12-Nitroxide stearate

In Table III, the positive interaction between IMZ stearate (6) and the hydroxybenzoate stabilizer UV-Chek AM-340 is shown. This degree of lifetime enhancement was not achieved in any of the HALS compounds synthesized in which the hydroxybenzoate group was present as an intramolecular substituent. The proximity of the hindered phenolic group may in some way affect generation of the nitroxide radicals from the amine nitrogen. 

Isotherms for monomolecular films of a series of nitroxide stearic acid and nitroxide palmitate and stearate (methyl ester) films are reported for the temperature range 9° 50°C. 

To understand the behavior of the mixed host-probe films, it is essential to understand the behavior of the pure films of both components. We previously investigated in detail the behavior of the pure films of 12-nitrox-ide stearate [2-( 10-carboxydecyl)-2-hexyl-4,4 -dimethyl-3-oxazolidinyloxyl] including its extraordinary temperature dependence (7, 8, 16). In this paper we extend our investigations to the pure films of other nitroxide stearic acid (and methyl ester) probes where the oxazolidine ring is attached to various carbon atoms of the stearic acid (or ester) hydrocarbon chain. This series of spin-label probes is one of those most extensively used to study cell membrane structure. It was used to define, among other things, an order parameter establishing the fluidity (17) and polarity profiles (18) of lipid bilayers. 

The 12-nitroxide stearic acid and the 8-nitroxide methyl palmitate were donated by J. D. Morrisett (John Baylor College of Medicine, Houston, Tex.). All other nitroxide stearic acid and stearate probes were purchased from Syva (California). All probe molecules were subsequently purified by preparative thin layer chromatography (TLC) until a single spot was obtained under all development conditions. TLC was carried out in a dry nitrogen atmosphere to avoid possible oxidation or hydrolysis during purification. Ultrapure silica gel, free from any plasticizers, was used to avoid possible further contamination. 

The results are shown in Figures 1 through 7. Figures 1 through 6 show isotherms over a range of temperatures for the 5-, 12-, and 16-nitroxide stearic acids, for the 5- and 16-nitroxide methyl stearates, and for the 8-nitroxide methyl palmitate over the range 9°-50°C. [We use 5-NS, 5-NS(Me), and 8-NP(Me) for the trivial names 5-nitroxide stearic acid, 5-nitroxide methyl stearate, and 8-nitroxide methyl palmitate, with... 

Figure 2. Surface pressure (dynes/cm) vs. area/molecule (A2) for 5-nitroxide methyl stearate [5-NS(Me)] at 20°,...

Fig. 3A. The change in t, of the spin labels of 12-nitroxide methyl stearate (I2NS) (open circles) and 16-nitroxide methyl stearate (I6NS) (solid circles) with mitochondrial membranes of mung bean (V. radiata) as a fimction of temperature. The spin labels were mixed with a suspension of the membranes at a molar ratio of about I spin label per ISO lipids. The motion of the spin label was calculated from first-derivative esr spectra determined over a temperature range of 16°-40°C for 12NS and 0°-38°C 16NS. The straight lines were computed by linear regression analysis, and the temperature for the change in slope of the straight lines determined by a statistical procedure described by Raison and Chapman (1976). Data bom Raison and Chapman (1976).

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