X-ray Crystallography.
X-ray crystallography is a technique used to determine the atomic and molecular structure of a
crystal using X-rays. The basic principle behind X-ray crystallography is that when an X-ray
beam is directed at a crystal, the X-rays are scattered by the atoms in the crystal, and the pattern
of scattered X-rays can be analyzed to determine the arrangement of atoms in the crystal lattice.
The process of X-ray crystallography involves several steps:
1. Crystal growth: A crystal of the substance to be studied is grown. The crystal should be
large enough to allow for accurate measurements of the X-ray diffraction pattern.
2. Data collection: The crystal is then mounted in a beam of X-rays and rotated to collect
data from different angles. The X-ray beam should be of high intensity and
monochromatic, meaning it contains only one wavelength of X-ray.
3. Data analysis: The data collected is analyzed using mathematical techniques to determine
the positions of the atoms in the crystal lattice. This involves solving the phase problem,
which is the challenge of determining the phase angle of each X-ray wave as it passes
through the crystal.
4. Model building and refinement: Once the positions of the atoms are known, a model of
the crystal structure is built using specialized software. The model is then refined by
comparing the calculated diffraction pattern with the observed pattern.
X-ray crystallography has numerous applications in many fields, including chemistry,
biochemistry, materials science, and pharmacology. It has been used to determine the structures
of proteins, DNA, and other biological molecules, as well as in the design of new drugs and
materials.
However, X-ray crystallography also has some limitations. It requires a pure and ordered crystal
sample, which can be challenging to obtain for some materials. Additionally, some materials may
be damaged by the X-rays used in the technique.