Abstract
Copper(II) tetraphenylporphine (CuTPP) has been found to partition favorably into dimyristoylphosphatidylcholine (DMPC) bilayer membranes. Electron paramagnetic resonance (EPR) spectra of oriented liquid-crystalline DMPC membranes indicate that for a high (≈1/25) CuTPP/DMPC molar ratio CuTPP is oriented with the plane of the molecule parallel to the bilayer surface. This result is in clear contrast to our previous observation that at low (≤1/100) CuTPP/DMPC molar ratio the plane of the molecule is preferentially perpendicular to the membrane surface (Pasenkiewicz-Gierula, M.; Subczynski, W. K.; Antholine, W. E. J. Phys. Chem. 1997, 101, 5596−5606). Measurements of the collision rate between CuTPP and the nitroxide moiety of stearic acid spin labels located at different depths in the membrane using saturation-recovery EPR spectroscopy lead to the conclusion that the change of the CuTPP orientation at a high CuTPP/DMPC molar ratio is coupled with self-association by planar stacking of CuTPP molecules near t...
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