What is X-ray crystallography?
X-rays are a type of electromagnetic radiation, just like visible light, but they have a shorter wavelength and higher energy than visible light. This enables X-rays to pass through most materials but still interact with the atomic nuclei within the material.
Here is a step-by-step explanation of how X-ray crystallography works:
1. Crystal preparation: Crystals must be used that have sufficient size and regularity for X-ray diffraction.
2. X-ray generation: A highly focused beam of monochromatic (single wavelength) X-rays is produced using an X-ray source such as a rotating anode or synchrotron.
3. Crystal mounting: The crystal is carefully aligned in the path of the X-ray beam.
4. Diffraction: X-rays interact with the electron clouds of the atoms within the crystal, causing the rays to scatter and produce a diffraction pattern. The diffraction pattern consists of a series of discrete spots or reflections on a detector, such as a photographic film or electronic sensor.
5. Data collection: The diffraction patterns collected from different orientations or angles of the crystal are captured using a detector. This results in a set of experimental data representing the intensity and position of the diffracted X-ray beams.
6. Data processing: The collected data is then subjected to various computational processes to extract the structural information. This involves steps like determining the crystal symmetry, calculating the structure factor (a mathematical expression related to the electron density), and correcting for various experimental errors.
7. Structural model building: Using the processed data, scientists build a three-dimensional model of the crystal structure. This is typically done using computer software and requires an iterative refinement process to ensure the model accurately matches the experimental data.
8. Analysis: The resulting crystal structure model allows scientists to visualize and analyze the arrangement of atoms within the crystal and determine their positions, symmetries, and bonding patterns. This information provides valuable insights into the molecular structure, chemical composition, and physical properties of the material.
X-ray crystallography is widely used in various fields, including chemistry, materials science, mineralogy, biology, and pharmacology, to understand the atomic-level details of crystalline materials and macromolecules such as proteins, minerals, and pharmaceuticals. Advancements in computational power and experimental techniques have made X-ray crystallography a powerful tool for investigating and understanding the structures and properties of a wide range of materials.