NEW GRINCH AB INITIO INTERPRETATION OF ELECTRON DENSITY DATA

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GRINCH II, Direct Map Interpretation. In the early 1980s Tom Williams, while a member of the GRIP project, built the GRINCH system for the ab-initio interpretation of electron density maps. Williams' system was based on work by Drs. Jonathan Greer, Carroll Johnson, and Stanley Swanson for representing electron density by marking the ridges of high local density. At least 50 copies of this system were disseminated to the crystallographic community. Graduate student Juraj Horacek of the current GRIP project team was re-examining this ridge line approach to ab-initio electron density interpretation using new, more powerful ridge line finding mathematics developed in our department by David Eberly for the analysis of medical images. Our new approach is distinguished from prior work in that we do not simply connect critical points but actually trace the ridges of high density through an interpolated function. This should help us avoid some kinds of common errors in map interpretation. We expect this work to lead to both new representations for electron density and to new methodologies for its interpretation as a molecular structure. Horacek decided to abandon or postpone his Ph.D. work in order to enter Cornell Business School. He worked on the project from May until September. He may work on it again this summer. We shall see. We do not now expect another student to pick up this work; if not, this subproject will be abandoned.