Crystal structure solution of small-to-medium-sized molecules at non-atomic resolution

Abstract

Data resolution limits the information carried by diffraction data and is therefore the most critical limit for the success ofab initiocrystal structure solution. To overcome this limit, two methods have recently been proposed, namely the correction of resolution bias in electron-density maps and extrapolation of the structure factors beyond the data resolution limit. The first method has successfully been applied to powder data and the second to protein data. Neither of them has been applied to single-crystal data from small or medium-sized molecules. A third technique, the active use of the PSI-0 triplets in a tangent procedure, was applied to small molecules in the early days of crystallography, but it soon became obsolete because of the great success of methods combining reciprocal and direct space techniques. This paper explores the role of data resolution for small-to-medium-sized molecules and studies the usefulness of three auxiliary techniques,i.e.active use of the PSI-0 triplets, resolution bias correction and extrapolation of the structure factors.