Hayato Ichimori

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.

Effect of deuterium oxide on the phase transitions of phospholipid bilayer membranes under high pressure

The present study demonstrates the substitution effect of hydrogen oxide (H 2 O) by deuterium oxide (D 2 O) on the phase transitions of dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC) bilayer membranes under high pressure. Substitution effect of H 2 O by D 2 O was as follows. With respect to the main transition from the ripple gel (P β ′ ) phase to the liquid crystalline (L α ) phase for DPPC and DSPC bilayer membranes, there was no significant difference in the main transition temperature in H 2 O and D 2 O. On the other hand, the pretransition temperature between lamellar gel (L β ′ ) phase and P β ′ phase for both lipids was significantly raised by the substitution of H 2 O by D 2 O. In H 2 O, a pressure-induced interdigitated gel (L β I) phase has been observed at pressures above 100 MPa for DPPC and 70 MPa for DSPC, respectively. It has been known that the L β I phase of DPPC bilayer in D 2 O is observed at higher pressure beyond 150 MPa by the method of neutron diffraction. In the present study, the temperature-pressure phase diagrams for DPPC and DSPC bilayers showed the transition temperature between P β ′ and L β I phases to be lowered in D 2 O, on the other hand, the transition temperature between L β ′ and L β I phases to be raised in D 2 O under high pressure. In other words, the pressure for appearance of the L β I phase was elevated by the substitution of H 2 O by D 2 O. The difference in transition temperatures by the water substitution is discussed by the difference of hydrophobic interaction in H 2 O and in D 2 O.

Effects of Cis and Trans Unsaturation on the Barotropic and Thermotropic Phase Behavior of Phospholipid Bilayers

In order to understand the effect of trans and cis unsaturation on the thermotropic and barotropic phase transition of lipid bilayer membranes, the phase transitions of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE), 1,2- dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and the corresponding phosphocholines (i. e., DSPC, DEPC and DOPC, respectively) were observed by high-pressure optical method and differential scanning calorimetry. For all of the lipid bilayers studied, the temperatures of transition from the gel phase to the liquid crystalline phase were almost linearly elevated by pressure. The substitution of trans or cis unsaturated acyl chain for the saturated acyl chain brought about the depression of phase-transition temperature. The values of ΔH and ΔV for the transition were remarkably reduced by the introduction of trans or cis double bond into the acyl chains. This situation is attributable to the geometrical configurations of cis and trans double bonds, which brings about the random packing of acyl chains in the gel state.

Effect of pressure on the bilayer phase transitions of N-methylated dipalmitoylphosphatidylethanolamines

The main-transition temperatures between gel and liquid crystalline phases for dipalmitoylphosphatidylmonomethylethanolamine (DPMePE) and dipalmitoylphosphatidyldimethylethanolamine (DPMe2PE) under high pressure were determined from differential scanning calorimetry (DSC) and optical methods. The thermodynamic quantities of main transition (enthalpy, entropy, and volume) were calculated and the results were compared with those of dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidylcholine (DPPC) to clarify the effect of N-methylation of DPPE on the main transition. The main-transition temperatures of N-methylated DPPEs increased linearly by applying pressure while they decreased with increasing the size of head group by stepwise N-methylation. On the other hand, there was no significant difference in thermodynamic quantities between the phospholipids. The difference in hydrophilic interactions between the different-sized polar head groups produces a great difference on the main-transition temperature and the packing arrangement of bilayer membrane in the gel phase.

Effect of pressure on the bilayer phase transition of diacylphosphatidylethanolamine

All the temperatures of the main transition between lamellar gel (L β ) and liquid crystaline (L α ) phases for dilauroyl-(DLPE), dimyristoly- (DMPE), dipamitoyl- (DPPE), and distearoyl-phosphatidylethanolamine (DSPE) bilayer membranes were elevated by pressure. The temperature ( T ) —pressure ( p ) phase boundary curve was best described by a smooth curve and not a linear function. The values of slope (d T /d p ) at ambient pressure were 0.230, 0.251, 0.264 and 0.275 K MPa −1 for DLPE, DMPE, DPPE and DSPE, respectively. The volume change associated with the main transition from L β ) to L α ) phase which was estimated from the Clapeyron-Clausius equation, was 13.0, 19.5, 27.2 and 35.3 cm 3 mol −1 for DLPE, DMPE, DPPE and DSPE, respectively, which increased linearly with an increase in the acyl chain length of lipids. Thermodynamic properties for the main transition of phosphatidylethanolamine (PE) bilayer membranes were compared with those for phosphatidylcholine (PC) bilayer membranes. Regarding the enthalpy and volume changes, the values for PEs and PCs with the same acyl chain are similar in magnitude to each other. However, the main-transition temperatures for PE bilayer membranes are significantly higher than those for PC. The difference in the maintransition temperature between PE and PC bilayer membranes may be attributable to the head group interaction in the bilayers.

New Transition of Dioleoylphosphatidylcholine Bilayer Membrane Under High Pressure

The phase transitions of l,2-dioleoyl-sn-glycero-3-phospho-choline (DOPC) bilayer membranes were observed by high-pressure optical methods. The so-called main transition between the liquid crystalline (Lα) and the lamellar gel (Lβ) phases was observed in water at above 0 °C under high pressure, in addition to the transition between the La and the lamellar crystalline (Lc) phases in 50% aqueous ethylene glycol. The pressure of the 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 °C, which has never been found by DSC methods. On the other hand, the temperature of the Lc/Lα phase transition in 50% aqueous ethylene glycol was found to be -12.0 °C at ambient pressure. The values of dT/dp were 0.233 KMPa-1 for the Lβ/Lα phase transition and 0.147 K MPa-1 for the Lc/Lα phase transition, respectively.

Effect of Pressure on the Phase Transitions of Dimyristoylphosphatidylethanolamine and Dimyristoylphosphatidylcholine Bilayers

The temperature (T) - pressure (p) phase diagrams of the dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidyl-ethanolamine (DMPE) multilamellar vesicles were constructed by the method of high-pressure light transmittance. DMPC bilayer membrane undergoes pretransition at 13.9 °C from the lamellar gel (Lβ’) phase to the ripple gel (Pβ’) phase, and succeedingly the main transition at 23.9 °C from the Pβ’ phase to the liquid crystalline (Lα) phase. The slopes of phase boundary, dT/dP were 0.212 K MPa-1 for the main transition and 0.13 KMPa-1 for the pretransition, respectively. On the other hand, DMPE bilayer membrane undergoes transition at 56.8 °C from the highly ordered subgel (Lc) phase to the La phase. The value of dT/dp for this transition was 0.195 K MPa-1. The main transition of DMPE bilayer membrane was observed at 49.6 °C and the value of dT/dp was 0.222 K MPa-1.