Lipids melting temperature

Lipid Melting Temperatures Membrane lipids in tissue samples obtained from different parts of the leg of a reindeer have different fatty acid compositions. Membrane lipids from tissue near the hooves contain a larger proportion of unsaturated fatty acids than those from tissue in the upper leg. What is the significance of this observation ... 

Figure 5.28 Circular dichroism spectra of DC8 9PC tubules prepared in (a) ethanol-water (7 3), (b) methanol-ethanol-water (35 35 20), and (c) methanol-water (70 30) and (d) DCj PC liposomes above melting temperature. All samples were prepared at lipid concentration of 2.0 mg/ml and spectra for tubules were recorded at 25°C. Liposome spectrum was recorded at 40°C and peak intensity is about 104 smaller than that from tubules.

Applications to fluorescent or fluorescently labeled proteins and nucleic acids, and to fluorescent lipid probes in phospholipid bilayers, have been reported. In the latter case, the diffusion coefficients measured above the chain melting temperature were found to be 10 7 cm2 s 1, which is in agreement with values obtained by other techniques. 

Fatty acid chains may contain no double bonds—that is, be satu rated, or contain one or more double bonds—that is, be mono- or polyunsaturated. When double bonds are present, they are nearly always in the cis rather than in the trans configuration. (See p. 362 for a discussion of the dietary occurrence of cis and trans unsatu- rated fatty acids.) The introduction of a cis double bond causes the I tfatty acid to bend or "kink" at that position (Figure 16.3). If the fatly acid has two or more double bonds, they are always spaced at three carbon intervals. [Note In general, addition of double bonds decreases the melting temperature (Tm) of a fatty acid, whereas j increasing the chain length increases the Tm. Because membrane lipids typically contain LCFA, the presence of double bonds in some fatty acids helps maintain the fluid nature of those lipids.]... 

Structure of triacylglycerols (TAG) The three fatty acids esterified] to a glycerol molecule are usually not of the same type. The fefy I acid on carbon 1 is typically saturated, that on carbon 2 is typi-j cally unsaturated, and that on carbon 3 can be either. Recall thal the presence of the unsaturated fatty acid(s) decrease(s) thl I melting temperature of the lipid. An example of a TAG molecule H shown in Figure 16.12. 

Essentially any combination of lipids can be used in this method. When working with lipids with a low melting temperature such as PC, care must be taken not to allow the temperature to rise too high, or agglomeration of powder particles will result. Any solvent that will dissolve the lipids can be used, but with ethanol or methanol, very precise regulation of evaporation conditions is required to ensure that dissolution of the sorbitol does not occur as the temperature rises. In these situations... 

The newly synthesized phenothiazine derivative 2-trifluoromethyl-10-[4-(methanesulfonylamido)butyl]-phenothiazine (FPhMS, see Fig. 1 for chemical structure) was also extensively studied in the context of its interaction with lipid bilayers. DSC was used to study the influence of this compound on model membranes formed from DMPE [80], DPPC [81], DMPC, and DMPG [82]. In all the studied lipid systems FPhMS (16) lowered Tm, caused broadening of transition peaks, and induced the decrease of AH. Melting temperatures were found to be reduced by the phenothiazine derivative to a similar extent when different lipids possessing acyl chains of the same length were compared. 

In addition to wax esters, the inclusion of a mid-chain keto or alcohol functional group to a long-chain hydrocarbon would cause a kink in the lipid chain and result in cuticular lipids with lower melting temperatures. An example is provided by the wax esters of secondary... 

Stratum corneum lipids and lanolin share an important physical characteristic in that they can coexist as solids and liquids at physiological temperatures.33 A differential scanning calorimetry thermogram of lanolin is similar to that of stratum corneum lipids, showing two broad (heterogenous) phase transitions with midpoint melting temperatures at 21.9 and 38.3°C.16 The lower temperature peak may represent the transition from a liquid crystal to a gel phase, which has also been described for lanolin alcohols.34... 

Permeability changes in full-thickness skin have been associated with temperature or solvent pretreatment. The molecular basis of these permeability changes has been attributed to lipid melting or protein conformational changes. The current studies have probed the role of lipid fluidity in the permeability of lipophilic solutes, and examined the effects of temperature on the physical nature of the stratum corneum by differential scanning calorimetry and thermal perturbation infrared spectroscopy. Combining molecular level studies that probe the physical nature of the stratum corneum with permeability results, a correlation between flux of lipophilic solutes and nature of the stratum corneum barrier emerges. 

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