Interaction of biphenyl-functionalized Eu2+-containing cryptate with albumin: Implications to contrast agents in magnetic resonance imaging

The influence of albumin on the efficacy of a Eu2+-containing complex capable of interacting with human serum albumin (HSA) was investigated at different field strengths (1.4, 3, 7, 9.4, and 11.7 T). Relaxometric measurements indicated that the presence of albumin at higher field strengths (>3 T) did not result in an increase in the relaxivity of the Eu2+ complex, but a relaxation enhancement of 171 ± 11% was observed at 1.4 T. Titration experiments using different percentages (2, 4.5, 6, 10, 15, and 25% w/v) of HSA and variable-temperature 17O NMR measurements were performed to understand the effect of albumin on the molecular properties of the biphenyl-functionalized Eu2+ complex that are relevant to magnetic resonance imaging.