Looking for the Origin of Allosteric Cooperativity in Metallopolymers

Abstract

The basic concept of allosteric cooperativity used in biology, chemistry and physics states that any change in the intermolecular host-guest interactions operating in multisite receptors can be assigned to intersite interactions. Using lanthanide metals as guests and linear multi-tridentate linear oligomers of variable lengths and geometries as hosts, this work shows that the quantitative modeling of metal loadings requires the consideration of a novel phenomenon originating from solvation processes. It stepwise modulates the intrinsic affinity of each isolated site in multisite receptors, and this without resorting to allosteric cooperativity. An easy-to-handle additive model predicts a negative power law dependence of the intrinsic affinity on the length of the linear metallopolymer. Applied to lanthanidopolymers, the latter common analysis overestimates cooperativity factors by more than two orders of magnitude.

A Rational Approach to Metal Loading of Organic Multi‐Site Polymers: Illusion or Reality?

“…(6) corresponds to the gas-phase intermetallic interaction Ln,Ln 1 2,gas E   , which amounts to less than 0.5 kJ/mol in {P3 N [Ln(hfa)3]m+1}, this whatever the selected lanthanoid. [29] Since the ratio Ln Ln ,gas ,sol i i f f can be reasonably taken as constant along the lanthanoid series for a given receptor, [21b] any modulation of [30] makes it negligible. Consequently, the two last terms of eq.…”

“…[29] Figure 10 coordinate lanthanoid radii, CD2Cl2 + 0.14 M dig, 298 K). [29] Altogether, the experimental magnitude -2 ≤ 1 R anticooperative process twice as large as thermal energy can be evidenced in {D2[Ln(pbta)3]2} (blue trace in Fig. 11).…”

“…Thermodynamic cycle for ligand exchange around a [Ln(hfa)3] container. [29] Being concerned by some inadequate approaches and approximations used since decades for tentatively analyzing allosteric cooperativity factors characterizing multivalent (bio)chemical receptors, we first critically questioned the consequences of our own choice to fix the concentration of diglyme co-ligand at 0.14 M. This condition is expressly required for transforming the ligand exchange process shown in Fig. 7a (eq.…”

Chemical Potential of the Solvent: A Crucial Player for Rationalizing Host–Guest Affinities

“…Since the magnitude of DG S exch mirrors x, the larger negative value found for lipophilic L3,c ompared with L1 and L2,i ndicates that the connection of flexible and poorly polarizable alkyl chains to the aromatic backbone drastically affects solute-solvent and solute-solute interactions, ap henomenon at the origin of demixing in block co-polymers [31] and of microphase separations in liquid crystals. [21,22] Lkþ½LaðhfaÞ 3 нLaðhfaÞ 3 Lk Q Lk;La 1;1;cond ¼ Fixing the total concentration of diglyme at dig jj tot = 0.14 m transforms Scheme 1i nto the conditional hostguest association reaction 8[ Eq.…”

“…In this context, some alarming results were recently reported fort he multiple binding of luminescent neutrall anthanide carriers [Ln(hfa) 3 (dig)] (i.e.,t he guest where hfa = hexafluoroacetylacetonate and dig = 2-{2-methoxyethoxy}ethane) to linear multi-tridentate ligands L N (i.e.,ahost possessing N-binding sites) because both the intrinsic affinities [21] and the cooperativity factors [22] extracted from the binding isotherms vary with polymer lengthsa nd total concentrations, al imitation which prevented the rational design of luminescent{ L N [Ln(hfa) 3 ] n }m etallopolymers in solution. (6) predicts some obvious deviations from the Langmuir isotherm as soon as the product HG jj eq c q ÀÁ DG S is not negligible and thus varies within the "useful dynamic range" of the target guest.…”