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PubMed1982

Adamantyl nitroxide: a spin label for probing membrane surfaces.

In an effort to understand more about the perturbing properties of adamantane-like molecules on biological membranes, the spin probe adamantyl nitroxide (2,2'-dimethyl-5-adamantyl oxazolidine-N-oxyl) was synthesized, purified and characterized. Electron paramagnetic resonance (EPR) spectra were then obtained from 1:50 and 1:200 mixtures of adamantyl nitroxide with dipalmitoyl and dipalmityl phosphatidylcholine multibilayers. Above the phase transition temperature of these lipids (41 degrees C for dipalmitoyl phosphatidylcholine and 43 degrees C for dipalmityl phosphatidylcholine) the spectra of adamantyl nitroxide are similar to control spectra obtained in liquid oleic acid. Below the phase transition temperatures, however, spectral differences were observed depending on: (1) the concentration of the spin probe in the lipid; (2) the linkage between the polar head group and the hydrocarbon tails of the phospholipid; (3) the temperature of the sample. Partitioning of adamantyl nitroxide between the aqueous and hydrocarbon phases of the sample is most prominent at probe-to-lipid ratios of 1:200 and at temperatures below the pre-transition temperature of the lipid (around 33 degrees C). Computer simulations of the above results, as well as additional experiments performed at 35 GHz, show that the results arise from true partitioning and not from asymmetric probe motion. Two conclusive results of these experiments are that spectra of adamantyl nitroxide in phospholipid multibilayers are sensitive to probe concentration and to the physical characteristics of the phospholipid which they probe. The spectral differences which arise when adamantyl nitroxide is used with ether- and ester-linked phospholipids indicate that it is a sensitive probe of membrane surfaces. Employment of this molecule in membrane research should prove to be useful in obtaining additional information about membrane surface events.

Adamantane↗
PubMed1984

Perturbation effect of local anaesthetics on synaptosomes: variation with depth of the spin label probe.

Stearic acids labeled with a doxyl group at the 5th, 12th and 16th carbon positions were used as the spin probes for an investigation of the perturbation effects of two local anaesthetics (the 2-piperidinoethylester of phenyl carbamic acid and the piperidinoethylester of 2-heptyloxyphenylcarbamic acid) on rat brain synaptosomes. For a quantitation of the perturbation effects we have studied the order parameter S of the spin probe, incorporated in the membrane, calculated from the ESR spectra as a function of temperature and concentration of local anaesthetics. The local anaesthetics had a different disordering efficiency at different depths of the membrane. It follows from our results that the perturbing effects of the anaesthetics increase relative to the depth of the membrane, and the extent of perturbation correlates with local anaesthetic activity.

Anesthetics, Local↗
PubMed2003

The potential of fluorescent and spin-labeled steroid analogs to mimic natural cholesterol.

Cholesterol analogs are often used to investigate lipid trafficking and membrane organization of native cholesterol. Here, the potential of various spin (doxyl moiety) and fluorescent (7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group) labeled cholesterol analogs as well as of fluorescent cholestatrienol and the naturally occurring dehydroergosterol to mimic the unique properties of native cholesterol in lipid membranes was studied in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes by electron paramagnetic resonance, nuclear magnetic resonance, and fluorescence spectroscopy. As cholesterol, all analogs undergo fluctuating motions of large amplitude parallel to the bilayer normal. Native cholesterol keeps a strict orientation in the membrane with the long axis parallel to the bilayer normal. Depending on the chemical modification or the position of the label, cholesterol analogs may adopt an "up-side-down" orientation in the membrane or may even fluctuate between "upright" and up-side-down orientation by rotational motions about the short axis not typical for native cholesterol. Those analogs are not able to induce a comparable condensation of phospholipid membranes as known for native cholesterol revealed by 2H nuclear magnetic resonance. However, cholesterol-induced lipid condensation is one of the key properties of native cholesterol, and, therefore, a well suited parameter to assess the potential of steroid analogs to mimic cholesterol. The study points to extreme caution when studying cholesterol behavior by the respective analogs. Among seven analogs investigated, only a spin-labeled cholesterol with the doxyl group at the end of the acyl chain and the fluorophore cholestatrienol mimic cholesterol satisfactorily. Dehydroergosterol has a similar upright orientation as cholesterol and could be used at low concentration (about 1 mol %), at which its lower potential to enhance lipid packing density does not perturb membrane organization.

Cholesterol↗