ORIENTATION-DEPENDENT STUDIES OF ALIGNED MEMBRANES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the study of membranes, there are several spectroscopic advantages when aligned membranes are available for study. One advantage is improved spectral resolution since the aligned membrane concentrates the spectral weight in a limited number of well-defined regions of the spectrum, whereas a vesicle spectrum represents a superposition of spectra corresponding to different orientations of the membrane normal relative to the external magnetic field (MOMD model). Another advantage of aligned membranes is a reduction in spectral ambiguity. In many cases substantially different sets of simulation parameters give very similar approximations of an experimental MOMD spectrum. The simulation of ESR spectra in aligned membranes, especially in the case of simultaneous fits for several orientations, is free from this ambiguity. The study of aligned membranes may provide particularly valuable information on the orientation of the nitroxide moiety relative to the membrane normal. Because all orientations of the membrane normal relative to the magnetic field are averaged in MOMD vesicle spectra, information about the orientation of the nitroxide moiety is poorly resolved. High frequency/high field spectroscopy, however, requires thin (100 micron) flat samples with B0 directed strictly perpendicular to the plane of the sample. To obtain high field spectra in an orientation different from 0¿ (here, the membrane normal corresponds to the sample normal) we apply microtome technique on ISDU aligned samples. A well-hydrated ISDU aligned membrane sample is cut into thin (~ 80 micron) slices where the slice normal is at a user controlled angle. 2 to 4 of these pieces, hermitically confined between two quartz microscope cover slips, form an aligned sample at a user-controlled orientation for high field ESR. We have successfully implemented this technique at 95 and 170/240GHz.