Electron paramagnetic resonance of slowly tumbling triradicals: Investigation of ΔM =1, ΔM = 2, and ΔM = 3 transitions

Kothe, G.; Waßmer, K.-H.; Naujok, A.; Ohmes, Ernst; Rieser, J.; Wallenfels, Kurt

doi:10.1016/0022-2364(79)90119-7

Cited by 7 publications

(6 citation statements)

References 12 publications

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“…For the intermolecular motion (chain reorientation), a diffusive process is assumed (rotation through a sequence of infinitesimally small angular steps). In that case the transition rates must satisfy the equations (Kothe et al, 1979):…”

Section: Discussionmentioning

confidence: 99%

Electron spin resonance study of phospholipid membranes employing a comprehensive line-shape model

Lange¹,

Marsh

Waßmer³

et al. 1985

Biochemistry

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115

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The electron spin resonance spectra of the 1-myristoyl-2-[6-(4,4-dimethyloxazolidine-N-oxyl)myristoyl]-sn-glycero- 3-phosphocholine spin-label in highly oriented, fully hydrated bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine have been studied as a function of temperature and magnetic field orientation. The oriented spectra show clear indications of slow motional components (rotational correlation times greater than 3 ns) even in the fluid phase (T greater than 23 degrees C), indicating that motional narrowing theory is not applicable to the spectral analysis. The spectra have been simulated by a comprehensive line-shape model that incorporates trans-gauche isomerization in addition to restricted anisotropic motion of the lipid long molecular axis and that is valid in all motional regimes. In the gel (L beta') phase the spin-label chains are found to be tilted at 28 degrees with respect to the normal of the orienting plane. In the intermediate (P beta') phase there is a continuous distribution of tilt angles between 0 degrees and 25 degrees. In fluid (L alpha) phase there is no net tilt of the lipid chains. The chains rotate at an intermediate rate about their long axis in the fluid phase (tau R,parallel = 1.4-6.6 ns for T = 50-25 degrees C), but the reorientation of the chain axis is much slower (tau R, perpendicular= 13-61 ns for T = 50-25 degrees C), whereas trans-gauche isomerization (at the C-6 position) is rapid (tau J less than or equal to 0.2 ns). Below the chain melting transition both chain reorientation and chain rotation are at the ESR rigid limit (tau R greater than or equal to 100 ns), and trans-gauche isomerization is in the slow-motion regime (tau J = 3.7-9.5 ns for T = 22-2 degrees C). The chain order parameter increases continuously with decreasing temperature in the fluid phase (SZZ = 0.47-0.61 for T = 50-25 degrees C), increases abruptly on going below the chain melting transition, and then increases continuously in the intermediate phase (SZZ = 0.79-0.85 for T = 22-14 degrees C) to an approximately constant value in the gel phase (SZZ congruent to 0.86 for T = 10-2 degrees C).(ABSTRACT TRUNCATED AT 400 WORDS)

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Section: Discussionmentioning

confidence: 99%

Electron spin resonance study of phospholipid membranes employing a comprehensive line-shape model

Lange¹,

Marsh

Waßmer³

et al. 1985

Biochemistry

Self Cite

115

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“…finitesimally small angular steps), the transition rates must satisfy the following equations (Kothe et al, 1979):…”

Section: Theorymentioning

confidence: 99%

Structure and dynamics of phospholipid membranes: an electron spin resonance study employing biradical probes

Meier¹,

Blume²,

Ohmes³

et al. 1982

Biochemistry

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The large zero-field splitting of rigid biradicals makes them important candidates for spin probes of phospholipid membranes. Here we develop an electron spin resonance line-shape model for such probes on the basis of the stochastic Liouville equation. Particular emphasis is given to the slow-diffusional regime, characteristic of bilayers in the gel phase. The theory is employed to study the line shapes of bis(verdazyl) biradicals, incorporated into oriented multibilayers of dimyristoylphosphatidylcholine. Computer simulations of the angular-dependent spectra provide the orientational distribution functions and rotational correlation times of the spin probes. They occupy two different sites in bilayer membrane. The orientational distribution of the spin probes is related to the structure of the phospholipid phases. In the L beta' phase the hydrocarbon chains are uniformly tilted by delta = 23 degrees with respect to the bilayer normal. For the P beta' phase we observe a random distribution of tilt angles from delta = 0 degree to delta = 19 degrees, indicating that the chains orient perpendicular to the local (rippled) bilayer surfaces. This structure has not been established previously. In agreement with other studies we find no tilt for the L alpha phase. The order parameters of the hydrocarbon chains increase with decreasing temperature, jumping from S less than or equal to 0.6 to S greater than or equal to 0.8 at the main transition. From the rotational correlation times of the spin probes, intrinsic bilayer viscosities of 0.08 P less than or equal to eta less than or equal to 20 P (50 degrees C greater than or equal to T greater than or equal to 1 degree C) are determined. An Arrhenius plot provides activation energies of the viscous flow. The values increase from Evisc approximately 10 kcal/mol in the L alpha phase to Evisc approximately 18 kcal/mol in the L beta' phase.

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“…[5] may therefore be replaced by time-independent equilibrium populations P(⍀ n ). Examples for different motional matrices ⌫ will follow.…”

Section: Time Dependence Of the Spin Density Matrixmentioning

confidence: 99%

“…For jump motions, the Euler angle sets ⍀ n mark the orientations of specific jump sites. For diffusive motions, the reorientation is approximated by a finite number of angular steps in the Euler angle spheres (5,6). In both cases, the motion is characterized by a differential equation involving a set of rate constants k (⍀n3⍀nЈ) :…”

Section: Time Dependence Of the Spin Density Matrixmentioning

confidence: 99%

“…Generally, a stationary Markov operator is defined which, being part of the stochastic Liouville equation, describes the motionally induced change of the spin density matrix. Integration of the first derivative of the density matrix elements in order to obtain the spectral lineshape results in a more or less complicated eigenvalue problem (5,6). Lately, a very effective approach for the simulation of spectra has been developed by N. J. Heaton (7), which takes account of the motionally induced time dependence of Hamiltonian operators for individual spins.…”

Section: Introductionmentioning

confidence: 99%

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Lineshape Calculations on Spreadsheet Software

Mayer

1999

Journal of Magnetic Resonance

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Electron paramagnetic resonance of slowly tumbling triradicals: Investigation of ΔM =1, ΔM = 2, and ΔM = 3 transitions

Cited by 7 publications

References 12 publications

Electron spin resonance study of phospholipid membranes employing a comprehensive line-shape model

Electron spin resonance study of phospholipid membranes employing a comprehensive line-shape model

Structure and dynamics of phospholipid membranes: an electron spin resonance study employing biradical probes

Lineshape Calculations on Spreadsheet Software

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