Effect of change of water structure on the phase transition of liposomes of dipalmitoyl phosphatidylcholine

Abstract

The role of water structure around model membrane systems (e.g., lipsomes) on phase transition of the lipid dipalmitoyl phosphatidylcholine was investigated. Water structure was altered by changingpH and by addition of solutes which are known breakers and makers of water structure. The structure makers broadened the zone of transition and changed the overall phase transition profile, while the main effect of structure breakers was to cause a shift in the transition temperature. The observed variation of Chapman transition temperature and broadening of zone of transition with varying pH is discussed in terms of altered water structure around the membrane-aqueous interface. Binding studies with the dye 1-anilino-8-napthalene sulfonate showed that structure makers or breakers did not bind to the liposome surface directly. Thus the structure makers and breakers act on the membranes perhaps by altering the water structure differentially. Possible associated mechanisms of action are discussed.

Storage Stability and Physical Characteristics of Tea-Polyphenol-Bearing Nanoliposomes Prepared with Milk Fat Globule Membrane Phospholipids

“…It is well established that structure and fluidity of lipid bilayers can be controlled by environmental pH. 36 The fluidity is found to be greater when the molecules forming the bilayers are charged than when they are uncharged, due to the increased intermolecular separation caused by electrostatic repulsion. 37 In most cases, liposomes have nonzero surface electric potentials, even though the liposomes are composed of neutral lipids.…”

Role of interfacial structured water in membrane: Osmotic properties ofl-α-egg lecithin liposomes

“…65 : 25 : 4, vol/vol) and therefore was used without further purification. Source and purity of other chemicals have been described previously [10].…”

“…TLC was performed at each stage of preparation and also at the end of the experiments as described earlier, No degradation of the phospholipid could be observed. Binding studies with the fluorescent dye, l-anilino,8-naphthalene sulfonate (ANS) were performed as described previously [10].…”

“…We have shown previously that alteration of water structure around the polar headgroup region of the bilayer by a series of reagents (known to affect structuring of water molecules in bulk also) influences the phase transition characteristics of dipalmitoyl phosphatidylcholine liposomes [10]. Such alteration of the phase equilibrium of liposomal membrane may therefore be expected to affect its permeability to water and solutes.…”

“…This eliminates the possibility of trend of the data being affected by differences in relative permeabilities of various structure makers and breakers and any effect these reagents may have on the aggregation and dispersion of the liposomes. Thus the effects of the structure makers and breakers on osmotic shrinkage properties of liposomes is controlled primarily by the influence these reagents exert on the phase equilibrium of the membrane and mechanism(s) of water permeation through it [4,10]. It may be mentioned here that the method of preparation of liposomes was chosen such that no concentration gradient of the reagent existed across the liposomal membrane.…”