The Weissenberg method, named after the German physicist Karl Weissenberg, is a technique used in x-ray crystallography for obtaining high-quality diffraction patterns from single crystals. This method is particularly useful for crystals that are small or poorly shaped, as it allows for the collection of diffraction data without the need for large, well-formed crystals.
Key features and principles of the Weissenberg method:
Rotation method: The Weissenberg method involves rotating a crystal about an axis perpendicular to the incident x-ray beam. The crystal is usually mounted on a spindle, and the rotation causes different crystallographic planes to intersect with the x-ray beam at various angles.
Continuous rotation: Unlike the rotation method used in some other crystallographic techniques, the Weissenberg method involves continuous rotation of the crystal during the data collection process. This continuous rotation helps to average out errors and enhances the quality of the diffraction data.
Fiber method: In the Weissenberg method, the crystal is often shaped into a thin, elongated fiber. This fiber shape facilitates continuous rotation without the need for frequent stops and reversals. The crystal is slowly rotated during data collection, and the x-ray detector records the diffraction pattern as the crystal rotates.
Image plate or film detectors: Traditional Weissenberg data collection used photographic film as the detector. In modern applications, image plates or area detectors are often employed for more efficient and accurate data collection.
Data processing: The collected diffraction images are processed to extract the intensities and phases of the diffracted x-rays. This information is crucial for determining the three-dimensional arrangement of atoms within the crystal lattice.
Applications: The Weissenberg method is valuable in cases where obtaining large, well-formed crystals is challenging. It has been widely used in the study of small organic crystals and biological macromolecules.
While the Weissenberg method has been historically important, advances in x-ray crystallography have led to the development of other techniques, such as the rotation method with area detectors. These modern techniques offer faster data collection and improved accuracy, contributing to the continued progress in structural biology and materials science.