Cyclen based bis-macrocyclic ligands as phosphates receptors. A potentiometric and NMR study

Abstract

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and four cyclen based bis-macrocycles ligands possessing ortho-(BOC), meta-(BMC), para-xylenyl (BPC) or 2,6-pyridinyl (BPyC) linker was investigated by potentiometric measurements and NMR spectroscopy. Each ligand gave protonated species in aqueous solution that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and Coulombic attraction between the organic host and the inorganic guest. The equilibrium constants for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed the importance of the distance between the two cyclen cores and underlined, especially for the triphosphate species, the contribution of the nitrogen atom of the pyridinyl spacer as a supplementary anchoring point in acidic medium.

Selective Binding of Glyphosate by a Ditopic Cyclic–Open‐Chain Polyazaligand in Aqueous Solution

“…Five spectra have been selected and are presented in Figure 3. The spectra suggest that, as described previously for similar bis-macrocyclic ligands, [22,23,25] the first two protons (log K 011 = 11.09, log K 012 = 10.27) occupy alternate positions (N6, N7, N8, or N9) on each cyclic core and the third and fourth constants (log K 013 = 9.20, log K 014 = 8.14) correspond to the binding of a further proton on each macrocyclic moiety, as evidenced by the simultaneous downfield shifts of the α-N protons (NCH 2 and NCH 2 Py) and β-N protons (NCH 2 CH 2 CH 2 N) from basic medium to pH 5.9. Note, the downfield shifts observed below pH 3 for the signals of the aromatic protons (Py) of L4py indicate that the fifth constant (log K 015 = 2.43) can be attributed to the protonation of the nitrogen atom of the pyridine linker.…”

“…In fact, L4py shows similar complexation behavior towards the three anions ( Figure 6, b). As previously observed for tetraazamacrocycle-based ditopic receptors, [22][23][24][25][26] L4py forms stable complexes with all three substrates in a wide pH range (2-10), the stability of the adducts decreasing only above pH 10. Despite the high percentage of complexes formed in the pH range 2-10 (65-90 %), L4py does not show any selectivity for the studied substrates.…”

“…In this way, dimeric and trimeric ligands based on cyclic or linear tetraamines linked by aromatic spacers proved to be attractive and selective hosts for these anions. [22][23][24][25][26][27][28][29] Recently, a series of mixed ligands composed of a cyclam unit and an acyclic amino moiety linked by a pyridine spacer presented high complexation constants with the anions mentioned above. In some cases, the nitrogen atom of the pyridine linker provided an additional anchor point for the anionic guest due to the formation of a hydrogen bond, which enhanced the overall stability of the complex.…”

From Flexible to Constrained Tris(tetraamine) Ligands: Synthesis, Acid–Base Properties, and Structural Effect on the Coordination Process with Nucleotides

“…Ditopic linear octaamines proved to be highly protonated and flexible receptors in neutral medium [6] and cyclen-based bismacrocycles proved to be rigid but more selective ligands for binding of ATP or polyphosphates. [7] Furthermore, polytopic protonsponge ligands, based on cross-bridged cyclens, were presented as constrained but efficient receptors. In continuation of these works focusing on the design of innovative anions receptors, [6,7] we present here the synthesis of tritopic tetraamine ligands with a mesitylenyl spacer followed by an acid-base study and their interaction with polyphosphate nucleotides by NMR and potentiometric investigations.…”

Synthesis and Biophysical Studies of Bis‐Macrocyclic Cobalt/Copper(II) Complexes Having a Pyridine Spacer with CT DNA and 5′‐GMP

“…The study of such macrocyclic complexes is notably important owing to the fact that they are utilized as new effective catalysts in chemical synthesis [11], apart from their use as models in biological systems [12]. Polyprotonated macrocycles behave as effective receptors for polycharged anions in aqueous solutions [13] [14]; they strongly associate to nucleotides via electrostatic interactions between the cationic binding sites (ammonium groups) of the receptor and the negatively charged polyphosphate chain.…”