Chapter 2 Dipolar interactions and interatomic distances

Abstract

The accurate determination of the interatomic distances is a prerequisite to achieve the three-dimensional structure of peptides, proteins, and macromolecules. This chapter describes a protocol for rotational echo double resonance (REDOR) and rotational resonance (RR) experiments for this purpose. There is a description of a systematic procedure to construct the three-dimensional structure from these distance constraints. The chapter also discusses the fundamentals and applications to obtaining interatomic distances from the recoupled dipolar interaction. REDOR is extensively used to determine the relatively remote interatomic distance of 2-8 Ǻ. When a number of isolated pairs are involved in a REDOR dephasing, the REDOR transformation could be useful in determining interatomic distances because it yields single peaks in the frequency domain for each heteronuclear coupling strength. REDOR and RR methods have been used extensively to determine the three-dimensional structure of biomolecules because the pulse sequence and the data analysis to yield the interatomic distance are simpler compared with the other methods.