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Open AccessArticle

Transition Metals Meet Scorpiand-like Ligands

by Salvador Blasco, Begoña Verdejo, María Paz Clares and Enrique García-España

Crystals 2023, 13(9), 1338; https://doi.org/10.3390/cryst13091338 - 1 Sep 2023

Cited by 1 | Viewed by 1671

Scorpiand-like ligands combine the preorganization of the donor atoms of macrocycles and the degrees of freedom of the linear ligands. We prepared the complexes of several of these ligands with transition metal ions and made a crystallographic and water solution speciation studies. The analysis of the resulting crystal structures show that the ligands have the ability to accommodate several metal ions and that the coordination geometry is mostly determined by the ligand. Ligand 6-[3,7-diazaheptyl]-3,6,9–triaza-1-(2,6)-pyridinacyclodecaphane (L3) is an hexadentate ligand that affords a family of isostructural crystals with Cu(II), Mn(II), Ni(II) and Zn(II). The attempts to obtain Co(II) crystals afforded the Co(III) structures instead. Ligand 6-[4-(2-pyridyl)-3-azabutyl]-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane (L2) is very similar to L3 and yields structures similar to it, but its behavior in solution is very different due to the different interaction with protons. Ligand 6-(2-aminoethyl)-3,6,9–triaza-1-(2,6)-pyridinacyclodecaphane (L1) is pentadentate and its complexes allow the metal to be more accessible from the solvent. A Zn(II) structure with L1 shows the species [ZnBrHL1]

^{2 +}

, which exists in a narrow pH range. Full article

(This article belongs to the Special Issue The Polyhedral Face of Coordination Chemistry)

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9 pages, 1070 KB

Open AccessArticle

Mn(II) Complexes of Enlarged Scorpiand-Type Azamacrocycles as Mimetics of MnSOD Enzyme

by Mario Inclán, María Teresa Albelda, Salvador Blasco, Carolina Serena, Javier Ugarte Chicote, Antonio García-España and Enrique García-España

Appl. Sci. 2022, 12(5), 2447; https://doi.org/10.3390/app12052447 - 26 Feb 2022

Cited by 1 | Viewed by 2188

Abstract

Living organisms depend on superoxide dismutase (SOD) enzymes to shield themselves from the deleterious effects of superoxide radical. In humans, alterations of these protective mechanisms have been linked to the pathogenesis of many diseases. However, the therapeutic use of the native enzyme is hindered by, among other things, its high molecular size, low stability, and immunogenicity. For this reason, synthetic SOD mimetic compounds of low molecular weight may have therapeutic potential. We present here three low-molecular-weight compounds, whose Mn²⁺ complexes can mimic, at least partially, the protective activity of SOD-enzymes. These compounds were characterized by NMR, potentiometry, and, to test whether they have protective activity in vitro, by their capacity to restore the growth of SOD-deficient strains of E. coli. In this report, we provide evidence that these compounds form stable complexes with Mn²⁺ and have an in vitro protective effect, restoring up to 75% the growth of the SOD-deficient E. coli. Full article

(This article belongs to the Special Issue Biomedical Applications of Supramolecular Chemistry)

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15 pages, 2948 KB

Open AccessArticle

Ditopic Aza-Scorpiand Ligands Interact Selectively with ds-RNA and Modulate the Interaction upon Formation of Zn²⁺ Complexes

by Lluís Guijarro, Álvaro Martínez-Camarena, Javier U. Chicote, Antonio García-España, Enrique García-España, Mario Inclán, Begoña Verdejo and Jorge González-García

Molecules 2021, 26(13), 3957; https://doi.org/10.3390/molecules26133957 - 28 Jun 2021

Cited by 2 | Viewed by 2649

Abstract

Nucleic acids are essential biomolecules in living systems and represent one of the main targets of chemists, biophysics, biologists, and nanotechnologists. New small molecules are continuously developed to target the duplex (ds) structure of DNA and, most recently, RNA to be used as therapeutics and/or biological tools. Stimuli-triggered systems can promote and hamper the interaction to biomolecules through external stimuli such as light and metal coordination. In this work, we report on the interaction with ds-DNA and ds-RNA of two aza-macrocycles able to coordinate Zn²⁺ metal ions and form binuclear complexes. The interaction of the aza-macrocycles and the Zn²⁺ metal complexes with duplex DNA and RNA was studied using UV thermal and fluorescence indicator displacement assays in combination with theoretical studies. Both ligands show a high affinity for ds-DNA/RNA and selectivity for ds-RNA. The ability to interact with these duplexes is blocked upon Zn²⁺ coordination, which was confirmed by the low variation in the melting temperature and poor displacement of the fluorescent dye from the ds-DNA/RNA. Cell viability assays show a decrease in the cytotoxicity of the metal complexes in comparison with the free ligands, which can be associated with the observed binding to the nucleic acids. Full article

(This article belongs to the Special Issue Ligand Binding to DNA and RNA)

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15 pages, 4532 KB

Open AccessFeature PaperArticle

Sensing Zn²⁺ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

by Matteo Savastano, Matteo Fiaschi, Giovanni Ferraro, Paola Gratteri, Palma Mariani, Antonio Bianchi and Carla Bazzicalupi

Molecules 2020, 25(6), 1355; https://doi.org/10.3390/molecules25061355 - 17 Mar 2020

Cited by 28 | Viewed by 4079

Abstract

Synthesis of the new scorpiand ligand L composed of a [9]aneN₃ macrocyclic ring bearing a CH₂CH₂NHCH₂-anthracene tail is reported. L forms both cation (Zn²⁺) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn²⁺ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn²⁺ in the pH range 6–10 down to nM concentrations of the metal ion. L can efficiently sense Zn²⁺ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion. Full article

(This article belongs to the Special Issue Exclusive Feature Papers in Inorganic Chemistry)

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9 pages, 927 KB

Open AccessArticle

Molecular Rearrangement of an Aza-Scorpiand Macrocycle Induced by pH: A Computational Study

by Jesus Vicente De Julián-Ortiz, Begoña Verdejo, Víctor Polo, Emili Besalú and Enrique García-España

Int. J. Mol. Sci. 2016, 17(7), 1131; https://doi.org/10.3390/ijms17071131 - 14 Jul 2016

Cited by 5 | Viewed by 4818

Abstract

Rearrangements and their control are a hot topic in supramolecular chemistry due to the possibilities that these phenomena open in the design of synthetic receptors and molecular machines. Macrocycle aza-scorpiands constitute an interesting system that can reorganize their spatial structure depending on pH variations or the presence of metal cations. In this study, the relative stabilities of these conformations were predicted computationally by semi-empirical and density functional theory approximations, and the reorganization from closed to open conformations was simulated by using the Monte Carlo multiple minimum method. Full article

(This article belongs to the Special Issue Big Data Analysis and QSAR/QSPR Research in Chemistry, Bio-Medical, and Network Sciences)

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