managed by ut-battelle for the department of energy dynamically polarized solid target for neutron...
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Managed by UT-Battellefor the Department of Energy
Dynamically Polarized Solid Target for Neutron Scattering
Josh Pierce,
J.K. Zhao
Oak Ridge National Laboratory
Don Crabb
University of Virginia
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The Spallation Neutron Source
• Completed May 2006.
• 1.4 MW, ~8x ISIS. the world’s recent leading pulsed spallation source.
• The peak neutron flux will be ~20–100x ILL, the world’s leading neutron scattering facility.
• SNS will be the new leading facility for neutron scattering.
• Room for eventual 24 instruments spanning physics, chemistry, biology, & materials science
3 Managed by UT-Battellefor the Department of Energy Presentation_name
Instruments and Sciences at SNS
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High-Flux Isotop Reactor (HFIR)
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Neutron Scattering Sciences at ORNL
Small Proteins
Micelles Colloids Vesicles
Critical Phenomena
Membranes
Crystal,Fiber,and
MagneticStructures
Liquids and Glasses
Polymers and Metals Alloys
Zeolites
Magnetic Films and Domains
Biological StructureViruses
d (Å)
Q (Å-1)Q (Å-1)
0.01 0.1 1 10 100
(meV
)10-5
10-4
10-3
10-2
10-1
100
101
102
103
104
d (Å)0.1110100
t (se
c)
10-16
10-15
10-14
10-13
10-12
10-11
10-10
10-9
10-8
Momentum Distributions
Itinerant Magnets
Crystal Fields
Molecular Vibrations
Lattice Vibrations
Small Molecule Diffusion
Large Scale Motions
Polymers and
Biological Systems
Tunneling Spectroscopy
Electron-Phonon Interactions
Hydrogen Modes
Molecular Reorientatio
n
Ultracold Neutrons Fundamental Physics
Slower Motions
Larger Objects
Q (Å-1)
d (Å)
Structure Dynamics
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Challenges in Biology
In post-genomics era, one of the main challenges in biology is From Gene to Structure and Function.
We know the basic principles of protein, RNA & DNA structure, the architectures of >20,000 proteins and of a few molecular machines. However, major challenges are still ahead.
Neutron scattering is a great tool for structural biology due to neutron’s sensitivity to hydrogen.
Polarization enhances neutron scattering’s ability greatly.
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Polarized Neutron Scattering
Hydrogen is the most abundant element in living matter (~50%), as well as in many other soft materials.
Hydrogen incoherent scattering is one of the largest sources of background.
Polarized neutron scattering from hydrogenous material drastically increases the signal-to-noise ratio.
00.0
148.5
1.8
42.0
14.7
79.8
106.4
0
20
40
60
80
100
120
140
160
-1 0 1
Proton Polarization
ProtonCoherent
Incoherent
Total
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Polarized Neutron Protein Crystallography
>10 fold increase in diffraction intensity.
>10 fold reduction in incoherent background.
Decrease data collection time.
Ability to study smaller crystals.
Reduce cost for sample generation by 1000 fold.
Allow better study of H/D exchange on protein surface and active sites.
Allow better studies on protein hydration.
Allow site-specific diffraction (combined with spin labeling).
Coherent Cross-seciton of a
typical sized protein (~40kDa)
10.47
0.85
25.82
0
5
10
15
20
25
30
-100% 0% 100%
[x 106]
Proton Polarization
d/d
(at
2 =0)
[ba
rn]
00
20
40
60
80
100
120
-1 0 1
Proton PolarizationTotal Cross-Section
[barn]
ProtonIncoherent
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Utilize Spin Diffusion
Presentation_name
• The size of the cluster ~ 15 Å in diameter.
• ~ 100 hydrogen atoms in the cluster.
• Use the ‘spin-cluster’ to spin label proteins.
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Experiments with polarized targets
50S Ribosome structure
Left: Crystal structure (Nissen et al 2000).
Right: Low resolution neutron scattering with polarized target (Zhao et al 1992). The experiment was carried out at the 5MW reactor. Similar result was NOT possible without polarized neutrons even at the best research reactor.
• Successfully demonstrated in solution scattering.
• Solution Scattering is low in information content.
• The future lies in high resolution studies.
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Dynamically Polarized Sample at SNS First stage: quick and portable
(between neutron beam lines) setup.– 7T solenoid & 5T compensated
magnet.– Using helium-4 cryostat.– Major components ready
(Magnet, MW generators, NMR, helium pumping system).
Second stage: custom and optimized setup for specific instruments, such as neutron protein crystallography:– Samples are very small (<< 1x1x1 mm3 ).– Compact apparatus needed.– Frozen spin mode desired.
Other applications: polarization filter for <1A neutrons.
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Case Study: EGV (ORNL-LDRD)
Davies et al, Biochemstry 34: 16210-16220 (2ENG.pdb)
Asp121: redAsp10: yellow
Endoglucanase V (EGV): What’s the catalytic mechanism.
– An important cellulase that catalyzes one of the steps in the breakdown of cellulose, a process which is critical for the production of biofuels.
– The active site of EGV resembles that of lysozyme, with Asp10 and Asp121 on each side of the groove.
– Asp121 is proposed to be the proton donor in the catalytic core.
– The pH-dependent protonation states of Asp121 is thought to correspond to the two conformers of Asp121.