Relaxation enhancing agent

Lauffer, R.B. (1991) Targeted relaxation enhancement agents for MRl. Magnetic Resonance in Medicine, 22, 339-342. 

Spin Labels. - Spin labels have traditionally been a tool of ESR spectroscopy, where the ESR resonance of the free radical label (usually a nitroxide-containing species, such as TEMPO) is observed directly. However, spin labels have increasingly become a tool of NMR as T1 relaxation enhancing agents. 

Protein-lipid interaction. Ellena et have studied the localization of perfluorocarbons in lipid membranes, using for this purpose Gd " and O2 as relaxation-enhancing agents of the resonance. 

Figure 8.6 The nitroxyl terminated dendrimer proton relaxation enhancement agent for potential use in MRI [46],...

All the Gd(III)-based contrast agents commercially available and those under development present one or more water molecules in their inner coordination sphere. The water molecule(s) is labile and the exchange from the coordination site in the complex and the bulk solvent represents the main source of the solvent relaxation enhancement. Therefore, the inner sphere longitudinal relaxivity is given by the following expression ... 

One possible route to design enzyme responsive agents is to synthesize paramagnetic inhibitors, whose binding to the active site of the protein can be signaled by the consequent relaxivity enhancement. An example of this approach has been provided by Anelli et al, who synthesized a linear Gd(III)... 

In the context of the development of new contrast agents for medical diagnostic imaging, the nanoparticulate carriers have indeed drawn special attention. These systems allow for an efficient site-specific delivery of targeted contrast agents and, due to their size, provide some relaxivity enhancement with respect to the isolated paramagnetic molecules. 

For monomer Gd(III) complexes the inner and outer sphere mechanisms contribute more or less to the same extent to the overall paramagnetic relaxation enhancement. The development of high relaxivity contrast agents mainly involves increasing the inner sphere term, since the outer sphere contribution can hardly be modified. For the new generation macromolecular agents, therefore, the inner sphere relaxivity becomes much more significant (over 90% of total relaxivity). 

Aime, S., Botta, M., Fasano, M., et al. (1996) Gd(III) complexes as contrast agents for magnetic resonance imaging a proton relaxation enhancement study of the interaction with human serum albumin. Journal of... 

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