Metal-based redox-responsive MRI contrast agents

Abstract

Coordination Chemistry and Catalysis Highlights  Use of metal-based complexes and nanoparticles as relaxation and PARACEST redox responsive contrast agents for MRI is reviewed  Ligand-based and metal-based T1 and PARACEST redox responsiveness was reported, in some cases in small animals in vivo.  Mn-based nanoparticles provide strong redox-active relaxation responses in in vivo animal studies.  Ratiometric methods provide in some cases quantitative redox evaluation of cells in vitro.

Molecular Sensors Operating by a Spin‐State Change in Solution: Application to Magnetic Resonance Imaging

“…Redox-sensitive coordination compounds whose change in the oxidation state is associated with a spin-state change have received quite some attention in recent years. [8] In particular for cobalt and copper chelates, one oxidation state exhibits a spin of zero, and thus satisfies the 4th hallmark feature from above, namely the opportunity to observe an off/on or an on/off response mechanism. Such chelates will generally react to a global change in redox potential rather than with a particular analyte.…”

“…Efforts to obtain sensors for Molecular MRI that respond by a change in their relaxivity, have been reviewed in the following articles. [2,5,6,7,8] The vast majority of examples discussed therein rely on concepts where the initial sensor is not MRIsilent (off). In fact, their relaxivity cannot be muted, just modulated, as a consequence of the encounter with the bioanalyte (X%-on/Y%-on).…”

The design of TACN-based molecular systems for different supramolecular functions

“…The latter mechanism is more energetically favoured than that found for the Cu 2+ dinuclear complex with L33, in agreement with the experimentally observed greater hydrolytic ability in the case of the Cu 2+ complex with L35. Beside simple alkyl/aryl groups, TACN has been also linked to a guanidinium group via more structured molecular scaffolds, such as a cone-calix [4]arene platform [91,92]. This is the case of the regioisomers L40 and L41, which differ in the position ( (40) for simplicity), respectively, while a modest 3.6-and 5.5-fold enhancement is observed in the case of the corresponding Zn 2+ complexes.…”

“…The creation of functions at the molecular level is one of the main goal of supramolecular chemistry [1]. In this respect, "coordinatively unsaturated" metal complexes of macrocyclic ligands have proven worthwhile for assembling functional supramolecular compounds with a variety of potential applications in chemistry, biology and medicine: from recognition and sensing of a guest substrate to functional and structural models of biomolecules and diagnostic and therapeutic agents [1][2][3][4][5][6][7][8][9].…”

“…Macrocyclic ligands, in particular polyaza-macrocycles, have been extensively considered as core components of functional supramolecular compounds because they can both be easily functionalised at the secondary N-donors, which is useful for their implementation in supramolecular systems, and they can afford kinetically and thermodynamically stable metal complexes leaving one or more coordination sites on the metal centre free to be occupied by more weakly bound ligands, which is instrumental to confer the desired function(s) to the final supramolecular platform [1][2][3][4][5][6][7][8][9][10].…”