Register to reply

X-ray diffraction

by tahaha
Tags: diffraction, xray
Share this thread:
tahaha
#1
May1-14, 11:37 PM
P: 5
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!
Phys.Org News Partner Chemistry news on Phys.org
Ice cream goes Southern, okra extracts may increase shelf-life
The fluorescent fingerprint of plastics
Researchers develop models to study polyelectrolytes, including DNA and RNA
UltrafastPED
#2
May2-14, 04:53 AM
Sci Advisor
Thanks
PF Gold
UltrafastPED's Avatar
P: 1,908
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/Exp...n-density.html


Improved 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/cry.../unit_cell.php

This site has introductory tutorials on x-ray diffraction:
http://www.doitpoms.ac.uk/tlplib/xra...tion/intro.php


Detergents are a complicated question - see http://www.piercenet.com/method/dete...ein-extraction


Register to reply

Related Discussions
Problem with diffraction equations (diffraction and astrophysics) Introductory Physics Homework 1
Diffraction: how to know the amount of slits from a diffraction pattern? Introductory Physics Homework 0
Diffraction grating (missing diffraction beam) Introductory Physics Homework 4
Diffraction grating problem, missing orders, diffraction minimum and maximums. Introductory Physics Homework 1
Interference, Diffraction, Diffraction Grading General Physics 1