XAS, ESR and Potentiometric Studies of Three DinuclearN,N′‐para‐Xylylenebis(tetraazamacrocycle)copper(II) Complexes − X‐ray Crystal Structure of [N,N′‐p‐Xylylenebis(cyclen)]copper(II)

Abstract

Dicopper complexes with N,N′‐p‐xylylenebis(cyclam or cyclen) and with the heteroditopic N,N′‐p‐xylylenebis(cyclam‐cyclen) were synthesized. An X‐ray study of the N,N′‐p‐xylylenebis(cyclen)dicopper complex showed that the copper(II) ion is five‐coordinate with an H2O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS− anion are coordinated in apical position to the square‐pyramidal copper(II) ion. Two alternating kinds of Cu2L4+ moieties are present in the chain, the first with two N4S chromophores and the second with two N5 chromophores. EXAFS and XANES results are in agreement with a five‐coordinate copper ion in the cyclen unit and a six‐coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu2L4+ species (ligand/metal ratio < 1) and mononuclear CuLHn(2+n)+ species (ligand/metal ratio > 1) were confirmed by an ESR study at variable pH. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Acetate as a model for aspartate-based CXCR4 chemokine receptor binding of cobalt and nickel complexes of cross-bridged tetraazamacrocycles

“…25 Acetate binding-In this work, we are using acetate as a model to better understand the binding of these cobalt and nickel complexes to the aspartate carboxylate side chain on the surface of the CXCR4 chemokine receptor. 16,18,20 In a recent study of Cu 2+ and Zn 2+ CXCR4 chemokine receptor antagonists, 23 we were able to discern several trends based on similar acetate-as-model crystal structures that shed light on the likely coordination environment in the antagonist/receptor interaction and rationalised our antagonist binding affinities and residence time data. 23 The aim of this study is to learn similar information about our cobalt and nickel antagonists.…”

“…Because of the significant challenges in production of X-ray quality bis-linked tetraazamacrocycle complex crystals, 18,23 single-macrocycle transition metal complexes are often used as models. 16,[18][19][20]23 To provide the most accurate model for our bis-macrocycle antagonists, which are linked through a xylene linker, we have synthesised a number of monobenzyl and dibenzyl 4 pendant arm containing cross-bridged tetraazamacrocycles (Fig. 3).…”

Homo- and heteropolynuclear Ni2+ and Cu2+ complexes of polytopic ligands, consisting of a tren unit substituted with three 12-membered tetraazamacrocycles

“…Therefore this species is stable and maintains its geometry under very different experimental conditions, as previously shown for other similar derivatives. 30 As the EPR parameters of A are close to those of the Cu 2+ complex with 1,4,7,10-tetraazacyclododecane, we assume that the geometry of the first coordination sphere around Cu 2+ is also square pyramidal but with a slight distortion, as is indicated by the A and g values. 31 In the case of the minor species B, the small A values, around 120 G, are close to the ones obtained for dimeric species where the hyperfine coupling constant is half that of monomeric species.…”

Azamacrocyclic Metal Complexes as CXCR4 Antagonists

“…The pyridyl zinc(II) complex was characterized previously, [37] and zinc(II) or copper(II) complex formation with these macrocyclic compounds has been reported elsewhere. [41,42,48,49] Detailed procedures and data are provided in the Supporting Information.…”