2D HETERONUCLEAR NMR MEASUREMENTS OF SPIN-LATTICE RELAXATION-TIMES IN THE ROTATING FRAME OF X NUCLEI IN HETERONUCLEAR HX SPIN SYSTEMS

Theoretical and experimental aspects of T1p are discussed for a heteronuclear HX two-spin system (T1pX) where only the X nucleus is spin-locked. An expression for T1pX in terms of spectral density functions and the effective magnetic field parameters is developed. It shows that T1pX offers potentially different information about the spectral densities than either T1X, T2X, or the steady-state NOEx. We present a 2D heteronuclear NMR pulse sequence for measuring site-specific T1pX's in biomolecules. The sequence is based on a double-INEPT transfer and applies a spin lock to the heteronuclei for variable delays. If a weak on-resonance spin lock is used, and if the spectral density functions are assumed to be Lorentzians, then T1pX, is theoretically indistinguishable from T2x. We conclude with an application of the pulse sequence to the uniformly 15N-enriched protein eglin c. The T1pX data reflect the differential mobility in the molecule. © 1991.