[Gd(Try-TTDA)(H2O)]2−: A new MRI contrast agent for copper ion sensingElectronic supplementary information (ESI) available: Procedures for 17O NMR and dissociation constant (Kd), ESI mass spectra (S1, S2, S4, S6, S8), HPLC chromatograms (S3, S5), Job's plot (S7), determination of dissociation constant (S9), emission spectra (S10), and quenching plot (S11). See DOI: 10.1039/c1dt10033e

In this study, we have developed two new l-tryptophan based contrast agents [Gd(Try-TTDA)(H2O)]2−and [Gd(Try-ac-DOTA)(H2O)]−. Upon addition of Cu(ii) to [Gd(Try-TTDA)(H2O)]2−, significant increases in the relaxivity (r1) and hydration number of [Gd(Try-TTDA)(H2O)]2−were observed. However, it only induced a minute increase in the relaxivity (r1) in the case of [Gd(Try-ac-DOTA)(H2O)]−. 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)(H2O)]2−the indole fluorescence was completely quenched. Moreover, the [Gd(Try-TTDA)(H2O)]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 vitroMR imaging using [Gd(Try-TTDA)(H2O)]2−in the presence of Cu(ii) implicates that this new smart contrast agent ([Gd(Try-TTDA)(H2O)]2−) can serve as a Cu(ii) sensor for MR imaging. [ABSTRACT FROM AUTHOR]