Zwitterionic Manganese and Gadolinium Metal–Organic Frameworks as Efficient Contrast Agents for in Vivo Magnetic Resonance Imaging

Two water-stable three-dimensional Mn- and Gd-based metal–organic frameworks (MOFs), {[Mn2(Cmdcp)2(H2O)2]·H2O}n (1) and {[Gd­(Cmdcp)­(H2O)3]­(NO3)·3H2O}n (2, H3CmdcpBr = N-(4-carboxy benzyl)-(3,5-dicarboxyl)­pyridinium bromide), have been prepared and analyzed. In vitro magnetic resonance imaging indicated that MOFs 1 and 2 possess relaxivity r1 values of 17.50 and 13.46 mM–1·S–1, respectively, which are superior to that of the control Gd-DTPA (r1 = 4.87 mM–1·S–1, DTPA = diethylene triamine pentaacetate). MOFs 1 and 2 also possessed good biocompatibility and low cytotoxicity against a model cell line. In vivo magnetic resonance images of treated Kunming mice indicated that kidneys showed remarkably positive signal enhancement after 15 min with intravenous administration of MOF 1 and the hyperintensity of both kidneys persisted for about 240 min with no obvious tissue damage. MOF 1 is therefore promising in vivo probes for imaging intravascular diseases and renal dysfunction.