Gadolinium chelate complex

Two types of micellar systems have been described, the first one includes Gd complexes capable of self-organization resulting in a supramolecular assembly 103), while the other class of micelles, also named mixed micelles is made of several components a lipophilic gadolinium chelate, one or several phospholipid(s) and a non-ionic surfactant containing a polyoxyethylene chain 104,105). 

The extra-renal excretion of the extracellular gadolinium complexes is negligible and no significant absorption after enteral application has been observed. The elimination half-life depends on the glomerular filtration rate, and on the cardiovascular function. No significant differences between the gadolinium chelates have been observed, their terminal half-lives in blood are in the range of 15 to 75 minutes in animals and 1-2 h in humans [65-67]. 

Another approach has been tackled with by Sessler et al. [37, 38] who described gadolinium(III) complexes with texaphyrins as potential MRI contrast agents. When the expanded porphyrin ring is subtituted by water solubilizing groups (Fig. 5), the chelate is sufficiently water soluble to be injected. It is... 

Lescop, C., Belorizky, E., Luneau, D. et al. (2002) Synthesis, stmctures, and magnetic properties of a series of lanthanum(III) and gadolinium(lll) complexes with chelating benzimidazole-substituted nitronyl nitroxide free radicals. Evidence for antiferromagnetic Gd - radical interactions. Inorganic Chemistry, 41, 3375-3384. 

Relaxation times measured with isotropic Gd(III) chelates can also be incorporated into the fitting process . Changes in relaxation times vary only with the distance (1/r ) from the gadolinium ion. Therefore, relative relaxation rates of the nuclei of the substrate provide relative distances from the gadolinium ion. Incorporation of relaxation data into the fitting process requires that the geometry of the gadolinium-substrate complex be identical to that of the other lanthanide-substrate complex used to measure shift data, which must be assumed with care . ... 

Hambright et al. (1988) have also studied the kinetics of displacement of the Gd " ion from the gadolinium(III) complex of TSPP by ethylenediaminetetraacetate (EDTA) giving Gd(EDTA) and H2(TSPP) as the main products. This represents the first example of metal removal from a metalloporphyrin by a chelating ligand. A mechanism has been proposed to account for the kinetic data. The water-soluble lanthanide complexes of TMPyP also undergo demetallation in the presence of EDTA (Haye and Hambright 1991). Similar to the acid solvolysis reactions, a linear relationship between log k and the ionic radius of the metal center can be established, and complexes with smaller metal center are more stable toward demetallation by EDTA. 

Carbon nanotubes have been also used as a macromolecular scaffold for Gdm complexes. An amphiphilic gadolinium(III) chelate bearing a C16 chain was adsorbed on multiwalled carbon nanotubes (264). The resulting suspensions were stable for several days. Longitudinal water proton relaxivities, r] showed a strong dependence on the GdL concentration, particularly at low field. The relaxivities decreased with increasing field as predicted by the SBM theory. Transverse water proton relaxation times, T2, were practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been... 

The requirements for a successful agent for the removal of radioactive actinides from the body are even more stringent than for the use of lanthanides in diagnosis. For gadolinium it is necessary that the hydroxypyridinonate complex is very stable, to avoid significant release of toxic Gd (aq), is sufficiently soluble, and has an appropriate HLB. For actinide elimination it is also necessary for the chelator to be sufficiently soluble and to have suitable targeting properties. It is also desirable that the chelator does not have such a... 

The modified Florence program is well-suited for fitting the experimental NMRD profiles for slowly-rotating complexes of gadolinium(HI), an S = 7/2 ion characterized by relatively low ZFS, whose electron spin relaxation can be considered to be in the Redfield limit. An example of fitting an NMRD profile for aqueous protons, using different methods, for a protein adduct of a Gd(HI) chelate capable of accommodating one water molecule in the first coordination sphere, is displayed in Fig. 11. Other examples will be provided in Chapter 3. 

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