Chain dynamics in the low-temperature phases of lipid membranes by electron spin-echo spectroscopy |
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Authors: | Bartucci Rosa Guzzi Rita Marsh Derek Sportelli Luigi |
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Institution: | Dipartimento di Fisica, Università della Calabria, I-87036 Arcavacata di Rende (CS), Italy. bartucci@fis.unical.it |
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Abstract: | Spin-echo decays of spin-labelled phospholipids have been recorded to study the chain dynamics in the low-temperature phases of dipalmitoyl phosphatidylcholine membranes with and without 50 mol% cholesterol. The phase-memory relaxation time, T(2M), depends on the position of spin-labelling in the sn-2 chain, and on the presence of cholesterol. A biphasic temperature dependence of T(2M) is obtained over the range 150-270 K. Echo-detected field-swept absorption EPR spectra were recorded as a function of the echo delay time, tau. The echo-detected EPR lineshapes show a strong dependence on tau, revealing anisotropic phase relaxation arising from torsional chain motions. Cholesterol has a large effect on torsional oscillations about the chain long axis. Small-amplitude chain motions in the low-temperature phases may be important for cryopreservation of membranes. |
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Keywords: | Lipid bilayer Spin label EPR Electron spin echo Chain librations Cryoprotection |
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