Toshio Mitsui

Structural Parameters of Dipalmitoyl Phosphatidylcholine Lamellar Phases and Bilayer Phase Transitions

Thicknesses d l of the lipid bilayer and d w of the water layer were determined separately with X-rays for dipalmitoyl phosphatidylcholine lamellar phase. In both cases of the presence and the absence of excess water, d l does not change appreciably at the pretransition (35°C) but drops down by about 5 A at the main transition (42°C) with increasing temperature. In the presence of excess water, d w jumps up by 4.0 A at the pretransition and by 2.0 A at the main transition. These results prove that there is practically no change of the tilting angle of hydrocarbon chains at the pretransition and that the remarkable increase of the repeat distance of the lamellar phase at the pretransition in the presence of excess water is caused by the increase of the thickness of the water layer.

Effects of cations on dipalmitoyl phosphatidylcholine/cholesterol/water systems

X-ray diffraction studies have been made on the effects of cations upon the dipalmitoyl phosphatidylcholine/water system, which originally consists of a lamellar phase with period of 64.5 A and of excess water. Addition of 1 mM CaCl2 destroys the lamellar structure and makes it swell into the excess water. The lamellar phase, however, reappears when the concentration of CaCl2 increases: a partially disordered lamellar phase with the repeat distance of 150-200 A comes out at the concentration of about 10 mM, the lamellar diffraction lines become sharp and the repeat distance decreases with increasing CaCl2 concentration. A small amount of uranyl acetate destroys the lameellar phase in pure water. MgCl2 induces the lamellar phase of large repeat distance, whereas LiCl, NaCl, KCl, SrCl2 and BaCl2 exhibit practically no effect by themselves. Addition of cholesterol to the phosphatidylcholine bilayers tends to stabilize the lamellar phase. The high-angle reflections indicate that molecular arrangements in phosphatidylcholine bilayers change at CaCl2 concentrations around 0.5 M. The bilayers at high CaCl2 concentration seem to consist of two phases of pure phosphatidylcholine and of equimolar mixture of phosphatidylcholine and cholesterol.

Studies of the crystal structure of triglycine sulfate in connection with its ferroelectric phase transition

The crystal structure of triglycine sulfate has been refined at 19°C and 37°C in the ferroelectric phase and at 57°C in the paraelectric phase, by using the data collected by a four-circle automatic diffractometer. Positions of 14 hydrogen atoms out of the 17 have been determined and those of the non-hydrogen atoms refined at 19°C, with the discrepancy factor R of 0.046. Refinement of the structures at 37°C and 57°C was made for non-hydrogen atoms, resulting in the R factor of 0.074 in both cases. The split atom method was used for the determination of the 57°C structure. Obtained results have established that the ferroelectric phase transition of TGS is of the order-disorder type.

The Ferroelectric Phase Transition in (Glycine)3·H2SO4 and Critical X-Ray Scattering

On the assumption that the ferroelectric phase transition in (Glycine) 3 ·H 2 SO 4 is of the order-disorder type, expressions for Bragg reflections and critical scattering of X-rays are given in terms of a long-range order parameter and pair correlation functions. Temperature dependence of the critical scattering is discussed on the basis of the Bragg-Williams approximation and of a modified Frohlich theory. Experimental observations agree with theoretical predictions, and prove that the phase transition is of the order-disorder type. The observed critical scattering exhibits a pronounced peak at the Curie point, suggesting that the local field theory is not a good approximation. The shape of the peak appears to be quite different from that in the ferromagnetic case. It has been found that the sulfur atoms do not shift appreciably when the glycine groups rotate. A method for evaluating the pair correlation function is proposed.

Hamaker constant and binding constants of Ca2+ and Mg2+ in dipalmitoyl phosphatidylcholine/water system

Abstract The critical concentration of mixed solution of CaCl 2 and MgCl 2 which induces a discontinuous increase in the lamellar period of dipalmitoyl phosphatidylcholine/water system is measured by means of X-ray diffraction. Obtained data permit simultaneous determination of the Hamaker constant A for the system and the binding constants of cations to the dipalmitoyl phosphatidylcholine membrane ( C Ca for Ca 2+ and C Mg for Mg 2+ ), with the results of A = (3.6 ± 0.8) × 10 −21 J, C Ca = 21 ± 9 M −1 , and C Mg = 2.5 ± 0.7 M −1 . The values of C Ca and C Mg seem to be modified where the intermembrane distance and/or the ionic concentrations become large. The electric potential and charge density on the surface of dipalmitoyl phosphatidylcholine membrane, which are caused by adsorbed cations, are calculated as functions of salt concentration and intermembrane separation. The surface potential ϕ S in the lamellar phase becomes almost independent of the salt concentration at low concentration: ϕ S ≈ 34 mV for 1 μ M −1 m M CaCl 2 solutions and ϕ S ≈ 18 mV for 1 μ M −5 m M MgCl 2 solutions.

A Note on the Classification of Ferroelectrics

It has been tried to classify newly discovered ferroelectrics as well as old ones according to their Curie-Weiss constants. Results have suggested that the displacive type ferroelectrics are not necessarily oxide crystals, and have also shown that small Curie-Weiss constants are not very rare in new ferroelectrics. Classification of ferroelectrics by the transition entropy is misleading in some cases.

Relation between growth temperature of E. coli and phase transition temperatures of its cytoplasmic and outer membranes.

Cells of wild-type E. coli B were grown at 17, 27 and 38 degrees C, and their cell membranes were fractionated into the cytoplasmic and the outer membranes. Chemical assay proved that the molar ratio of saturated to unsaturated fatty acids increases in phospholipids extracted from each membrane as the growth temperature increases. The transition temperature at which the solid phase disappears was determined by X-ray diffraction in these biomembranes and also membranes of extracted phospholipids and of extracted lipopolysaccharide. The transition temperatures of the cytoplasmic membrane and of the membranes of phospholipids extracted from the cytoplasmic and the outer membranes increased with the growth temperature in good parallelism to the molar ratio of saturated to unsaturated fatty acids. The transition temperature of the outer membrane was less sensitive to the growth temperature, presumably due to the presence of lipopolysaccharide. The transition temperature of the membranes of lipopolysaccharide extracted from the outer membrane was 25 degrees C, for the cells grown at 27 and 37 degrees C. For the cells grown at 17 degrees C, the extracted lipopolysaccharide gave a broad diffraction peak and did not exhibit a solid-fluid phase transition between --5 and 40 degrees C.

Phase transitions of the purple membrane and the brown holo-membrane X-ray diffraction, circular dichroism spectrum and absorption spectrum studies

Abstract The phase transition of the purple membrane observed by differential scanning calorimetry (Jackson, M.B. and Sturtevant, J.M. (1978) Biochemistry 17, 911–915) has been investigated by X-ray diffraction, circular dichroism and absorption spectrum, in comparison with the phase transition in the brown holo-membrane. The two-dimensional crystal of bacteriorhodopsin transformed into two-dimensional liquid around 74–78°C in the purple membrane and around 50–60°C in the brown holo-membrane. The X-ray diffraction patterns obtained at 78°C for the purple membrane and at 60°C for the brown holo-membrane exhibit several broad peaks. Analysis of the pattern suggests that bacteriorhodopsin molecules aggregate in trimers even above the phase transition temperature. The negative circular dichroism band in the visible region is still present at 80°C in the purple membrane and at 60°C in the brown holo-membrane, but becomes negligibly small at 70°C in the brown holo-membrane. The 560 nm absorption peak due to bacteriorhodopsin changes its position and height drastically around 80°C in the brown holo-membrane as in the purple membrane. X-ray diffraction studies have been made on membranes of total lipids extracted from the purple membrane. No indication of the phase transition has been found between −81°C and 77°C.

Critical phenomena in ferroelectric phase transitions I. Experimental observations and qualitative discussion

A review is made of experimental studies of the critical phenomena in ferroelectric phase transitions of the order-disorder type.The static critical indices obtained so far agree well with those given by the mean field theory except in the extreme vicinity of the critical point. Recent observations on the critical x-ray scattering, the critical slowing-down and the anomalies in transport processes are surveyed and their significance is discussed qualitatively.

Relationship between growth temperature of Anacystis nidulans and phase transition temperature of its thylakoid membranes

The temperatures of the lipid phase transition at which the solid phase disappears were determined by using the X-ray diffraction method in thylakoid membranes of the blue-green alga, Anacystis nidulans. The temperatures were determined as 26 and 16 degrees C for cells grown at 38 and 28 degrees C, respectively.