Applications of SANS I

SANS with Magnetic Contrast  n = eh 2mp neutron magnetic moment Neutrons are scattered by inhomogeneities in the scattering length density of a material Chemical contrast ( ) 2  (  p  o ) 2 “particle” matrix And, by inhomogeneities in the magnetization (magnetic moment per unit volume) of a material Magnetic contrast (M) 2  (M p  M o ) 2 SANS with Magnetic Contrast Inhomogeneities in magnitude and direction of M produce scattering, e.g. domain walls Q I(Q┴) ┴ I(Q) Sample with randomly oriented Magnetic domains Magnetic contrast   2 (M)  (M p  M o ) 2 SANS with Magnetic Contrast By aligning magnetic domains with an applied magnetic field, domain wall scattering is eliminated Q I(Q ) ┴ I(Q) Sample with randomly oriented Magnetic domains Magnetic contrast   2 (M)  (M p  M o ) 2 SANS with Magnetic Contrast (unpolarized neutrons) Magnetic contrast I(Q┴) (M) 2  (Mp  M o ) 2 Nuclear contrast I(Q) ( ) 2  (  p  o ) 2 “particle” matrix I(Q)  ( 2  M2 sin 2 φ) F2 (Q) S(Q)  similar terms for each species I(Q )  2  M 2  I(Q|| )  2 Magnetic scattering comes From M  Q only! Using SANS to Correlate Radiation Dose with Microstructural Changes in Reactor Pressure Vessel Steels G. R. Odette, G. Lucas, et al. (U. California at Santa Barbara) Reactor Vessel Measurements aimed at determining what factors and mechanisms cause reactor vessels to embrittle SANS is particularly useful because of its sensitivity to both chemical and magnetic inhomogeneities Typical SANS Patterns for Reactor Pressure Vessel Steels Irradiated sample Unirradiated sample H H log I(Q) I(Q ) Carbide Precipitates Irradiated sample Irradiated sample I(Q|| ) Copper-rich Precipitates Small Cavities Q I(Q )  2  M 2  I(Q|| )  2 = 11 for pure Cu = 1.5 for voids Type II Superconductor Mixed state Normal state H (kG)  H Hc2 mixed state normal conductor Hc1 T (K) Meissner state Complete flux penetration Complete magnetic flux exclusion Diffraction from fluxoid lattices Neutron diffraction reveals: SANS 2D detector • fluxoid size, shape and interface thickness • fluxoid lattice symmetry • fluxoid interactions • details of phase tranisitions • strength of pinning centers n  H Sample in mixed state with magnetic field along beam direction Vortex Matter in Superconductor Nb T=4.6 K 3.05 kG Real space depiction of vortex lattice H (kG) Hc2 Hc1 T (K) 2.15 kG 3.75 kG 1.1 kG 4.1 K 4.4 K 4.6 K X. S. Ling and S.-R. Park (Brown University) S.-M Choi, D. Dender and J. Lynn, (NCNR/NIST) Characterization of Protein/RNA Complexes: Contrast Variation Deborah Kuzmanovic, Catherine O’ Connell, NIST Biotech. Div. Susan Krueger, NIST NCNR Charles Wick, Aberdeen Proving Ground MS2 Bacteriophage Small Angle Scattering from Macromolecules in Solution Reciprocal Space Form Factor, F(q) =  Real Space Macromolecule in Solvent Scattering Length  Density, ρ( r ) in V  V ρ(r ) e  i q r  dr  + s (0) ρs  V e i q r  Solvent of Infinite Extent (Not Observed!) dr  Scattering Length Density, ρs in V  2 I(q)  n  F(Q)  SANS Data Analysis Low Angles: QRg ~ 1 2 2 Radius of Gyration (Rg) - 13 Q R g Guinier Approx. I(Q)  I(0) e   Not model specific Simple shape models from Rg, Mw and V I(0)/c = constant x Mw Higher Angles:   Model specific Calculate I(Q) for model and compare to data Distance Distribution Function P(r)  r 2γ(r) Debye-Porod Correlation Function 4P(r)  number of distances within the molecule I(Q)  4V  P(r) sin(Qr) dr 0 Qr Dmax  maximum distance within the molecule Dmax P(0) = 0 P(2rDmax) = 0 Standard Assays for Diseases Commercially available model recombinant noninfectious virus can be used as a RNA carrier Any gene (RNA) for a disease of interest can be incorporated for use in clinical assays. Promoter Coat Protein Standard RNA Packaging Vector Transcription Translation 1 Standard RNA Assembly 90 Dimers One Particle of Armored RNATM Samples for SANS Measurements  WT MS2 phage (3500bp) – Wild-type – Found in nature – Infectious (to bacteria only)  Empty capsid (0bp) Recombinant RNA samples:  Lambda phage (1000bp)  HCV (500bp) IS there one RNA per capsid? Capsid and WT MS2 Protein Capsid and WT MS2 protein structures look similar when measured in 65% D2O solvent, where I(Q)RNA ~ 0. Contrast Variation of MS2 Complexes Deuterated Lipid Head Group CD2 RNA Core Protein Shell Contrast () Lipid Head Group CH2 Structure and Mw Determination Scattered intensity and Mw from protein and RNA components can be determined separately by making measurements at several contrasts. I(q) = 12 I1(q) + 1 2I12(q) + 22 I2(q)      I(0) n  2     1    Δρ  Δρ1  2     Mw1    Mw 2 N A d1  d  N  A 2           Knowns: 1, 2: contrast for components 1 and 2 contrast: Δρ ρ - ρs d1, d2: mass density for components 1 and 2 n: Mw-independent number density (IVDS) Structure and Mw of WT MS2 Phage SANS+IVDS Results Protein Mw= 2.5(±0.3) x106 RNA Mw= 1.0(±0.2) x106 Total Mw= 3.5(±0.5) x106 RNA in core packs tightly within a radius of ~ 80Å. Structure of MS2 Complexes Wild-type MS2 HCV Armored RNATM 0% and 10% D2O: RNA scattering is strongest 100% D2O: RNA scattering is weaker 85% D2O: RNA scattering is weakest Structure of MS2 Complexes Wild-type MS2 HCV Armored RNATM Protein shell is less well-defined in HCV particles. RNA is not as tightly packed in HCV particles. Conclusions       Empty capsid and WT MS2 protein shell have similar structures. Protein shell is thicker and less well-defined in HCV and  particles. RNA is WT MS2 is tightly packed within a radius of ~80Å. RNA is not as tightly packed in HCV and  particles. Mw measurements confirmed the known amounts of protein and RNA in WT MS2. Freshly prepared HCV and  particles likely contain more than one RNA per capsid.