Hitoshi Matsuki

Thermodynamic studies on adsorption at interfaces: VII. Adsorption and micelle formation of binary surfactant mixtures

Abstract By extending the thermodynamic method developed in this series, a thermodynamic formulation has been proposed to account for the behavior of the adsorbed films of binary surfactant mixtures at interfaces. Further, this formulation has been extended so as to be applicable to the mixed adsorbed films in equilibrium with mixed micelles. The surface tension of the aqueous solution of a decylammonium bromide (DeAB)-dodecylammonium chloride (DAC) mixture has been measured as a function of the total molality of DeAB and DAC and the mole fraction of DAC in the total surfactant at 298.15 K under atmospheric pressure. The total surface density and the compositions in the adsorbed film and micelle have been evaluated by applying the thermodynamic equations derived to the experimental results. It has been concluded on the basis of the surface tension-composition and critical micelle concentration (CMC)-composition diagrams that DeAB and DAC mix slightly nonideally with each other in both the adsorbed film and the micelle.

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.

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.

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.

Thermotropic and Barotropic Phase Behavior of Phosphatidylcholine Bilayers

Bilayers formed by phospholipids are frequently used as model biological membranes in various life science studies. A characteristic feature of phospholipid bilayers is to undergo a structural change called a phase transition in response to environmental changes of their surroundings. In this review, we focus our attention on phase transitions of some major phospholipids contained in biological membranes, phosphatidylcholines (PCs), depending on temperature and pressure. Bilayers of dipalmitoylphosphatidylcholine (DPPC), which is the most representative lipid in model membrane studies, will first be explained. Then, the bilayer phase behavior of various kinds of PCs with different molecular structures is revealed from the temperature–pressure phase diagrams, and the difference in phase stability among these PC bilayers is discussed in connection with the molecular structure of the PC molecules. Furthermore, the solvent effect on the phase behavior is also described briefly.

Effect of local anesthetics on the phase transition temperatures of ether- and ester-linked phospholipid bilayer membranes

Abstract The phase-transition temperatures of ester-linked dipalmitoylphosphatidylcholine (DPPC) and ether-linked dihexadecylphosphatidylcholine (DHPC) bilayer membranes were measured as a function of the concentration of local anesthetics, dibucaine (DC·HCl), tetracaine (TC·HCl), bupivacaine (BC·HCl), lidocaine (LC·HCl) and procaine hydrochlorides (PC·HCl). The temperature of the main transition for both lipid bilayers was depressed by all the anesthetics added in a dose-dependent manner; the order of the depression of transition temperature was DC·HCl>TC·HCl>BC·HCl>LC·HCl>PC·HCl. The pretransition temperature of DPPC bilayer membrane from the lamellar gel ( L β ′ ) to the ripple gel ( P β ′ ) phase was depressed by the addition of local anesthetics, while the DHPC bilayer membrane undergoes the pretransition from the interdigitated gel ( L β I ) to the P β ′ phase and the elevation of pretransition temperature was observed by the addition of local anesthetics. The presence of local anesthetics stabilize the L β I phase of lipid bilayer membranes. When the more hydrophobic anesthetics such as DC·HCl and TC·HCl were added sufficiently to the bilayer membrane system, the interdigitation of bilayers was induced in the DPPC membrane system and the P β ′ phase disappeared in the DHPC membrane system. From the colligative thermodynamic framework, three kinds of differential partition coefficients corresponding to three phase-transitions, K ( L α )– K ( P β ′ ), K ( P β ′ )– K ( L β ′ ) and K ( P β ′ )– K ( L β I ), where K ( L α ), K ( P β ′ ), K ( L β ′ ) and K ( L β I ) refer to the partition coefficients of an anesthetic into the L α , P β ′ , L β ′ and L β I phases of lipid bilayer membranes, were evaluated from the depression (or elevation) of the phase-transition temperature. The transfer free energy of anesthetics from the aqueous phase to the L α phase of bilayers, Δ G tr ∘ =− RT ln K ( L α ), was well correlated to the local anesthetic potencies.

Partitioning of local anesthetic dibucaine into bilayer membranes of dimyristoylphosphatidylcholine

Abstract Binding of a local anesthetic dibucaine to dimyristoylphosphatidylcholine (DMPC) bilayer membranes was studied by using an ion-selective electrode sensitive to dibucaine cation. DMPC bilayer membrane-buffer partition coefficient was directly determined as a function of anesthetic concentration, temperature and pH. The limiting partition coefficient extrapolated to infinite dilution was employed because the values of partition coefficients were dependent upon the dibucaine concentration. DMPC multilamellar vesicles undergo the thermotropic pretransition from the lamellar gel ( L β ′ ) to the ripple gel ( P β ′ ) phase as well as the main transition from the P β ′ phase to the liquid crystal ( L α ) phase. The limiting partition coefficients at pH 5.4 were 2000, 5500 and 32 000 for the L β ′ , P β ′ and L α phases, respectively. Each of the three states of membranes exhibited a different receptivity to dibucaine partitioning. The limiting partition coefficients were determined as a function of pH at the temperatures corresponding to three states of membranes. The partition coefficients of charged and uncharged anesthetic dibucaine into the DMPC bilayer membranes were estimated from the pH-dependence of the limiting partition coefficients. The three states of DMPC membranes were more receptive to the uncharged dibucaine than the charged species.

Specific and non-specific binding of long-chain fatty acids to firefly luciferase: cutoff at octanoate

Firefly luciferase emits a burst of light when the substrates luciferin and ATP are mixed in the presence of oxygen. We (I. Ueda, A. Suzuki, Biophys. J. 75 (1998) 1052-1057) reported that long-chain fatty acids are specific inhibitors of firefly luciferase in competition with luciferin in microM ranges. They increased the thermal transition temperature. In contrast, 1-alkanols of the same carbon chain length inhibited the enzyme non-competitively in mM ranges and decreased the transition temperature. The present study showed that the action of fatty acids switched from specific to non-specific when the carbon chain length was reduced below C8 (octanoate). The fatty acids longer than C10 inhibited the enzyme in microM ranges whereas those shorter than C8 required mM ranges to inhibit it. The longer fatty acids increased whereas shorter fatty acids decreased the transition temperature. The Hill coefficients of longer chain bindings were less than one whereas those of shorter chain were more than one. The shorter fatty acids interacted with the enzyme cooperatively at multiple sites. Binding of the longer fatty acids is limited. Fatty acids longer than C10 are high-affinity specific binders and followed Koshlands induced-fit model. Those shorter than C8 are low-affinity non-specific denaturants and followed Eyrings rate process model. These results contradict the general consensus that the size of the receptor cavity discriminates specific binders.

Difference in surface activities between uncharged and charged local anesthetics: correlation with their anesthetic potencies

Abstract The surface activities of six uncharged local anesthetics, dibucaine (DC), bupivacaine (BC), lidocaine (LC), mepivacaine (MC), benzocaine (BzC), and benzyl alcohol (BzOH) were investigated by taking surface tension measurements of their aqueous solutions. The surface densities of the uncharged anesthetics were calculated from the application of thermodynamic equations to the surface tension data. The surface activities for uncharged anesthetics became higher in the order of their hydrophobicities, BzOH