In paramagnetic systems, characterized by the presence of unpaired electron(s) in molecular orbitals, a further interaction occurs, which is the dipole-dipole interaction between the electron magnetic moment and the nuclear magnetic moment. Since the magnetic moment of the free electron is 658.2 times larger than the magnetic moment of the proton, this interaction can contribute to the relaxation rate of a hydrogen nucleus at distance r from the unpaired electron(s), e.g. from a paramagnetic metal ion, much more than the dipole-dipole interaction between proton magnetic moments, even if the distance r is larger than the distance between hydrogen nuclei. In the presence of chemical exchange, this paramagnetic enhancement can be transferred to all water protons. The paramagnetic enhancement to the nuclear relaxation of bulk water protons (𝑅 1𝑝 ) is often described by the Solomon-Bloembergen-Morgan (SBM) equations 𝑅 1𝑝 = 𝑓 𝑀 (𝑅 1𝑀 -1 + 𝜏 𝑀 ) -1 (5)