Thermodynamics of Self‐Assembly of Dicarboxylate Ions with Binuclear Lanthanide Complexes

Abstract

Self-assembly of a range of carboxylic acids (benzoic acid, dinicotinic acid, nicotinic acid, and isophthalic acid) with the europium complex of 5-nitro-α,α′-bis(DO3Ayl)-m-xylene (where DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) has been explored to establish the thermodynamics of binding in a range of solvent systems and in a range of aqueous buffer solutions. In this system, profound effects are observed as a consequence of competition by the hydroxide ion, which outcompetes even dinicotinate at high pH. In the case of isophthalate, which binds most strongly, and dinicotinate, both enthalpic and entropic contributions to binding have been identified. The europium complex with 5-nitro-α,α′-bis(DO3Ayl)-m-xylene is found to have a solution structure significantly different from the related europium complex of 5-amino-α,α′-bis(DO3Ayl)-m-xylene. It is found that phosphate binds strongly to the europium complex of the nitro derivate but not to the europium complex of amino derivative. Lactate, citrate, and pyruvate also bind strongly to 5-nitro-α,α′-bis(Eu⋅DO3Ayl)-m-xylene, and it is concluded that the solution structure of this binuclear lanthanide complex is significantly different from that of the amino-substituted complex.

Kinetically Inert Lanthanide Complexes as Reporter Groups for Binding of Potassium by 18-crown-6

“…Here we stipulate that secondary effects-such as unspecific binding and ionic strength-drastically alter the photophysical properties of the Ln.L 3 complexes upon addition of an excess of potassium chloride. [71][72] Note that the increase in intensity of emission from Ln.L 3 greatly exceeds the changes in intensity in Ln.L 2 upon binding of potassium.…”

“…The line shape and branching ratio in the emission spectrum of a lanthanide ion in solution changes according to the symmetry and donor set of the coordination environment, as well as with changes in the surrounding solution. [34][35][36][37][38][39] Thus, the solution structure of a lanthanide containing system can be probed by luminescence spectroscopy, 24,40 and the solution composition may be investigated by observing changes in the lanthanide centered luminescence. [41][42] A pre-requisite for using lanthanide complexes as contrast agents is that the toxic lanthanide ions are not released and subsequently accumulated in the patient.…”

Advances in anion binding and sensing using luminescent lanthanide complexes

“…Lactate displaces the two inner sphere water molecules, signalled by an increase in Tb(III) emission intensity, particularly the band at 546 nm, which plateaued aer 100 equivalents of lactate (600 mM). DFT studies supported chelation of lactate to the Ln(III) ion through the OH and CO 99 Initially, anion titrations were conducted in methanol, in the presence of 1 mM LiOH, to ensure full deprotonation of the dicarboxylates and a constant ionic strength. The nitro derivative [Eu 2 -58] showed selectivity for isophthalate over dinicotinate, nicotinate and benzoate, with log K a (298 K) ¼ 4.3, 2.8, 3.4, and 2.7, respectively.…”

“…In subsequent work, the same authors quantified the entropic and enthalpic contributions to the binding of isophthalate and nicotinate to structurally similar binuclear complexes [Eu 2 - 57 ] and [Eu 2 - 58 ]. 99 Initially, anion titrations were conducted in methanol, in the presence of 1 mM LiOH, to ensure full deprotonation of the dicarboxylates and a constant ionic strength. The nitro derivative [Eu 2 - 58 ] showed selectivity for isophthalate over dinicotinate, nicotinate and benzoate, with log K a (298 K) = 4.3, 2.8, 3.4, and 2.7, respectively.…”

Investigating subtle 4f vs. 5f coordination differences using kinetically inert Eu(iii), Tb(iii), and Cm(iii) complexes of a coumarin-appended 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate (DO3A) ligand

“…This new level of control informs the design of responsive luminescent probes, [21][22][23][24][25][26] and allows for detailed physico-chemical investigations in solution. 19,[27][28][29][30][31][32] Extensive published work has determined that ligands comprising a cyclen scaffold and three or four carboxylate (e.g. DO3A, DOTA…) or carboxamide (e.g.…”