Phosphatidylcholine melting temperature

Table 12.3 The melting temperature of phosphatidylcholine containing different pairs of...

GlvcoDhorin-Lioid Monolayers at the Air-Water Interface. Further to the study of pure glycophorin monolayers we investigated the interaction between the glycophorin and dipalmitoyl-phosphatidylcholine (DPPC) in mixed monolayers at the air-water interface (27). Pure DPPC undergoes the characteristic liquid expanded (L ) to intermediate state (I) transition in monolayers at temperatures below the chain-melting temperature (- 42 C) of... 

Another method relies on thermal properties of lipid membranes. Every lipid bilayer is characterized by a phase transition, from solid-like to liquid-like states. It is known that at the transition temperature (called melting temperature, r ), the bilayer permeability is maximal. It is then possible to exploit this higher permeability to allow solutes pass through the membrane (Figure 17.5.4). It has been reported, for example, that ATP permeability increase by a factor -100 in dimyristoyl phosphatidylcholine vesicles, and that such vesicles can therefore be fed with ATP by keeping them at the (23.3 °C). It... 

Table 10.4 Bending moduli (Cc of various phosphatidylcholine bilayers in water at different temperature T and melting temperature T. ...

It is interesting that modifying solution conditions by adding different concentrations of ethanol can produce a biphasic effect on melting transition temperatures of lipid-like systems (e.g., acyl chains of hydrocarbons). For example, low concentrations of ethanol reduce the Tm of phosphatidylcholine bilayers, whereas higher concentrations increase the Tm of the same system.122 This effect has been shown to depend upon acyl chain length and can be explained by the... 

The temperature dependence of the thickness of foam bilayers shows the occurrence of a first-order phase transition of melting of hydrocarbon tails of the phospholipid molecules. This melting is realised at a temperature very close to the temperature of the corresponding phase transition in fully hydrated water dispersions of phosphatidylcholines. This result is in agreement with the theoretical considerations of Nagle [436] for the decisive role of van der Waals attractions between hydrocarbon chains of phospholipid molecules for the chainmelting phase transition in bilayer systems. 

Hence, the interaction between lipid molecules is very similar in these foam bilayers and it can be supposed that the AF foam bilayers are in the liquid crystalline state within the temperature range studied. This assumption is in agreement with the fact that amniotic fluid contains substantial amount of unsaturated phospholipids, which as known [45], lower considerably the temperature of the chain-melting phase transition. Bearing in mind the similarity of the phase behaviour of a phosphatidylcholine aqueous dispersion and foam bilayers [38-40], it can be supposed that at the temperatures which are important for in vivo systems, the foam bilayers are in the liquid crystalline state. This assumption allows to determine the critical concentration of phosphatidylcholines in amniotic fluid, necessary for formation of a foam bilayer by extrapolation of the Arrhenius dependence of C, for AF foam bilayers to 37°C. Thus, at 37°C C, = 19.9 jxg cm 3 and d, = 1.47. This value of C, at 37°C corresponds to the lower limit (found by other methods [46,47]) of phosphatidylcholine concentration which permits to classify as mature a sample of amniotic fluid. The above value... 

Lavialle et al. [74] have also obtained information on the lipid-protein boundary. These authors studied the interaction of melittin, a polypeptide consisting of 26 amino acid residues, with dimyristoyl phosphatidylcholine. The results illustrated in Fig. 20 show that for a lipid-melittin molar ratio of 14 1 two order-disorder transitions are observed, one above (at 29 °C) an one below (at 17 °C) the transition for the pure lipid (at 22.5 °C). The low temperature transition is associated with a depression of the main lipid phase transition while the 29°C transition is associated with the melting behavior of approximately seven inunobilized boundary lipids which surround the hydrophobic portion of the melittin. 

Multilamellar dispersions of homogeneous phosphatidylcholines exhibit two reversible phase transitions. The major chain-melting transition is a sharp symmetrical first-order endothermic transition in the DSC thermogram. For a series of saturated phospholipids, the enthalpy of the main transition is a linear function of the transition temperature (Fig. 10) [94], and the extrapolation to zero enthalpy suggests that saturated phosphatidylcholines with hydrocarbon chains shorter than 12 carbon atoms cannot form stable bilayers. 

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