A novel method for improvement of visualization of power spectra for sorting cryo-electron micrographs and their local areas

International audienceIn a context of automation of cryo-electron microscopy, we developed a novel method for improving visibility of diffraction rings in the power spectra of cryo-electron micrographs of vitreous ice (without carbon film or high concentration of diffracting material). We used these enhanced spectra to semi-automatically detect and remove micrographs and/or local areas introducing errors in the global 3D map (drifted and charged areas) or those unable to increase global signal-to-noise ratio (non-diffracting areas). Our strategy also allows a detection of micrographs/areas with a strong astigmatism. These images should be removed when using algorithms that do not correct astigmatism. Our sorting method is simple and fast since it uses the normalized cross-correlation between enhanced spectra and their copies rotated by 90. It owes its success mainly to the novel pre-processing of power spectra. The improved visibility also allows an easier visual check of accuracy of sorting. We show that our algorithm can even improve the visibility of diffraction rings of cryo-electron micrographs of pure water. Moreover, we show that this visibility depends strongly on ice thickness. This algorithm is implemented in the Xmipp (open-source image processing package) and is freely available for implementation in any other software package

3D electron microscopy of biological nanomachines: principles and applications

International audienceTransmission electron microscopy is a power-ful technique for studying the three-dimensional (3D) struc-ture of a wide range of biological specimens. Knowledge ofthis structure is crucial for fully understanding complexrelationships among macromolecular complexes and organ-elles in living cells. In this paper, we present the principlesand main application domains of 3D transmission electronmicroscopy in structural biology. Moreover, we survey current developments needed in this Weld, and discuss theclose relationship of 3D transmission electron microscopy withother experimental techniques aimed at obtaining structuraland dynamical information from the scale of whole livingcells to atomic structure of macromolecular complexes

Matériaux moléculaires magnétiques à haute température : étude d’une classe de composés synthétisés à partir de l’acide aminonaphtalène-sulfonique et d’aniline

Dans cet article nous reportons les propriétés magnétiques d'une classe de matériaux moléculaires synthétisés à partir de l'acide aminonaphtalènesulfonique et d'aniline