Global shape complementarity

In nearly all chemically important problems, shape complementarity refers to local shape properties. Most of the typical molecular interactions where shape complementarity is relevant involve only some local moieties of the molecules. Global shape complementarity is more difficult to achieve and seldom plays a role. 

The catalytic activity of zeolites also involves shape complementarity. The cavities of zeolites are interconnected by various channels, consequently, in a strict sense, a cavity does not fully surround a molecule that enters the zeolite. As a result, for high density zeolite MIDCO s only local shape complementarity is possible. Nevertheless, the low density MIDCO s of zeolites contain closed internal contour surfaces corresponding to the cavities and for these parts of MIDCO s global shape complementarity is relevant. The shapes of these MIDCO s may approximately complement the shapes of the MIDCO s of a molecule inside the cavity. 

It is now possible to analyze macromolecular electron densities at a resolution far exceeding the resolution of current x-ray diffraction and other experimental and macromolecular computational techniques. The MEDLA method presents a new perspective for the analysis of global and local shape, molecular similarity, and complementarity. 

A properly folded chain molecule can form a cavity with a shape globally complementing the shape of an enclosed, quasi-spherical molecule. If, however, the enclosed molecule has a toroidal or more complicated topology, where the hole of the torus is small so the surrounding chain molecule cannot enter this hole, then an approximate global complementarity by a chain molecule is unlikely to reflect the correct topology of the enclosed molecule. 

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