Recent developments in the design of bifunctional chelators for metal-based radiopharmaceuticals used in Positron Emission Tomography

Bispidines are extremely rigid ligands, easy to prepare in a large variety, with denticities of four to ten, various donor sets and charges, for mono- and oligonuclear transition metal, main group and rare earth complexes. In the last approx. 20 years significantly more than 50 new bispidine based ligands were prepared and their coordination chemistry studied. Biological probes and medicinal applications is one main area in bispidine coordination chemistry, where fast complex formation, high stability, metal ion selectivity and inertness are of utmost importance. Oxygen activation and oxidation catalysis is another main focus in bispidine coordination chemistry, with catalyst efficiency and stability as well as product selectivity as important requirements. Particularly successful applications in these areas are presented and discussed in detail, in addition to fundamental principles that show the importance of ligand rigidity, cavity size and shape as overarching fundamental properties.

Bispidine Coordination Chemistry

Four new coordination polymers, namely, [Co(BIPA)(titmb)]·H2O (1), [Co3(BIPA)3(titmb)2]·0.73H2O (2), [Ni(SDBA)(bix)]·2H2O (3) and [Ni(SDBA)(bix)(H2O)]·0.38H2O (4) (H2BIPA = 5-bromoisophthalic acid, H2SDBA = 4,4′-dicarboxybiphenyl sulfone, titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-tri-methylbenzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), were obtained under hydrothermal conditions. Four complexes were characterized by elemental analyses, IR spectra, thermogravimetric analyses and single-crystal X-ray diffraction. Complexes 1 and 2 are polymorphs formed from Co(II) cations, BIPA2− anions, titmb ligands and water molecules, showing a three-dimensional (3,5)-connected network with the topology of (63)(69.8) for 1 and a three-dimensional (3,4)-connected coordination framework with the topology of (4.6.8)(4.62.83)(6.85)(62.83.10)(83) for 2. Complexes 3 and 4 are also two polymorphs constructed from Ni(II) cations, SDBA2− anions, bix ligands and water molecules. Complex 3 exhibits a two-dimensional lamella structure with (4,4) topology, whereas complex 4 displays a two-dimensional 2-fold interpenetrating (6,3) network. It is shown that the reaction temperature plays a crucial role in the formation of the final products. Moreover, the nonlinear optical and ferroelectric properties of 1 have also been investigated.

Temperature-induced assembly of MOF polymorphs: Syntheses, structures and physical properties

Pentadentate bispidine ligands (3,7-diazabicyclo[3.3.1]nonanes) are optimized for maximum complex stability and facile functionalization with respect to their coupling to biological vector molecules and/or fluorescence markers for PET (positron emission tomography) and multimodal imaging (i.e., PET and optical imaging). The pentadentate ligand with two tertiary amine donors, two p-methoxy substituted pyridines, and one unsubsituted pyridine group is shown to best fulfill important conditions for PET applications, i.e., fast complexation with CuII and high in vivo stability, and this was predicted from the solution chemistry, in particular the CuII/I redox potentials. Also, solvent partition experiments to model the lipophilicity of the CuII complexes indicate that the bis p-methoxy substituted ligand leads to cationic complexes with an appreciable lipophilicity. This is supported by the biodistribution experiments that show that the complex with the p-methoxy substituted ligand is excreted very quickly an...

Optimization of Pentadentate Bispidines as Bifunctional Chelators for 64Cu Positron Emission Tomography (PET)

Bispidines (3,7-diazabicyclo[3.3.1]nonanes) as very rigid and highly preorganized ligands find broad application in the field of coordination chemistry, and the redox potentials of their transition-metal complexes are of importance in oxidation reactions by high-valent iron complexes, aziridination catalyzed by copper complexes, and imaging by 64Cu positron emission tomography tracers. Here, we show that the redox potentials and stability constants of the copper(II) complexes of 15 tetradentate bispidines can be varied by substitution of the pyridine rings (variation of the redox potential over ca. 450 mV and of the complex stability over approximately 10 log units). It is also shown that these variations are predictable by the pKa values of the pyridine groups as well as by the Hammett parameters of the substituents, and the density functional theory based energy decomposition analysis also allows one to accurately predict the redox potentials and concomitant complex stability. It is shown that the main ...

Tuning of the properties of transition-metal bispidine complexes by variation of the basicity of the aromatic donor groups.

Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand | NOVA. The University of Newcastle's Digital Repository

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Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand | NOVA. The University of Newcastle's Digital Repository