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Measurements of the nuclear magnetic resonance relaxation times T1 and T2 of the water protons in aqueous solutions of nucleic acids and magnetic metal ions allow one to determine details about the metal-ion binding. When Mn2+ is bound, the rotation of its hydration sphere becomes slower, so that its effectiveness in reducing the proton T1 from its value in pure water is enhanced. This relaxation enhancement has been measured for Mn2+ bound to DNA, RNA, synthetic polynucleotides, and E. coli ribosomes. Compared to water as unity, the enhancement factors range from 3.7 for polyuridylic acid to 16.7 for polyadenylic acid. The equilibrium constants for binding, and the concentration of binding sites have been calculated from the dependence of enhancement upon Mn2+ concentration.
Eisinger et al. (Fri,) studied this question.