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

2 Managed by UT-Battellefor the Department of Energy Presentation_name

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

4 Managed by UT-Battellefor the Department of Energy Presentation_name

High-Flux Isotop Reactor (HFIR)

5 Managed by UT-Battellefor the Department of Energy Presentation_name

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

6 Managed by UT-Battellefor the Department of Energy Presentation_name

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.

7 Managed by UT-Battellefor the Department of Energy Presentation_name

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

8 Managed by UT-Battellefor the Department of Energy Presentation_name

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

9 Managed by UT-Battellefor the Department of Energy

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.

10 Managed by UT-Battellefor the Department of Energy Presentation_name

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.

11 Managed by UT-Battellefor the Department of Energy Presentation_name

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.

12 Managed by UT-Battellefor the Department of Energy Presentation_name

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.