipids to Taste Substances.

We have examined static responses of Millipore membranes infiltrated with only dioleyl phosphate (DOPH), DOPH and dioleoyl phosphatidylethanolamine (DOPE), and DOPH and cholesterol to a bitter (strychnine sulfate), a sour (HCl), a salty (NaCl) and a sweet (sucrose) substances. The DOPE-mixed membrane responded more sensitively to HCl. The cholesterol-mixed membrane responded more sensitively to strychnine, NaCl and sucrose. The present results are similar to the assumption that all sensory cells do not respond uniformly to a chemical substance in the biological system because of a difference of the membrane composition of sensory cells.

Model Study of Spontaneous Discharge Fluctuations of a Membrane Potential

A discharge model is presented to simulate self-induced oscillations of a tonically autoactive neuron (TAN) of an African giant snail and a dioleyl phosphate (DOPH) Millipore membrane system. In this model, the pulse interval is determined by the accumulated ionic charges in a cell and the threshold level of discharge. The relationship of the fluctuations of these two parameters to the discharge interval fluctuations is simulated.

Effect of local anesthetics on the electrical characteristics of an excitable model membrane composed of dioleyl phosphate

The effects of local anesthetics (tetracaine, procaine and lidocaine) on self-sustained electrical oscillations were studied for a lipid membrane comprising dioleyl phosphate (DOPH). This model membrane exhibits oscillation of the membrane potential in a manner similar to that of nerve membranes, i.e., repetitive firing, in the presence of an ion-concentration gradient, on the application of d.c. electric current. Relatively weak anesthetics such as procaine and lidocaine increased the frequency of self-sustained oscillation, and finally induced aperiodic, rapid oscillation. The strong anesthetic tetracaine inhibited oscillation.

Effect of local anesthetics on the electrical characteristics of an excitable model membrane composed of dioleyl phosphate

The local anesthetics, tetracaine, procaine and lidocaine, interacted with a negatively charged lipid membrane composed of dioleyl phosphate (DOPH), which exhibited a self-sustained oscillation of the membrane potential. The anesthetics depolarized the membrane potential when present in increasing concentrations, whereas they increased the membrane resistance at low concentrations and decreased it at high concentrations. The above results were analyzed on the basis of electrochemical theory taking into account ion flux across the membrane. The electrical characteristics are affected by both the hydrophobicity and the diffusion constant of local anesthetics within the membrane.

Effect of Taste Substances on Aperiodic Oscillation of an Electric Potential in a Synthetic Lipid Membrane

A correlation dimension and a distribution pattern of spectrum intensities of a self-sustained electric oscillation were studied for an aperiodic oscillation induced by an application of electric current on a membrane of a synthetic lipid, dioleyl phosphate. The estimated dimension showed a remarkable deviation in the presence of taste substances such as quinine (above a certain threshold value) from that in the absence of these taste substances; this deviation was accompanied by a change in spectrum pattern. The present result indicates that the two variables extracted from the aperiodic oscillations will be useful as sensing information in a chemical taste sensor using lipid membranes.

Effect of several sweet substances on the electrical characteristics of a dioleyl phosphate-millipore membrane.

Sweet substances (sucrose, lactose, glucose, fructose, galactose, glycerin and aspartame), excepting Na saccharin, effectively interacted with a negatively-charged lipid membrane of dioleyl phosphate (DOPH). These sweet substances decreased the membrane resistance and depolarized the membrane potential. This response differed from those to bitter, sour and salty substances. Together with the result for transient response, it is suggested that sweet substances could penetrate the lipid membrane. Mono- and disaccharides exerted their effects at a concentration corresponding to the threshold value of taste sensation in vivo. Aspartame, which is about 100-fold sweeter than sucrose, was effective at one-hundredth of this concentration. In addition, the effect of sweet substances on a positively-charged lipid membrane was studied. Changes in the membrane electrical potential and resistance were observed by employing Na saccharin, which had no effect on the DOPH membrane.

Characteristics of Ca 2+-induced structural changes of millipore-doph artificial membranes. Possibility of Calcium Ion detection

The surface structure of an artificial membrane composed of a Millipore filter and a synthetic lipid analogue, dioleylphosphate (DOPH), immersed in KCl solution, changes when the concentration of CaCl 2 added to the KCl solution on one side of the membrane reaches a critical value. Using a photomultiplier mounted on the eyepiece of a stereoscopic microscope the structure change can be measured quantitatively as a variation of the intensity of the light reflected from the membrane surface. In the presence of calcium ions, the intensity decreased to approximately 50% of the value in the original hydrophilic state of the membrane in KCl solution only. However, the degree of structural change was dependent on adsorption density of DOPH, solution temperature and solution pH. On the other hand, using the light reflectance curves obtained from the structural observations, the concentration of an unknown amount of CaCl 2 in a KCl solution can be determined. Since the reflectance curves shift significantly with variation of the density of DOPH adsorbed on the Millipore filter, it is possible to detect a wide range of CaCl 2 concentrations, the detection range stretching from 0.1 to 50 m M CaCl 2.

Electric oscillation in an excitable model membrane impregnated with lipid analogues.

A model membrane constructed from a Millipore filter, whose pores were impregnated with dioleyl phosphate, exhibited an electric self-oscillation under nonequilibrium conditions. The membrane interposed between two solutions with the same KCl concentrations showed no temporal change in membrane potential. However, the potential became oscillatory on application of an electric current to the membrane. The frequency was proportional to the magnitude of the electric current. When both KCl solutions were replaced by NaCl solutions, a similar trend was observed, although the oscillation was not as regular as in the case of KCl. A membrane placed between equimolar solutions of KCl and NaCl, on the other hand, gave rise to an oscillation even without current application. When a membrane was placed between 5 mM KCl and 100 mM KCl, it was found that NaCl added to the 5 mM KCl side had a pronounced effect on the membrane with respect to the frequency response of the oscillation. These results indicate that the dioleyl phosphate membrane discriminates Na+ from K+.

Sustained resistance oscillation of millipore DOPH model membrane with calcium ions

The Millipore DOPH membrane, which consists of a synthetic lipid analogue — dioleylphosphate (DOPH) — absorbed in a Millipore filter, increased its membrane resistance by a factor of 10 4 when Ca 2+ ions combined with it. The membrane resistance experienced an oscillatory change when a constant direct current and static pressure were simultaneously applied. This stable oscillation continued for several hours during the application of the stimuli. The conditions under which the oscillation appeared were as follows: the current stimulus was kept below 0.1 μA, and the pressure stimulus, from 15 to 35 mmHg, was applied as a step function. It was possible to replace the voltage difference across the membrane caused by the constant current flow by the steady membrane potential which was generated by a KCl concentration gradient. Using this replacement, an oscillatory change of the membrane potential was observed at application of pressure as stimulus only; the oscillation frequency increased from 0.8 to 3.5 Hz in the pressure range 13 to 22 mmHg. The increase in membrane resistance was caused by Ca 2+ ions combining with O - of the hydrophilic group in the DOPH molecule. The effect was stronger with Ca 2+ ions than with other divalent cations (Sr 2+, Ba 2+, Mg 2+).