BME 210 Lecture 16 X-ray crystallography

BME 210 Lecture 16 X-ray crystallography - 16. X-ray...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
16. X-ray crystallography
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
X-ray crystallography X-ray crystallography - a method of determining the arrangement of atoms in a crystal using diffraction of X-rays • This is the main method for determination of the 3D structure of bio-molecules; it produced ≈49,000 structures • The other method, Nuclear Magnetic Resonance Spectroscopy, produced ≈8,000 structures
Background image of page 2
Bragg’s Diffraction • X-rays are shined on a 3- dimensional periodic structure (e.g., atoms in a crystal) Electronic clouds surrounding atomic planes scatter (reflect) X- rays • Rays reflected from two neighboring parallel atomic planes travel distances differed by 2a = 2d*sin( ) • Depending on the path difference, the two rays may interfere constructively or destructively producing bright or dark spots a X-rays
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
) sin( 2 d n Bragg’s Law • λ- the wavelength of x-rays • n - an integer • d - the spacing between the planes in the atomic lattice • θ- the angle between the incident ray and the scattering planes n 2 a Rays interfere constructively bright “reflections”
Background image of page 4
) sin( 2 d n Pattern of X-ray interference The interference pattern contains information about the atomic plane distances d Constructive interference crystals reflect X-rays only at certain angles of incidence ( ), which are determined by atomic plane distances
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
X-rays X-rays - electromagnetic radiation with photon energy of ≈ 20-150 keV (wavelength λ 0.1 - 0.01 nm) 1 eV - energy acquired by electron passing voltage difference of 1 V Photon energy, E: E = q e V = hν = hc/λ λ = hc/E h – Planck constant (6.63*10 -34 Js) ν – photon frequency λ – photon wavelength c – speed of light (3*10 8 m/s) q e – electron charge (1.6*10 -19 C) V – voltage difference X-rays wavelength (0.1 - 0.01 nm) is comparable to inter-atomic distances they can be used for structural studies X-rays were discovered by W. Roentgen in 1895. Nobel Prize in 1901
Background image of page 6
Diffraction pattern of arbitrary structure The X-ray diffraction pattern of an arbitrary structure is the Fourier Transform of its electron density: Electron density Diffraction Pattern FT
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/28/2010 for the course BME eng. biolo taught by Professor Fast during the Spring '10 term at University of Alabama at Birmingham.

Page1 / 27

BME 210 Lecture 16 X-ray crystallography - 16. X-ray...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online