contemporary hiftory
LEONARD editedFINE by: Columbia University New York. NY 10027
ERICS. PROSKAUER
Discovery of NMR Paramagnetic Shift Reagents Jasper A. Jackson' Los Alamos National Laboratory, Los Alamos, NM 87544
The concept of a paramagnetic shift reagent was conceived by Henry Tauhe in the summer of 1959 (Fig. 1) at Los Alamos, where he was a summer consultant. I t was instrumental in the first observation of adistinct signal from water in the first coordination sphere of an ion in aqueous solutiom2 At the time, we had been trying for more than a year to observe a separate oxygen-17 NMR signal from the first coordination sphere of cations in aqueous solution. These water molecules are relatively tightly hound (lifetimes >-I ms). No matter how we varied the solution and instrumental parameters, we saw only a single water signal. One morning, Taube came to the laboratory and said that while shaving he had had an idea: why not add a second (paramagnetic) ion to the solution? If the lifetime for exchange with bulk water of the water of hydration of this ion was short enough, then all the bulk water would experience an average shifted magnetic field and the hulk water signal would appear downfield from the original location. The water in the hydration sphere of the cation under study, with long residence time in its nonmagnetic environment, would appear as a second, unsbifted signal. Tauhe had been studying hydration of cations for several years and suggested adding Co2+ ions to the solution of aluminum perchlorate we had been studying. When we ran the spectrum, lo and hehold, there was a broadened, shifted peak representing bulk water and a small residual peak a t the unshifted position just as he had predicted. This was the first experiment illustrating the paramagnetic shift reagent principle. We then tested the shifting influence of the other iron group elements and the lanthanides. The rare earths were shown to be powerful shifters and, except for dysprosium, to broaden very little.3 Taken from the original paper in the Journal of Chemical Physics, Figure 2 shows H 2 0 signals from (heavy) water enriched two times over the normal oxvpen-17 abundance. -N\1R cpertrosropisti Trained on modern instruments may haw difficult!. rerugnizing the"peaks" in this spertrurn, but this was standard 30 years ago
Figure 1. Henry Taube (ca. 1960).
'Address correspondence to: 120 Sherwood, Los Alamos, NM 87544.
Jackson, J. A,; Lemons, J. F.: Taube, H. J. Chem. Phys. 1960,32, 553.
"ewis, W. B.; Jackson, J. A.; Phys. 1962, 36,694. 140
Lemons, J.
F.; Taube, H. J.
Journal of Chemical Education
Chem. Figure 2.Oxygen-I7 NMR spectrum.
