Abstract:Pressure-jump initiated time-resolved x-ray diffraction studies of dynamics of the hydration of the hexagonal phase in biological membranes show that (i) the relaxation of the unit cell spacing is non-exponential in time; (ii) the Bragg peaks shift smoothly to their final positions without significant broadening or loss in crystalline order. This suggests that the hydration is not diffusion limited but occurs via a rather homogeneous swelling of the whole lattice, described by power law kinetics with an expone… Show more
“…The software package “Microcal Origin” was used to fit the whole region containing peaks i, ii, and iii as well as the two reflections as a sum of five Lorentzian peaks. The choice of peak shape was made following a similar treatment by Osterberg et al A sample spectra taken from Figure is shown in Figure , together with such a multi-Lorentzian fit. 9 Sample plot with Lorenzian fits.…”
In this paper, we present data on the transition from the lamellar (LR) to the gyroid inverse bicontinuous cubic (Q II G ) mesophase. The system investigated was 2:1 lauric acid (LA)/dilauroylphosphatidylcholine (DLPC), at a fixed overall hydration of 50% water by weight. The phase transition was induced by a pressure jump and monitored by time-resolved X-ray diffraction (TRXRD). We observe the gradual appearance of signals from the emergent Q II G phase and an accompanying disappearance of signals from the initial LR phase. These changes correspond to a transformation occurring over a time scale which varies between seconds and minutes. We further observe that the lattice parameters of both the initial LR and final Q II G phases change throughout the transformation. We suggest that this reflects a competition between the two phases for the limited amount of water available. In addition, we suggest a mechanism whereby the transformation from LR to Q II G proceeds via an intermediate phase, which we suggest is the diamond inverse bicontinuous cubic phase (Q II D ). We present evidence for its identity and suggest mechanistic pathways for its formation from the LR phase and subsequent transformation into the Q II G phase.
“…The software package “Microcal Origin” was used to fit the whole region containing peaks i, ii, and iii as well as the two reflections as a sum of five Lorentzian peaks. The choice of peak shape was made following a similar treatment by Osterberg et al A sample spectra taken from Figure is shown in Figure , together with such a multi-Lorentzian fit. 9 Sample plot with Lorenzian fits.…”
In this paper, we present data on the transition from the lamellar (LR) to the gyroid inverse bicontinuous cubic (Q II G ) mesophase. The system investigated was 2:1 lauric acid (LA)/dilauroylphosphatidylcholine (DLPC), at a fixed overall hydration of 50% water by weight. The phase transition was induced by a pressure jump and monitored by time-resolved X-ray diffraction (TRXRD). We observe the gradual appearance of signals from the emergent Q II G phase and an accompanying disappearance of signals from the initial LR phase. These changes correspond to a transformation occurring over a time scale which varies between seconds and minutes. We further observe that the lattice parameters of both the initial LR and final Q II G phases change throughout the transformation. We suggest that this reflects a competition between the two phases for the limited amount of water available. In addition, we suggest a mechanism whereby the transformation from LR to Q II G proceeds via an intermediate phase, which we suggest is the diamond inverse bicontinuous cubic phase (Q II D ). We present evidence for its identity and suggest mechanistic pathways for its formation from the LR phase and subsequent transformation into the Q II G phase.
“…To demonstrate the performance ͑limits and resolutions͒ of the presented high pressure system we have investigated the barotropic and thermotropic phase transitions of a phospholipid/water dispersion using pressure jumps and temperature scans at constant elevated pressure. The static ͑equi-librium͒ p-T phase behavior of the phospholipid dioleoylphosphatidylethanolamine DOPE 15 is already well characterized 11 and shows several well distinguishable structures, consisting of one-dimensional lamellar lattices (L ␣ ,L  ) and a two-dimensional inverted-hexagonal (H II ) lattice within the p-T range accessible with our setup. By applying pressure-jumps and temperature-scans at different pressures, one can study the dynamics of these phase transitions when the system crosses the p-T phase boundary from one phase into another along the isothermic or isobaric line in the phase diagram.…”
Section: Performance Of the Instrumentmentioning
confidence: 86%
“…[1][2][3][4][5] Understanding the dynamics of supra-and macromolecular processes is one of the objectives, which have stimulated the construction of high-flux synchrotron sources. The availability of these has been shifting the scope of interest to time-resolved measurements, of which processes induced by pressure jumps [6][7][8][9][10][11] are particularly important.…”
An instrument to facilitate small-and wide-angle x-ray scattering measurements of samples under elevated hydrostatic pressures or exposed to pressure jumps is described. Pressure from atmospheric up to 0.35 GPa is produced by a motor-driven, piston-type generator and transferred through a network containing pressurizing liquid to a sample cell. The cell, with the optical path length of 1.6 mm, has two Beryllium windows with a total transmission of 0.4 ͑for x rays of ϭ0.154 nm) and low background scattering. Scattering can be observed at angles up to 30°. Samples can be solid or liquid with a minimal volume less than 30 l and the irradiated volume up to 3 l. Separation of the samples from the pressurizing medium is accomplished by Teflon pistons. The high-pressure network has two sections separated by a pneumatic valve. The inner section is connected permanently to the cell and the outer one to the pressure generator. For pressure jumps, the outer section is brought to a different pressure level than the inner one and the jumps are accomplished by opening fast the connection between both sections. At the same time a trigger signal is sent to the data acquisition electronics. All functions of the instrument are PC controlled. To illustrate the performance characteristics of the instrument, time-resolved small-angle x-ray scattering measurements of phase transitions in liquid crystalline phospholipid, dioleoylphosphatidylethanolamine are shown. Pressure-jump experiments with 5 ms time resolution as well as temperature scans at a constant elevated pressure are presented.
“…There is evidence that elements of nonlamellar structures formed by lipids are featured as intermediates in a number of biologically important processes . However, while much work has been done on the equilibrium properties of these inverse phases, kinetic and mechanistic studies of lyotropic phase transitions , have largely been confined to transformations between different lamellar structures − and between lamellar and inverse hexagonal phases − and not between nonlamellar structures. , The present Letter describes some results for phase transitions between purely nonlamellar inverse structures, obtained using time-resolved X-ray diffraction. In particular, we have followed the kinetics of a transition between the and inverse bicontinuous cubic phases.…”
Time-resolved X-ray diffraction was employed to monitor transitions, induced by pressure jumps, between
inverse lyotropic liquid crystalline phases of the mixed lipid system lauric acid/dilauroylphosphatidylcholine
(2:1 molar ratio) in water. We studied transitions between the gyroid,
, and the double diamond,
,
inverse bicontinuous cubic phases and between
and the inverse hexagonal, HII, phase at a fixed water
composition of 50 wt %. The transition
→
occurred within the 0.5 s time resolution of our X-ray
measurements. This transition occurs without any change in water content within the mesophase but with
a small change in the total topology. The transition
→ (
+ HII + excess water) was observed at 59.3,
62.8, and 66.9 °C. The process appeared to follow first-order kinetics, with rate constants of 0.11, 0.17,
and 0.26 s-1, respectively. The reverse transition occurred much more quickly, being completed in <1 s.
In both cases, intermediate structures were observed, including the appearance of the inverse bicontinuous
cubic phase based on Schwarz's P minimal surface,
. We found that the latter intermediate had, to first
order, the same curvature elastic energy as the
phase but a greater water content. Building on earlier
work (Erbes, J.; Winter, R.; Rapp, G. Ber. Bunsen-Ges. Phys. Chem. Chem.
Phys.
1996, 100, 1713−1722),
we consider the rate to depend on the difference between the final pressure and the pressure at the phase
transition boundary and suggest that this can explain both the temperature dependence of the transition
→ (
+ HII + excess water) and the higher rate of the reverse process.
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