Metal Complexes with Macrocyclic Ligands. Part XXI. A nonlinear relationship between the stability of Cu²⁺ complexes and their complexation rate with 1,4,8,11‐tetraazacyclotetradecane

Abstract

Dedicated to Prof. Dr. S. Fullub on the occasion of his 60th birthday (14.VI.85)The kinetics of the reaction ( I ) between 1,4,8,1l-tetraazacyclotetradecane (Cy) and a series of Cu(I1) complexes CuL (L = glycolate, malonate, succinate, picolinate, glycinate, iminodiacetate, nitrilotriacetate, N-(2-hydroxyethyl)ethylenediaminetriacetate, ethylenediamine, 1,3-diaminopropane, diethylenetriamine and N,N-bis(3-aminopropylamine) were studied spectrophotometrically at 25" and Z = 0.5 (KNO,). From the analysis of the log kOb,/log [L] profiles obtained at different pH values the resolved bimolecular rate constants k:,",!$ (Table 3) were obtained by a nonlinear curve-fitting procedure. For nearly all systems studied, the rate constant k$k, describing the reaction between the 1 :1 complex CuL and the monoprotonated form of the macrocycle CyH, was obtained. The nonlinear relationship between log k,!$ and log KCuL and its nature is discussed. It is shown that the inverse relationship between reactivity and stability described by others is only a special case of the more general Eqn. 3 described here.Introduction. -Ligand-ligand replacement reactions have been studied in detail and many aspects of the reaction mechanism are well-understood [2]. In general, these reactions proceed through intermediates in which the incoming ligand is partially coordinated and the expelled ligand is partially dissociated. From the detailed analysis of such mechanisms, one can predict the rate of a ligand-ligand exchange process, if one knows the stability of the intermediate. Another possibility to predict rates comes from the observation that an inverse relationship between the stability of the starting complex and its reactivity exists. This has been found for open-chain ligands [3] as well as for cyclic polyamines [4].During our studies on the kinetics of complexation reactions with tetraazamacrocycles in the absence [5] and presence [l] of additional ligands, we became interested whether this rule applies to a large number of chelators with different donor atoms. For such a study the complexation of 1,4,8,ll-tetraazacyclotetradecane (Cy) with a large variety of Cu" complexes seemed ideal, because the reaction can easely be followed, and the rates are accessible to measurements.

Reactions of py[13]aneN4 with the copper(II) complexes of diglycine and triglycine

“…This indicates that the reactions of protonated py [13]aneN 4 with the Cu(II)-peptide complexes have negligible electrostatic effects. The same observation was reported previously [5] for the reactions of LH þ of cyclam with the complexes of Cu 2þ aq , CuG þ and CuIDA (G ¼ glycinate; IDA ¼ iminodiacetate).…”

“…Previous studies [5,13,14] have shown that the monoprotonated forms of tetraazamacrocycles, LH þ , are several orders more reactive than the higher protonated species, even for reactions in which the concentration of the LH þ species is less than 0.01% of LH þ2 2 [13]. If it is assumed that the reactions of the species LH þ3 3 , LH þ2 2 and L with Cu(II) diglycine (CuGG) are not kinetically significant in the pH range used in this work, the kinetically important reactions are those shown in Scheme 1.…”

“…In an attempt to check the validity of this rule for a large number of chelators with different donor atoms, a study was carried out on the kinetics of the reaction of cyclam (1,4,8,11-tetraazacyclotetradecane) with a series of Cu(II) complexes for which the formation constants (K CuL ) span over 15 orders of magnitude [5]. The study concluded that for complexes with formation constants greater than 10 10 , there is an inverse relationship between K CuL and their reactivities towards cyclam.…”

Kinetics and Mechanism of Complex Formation of Nickel(II) with Tetra-N-alkylated Cyclam in N,N-Dimethylformamide (DMF): Comparative Study on the Reactivity and Solvent Exchange of the Species Ni(DMF)62+ and Ni(DMF)5Cl+

“…To our knowledge, there are no reports so far on the kinetic effect of coordinating anions or other ligands on complex formation reactions of transition metals with macrocyclic N-donor or S-donor ligands in nonaqueous media. Wu and Kaden studied the kinetics of complexation reactions of nickel(II)24a and copper(II) 24b with cyclam in the presence of additional ligands in aqueous solution. They found that the rate of the reaction of the partially complexed, hydrated metal species NiX z and CuX z with monoprotonated cyclam increases by a factor of approximately 10 upon going from z = +2 (X = water) to z = +1 (X = acetate), 0 (X = oxalate), and −1 (X = tricarballylate).…”

Labelling monoclonal antibodies with macrocyclic radiometal complexes. A challenge for coordination chemists

“…2). 15 Since previous experiments showed that the rate of Cu 2+ incorporation can be increased by addition of acetate ions, 16 we incorporated 64 Cu 2+ into the conjugate antibody in acetate buffer solution. Animal experiments demonstrated that the labelled conjugate antibody still binds to the receptors expressed by the tumour cells, resulting in a very good blood/tumour ratio and thus allows the detection of the size and position of the tumour with high precision (Fig.…”