Unraveling X-Ray Diffraction: Questions & Answers

In summary, the conversation discusses the use of x-ray crystallography in characterizing proteins, with a focus on improving resolution and understanding the role of unit cells and detergents. The resolution is affected by factors such as crystal size and purity, and the choice of unit cell is arbitrary as long as it contains all atoms of the molecule. Detergents can interfere with crystallization and more information can be found on their effects online.
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tahaha
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I'm working on a physical chemistry project that is a report on a paper that uses X-ray crystallography to characterize a protein. So I am studying X-ray crystallography more in depth than the book introduces, and I have a few questions that I couldn't really find answers to online.

1. How does measuring more diffraction peaks improve resolution? Does that mean a LARGER crystal improve resolution? (I don't think it's that simple...)

2. How is the resolution defined? People online seem to say that the limit is wavelength/2, but I'm having trouble deriving it from the Bragg Law (I think a larger diffraction angle means higher resolution?)

3. Regarding the unit cell, do you just "choose" the shape and dimensions of the unit cell (square, triangular, oblique, etc.) as long as it contains at least one of each atom of your molecule? How does this choice affect the resolution?

4. This is pretty much a technical question: How do detergents interrupt crystallization?

Thank you!
 
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Resolution is related to the instrument being used, as well as the sample. Larger, purer crystals give better data; if you are using powder diffraction then the purity is important, as well as the total quantity of material. See
http://www.proteinstructures.com/Experimental/Experimental/electron-density.htmlImproved separation of the diffraction peaks requires pure materials, or a binder that is "transparent" to the x-rays. Analysis is improved with more peaks and accurate intensity measurements - just imagine if the peaks were blurred together ...

The choice of unit cell arbitrary - as long you can "tile" the entire crystal with it; see http://www.doitpoms.ac.uk/tlplib/crystallography3/unit_cell.php

This site has introductory tutorials on x-ray diffraction:
http://www.doitpoms.ac.uk/tlplib/xray-diffraction/intro.phpDetergents are a complicated question - see http://www.piercenet.com/method/detergents-cell-lysis-protein-extraction
 
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1. What is X-Ray Diffraction?

X-Ray Diffraction is a technique used to study the structure of materials at the atomic level. It involves shining a beam of X-rays onto a sample and analyzing the resulting diffraction pattern to determine the arrangement of atoms within the material.

2. How does X-Ray Diffraction work?

X-Rays have a very short wavelength, allowing them to interact with the atomic structure of a material. When an X-ray beam strikes a sample, it causes the atoms to diffract the X-rays in different directions. The resulting diffraction pattern is captured by a detector and can be used to analyze the atomic arrangement of the material.

3. What types of materials can X-Ray Diffraction be used on?

X-Ray Diffraction can be used on a wide range of materials, including crystals, powders, thin films, and liquids. It is commonly used in the fields of chemistry, physics, materials science, and geology to study the atomic structure of various substances.

4. What information can be obtained from X-Ray Diffraction?

X-Ray Diffraction can provide valuable information about the crystal structure, lattice parameters, and interatomic spacing of a material. It can also be used to identify the type of crystal structure present and determine the orientation of the crystal lattice.

5. Are there any limitations to X-Ray Diffraction?

While X-Ray Diffraction is a powerful tool for studying the atomic structure of materials, it does have some limitations. It is unable to provide information about the arrangement of atoms in non-crystalline materials, such as liquids or glasses. It also cannot detect the presence of impurities or defects in a crystal lattice.

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