Chemistry and Physics of Lipids 141 (2006) 142–157 Review Time-resolved electron spin resonance studies of spin-labelled lipids in membranes Rosa Bartucci a,∗ , Denis A. Erilov b , Rita Guzzi a , Luigi Sportelli a , Sergei A. Dzuba c , Derek Marsh d a Dipartimento di Fisica, Universit` a della Calabria, I-87036 Arcavacata di Rende (CS), Italy b Institut f ¨ ur Molekularbiologie und Biophysik, Eidgen¨ ossische Technische Hochschule H¨ onggerberg, Z¨ urich, Switzerland c Institute of Chemical Kinetics and Combustion, Russian Academy of Science, 630090 Novosibirsk, Russian Federation d Max-Planck-Institut f¨ ur Biophysikalische Chemie, Abteilung Spektroskopie, D-37077 G¨ ottingen, Germany Received 28 November 2005; accepted 20 February 2006 Available online 13 March 2006 Abstract Recently, developments in time-resolved spin-label electron spin resonance (ESR) spectroscopy have contributed considerably to the study of biomembranes. Two different applications of electron spin echo spectroscopy of spin-labelled phospholipids are reviewed here: (1) the use of partially relaxed echo-detected ESR spectra to study the librational lipid-chain motions in the low- temperature phases of phospholipid bilayers; (2) the use of electron spin echo envelope modulation spectroscopy to determine the penetration of water into phospholipid membranes. Results are described for phosphatidylcholine bilayer membranes, with and without equimolar cholesterol, that are obtained with phosphatidylcholine spin probes site-specifically labelled throughout the sn-2 chain. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Electron spin resonance; Electron spin echo; Spin labels; Librational chain motions; Transmembrane water penetration Contents 1. Introduction ............................................................................................... 143 2. Electron spin echo decays and lipid mobility ................................................................. 143 2.1. Two-pulse echo-detected spectra for determining rapid rotational motion .................................. 144 2.2. Simulation of ED-ESR spectra for librational motion ................................................... 146 2.3. Chain librational amplitudes and correlation times ...................................................... 147 2.4. Chain length dependence of the librational motion ...................................................... 148 2.5. Three-pulse echo-detected spectra for determining slow rotational motion ................................. 149 2.6. Conclusions from ED-ESR studies of lipid chain motion ................................................ 151 3. ESE envelope modulation for determination of water penetration in membranes .................................. 151 3.1. Three-pulse 2 H-ESEEM determinations of D 2 O penetration ............................................. 152 3.2. Transmembrane water penetration profiles ............................................................. 152 ∗ Corresponding author. Tel.: +39 0984 496074; fax: +39 0984 494401. E-mail address: bartucci@fis.unical.it (R. Bartucci). 0009-3084/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.chemphyslip.2006.02.009