Interlamellar attachment

Figure 4 The modified stalk mechanism of membrane fusion and inverted phase formation, (a) planar lamellar (La) phase bilayers (b) the stalk intermediate the stalk is cylindrically-symmetrical about the dashed vertical axis (c) the TMC (trans monolayer contact) or hemifusion structure the TMC can rupture to form a fusion pore, referred to as interlamellar attachment, ILA (d) (e) If ILAs accumulate in large numbers, they can rearrange to form Qn phases, (f) For systems close to the La/H phase boundary, TMCs can also aggregate to form H precursors and assemble Into H domains. The balance between Qn and H phase formation Is dictated by the value of the Gaussian curvature elastic modulus of the bIlayer (reproduced from (25) with permission of the Biophysical Society) The stalk in (b) is structural unit of the rhombohedral phase (b ) electron density distribution for the stalk fragment of the rhombohedral phase, along with a cartoon of a stalk with two lipid monolayers merged to form a hourglass structure (reproduced from (26) with permission of the Biophysical Society).

Figure 7.11 Left Proposed mechanism for the formation of an interlamellar attachment via a stalk and a transmonolayer contact (TMC). Right Square lattices of ILA can readily form the qp phase. Reproduced from Reference 47 with permission of the American Chemical Society.

Figure 1 A generalized diagram of the structure of the cetostearyl alcohol gel found in topical and vaginal creams. The bilayers are formed principally of cetostearyl alcohol. The hydrophilic poly(oxyethylene) chains attached to the 5-carbon sorbitan rings in Polysorbate 60 retard water drainage from the interlamellar space and keep the lamellae from collapsing into a dense crystalline structure.

The interface between the lamellar crystals and the non-crystalline, interlamellar region was studied using the technique of the Gibbs dividing surface. In so doing, one is able isolate the effects of the interface alone, irrespective of thickness of the lamellae and, to some degree, of the interlamellar domain. Therefore, the properties attached to the sharp interface can be used in a three-component model with arbitrary composition, which accounts for the interface contribution explicitly, in addition to the crystal and melt bulk contributions. 

Semicrystalline polymers contain liquid-like amorphous and ordered crystalline phases. When solidified from the pure melt, these polymers show a spherulitic structure in which crystalline lamellae composed of folded chain crystallites radiate from the center of the spherulite in such a way that a constant long period or crystallinity is apvproximately maintained. The amorphous regions reside in the interlamellar regions in the form of tie chains, whose ends are attached to adjacent lamellae loop chains, whose ends are attached to the same lamella cilia chains with only one end attached to a lamella (or dangling chain ends), and floating chains which are not attached to any lamellae. This hierarchical structure is illustrated in Figure 1. 

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