Six, Seven or Eight Coordinate FeII, CoII or NiII Complexes of Amide-Appended Tetraazamacrocycles for ParaCEST Thermometry

FeII, CoII and NiII complexes of two tetraazamacrocycles (1,4,8,11‐tetrakis(carbamoylmethyl)‐1,4,8,11‐tetraazacyclotetradecane (L1) and 1,4,7,10‐tetrakis(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane (L2) show promise as paraCEST agents for registration of temperature (paraCEST=paramagnetic chemic...

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Bibliographic Details
Published in:Chemistry : a European journal 2015-12, Vol.21 (50), p.18290-18300
Main Authors: Olatunde, Abiola O., Bond, Christopher J., Dorazio, Sarina J., Cox, Jordan M., Benedict, Jason B., Daddario, Michael D., Spernyak, Joseph A., Morrow, Janet R.
Format: Article
Language:English
Subjects:
chemical exchange saturation transfer
Chemistry
imaging agents
macrocycles
magnetic resonance imaging
NMR spectroscopy
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Summary:FeII, CoII and NiII complexes of two tetraazamacrocycles (1,4,8,11‐tetrakis(carbamoylmethyl)‐1,4,8,11‐tetraazacyclotetradecane (L1) and 1,4,7,10‐tetrakis(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane (L2) show promise as paraCEST agents for registration of temperature (paraCEST=paramagnetic chemical exchange saturation transfer). The FeII, CoII and NiII complexes of L1 show up to four CEST peaks shifted ≤112 ppm, whereas analogous complexes of L2 show only a single CEST peak at ≤69 ppm. Comparison of the temperature coefficients (CT) of the CEST peaks of [Co(L2)]2+, [Fe(L2)]2+, [Ni(L1)]2+ and [Co(L1)]2+ showed that a CEST peak of [Co(L1)]2+ gave the largest CT (−0.66 ppm oC−1 at 4.7 T). NMR spectral and CEST properties of these complexes correspond to coordination complex symmetry as shown by structural data. The [Ni(L1)]2+ and [Co(L1)]2+ complexes have a six‐coordinate metal ion bound to the 1‐, 4‐amide oxygen atoms and four nitrogen atoms of the tetraazamacrocycle. The [Fe(L2)]2+ complex has an unusual eight‐coordinate FeII bound to four amide oxygen atoms and four macrocyclic nitrogen atoms. For [Co(L2)]2+, one structure has seven‐coordinate CoII with three bound amide pendents and a second structure has a six‐coordinate CoII with two bound amide pendents. Changes in coordination affect MRI contrast: The remarkably different chemical exchange saturation transfer (CEST) spectra of CoII, FeII or NiII complexes of amide‐appended macrocycles is based on the different coordination geometries for complexes of the two ligands. The complexes with the most highly shifted CEST peaks show promise for the development as magnetic resonance imaging (MRI) temperature probes for thermometry.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201503125