# Fundamentals of X-ray crystallography

Blog Post created by Alex Dean on Jun 6, 2018

For hundreds of years, scientist have not found a satisfying way of studying molecules until the emergence of X-ray crystallography, which was discovered by William Henry Bragg and his son William Lawrence Bragg around 100 years ago in an experiment they conducted. This method greatly revolutionized the way how molecules are studied and its refined version is still viewed as one of the most important tools in today’s scientific community.

What is X-ray crystallography?

X-ray crystallography, as its name suggests, is a technique that uses X-ray diffraction patterns to specify the three-dimensional structures of molecules like proteins, small organic molecules, and other materials. Most importantly, the substance to be X-rayed should be in crystalline form.

Without knowing Bragg’s Law, it is difficult for the majority to leap from a spotty cross to gain an understanding of the underlying structure of invisible atoms. Among all the structures discovered and determined by X-ray crystallography, DNA is probably the most famous one with which the general public is familiar. Actually, this number is far more than thousands, including structures of table salt, drugs, materials and massive intricate proteins. X-ray crystallography has exerted such a huge impact that UN has named 2014 the International Year of Crystallography.

How does X-ray crystallography work?

The following is about how X-ray crystallography actually works:

“When the X-ray beam is turned on, X-rays hit the crystal. A pattern of spots is made on the screen at the other side. The pattern shows where the X-rays hit particles inside the crystal. This is called a diffraction pattern. Some spots are darker than others. Then we use a computer to change the spot pattern into a picture which clearly shows how the particles in the crystal are arranged. During this process, a mathematics method called Fourier transformation is employed. Back to the times of William Henry and William Lawrence when they invented X-ray crystallography in 1912, all the calculations were done by hand.”

Fourier transformation played a part in specifying the structures of many important molecules, including DNA in the 1950s, antibiotic penicillin in 1946, vitamin B12 in 1956 and insulin in 1969.

X-ray crystallography in the future

Overall, the future of X-ray crystallography is bright. Researchers and chemists often have a love-hate relationship with X-ray crystallography. Why hate it? It’s because this method requires the target of interest to be crystals and even of certain quality and size. What put most chemists into a dilemma is the extreme difficulty of producing a crystal of a complex molecule. Since such trials often met with failure, a great many scientists has built their careers by just learning how to build good quality crystals of a particular protein.