Nobutake Tamai

Solution properties of celluloses from different biological origins in LiCl · DMAc

Differences in the solution properties of cellulose in 8%LiCl · DMAc (dimethyl acetamide) were investigated usingcelluloses from different origins. The latter included plants (dissolving pulp(DP), cotton linters (CC), and kraft pulp), bacteria (Acetobacterxylinum, BC), and marine animals (tunicin fromHalocynthia). The celluloses from plants and bacteriaformed LiCl · DMAc solutions that were isotropic andanisotropic, respectively; and the animal cellulose was insoluble. The weightaverage molecular weights, Mw, of DP, CC and BC were found to be98.2 × 104,170 × 104 and192 × 104, respectively. The solutionviscositieswere proportional to cα (c; polymer concentration) in thedilute and semi-dilute regions, where the exponent α was 1 for allsamplesin the dilute region; in the semi-dilute region, it was 4 for the DP and CCsolutions and 3 for the BC solution. Molecular weight differences werecompensated by plotting the viscosity against cMw orc[η] (where [η] is the limiting viscosity number).The difference in viscosity behavior at elevated solutionconcentration indicates that the cellulose molecules from DP and CC behave asflexible polymer chains and those of BC as rod-like ones.These results suggest that differences in molecular structure andproperties exist between celluloses from different sources, and that thesedifferences relate to the mechanism or the type of the intermolecularinteraction between the celluloses of plants (DP and CC) and those of bacteria(BC).

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 vesicle size on the prodan fluorescence in diheptadecanoylphosphatidylcholine bilayer membrane under atmospheric and high pressures.

The bilayer phase behavior of diheptadecanoylphosphatidylcholine (C17PC) with different vesicle sizes (large multilamellar vesicle (LMV) and giant multilamellar vesicle (GMV)) was investigated by fluorescence spectroscopy using a polarity-sensitive fluorescent probe Prodan under atmospheric and high pressures. The difference in phase transitions and thermodynamic quantities of the transition was hardly observed between LMV and GMV used here. On the contrary, the Prodan fluorescence in the bilayer membranes changed depending on the size of vesicles as well as on the phase states. From the second derivative of fluorescence spectra, the three-dimensional image plots in which we can see the location of Prodan in the bilayer membrane as blue valleys were constructed for LMV and GMV under atmospheric pressure. The following characteristic behavior was found: (1) the Prodan molecules in GMV can be distributed to not only adjacent glycerol backbone region, but also near bulk-water region in the lamellar gel or ripple gel phase; (2) the blue valleys of GMV became deeper than those of LMV because of the greater surface density of the Prodan molecules per unit area of GMV than LMV; (3) the liquid crystalline phase of the bilayer excludes the Prodan molecules to a more hydrophilic region at the membrane surface with an increase in vesicle size; (4) the accurate information as to the phase transitions is gradually lost with increasing vesicle size. Under the high-pressure condition, the difference in Prodan fluorescence between LMV and GMV was essentially the same as the difference under atmospheric pressure except for the existence of the pressure-induced interdigitated gel phase. Further, we found that Prodan fluorescence spectra in the interdigitated gel phase were especially affected by the size of vesicles. This study revealed that the Prodan molecules can move around the headgroup region by responding not only to the phase state but also to the vesicle size, and they become a useful membrane probe, detecting important membrane properties such as the packing stress.

Barotropic and thermotropic bilayer phase behavior of positional isomers of unsaturated mixed-chain phosphatidylcholines

The bilayer phase transitions of six kinds of mixed-chain phosphatidylcholines (PCs) with an unsaturated acyl chain in the sn-1 or sn-2 position, 1-oleoyl-2-stearoyl- (OSPC), 1-stearoyl-2-oleoyl- (SOPC), 1-oleoyl-2-palmitoyl- (OPPC), 1-palmitoyl-2-oleoyl- (POPC), 1-oleoyl-2-myristoyl- (OMPC) and 1-myristoyl-2-oleoyl-sn-glycero-3-phosphocholine (MOPC), were observed by means of differential scanning calorimetry (DSC) and high-pressure light transmittance measurements. Bilayer membranes of SOPC, POPC and MOPC with an unsaturated acyl chain in the sn-2 position exhibited only one phase transition, which was identified as the main transition between the lamellar gel (L(beta)) and liquid crystalline (L(alpha)) phases. On the other hand, the bilayer membranes of OSPC, OPPC and OMPC with an unsaturated acyl chain in the sn-1 position exhibited not only the main transition but also a transition from the lamellar crystal (L(c)) to the L(beta) (or L(alpha)) phase. The stability of their gel phases was markedly affected by pressure and chain length of the saturated acyl chain in the sn-2 position. Considering the effective chain lengths of unsaturated mixed-chain PCs, the difference in the effective chain length between the sn-1 and sn-2 acyl chains was proven to be closely related to the temperature difference of the main transition. That is, a mismatch of the effective chain length promotes a temperature difference of the main transition between the positional isomers. Anomalously small volume changes of the L(c)/L(alpha) transition for the OPPC and OMPC bilayers were found despite their large enthalpy changes. This behavior is attributable to the existence of a cis double bond and to significant inequivalence between the sn-1 and sn-2 acyl chains, which brings about a small volume change for chain melting due to loose chain packing, corresponding to a large partial molar volume, even in the L(c) phase. Further, the bilayer behavior of unsaturated mixed-chain PCs containing an unsaturated acyl chain in the sn-1 or sn-2 position was well explained by the chemical-potential diagram of a lipid in each phase.

Pressure effect on the bilayer phase transition of asymmetric lipids with an unsaturated acyl chain

The bilayer phase transitions of mixed‐chain lipids with monounsaturated acyl chain in the sn‐2 position, 1‐myristoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (MOPC), 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC), and 1‐stearoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (SOPC), and with a polyunsaturated acyl chain in the sn‐2 position, 1‐stearoyl‐2‐linoleoyl‐sn‐glycero‐3‐phosphocholine (SLPC), 1‐stearoyl‐2‐arachidonoyl‐sn‐glycero‐3‐phosphocholine (SAPC), and 1‐stearoyl‐2‐docosahexaenoyl‐sn‐glycero‐3‐phosphocholine (SDPC), were observed by differential scanning calorimetry (DSC) under ambient pressure and by light‐transmittance measurements under high pressure. The DSC thermogram for each lipid bilayer showed only one transition between the lamellar gel and liquid crystalline phases. The introduction of one or two cis double bonds into the sn‐2 acyl chain caused the significant depression of the main‐transition temperature and an obvious decrease of enthalpy and volume changes associated with the transition. These features are attributable to loose packing of saturated and unsaturated acyl chains in the bilayer gel phase. The existence of four or six double bonds in the sn‐2 chain produced no further decrease in the transition temperature, and in fact six double bonds caused a slight increase in the transition temperature. Thermodynamic properties associated with the bilayer phase transition were discussed.

Network structure of curdlan in DMSO and mixture of DMSO and water.

The viscoelastic property of curdlan solution in dimethyl sulfoxide (DMSO) was investigated. We discuss the difference in the viscoelastic properties of curdlan solution in DMSO and that in 0.1 N NaOH aqueous solution. The viscoelastic function for curdlan solution in 0.1 N NaOH aqueous solution showed the Newtonian flow at the concentration of curdlan as high as 10 wt %. On the other hand, the Newtonian flow was observed in the concentrations below 7 wt % for curdlan solution in DMSO, and the plateau region appeared beyond this concentration. It was revealed by small angle x-ray diffraction measurements that the difference in the mechanical property would be originated from the difference in the network structure. The overlapping concentration c* was calculated on the basis of the mean field theory, and disagreement between theoretical prediction and experimental result was shown. We clarified that the above disagreement can be explained by the polydispersity of the curdlan sample, assuming adequate distribution functions. The static structure of the gel prepared by adding water to curdlan solution in DMSO was investigated. It was clarified by the dynamic viscoelasticity measurement that the cross-linking density increases with increasing the water content.

Prodan fluorescence detects the bilayer packing of asymmetric phospholipids.

The bilayer phase behavior of asymmetric phospholipids, palmitoylstearoylphosphatidylcholine (PSPC) and stearoylpalmitoylphosphatidylcholine (SPPC), with different vesicle sizes (large multilamellar vesicle (LMV) and giant multilamellar vesicle (GMV)) was investigated by fluorescence spectroscopy using a polarity-sensitive fluorescent probe Prodan under high pressure. The results were compared with those of a symmetric phospholipid, diheptadecanoyl PC (C17PC). The difference in phase transitions of the PSPC and SPPC bilayers and in thermodynamic quantities of the transitions was hardly observed between LMV and GMV as the case of the C17PC bilayer. On the other hand, the Prodan fluorescence showed clear differences between LMV and GMV of the asymmetric PC bilayers. From the second derivative of Prodan fluorescence spectra, the three dimensional image plots in which we can clearly see the location of Prodan in the bilayer membrane as blue valleys were constructed for LMV and GMV under high pressure. We revealed from the plots that the bilayer packing is significantly dependent on not only the vesicle size but also the acyl-chain asymmetry of PC molecule in addition to the phase states. It was found that the packing of the gel phases of the asymmetric PC bilayers is weaker than that of the symmetric PC bilayer, and the size of vesicle affects the packing of the interdigitated gel phase the most markedly among three gel phases. This study suggests that the Prodan molecules can detect the effect of vesicle size on the phase states for the asymmetric PC bilayers, and they become a useful indicator for various membrane properties, especially bilayer interdigitation.

How does acyl chain length affect thermotropic phase behavior of saturated diacylphosphatidylcholine-cholesterol binary bilayers?

Thermotropic phase behavior of diacylphosphatidylcholine (CnPC)-cholesterol binary bilayers (n=14-16) was examined by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry. The former technique can detect structural changes of the bilayer in response to the changes in polarity around Prodan molecules partitioned in a relatively hydrophilic region of the bilayer, while the latter is sensitive to the conformational changes of the acyl chains. On the basis of the data from both techniques, we propose possible temperature T-cholesterol composition Xch phase diagrams for these binary bilayers. A notable feature of our phase diagrams, including our previous results for diheptadecanoylphosphatidylcholine (C17PC) and distearoylphosphatidylcholine (C18PC), is that there is a peritectic-like point around Xch=0.15, which can be interpreted as indicating the formation of a 1:6-complex of cholesterol and CnPCs within the binary bilayer irrespective of the acyl chain length. We could give a reasonable explanation for such complex formation using the modified superlattice view. Our results also showed that the Xch value of the abolition of the main transition is almost constant for n=14-17 (ca. 0.33), while it increases to ca. 0.50 for n=18. By contrast, a biphasic n-dependence of Xch was observed for the abolition of the pretransition, suggesting that there are at least two antagonistic n-dependent factors. We speculate that this could be explained by the enhancement of the van der Waals interaction with increases in n and the weakening of the repulsion between the neighboring headgroups with decreases in n.

Thermotropic and Barotropic Phase Transitions of Dialkyldimethylammonium Bromide Bilayer Membranes: Effect of Chain Length

The bilayer phase transitions of dialkyldimethylammonium bromides (2C(n)Br; n = 12, 14, 16) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. Under atmospheric pressure, the 2C(12)Br bilayer membrane underwent the stable transition from the lamellar crystal (L(c)) phase to the liquid crystalline (L(α)) phase. The 2C(14)Br bilayer underwent the main transition from the metastable lamellar gel (L(β)) phase to the metastable L(α) phase in addition to the stable L(c)/L(α) transition. For the 2C(16)Br bilayer, moreover, three kinds of phase transitions were observed: the metastable main transition, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable L(α) phase, and the stable lamellar crystal (L(c(1)))/L(α) transition. The temperatures of all the phase transitions elevated almost linearly with increasing pressure. The temperature (T)-pressure (p) phase diagrams of the 2C(12)Br and 2C(14)Br bilayers were simple, but that of the 2C(16)Br bilayer was complex; that is, the T-p curves for the metastable main transition and the L(c(2))/L(α) transition intersect at ca. 25 MPa, which means the inversion of the relative phase stability between the metastable phases of L(β) and L(c(2)) above and below the pressure. Moreover, the T-p curve of the L(c(2))/L(α) transition was separated into two curves under high pressure, and as a result, the pressure-induced L(c(2P)) phase appeared in between. Thermodynamic quantities for phase transitions of the 2C(n)Br bilayers increased with an increase in alkyl-chain length. The chain-length dependence of the phase-transition temperature for all kinds of transitions observed suggests that the stable L(c(1))/L(α) transition incorporates the metastable L(c(2))/L(α) transition in the bilayers of 2C(n)Br with shorter alkyl chains, and the main-transition of the 2C(12)Br bilayer would occur at a temperature below 0 °C.

Hydrostatic pressure reveals bilayer phase behavior of dioctadecyldimethylammonium bromide and chloride.

Bilayer phase transitions of dioctadecyldimethylammonium bromide (2C(18)Br) and chloride (2C(18)Cl) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. The 2C(18)Br bilayer membrane showed different kinds of transitions depending on preparation methods of samples under atmospheric pressure. Under certain conditions, the 2C(18)Br bilayer underwent three kinds of transitions, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable lamellar gel (L(β)) phase at 35.4 °C, the metastable main transition from the metastable L(β) phase to the metastable liquid crystalline (L(α)) phase at 44.5 °C, and the stable transition from the stable lamellar crystal (L(c(1))) phase to the stable L(α) phase at 52.8 °C. On the contrary, the 2C(18)Cl bilayer underwent two kinds of transitions, the stable transition from the stable L(c) phase to the stable L(β) phase at 19.7 °C and the stable main transition from the stable L(β) phase to the stable L(α) phase at 39.9 °C. The temperatures of the phase transitions of the 2C(18)Br and 2C(18)Cl bilayers were almost linearly elevated by applying pressure. It was found from the temperature (T)-pressure (p) phase diagram of the 2C(18)Br bilayer that the T-p curves for the main transition and the L(c(1))/L(α) transition intersect at ca. 130 MPa because of the larger slope of the former transition curve. On the other hand, the T-p phase diagram of the 2C(18)Cl bilayer took a simple shape. The thermodynamic properties for the main transition of the 2C(18)Br and 2C(18)Cl bilayers were comparable to each other, whereas those for the L(c(1))/L(α) transition of the 2C(18)Br bilayer showed considerably high values, signifying that the L(c(1)) phase of the 2C(18)Br bilayer is extremely stable. These differences observed in both bilayers are attributable to the difference in interaction between a surfactant and its counterion.