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.