Seven-Coordinate CoII, FeII and Six-Coordinate NiII Amide-Appended Macrocyclic Complexes as ParaCEST Agents in Biological Media
| Autor: | Michael D. Daddario, Abiola O. Olatunde, Joseph A. Spernyak, Jordan M. Cox, Jason B. Benedict, Janet R. Morrow |
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| Rok vydání: | 2014 |
| Předmět: |
Macrocyclic Compounds
Magnetic Resonance Spectroscopy Stereochemistry Metal ions in aqueous solution Molecular Conformation Contrast Media Article Dissociation (chemistry) Inorganic Chemistry chemistry.chemical_compound Pentagonal bipyramidal molecular geometry Egg White Coordination Complexes Nickel Amide Octahedral molecular geometry Animals Ferrous Compounds Physical and Theoretical Chemistry Cobalt Nuclear magnetic resonance spectroscopy Amides 3. Good health Crystallography chemistry Proton NMR Rabbits Macrocyclic ligand |
| Zdroj: | Inorganic Chemistry |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | The solution chemistry and solid-state structures of the CoII, FeII, and NiII complexes of 7,13-bis(carbamoylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L) are reported as members of a new class of paramagnetic chemical exchange saturation transfer (paraCEST) MRI contrast agents that contain transition metal ions. Crystallographic data show that nitrogen and oxygen donor atoms of the macrocyclic ligand coordinate to the metal ions to generate complexes with distorted pentagonal bipyramidal geometry for [Co(L)]Cl2·2H2O or [Fe(L)](CF3SO3)2. The NiII complex [Ni(L)](CF3SO3)2·H2O features a hexadentate ligand in a distorted octahedral geometry. The proton NMR spectra of all three complexes show highly dispersed and relatively sharp proton resonances. The complexes were further characterized by monitoring their dissociation under biologically relevant conditions including solutions containing phosphate and carbonate, ZnCl2, or acidic conditions. Solutions of the paraCEST agents in 20 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (pH 7.4) and 100 mM NaCl showed highly shifted and intense CEST peaks at 59, 72, and 92 ppm away from bulk water for [Co(L)]2+, [Ni(L)]2+, and [Fe(L)]2+, respectively at 37 °C on a 11.7 T NMR spectrometer. CEST spectra with corresponding rate constants for proton exchange are reported in 4% agarose gel (w/w), rabbit serum, egg white, or buffered solutions. CEST phantoms of 4 mM complex in buffer, 4% agarose gel (w/w), or rabbit serum on a 4.7 T MRI scanner at 37 °C, are compared. The most substantial change was observed for the reactive [Ni(L)]2+, which showed reduced CEST contrast in rabbit serum and egg white. The complexes with the least highly shifted CEST peaks ([Co(L)]2+ and [Ni(L)]2+) showed a reduction in CEST contrast in 4% agarose gel (w/w) compared to that in buffered solutions, while the CEST effect for [Fe(L)]2+ in 4% agarose gel (w/w) was not substantially different. The crystal structures, solution chemistry, and CEST properties of FeII, CoII, and NiII complexes of 7,13-bis(carbamoylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane ligand (L) in rabbit serum, 4% agarose, egg white, and buffer solutions are compared. The [Ni(L)]2+ complex is the most reactive of all the complexes in serum and egg white, corresponding to the misfit of the NiII ion in the macrocyclic ligand cavity. |
| Databáze: | OpenAIRE |
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