A benzimidazole functionalised DO3A chelator showing pH switchable coordination modes with lanthanide ions

Abstract

The synthesis of a new macrocyclic chelator incorporating a benzimidazole heterocycle is reported. Lanthanide complexes with macrocyclic chelators based on 1,4,7,10-tetra(carboxymethyl)-1,4,7,10-tetraazacyclododecane (DOTA) and 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane (DO3A) are of interest in luminescent, radiopharmaceutical and magnetic resonance (MR) biomedical imaging applications. The benzimidazole DO3A chelator allows for sensitisation of europium(iii), terbium(iii) and ytterbium(iii) luminescence by the heterocycle and also shows a pH dependent coordination change due to protonation of the chelator (pKa = 4.1 for the europium(iii) complex). The thermodynamic stability of the complexes has been investigated by potentiometric titration with the gadolinium(iii) complex showing significantly higher stability than the zinc(ii) complex, where log βZnLH = 28.1 and log βGdLH = 32.1.

Structural, magnetic, redox and theoretical characterization of seven-coordinate first-row transition metal complexes with a macrocyclic ligand containing two benzimidazolyl N-pendant arms

“…1, L7, 36 differently-substituted triazacyclononanes L8, 42,43 tetraazacyclododecanes (cyclenes) L9, 44,45 its dioxa-derivative L10, 46 tetraazacyclotetradecanes (cyclames) L11 47 and its DO3A derivative L12). 48 Thus, in this paper, a structurally new ligand, L, has been synthesized and its Mn II , Fe II , Co II and Ni II complexes have been prepared and studied in detail. Their structural, magnetic and redox properties were thoroughly investigated and compared with those of previously studied systems containing ligands L2 and L3.…”

Synthesis and spectroscopy of anionic tridentate benzimidazole-pyridine carboxylate and tetrazolate chromophore ligands

“…An attempt to make carboxylate ligand 'HL8' from 4 worked for the first three steps (see the intermediates L8-NO 2 , L8-CH 2 OH, L8-CHO and the structure of ligand 'HL8' in the Supplementary material); however, oxidation of the carboxaldehyde L8-CHO to the carboxylic acid 'HL8' with H 2 O 2 in formic acid [26] resulted in oxidative decomposition, probably because of the presence of electron-rich diphenylamino group (Supplementary material). The benzimidazole-pyridines L8-CH 2 OH and L8-CHO (Supplementary material) can be used as ligands themselves and as precursors to polydentate ligands [20]. The ligands derived from 4 are likely to exhibit low-energy intra-ligand diphenylamine-to-benzimidazole charge-transfer absorption transition.…”

“…S2, Supplementary material)[20]. The lowest-energy absorption transition and the triplet state of the new ligands and their lanthanum complexes exhibit the following trends (Figs.…”

“…Polydentate carboxylate [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and tetrazolate [21][22][23][24] ligands are strong chelators for lanthanide ions and efficient sensitizers of their luminescence. Here, we report on synthesis and spectroscopy of anionic tridentate carboxylate and tetrazolate benzimidazole-pyridine ligands HL1-HL7 that are functionalized with chromophore and solubilizing groups (Schemes 1 and 2).…”

Investigations into the effects of linker length elongation on the behaviour of calcium-responsive MRI probes

“…The signals of the most shifted axial protons are observed between 20 and 28 ppm, a range that is typical of square antiprismatic coordination (SAP) around the metal ion. [20][21][22][23] The signals due to the axial protons of the twisted square antiprismatic (TSAP) isomers are usually observed around 10-15 ppm. The resonances due to the TSAP isomer are barely visible in the case of EuL 2 , while for EuL 1 the population of the TSAP isomer can be estimated to be 10-15%.…”