Shoji Kaneshina

Partition equilibrium of inhalation anesthetics and alcohols between water and membranes of phospholipids with varying acyl chain-lengths

From the depression of the phase-transition temperature of phospholipid membranes, the partition coefficients of inhalation anesthetics (methoxyflurane, halothane, enflurane, chloroform and diethyl ether) and alcohols (benzyl alcohol and homologous n-alcohols up to C = 7) between phospholipid vesicle membranes and water were determined. The phospholipids used were dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines. It was found that the difference in the acyl chain length of the three phospholipids did not affect the partition coefficients of the inhalation anesthetics and benzyl alcohol. The actions of these drugs are apparently directed mainly to the interfacial region. In contrast, n-alcohols tend to bind more tightly to the phospholipid vesicles with longer acyl chains. The absolute values of the transfer free energies of n-alcohols increased with the increase of the length of the alkyl chain of the alcohols. The increment was 3.43 kJ per each carbon atom. The numerical values of the partition coefficients are not identical when different expressions for solute concentrations (mole fraction, molality and molarity) are employed. The conversion factors among these values were estimated from the molecular weights and the partial molal volumes of the phospholipids in aqueous solution determined by oscillation densimetry.

Micelle formation of sodium alkylsulfate under high pressures

Abstract Under high pressures up to 3000 atm, the effects of added salt, chain length, and temperature on the critical micelle concentration (CMC) of sodium dodecylsulfate (SDS) were investigated. The linear relationship between the logarithm of the CMC and of the gegenion concentration was confirmed at high pressures up to 3000 atm. From the behavior of gegenion under pressure, the variation of the aggregation number of micelles with pressure was estimated; initial compression seems to cause the micelle to disaggregate, resulting in the formation of a number of small micelles. The well known fact, at atmospheric pressure, that the CMCs of SDS and its homologous surfactants decrease logarithmically with an increase in the number of carbon atoms in the alkyl chain was confirmed even at pressures up to 3000 atm. From these results, the contributions of hydrocarbon tail and ionic head to the standard free energy and partial molal volume changes on micellization are discussed. Finally, the CMC of SDS was determined at various pressures and temperatures of 17 to 40°C. The temperature at which the CMC becomes minimum tends to shift toward the lower temperature as the pressure increases. The changes of partial molal entropy and enthalpy on micellization, which decrease as the temperature is raised and increase as the pressure increases to a certain value, could be qualitatively explained by the formation of an “iceberg” structure of water around the hydrocarbon tail in the monomer state. Further, the micelle-forming properties are discussed in terms of the temperature and pressure dependence of the CMC.

Effect of local anesthetics on the bilayer membrane of dipalmitoylphosphatidylcholine: interdigitation of lipid bilayer and vesicle–micelle transition

The phase transitions of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane were observed by means of differential scanning calorimetry (DSC) as a function of the concentration of local anesthetics, dibucaine (DC x HCl), tetracaine (TC x HCl), lidocaine (LC x HCl) and procaine hydrochlorides (PC x HCl). LC x HCl and PC x HCl depressed monotonously the temperatures of the main- and pre-transition of DPPC bilayer membrane. The enthalpy changes of both transitions decreased slightly with an increase in anesthetic concentration up to 160 mmol kg(-1). In contrast, the addition of TC x HCl or DC x HCl, having the ability to form a micelle by itself, induced the complex phase behavior of DPPC bilayer membrane including the vesicle-to-micelle transition. The depression of both temperatures of the main- and pre-transition, which is accompanied with a decrease in enthalpy, was observed by the addition of TC x HCl up to 21 mmol kg(-1) or DC x HCl up to 11 mmol kg(-1). The pretransition disappeared when these concentrations of anesthetic were added, and the interdigitated gel phase appeared above these concentrations. The appearance of the interdigitated gel phase, instead of the ripple gel phase, brings about the stabilization of the gel phase by 1.8-2.4 kcal mol(-1). In the concentration range of 70-120 mmol kg(-1) TC x HCl (or 40-60 mmol kg(-1) DC x HCl), the enthalpy of the main transition exhibited a drastic decrease, resulting in the virtual disappearance of the main transition. This process includes the decrease in vesicle size with increasing anesthetic concentration, resulting in the mixed micelle of DPPC and anesthetics. Therefore, in this range of anesthetic concentration, the DPPC vesicle solubilized an anesthetic which coexists with the DPPC-anesthetic mixed micelle. Above the concentration of 120 mmol kg(-1) TC x HCl (or 60 mmol kg(-1) DC x HCl), there exists the DPPC-anesthetic mixed micelle. Two types of new transitions concerned with the mixed micelle of DPPC and micelle-forming anesthetics were observed by DSC.

Partial molal volumes of surfactant and its homologous salts under high pressure

Abstract The compressions of solutions of sodium alkylsulfates and alkyltrimethylammonium bromides and then the partial molal volumes of these salts under pressure were determined. The partial molal volume of surfactant in micellar state decreased with increase in pressure and that of alkyltrimethylammonium bromide in singly dispersed state decreased also with pressure, while the partial molal volume of sodium alkylsulfate in singly dispersed state increased with increase in pressure. The changes of the partial molal volume on micellization determined directly were compared with that obtained indirectly from the pressure dependence of the critical micelle concentration.

Transfer of anesthetics and alcohols into ionic surfactant micelles in relation to depression of krafft point and critical micelle concentration, and interfacial action of anesthetics

Abstract The Krafft points of sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) decreased linearly with the increase of the concentration of added alcohols (1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol). On the basis of a theory which treats the Krafft point as the melting point of the hydrated solid surfactant, the partition coefficients, K , of alcohols between the aqueous and the micellar phases were calculated from the Krafft-point depressions by the aid of thermodynamics. The values of K obtained by the present method were in good agreement with those measured by other methods. The transfer free energies of alcohols from the bulk solution to the SDS and STS micelles, ΔG p o = − RT In K , decreased linearly with the increase of the carbon number of the alcohol. ΔG p o per methylene group was almost the same for both SDS and STS micelles: −2.45 kJ mol −1 for the SDS micelle and −2.51 kJ mol −1 for the STS micelle. However, the values of ΔG p o of the alcohols into the STS micelle were more negative compared with those into the SDS micelle. This means that the more hydrophobic micelles are favored for the transfer of alcohol. The method presented here is generally applicable to determine the micelle/water partition coefficients of solutes which form mixed micelle. The partition coefficients of inhalation anesthetics between the aqueous and SDS micellar phases were methoxyflurane 1320, halothane 1140, and enflurane 990. These values are in the same order of their clinical potencies. The critical micelle concentration (CMC) of SDS was measured by the conductivity method as a function of the added anesthetics. The CMC decreased linearly with the increase of the anesthetic concentration. The decrease of the CMC by anesthetics was correlated to the micelle/water partition coefficient of these anesthetics by means of the relation proposed by Shirahama and Kashiwabara ( J. Colloid Interface Sci. 36 , 65 (1971)) , and was ascribed mainly to the increase in entropy of mixing in the micelle due to the solubilization of the inhalation anesthetics. The decrease of CMC by anesthetics was accompanied by a small but unequivocal release of the counterions from the micellar surfaces which indicates the tendency of anesthetics to dehydrate the interface.

Thermodynamics of pressure—anesthetic antagonism on the phase transition of lipid membranes: Displacement of anesthetic molecules

Abstract From the depression of the phase-transition temperature of dipalmitoylphosphatidylcholine vesicle membranes by inhalation anesthetics (halothane, methoxyflurane, enflurane, and chloroform), the apparent partition coefficient, K app , of these drugs between the lipid membrane and water was estimated and the effect of hydrostatic pressure upon the partition was examined. By assuming nonzero partition of anesthetics into the solid-gel membrane, K app is defined as (1 - k ) K , where K is the partition coefficient between the liquid-crystalline membrane and water, and k is the partition coefficient between the liquid-crystalline membrane and the solid-gel membrane. The value of K app was little affected by the change of temperature but was significantly decreased by the high pressure. The high pressure squeezed out the anesthetic molecules from the liquid-crystalline membrane, as evidenced by the decrease of the partition coefficient. The decrement of the number of the anesthetic molecules from that adsorbed at ambient pressure was halothane 10.4 × 10 −2 , chloroform 6.42 × 10 −2 , enflurane 9.58 × 10 −2 , and methoxyflurane 8.45 × 10 −2 % per 1 bar. The volume change due to the transfer of anesthetics from the aqueous phase to the lipid membrane, calculated from the pressure dependence of the apparent partition coefficient, was found to show a large positive value of about 15% of their molal volume. The magnitude of the volume increase is rather large and is difficult to ascribe to the breakage of anesthetic-water contact alone. The volume increase may be caused by the following factors: the structural change of the membrane, the change of the interaction forces between membrane and water due to anesthetic adsorption, the change of interaction between the anesthetics and water, etc. The positive sign indicates that anesthetics must be translocated from the lipid membrane into the aqueous phase by high pressure. Although pressure reversal of anesthesia may be caused mainly by restoration of order in the membrane and by enhancement of the cooperativity of the phase transition, displacement of anesthetics from the binding sites may also contribute to the phenomenon.

THERMOTROPIC AND BAROTROPIC PHASE TRANSITION ON BILAYER MEMBRANES OF PHOSPHOLIPIDS WITH VARYING ACYL CHAIN-LENGTHS

The bilayer phase-transitions of a series of 1,2-diacylphosphatidylcholines containing linear saturated acyl chain of even- and odd-number carbons (C=12, 13, 14, 15, 16, 17 and 18) were observed by two kinds of optical methods. One is the observation of isothermal barotropic phase transition and the other is the isobaric thermotropic phase transition. The temperature of the main transition from the ripple gel phase to the liquid crystal phase for each lipid was elevated linearly by pressure in the range of 150 MPa. The slope of the temperature–pressure diagram, d T /d p , was in the range 0.20–0.23 K MPa −1 depending on the acyl chain-length. The chain length dependence of the main transition temperature under ambient pressure described a smooth curve with no evidence of odd/even discontinuities. The phase transition enthalpy, Δ H , which was determined by the differential scanning calorimetry (DSC), increased with an increase in the acyl chain-length. The Δ H vs. chain-length curve was non-linear and convex upward. The volume change, Δ V , associated with the transition was calculated from the values of Δ H and d T /d p by means of the Clapeyron–Clausius equation. The values of Δ V increased with an increase in the acyl chain-length, which were best described by a smooth curve and not a linear function. The increment of the transition volume tends to be moderated as the length of the hydrocarbon chain is increased and amounts to 1.4 cm 3 mol −1 per one methylene group. Non linear properties of thermodynamic quantities with respect to the acyl chain-length seem to be attributable to the end-group effects of the fatty acyl chains.

Barotropic phase transitions of dioleoylphosphatidylcholine and stearoyl-oleoylphosphatidylcholine bilayer membranes.

In order to understand the effect of cis unsaturation on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) bilayer membranes were observed by high-pressure optical method. With respect to DOPC bilayer membrane, the so-called main transition between the liquid crystalline (Lalpha) and the lamellar gel (Lbeta) phases was observed in water at above 0 degrees C under high pressure, in addition to the transition between the Lalpha and the lamellar crystalline (L(C)) phases in 50% aqueous ethylene glycol. The pressure of main transition increased linearly with an increase in temperature. Extrapolation of temperature (T)-pressure (P) phase boundary to ambient pressure suggests the temperature of the main transition to be -40.3 degrees C, which has never been found by the DSC method. On the other hand, the temperature of L(C)/Lalpha phase transition in 50% aqueous ethylene glycol was found to be -12.0 degrees C at ambient pressure. The main transition temperatures for DSPC, SOPC and DOPC are 55.6, 6.7 and -40.3 degrees C, respectively, at ambient pressure. The substitution of cis unsaturated chain for saturated chains of DSPC brings about the depression of the main transition temperature by about 48 (+/-1) degrees C for each chain. The volume changes (deltaV) associated with the transitions were calculated from the transition enthalpy (deltaH) and the slope of T-P diagram (dT/dP) by means of the Clapeyron-Clausius equation. The value of deltaV for the main transition of SOPC bilayer membranes was reduced to half the volume change for DSPC bilayers, which means the introduction of the cis double bond in the acyl chain of lipids brings about the reduction of deltaV because of the disordered packing of unsaturated chains in the gel phase of lipid bilayer membranes.

Unisotropic solubilization of an inhalation anesthetic, methoxyflurane, into the interfacial region of cationic surfactant micelles.

Abstract Proton-NMR shows that methoxyflurane (HCCl2-CF2-O-CH3) binds hexadecyltrimethylammonium bromide micelles only at the interfacial regions and does not mix with the lipid core isotropically. The protons of the -O-CH3 end is oriented into the hydrophobic interior, while the proton of the HCCl2-end stays at the interfacial region in the close vicinity of the aqueous phase.

Effect of unsaturated acyl chains on the thermotropic and barotropic phase transitions of phospholipid bilayer membranes

Abstract In order to understand the effect of unsaturation on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of 1,2-distearoyl- sn -glycero-3-phosphocholine (DSPC), 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC), 1,2-dielaidoyl- sn -glycero-3-phosphocholine (DEPC), 1-oleoyl-2-stearoyl- sn -glycero-3-phosphocholine (OSPC), 1-stearoyl-2-oleoyl- sn -glycero-3-phosphocholine (SOPC), 1-stearoyl-2-arachidonoyl- sn -glycero-3-phosphocholine (SAPC), 1-stearoyl-2-docosahexaenoyl- sn -glycero-3-phosphocholine (SDPC) and 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphocholine (POPC) bilayer membranes were observed by high-pressure optical method and differential scanning calorimetry. For all of the lipids studied, the temperatures of the so-called main transition between the liquid crystalline (L α ) and the lamellar gel (L β ) phases were almost linearly elevated by pressure. The values of d T /d P for monounsaturated lipids (SOPC, OSPC and POPC) lie around 0.18 K/MPa, which are smaller than that for the saturated lipid DSPC, 0.23 K/MPa. The polyunsaturated lipids (SAPC and SDPC) have rather small values of d T /d P . The temperatures of L β /L α transition for DSPC, SOPC, OSPC and DOPC were 55.6, 6.7, 8.7 and −40.3°C, respectively. The substitution of cis unsaturated chain for saturated chains of DSPC brings about the depression of transition temperature by 47°C for sn -1 chain and 49°C for sn -2 chain. The volume change (Δ V ) associated with the transitions were calculated from the transition enthalpy (Δ H ) and the value of d T /d P by means of the Clapeyron–Clausius equation. The values of Δ V for SOPC, OSPC and POPC, which have an only cis double bond in sn -1 or sn -2 chain, were 18.9, 17.4 and 15.5 cm 3 /mol, respectively. These values are smaller than that for the saturated DSPC, 31.6 cm 3 /mol, and larger than that for the polyunsaturated SAPC, 10.1 cm 3 /mol. It seems that the Δ V for the L β /L α transition is obviously dependent on the number of cis double bonds in the acyl chains. With respect to the bilayer membranes of DEPC, SOPC and OSPC, the transition between the lamellar crystalline (L c ) and the L β phases was observed; the values of d T /d P were 0.108, 0.093 and 0.105 K/MPa, respectively, which are almost the same. The values of Δ V for the L c /L α transition of trans unsaturated DEPC and cis unsaturated DOPC were 28.4 and 36.7 cm 3 /mol, and the values of Δ H were 59.2 and 65.3 kJ/mol, respectively. This difference may be directly attributed to the different geometrical configurations of trans and cis double bonds.