Isomeric Co(<scp>ii</scp>) paraCEST agents as pH responsive MRI probes

Bond, Christopher J.; Cineus, Roy; Nazarenko, Alexander Y.; Spernyak, Joseph A.; Morrow, Janet R.

doi:10.1039/c9dt04558a

Cited by 16 publications

(21 citation statements)

References 31 publications

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“…The solution 1 H NMR data for [Co(L1)] 2+ and [Co(L2)] 2+ , as described above, in conjunction with the structural data support the predominance of the cis ‐I form in solution. The minor form of [Co(L1)] 2+ is most likely the 1,4‐isomer in trans ‐III form, based on comparison of proton shifts to that of the [Co(L4)] 2+ isomers . The z ‐spectra of the two complexes also support this analysis by showing weak CEST peaks characteristic of OH exchangeable protons bound to Co II .…”

Section: Resultsmentioning

confidence: 74%

Co^II Complexes as Liposomal CEST Agents

et al. 2020

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Three paramagnetic CoII macrocyclic complexes containing 2‐hydroxypropyl pendant groups, 1,1′,1′′,1′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetrakis‐ (propan‐2‐ol) ([Co(L1)]2+, 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(propan‐2‐ol) ([Co(L2)]2+), and 1,1′‐(4,11‐dibenzyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐diyl)bis(octadecan‐2‐ol) ([Co(L3)]2+) were synthesized to prepare transition metal liposomal chemical exchange saturation transfer (lipoCEST) agents. In solution, ([Co(L1)]2+) forms two isomers as shown by 1H NMR spectroscopy. X‐ray crystallographic studies show one isomer with 1,8‐pendants in cis‐configuration and a second isomer with 1,4‐pendants in trans‐configuration. The [Co(L2)]2+ complex has 1,8‐pendants in a cis‐configuration. Remarkably, the paramagnetic‐induced shift of water 1H NMR resonances in the presence of the [Co(L1)]2+ complex is as large as that observed for one of the most effective LnIII water proton shift agents. Incorporation of [Co(L1)]2+ into the liposome aqueous core, followed by dialysis against a solution of 300 mOsm L−1 produces a CEST peak at 3.5 ppm. Incorporation of the amphiphilic [Co(L3)]2+ complex into the liposome bilayer produces a more highly shifted CEST peak at −13 ppm. Taken together, these data demonstrate the feasibility of preparing CoII lipoCEST agents.

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Section: Resultsmentioning

confidence: 74%

Co^II Complexes as Liposomal CEST Agents

et al. 2020

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“…In other words, each paraCEST agent may produce a CEST peak at a distinct frequency, so that multiple CEST agents can be monitored and distinguished simultaneously . CEST agents are extremely sensitive to pH, which is attributed to acid- or base-catalyzed proton exchange. ,, The shift of the exchangeable proton and the corresponding CEST peak are temperature dependent. , One drawback of transition-metal ion paraCEST agents is that even in simple solution (phantoms) low millimolar concentrations are required. This concentration is at least 10-fold higher than that for T 1 agents. , Under in vivo conditions, the heterogeneity of environments coupled with the extreme sensitivity to the environment makes it challenging to obtain contrast .…”

Section: Categorization Of First-row Transition-metal Mri Probesmentioning

confidence: 99%

Redox-Responsive MRI Probes Based on First-Row Transition-Metal Complexes

et al. 2022

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The presence of multiple oxidation and spin states of first-row transition-metal complexes facilitates the development of switchable MRI probes. Redox-responsive probes capitalize on a change in the magnetic properties of the different oxidation states of the paramagnetic metal ion center upon exposure to biological oxidants and reductants. Transition-metal complexes that are useful for MRI can be categorized according to whether they accelerate water proton relaxation (T 1 or T 2 agents), induce paramagnetic shifts of 1 H or 19 F resonances (paraSHIFT agents), or are chemical exchange saturation transfer (CEST) agents. The various oxidation state couples and their properties as MRI probes are summarized with a focus on Co(II)/Co(III) or Fe(II)/Fe(III) complexes as small molecules or as liposomal agents. Solution studies of these MRI probes are reviewed with an emphasis on redox changes upon treatment with oxidants or with enzymes that are physiologically important in inflammation and disease. Finally, we outline the challenges of developing these probes further for in vivo MRI applications.

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“…The amide protons of the Co 2+ CCRM complex (Scheme 8) generate strong, pH dependent CEST effects allowing for ratiometric pH readout, and importantly, the kinetic inertness of this trans isomer is very good for a Co 2+ chelate. [47] In a different approach, the 19 F MRI signal of a Fe 2+ DOTAM chelate decorated with 4 CF 3 units was used for probe quantification and ratiometric pH determination. [48] To improve pH sensitivity, Harris et al incorporated two distinct ligand scaffolds in a single, dinuclear Co 2+ L15-editronate complex (Scheme 8).…”

Section: Paracest Agentsmentioning

confidence: 99%

Metal-based environment-sensitive MRI contrast agents

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2021

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Isomeric Co(ii) paraCEST agents as pH responsive MRI probes

Abstract: Two isomeric Co(ii) paraCEST MRI probes produce a signal correlated to pH in solution and in tissue homogenate.

Cited by 16 publications

References 31 publications

Co^II Complexes as Liposomal CEST Agents

Co^II Complexes as Liposomal CEST Agents

Redox-Responsive MRI Probes Based on First-Row Transition-Metal Complexes

Metal-based environment-sensitive MRI contrast agents

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Isomeric Co(ii) paraCEST agents as pH responsive MRI probes

Abstract: Two isomeric Co(ii) paraCEST MRI probes produce a signal correlated to pH in solution and in tissue homogenate.

Cited by 16 publications

References 31 publications

CoII Complexes as Liposomal CEST Agents

CoII Complexes as Liposomal CEST Agents

Redox-Responsive MRI Probes Based on First-Row Transition-Metal Complexes

Metal-based environment-sensitive MRI contrast agents

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Product

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Co^II Complexes as Liposomal CEST Agents

Co^II Complexes as Liposomal CEST Agents