SCATTERING OF NEUTRONS AND X-RAYS kiki k i - k f = q hω ENERGY TRANSFER hq MOMENTUM TRANSFER kfkf Dynamic structure factor O r,t COHERENT INCOHERENT SCATTERING g (r,t) g s (r,t) QUASIELASTIC DIFFUSIVE MOTIONS INELASTIC VIBRATIONAL COHERENT INCOHERENT STRUCTURAL FT [ g s (r, )] NUCLEAR PROB. DISTRIBUTION ELASTIC Elastic Quasielastic Inelastic Energy transfer, ω Δω e Δω q e S (q,ω) = e i(ωt-q·r) g(r,t) dr dt
Neutron Diffraction 1) Scattering from nuclei - combined x-n analysis of small molecules. 2) Scattering power does not depend on atomic number. - hydrogens scatter strongly - deuterium and hydrogen opposite signs. 3) Small-angle scattering - contrast matching. 4) Solution scattering with isotope substitution - partial structure factors. 4) Enzyme structures - proton positions - water structure - no solution to phase problem - large crystals required - need nuclear reactor or spallation source.
Protein Hydration. Svergun et al: First 3Å hydration layer ~10% denser than bulk water FRANCI MERZEL
Geometric R g from MD simulation = 14.1 0.1Å SMALL-ANGLE SCATTERING RADII OF GYRATION
Statistical Models of a Strongly Unfolded Protein
Low q : Size Radius of Gyration (R g ) Include Higher q : Chain Configurational Statistics q(Å -1 ) P(q) Small Angle Neutron Scattering
P(q) q(Å -1 ) Freely Jointed ChainsExcluded Volume Chains Phosphoglycerate Kinase in 4M GdnDCl R g Nat ~ 23Å R g Den ~ 90Å FJChains ANDREI PETRESCU PATRICK CALMETTES DOMINIQUE DURAND
EVB (Exluded Volume Beta) EVN (Exluded Volume Native) Low Resolution MC Simulation Scattering Profile of the Models Atomic Level Modeling LE (Locally Extended)
EVN EVB LE EVN EVB LE Snapshots of Atomic-Detail Models of Strongly-Unfolded PGK
Lattice Vibrations - PERIODIC in TIME and SPACE. - DISPERSION RELATIONSHIP between FREQUENCY and WAVEVECTOR OPTICAL ACOUSTICAL 0 1 l =180 o = =2l q= /l COHERENT INELASTIC NEUTRON SCATTERING
CRYSTALLINE L-ALANINE : LATTICE DYNAMICS EXPERIMENT - Triple-Axis Coherent Inelastic Neutron Scattering THEORY - (i) Ab Initio Quantum Chemistry H-Bond and Rotational Potentials (ii) Energy Minimization + Harmonic Analysis. PHONON DISPERSION CURVES CM -1 THz Calculated Experimental
COHERENT INELASTIC NEUTRON SCATTERING INTENSITIES INTENSITY SCATTERING VECTOR MODE POLARIZATION VECTOR CALCULATED EXPERIMENTAL b*direction
UREA-ALKANE INCLUSION COMPOUND DIFFUSIVE ALKANE DYNAMICS AT 180K Three Simulation Models Urea ‘HOST’ C 19 H 40 ‘GUEST’
QUASIELASTIC INCOHERENT NEUTRON SCATTERING Experiment compared with Simulation DIRECTION PARALLEL TO CHAIN AXIS DIRECTION PERPENDICULAR TO CHAIN AXIS = experiment 1 chain 3 chains 5 chains 10 chains
ROTATIONAL PROBABILITY DISTRIBUTIONS OF ALKANE CHAINS ROTATIONAL ANGLE, TWO SINGLE CHAINS Average Over Chains V( )= Rotational Potential Potential of Mean Force=-kTlogP( ) Elastic Incoherent Structure Factor Experiment & Simulation Converged (t ) Probability Distributions, P( )