POLARIZED NEUTRON SCATTERING FROM POLARIZED NUCLEAR SPINS. H. B. Stuhrmann¹, B. van den Brandt², P. Hautle², J. A. Konter², S. Mango², T. O. Niinikoski³, M. Schmitt¹, R. Willumeit¹, J. Zhao¹, K. H. Nierhaus^{4, 1)}GKSS Forschungszentrum D-21502 Geesthacht, Germany, ²⁾Paul Scherrer Institut, CH-5232 Villigen, Switzerland, ³⁾T. O. Niinikoski, CERN-PPE, CH-1211 Geneva, Switzerland, ⁴⁾K. H. Nierhaus, MPI für Molekulare Genetik, D-14195 Berlin, Germany

The scattering amplitude of neutron scattering by protons is known for its strong dependence on the polarization direction of the interacting spins. Polarized deuterons show a much weaker effect. This is the basis for nuclear spin contrast variation which is applied to the study of the in situ structure of macromolecular components of complex assemblies (1). Results of polarized neutron scattering from protonated tRNA in a deuterated ribosome clearly differentiate between the pretranslocational and the postranslocational state of the functional complex. Moreover the site of a small protonated mRNA fragment (14 kD) bound to the completely deuterated functional complex of the ribosome could be identified.

The alternative to 'pre-contrasting' by isotopic substitution is the creation of contrast by selective nuclear spin depolarization or even better by reversal of nuclear spin polarization using the method of adiabatic fast passage. In dynamically polarized targets a frequency limited rf scan across the NMR profile acts preferentially on nuclei which are not close to the paramagnetic centers. The polarization of the nuclear spins near unpaired electrons remains unchanged. The size and the lifetime of the electronic spin label bound nuclear polarization domains appears to be largely spin diffusion controlled.

(1) H. B. Stuhrmann, N. Burkhardt, G. Dietrich, R. Jünemann, W. Meerwinck, M. Schmitt, J. Wadzack, R. Willumeit, J. Zhao, K. H. Nierhaus (1995) Nucl. Instr. and Methods A 356 124-132