xrays ppt by jaismin m pharmacy qa 1.pptx
- 1. INTRO: • X-ray crystallography is the study of crystal structures through X-ray diffraction techniques. It is not an imaging technique. • When an X-ray beam bombards a crystalline lattice in a given orientation, the beam is scattered in a definite manner characterized by the atomic structure of the lattice. • Modern X-ray crystallography provides the most powerful and accurate method for determining single-crystal structures. • Through X-ray crystallography the chemical structure of thousands of organic, inorganic, organometallic, and biological compounds are determined every year. . diffraction of rays by crystals. Crystals are necessary because it is neither possible to see nor handle single molecules.
- 3. DIFFERENT X-RAY METHODS : A variety of x-ray technique and methods are in use but we shall classify all methods into three main categories:- 1. X-ray absorption 2. X-ray fluorescence 3. X-ray diffraction ▸ X-ray absorption:- In this method a beam of x-rays is allowed to pass through the sample and the fraction of x-ray photons absorbed is considered to be a measure of the concentration of absorbing substance. ▸ X-ray fluorescence:- In this method x-rays are generated within the sample and by measuring the wavelength and intensity of the generated x-rays one can perform qualitative and quantitative analysis. X- rays fluorescence method is non-destructive and frequently requires very little sample preparation. ▸ X-ray diffraction method:-These methods are based on the scattering of x-rays by crystals. By this methods, one can identify the crystal structure of various solid compounds. This methods are extremely important as compared to other two methods.
- 4. Production of X-Rays : • X-rays are generated when high velocity electrons strikes on a metal target. • Approximately 1% of the total energy of the electron beam is converted into x- radiation. • The remainder being scattered as heat. • Many types of x-ray tubes are available which are used for producing x-rays. • The electrons are accelerated towards the target • On striking the target the electrons transfer their energy to its metallic surface which gives off x-ray radiation
- 5. X-RAY TUBE : a. Positive voltage in the form of anode having a target. b. Battery to emit thermos ionic electrons. c. Cathode-filament of tungsten metal.
- 6. DIFFRACTION AND THE BRAGG’S LAW : • Bragg's Law was introduced by Sir W. H. Bragg and his son Sir W. L. Bragg. • According to the law, when the x-ray is incident on a crystal surface, its angle of incidence will reflect back with a same angle of scattering. • Diffraction will never occur, if Bragg's equation is not satisfied. • Bragg's Law means that diffraction can occur only when the following equation is satisfied:
- 7. PROCEDURE : First step- protein crystallization The process begins by crystallizing a protein of interest. 4 critical steps are taken to achieve protein crystallization: Purify the protein. Determine the purity of the protein and if not pure (usually>99%), then must undergo further purification. Protein must be precipitated by dissolving it in an appropriate solvent(water- buffer soln. w/ organic salt). The solution has to be brought to supersaturation by adding a salt to the concentrated solution of the protein. Let the actual crystals grow. Since nuclei crystals are formed this will lead to obtaining actual crystal growth.
- 8. • Second Step – xrays strike on crystal X-rays are generated and directed toward the crystallized protein. Then, the x-rays are shot at the protein crystal resulting in some of the x-rays going through the crystal and the rest being scattered in various directions. The crystal is rotated so that the x-rays are able to hit the protein from all sides and angles. The pattern on the emulsion due to scattering reveals much information about the structure of the protein. The intensities of the spots and their positions are thus are the basic experimental data of the analysis.
- 9. Third step : Mapping and analysis An electron density map is created based on the measured intensities of the diffraction pattern on the film. A Fourier Transform can be applied to the intensities on the film to reconstruct the electron density distribution of the crystal. The mapping gives a three-dimensional representation of the electron densities observed through the x-ray crystallography When interpreting the electron density map, resolution needs to be taken into account A resolution of 5Å - 10Å(angstrom) can reveal the structure of polypeptide chains, 3Å - 4Å of groups of atoms, and 1Å - 1.5Å of individual atoms.
- 10. INSTRUMENTATION : Source of X- Ray Collimator Monochromator • Filter • Crystal monochromator a) Flat crystal monochromator b) Curved crystal monochromator 10 Detectors • Photographic method • Counter method a) Geiger – Muller tube counter b) Proportional counter c) Scintillation detector d) Solid state semi conductor detectors e) Semi conductor detectors
- 11. 1. X rays source : The x-ray most common 15 source of x ray is an x ray tube. .The tube is evacuated and contains a copper block with metal target anode , and a tungsten filament cathode with high voltage between them. 2. Collimator : comprises of two closely packed metal plate which are 0.3mm apart from each other. The x ray beam originate from x ray source passes through this gap and follow single line path. 3. Monochromater : It act as Xray filter which removes unwanted rays ,generally 12-24 Armstrong rays has been in x ray. 4. Detector : the captured data has been send to computer for further processing by detector where 3D structure of crystal gets develop. Following detectors are used for detection: • Photographic method • Counter method 4. Geiger – Muller tube counter 5. Proportional counter 11
- 12. TYPES OF CRYSTAL : Crystal Lattice • A crystal lattice is a 3-D arrangement of unit cells. • Unit cell is the smallest unit of a crystal. • A crystal’s unit cell dimensions are defined by six numbers, the lengths of the 3 axes, a, b, and c, and the three inter axial angles, α, β and γ
- 13. Bravais Lattice Bravais Lattice refers to the 14 different 3-dimensional configurations into which atoms can be arranged in crystals.
- 16. APPLICATIONS : 1. Structure of crystals : • X-ray Diffraction Method is non-destructive and gives information on the molecular structure of the sample. • Comparing diffraction patterns from crystal of unknown composition with patterns from crystal of known compounds permits the identification of unknown crystalline compound. • This method can also be used to distinguish between a mixture of crystals. • It is occasionally necessary to check moving parts for metal fatigue, such as airplane wings. This check can be done by x-ray diffraction without removing the part from its position and without weakening it in the process of testing