Physical Chemistry The Journal of zyxwvut Registered in zyxwvutsrqponm US. Patent Office zyxwvutsrqpo 0 Copyright, 1981, by the American Chemical Society zyxwvu VOLUME 85, NUMBER 12 JUNE 11, 1981 zy LETTERS Effects of Defect Annealing on Concentration-Dependent ESR Spectra from Hydrated Dimyristoylphosp hatidylcholine Eva Melrovitcht and Jack H. Freed* zyxwvut Baker Laboratory of Chemistry, Cornel1 University, Ithaca, New York zyxwvut 14853 (Received: February 4, 198 1; In Final Form: April 20, IS8I) zy This work reports the dramatic ESR spectral changes which occur for fully hydrated multilayers of di- myristoylphosphatidylcholine (DMPG) having significant concentrations of spin-label, which have been allowed to anneal over a period of 30 days. The ESR spectra initially show concentration-dependent line broadening but then gradually become characteristic of concentration-independentspectra. Spin concentration measurements show no significant loss of radical concentration. These observations may be related to recent work of Chan and Webb showing that intially there are extensive structural defects, which gradually anneal out in the same time period. The study of concentration-dependent ESR spectra of spin-labeled phospholipids has been shown by McConnell and co-worker~l-~ as well as by Sackmann and T r a ~ b l e ~ 9 ~ to allow the estimate of diffusion coefficients D for lateral diffusion in membranes. The method of fluorescence re- covery has been used for the same purpose.6-8 Recently, Chan and Webbghave developed a technique for carefully annealing fully hydrated multilayers to remove the defects in their multilayer structure. They find that after initial annealing the remaining defects are elementary edge dis- locations, which are abrupt terminations of single bilayers. They have obtained fluorescent intensity results on these annealed samples that imply a great slowing down of in- terbilayer permeation by fluorescent probes in the liquid crystalline La phase, and, using fluorescence bleaching, they find that in the gel phase, intrabilayer diffusion is greatly slowed down. These results are to be expected if Isotope Department, Weizmann Institute of Science, Rehovot, Israel the primary diffusion of the phospholipids in nonannealed multilayers is along defect channels due to edge (and/or screw) dislocations. Chan and Webb find that the an- nealing procedure for fully hydrated multilayers is very slow, taking about 2-4 weeks for virtual completion. ~~ (1) P. Deveaux and H. M. McConnell, J. Am. Chem. Soc., 94, 4475 (1972). (2) (a) C. J. Scandella, P. Devaux, and zyxw H. M. McConnell, Proc. Natl. Acad. Sci. U.S.A., 69, 2056 (1972); (b) P. Devaux, C. J. Scandella, and H. M. McConnell, J. Mag. Reson., 9, 474 (1973). (3) H. M. McConnell in “Spin Labeling: Theory and Applications”, L. J. Berliner, Ed., Academic Press, New York, 1976, Chapter 13. (4) E. Sackmann and H. Trauble, J. Am. Chem. SOC., 94,4492 (1972). (5) H. Trauble and E. Sackmann, J. Am. Chem. Soc., 94,4499 (1972). (6) E. S. Wu, K. Jacobson, and D. Papahadjapoulos, Biochemistry, 16, (7) P. F. Fahey, D. E. Koppell, L. S. Barak, D. E. Wolf, E. L. Elson, (8) B. A. Smith and H. M. McConnell, Proc. Natl. Acad. Sci. U.S.A., (9) W. Chan and W. W. Webb, Phys. Reu. Lett., 46,39 (1981); 46,603 3936 (1977). and W. W. Webb, Science, 195, 305 (1976). 75, 2759 (1978). (1981). 0022-3654/81/2085-1617$01.25/0 0 1981 American Chemical Society