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Brown AM, Butman JL, Lengacher R, Vargo NP, Martin KE, Koller A, Śmiłowicz D, Boros E, Robinson JR. N, N-Alkylation Clarifies the Role of N- and O-Protonated Intermediates in Cyclen-Based 64Cu Radiopharmaceuticals. Inorg Chem 2023; 62:1362-1376. [PMID: 36490364 DOI: 10.1021/acs.inorgchem.2c02907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Radioisotopes of Cu, such as 64Cu and 67Cu, are alluring targets for imaging (e.g., positron emission tomography, PET) and radiotherapeutic applications. Cyclen-based macrocyclic polyaminocarboxylates are one of the most frequently examined bifunctional chelators in vitro and in vivo, including the FDA-approved 64Cu radiopharmaceutical, Cu(DOTATATE) (Detectnet); however, connections between the structure of plausible reactive intermediates and their stability under physiologically relevant conditions remain to be established. In this study, we share the synthesis of a cyclen-based, N,N-alkylated spirocyclic chelate, H2DO3AC4H8, which serves as a model for N-protonation. Our combined experimental (in vitro and in vivo) and computational studies unravel complex pH-dependent speciation and enable side-by-side comparison of N- and O-protonated species of relevant 64Cu radiopharmaceuticals. Our studies suggest that N-protonated species are not inherently unstable species under physiological conditions and demonstrate the potential of N,N-alkylation as a tool for the rational design of future radiopharmaceuticals.
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Affiliation(s)
- Alexander M Brown
- Department of Chemistry, Brown University, Providence, Rhode Island02912, United States
| | - Jana L Butman
- Department of Chemistry, Brown University, Providence, Rhode Island02912, United States
| | - Raphael Lengacher
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York11794, United States
| | - Natasha P Vargo
- Department of Chemistry, Brown University, Providence, Rhode Island02912, United States
| | - Kirsten E Martin
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York11794, United States
| | - Angus Koller
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York11794, United States
| | - Dariusz Śmiłowicz
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York11794, United States
| | - Eszter Boros
- Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York11794, United States
| | - Jerome R Robinson
- Department of Chemistry, Brown University, Providence, Rhode Island02912, United States
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Uzal-Varela R, Patinec V, Tripier R, Valencia L, Maneiro M, Canle M, Platas-Iglesias C, Esteban-Gómez D, Iglesias E. On the dissociation pathways of copper complexes relevant as PET imaging agents. J Inorg Biochem 2022; 236:111951. [PMID: 35963110 DOI: 10.1016/j.jinorgbio.2022.111951] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 07/15/2022] [Accepted: 07/27/2022] [Indexed: 02/07/2023]
Abstract
Several bifunctional chelators have been synthesized in the last years for the development of new 64Cu-based PET agents for in vivo imaging. When designing a metal-based PET probe, it is important to achieve high stability and kinetic inertness once the radioisotope is coordinated. Different competitive assays are commonly used to evaluate the possible dissociation mechanisms that may induce Cu(II) release in the body. Among them, acid-assisted dissociation tests or transchelation challenges employing EDTA or SOD are frequently used to evaluate both solution thermodynamics and the kinetic behavior of potential metal-based systems. Despite of this, the Cu(II)/Cu(I) bioreduction pathway that could be promoted by the presence of bioreductants still remains little explored. To fill this gap we present here a detailed spectroscopic study of the kinetic behavior of different macrocyclic Cu(II) complexes. The complexes investigated include the cross-bridge cyclam derivative [Cu(CB-TE1A)]+, whose structure was determined using single-crystal X-ray diffraction. The acid-assisted dissociation mechanism was investigated using HClO4 and HCl to analyse the effect of the counterion on the rate constants. The complexes were selected so that the effects of complex charge and coordination polyhedron could be assessed. Cyclic voltammetry experiments were conducted to investigate whether the reduction to Cu(I) falls within the window of common bioreducing agents. The most striking behavior concerns the [Cu(NO2Th)]2+ complex, a 1,4,7-triazacyclononane derivative containing two methylthiazolyl pendant arms. This complex is extremely inert with respect to dissociation following the acid-catalyzed mechanism, but dissociates rather quickly in the presence of a bioreductant like ascorbic acid.
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Affiliation(s)
- Rocío Uzal-Varela
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain
| | - Véronique Patinec
- Univ Brest, UMR-CNRS 6521 CEMCA, 6 avenue Victor le Gorgeu, 29238 Brest, France
| | - Raphaël Tripier
- Univ Brest, UMR-CNRS 6521 CEMCA, 6 avenue Victor le Gorgeu, 29238 Brest, France
| | - Laura Valencia
- Departamento de Química Inorgánica, Universidade de Vigo, Facultad de Ciencias, 36310 Pontevedra, Spain
| | - Marcelino Maneiro
- Departamento de Química Inorgánica, Universidade de Santiago de Compostela, Facultade de Ciencias, 27002 Lugo, Spain
| | - Moisés Canle
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain
| | - Carlos Platas-Iglesias
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain
| | - David Esteban-Gómez
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain.
| | - Emilia Iglesias
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, 15071 A Coruña, Galicia, Spain.
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Tosato M, Pelosato M, Franchi S, Isse AA, May NV, Zanoni G, Mancin F, Pastore P, Badocco D, Asti M, Di Marco V. When ring makes the difference: coordination properties of Cu 2+/Cu + complexes with sulfur-pendant polyazamacrocycles for radiopharmaceutical applications. NEW J CHEM 2022. [DOI: 10.1039/d2nj01032a] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Cu2+/+ complexes formed by sulfur-containing polyazamacrocycles were studied in aqueous solution using potentiometry, UV-Vis, NMR, EPR, and cyclic voltammetry.
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Affiliation(s)
- Marianna Tosato
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Matteo Pelosato
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Sara Franchi
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | | | - Nóra Veronica May
- Centre for Structural Science, Research Centre for Natural Sciences, 1117 Budapest, Hungary
| | - Giordano Zanoni
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Fabrizio Mancin
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Paolo Pastore
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Denis Badocco
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Mattia Asti
- Radiopharmaceutical Chemistry Section, Nuclear Medicine Unit, AUSL-IRCCS di Reggio Emilia, 42122 Reggio Emilia, Italy
| | - Valerio Di Marco
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
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4
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Kubíček V, Böhmová Z, Ševčíková R, Vaněk J, Lubal P, Poláková Z, Michalicová R, Kotek J, Hermann P. NOTA Complexes with Copper(II) and Divalent Metal Ions: Kinetic and Thermodynamic Studies. Inorg Chem 2018; 57:3061-3072. [PMID: 29488748 DOI: 10.1021/acs.inorgchem.7b02929] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
H3nota derivatives are among the most studied macrocyclic ligands and are widely used for metal ion binding in biology and medicine. Despite more than 40 years of chemical research on H3nota, the comprehensive study of its solution chemistry has been overlooked. Thus, the coordination behavior of H3nota with several divalent metal ions was studied in detail with respect to its application as a chelator for copper radioisotopes in medical imaging and therapy. In the solid-state structure of the free ligand in zwitterionic form, one proton is bound in the macrocyclic cavity through a strong intramolecular hydrogen-bond system supporting the high basicity of the ring amine groups (log Ka = 13.17). The high stability of the [Cu(nota)]- complex (log KML = 23.33) results in quantitative complex formation, even at pH <1.5. The ligand is moderately selective for Cu(II) over other metal ions (e.g., log KML(Zn) = 22.32 and log KML(Ni) = 19.24). This ligand forms a more stable complex with Mg(II) than with Ca(II) and forms surprisingly stable complexes with alkali-metal ions (stability order Li(I) > Na(I) > K(I)). Thus, H3nota shows high selectivity for small metal ions. The [Cu(nota)]- complex is hexacoordinated at neutral pH, and the equatorial N2O2 interaction is strengthened by complex protonation. Detailed kinetic studies showed that the Cu(II) complex is formed quickly (millisecond time scale at cCu ≈ 0.1 mM) through an out-of-cage intermediate. Conversely, conductivity measurements revealed that the Zn(II) complex is formed much more slowly than the Cu(II) complex. The Cu(II) complex has medium kinetic inertness (τ1/2 46 s; pH 0, 25 °C) and is less resistant to acid-assisted decomplexation than Cu(II) complexes with H4dota and H4teta. Surprisingly, [Cu(nota)]- decomplexation is decelerated in the presence of Zn(II) ions due to the formation of a stable dinuclear complex. In conclusion, H3nota is a good carrier of copper radionuclides because the [Cu(nota)]- complex is predominantly formed over complexes with common impurities in radiochemical formulations, Zn(II) and Ni(II), for thermodynamic and, primarily, for kinetic reasons. Furthermore, the in vivo stability of the [Cu(nota)]- complex may be increased due to the formation of dinuclear complexes when it interacts with biometals.
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Affiliation(s)
- Vojtěch Kubíček
- Department of Inorganic Chemistry, Faculty of Science , Charles University , Hlavova 8 , 128 40 Prague 2 , Czech Republic
| | - Zuzana Böhmová
- Department of Inorganic Chemistry, Faculty of Science , Charles University , Hlavova 8 , 128 40 Prague 2 , Czech Republic
| | - Romana Ševčíková
- Department of Chemistry , Masaryk University , Kotlářská 2 , 611 37 Brno , Czech Republic
| | - Jakub Vaněk
- Department of Chemistry , Masaryk University , Kotlářská 2 , 611 37 Brno , Czech Republic.,Central European Institute of Technology (CEITEC) , Masaryk University , Kamenice 5 , 625 00 Brno , Czech Republic
| | - Přemysl Lubal
- Department of Chemistry , Masaryk University , Kotlářská 2 , 611 37 Brno , Czech Republic.,Central European Institute of Technology (CEITEC) , Masaryk University , Kamenice 5 , 625 00 Brno , Czech Republic
| | - Zuzana Poláková
- Department of Inorganic Chemistry, Faculty of Science , Charles University , Hlavova 8 , 128 40 Prague 2 , Czech Republic
| | - Romana Michalicová
- Department of Chemistry , Masaryk University , Kotlářská 2 , 611 37 Brno , Czech Republic
| | - Jan Kotek
- Department of Inorganic Chemistry, Faculty of Science , Charles University , Hlavova 8 , 128 40 Prague 2 , Czech Republic
| | - Petr Hermann
- Department of Inorganic Chemistry, Faculty of Science , Charles University , Hlavova 8 , 128 40 Prague 2 , Czech Republic
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5
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Ševčík R, Vaněk J, Michalicová R, Lubal P, Hermann P, Santos IC, Santos I, Campello MPC. Formation and decomplexation kinetics of copper(ii) complexes with cyclen derivatives having mixed carboxylate and phosphonate pendant arms. Dalton Trans 2018; 45:12723-33. [PMID: 27460053 DOI: 10.1039/c6dt01127f] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The kinetic properties of Cu(ii) complexes of H4dota and its analogues with one (H5do3ap), two in the 1,7-position (trans-H6do2a2p), three (H7doa3p) and four (H8dotp) phosphonic acid pendant arms were investigated. The formation of a Cu(ii) complex with H4dota, trans-H6do2a2p and H8dotp at a slightly acidic pH is faster for the phosphonic acid derivatives than for H4dota, but with no simple dependence on the number of -CH2PO3H2 substituents (trans-H6do2a2p > H8dotp > H4dota; pH 4-6). Relative differences in the reactivity among the differently protonated species (HnL(x-)) of the same ligand are successively decreased with the more phosphonic acid groups in the ligand. The faster complexation is probably caused by the higher ability of phosphonates to bind the metal ion and/or to assist in the transfer of protons from the ring amine groups to the bulk water. The acid-assisted decomplexation kinetics of the complexes was followed in highly acidic solutions ([H(+)] = 0.01-5 M) and at different temperatures (15-70 °C) to determine the activation parameters of the reaction. The kinetic inertness of the Cu(ii) complexes follows the order: H4dota > H5do3ap > trans-H6do2a2p > H7doa3p > H8dotp. To obtain information on the influence of additional pendant arms, analogous data were obtained for trans-H2do2a. The ligand is less reactive than H4dota, but the kinetic inertness of its Cu(ii) complex is similar to that of the H4dota complex. As it was considered that the published thermodynamics data on the Cu(ii)-H8dotp system are probably incorrect, the system was re-investigated. It showed a very high stability for the [Cu(dotp)](6-) species and the easy formation of several Cu2L species in the presence of an excess of the metal ion. Also, the structure of the (H6doa3p)(-) anion in the solid state was determined. These experimental data demonstrate that the substitution of acetic acid pendant arms by methylphosphonic acid ones in H4dota-like ligands increases the rate of complexation but significantly decreases the kinetic inertness of the Cu(ii) complexes.
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Affiliation(s)
- R Ševčík
- Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic.
| | - J Vaněk
- Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic. and Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
| | - R Michalicová
- Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic.
| | - P Lubal
- Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic. and Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
| | - P Hermann
- Department of Inorganic Chemistry, Faculty of Science, Universita Karlova (Charles University), Hlavova 2030, 128 40 Prague 2, Czech Republic
| | - I C Santos
- Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal.
| | - I Santos
- Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal.
| | - M P C Campello
- Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal.
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6
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Moreno S, Ortega P, de la Mata FJ, Ottaviani MF, Cangiotti M, Fattori A, Muñoz-Fernández MÁ, Gómez R. Bifunctional Chelating Agents Based on Ionic Carbosilane Dendrons with DO3A at the Focal Point and Their Complexation Behavior with Copper(II). Inorg Chem 2015; 54:8943-56. [DOI: 10.1021/acs.inorgchem.5b01047] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Silvia Moreno
- Departamento
de Química Orgánica e Inorgánica, Universidad de Alcalá, Edificio de Farmacia 28871, Alcalá de Henares, Spain
- Spain/Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), C/ Poeta Mariano Esquillor s/n 50018, Zaragoza, Spain
| | - Paula Ortega
- Departamento
de Química Orgánica e Inorgánica, Universidad de Alcalá, Edificio de Farmacia 28871, Alcalá de Henares, Spain
- Spain/Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), C/ Poeta Mariano Esquillor s/n 50018, Zaragoza, Spain
| | - Francisco Javier de la Mata
- Departamento
de Química Orgánica e Inorgánica, Universidad de Alcalá, Edificio de Farmacia 28871, Alcalá de Henares, Spain
- Spain/Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), C/ Poeta Mariano Esquillor s/n 50018, Zaragoza, Spain
| | - Maria Francesca. Ottaviani
- Departments
of Earth, Life and Environment Sciences, University of Urbino, Via Ca’ le Suore 2/4, Urbino 61029, Italy
| | - Michela Cangiotti
- Departments
of Earth, Life and Environment Sciences, University of Urbino, Via Ca’ le Suore 2/4, Urbino 61029, Italy
| | - Alberto Fattori
- Departments
of Earth, Life and Environment Sciences, University of Urbino, Via Ca’ le Suore 2/4, Urbino 61029, Italy
| | - María Ángeles Muñoz-Fernández
- Laboratorio
de Inmunobiologia Molecular, Hospital General Universitario Gregorio Marañon, Madrid, Spain
- Spain/Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), C/ Poeta Mariano Esquillor s/n 50018, Zaragoza, Spain
| | - Rafael Gómez
- Departamento
de Química Orgánica e Inorgánica, Universidad de Alcalá, Edificio de Farmacia 28871, Alcalá de Henares, Spain
- Spain/Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), C/ Poeta Mariano Esquillor s/n 50018, Zaragoza, Spain
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7
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Baranyai Z, Reich D, Vágner A, Weineisen M, Tóth I, Wester HJ, Notni J. A shortcut to high-affinity Ga-68 and Cu-64 radiopharmaceuticals: one-pot click chemistry trimerisation on the TRAP platform. Dalton Trans 2015; 44:11137-46. [PMID: 25999035 DOI: 10.1039/c5dt00576k] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Due to its 3 carbonic acid groups being available for bioconjugation, the TRAP chelator (1,4,7-triazacyclononane-1,4,7-tris(methylene(2-carboxyethylphosphinic acid))) is chosen for the synthesis of trimeric bioconjugates for radiolabelling. We optimized a protocol for bio-orthogonal TRAP conjugation via Cu(I)-catalyzed Huisgen-cycloaddition of terminal azides and alkynes (CuAAC), including a detailed investigation of kinetic properties of Cu(II)-TRAP complexes. TRAP building blocks for CuAAC, TRAP(alkyne)3 and TRAP(azide)3 were obtained by amide coupling of propargylamine/3-azidopropyl-1-amine, respectively. For Cu(II) complexes of neat and triply amide-functionalized TRAP, the equilibrium properties as well as pseudo-first-order Cu(II)-transchelation, using 10 to 30 eq. of NOTA and EDTA, were studied by UV-spectrophotometry. Dissociation of any Cu(II)-TRAP species was found to be independent on the nature or excess of a competing chelator, confirming a proton-driven two-step mechanism. The respective thermodynamic stability constants (log K(ML): 19.1 and 17.6) and dissociation rates (k: 38 × 10(-6) and 7 × 10(-6) s(-1), 298 K, pH 4) show that the Cu(II) complex of the TRAP-conjugate possesses lower thermodynamic stability but higher kinetic inertness. At pH 2-3, its demetallation with NOTA was complete within several hours/days at room temperature, respectively, enabling facile Cu(II) removal after click coupling by direct addition of NOTA trihydrochloride to the CuAAC reaction mixture. Notwithstanding this, an extrapolated dissociation half life of >100 h at 37 °C and pH 7 confirms the suitability of TRAP-bioconjugates for application in Cu-64 PET (cf. t(1/2)(Cu-64) = 12.7 h). To showcase advantages of the method, TRAP(DUPA-Pep)3, a trimer of the PSMA inhibitor DUPA-Pep, was synthesized using 1 eq. TRAP(alkyne)3, 3.3 eq. DUPA-Pep-azide, 10 eq. Na ascorbate, and 1.2 eq. Cu(II)-acetate. Its PSMA affinity (IC50), determined by the competition assay on LNCaP cells, was 18-times higher than that of the corresponding DOTAGA monomer (IC50: 2 ± 0.1 vs. 36 ± 4 nM), resulting in markedly improved contrast in Ga-68-PET imaging. In conclusion, the kinetic inertness profile of Cu(II)-TRAP conjugates allows for simple Cu(II) removal after click functionalisation by means of transchelation, but also confirms their suitability for Cu-64-PET as demonstrated previously (Dalton Trans., 2012, 41, 13803).
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Affiliation(s)
- Zsolt Baranyai
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4032, Hungary
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8
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Fodor T, Bányai I, Bényei A, Platas-Iglesias C, Purgel M, Horváth GL, Zékány L, Tircsó G, Tóth I. [Tl(III)(dota)](-): An Extraordinarily Robust Macrocyclic Complex. Inorg Chem 2015; 54:5426-37. [PMID: 25977977 DOI: 10.1021/acs.inorgchem.5b00458] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The X-ray structure of {C(NH2)3}[Tl(dota)]·H2O shows that the Tl(3+) ion is deeply buried in the macrocyclic cavity of the dota(4-) ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) with average Tl-N and Tl-O distances of 2.464 and 2.365 Å, respectively. The metal ion is directly coordinated to the eight donor atoms of the ligand, which results in a twisted square antiprismatic (TSAP') coordination around Tl(3+). A multinuclear (1)H, (13)C, and (205)Tl NMR study combined with DFT calculations confirmed the TSAP' structure of the complex in aqueous solution, which exists as the Λ(λλλλ)/Δ(δδδδ) enantiomeric pair. (205)Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl(dota)](-) + H(+) ⇆ [Tl(Hdota)] to be determined, which turned out to be pK(H)Tl(dota) = 1.4 ± 0.1. [Tl(dota)](-) does not react with Br(-), even when using an excess of the anion, but it forms a weak mixed complex with cyanide, [Tl(dota)](-) + CN(-) ⇆ [Tl(dota)(CN)](2-), with an equilibrium constant of Kmix = 6.0 ± 0.8. The dissociation of the [Tl(dota)](-) complex was determined by UV-vis spectrophotometry under acidic conditions using a large excess of Br(-), and it was found to follow proton-assisted kinetics and to take place very slowly (∼10 days), even in 1 M HClO4, with the estimated half-life of the process being in the 10(9) h range at neutral pH. The solution dynamics of [Tl(dota)](-) were investigated using (13)C NMR spectroscopy and DFT calculations. The (13)C NMR spectra recorded at low temperature (272 K) point to C4 symmetry of the complex in solution, which averages to C4v as the temperature increases. This dynamic behavior was attributed to the Λ(λλλλ) ↔ Δ(δδδδ) enantiomerization process, which involves both the inversion of the macrocyclic unit and the rotation of the pendant arms. According to our calculations, the arm-rotation process limits the Λ(λλλλ) ↔ Δ(δδδδ) interconversion.
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Affiliation(s)
| | | | | | - Carlos Platas-Iglesias
- ∥Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, Campus da Zapateira-Rúa da Fraga 10, 15008 A Coruña, Spain
| | - Mihály Purgel
- ⊥MTA-DE Homogeneous Catalysis and Reaction Mechanisms Research Group, H-4032 Debrecen, Egyetem tér 1, Hungary
| | - Gábor L Horváth
- #Institute of Innate Immunity, University Hospital, University of Bonn, 53127 Bonn, Germany
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9
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Ševčík R, Vaněk J, Lubal P, Kotková Z, Kotek J, Hermann P. Formation and dissociation kinetics of copper(II) complexes with tetraphosphorus acid DOTA analogs. Polyhedron 2014. [DOI: 10.1016/j.poly.2013.09.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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