Paramagnetic chemical exchange

PARACEST Paramagnetic Chemical Exchange Saturation Transfer TPA Two-Photon Absorption... 

Hammell J, Buttarazzi L, Huang C-H, Morrow JR. Eu(III) complexes as anion-responsive luminescent sensors and paramagnetic chemical exchange saturation transfer agents. Inorg Chem. 2011 50 4857 867. 

Beside classical MRI, based on the measurement of water abundance in tissues and variation of its relaxation rates, other techniques such as chemical exchange saturation transfer (CEST) and its improved form using paramagnetic compounds (PARACEST) are currently investigated to improve the potential of MRI diagnosis. 

In analogy with the chemical shift, the relaxation rates of the bulk nuclei will be termed / id and Ri. In the presence of chemical exchange with nuclei in the paramagnetic site, such rates will be enhanced by an amount V ip or Rip, and the measured values will be... 

Fig. 8.4. The first EXSY experiment on a paramagnetic system [1] the 300 MHz spectrum, taken with mixing time of 50 ms, shows species in chemical exchange belonging to two different redox states of a cytochrome d, a protein containing four low spin hemes. The signals marked M1-M7 represent various heme methyl groups. EXSY cross peaks are observed between M, of two species containing two (II) or three (III) oxidized hemes, respectively.

For any nucleus i of a paramagnetic lanthanide complex in the absence of significant chemical exchange, the experimental longitudinal (l/7 p) and transversal (1 /7 xp) nuclear relaxation rates are given by eqs. (4), (5) in which 7]dia corresponds to the characteristic relaxation times of the same nucleus i in the analogous diamagnetic complex (R = La, Y, Lu) and 7)para are... 

For a paramagnetic protein molecule such as deoxy-Hb, the 7V1 and 7V1 values in the absence of chemical exchange have been calculated as the sum of the dipole-dipole interactions... 

Addition of a small amount of a paramagnetic lanthanide shift reagent to a solution of ligand results in chemical shift of the ligand NMR spectrum which is proportional to Ln/L ratio at low values. The condition of rapid chemical exchange must prevail when tb, the mean lifetime of the complex is much shorter than 1 /Ab. The condition is Tb [Pg.796]

---