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 (H2 O)2 ]·H2 O}n (1) and {[Gd(Cmdcp)(H2 O)3 ](NO3 )·3H2 O}n (2, H3 CmdcpBr = 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.