Complexation Properties of N,N′,N″,N′′′‐[1,4,7,10‐Tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(1‐oxoethane‐2,1‐diyl)]tetrakis[glycine] (H₄dotagl). Equilibrium, Kinetic, and Relaxation Behavior of the Lanthanide(III) Complexes

Abstract

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Synthesis and Characterization of DOTA‐(amide)4 Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

“…The protonation constants (log K i H ) of these tetraamide ligands are listed and compared to the literature values for DOTA and DOTA-(gly) 4 in Table 1 (the values shown in parentheses are the standard deviations). [11,19] Our data agree well with the published values except for the variation in the first pK a of the ligand DOTAM, where the difference is larger than one order of magnitude. This variation can be attributed to the different ionic strength used in the present study.…”

“…[13] The stability constants of the [Ln{DOTA-(EtAm) 4 }] 3+ and [Ln {DOTA-(gly) 4 }] − complexes are nearly identical for most lanthanides, as one would expect for systems with similar structures and ligand basicities. [11] The data also show that the stabilities are not influenced by the overall charge on these complexes and that the extended glycinate groups do not coordinate to the central metal ions in ML complexes.…”

“…[8][9][10]27] Evidence for a similar stable intermediate has been reported during formation of the [Ln{DOTA-(gly) 4 }] − complexes as well. [11] Furthermore, an interesting structure that is thought to be the reactive intermediate in the formation of [Ln(DOTAM)] 3+ complexes was characterized recently by X-ray diffraction. [28] The visible spectra of solutions recorded after mixing DOTA-(MeAm) 4 with CeCl 3 (both reagents were present at 5 ×10 −4 M) at pH 5.26 are shown in Figure 3.…”

“…[8][9][10] A recently published report on the thermodynamic stability and kinetics of [Ln{DOTA-(gly) 4 }] − complex formation demonstrated that both the basicity of the amide ligands and the stability of the complexes are several orders of magnitude lower than for their [Ln(DOTA)] − analogues. [11] It was also shown that spontaneous dissociation of [Eu{DOTA-(gly) 4 }] − occurs somewhat faster than [Eu (DOTA)] − , but that acid-catalyzed dissociation of the protonated intermediate [Eu{H 4 DOTA-(gly) 4 }] 3+ seems to occur more slowly than for its protonated [Eu(H 2 DOTA)] + analog. [9,11] This suggests that these systems may in fact be suitable for in vivo imaging applications.…”

“…[11] It was also shown that spontaneous dissociation of [Eu{DOTA-(gly) 4 }] − occurs somewhat faster than [Eu (DOTA)] − , but that acid-catalyzed dissociation of the protonated intermediate [Eu{H 4 DOTA-(gly) 4 }] 3+ seems to occur more slowly than for its protonated [Eu(H 2 DOTA)] + analog. [9,11] This suggests that these systems may in fact be suitable for in vivo imaging applications.…”