Macrocyclic ligands with 18-membered rings containing pyridine or furan groups: preparation, protonation, and complexation by metal ions

Abstract

The synthesis of 18-membered macrocyclic ligands containing saturated amine and either pyridine or furan heterocyclic units is described. The protonation equilibria were studied by potentiometric titrations in which four protonation steps were observed for each ligand in the pH ranges 3-12. The protonation mechanism of these macrocyclic ligands was determined from potentiometric titrations followed by NMR and is consistent with protonation of only the saturated amine groups in the pH range studied. The formation constants for complexes of pyo2[18]dieneN6 with Ca(II), Mg(II), Mn(II), Cu(II), Zn(II), Cd(II), La(III), and Gd(III), determined potentiometrically, follow the order of the Irving-Williams series and are consistent with 1:1 metal ion binding. Furthermore, py02[18]dieneN6 binds as well or better than its saturated homolog, [ 18]aneN6. In contrast, furo2[l 8]aneN402 doesnot bind effectively in comparison to the saturated homolog, trans-[ 18]aneN402. The difference in binding may be due to a combination of enthalpic (polarity of ligating groups and steric strain of the ligand) and entropic (rigidity of the ligand) contributions.

Evidence of Molecular Fragmentation inside the Charged Droplets Produced by Electrospray Process

“…Such a macrocycle should have strong proton affinity due to the presence of four tertiary amine groups in the periphery. Earlier work on similar pyridine containing amine macrocycle showed that protonation in acidic solution only occurs at the amine nitrogens, not at the pyridyl nitrogens [44].…”

“…The maximum protonation sites of the macrocycle M 4p was earlier shown to be four [44]. Hence it can form a quadruply-protonated state [M 4p + 4H] 4+ along with singly-, doubly-, and triply-protonated states.…”

Development of electrochemical sensors for nano scale Tb(III) ion determination based on pendant macrocyclic ligands

“…The macrocycle L was synthesized following a literature method [29]. To a refluxing solution of 2,6-diacetylpyridine (1.63 g, 10 mmol) and BaCl 2 ·2H 2 O (1.22 g, 5 mmol) in anhydrous methanol (50 mL), a 10 mL methanolic solution of ethylenediamine (0.67 mL, 10 mmol) was added slowly.…”

Mn(II) azamacrocyclic bromide complexes with different nuclearities

“…The ligands L 1 and L 4 were prepared according to a modification of a literature method [31,32]. The ligands with nitrile pendantarms (L 2 , L 3 , L 5 and L 6 ) were synthesized starting from the precursors L 1 and L 4 [17][18][19].…”