Thesis Title: Subtitle - NMR Spectroscopy Research Group

4 Chapter 1. Introduction.
In contrast to NOE or 3 J coupling effects that are short-range (measureable for distance
below 6 Å) and local (each measurement concerns an independent group of atoms), paramagnetic
NMR introduces new effects that are long-range (measured up to 40 Å), and global (i.e. their effect
is described for all spins in a common frame centered on the paramagnetic lanthanide).
1.2 Paramagnetic NMR
1.2.1 The four paramagnetic effects in NMR
When a paramagnetic centre with unpaired electrons, such as a lanthanide ion, is present in
a protein, the observed NMR spectrum changes due to induced paramagnetic effects. By
comparison of the diamagnetic and paramagnetic spectra, one can observe the following four
paramagnetic effects:
The pseudocontact shift (PCS): It is given by equation (1.1), where the spin of interest is
described by its polar coordinate in an internal frame (the Δχ-tensor frame) centered on the
paramagnetic center (Figure 1.2.a).
(1.1)
Δχax = χz – (χz + χy)/2 and Δχrh = (χx - χy) are respectively the axial and rhombic component
that describe the anisotropic effect; r, θ and θ are the polar coordinate of the spin in the Δχ-tensor
frame (Figure 1.2.a). The PCS is a long range effect (up to 40 Å) which decays with 1/r 3 , and is
measured as the difference between the paramagnetic and diamagnetic chemical shift (Figure 1.3).
The residual dipolar coupling (RDC): With an attached paramagnetic lanthanide, a
protein weakly aligns with respect to the magnetic field. RDCs are manifested as increases or
decreases of the magnitudes of multiplet splittings that can be observed in undecoupled NMR
spectra (Figure 1.3). The RDC can also be back-calculated (equation (1.2)) provided that the
orientation of the two spins with respect to the alignment tensor is known (Figure 1.2.b).
with:
(1.2)