Thermodynamic Stability and Speciation of Ga(III) and Zr(IV) Complexes with High-Denticity Hydroxamate Chelators.
Inorg Chem 2021;
60:13332-13347. [PMID:
34414758 PMCID:
PMC8424644 DOI:
10.1021/acs.inorgchem.1c01622]
[Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Increasing attention
has been recently devoted to 89Zr(IV) and 68Ga(III) radionuclides, due to their favorable
decay characteristics for positron emission tomography (PET). In the
present paper, a deep investigation is presented on Ga(III) and Zr(IV)
complexes with a series of tri-(H3L1, H3L3, H3L4 and desferrioxamine
E, DFOE) and tetrahydroxamate (H4L2) ligands. Herein, we describe the rational
design and synthesis of two cyclic complexing agents (H3L1 and H4L2) bearing three and four hydroxamate
chelating groups, respectively. The ligand structures allow us to
take advantage of the macrocyclic effect; the H4L2 chelator contains an additional side
amino group available for a possible further conjugation with a biomolecule.
The thermodynamic stability of Ga(III) and Zr(IV) complexes in solution
has been measured using a combination of potentiometric and pH-dependent
UV–vis titrations, on the basis of metal–metal competition.
The Zr(IV)-H4L2 complex
is characterized by one of the highest formation constants reported
to date for a tetrahydroxamate zirconium chelate (log β = 45.9,
pZr = 37.0), although the complex-stability increase derived from
the introduction of the fourth hydroxamate binding unit is lower than
that predicted by theoretical calculations. Solution studies on Ga(III)
complexes revealed that H3L1 and H4L2 are stronger chelators in comparison to DFOB. The complex stability
obtained with the new ligands is also compared with that previously
reported for other hydroxamate ligands. In addition to increasing
the library of the thermodynamic stability data of Ga(III) and Zr(IV)
complexes, the present work allows new insights into Ga(III) and Zr(IV)
coordination chemistry and thermodynamics and broadens the selection
of available chelators for 68Ga(III) and 89Zr(IV).
Solution equilibria studies on Ga(III)
and Zr(IV) complexes
with a series of tri- and tetrahydroxamate ligands are presented.
For this purpose, the rational design and synthesis of two cyclic
complexing agents bearing three and four hydroxamate chelating groups
was performed. The thermodynamic and speciation studies allow a discussion
of the structure−complex stability dependence. The Zr(IV)-tetrahydroxamate
complex is characterized by one of the highest formation constants
reported to date for a hydroxamate zirconium chelator.
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