Interdigitated gel phases

FIG. 4 Phase diagram of fully hydrated DPPC bilayers. Different phases found are also schematically shown Lp, gel P, rippled gel L I, interdigitated gel and L , liquid crystalline phases. (From Ref. 50. Copyright 1999 The Japan Society of High Pressure Science and Technology.)... 

Fig. 17. NMR spectrum obtained using a single 90° pulse without H decoupling in pure DPPC bilayers at 50 °C and 1 bar (a) and P NMR spectra obtained using a fully phase-cycled Hahn echo sequence with inversely gated H decoupling in pure DPPC bilayers at 50 °C and 1 bar in the LC phase (b), 1 kbar in the GI phase (c), 1.75 kbar in the interdigitated Gi gel phase (d), 2.5 kbar in the GII gel phase (e), 3.7 kbar in the GUI gel phase (f), and 5.1 kbar in the GX gel phase (g) (after Refs. 4, 18).

In the gel phases of these systems [310], the surfactant molecules are in extended conformations and packed hexagonally in bilayers. A cut-away cartoon representation of the layers is presented in Figure 56 the KS and KP gel layers are nearly completely interdigitated the KSO gel layers are without interdigitation, and KS and 1-octadecanol molecules alternate within a hexagonal layer. 

At temperatures below the main transition, a basic equilibrium stracture is the subgel (crystalline) Lc phase. Its formation usually requires prolonged low-temperature incubation. In addition to the Lc phase, many intermediate stable, metastable, and transient lamellar gel structures are adopted by different lipid classes—with perpendicular or tilted chains with respect to the bilayer plane, with fully interdigitated, partially interdigitated, or noninterdigitated chains, rippled bilayers with various ripple periods, and so forth. (Fig. 1). Several polymorphic phase transitions between these structures have been reported. Well-known examples of polymorphic transitions are the subtransition (Lc- L ) and the pretransition (Lp/- Fp/) in phosphatidylcholines (33). Recently, a polymorphic transition that included rapid, reversible transformation of the usual gel phase into a metastable, more ordered gel phase with orthorhombic hydrocarbon chain-packing (so-called Y-transition) was reported to represent a common pathway of the bilayer transformation into a subgel (crystalline) Lc phase (62). 

Figure 8 Isotropic magnetic parameter gis and Aisofor TEMPO in a series of protic and aprotic solvents and their mixtures 1, water 2, water/ethanol solution (7 3, v/v) 3, water/ethanol solution (3 7, v/v) 4, methanol 5, ethanol 6, isopropanol 1, acetone 8, olive oil/ethanol solution (9 1, w/w) 9, acetonitrile 10, olive oil 11, toluene 12, hexane. The isotropic g-factor of TEMPO in water was taken as a reference point i.e. Agiso = 0). The estimated errors are within the size of the symbols. Magnetic parameters for TEMPO partitioned in the lipid phase of the DPPC bilayer are shown as filled sguares. Parameters corresponding to the membrane in the gel phase (before the main phase transition) are marked as A and above the phase transition piso at ca. 45 °C) are marked as B. Parameters for two components of TEMPO in non-agueous phase of DPPC bilayer interdigitated by 1.2 M ethanol are marked as C and D...

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