Thickness measurement of glucose-embedded crotoxin complex crystals by EELS

Abstract

In three-dimensional structure determination of macromolccules by electron crystallography it is necessary to combine diffraction patterns and images recorded at various tilt angles from different crystals. In order to merge these data sets successfully all the crystals should have the same thickness. It has been proposed that parallel electron energy loss spectroscopy (EELS) might provide a useful means of assessing the thickness of a beam-sensitive organic crystal prior to recording the high-resolution structural data. This can be achieved by measuring the fraction of the total transmitted electrons that do not lose energy, i.e., the zero-loss intensity. If Izis the integrated zero-loss intensity and Itotis the total integrated intensity in the energy loss spectrum, then the specimen thickness, t, is given in terms of the total inelastic mean free path, λi, by, t/λi= ln(Itot/Iz). Results recently obtained fromn-paraffin crystals have shown that it is feasible to determine the number of unit cell layers under low electron dose conditions.