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Helen Nguyen Chem. 12B Seminar Presentation Spring ‘05.

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Presentation on theme: "Helen Nguyen Chem. 12B Seminar Presentation Spring ‘05."— Presentation transcript:

1 Helen Nguyen Chem. 12B Seminar Presentation Spring ‘05

2 1. History of crystallography _ Definition and Greek roots _ 1895, W.C.Roentgen _ 1912, Max von Laue 2. How does it work and what does it use for? _ Useful in phase identification _ Cover the enumeration of the symmetry patterns 3. Methods and diffraction patterns. _ X-ray diffraction _ Electron diffraction _ Neutron diffraction 4. Determination of the first protein using crystallography _ Myoglobin _The experiment _ Brag’s law 5. Advantage and disadvantage 6. Elucidation relative stereochemistry.

3 Method uses to study crystals. Crystallon-solid Graphein means write X-ray Diffraction Electron Diffraction Neutron Diffraction

4 1895- W.C.Roentgen William Lawrence Bragg Determine the crystalline spacing for a number of substances. Collimated x-rays to diffract off of different crystal planes. Roentgen

5 What is Electron Diffraction? By firing a beam of electrons at a sample and observe their deflection. The electrons are deflected as waves, as in classical diffraction. Restriction? Performing of crystal? Scattered Electrons by…? Limitation of penetration? Transmission Electron Microscope (TEM).

6 Neutron Diffraction Determine the atomic structure of a material. Found in the atomic nucleus. All quantum particles can exhibit wave phenomena  associate with light or sound Requirements Interaction? Do not? Reveal? Neutrons v.s X-ray Helium atom (schematic) Showing two protons (red), two neutrons (green) and two electrons (yellow).

7 X-ray diffraction Visualize the electron clouds around atoms. Most important. Pattern? Analyzing The lattice is revealed Bragg's law Interact with the incoming X-ray photons to diffract them Myoglobin, Max Perutz and Sir John Cowdery Kendrew

8 How Brag’s law is used X-rays hit an atom Make the electronic cloud move Rayleigh scattering/Re-radiate waves Constructive/destructive

9 An Experiment Using X-ray Diffraction Study: a. how oxygen diffused within the protein b. how oxygen is finally released into the surrounding solvent Substitution of carbon dioxide Advantage?/Trigger ligand released The mutant L29F of myoglobin Conformational changes/ first few hundred picoseconds

10 Figure 1. 3D (left and center) and 2D (right) representations of the terpenoid, atisane. In the 3D model on the left, carbon atoms are represented by gray spheres, white spheres represent the hydrogen atoms and the cylinders represent the bonds. The model is enveloped in a "mesh" representation of the molecular surface, colored by areas of positive (red) and negative (blue) electric charge. In the 3D model (center), the light- blue spheres represent carbon atoms, the white spheres are hydrogen atoms, and the cylinders in between the atoms correspond to single-bonds.

11 How does X-ray Diffraction Apply to Current Days? Used to determine how drugs, such as anti- cancer medications Molecule must be crystallized/why? Determine a structure/Paintaking? Diffractometer, a machine that emits a beam of x-rays An X-ray picture (radiograph) taken by Röntgen Röntgen

12 X-ray Application Cont’ Diffraction images What important?/Problem solving--- combination and computational methods A model made up of atoms is built and refined against the observed data X-rays can reveal the details of bones and teeth

13 Conclusion X-ray, Neutron, and Electron are the three diffraction methods X-ray is the method that determined the first protein molecule which is myoglobin by Max Perutz and Sir John Cowdery Kendrew with the use of Brag’s law. Today X-ray is used to determine how drugs, such as anti-cancer medications

14 Bibliography MAT15/http://www.esrf.fr/UsersAndScience/Publications/Highlights/2003/Materials/ MAT15/


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