High relaxivity linear Gd(DTPA)-polymer conjugates: The role of hydrophobic interactions
✍ Scribed by Kenneth E. Kellar; P. Mark Henrichs; Robert Hollister; Seymour H. Koenig; Jennifer Eck; Donna Wei
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 616 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0740-3194
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✦ Synopsis
Abstract
A series of linear copolymers of DTPA‐class Gd^3+^ conjugates, linked by α,ω‐alkyldiamides with a varying number (n) of methylenes separating the amide function, were synthesized. Surprisingly, their relaxivities at all fields increased with increasing n. At MRI fields and 35°C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer‐based Gd^3+^ chelates. The magnetic field dependence of solvent proton 1/T~1~ was measured for aqueous urea‐free and urea‐containing polymer solutions. The results for urea‐free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic interactions of the methylene groups with solvent. This hypothesis is supported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions. The relaxivities are also independent of polymer concentration, indicating that the hydrophobic interactions are intramolecular.