X ray crystallography and X ray Diffraction

This is the short description about x ray crystallography.
simplest and easy to understand.
Procedure of X ray Diffraction.
Advantages and Disadvantages of X ray Crystallography

1. X-RAY CRYSTALLOGRAPHY Presented By: Faisal Ur Rehman Roll Number: 16103 Department of Bioinformatics & Biotechnology

2. INTRODUCTION X-Ray Crystallography is a technique used for identifying the atomic and molecular structure of a crystal, in which the crystalline   atoms cause a beam of incident  X-rays   to   diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a  crystallographer  can produce a three-dimensional picture of the density of  electrons  within the crystal. From this  electron density , we can be determined: (i)- Positions of atoms within C rystal (ii)- Chemical bonds (iii)- Disorder (iv)- And various other Information's The method also revealed the structure and function of many biological molecules, including  vitamins , drugs ,  proteins  and  nucleic acids  such as  DNA .

3. HISTORY The British physicist Sir William Henry Bragg pioneered the determination of crustal structure ( arrangement of atoms, ions ) by X-ray diffraction methods. Using X-ray crystal data , Dr. James Watson and Dr. Francis Crick were able to determine the helix structure of DNA in 1953 . In 1998 Dr. Peter Kim , a scientist, was able to determine the structure of a key protein responsible for the HIV infection process . X-ray crystallography is a complex field that has been associated with several of science’s major breakthroughs in the 20th century

4. X-RAY DIFFRACTION X-Ray Crystallography uses the uniformity of light diffraction of crystals to determine the structure of a molecule or atom. Then they use an X-ray beam to “ hit ” the crystallized molecule . The electrons surrounding the molecule diffract as the X-rays hit them. This forms a pattern , this type of pattern is called the X-ray diffraction pattern . This is an X-ray diffraction pattern formed when X-rays are focused on a crystalline material , in this case a protein . Each dot, called a reflection , forms when X-rays passing through the crystal and scattered.

5. SINGLE X-RAY DIFFRACTION The oldest and most accurate method of X-ray   crystallography is single-crystal X-ray diffraction , in which a beam of X-rays strikes a single crystal , producing scattered beams. When they land on a piece of film or other detector , these beams make a diffraction pattern of spots ; the strengths and angles of these beams are recorded as the crystal is gradually rotated . Each spot is called a  reflection , since it corresponds to the reflection of the X-rays from one set of evenly spaced p laines within the crystal. For single crystals of sufficient purity and regularity , X-ray diffraction data can determine the mean chemical bond lengths and angles . Workflow for solving the structure of a molecule by X-ray crystallography

6. SINGLE X-RAY DIFFRACTION PROCESS

7. INSTRUMENT COMPONENTS OF X-RAY DIFFRACTION Generally a typical x-ray diffraction contain below parts : Detector X-ray source Crystal on the end of mounting needle Liquid nitrogen steam to keep crystal cold Movable mount to rotate crystal

8. PROCEDURE First Step : I n first-step, Researchers crystallize an atom or molecule , because the precise position of each atom in a molecule can only be determined if the molecule is crystallized. If the molecule or atom is not in a crystallized form, the X-rays will diffract unpredictably and the data retrieved will be too difficult but not impossible to understand. The crystal should be sufficiently large (typically larger than 0.1 mm in all dimensions), pure in composition and regular in structure , with no significant internal mistakes such as cracks or twinning .

9. Second Step : The crystal is placed in an intense beam of X-rays , usually of a single wavelength ( monochromatic X-rays ), producing the regular pattern of reflections . As the crystal is gradually rotated , previous reflections disappear and new ones appear; the intensity of every spot is recorded at every orientation of the crystal . Third & Final Step : In the third step, these data are combined computationally with complementary chemical information to produce and refine a model of the arrangement of atoms within the crystal . The final, refined model of the atomic arrangement now called a crystal structure is usually stored in a public database .

10. USES OF X-RAY CRSYTALLOGRAPHY Used to study many materials which form crystals like salts , metals , minerals , semiconductors , as well as various inorganic , organic and biological molecules . Also Use to determine electron density , the mean positions of the atoms in the crystal their chemical bonds , their disorder and various other information. Used for identification of Size of atoms , the lengths and types of chemical bonds . The method also revealed the structure and function of many biological molecules , including vitamins , drugs , proteins and nucleic acids such as DNA . Scientists also uses the X-ray crystallography to determine structure of HIV protease, that is a viral enzyme critical in HIV’s life cycle . X-ray diffraction technique has also been applied for analyzing the chemical composition of milk stones .

11. ADVANTAGES AND DISADVANTAGES OF X-RAY CRYSTALLOGRAPHY Advantages: X-ray is the cheapest, the most convenient and widely used method. X-rays are not absorbed very much by air , so the specimen need not be in an evacuated chamber . Disadvantages: They do not interact very strongly with lighter elements . It is relatively low in sensitivity .

12. CONCLUSION X-Ray crystallography allowed for the discovery of the structure of DNA . Allows researchers today to see how certain factors may effect protein structure . Allows researchers today to see how secondary protein structures in protein residues can fold depending on different environmental factors.

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