Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 26, Pages 10780-10785Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0702393104
Keywords
multifunctional imaging; MRI contrast agent; fluorescence dye; cell permeability
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We report a molecular platform for dual-function fluorescence/MRI sensing of mobile zinc. Zinc-selective binding units were strategically attached to a water-soluble porphyrin template. The synthetic strategy for achieving the designed target ligand is flexible and convenient, and the key intermediates can be applied as general building blocks for the construction of other metal sensors based on a similar mechanism. The metal-free form, (DPA-C-2)(2)-TPPS3 (1), where DPA is dipicolylamine and TPPS3 is 5-phenyl-10,15,20-tris(4-sulfonatophenyl)porphine, is an excellent fluorescent sensor for zinc. It has certain superior physical properties compared with earlier-generation zinc sensors including emission in the red and near-IR regions [lambda(em) = 645 nm (s) and 715 nm (m)], with a large Stokes shift of > 230 nm. The fluorescence intensity of 1 increases by > 10-fold upon zinc binding. The fluorescence turn-on is highly selective for zinc versus other divalent metal ions and is relatively pH-insensitive within the biologically relevant pH window. The manganese derivative, [(DPA-C-2)(2)-TPPS3Mn(III)] (2), switches the function of the molecule to generate an MRI contrast agent. In the presence of zinc, the relaxivity of 2 in aqueous solution is significantly altered, which makes it a promising zinc MRI sensor. Both metal-free and Mn(III)-inserted forms are efficiently taken up by live cells, and the intracellular zinc can be imaged by either fluorescence or MR, respectively. We anticipate that in vivo applications of the probes will facilitate a deeper understanding of the physiological roles of zinc and allow detection of abnormal zinc homeostasis for pathological diagnoses.
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