2. ELECTRO MAGNETIC SPECTRUM
Electro magnetic spectrum is the entire range of electro
magnetic waves from lower to higher frequency. It
contain various types of radiations.
gamma rays, x-rays, UV-Visible, IR, Micro waves and
X-rays have the short wavelengths to see the atoms and
molecular structure of molecules.
Wavelength range is 1-10 Å
Discovered by Wilhelm Rontgen in 1895.
It can be generated by reducing the speed of electrons.
5. X-ray Crystallography
It is a scientific method of determining the precise
arrangements of atoms in a crystal where beams of x-ray
strikes a crystal and causes the beam of light to diffract
into specific directions.
This method is widely used to obtain high resolution
protein structural information.
This technique relies the dual nature of x-rays to discover
information about structure of crystalline materials.
The pattern produced by the diffraction of x-rays through
the closely spaced lattice of atoms in a crystal is
recorded and analysed to reveal the nature of that lattice.
The sample that is in crystalline form is bombarded
with beam of x-rays , then most of the x-ray pass
straight through the crystal some are diffracted by it.
The resulting pattern recorded by a detector .
Pattern is the three dimensional structure of sample
This method can give detailed atomic structure such as
about ligands, inhibitors, ions, and other molecules.
8. Bragg’s Law
It is a fundamental law and valid for monochromatic x-
rays only and it is used to calculate interplanar spacing
using x-ray diffraction spectra
It defines the spacing(d) of atomic planes and incident
angle(Ө) at which x-rays of a particular wavelength will
reflect in phase.
nλ = 2d sinθ
The Bragg’s equation is,
10. Single X-ray Crystallography
It is the oldest and more precise model
A beam of x-rays strikes a single crystal, producing
It has three steps,
12. Nature of the Crystal
The crystal should be large , pure in composition and
regular in structure, with no significant internal
imperfections such as crack or twinning.
The crystal placed in an intense beam of x-rays , usually
single wavelength producing regular pattern of
When the crystal is rotated that time reflection will
change and intensity will be recorded.
These data are combined computationally with
complementary chemical information to produce and
refine a model of the arrangement of atoms with in the
Determination of unit cell, bond-lengths, bond-angles
Variations in crystal lattice
With specialized chambers, structures of high pressure
and/or temperature phases can be determined
Powder patterns can also be derived from single-crystals
by use of specialized cameras (Gandalf) applications.
The unit cell is larger and more complex.
The atomic level picture provided by x-ray
crystallography become less well resolved.
X-ray generated in the tube T are passed through a slit,
so as to obtained a narrow beam which is then allowed to
strike single crystal which is mounted on the turn table.
The crystal is rotated gradually by means of the turn table
as to increase the glancing angle.
The intensities of the reflected rays are measured on a
recording device. The process is carried out for each
plane of the crystal till the angles for reflection θ give the
The lowest angle at which the maximum reflection occurs
corresponds to n= 1. this is first order reflection and so
Used for the crystal with simple structure
Powder contain small crystal that are oriented in all
As a result x-rays are scattered from all sets of planes.
Scattered rays are detected by using an x-ray sensitive
The finely powdered substance is kept in the form of a
cylinder inside a thin glass tube.
Narrow beam of x-rays is allowed to fall on the powder.21
22. The diffracted x-rays strike a strip of photographic film
arranged in the form of a cylindrical arc.
In this method rotation is not needed because powder
sample contains micro crystals arranged in all possible
A large number of them will have their lattice planes in
corrected positions for maximum x-ray reflection to
We get lighted areas in the form of arcs of lines at
different distances from the incident beam.
Non-destructive nature, high sensitivity,
Easy sample preparation,
System is user friendly, operational procedure is
convenient, fast , effective resolution.
Low maintenance cost, proper automation, easy data
interpretation that could be used for both qualitative and
Use of harmful radiations.
25. Factors Affecting X-ray Crystallography
Purity of sample
pH of solution
Volume of crystallisation
26. Advantages and Disadvantages
X-rays are the least expensive, most convenient and
widely used to determine crystal structures.
X-rays are not absorbed very much by air, so the sample
need not be in an evacuated chamber.
X-rays do not interact very strongly with higher elements.
Distinguishing between crystalline & amorphous
Determination of the structure of crystalline materials.
Determination of electron distribution within the atoms &
throughout the unit cell.
28. Determination of the orientation of single crystals.
Determination of the texture of polygrained materials.
Measurement of strain and small grain size………
29. Medical Applications
In diagnosis & treatment
CT or CAT(computerized axial tomography)
The advent of x-ray diffraction in the early 20th century
transformed crystallography from an area of scientific
inquiry largely limited to physics, mineralogy, and
mathematics to a highly interdisciplinary field which now
includes nearly all life and physical sciences as well as
material science and engineering.