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7. Exploring the Limits of Ligand Rigidification in Transition Metal Complexes with Mono-N-Functionalized Pyclen Derivatives

Author

Nizou, Gwladys, primary, Garda, Zoltán, additional, Molnár, Enikő, additional, Esteban-Gómez, David, additional, Le Fur, Mariane, additional, Fougère, Olivier, additional, Rousseaux, Olivier, additional, Platas-Iglesias, Carlos, additional, Tripier, Raphaël, additional, Tircsó, Gyula, additional, and Beyler, Maryline, additional

Published
2024
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12. Improving the In Vivo Stability of [52Mn]Mn(II) Complexes with 18-Membered Macrocyclic Chelators for PET Imaging

Author

Harriswangler, Charlene, Omweri, James M., Saini, Shefali, Valencia, Laura, Esteban-Gómez, David, Ranga, Madalina, Guidolin, Nicol, Baranyai, Zsolt, Lapi, Suzanne E., and Platas-Iglesias, Carlos

Abstract

We report the [natMn/52Mn]Mn(II) complexes of the macrocyclic chelators PYAN [3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane] and CHXPYAN [(41R,42R,101R,102R)-3,5,9,11-tetraaza-1,7(2,6)-dipyridina-4,10(1,2)-dicyclohexanacyclododecaphane]. The X-ray crystal structures of Mn-PYAN and Mn-CHXPYAN evidence distorted octahedral geometries through coordination of the nitrogen atoms of the macrocycles. Cyclic voltammetry studies evidence reversible processes due to the Mn(II)/Mn(III) pair, indicating that the complexes are resistant to oxidation. CHXPYAN forms a more thermodynamically stable and kinetically inert Mn(II) complex than PYAN. Radiochemical studies with the radioactive isotope manganese-52 (52Mn, t1/2= 5.6 days) evidenced better radiochemical yields for CHXPYAN than for PYAN. Both [52Mn]Mn(II) complexes remained stable in mouse and human serum, so in vivo stability studies were carried out. Positron emission tomography/computed tomography scans and biodistribution assays indicated that [52Mn]Mn-PYAN has a distribution pattern similar to that of [52Mn]MnCl2, showing persistent radioactivity accumulation in the kidneys. Conversely, [52Mn]Mn-CHXPYAN remained stable in vivo, clearing quickly from the liver and kidneys.

Published
2024
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13. Incorporation of Carboxylate Pendant Arms into 18‐Membered Macrocycles: Effects on [nat/203Pb]Pb(II) Complexation.

Author

Harriswangler, Charlene, McNeil, Brooke L., Brandariz, Isabel, Valencia, Laura, Esteban‐Gómez, David, Ramogida, Caterina F., and Platas‐Iglesias, Carlos

Subjects
SINGLE-photon emission computed tomography, STABILITY constants, RADIOISOTOPES
Abstract

We present a detailed investigation on the coordination chemistry of [nat/203Pb]Pb(II) with chelators H4PYTA and H4CHX‐PYTA. These chelators belong to the family of ligands derived from the 18‐membered macrocyclic backbone PYAN and present varying degrees of rigidity due to the presence of either ethyl or cyclohexyl spacers. A complete study of the stable Pb(II) complexes is carried out via NMR, X‐Ray crystallography, stability constant determination and computational studies. While these studies indicated that Pb(II) complexation is achieved, and the thermodynamic stability of the resulting complexes is very high, a certain degree of fluxionality does exist in both cases. Nevertheless, radiolabeling studies were carried out using SPECT (single photon emission computed tomography) compatible isotope lead‐203 (203Pb, t1/2=51.9 h), and while both chelators complex the radioisotope, the incorporation of carboxylate pendant arms appears to be detrimental towards the stability of the complexes when compared to the previously described amide analogues. Additionally, incorporation of a cyclohexyl spacer does not improve the kinetic inertness of the system. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Donor Radii in Rare-Earth Complexes

Author

Harriswangler, Charlene, primary, Frías, Juan C., additional, Albelda, M. Teresa, additional, Valencia, Laura, additional, García-España, Enrique, additional, Esteban-Gómez, David, additional, and Platas-Iglesias, Carlos, additional

Published
2023
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16. Effect of Magnetic Anisotropy on the 1H NMR Paramagnetic Shifts and Relaxation Rates of Small Dysprosium(III) Complexes

Author

Harriswangler, Charlene, primary, Lucio-Martínez, Fátima, additional, Godec, Léna, additional, Soro, Lohona Kevin, additional, Fernández-Fariña, Sandra, additional, Valencia, Laura, additional, Rodríguez-Rodríguez, Aurora, additional, Esteban-Gómez, David, additional, Charbonnière, Loïc J., additional, and Platas-Iglesias, Carlos, additional

Published
2023
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18. Unravelling the 6sp ← 6s absorption spectra of Bi(III) complexes.

Author

Harriswangler, Charlene, Lucio-Martínez, Fátima, Rodríguez-Rodríguez, Aurora, Esteban-Gómez, David, and Platas-Iglesias, Carlos

Subjects
ABSORPTION spectra, TERNARY forms, COORDINATE covalent bond, PERTURBATION theory, SPIN-orbit interactions, VALENCE (Chemistry), INFRARED absorption
Abstract

We report a spectroscopic and computational study that investigates the absorption spectra of Bi(III) complexes, which often show an absorption band in the UV region (∼270–350 nm) due to 6sp ← 6s transitions. We investigated the spectra of three simple complexes, [BiCl5]2−, [BiCl6]3− and [Bi(DMSO)8]3+, which show absorption maxima at 334, 326 and 279 nm due to 3P1 ← 1S0 transitions. Theoretical calculations based on quasi-degenerate N-electron valence perturbation theory to second order (QD-NEVPT2) provide an accurate description of the absorption spectra when employing CAS(2,9) wave functions. We next investigated the absorption spectra of the [Bi(NOTA)] complex (H3NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid), which forms ternary complexes [Bi(NOTA)X]− (X = Cl, Br or I) in the presence of excess halide in aqueous solutions. Halide binding has an important impact on the position of the 3P1 ← 1S0 transition, which shifts progressively to longer wavelengths from 282 nm ([Bi(NOTA)]) to 298 nm (X = Cl), 305 nm (X = Br) and 325 nm (X = I). Subsequent QD-NEVPT2 calculations indicate that this effect is related to the progressive stabilization of the spin–orbit free states associated with the 6s16p1 configuration on increasing the covalent character of the metal–ligand(s) bonds, rather than with significant differences in spin–orbit coupling (SOC). These studies provide valuable insight into the coordination chemistry of Bi(III), an ion with increasing interest in targeted alpha therapy due to the possible application of bismuth isotopes bismuth-212 (212Bi, t1/2 = 60.6 min) and bismuth-213 (213Bi, t1/2 = 45.6 min). [ABSTRACT FROM AUTHOR]

Published
2024
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20. Bipyridil-based chelators for Gd(III) complexation: kinetic, structural and relaxation properties.

Author

Bunda, Szilvia, Lihi, Norbert, Szaniszló, Zsófia, Esteban-Gómez, David, Platas-Iglesias, Carlos, Kéri, Mónika, Papp, Gábor, and Kálmán, Ferenc Krisztián

Subjects
GADOLINIUM, MAGNETIC resonance imaging, LUMINESCENCE measurement, INTRAVENOUS injections, CONTRAST media, FLUORESCENT probes
Abstract

In the last 20 years, research in the field of MRI (magnetic resonance imaging) contrast agents (CAs) has been intensified due to the emergence of a disease called nephrogenic systemic fibrosis (NSF). NSF has been linked to the in vivo dissociation of certain Gd(III)-based compounds applied in MRI as CAs. To prevent the dechelation of the probes after intravenous injection, the improvement of their in vivo stability is highly desired. The inertness of the Gd(III) chelates can be increased through the rigidification of the ligand structure. One of the potential ligands is (2,2′,2′′,2′′′-(([2,2′-bipyridine]-6,6′-diylbis(methylene))bis(azanetriyl))tetraacetic acid) (H4DIPTA), which has been successfully used as a fluorescent probe for lanthanides; however, it has never been considered as a potential chelator for Gd(III) ions. In this paper, we report the thermodynamic, kinetic and structural features of the complex formed between Gd(III) and DIPTA. Since the solubility of the [Gd(DIPTA)]− chelate is very low under acidic conditions, hampering its thermodynamic characterization, we can only assume that its stability is close to that determined for the structural analogue [Gd(FENTA)]− (H4FENTA: (1,10-phenanthroline-2,9-diyl)bis(methyliminodiacetic acid)), which is similar to that determined for the agent [Gd(DTPA)]2− routinely used in clinical practice. Unfortunately, the inertness of [Gd(DIPTA)]− is significantly lower (t1/2 = 1.34 h) than that observed for [Gd(EGTA)]− and [Gd(DTPA)]2− as a result of its spontaneous dissociation pathway during dechelation. The relaxivity values of [Gd(DIPTA)]− are comparable with those of [Gd(FENTA)]− and somewhat higher than the values characterizing [Gd(DTPA)]2−. Luminescence lifetime measurements indicate the presence of one water molecule (q = 1) in the inner sphere of the complex with a relatively high water exchange rate (k298ex = 43(5) × 106 s−1). DFT calculations suggest a rigid distorted tricapped trigonal prismatic polyhedron for the Gd(III) complex. On the basis of these results, we can conclude that the bipyridine backbone is not favourable with respect to the inertness of the chelate. [ABSTRACT FROM AUTHOR]

Published
2023
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22. Probing Tyrosine Nitration with a Small TbIII-Metallopeptide

Author

Sánchez-Fernández, Rosalía, Sánchez-Temprano, Agustín, Esteban-Gómez, David, Pazos, Elena, Sánchez-Fernández, Rosalía, Sánchez-Temprano, Agustín, Esteban-Gómez, David, and Pazos, Elena

Abstract

[Abstract] Tyrosine nitration, a post-translational modification (PTM) that takes place under nitrosative stress conditions, occurs through a non-enzymatic peroxynitrite-mediated reaction. Although protein nitration has long been considered an irreversible PTM involved in nitrosative stress-associated diseases, it has also been suggested to be a regulatory mechanism of signal transduction. Therefore, the development of tools that help to understand this protein modification is of great interest. Herein, we explore a TbIII-chelating metallopeptide to monitor tyrosine nitration. The luminescence of this probe decreases significantly between its non-nitrated and nitrated states, and this reduction in the luminescence intensity is directly related to the degree of tyrosine nitration after treatment with peroxynitrite. Remarkably, the luminescence intensity changes after nitration are not affected in the presence of complex biological media, which makes it a promising tool for understanding this protein modification.

Published
2023

29. Chapter 2. Gadolinium-based Contrast Agents

Author

Helm, Lothar, primary, Morrow, Janet R., additional, Bond, Christopher J., additional, Carniato, Fabio, additional, Botta, Mauro, additional, Braun, Mihály, additional, Baranyai, Zsolt, additional, Pujales-Paradela, Rosa, additional, Regueiro-Figueroa, Martín, additional, Esteban-Gómez, David, additional, Platas-Iglesias, Carlos, additional, and Scholl, Timothy J., additional

Published
2017
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34. Versatile Macrocyclic Platform for the Complexation of [ⁿᵃᵗY/⁹⁰Y]Yttrium and Lanthanide Ions

Author

Harriswangler, Charlene, Caneda-Martínez, Laura, Rousseaux, Olivier, Esteban-Gómez, David, Fougère, Olivier, Pujales-Paradela, Rosa, Valencia, Laura, Fernández-Pérez, María-Isabel, Lepareur, Nicolas, and Platas-Iglesias, Carlos

Abstract

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] We report a macrocyclic ligand (H3L6) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the YL6 and TbL6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (1H, 13C, and 89Y) and DFT calculations indicated that the structure of the YL6 complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the EuL6 and TbL6 complexes revealed Ln3+-centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The YL6 complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10–5 M). Studies using the 90Y-nuclide confirmed fast radiolabeling since [90Y]YL6 is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the [90Y]YL6 complex. All of these experiments combined suggest the potential application of H3L6 derivatives as Y-based radiopharmaceuticals. C.P.-I., and D.E.-G. thank Ministerio de Ciencia e Innovación (Grant PID2019-108352RJ-I00) and Xunta de Galicia (Grant ED431B 2020/52) for generous financial support. The authors are indebted to Centro de Supercomputación of Galicia (CESGA) for providing the computer facilities. C.H. thanks Ministerio de Ciencia e Innovación (Grant PRE2020-092888) and Xunta de Galicia (Grant ED481A 2021/070) for funding her PhD contracts. N.L. acknowledges Labex IRON (grant no. ANR-11-LABX-0018) and Guerbet for financial support. L.V. is indebted to CACTI (Universidade de Vigo) for X-ray measurements. Funding for open access provided by Universidade da Coruña/CISUG Xunta de Galicia; ED431B 2020/52 Xunta de Galicia; ED481A 2021/070 Labex Iron; ANR-11-LABX-0018

Published
2022

35. Synthesis and Structural Analysis of Push-Pull Imidazole-Triazole Based Fluorescent Bifunctional Chemosensor for CU2+ and FE2+ Detection

Author

Da Lama Vázquez, Ana, Pérez Sestelo, José, Valencia, Laura, Esteban-Gómez, David, Sarandeses, Luis A., Martínez, Montserrat, Da Lama Vázquez, Ana, Pérez Sestelo, José, Valencia, Laura, Esteban-Gómez, David, Sarandeses, Luis A., and Martínez, Montserrat

Abstract

[Abstract] Fluorescent imidazole-triazole based ligands L1 and L2 have been designed as chemical push-pull chemosensors for divalent metal ions and synthesized through palladium-catalyzed cross-coupling reactions using indium organometallics and click chemistry. The novel ligands exhibit intense absorption in the ultraviolet region with high molar extinction coefficients, and strong fluorescence emission with large Stokes displacements. On the basis of UV–Vis absorption spectroscopy and fluorescence emission data in acetonitrile, L1 is shown as a bifuncional chemosensor with differential response for Fe2+ and Cu2+ over a range of selected 3d divalent and other metal ions. The binding site of the ligand was established by single-crystal X-ray diffraction and 1H NMR spectroscopy studies. The association constants, determined by spectrofluorimetric titrations, show a steady binding affinity of L1 for Cu2+ and Fe2+ in comparison with other previously reported fluorescent bidentate chemosensors, offering the lowest limit of detection (LOD) with Cu2+. DFT calculations provide a rationale properly understanding and interpreting the experimentally observed results. Indeed, a mechanism of the different optical responses of L1 towards 3d divalent metal ions is proposed.

Published
2022

36. Rigidified Derivative of the Non-macrocyclic Ligand H₄OCTAPA for Stable Lanthanide(III) Complexation

Author

Lucio Martínez, Fátima, Garda, Zoltán, Váradi, Balázs, Kálmán, Ferenc, Esteban-Gómez, David, Tóth, Éva, Tircsó, Gyula, Platas-Iglesias, Carlos, Lucio Martínez, Fátima, Garda, Zoltán, Váradi, Balázs, Kálmán, Ferenc, Esteban-Gómez, David, Tóth, Éva, Tircsó, Gyula, and Platas-Iglesias, Carlos

Abstract

[Abstract] The stability constants of lanthanide complexes with the potentially octadentate ligand CHXOCTAPA4–, which contains a rigid 1,2-diaminocyclohexane scaffold functionalized with two acetate and two picolinate pendant arms, reveal the formation of stable complexes [log KLaL = 17.82(1) and log KYbL = 19.65(1)]. Luminescence studies on the Eu3+ and Tb3+ analogues evidenced rather high emission quantum yields of 3.4 and 11%, respectively. The emission lifetimes recorded in H2O and D2O solutions indicate the presence of a water molecule coordinated to the metal ion. 1H nuclear magnetic relaxation dispersion profiles and 17O NMR chemical shift and relaxation measurements point to a rather low water exchange rate of the coordinated water molecule (kex298 = 1.58 × 106 s–1) and relatively high relaxivities of 5.6 and 4.5 mM–1 s–1 at 20 MHz and 25 and 37 °C, respectively. Density functional theory calculations and analysis of the paramagnetic shifts induced by Yb3+ indicate that the complexes adopt an unprecedented cis geometry with the two picolinate groups situated on the same side of the coordination sphere. Dissociation kinetics experiments were conducted by investigating the exchange reactions of LuL occurring with Cu2+. The results confirmed the beneficial effect of the rigid cyclohexyl group on the inertness of the Lu3+ complex. Complex dissociation occurs following proton- and metal-assisted pathways. The latter is relatively efficient at neutral pH, thanks to the formation of a heterodinuclear hydroxo complex.

Published
2022

38. Rigid H4OCTAPA derivatives as model chelators for the development of Bi(III)-based radiopharmaceuticals.

Author

Lucio-Martínez, Fátima, Esteban-Gómez, David, Valencia, Laura, Horváth, Dávid, Szücs, Dániel, Fekete, Anikó, Szikra, Dezső, Tircsó, Gyula, and Platas-Iglesias, Carlos

Subjects
*RADIOPHARMACEUTICALS, *RADIOLABELING, *LIGANDS (Chemistry), *CATIONS
Abstract

Octadentate ligands containing ethyl (H4OCTAPA), cyclohexyl (H4CHXOCTAPA) or cyclopentyl (H4CpOCTAPA) spacers were assessed as chelators for Bi(III)-based radiopharmaceuticals. The H4CHXOCTAPA chelator displays excellent properties, including 205/206Bi-nuclide radiolabelling under mild conditions, excellent stability in serum and in the presence of competing cations or H5DTPA. The poor performance of H4CpOCTAPA appears to be related to the stereochemical activity of the Bi(III) lone pair. [ABSTRACT FROM AUTHOR]

Published
2023
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44. Prediction of Gd(Iii) Complex Thermodynamic Stability

Author

Rodríguez-Rodríguez, Aurora, primary, Uzal-Varela, Rocío, additional, Wang, Huan, additional, Esteban-Gómez, David, additional, Brandariz, Isabel, additional, Gale, Eric M., additional, Caravan, Peter, additional, and Platas-Iglesias, Carlos, additional

Published
2022
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49. Complexation of C-Functionalized Cyclams with Copper(II) and Zinc(II): Similarities and Changes When Compared to Parent Cyclam Analogues

Author

Lelong, Evan, primary, Suh, Jong-Min, additional, Kim, Gunhee, additional, Esteban-Gómez, David, additional, Cordier, Marie, additional, Lim, Mi Hee, additional, Delgado, Rita, additional, Royal, Guy, additional, Platas-Iglesias, Carlos, additional, Bernard, Hélène, additional, and Tripier, Raphaël, additional

Published
2021
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50. Understanding the Effect of the Electron Spin Relaxation on the Relaxivities of Mn(II) Complexes with Triazacyclononane Derivatives

Author

Uzal-Varela, Rocío, Valencia, Laura, Lalli, Daniela, Maneiro, Marcelino, Esteban-Gómez, David, Platas-Iglesias, Carlos, Botta, Mauro, Rodríguez-Rodríguez, Aurora, Uzal-Varela, Rocío, Valencia, Laura, Lalli, Daniela, Maneiro, Marcelino, Esteban-Gómez, David, Platas-Iglesias, Carlos, Botta, Mauro, and Rodríguez-Rodríguez, Aurora

Abstract

[Abstract] Investigating the relaxation of water ¹H nuclei induced by paramagnetic Mn(II) complexes is important to understand the mechanisms that control the efficiency of contrast agents used in diagnostic magnetic resonance imaging (MRI). Herein, a series of potentially hexadentate triazacyclononane (TACN) derivatives containing different pendant arms were designed to explore the relaxation of the electron spin in the corresponding Mn(II) complexes by using a combination of ¹H NMR relaxometry and theoretical calculations. These ligands include 1,4,7-triazacyclononane-1,4,7-triacetic acid (H₃NOTA) and three derivatives in which an acetate group is replaced by sulfonamide (H₃NOƨASAm), amide (H₂NOƨAM), or pyridyl (H₂NOƨAPy) pendants. The analogue of H₃NOTA containing three propionate pendant arms (H₃NOTPrA) was also investigated. The X-ray structure of the derivative containing two acetate groups and a sulfonamide pendant arm [Mn(NOƨASAm)]⁻ evidenced six-coordination of the ligand to the metal ion, with the coordination polyhedron being close to a trigonal prism. The relaxivities of all complexes at 20 MHz and 25 °C (1.1–1.3 mM⁻¹ s⁻¹) are typical of systems that lack water molecules coordinated to the metal ion. The nuclear magnetic relaxation profiles evidence significant differences in the relaxivities of the complexes at low fields (<1 MHz), which are associated with different spin relaxation rates. The zero field splitting (ZFS) parameters calculated by using DFT and CASSCF methods show that electronic relaxation is relatively insensitive to the nature of the donor atoms. However, the twist angle of the two tripodal faces that delineate the coordination polyhedron, defined by the N atoms of the TACN unit (lower face) and the donor atoms of the pendant arms (upper face), has an important effect in the ZFS parameters. A twist angle close to the ideal value for an octahedral coordination (60°), such as that in [Mn(NOTPrA)]⁻, leads to a small ZFS energy, whereas thi

Published
2021

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