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X ray crystallography. presentation

  2. CONTENTS  Introduction  X-ray diffraction  X-ray Techiniques  Production of X-rays  Sources of X-rays  X-ray diffraction method  Bragg’s law and Diffraction  Deriving Bragg’s law  Application of XRD
  3. INTRODUCTION  X-Ray crystallography is a powerfull technique for visualizing the structure of proteins.  It is a tool used for identifying the atomic and molecular structure of crystal.  In crystallography the crystalline atoms cause a beam of incident x-ray to differact into many specific direction.  Then crystallographer can produce three dimentional picture of the density of electrons with in the crystals .  From the electron density ,the mean positions of the atoms in the crystal can be determined.  X-ray crystallography can locate every atom in a zeolite, an aluminosilicate.
  4. X –RAY DIFFRACTION  Wave length of x-ray region = 0.1 to 100 A anstrons.  For analytical purposes range of 0.7 – 2 .0 anstrons.  X-Rays are generated when light velocity electrons are on the the metal target.  X-Ray crystallography uses the uniformity of light diffraction of crystals to determine the structure of molecules or atoms.  Then X-Ray beam is used to hit the crystallized molecule.  The Electron sorrounding the molecule diffract as the x- rays hit them.  This forms a pattern . This type of pattern is known as x- Ray diffraction pattern.
  5. X-RAY TECHNIQUES They are classiffied into 3 types .  X-ray absorption method : In this method ,a beam of x- rays is allowed to pass and the sample which is having the fraction of x-ray photons absorbed is consider to be a measure of the concentration of the absorbing substance .These methods are helpful in elemental analysis .  X-ray diffraction methods : These methods are based on the scattering of x-rays by crystals .This technique is helpfull in identification of crystal structure of various solid compounds.  X-ray flourescence method : In this methods x-rays are generated conc in the sample and by measuring the wave length and intensity of the generated x-rays ,one can perform quality and quantity analysis.
  6. PRODUCTION OF X-RAY  Power is send to X-Ray tube via cables .  Ma ( milliamperage ) is send to filament on cathode side.  Filament heats up electron “ boil off ”  Negetive charge  Positive Voltage ( KVP ) is applied to ANODE.  Negetive Electrons = attracted across the tube to the positive ANODE.  Electrons “ Slam into” anode suddenly stopped .  X-Ray photons are created .  Elecron beam is focused from the cathode to the anode target by the focusing cup.  Electron interact with the electrons on the tungstuns atoms of target material.  Photons send to through the window port towards the patient.
  7. SOURCES OF X-RAY X-RAY sources abound around us .They include the following  Natural x-ray sources .  Astrophysical x-ray source.  X-ray background.  Naturally occuring radionuclides. • Artificial x-ray sources.  Radiopharmaceutical in radiopharmacology.  Radioactive tracer.  Brachytherapy • X-ray tube : A vacume tube that producas x-rays when current flow through it. • X-ray laser. • X-ray generator. • Synchrotron radiation . • Cyclotron radiation.
  8. X-RAY DIFFRACTION METHOD These are generally used for investigating the internal structures and crystal structures of various compounds . They are :  Laue’s photographic method. • Transmission method. • Black reflection method.  Rotating crystal method .  Powder method .
  10. TRANSMISSION METHOD In the transmission laue method , the film is placed behind the crystal to record beams which are transmitted through the crystal. One side of the cone of Laue reflections is defined by the transmitted beam. The film intersects the cone , with the diffraction generally lying on an ellipse. • Can be used to orient crystals for solid state experiment. • Most suitable for the investigation of preferred orientation sheet particularly confined to lower diffraction angles. • Also used in determination of symmetry of single crystals.
  12. BLACK REFLECTION METHOD  In the black reflection method the film is placed between the x-ray source and the crystal .The beam which are differacted in a backward direction are recorded.  One side of the cone of laue reflection is defined by the transmitted beam .The film intersects the cone ,with the diffraction spots generally lying on an hyperbola.  The method is similar to transmission method however black reflection is the only method for the study of large and thick specimens.
  13. DISADVANTAGES  Big crystals are requied .  Crystal orientation is determined from the position of the spots can be indexed, attributed to a particular plane ,using special chart.  The Greninger chart is used for back reflection patterns and the Leonhardt chart for transmission patterns .  The Laue technique can also be used to assess crystal perfection from the size and shape.
  15. PHOTOGRAPHS CAN BE TAKEN BY:  Complete rotation method : In this method series of complete revelutions occur.  Each set of a plane is a crystal diffracts four times during rotation.  Four diffracted beams are distributed into rectangular pattern in the central point of photograph.  Oscillation method : The crystal is oscillated at an angle of 15 degree or 30 degree.  The photographic plate is also moved back and forth with the crystal.  The position of the spot on the plate indicates the orientation of the crystal at which the spot was formed.
  17. POWDER CRYSTAL METHOD X-Ray powder diffraction is a rapid analytical technique primarly used for phase identification of crystalline material and can provide information on unit cell dimensions .The analysed material is finely ground ,homogenised and average bulk composition is determined. • Fine powder is struck on a hair with gum, it is suspended vertically in the axis of a cylindrical camera.  When monochromatic beam is allowed to pass different possibilities may happen. 1.There will be some particles out of random orientation of small crystals in the fine powder.
  18. POWDER CRYSTAL METHOD 2. Another fraction of grains will have another set of planes in the correct positions for the reflection to occur. 3. Reflection are possible in different orders for each set.  If the angle of incidence is then angle of reflection will be 2 .  If the radius is r the circumference 2 r corresponds to a scattering angle of 360 degree. = 360*1 / r  From the above eqvation the valve of can be calculated and substituted in bragg’s equation to get the value of d.
  19. APPLICATIONS OF XRD  Structure of crystal.  Polymer characterisation.  Particle size determination.  Spot counting method.  Broadning of diffraction lines .  Low angle scattering. o Applications of diffraction method to complexes.  Determination of cis trans isomerism.  Determination of linkage isomerism o Miscellaneous applications.
  20. THANKS

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