In situ shape and distance measurements in neutron scattering and diffraction

Neutron scattering combined with selective isotopic labeling and contrast matching is useful for obtaining in situ structural information about a selected particle, or particles, in a macromolecular complex. The observed intensities, however, may be distorted by inter-complex interference and by scattering-length-density fluctuations of the (otherwise) contrast-matched portions. Methods have been proposed to cancel out such distortions (Hoppe's method, the Statistical Labeling Method, and the Triple Isotopic Substitution Method). With these methods as well as related unmixed-sample methods, structural information about the selected particle(s) can be obtained without these distortions. We have generalized these methods so that, in addition to globular particles in solution, they can be applied to in situ structures of systems having underlying symmetry and/or net orientation as well. The information obtainable from such experiments is discussed.