Experimental Electron Paramagnetic Resonance Spectra Research Articles

Multiequilibrium binding of a spin-labeled local anesthetic in phosphatidylcholine bilayers

The equilibria among spin-labeled amine local anesthetic species in dioleoylphosphatidylcholine liposomes at an anesthetic:lipid mole ratio of 1:100 are investigated. Electron spin resonance (ESR) spectra demonstrate that anesthetic mobility within the bilayer is charge-dependent, with the uncharged species the more mobile. Partition coefficient measurements confirm ESR evidence that changes in anesthetic mobility represent anesthetic-phospholipid interaction and not changes in bilayer fluidity. Spin-exchange attenuation experiments show that anesthetics within the bilayer are accessible to the aqueous medium. Dependence of tertiary-amine anesthetic pK on dielectric constant has been used to estimate the interfacial pK . We propose a model of equilibria among species of the tertiary amine anesthetic in the aqueous medium and those intercalated in the bilayer, including a species electrostatically bound to the lipid phosphate. Using experimentally determined equilibrium constants, the model provides the binding constant between the electrostatically bound and unbound cationic anesthetics within the bilayer. The model simulates the pH dependence of the mobile fraction of total anesthetic population determined by subtraction techniques on experimental ESR spectra.

Résonance de spin électronique de Gd et d'Eu dans les supraconducteurs SnMo 6 S 8 et PbMo 6 S 8 en poudre

The basic ideas of electron spin resonance (ESR) for paramagnetic ions diluted in superconducting compounds are presented. The resolved powder spectra and the fine structure narrowing process are discussed for S-state using a crystal field hamiltonian (Xc) involving only the b° parameter. The experimental ESR spectra at 35 GHz and 60 GHz for ~1 at. percent Gd+3 and Eu+2 in MMo6Sg (M Pb, Sn) are simulated and interpreted. For both ions SKC is dominated by a negative b°- Two values of the exchange parameter (/) are obtained: one from the ion to electron relaxation rate (Sie), the other from the g-shift. This latter is positive for Gd, but negative for Eu. The two values of J are of the order of 10 meV for both ions. The decrease of Sie below the superconducting critical temperature (Tc), seen through the fine structure narrowing process, allows us to extract an energy gap parameter of 2A(0)/fcBTc =5. The results are discussed and compared with experimental and theoreti¬ cal data in literature.

Lipid spin labels in lecithin multilayers. A study of motion along fatty acid chains

Oriented multilayers may be prepared by drying phospholipid dispersions on a glass slide. They provide a convenient model with which to examine motion and orientation in lipid bilayer structures. The lecithin multilayers were examined using a series of four spin labels, consisting of nitroxide free radicals bonded to the 5, 7, 12 or 16 position of stearic acid. Accurate electron spin resonance tensor elements needed to interpret the data were obtained using the nitroxide 2-doxylpropane (the 4′, 4′-dimethyloxazolidine- N-oxyl derivative of acetone) oriented in host single crystals of 2,2,4,4-tetramethylcyclobutanedione. In the multilayers, all four lipid spin labels were found to orient with their long axes perpendicular to the glass slide, but there is a pronounced systematic variation in anisotropy, dependent on the positional isomer used. The anisotropy of the electron spin resonance spectra was measured and tabulated for various degrees of hydration of the lecithin multilayers. Changes in segmental regions were examined by utilizing temperature to change the motion. The splittings can be accounted for in terms of restricted anisotropic motion, and computer simulations based on restricted anisotropic motion and a Gaussian distribution of orientations are in good agreement with the experimental electron spin resonance spectra. The molecular motion increases as the label is moved further from the carboxylend, and for all four spin labels studied, raising the relative humidity increases the molecular motion of the labels in the lecithin multilayers. The effects of hydration are most pronounced when the label is near the carboxyl group of the stearic acid probe. Relative regional differences in motion along the lipid chains tend to be maintained over a wide temperature range.

Two forms of copper (II) in fungal laccase

1. 1. The nature of different forms of copper in fungal laccase ( p-diphenol:O 2 oxidoreductase, EC 1.10.3.2) and their possible role in the catalytic activity has been studied by electron paramagnetic resonance (EPR) and proton relaxation measurements. 2. 2. By comparisons between experimental and simulated EPR spectra at 9 and 35 GHz it is shown that both laccase A and B contain two forms of Cu 2+, each corresponding to 1 atom per mole of protein. One (represented by Signal 1) corresponds to the spectrally unique form described earlier and shows a small deviation from axial symmetry, while the other one (Signal 2) represents the form earlier attributed to denatured molecules. Data obtained here suggest that both forms are present in the same protein molecule. 3. 3. Proton relaxation measurements show that neither form binds easily exchangeable water. However, the form with Signal 2 gives the largest contribution to the enhancement, indicating that it is more available. This is supported by the finding that only this form is affected by various solutes. 4. 4. Denaturation of the enzyme with guanidine · HCl destroys Signal 1 as well as the characteristic absorption at 610 mμ. Treatment with azide, on the other hand, decreases Signal 2 without affecting the blue colour. 5. 5. The rates of reduction by quinol of Cu 2+ giving Signals 1 and 2, as well as of the corresponding forms in ceruloplasmin, and of added Cu 2+ have been measured. Signal 1 is reduced much more rapidly than Signal 2, but this still reacts considerably faster than added Cu 2+. 6. 6. Treatment of the enzyme with cyanide produces, with concomitant loss of oxidase activity, an entirely new EPR spectrum corresponding to 40% of the original intensity. The treatment is entirely reversible which indicates that Cu 2+ is still at its original binding site. The new spectrum suggests coordination of Cu 2+ to three to four N atoms.

Electron spin resonance studies of the hydroxyl radical in ?-irradiated ice

A comparison of simulated with experimental electron spin resonance spectra of ice and deuterium oxide γ-irradiated at 77°K indicates that the g- and A-tensors of the hydroxyl radical in ice do not prossess axial symmetry, although many interpretative difficulties remain.

Electron spin resonance studies of the hydroxyl radical in γ-irradiated ice

A comparison of simulated with experimental electron spin resonance spectra of ice and deuterium oxide γ-irradiated at 77°K indicates that the g- and A-tensors of the hydroxyl radical in ice do not prossess axial symmetry, although many interpretative difficulties remain.