Small, Fluorinated Mn Chelate as an Efficient H and F MRI Probe.

We explore the potential of fluorine-containing small Mn chelates as alternatives to perfluorinated nanoparticles, widely used as F MRI probes. In MnL1, the cyclohexanediamine skeleton and two piperidine rings, involving each a metal-coordinating amide group and an appended CF moiety, provide high rigidity to the complex. This allows for good control of the Mn-F distance (r=8.

[Mn]Mn-BPPA-Trastuzumab: A Promising HER2-Specific PET Radiotracer.

This study aimed to develop a novel radiotracer using trastuzumab and the long-lived [Mn]Mn isotope for HER2-targeted therapy selection and monitoring. A new Mn(II) chelator, BPPA, synthesized from a rigid bispyclen platform possessing a picolinate pendant arm, formed a stable and inert Mn(II) complex with favorable relaxation properties. BPPA was converted into a bifunctional chelator (BFC), conjugated to trastuzumab, and labeled with [Mn]Mn isotope.

Exploring the Limits of Ligand Rigidification in Transition Metal Complexes with Mono--Functionalized Pyclen Derivatives.

We report the synthesis of a new family of side-bridged pyclen ligands. The incorporation of an ethylene bridge between two adjacent nitrogen atoms was reached from the pyclen-oxalate precursor described previously. Three new side-bridged pyclen macrocycles, H, , and H, were obtained with the aim to assess their coordination properties toward Cu and Zn ions.

Improving the potential of paraCEST through magnetic-coupling induced line sharpening.

Magnetic coupling between paramagnetic centers is a crucial phenomenon in the design of efficient MRI contrast agents. In this study, we investigate the paraCEST properties and magnetic coupling effects of a novel homodinuclear Ni(ii) complex, 1, containing a Robson type macrocyclic ligand. A thorough analysis of the complex's electronic and magnetic properties revealed that the magnetic coupling effect reduces the transverse relaxation rate and enhances the sharpness of the proton resonances, leading to enhanced CEST efficiency.

Gd Complexes for MRI Detection of Zn in the Presence of Human Serum Albumin: Structure-Activity Relationships.

Zn-responsive magnetic resonance imaging (MRI) contrast agents are typically composed of a Gd chelate conjugated to a Zn-binding moiety via a linker. They allow for Zn detection in the presence of human serum albumin (HSA). In order to decipher the key parameters that drive their Zn-dependent MRI response, we designed a pyridine-based ligand, , and compared the properties of to those of analogue complexes with varying Gd core, Zn-binding moiety, or linker sizes.

H Derivatives Possessing Picolyl and Picolinate Pendants for Ga Coordination and Ga Radiolabeling.

We synthesized, thanks to the regiospecific -functionalization using an orthoamide intermediate, two 1,4,7-triazacyclononane derivatives containing an acetate arm and either a methylpyridine or a picolinic acid group, respectively, H and H, as new Ga chelators for potential use in nuclear medicine. The corresponding Ga complexes were synthesized and structurally characterized in solution by H and C NMR. The [Ga()] complex appears to exist in solution as two diasteroisomeric pairs of enantiomers, as confirmed by density functional theory (DFT) calculations, while for [Ga()], a single species is present in solution.

Rigid HOCTAPA derivatives as model chelators for the development of Bi(III)-based radiopharmaceuticals.

Octadentate ligands containing ethyl (HOCTAPA), cyclohexyl (HOCTAPA) or cyclopentyl (HOCTAPA) spacers were assessed as chelators for Bi(III)-based radiopharmaceuticals. The HOCTAPA chelator displays excellent properties, including Bi-nuclide radiolabelling under mild conditions, excellent stability in serum and in the presence of competing cations or HDTPA. The poor performance of HOCTAPA appears to be related to the stereochemical activity of the Bi(III) lone pair.

Synthesis and characterization of two piperazine containing macrocycles and their transition metal complexes.

Rigidification of the ligand scaffolds has been a particular mechanism of interest employed to achieve properties suitable for MRI contrast, catalysis, or other applications of metal complexes. Towards the goal of targeting a 15-anePyNPip type ligand, a serendipitous isolation of a 30-anePyNPip aza-macrocycle was achieved, instead. X-ray diffraction and determination of pK events were carried out and compared to 17-anePyNPip.

Physico-Chemical Characterization of a Highly Rigid Gd(III) Complex Formed with a Phenanthroline Derivative Ligand.

The discovery of the nephrogenic systemic fibrosis (NSF) and its link with the dissociation of certain Gd(III)-based contrast agents (CAs) applied in the magnetic resonance imaging (MRI) induced a still growing research to replace the compromised agents with safer alternatives. In recent years, several ligands were designed to exploit the luminescence properties of the lanthanides, containing structurally constrained aromatic moieties, which may form rigid Gd(III) complexes. One of these ligands is (1,10-phenanthroline-2,9-diyl)bis(methyliminodiacetic acid) (HFENTA) designed and synthesized to sensitize Eu(III) and Tb(III) luminescence.

Synthesis, Physicochemical, Labeling and In Vivo Characterization of Sc-Labeled DO3AM-NI as a Hypoxia-Sensitive PET Probe.

Hypoxia promotes angiogenesis, which is crucial for tumor growth, and induces malignant progression and increases the therapeutic resistance. Positron emission tomography (PET) enables the detection of the hypoxic regions in tumors using 2-nitroimidazole-based radiopharmaceuticals. We describe here a physicochemical study of the Sc(DO3AM-NI) complex, which indicates: (a) relatively slow formation of the Sc(DO3AM-NI) chelate in acidic solution; (b) lower thermodynamic stability than the reference Sc(DOTA); (c) however, it is substantially more inert and consequently can be regarded as an excellent Sc-binder system.

Rigidified Derivative of the Non-macrocyclic Ligand HOCTAPA for Stable Lanthanide(III) Complexation.

The stability constants of lanthanide complexes with the potentially octadentate ligand OCTAPA, which contains a rigid 1,2-diaminocyclohexane scaffold functionalized with two acetate and two picolinate pendant arms, reveal the formation of stable complexes [log = 17.82(1) and log = 19.65(1)].

A New Oxygen Containing Pyclen-Type Ligand as a Manganese(II) Binder for MRI and Mn PET Applications: Equilibrium, Kinetic, Relaxometric, Structural and Radiochemical Studies.

A new pyclen-3,9-diacetate derivative ligand (H) was synthesized possessing an etheric O-atom opposite to the pyridine ring, to improve the dissociation kinetics of its Mn(II) complex (pyclen = 3,6,9,15-tetraazabicyclo(9.3.1)pentadeca-1(15),11,13-triene).

How the Chemical Properties of GBCAs Influence Their Safety Profiles In Vivo.

The extracellular class of gadolinium-based contrast agents (GBCAs) is an essential tool for clinical diagnosis and disease management. In order to better understand the issues associated with GBCA administration and gadolinium retention and deposition in the human brain, the chemical properties of GBCAs such as relative thermodynamic and kinetic stabilities and their likelihood of forming gadolinium deposits in vivo will be reviewed. The chemical form of gadolinium causing the hyperintensity is an open question.

Stable and inert macrocyclic cobalt(II) and nickel(II) complexes with paraCEST response.

We report the synthesis of the macrocyclic ligands 3,9-PC2AMH (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)diacetamide) and 3,9-PC2AMtBu (2,2'-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,9-diyl)bis(-butyl)acetamide) which contain a pyclen platform functionalized with acetamide or -butylacetamide pendant arms at positions 3 and 9 of the macrocyclic unit. The corresponding Co(II) and Ni(II) complexes were prepared, isolated and characterised as potential paramagnetic chemical exchange saturation transfer (paraCEST) agents. The X-ray structures of the Ni(II) complexes reveal six-coordination of the ligands to the metal ion.

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability, Formation and Dissociation Kinetics, and Solution Dynamic NMR Studies.

The thermodynamic, kinetic, and structural properties of Ln complexes with the bifunctional DO3A-ACE ligand and its amide derivative DO3A-BACE (modelling the case where DO3A-ACE ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg and Ca complexes of DO3A-ACE and DO3A-BACE complexes are lower than for DOTA and DO3A, while the Zn and Cu complexes have similar and higher stability than for DOTA and DO3A complexes. The stability constants of the Ln(DO3A-BACE) complexes increase from Ce to Gd but remain practically constant for the late Ln ions (represented by Yb).

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference.

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate () or piperidineacetamide () pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X-ray structure of [Mn()(HO)]·2HO shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment.

Pyclen-Based Ligands Bearing Pendant Picolinate Arms for Gadolinium Complexation.

We report the synthesis of two pyclen-based regioisomer ligands (pyclen = 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene) functionalized with picolinic acid pendant arms either at positions () or () of the macrocyclic fragment.

Complexation of Mn(II) by Rigid Pyclen Diacetates: Equilibrium, Kinetic, Relaxometric, Density Functional Theory, and Superoxide Dismutase Activity Studies.

We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene) functionalized with acetate pendant arms at either positions 3,6 () or 3,9 () of the macrocyclic fragment.

Manganese Complex of a Rigidified 15-Membered Macrocycle: A Comprehensive Study.

Owing to the increasing importance of manganese(II) complexes in the field of magnetic resonance imaging (MRI), large efforts have been devoted to find an appropriate ligand for Mn(II) ion encapsulation by providing balance between the seemingly contradictory requirements (i.e., thermodynamic stability and kinetic inertness vs low ligand denticity enabling water molecule(s) to be coordinated in its metal center).

Mn(II)-Based MRI Contrast Agent Candidate for Vascular Imaging.

Toxicity concerns related to Gd(III)-based magnetic resonance imaging (MRI) agents prompted an intensive research toward their replacement by complexes of essential metal ions, like Mn(II). Here, we report a macrocyclic chelate, [Mn(PC2A-BP)], which possesses high thermodynamic stability (log = 14.86 and pMn=8.

Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cyclen-Based Ligands across the Lanthanide Series.

We report a detailed study of the thermodynamic stability and dissociation kinetics of lanthanide complexes with two ligands containing a cyclen unit, a methyl group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-HDO2APA) or trans (1,7-HDO2APA) positions. The stability constants of the Gd complexes with these two ligands are very similar, with log values of 16.98 and 16.

Comparison of the equilibrium, kinetic and water exchange properties of some metal ion-DOTA and DOTA-bis(amide) complexes.

The 1,7-diacetate-4,10-diacetamide substituted 1,4,7,10-tetraazacyclododecane structural unit is common to several responsive Magnetic Resonance Imaging (MRI) contrast agents (CAs). While some of these complexes (agents capable of sensing fluctuations in Zn, Ca etc. ions) have already been tested in vivo, the detailed physico-chemical characterization of such ligands have not been fully studied.

Picolinate-appended tacn complexes for bimodal imaging: Radiolabeling, relaxivity, photophysical and electrochemical studies.

Based on our previous works involving two 1,4,7-triazacyclononane (tacn)-based ligands Hno2py1pa (1-Picolinic acid-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane) and Hno1pa (1-Picolinic acid-1,4,7-triazacyclononane), we report here the synthesis of analogues bearing picolinate-based π-conjugated ILCT (Intra-Ligand Charge Transfer) transition antenna (HL1, HL2), using regiospecific N-functionalization of the tacn skeleton and their related transition metal complexes (e.g. Cu, Zn and Mn).

Stable and Inert Mn(II)-Based and pH-Responsive Contrast Agents.

Smart/intelligent contrast agent candidates for MRI based on Mn(II) ion are rare, as it usually forms labile complexes with polyaminocarboxylate-type ligands. Here, we report the first example of a Mn(II) complex that can be activated by changing the pH of its local environment. The PC2A-EA ligand with an ethylamine pendant arm was found to form a thermodynamically stable (log = 19.