“…The calculated order of binding affinities at the interface (Na + < K + < Rb + < Cs + ) is the same as the experimental order of free energies of extraction by L from water to chloroform. 5,7 At a quantitative level, the numbers cannot be simply compared, because L is conformationally mobile and extracts Cs + in the 1,3-alternate conformation but extracts (weakly) Na + is the cone conformation. In our simulations, L remains 1,3-alternate in all cation complexes, such as in the conformationally locked 1,3dialkoxy analogues of L, which also display the same order of extraction selectivites.…”
Section: Ion Recognition At the Interfacementioning
confidence: 99%
“…As solutes we consider an ionophore L ( L = 1,3-dimethoxycalix-4-arene-crown-6; see Chart ), in its free and complexed L M + states (M + = Cs + /Na + ), and a M + cation also free and complexed, with different counterions. L and 1,3-alternate calixarene analogues belong to a new class of extractant molecules for Cs + ions. − The Cs + /Na + selectivity, observed in the liquid−liquid water−chloroform system, as well as in supported liquid membranes systems, is of high interest in the context of Cs + decontamination from nuclear wastes. − 1 The L M + Complex 2 Representation of the Simulation Box, with the Two Liquid Phases after Full Phase Separation…”
Section: Introductionmentioning
confidence: 99%
“…L and 1,3-alternate calixarene analogues belong to a new class of extractant molecules for Cs + ions. [5][6][7] The Cs + /Na + selectivity, observed in the liquid-liquid water-chloroform system, as well as in supported liquid membranes systems, is of high interest in the context of Cs + decontamination from nuclear wastes. [8][9][10] More specifically, we simulated the demixing of neat binary solutions and of solutions containing the inclusion complex LCs + , with Cl -/Picas counterions.…”
We report a series of molecular dynamics simulations on the demixing of “homogeneous” binary water−chloroform mixtures containing species involved in the assisted ion extraction process. We consider an
ionophore L (L = 1,3-alternate calix4arene-crown6), uncomplexed salts of Cs+ and the LCs+ and LNa+
cation complexes with a lipophilic (Pic-) and a hydrophilic (Cl-) counterion, respectively, as being solutes.
In all cases, the liquids separate rapidly, leading to two solvent slabs separated by a well-defined interface.
However, the final state is very different, depending on the hydrophilic/hydrophobic balance of the solutes:
the Cs+ and NO3
- ions of the CsNO3 salt are completely immersed in the aqueous phase, whereas Pic-
anions display a strong adsorption at the interface. The LCs+ complex and the free ligand L, although more
soluble in the organic phase than in water, also display a surfactant like behavior. Similar conclusions are
obtained when L, LCs+, Cs+ Pic-, and Cs+ NO3
- ions are simultaneously present in the solution. On the
basis of free energy perturbation calculations on LM+ complexes, we calculate a marked Cs+/Na+ recognition
by L
at the
interface. These results have important implications concerning the mechanism of ionophore
assisted liquid−liquid ion extraction and recognition processes at the interface.
“…The calculated order of binding affinities at the interface (Na + < K + < Rb + < Cs + ) is the same as the experimental order of free energies of extraction by L from water to chloroform. 5,7 At a quantitative level, the numbers cannot be simply compared, because L is conformationally mobile and extracts Cs + in the 1,3-alternate conformation but extracts (weakly) Na + is the cone conformation. In our simulations, L remains 1,3-alternate in all cation complexes, such as in the conformationally locked 1,3dialkoxy analogues of L, which also display the same order of extraction selectivites.…”
Section: Ion Recognition At the Interfacementioning
confidence: 99%
“…As solutes we consider an ionophore L ( L = 1,3-dimethoxycalix-4-arene-crown-6; see Chart ), in its free and complexed L M + states (M + = Cs + /Na + ), and a M + cation also free and complexed, with different counterions. L and 1,3-alternate calixarene analogues belong to a new class of extractant molecules for Cs + ions. − The Cs + /Na + selectivity, observed in the liquid−liquid water−chloroform system, as well as in supported liquid membranes systems, is of high interest in the context of Cs + decontamination from nuclear wastes. − 1 The L M + Complex 2 Representation of the Simulation Box, with the Two Liquid Phases after Full Phase Separation…”
Section: Introductionmentioning
confidence: 99%
“…L and 1,3-alternate calixarene analogues belong to a new class of extractant molecules for Cs + ions. [5][6][7] The Cs + /Na + selectivity, observed in the liquid-liquid water-chloroform system, as well as in supported liquid membranes systems, is of high interest in the context of Cs + decontamination from nuclear wastes. [8][9][10] More specifically, we simulated the demixing of neat binary solutions and of solutions containing the inclusion complex LCs + , with Cl -/Picas counterions.…”
We report a series of molecular dynamics simulations on the demixing of “homogeneous” binary water−chloroform mixtures containing species involved in the assisted ion extraction process. We consider an
ionophore L (L = 1,3-alternate calix4arene-crown6), uncomplexed salts of Cs+ and the LCs+ and LNa+
cation complexes with a lipophilic (Pic-) and a hydrophilic (Cl-) counterion, respectively, as being solutes.
In all cases, the liquids separate rapidly, leading to two solvent slabs separated by a well-defined interface.
However, the final state is very different, depending on the hydrophilic/hydrophobic balance of the solutes:
the Cs+ and NO3
- ions of the CsNO3 salt are completely immersed in the aqueous phase, whereas Pic-
anions display a strong adsorption at the interface. The LCs+ complex and the free ligand L, although more
soluble in the organic phase than in water, also display a surfactant like behavior. Similar conclusions are
obtained when L, LCs+, Cs+ Pic-, and Cs+ NO3
- ions are simultaneously present in the solution. On the
basis of free energy perturbation calculations on LM+ complexes, we calculate a marked Cs+/Na+ recognition
by L
at the
interface. These results have important implications concerning the mechanism of ionophore
assisted liquid−liquid ion extraction and recognition processes at the interface.
“…Calixarenes are a special class of cyclophanes that have been used as such, or after functionalization, for the recognition of neutral molecules, cations, and even anions . Among the various calixarene derivatives, water-soluble calixarenes are becoming increasingly important in supramolecular chemistry because they allow the study of basic forces involved in the host−guest recognition processes in a solvent where most biological processes occur .…”
The complex stability constants (Ka) and thermodynamic parameters (DeltaG degrees, DeltaH degrees, and TDeltaS degrees) for 1:1 complexation of water-soluble calix[4]arene, thiacalix[4]arene, and calix[5]arene sulfonates with pyridine and their methylated derivatives have been determined by means of isothermal titration calorimetry at pH 2.0 and 7.2 at 298.15 K, and their binding modes have been investigated by NMR spectroscopy. The results obtained show that sulfonatocalixarenes afford stronger binding ability toward pyridine guests at pH 2.0, attributable to the positive electrostatic interactions and the more extensive desolvation effects, but present higher molecular selectivity at pH 7.2 owing to the strengthened C-H...pi interactions. The pH-responsible binding ability and molecular selectivity are discussed from the viewpoint of electrostatic, pi-stacking, van der Waals interactions and size-fit relationship between host and guest. A close comparison further demonstrates that the C-H...pi interactions and van der Waals interactions play a more important role than pi...pi interactions in the present inclusion complexation.
“…The complexation of alkali metal and ammonium cations by functionalized calix[n]arenes is a topic of current interest in supramolecular chemistry. − In particular, the efficiency and selectivity of ion recognition by calixarene ligands have been studied in homogeneous solution 1-4 and in membrane transport 5,6 as a function of the calixarene backbone, the nature of the binding groups introduced, and the conformational properties of the calix. More recently calixarene receptors have been also used in monolayers at the water−air interface, − which is becoming a suitable technique to study biomimetic molecular recognition phenomena …”
p-tert-Butylcalix[6]arene, CAL6,
has been functionalized by the introduction of amide moieties
(OCH2CONEt2) on the six phenolic OH groups to give the
corresponding hexamide, HXAM, which shows an
interesting selectivity toward the guanidinium cation. The present
study reports the behavior of HXAM
monolayers at the water−air interface as a function of temperature
and subphase composition. The
parameters obtained from the spreading isotherms (limiting areas,
A
o, compressibility moduli,
C
s
-1 =
(1/A)(∂π/∂A), and changes in the Gibbs
free energy upon passing from water to salt subphase,
ΔG
salt-water)
and the surface potential data show that the HXAM assumes a
“cone-shaped” conformation. The molecules
are in a parallel orientation at the water−air interface with the six
amide groups in the water phase.
Changes in the subphase from water to salt solutions (NaCl, KCl,
CsCl, guanidinium thiocyanate) affect
the spreading isotherms but not the surface potential behavior.
The results are discussed in terms of the
two-dimensional phases of the monomolecular films, the stoichiometry of
the complexes with the cations,
and the conformations of uncomplexed and complexed HXAM molecules.
The comparison of these results
with those of the unsubstituted CAL6 behavior shows the high
selectivity of HXAM monolayers toward
the guanidinium cation.
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