XRay Diffraction I XRay Diffraction Uses XRays to identify the arrangement of atoms molecules or ions within a crystalline solid Quantitative and qualitative Ooi L Principles of Xray Crystallography ID: 253285
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Slide1
(X-Ray Crystallography)
X-Ray DiffractionSlide2
I. X-Ray Diffraction
Uses X-Rays to identify the arrangement of atoms, molecules, or ions within a crystalline solid
Quantitative and qualitative
Ooi
, L.
Principles of X-ray Crystallography
(2010)Slide3
A. X-Rays
0.1 – 100 Angstroms (
Å)Useful Range: 0.5 – 2.5 ÅSlide4
B. Amorphous Substances
1. Gases and Liquids
Extremely difficult
2. Non-crystalline Solids
Atoms are not regularly arranged or regularly shapedInterferenceFiber DiffractionSlide5
Atoms
are
regularly arranged
“The Unit Cell” – a cookie cutter
C
.
Crystalline Solids
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd
ed.
(2006)Slide6
II. X-Ray C
rystallography
A. Small-molecule crystallography
Up to ~100 atomsOrganic molecules, catalysts, newly synthesized drugs, etc.
Identify each atomB. Macromolecular (protein) crystallography Large biological molecules – nucleic acids and proteinsIdentify 2° structureNote: must show that the crystal structure (asymmetric unit) is comparable to structure in solution (biological unit) Slide7
III. X-Ray
Diffractometer
Ooi
, L. Principles of X-ray Crystallography
(2010)Slide8
A. X-Ray Source
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd ed. (2006)
1. X-Ray Tube (a)2. Rotating Anode (b) Slide9
3. Particle Storage Ring (Synchrotron Radiation)
Particle Accelerator
Ooi
, L.
Principles of X-ray Crystallography
(2010)Slide10
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd
ed.
(2006)
National Synchrotron Light Source at Brookhaven National Lab (Long Island)
Slide11
B. Collimator
Narrow metal tube that selects and reflects the X-Rays into parallel paths
Ooi, L. Principles of X-ray Crystallography (2010)Slide12
C. Crystal (Sample)
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd ed. (2006)
1. Growth – Screens Crystal vs. useless blob2. OptimizationQuantity3. Crystal QualityPurity
4. Mount for Data Collection
Cryocrystallography
Note:
Diffracted in “mother liquor”Slide13
D. Camera
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd ed. (2006)
Goniometer
Goniostat
Slide14
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd
ed.
(2006)Slide15
E. Detector
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd ed. (2006)
1. Charged Couple Device (CCD)2. Image Plate (IP) Slide16
IV. Data Analysis
Measure intensity and position of diffracted
X-Rays
Intensity: strength of diffracted beamPosition:
direction in which beam was diffracted by the crystal
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd
ed.
(2006)Slide17
Ooi
, L.
Principles of X-ray Crystallography
(2010)
Computer calculates this data from the diffraction
patternSlide18
A. Fournier Sum
Based on simple waves
f(x) = F
cos 2π
(hx + α)
F = f
0
+ f
1
+ f
2
+ …Rhodes, G. Crystallography Made Crystal Clear, 3rd ed. (2006)Slide19
B. Bragg’s Law
States: diffraction spots occur when 2
d sin θ = n
λ
Rhodes, G.
Crystallography Made Crystal Clear, 3
rd
ed.
(2006)Slide20Slide21Slide22
Molecular structure in solid crystalline state with extreme certainty
Direct inference of data
Provides limitless info.
CrystalsSlow
HydrogenStill just a modelBenefits
Downfalls