Headgroup packing

Mo GCH, Yip CM (2009) Supported lipid bilayer templated J-aggregate growth role of stabilizing cation-7i interactions and headgroup packing. Langmuir 25 10719-10729... 

The two distinct types of SDS headgroup packing indicated by the difference spectra are consistent with the spherocylindrical model of rod micelle formation discussed above. The increase in absorbance of the difference bands with increasing salt concentration indicates a continual increase in the number of relatively ordered SDS molecules packing into the cylindrical portion of the micelle, with the subtraction procedure simply eliminating the spectral contributions from the hemispherical endcaps. 

In contrast to this the phase transition of polymeric liposomes is retained if the polymer chain is more flexible or located on the surface of the vesicles instead in the hydrophobic core. The polymerized vesicles of the methacrylamide (19), for instance, show a phase transition temperature which is even slightly lower than the one of the corresponding monomer vesicles (27) as shown in fig. 13. This could be explained by a disordering influence of the pol3mier chain on the headgroup packing. 

Additional evidence for changes in headgroup packing at this mole fraction comes from the 8, CHj-N (1398 cm ) band, and a-CH2 scissoring (1420 cm ) bands (Figure 16). The 5, and 5 a-CH2 bands are found to split into... 

In otlier words, tire micelle surface is not densely packed witli headgroups, but also comprises intennediate and end of chain segments of tire tailgroups. Such segments reasonably interact witli water, consistent witli dynamical measurements. Given tliat tire lifetime of individual surfactants in micelles is of tire order of microseconds and tliat of micelles is of tire order of milliseconds, it is clear tliat tire dynamical equilibria associated witli micellar stmctures is one tliat brings most segments of surfactant into contact witli water. The core of nonnal micelles probably remains fairly dry , however. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

FIG. 5 Schematic representation of packing arrangements of natural amphipathic double-chain lipids with different headgroup size in crystalline bilayers. The small filled circles indicate the accommodation of spacer molecules, such as water or ions. (Reprinted by permission from Ref 14, copyright 1992, Elsevier Science.)... 

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