Saturation Magnetization transfer

E. L. Lim, K. G. Hollingsworth, P. E. Thelwall and R. Taylor, Measuring the acute effect of insulin infusion on ATP turnover rate in human skeletal muscle using phosphorus-31 magnetic resonance saturation transfer spectroscopy. NMR Biomed., 2010, 23,952-957. 

From the functional form of Eq. (4.30) it is easy to predict the behavior of saturation transfer as a function of the exchange rate. When the rate constant for the B - A transformation (k i) is much smaller than the longitudinal relaxation rate of the nucleus in the B site (Rf), the saturation transfer tends to zero. When the rate constant is much higher, the saturation transfer tends to —1, i.e. there is a total transfer of magnetization to the B site when the A site is kept saturated. Note that these conditions are referred to as fast exchange, even if the exchange is still slow with respect to the chemical shift separation. Fast exchange conditions on the... 

Saturation transfer difference nuclear magnetic resonance experiments have shown that there is a strong interaction between the enzyme and the (R)-enantiomers of the alcohols, but not the (S)-enantiomers (H. W. Anthonsen, unpublished results). As described above, addition of a small amount of pure (R)-alcohols increased the 5-value of kinetic resolution and, moreover, the effect disappeared quickly. The reason is probably that the alcohol moves into the active site where it is esterified. A future goal is to find an additive that can bind irreversibly to this unknown allosteric site, thus causing a lasting effect. 

Figure 21 Saturation transfer experiment the downfield branch of the Pa doublet of 1 was inverted using a DANTE selective excitation pulse. The exchange of the magnetization was followed as a function of mixing time. T was found to be 1.26 s and exchange = 2.85 s at 300 K. (From J. M. Brown, and P. A. Chaloner and G. A. Morris (1987)/. Chem. Soc. Perkin Trans. 2, 1583. Reproduced by permission of The Royal Society of Chemistry)...

Ward, K.M., Aletras, A.H., and Balaban, R.S. (2000) A new class of contrast agents for MRl based on proton chemical exchange dependent saturation transfer (CEST). Journal of Magnetic Resonance, 143, 79—87. 

A second variation of saturation transfer experiment has been devised by Dalvit and coworkers that uses the transfer of magnetization from the water (167). Water is intimately associated with proteins being bound either within or on the surface of the macromolecu-lar structure. Saturation of the water resonance will lead to protein saturation through a variety of mechanisms, including saturation of the aH resonances, saturation of exchanging protein resonances, and NOE interactions between water and the protein. If a compound is bound to the protein it will also become saturated, and this effect can be used as an indication of ligand binding (167). 

Dowd T, Barac-Nieto M, Gupta RK, Spitzer A 31P nuclear magnetic resonance and saturation transfer studies of the isolated perfused rat kidney. Ren Physiol Biochem 12 161 -70,1989... 

Choice of magnetic field modulation frequency is based on the following considerations (1) minimization of noise by converting resonance information to a relatively noise-free frequency, (2) experiments where the field modulation is itself in the spin Hamiltonian and is a crucial physical parameter such as saturation transfer spec-... 

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