Doxyl-stearic acid

I). We interpret the cholesterol-induced increase in hydrogen bonding below Tc (Figure 3A) as being due to an opening of the bilayer which allows more solvent to penetrate. Similar conclusions were reached from studies of doxyl stearic acid spin probes in frozen lipid vesicles... 

Figure 7 Plot of the change in the product of the coupling and maximum saturation factors as a function of macromolecular structure. At lower pH values, the spin-labelled lipids are present as vesicles and vesicular aggregates, while at higher pH values, micelles are formed. The higher psmax values for the micelles imply greater water accessibility to the radical site. The solid circles represent 16-DS (16-doxyl stearic acid, spin-labelled at the end of the lipid tail) while the open circles represent 5-DS (5-doxyl stearic acid, spin-labelled near the polar head group). Reproduced with permission from Ref. [70].

ESR spectroscopy has also been used to study dynamics in more complex systems on oxide surfaces, i.e. self-assembled molecular (SAM) films [136, 137]. Fig. 28 shows ESR spectra taken for spin labeled stearic acid, namely n-doxyl-stearic acid (n-DXSA) immersed onto a thin alumina film. These nitrox-ides, with an oxazolidinyl ring as paramagnetic group connected to different positions of the aliphatic chain, are well known as paramagnetic probes in the study of natural and synthetic membranes. The spin labeled molecules are pres-... 

Fig. 28. Electron spin resonance spectra of 5-doxyl-stearic acid (a) and 16-doxyl-stearic acid (b) on AI2O3 as a function of temperature [136, 137].

In these studies the spectral response of 7-doxyl stearic acid which is co-adsorbed along with the... 

FIGURE 7.26 Effect of water on the order parameter, S, calculated from the ESR spectra of 7-doxyl stearic acid co-adsorbed with AOT at the alumina-cyclohexane interface. 

Fig. 4.24. ESR spectra of 16-doxyl stearic acid in solloids (hemimicelles), micelles and ethanol-glycerol mixtures and comparison of corresponding rotational correlation times and viscosities.

Fig. 2 Chemical structures of common nitroxide spin probes Fremy s salt (potassium nitrosodi-sulfonate) TEMPO and derivatives (2,2,6,6-tetramethylpiperidine-l-oxyl), DOXYL (4,4-dimethyl-oxazolidine-l-oxyl) PROXYL (2,2,5,5-tetramethylpyrrolidine-l-oxyl) Dehydro-PROXYL (2,2,5,5-tetramethylpyrroline-l-oxyl) 5-DSA (5-DOXYL stearic acid) 16-DSA (16-DOXYL stearic...

The dynamic lipid stmcture of membranes was studied by EPR - spectroscopy by use of computerized radio-spectrometer Bruker200D (Germany) and spin - probes two nitroxyl radicals 5- and 16-doxyl-stearic acids (5-and 16-DSA) from Sigma (USA). The radicals prepared in concentration... 

The sensitized cascade reported in Ref [16] consisting of triplet ds-trans photoisomerization of the excited stilbene includes the triplet sensitizer (erythrosin B), the photochrome stilbene derivative probe (4-dimethylamino-4 -aminostilbene), and nitroxide radicals (5-doxyl stearic acid) quenching the excited triplet state of the sensitizer (Figure 10.11). 

A similar analysis, making use of both continuous wave (CW) ESR and pulsed ESR, was performed for amino-terminated-PAMAM dendrimers interacting with a more suitable model of biological membrane if compared to micelles, that is, vesicles, consisting of dimyristoylphosphatidylcoline (DMPC). In this case, the probes added to the vesicles were doxyl stearic acid spin probes with the doxyl group... 

The EPR of the labelled-formulation control exhibits two low-field peaks as illustrated in Figure 3, which shows the EPR spectrum of a vehicle (fomb-lin -RT-15) incubated with 5-doxyl stearic acid. The spectrum resembles that of an immobilized spin probe. The value of 5 of the strongly immobilized probe can be calculated from the spectra using the equation ... 

Figure 4 EPR spectra of a labelled reactive topical skin protectant with 12- and 7-doxyl in selected controls and exposed samples. The graph shows a plot of EPR signal integral (relative units) obtained from the labelled formulation as a function of H-MG concentrations for spin-label probes, 5-, 7-, 12-, and 16-doxyl stearic acids.

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