Ichiro Hatta

Time-resolved x-ray diffraction and calorimetric studies at low scan rates: II. On the fine structure of the phase transitions in hydrated dipalmitoylphosphatidylethanolamine

The phase transitions of dipalmitoylphosphatidylethanolamine (DPPE) in excess water have been examined by low-angle time-resolved x-ray diffraction and calorimetry at low scan rates. The lamellar subgel/lamellar liquid-crystalline (L(c) --> L(alpha)), lamellar gel/lamellar liquid-crystalline (L(beta) --> L(alpha)), and lamellar liquid-crystalline/lamellar gel (L(alpha) --> L(beta)) phase transitions proceed via coexistence of the initial and final phases with no detectable intermediates at scan rates 0.1 and 0.5 degrees C/min. At constant temperature within the region of the L(beta) --> L(alpha) transition the ratio of the two coexisting phases was found to be stable for over 30 min. The state of stable phase coexistence was preceded by a 150-s relaxation taking place at constant temperature after termination of the heating scan in the transition region. While no intermediate structures were present in the coexistence region, a well reproducible multipeak pattern, with at least four prominent heat capacity peaks separated in temperature by 0.4-0.5 degrees C, has been observed in the cooling transition (L(alpha) --> L(beta)) by calorimetry. The multipeak pattern became distinct with an increase of incubation time in the liquid-crystalline phase. It was also clearly resolved in the x-ray diffraction intensity versus temperature plots recorded at slow cooling rates. These data suggest that the equilibrium state of the L(alpha) phase of hydrated DPPE is represented by a mixture of domains that differ in thermal behavior, but cannot be distinguished structurally by x-ray scattering.

Swelling of intercellular lipid lamellar structure with short repeat distance in hairless mouse stratum corneum as studied by X-ray diffraction.

Lamellar structures of intercellular lipids in stratum corneum of hairless mouse were studied at various water contents by small-angle X-ray diffraction. At room temperature there are at least two lamellar structures, long and short lamellar structures, with repeat distances of 13.6 and around 6 nm, respectively. The long lamellar spacing is almost constant over the water content from 0% w/w to 80% w/w that is consistent with the previously reported results. For the short lamellar structure we found that with increasing the water content the lamellar spacing becomes larger, that is, from 12 to 50% w/w the short lamellar spacing increases from 5.8 to 6.6 nm. In addition to the previously reported result that at the water content of about 20% w/w the X-ray diffraction peak for the long lamellar structure becomes sharp, we found that this is also the case for the short lamellar structure. Below the water content of about 12% w/w the X-ray diffraction peak for the short lamellar structure dies out and conversely above the water content of about 50% w/w it becomes weak and finally merges into the second-order diffraction peak for the long lamellar structure. Considering the matching of the long lamellar spacing that is unchanged with the water content and twice the short lamellar spacing that changes as a function of the water content, it is likely that the swelling of the short lamellar structure plays an important role in the regulation of water stored in stratum corneum.

Metastable ripple phase of fully hydrated dipalmitoylphosphatidylcholine as studied by small angle x-ray scattering

Fully hydrated dipalmitoylphosphatidylcholine (DPPC) undergoes liquid crystalline to metastable P(beta), phase transition in cooling. A small angle x-ray scattering study has been performed for obtaining further evidence about the structure of this phase. From a high-resolution observation of x-ray diffraction profiles, a distinct multipeak pattern has become obvious. Among them the (01) reflection in the secondary ripple structure is identified clearly. There are peaks assigned straightforwardly to (10) and (20) reflections in the primary ripple structure and peaks assigned to (10) and (20) reflections in the secondary ripple structure. Therefore the multipeak pattern is due to superposition of the reflections cause by the primary and secondary ripple structures. The lattice parameters are estimated as follows: for the primary ripple structure a = 7.09 nm, b = 13.64 nm, and gamma = 95 degrees , and for the secondary ripple structure a = 8.2 nm, b = 26.6 nm, and gamma = 90 degrees . The lattice parameters thus obtained for the secondary ripple structure are not conclusive, however. The hydrocarbon chains in the primary ripple structure have been reported as being tilted against the bilayer plane and, on the other hand, the hydrocarbon chains in the secondary ripple structure are likely to be perpendicular to the bilayer plane. This fact seems to be related to a sequential mechanism of phase transitions. On heating from the L(beta), phase where the hydrocarbon chains are tilted the primary ripple structure having tilted hydrocarbon chains takes place and on cooling from the L(alpha) phase where the hydrocarbon chains are not tilted the secondary ripple structure with untilted chains tends to be stabilized. It appears that the truly metastable ripple phase is expressed by the second ripple structure although in the course of the actual cooling transition both the secondary and primary ripple structures form and coexist.

Thermal diffusivity measurements of thin films and multilayered composites

This review discusses the following methods for measuring thermal diffusivity of thin materials: ac calorimetric method, flash method, mirage-effect method, picosecond time-resolved thermoreflectance method, photoacoustic method, etc. The measurements are classified into the following three cases: (a) that yield thermal diffusivity parallel to the surface of a thin material, (b) that yield thermal diffusivity perpendicular to the surface, and (c) that yield thermal diffusivity perpendicular to the surface of a thin material but deposited on a solid substrate. The contribution of inhomogeneity in the spatial distribution of the imparted thermal energy and obscureness at the edge of the restricted region, to which uniform thermal energy is imparted, is considered in each case. The contribution of temporal distortion of the temperature pulse, waves, etc., is considered in each measurement. The proper thickness of samples required for the measurements is discussed. In some of the measurements, the applicable materials are restricted, for instance, thermoreflectance measurements are applicable to metallic samples only.

Electrostatic interaction of poly(L-lysine) with dipalmitoylphosphatidic acid studied by X-ray diffraction.

Structure of dipalmitoylphosphatidic acid (DPPA) bilayers in the presence of poly(L-lysine) is proposed from the results of X-ray diffraction obtained by a storage phosphor detector with a high resolution called an imaging plate. The small-angle X-ray diffraction pattern exhibits that DPPA/poly(L-lysine) complex forms a highly ordered multilamellar structure. The electron density profile of the DPPA/poly(L-lysine) complex draws that only one poly(L-lysine) layer is intercalated between the neighboring DPPA bilayers. The wide-angle X-ray diffraction pattern suggests that the presence of poly(L-lysine) hardly affects the nature of hydrocarbon chain packing in the DPPA bilayers. The X-ray reflection from the DPPA/poly(L-lysine) complex indicates that the poly(L-lysine) molecules adopt a beta-sheet conformation on the surface of the DPPA bilayers. The both surface areas occupied by a headgroup of the DPPA and by a lysine residue in poly(L-lysine) are estimated from the observed spacings. The number ratio of lysine residues to DPPA headgroups per unit area is greater than unity. Therefore, one DPPA headgroup interacts with more than one lysine residue electrostatically, i.e., the electric charge distributions in both the surface of a DPPA bilayer and the poly(L-lysine) beta-sheet are incommensurate.

Temperature dependence of the ripple structure in dimyristoylphosphatidylcholine studied by synchrotron X-ray small-angle diffraction

The ripple structure of 1,2-dimyristoyl-L-phosphatidylcholine (DMPC) multibilayer containing excess water (60 wt%) was studied by synchrotron X-ray small-angle diffraction. The (0,1) spacing which corresponds to the ripple repeat distance depends on temperature: At 13 degrees C the (0,1) spacing is 14.15 nm, the spacing decreases at higher temperatures and reaches 12.1 nm at 23.5 degrees C, just below the main transition temperature. The spacing is in good agreement between heating process and cooling process except for the supercooling region. The result suggests that the rearrangement of the ripple structure takes place during temperature change successively. The Landau-de Gennes free energy equation explains well the temperature dependence of the ripple repeat distance.

Development of ac Calorimetric Method for Thermal Diffusivity Measurement IV: Films with Low Thermal Diffusivity and Very Thin Films

In the ac calorimetric thermal diffusivity measurement of a thin film with low thermal diffusivity and a very thin film, it happens that the atmosphere surrounding the films significantly affects thermal diffusivity measured when the contribution of propagation of ac temperature waves in the atmosphere is not neglected. In fact, the measurement in a polymer film or in a very thin film should be carried out under vacuum, in which ac temperature waves no longer propagate. The experimental tests were made for polypropylene films and a borosilicate glass plate. The measurement under vacuum is not always required for every kind of film. The condition which is required for the measurement in the air is discussed. In addition, various problems which occur in the measurement of thin films with low thermal diffusivity and very thin films are considered.

Structural analysis of cell membrane complex of a hair fibre by micro‐beam X‐ray diffraction

The cell membrane complex in the cuticle of a human hair fibre or a rat whisker is composed of three layers, that is, β, δ and β layers. The X-ray diffraction technique is a powerful tool to investigate the pathway of aqueous molecules and ions across the cuticle. Small-angle scattering experiments using a micro X-ray beam, which can be applied to a cuticle of 5 µm thickness, provide the structural information on the cell membrane complex without interference from other structures. Taking into account the variation of thickness in the δ and β layers, the overall features of the diffraction profile in a small-angle region can be explained satisfactorily. The method makes it possible to analyse the structure of β, δ and β layers without assuming an ambiguous background in the diffraction profile, and was used for the analysis of a human hair fibre and a rat whisker. In a rat whisker, the X-ray diffraction was stronger and the variation in the layer thickness smaller than in a human hair fibre. This may be due to the fact that the rat whisker had not been washed with soap or cosmetically treated, whereas the variation may depend on the lipids or the proteins that each species naturally has. It is proposed that the method represents convenient tool for quantitative analysis to estimate the thickness of δ and β layers in the cell membrane complex.

Effect of Sample Edge in ac Calorimetric Method for Measuring Thermal Diffusivity of Thin Films with High Thermal Diffusivity

In the ac calorimetric thermal diffusivity measurement of a thin film with high thermal diffusivity, the reflection of ac temperature waves at the edge of the film is no longer disregarded. From a theoretical consideration, the condition required for the measurement on such a sample is proposed.

Phase transitions and polymorphism in phospholipids

Abstract An assembly of phospholipids dispersed in water exhibits a variety of phases in a narrow temperature range, i.e., subgel Lc. phase, gel Lβ. (or Lβ) phase, interdigitated gel Lβ1 phase, ripple gel Pβ. phase, liquid crystalline Lα phase, cubic Q phase, hexagonal HII phase, etc. The characteristics of the structures in these phases are discussed. Some of the phase transitions are considered in terms of the critical packing parameter developed by Israelachvili, Marcelja and Horn (Quart. Rev. Biophys, 13, 121 ((1980)). For much further consideration, heterogeneity in the bilayer structure of phospholipids should be taken into account. In connection with this nature, the importance of a sequential mechanism in the phase transitions of phospholipids is pointed out.