Evaluation of reflection intensities for the components of multiple Laue diffraction spots. III. Using a real-space density modification method

Abstract

In a Laue diffraction pattern, 10-20% of the spots result from the exact superposition of two or more reflections that are 'harmonics', e.g. hkl; 2h 2k 2l,...; a high proportion of these are low-resolution reflections. For the solution of large or difficult structural problems, the intensities of the remaining 80-90% of the reflections, measurable as singles, may not be sufficient and thus the evaluation of the intensities of the components of the multiple spots is important. A new procedure, DECONV, for this deconvolution using real-space density modifications on the Patterson map is given. This development is based on a procedure in reciprocal space related to direct methods [Hao, Campbell, Harding and Helliwell (1993). Acta Cryst. A49, 528-531]. A Patterson map is calculated using single reflections and modified by removing negative densities and squaring with an appropriate adjustment at the origin peak. The procedure can be repeated until convergence is reached. It has been tested with Laue diffraction data from 4Zn insulin and cytochrome c peroxidase (CCP). 304 and 1134 reflection intensities were evaluated from multiple spots of insulin and CCP, respectively; the mean fractional differences (on F), showing the agreement with high-quality monochromatic data, were 0.27 and 0.21, respectively.