Syntheses and solid state structures of cyclam-based copper and zinc compounds

A Bridge too Far? Comparison of Transition Metal Complexes of Dibenzyltetraazamacrocycles with and without Ethylene Cross-Bridges: X-ray Crystal Structures, Kinetic Stability, and Electronic Properties

Tetraazamacrocycles, cyclic molecules with four nitrogen atoms, have long been known to produce highly stable transition metal complexes. Cross-bridging such molecules with two-carbon chains has been shown to enhance the stability of these complexes even further. This provides enough stability to use the resulting compounds in applications as diverse and demanding as aqueous, green oxidation catalysis all the way to drug molecules injected into humans. Although the stability of these compounds is believed to result from the increased rigidity and topological complexity imparted by the cross-bridge, there is insufficient experimental data to exclude other causes. In this study, standard organic and inorganic synthetic methods were used to produce unbridged dibenzyl tetraazamacrocycle complexes of Co, Ni, Cu, and Zn that are analogues of known cross-bridged tetraazamacrocycles and their transition metal complexes to allow direct comparison of molecules that are identical except for the cross-bridge. The syntheses of the known tetraazamacrocycles and the new transition metal complexes were successful with high yields and purity. Initial chemical characterization of the complexes was conducted by UV-Visible spectroscopy, while cyclic voltammetry showed more marked differences in electronic properties from bridged versions. Direct comparison studies of the unbridged and bridged compounds' kinetic stabilities, as demonstrated by decomposition using high acid concentration and elevated temperature, showed that the cyclen-based complex stability did not benefit from cross-bridging. This is likely due to poor complementarity with the Cu2+ ion while cyclam-based complexes benefited greatly. We conclude that ligand-metal complementarity must be maintained in order for the topological and rigidity constraints imparted by the cross-bridge to contribute significantly to complex robustness.

Silva E, Cerqueira F, Pinto E, Alves LG. Cyclam-based iron(iii) and copper(ii) complexes: synthesis, characterization and application as antifungal agents

Cyclam-based complexes of formulae [{H2(4-CF3PhCH2)2Cyclam}FeCl2]Cl and [{H2(4-CF3PhCH2)2Cyclam}Cu](CH3COO)2·2H2O reveal antifungal activity against diverse unicellular and multicellular fungal species.

New Cyclams and Their Copper(II) and Iron(III) Complexes: Synthesis and Potential Application as Anticancer Agents

New cyclam derivatives (HOCH₂ CH₂ CH₂ )₂ (PhCH₂ )₂ Cyclam and (HOCH₂ CH₂ CH₂ )₂ ( 4 - CF 3 PhCH₂ )₂ Cyclam, as well as their Cu^II and Fe^III complexes, were synthesized and characterized and their stability in cellular media was assessed. The cytotoxic effect of all compounds was examined on human cervical cancer (HeLa) cells, revealing strong anticancer activity. After 24 h, only complexes with the (HOCH₂ CH₂ CH₂ )₂ ( 4 - CF 3 PhCH₂ )₂ Cyclam ligand are cytotoxic, whereas after incubation for 72 h all compounds show significant antiproliferative effects. Notably, compounds containing 4 - CF 3 PhCH₂ pendant arms on the cyclam ring revealed the most activity, with cytotoxicity values up to 12 times higher than those of cisplatin. All metal complexes seem to induce cell death through the formation of reactive oxygen species.

Synthesis and Evaluation of 1,8-Disubstituted-Cyclam/Naphthalimide Conjugates as Probes for Metal Ions

Fluorescent molecular probes for metal ions have a raft of potential applications in chemistry and biomedicine. We report the synthesis and photophysical characterisation of 1,8‐disubstituted‐cyclam/naphthalimide conjugates and their zinc complexes. An efficient synthesis of 1,8‐bis‐(2‐azidoethyl)cyclam has been developed and used to prepare 1,8‐disubstituted triazolyl‐cyclam systems, in which the pendant group is connected to triazole C4. UV/Vis and fluorescence emission spectra, zinc binding experiments, fluorescence quantum yield and lifetime measurements and pH titrations of the resultant bis‐naphthalimide ligand elucidate a complex pattern of photophysical behaviour. Important differences arise from the inclusion of two fluorophores in the one probe and from the variation of triazole substitution pattern (dye at C4 vs. N1). Introducing a second fluorophore greatly extends fluorescence lifetimes, whereas the altered substitution pattern at the cyclam amines exerts a major influence on fluorescence output and metal binding. Crystal structures of two key zinc complexes evidence variations in triazole coordination that mirror the solution‐phase behaviour of these systems.

Amino acid derived CuII compounds as catalysts for asymmetric oxidative coupling of 2-naphthol

Several chiral amino acid-derived Cu^II complexes were prepared and used as catalysts in the aerobic oxidative coupling of 2-naphthol. Moderate homocoupling product yields and enantiomeric excesses were obtained under mild, aqueous conditions.