Gel-liquid crystalline transition

DNA arranges into rectangular superlattice in the low-temperature gel phase of saturated cationic lipids [83, 84]. This is evidenced by two or three diffuse reflections in addition to the set of lamellar reflections these are attributed to DNA ordering both within the layer and across the lipid bilayers, from one DNA layer to another. These reflections index on a centered rectangular lattice. Noteworthy, DNA does not affect the gel-liquid crystalline transition temperatures of the lipoplexes [16, 19, 84]. This transition is associated with loss of the DNA inter-lamellar correlation. 

Figure 10.12 The gel-liquid crystalline transition in a synthetic lipid... 

Gel-liquid crystalline transitions can also be induced isothermally by changes in pH, Ca and ionic strength [109=111] in negatively charged phospholipids. Especially the effect of Ca " can be dramatic. Ca " can increase the transition temperature of phosphatidylglycerol and phosphatidylserine by more than 50 °C, thereby forming a so-called cylindrical [110] or cochleated structure [112], Recently it has... 

The phase transition of bilayer lipids is related to the highly ordered arrangement of the lipids inside the vesicle. In the ordered gel state below a characteristic temperature, the lipid hydrocarbon chains are in an all-trans configuration. When the temperature is increased, an endothermic phase transition occurs, during which there is a trans-gauche rotational isomerization along the chains which results in a lateral expansion and decrease in thickness of the bilayer. This so-called gel to liquid-crystalline transition has been demonstrated in many different lipid systems and the relationship of the transition to molecular structure and environmental conditions has been studied extensively. 

An increase indicates a broadening lifetime distribution. Gel-liquid-crystalline phase transition. 

Koynova R, MacDonald RC (2004) Columnar DNA superlattices in lamellar oethylpho-sphatidylcholine lipoplexes mechanism of the gel-liquid crystalline lipid phase transition. Nano Lett 4 1475-1479... 

Koynova R, Wang L, MacDonald RC (2007) Synergy in lipofection by cationic lipid mixtures superior activity at the gel-liquid crystalline phase transition. J Phys Chem B 111 7786-7795... 

A later publication from the same group [153] reporting on 31P- and 2H-NMR and DSC studies on zwitterionic and anionic phospholipids in the absence and presence of doxombicin (adriamycin) described different results [152], Doxorubicin had a stronger disordering effect on the membrane of lipid mixtures enriched with anionic lipids. However, extensive segregation of DOPE and DOPA or DPS was not observed even under conditions of Hlrphase formation . According to the authors, the reason for this discrepancy was that in the earlier paper the phase separation was obtained with membranes subject to gel-liquid crystalline phase transition , which was, however, discounted in the first paper. 

An obvious hypothesis is that this unusual membrane lipid composition is related directly to membrane function in some way. Within the restricted area of lipid bilayers, lipid composition is known to be an important determinant of physical properties. There are several prominent examples. First, the temperature at which the hydrocarbon chains melt when assembled in bilayers (the gel-to-liquid-crystalline transition temperature, marks an abrupt change in many of the physical properties of such bilayer systems for example, water permeability through such bilayers increases by several orders of magnitude above the transition. Second, the presence of cholesterol within bilayers composed of amphipathic lipids has a profound effect on lipid motion, mechanical properties (such as resistance to shear), and permeability to water. 

From a biologic viewpoint, of greatest interest are the transitions that involve the physiologically important lamellar liquid-crystalline phase, namely, the gel- liquid-crystalline (melting) transition, and the lamellar- nonlamellar mesomorphic transitions. 

Table 1 Gel — liquid-crystalline and lamellar — nonlamellar phase transition temperatures [°C] of fully hydrated lipids as a function of the lipid polar head group and hydrocarbon chain length (33, 46, 52, 55, 56)...

Table 2 Decrease of the gel-liquid-crystalline (Lp La) transition temperatures of fully hydrated acyl-chain phosphatidylcholines with increasing sn- 2 chain unsaturation (33)...

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