Gel Phases L

From measurement of relaxation times, a detailed analysis of intramolecular, molecular and collective motions that occur in a membrane with temperature change may be observed. Figure 8.10. Correlation times are plotted in a log scale as a function of the reciprocal of temperature in order to have a direct reading of activation energies from the slopes of the lines the steeper the slope, the higher the E. In the gel phase (L, P >) there are only intramolecular (ti 2,3) and molecular motions (,t//, ) whose To ranges from the ms to the ns. In the fluid, Lq, phase, above T, there... 

The gel phase (L ) closely resembles the lamellar phase (Figure 21.10) in that it is comprised of surfactant layers, but it differs in its very high viscosity. The term gel again originates from industry where these systems were observed to have a gel-like rheology. However, these states should not be confused with polymer gels or gels formed by hydrocolloid systems, since they are... 

Figure 3.4 The temperature-concentration phase diagrams of BPS-m (m=5,10,20, and 30) with BmimPFj. The phase abbreviations are as follows micellar phase (1 ), discontinuous cubic liquid crystal phase (1 ), hexagonal liquid crystal phase (H ), lamellar liquid crystal phase (L ), lamellar gel phase (L ), reverse micellar phase (L ), ionic liquid phase (IL), and two-phase separation (II). The chemical structure of j0-sitosterol ethoxylates as a typical example of BPS-m is also shown in this figure. Reproduced from Sakai et al. [37] with permission from Japan Oil Chemists Society.

FIG. 4 Phase diagram of fully hydrated DPPC bilayers. Different phases found are also schematically shown Lp, gel P, rippled gel L I, interdigitated gel and L , liquid crystalline phases. (From Ref. 50. Copyright 1999 The Japan Society of High Pressure Science and Technology.)... 

Dicker F.L., Hayden O., Bioimprinting of polymers and sol-gel phases. Selective detection of yeast with imprinted polymers. Anal. Chem. 2002 74 1302-1306. 

M. Vincent, J. Gallay, J. de Bony, and J.-F. Tocanne, Steady-state and time-resolved fluorescence anisotropy study of phospholipid molecular motion in the gel phase using l-palmitoyl-2-[9-(2-anthryl)-nonanoyl]-sn-glycero-3-phosphocholine as probe, Ear, J. Biochem. 250, 341-347 (1985). 

The reason why one chose to follow the main liquid-crystalline to gel phase transition in DPPC by monitoring the linewidth of the various or natural abundance resonance is evident when we consider the expressions for the spin-lattice relaxation time (Ti) and the spin-spin relaxation time T2). The first one is given by 1/Ti oc [/i(ft>o) + 72(2ft>o)] where Ji coq) is the Fourier transform of the correlation function at the resonance frequency o>o and is a constant related to internuclear separation. The relaxation rate l/Ti thus reflects motions at coq and 2coq. In contrast, the expression for T2 shows that 1/T2 monitors slow motions IjTi oc. B[/o(0) -I- /i(ft>o) + /2(2u>o)], where /o(0) is the Fourier component of the correlation function at zero frequency. Since the linewidth vi/2 (full-width at half-maximum intensity) is proportional to 1 / T2, the changes of linewidth will reflect changes in the mobility of various carbon atoms in the DPPC bilayer. 

Norlen, L. 2001. Skin barrier structure and function The single gel phase model. J Invest Dermatol 117 830. 

An aliphatic ketone (9-heptadecanone) and two keto derivatives of stearic acid (as potassium salts) containing a ketone functionality either at position 5 or 12 were incorporated into bilayers of the phospholipid l,2-dihexadecyl-sn-glycero-3-phosphocholine. Infrared spectra of these mixtures were measured as a function of temperature and amount of added cholesterol. It was found that the presence of cholesterol in these bilayers induces changes in the location of the guest ketone and that these changes are dependent on both temperature and cholesterol concentration. It is also demonstrated that, in the gel phase, the presence of cholesterol induces larger intersheadgroup separations and, therefore, water penetrates deeper into the lipid bilayer. 

Norlen, L., Does the single gel phase exist in stratum corneum Reply. To the editor, J. Invest. Dermatol., 118, 899, 2002. 

Here, we find up to four phases. The liquid phases (L) are translucent after centrifugation, but the gel phase (G) remains turbid and has a honey-like to solid consistency. A correct solvent extraction operation is with only one organic phase. As can... 

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