Rigid versions of PDTA⁴⁻ incorporating a 1,3-diaminocyclobutyl spacer for Mn²⁺ complexation: stability, water exchange dynamics and relaxivity

Abstract

Rigid derivatives of the acyclic ligand PDTA4 (H4PDTA = propylenediamine-N,N,N′,N′-tetraacetic acid) were prepared by functionalization of a cis-1,3-cyclobutanediamine spacer. The new ligands contain either four acetate groups attached to the...

A systematic investigation of the NMR relaxation properties of Fe(iii)-EDTA derivatives and their potential as MRI contrast agents

“…A similar situation was observed for the corresponding Mn(II) complex and related systems. 38 The r 1p values measured for PhDTA 4− , CpDTA 4− and c-CDTA 4− complexes remain constant within experimental error below pH 6 down to pH ∼ 2.5, as observed previously for the EDTA 4− and t-CDTA 4− analogues. 17 However, an increase in relaxivity is observed at low pH for the complexes of 1,3-CBuDTA 4− , 1,3-CBuDEDPA 2− and PDTA 4− .…”

“…Ligand H 4 PDTA is commercially available, while H 4 PhDTA 36,37 and 1,3-H 4 CBuDTA 38 were prepared following the literature procedures. The synthesis of H 4 CpDTA was achieved by alkylation of trans-cyclopentane-1,2-diamine with tert-butyl bromoacetate in acetonitrile at room temperature, using K 2 CO 3 as a base.…”

“…This afforded the following thermodynamic parameters for the equilibrium expressed in eqn (3): ΔH°= 42.2 ± 3.4 kJ mol −1 and ΔS°= +129 ± 11 J mol −1 K −1 . The positive reaction entropy is typical of dehydration reactions involving both lanthanide [70][71][72][73] and transition metal ions, 28,38 due to water release. The positive reaction enthalpy is probably related to the energy cost associated with the breaking of the Fe-OH 2 bond.…”

Thermodynamic Stability of Mn(II) Complexes with Aminocarboxylate Ligands Analyzed Using Structural Descriptors

“…Among the nonmacrocyclic ligands, two families have been widely investigated for Mn(II) complexation. The first class comprises H 4 EDTA ( L4 , Chart 1 ) and its derivatives, including: (1) EDTA analogues in which the ethyl spacer is replaced by propyl (H 4 PDTA, L3 ), 70 cyclohexyl (H 4 CDTA, L14 ), 71 phenyl (H 4 PhDTA, L16 ), 72 1,2-cyclobutyl, 73 or 1,3-cyclobutyl 74 (H 4 CBDTA, L5 ) groups. (2) Ligands bearing one of these spacers in which some of the acetic acid arms are replaced by donor groups such as phenols (i.e., L17 – L19 ) or pyridine groups (i.e.…”

“…H 4 CDTA, L14 ) results in increased stability, while all remaining modifications result in lower log K MnL values than for the parent complex. We note that the use of 1,2-cyclobutyl or cis -1,3-cyclobutyl spacers yields complexes with very similar stabilities. , Thus, these structural modifications, consisting in replacing an ethyl group such as that in H 4 EDTA by a cyclobutyl ring, are described by the same structural descriptor SCybu. Similarly, the complexes of cis - and trans -H 4 CDTA give also very similar values of log K MnL , and thus these structural modifications are described by a single structural descriptor SCyhx.…”