The wrapping phenomenon in air-dried and negatively stained preparations.

We demonstrate that the interface energies involved in the direct preparation of supramolecular structures onto supporting films leads very frequently to a smooth wrapping of the supporting film around approximately one third to one half of the structure. We conclude that in such cases the structure is more rigid than the supporting film; examples being ribosomes, small viruses and small glass fragments. Other structures are less rigid and become significantly flattened. Complete flattening is frequently observed with empty virus capsids. The sandwich technique, by which a specimen is placed between two supporting films, in general leads to increased flattening. Only in few cases (e.g. ribosomes) are biological particles rigid enough to resist flattening and become wrapped from both sides.