Gd(Try-TTDA)(H2O)]2-: a new MRI contrast agent for copper ion sensing

In this study, we have developed two new L-tryptophan based contrast agents Gd(Try-TTDA)(H(2)O)](2-) and Gd(Try-ac-DOTA)(H(2)O)](-). Upon addition of Cu(II) to Gd(Try-TTDA)(H(2)O)](2-), significant increases in the relaxivity (r(1)) and hydration number of Gd(Try-TTDA)(H(2)O)](2-) were observed. However, it only induced a minute increase in the relaxivity (r(1)) in the case of Gd(Try-ac-DOTA)(H(2)O)](-). Furthermore, the interaction of Cu(II) with the indole ring of Gd(III) complexes was explored by measuring the intrinsic fluorescence of the tryptophan of the Gd(III) complex. With the addition of one equivalent of Cu(II) to Gd(Try-TTDA)(H(2)O)](2-) the indole fluorescence was completely quenched. Moreover, the Gd(Try-TTDA)(H(2)O)](2-) complex shows excellent selectivity towards Cu(II) over other metal ions (Cu(II) > La(III) > Mg(II)). Importantly, the significant signal intensity (2073 ± 67) for in vitro MR imaging using Gd(Try-TTDA)(H(2)O)](2-) in the presence of Cu(II) implicates that this new smart contrast agent (Gd(Try-TTDA)(H(2)O)](2-)) can serve as a Cu(II) sensor for MR imaging.