2. X-ray crystallography is the experimental science determining the
atomic and molecular structure of a crystal, in which the crystalline
structure causes a beam of incident X-rays to diffract into many
specific directions
Useful in biochemistry to solve the 3D structures of complex
biomolecules.
Bridge the gaps between physics, chemistry, and biology.
X-ray diffraction (XRD) is a widely used technique to assess the
crystallinity and structure of solid samples. In summary, the crystal
X-ray diffraction phenomenon results from a scattering process in
which X-rays are scattered by the electrons of atoms present in the
sample without changing the wavelength
3. ◦ X-rays are a type of radiation called electromagnetic waves. X-ray
imaging creates pictures of the inside of your body. The images show the
parts of your body in different shades of black and white. This is because
different tissues absorb different amounts of radiation
• Solid-state physics
• Biophysics
• Medical physics
• Chemistry and Biochemistry
4. 1895 X-rays discovered by Roentgen
1914 First diffraction pattern of a crystal made by Knipping
and von Laue
1915 Theory to determine crystal structure from diffraction
pattern developed by Bragg.
1953 DNA structure solved by Watson and Crick
Now Diffraction improved by computer technology;
methods used to determine atomic structures and in
medical applications
5. Wave Interacting with a Single Particle
Incident beams scattered uniformly in all directions
Wave Interacting with a Solid
Scattered beams interfere constructively in some directions,
producing diffracted beams
Random arrangements cause beams to randomly interfere and no
distinctive pattern is produced
Crystalline Material
Regular pattern of crystalline atoms produces regular diffraction
pattern.
Diffraction pattern gives information on crystal structure
6. • Similar principle to multiple slit experiments
• Constructive and destructive interference patterns depend on
lattice spacing (d) and wavelength of radiation (l)
• By varying wavelength and observing diffraction patterns,
information about lattice spacing is obtained
7.
8. Concept
The concept of XRD can be explained as follows:
X-Rays
X-rays are the form of high energy electromagnetic radiation. These have a
wavelength ranging from 10picometers to 10nanometers.
X-rays have much higher energy and much shorter wavelengths than UV light.
These are useful to take the images of the human body, i.e., they can see
through a person's skin and reveal images of the bones beneath it.
Diffraction
It is the slight bending of the light as it passed around the edge of an object. It
occurs when a wave encounters an obstacle or a slit.
X-Ray Production
The x-rays are generated by a cathode ray tube, filtered to produce
monochromatic radiation, collimated to concentrate and directed toward the
sample.
Accelerating electrons with high voltages are allowed to collide with a metal
target.
9. ◦ X-ray diffraction is based on constructive interference of monochromatic X-
rays and a crystalline sample. These X-rays are generated by a cathode ray
tube, filtered to produce monochromatic radiation, collimated to concentrate,
and directed toward the sample.
◦ When a monochromatic x-ray incident occurs on a crystal. The atomic
electrons in the Crystal are sent into vibration. With the same frequency as
that of the frequency of the incident ray and are accelerated. These
Accelerated electrons then emit the radiation of the same frequency as that of
incident x-rays in all directions.
◦ If the wavelength of incident radiation is large compared to the dimensions of
the Crystal. Then the radiated X-ray are in phase with each. But since the
atomic dimension are nearly equal to the wavelength of X-Ray.
10. 1. COLLIMATOR
X-rays are generated by the target material when allowed to pass through a collimator. It
consists of two sets of closely packed metal plates separated by a small gap.
Collimator absorbs all the x-rays, but the narrow beam that passes between the gaps is not
absorbed.
2.MONOCHROMATORS
Monochromators used are the following types:
Filters
The filter is a window of material that absorbs undesirable radiation but allows the
radiation of the required wavelength to pass.
CRYSTAL MONOCHROMATORS
These are made up of a suitable crystalline material positioned in the x-ray beam so that
the angle of reflecting planes satisfied the Bragg's equation for the required wavelength,
and the beam is split up into component wavelengths.
The crystals used in monochromators are made up of materials like Sodium Chloride,
Lithium Fluoride, and Quartz.
11. 3. DETECTORS
Detectors use different types of methods to detect X-rays. They are:
a. Photographic Methods
Plane or cylindrical film is used, which is developed after exposure to x-rays.
Blackening of the developed film is always expressed in terms of density units D.
D = log I0 / I
Where,
I0 = Incident intensities.
I = Transmitted intensities.
D = Total energy that causes the blackening of the film.
b. Counter Methods
It is further divided as follows:
◦
i) Geiger-Muller Tube Counter
Filled with an inert gas like Argon.
The electrons are accelerated by the potential gradient and cause the ionisation of a large number of argon
atoms resulting in the production of an avalanche of electrons that are travelling towards the central anode
12. ii) Proportional Counter
Construction is similar to the Gieger tube counter.
It is filled with heavier gases like Xenon and Krypton.
Heavier gases are preferred because they are easily ionised.
It is operated at a voltage below the Gieger plateau.
The dead time is very short (~0.2 microseconds); it can be used
to count high rates without significant error.
◦
iii) Scintillation Detectors
In a scintillation detector, there is a large sodium iodide crystal
activated with a small amount of thallium.
When an x-ray is an incident upon the crystal, the pulses of
visible light are emitted which can be detected by a
photomultiplier tube. It is useful for measuring x-rays of short
wavelengths.
Crystals used in these detectors include Sodium Iodide,
Anthracene, Naphthalene and p-terpineol.
13. 1.When X-rays enters the Geiger tube, a collision occurs between the gas
molecule and X-rays. Thereby electrons are ejected out of atoms of neutral
molecules of argon gas.
2.This causes production of positive molecular ions and free electrons. These
electrons being negatively charged, moves towards anode and positively charged
argon ions moves toward cathode.
3. A potential gradient is applied to accelerate electrons. This causes electrons to
pick much energy to eject more electrons out of atom.
4.This in turn picks up further energy and liberates even more electrons. Such a
progressive process is called avalanche.
5. Positive ions hit the cathodic half cylinder with enough energy to eject further
more electrons. Therefore avalanche of electrons incline on wire which is
detected as a pulse of electric current. The electric pulse so generated indicates
passing of a charged particle through the tube. This pulse can be read or
measured through a meter
14. Find structure to determine function of proteins
Convenient three letter acronym: XRD
Distinguish between different crystal structures with identical compositions
Study crystal deformation and stress properties
Study of rapid biological and chemical processes
DRUG DEVELOPMENT: • XRD provides details on degree of crystallinity and amorphous
content of synthetic mixtures.
POLYMORPHISM -polymorphic content can impact properties such as solubility and dissolution
rate, bioavailability and stability so it is important to collect details on polymorphic properties of
ingredients of a drug materia
MANUFACTURING PROCESS CONTROL- Manufacturing process can involve morphological
changes in crystalline phase due to introduction of stress forces. Such changes can influence a
drug’s bioavailability The nondestructive nature of XRD analysis makes it an ideal choice to fix the
safe tableting pressure range so that the dosage form achieves its targeted dissolution rate and bio
availability.
