Recognition of Biologically and Environmentally Important Phosphate Anions by Calix[4]pyrrole: Thermodynamic Aspects (original) (raw)
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Anion Complexation by Calix[3]thieno[1]pyrrole: The Medium Effect
Journal of Physical Chemistry B, 2006
The interaction of calix[3]thieno[1]pyrrole, 1, and halide and dihydrogen phosphate anions in a variety of solvents (acetonitrile, propylene carbonate, N,N-dimethylformamide, and dimethyl sulfoxide) has been investigated through 1 H NMR, conductance measurements, and titration calorimetry. 1 H NMR measurements reveal the sites of interaction of the ligand with the anions in CD 3 CN while the composition of the complex was determined through conductance measurements. A quantitative assessment of anion-ligand interactions is provided. Thus the thermodynamics of complexation of 1 with halide and dihydrogen phosphate anions in dipolar aprotic media at 298.15 K is reported. These data are interpreted in terms of the thermodynamics of transfer of reactants and product from a reference solvent (acetonitrile) to other solvents. The crucial role played by the solvent on the ability of the ligand to interact with anions and on the composition of the complex is demonstrated.
The Journal of Physical Chemistry B, 2007
A modified calix[4]pyrrole, namely meso-tetramethyl-tetrakis-(4-hydroxyphenyl) calix[4]pyrrole, 1, has been synthesized and characterized. 1 H NMR investigations in various deuterated solvents seems to indicate that this receptor interacts with acetone-d 6. The solution thermodynamics of 1 in various solvents is reported. Complexation studies in CD 3 CN show that the NH and OH functionalities of 1 are the active sites of its interaction with the fluoride and the dihydrogen phosphate anions. The composition of the anion complexes was established through conductance measurements. In all cases, 1:1 complexes are formed. The thermodynamics of anion complexation in acetonitrile and N,N-dimethylformamide is discussed comparatively with previous reported data for the parent calix[4]pyrrole, 2, and these anions in these solvents. The medium effect on anion complexation is discussed in terms of the solvation properties of the reactants and the product in acetonitrile and N,N-dimethylformamide. An oligomeric material containing 1 as anchor group was synthesized and characterized by mass spectrometry. Preliminary studies have been performed to assess the extracting properties of this oligomer for the removal of phosphates from aqueous solutions. The effects of pH, temperature on the extraction of this anion salt from water, as well as the kinetics of the process (fast) were investigated.
Inorganic Chemistry, 2008
Alkaline-earth metal phosphates containing nitrogen-donor ligands have been prepared by the reaction of alkalineearth metal acetates M(OAc) 2 • xH 2 O (M) Mg, Ca, Sr, Ba) with 2,6-diisopropylphenyl phosphate (dippH 2) in the absence and presence of 1,10-phenanthroline (phen). Interaction of strontium or barium acetate with dippH 2 in methanol at room temperature leads to the isolation of ionic phosphates [{M 2 (µ-H 2 O) 4 (H 2 O) 10 }{dipp} 2 ] • 4L [M) Sr, L) CH 3 OH (1); M) Ba, L) H 2 O (2)]. The addition of a bidentate nitrogen-donor phen to these reactions leads to the isolation of dinuclear metal phosphates [Mg(dipp)(phen)(CH 3 OH) 2 ] 2 (3) and [M(dippH) 2 (phen) 2 (H 2 O)] 2 [M) Ca (4), Sr (5), Ba (6)]. While ionic phosphates 1 and 2 are soluble in water, the predominately covalent dimeric compounds 3-6 are insoluble in all common solvents including water. The new compounds have been characterized in the solid state by elemental analysis, IR, UV-vis, and emission spectroscopy, and single-crystal X-ray diffraction studies. The cationic part in 1 and 2 is a {M 2 (µ-H 2 O) 4 (H 2 O) 10 } unit, where each metal ion is surrounded by four bridging and five terminal water molecules as ligands. The dipp anion does not directly bind to the metal ions but is extensively hydrogen-bonded to the cationic unit through the phosphate oxygen and water hydrogen atoms to result in an infinitely layered structure where the hydrophobic aryl group protrudes out of the hydrophilic layer formed by the cationic part and-PO 3 2units. In contrast, compounds 3-6 are discrete dimeric molecules built around a central M 2 O 4 P 2 eight-membered ring. While the dippH 2 ligand exists in a doubly deprotonated form in 3, two monodeprotonated dippH 2 ligands are present per metal ion in compounds 4-6. While 3 prefers only one phen ligand in the metal coordination sphere, two phen ligands chelate each metal ion in 4-6. The conformations of the eight-membered rings in 3-6 vary significantly from each other depending on the size of the cation and the coordination number around the metal. Further, intermolecular hydrogen bonding involving the phenanthroline C-H linkages result, in a gridlike structure in 1, one-dimensional chains in isostructural 2 and 3, and a two-dimensional layer arrangement in 4. Compounds 3-6 are the only examples of alkaline-earth metal phosphate complexes with neutral M-N donor bonds. The thermal behavior of compounds 1-6 has been examined with the help of thermogravimetric analysis and differential scanning calorimetry and also by bulk thermolysis followed by powder X-ray diffraction measurements. While compounds 1 and 2 yield M 2 P 2 O 7 , decomposition of 4-6 results in the formation of M(PO 3) 2 , consistent with the M-P ratio in the precursor complexes.
Journal of Structural Chemistry, 2015
Sterically hindered meso-tetramethyl-meso-tetraarylcalix[4]pyrroles 1-4 where aryl is p-fluorophenyl 1, p-chlorophenyl 2, and p-methylphenyl 3, 4 (configurational isomers) are synthesized and purified by the recrystallization technique. They are characterized by IR, 1 H and 13 C NMR, and mass spectroscopy. Configurational isomers DDEE (3) and DDDD (4) of meso-tetramethylmeso-tetramethylphenylcalix[4]pyrroles are assigned by the 1 H NMR studies and confirmed by the X-ray diffraction analysis. The single crystal X-ray diffraction analysis reveals that the ethanol adduct of 1, the acetone adduct of 2 and 3 adopt the 1,2-conformation while the acetone-water adduct of 1 and the acetone adduct of 4 adopt partial cone and cone conformations respectively. The conformational diversity is due to non-covalent interactions among the encapsulated guest, pyrrolic NH protons, and meso-substituents. Anion binding studies (F-, Cl-, CH 3 COO-, 4 HSO) are carried out through 1 H NMR titrations; the binding constants are evaluated using the EQNMR program, displaying that they are more selective towards fluoride rather than other anions with the 1:1 stoichiometry. The configuration of compounds drastically influences the ion-recognition processes.
2012
Tin(II) interaction with different phosphate ligands, namely phosphate (PO 4 ), pyrophosphate (PP), tripolyphosphate (TPP), monofluorophosphate (MFP) and adenosine-5′-triphosphate (ATP), was studied at T=298.15 K by potentiometry and voltammetry at different ionic strengths (0.15≤I/mol L −1 ≤1.00) in NaNO 3 . We also compared our results with those experimentally determined for the Zn/PO 4 and Zn/TPP systems. As concerns the Zn/PP, the Zn/ATP and the Zn/MFP systems, we performed a critical literature analysis. In all cases the stability constants observed for the Sn/L species resulted to be higher with respect to the analogous Zn/L ones. The rough correlation (valid for the ML species) log K ML (Sn)=3.01·log K ML (Zn)−8.13 was obtained from the stability data of the complexes of these cations. In addition, the stability trend found for a given metal cation was: PP~PO 4 >>TPP>>MFP~ATP. The ionic strength dependence of the stability constants was studied by the extended Debye-Hückel and the SIT (Specific ion Interaction Theory) equations. Speciation and sequestration studies were also performed, and pL 0.5 values (i.e., the total ligand concentration necessary to bind 50% of cation present in trace) were calculated for all the systems at different pH and ionic strengths. In this case, as an example at pH =7.0 and I=0.15 mol L − 1 , the sequestration trend was: PO 4 >PP~MFP>>TPP>ATP. The dependence of pL 0.5 values on pH and ionic strength was modeled by means of two empirical relationships.
Complexation of Calix[4]arene Derivatives and Trivalent Cations in Dipolar Aprotic Media
The Journal of Physical Chemistry A, 2004
The complexation of p-tert-butylcalix [4]arene tetraethanoate, 1a, p-tert-butylcalix [4]arene tetramethyl ketone, 1b, and p-tert-butylcalix [4]arene tetraacetamide, 1c, and trivalent cations was investigated in acetonitrile and N,N-dimethylformamide at 298.15 K using several techniques. 1 H NMR measurements in CD 3 CN at 298 K were carried out for the systems involving 1a, 1b, and 1c as ligands and Sc 3+ , Y 3+ , Eu 3+ , and Yb 3+ as cations. For the latter ligand, 1 H NMR titration with La 3+ was also carried out to assess the sites of interaction of these ligands and the appropriate cation in this solvent. Conductance measurements were performed in acetonitrile and N,N-dimethylformamide with the aim of determining the composition of the metal ion complexes. Stability constants and derived standard Gibbs energies, enthalpies, and entropies reveal that, as far as 1b is concerned, this ligand is not able to distinguish among the trivalent cations as a result of a remarkable enthalpy-entropy compensation effect. This is not the case for 1c and these cations in acetonitrile and to a lesser extent in N,N-dimethylformamide. The selective behavior of this ligand for these metal cations is reflected in the stability constants, which are higher in acetonitrile than in N,N-dimethylformamide. A plot of log K s values against the cation radius shows a "selectivity" peak. In acetonitrile, the complex stability is greater than that previously observed for an analogous derivative and these cations in this solvent. The medium effect on the complexation process is discussed.
Inorganic Chemistry, 2013
Some metal ion complexing properties of DPP (2,9-Di(pyrid-2yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide-(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense π−π* transitions in the absorption spectra of aqueous solutions of 10 −5 M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K 1 (DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K 1 versus 1/r + (r + = ionic radius for 8coordination). For Ln(III) ions larger than Sm(III), there is a steady rise in log K 1 from La(III) to Sm(III), while for Ln(III) ions smaller than Sm(III), log K 1 decreases slightly to the smallest Ln(III) ion, Lu(III). This pattern of variation of log K 1 with varying size of Ln(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (∑U) were calculated for the [Ln(DPP)(H 2 O) 5 ] 3+ and [Ln(qpy)(H 2 O) 5 ] 3+ (qpy = quaterpyrdine) complexes of all the Ln(III) ions. The ideal M−N bond lengths used for the Ln(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln(III) ions with polypyridyl ligands. Similarly, the ideal M−O bond lengths were those for complexes of the Ln(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ∑U versus ideal M−N length, a minimum in ∑U occurred at Pm(III), adjacent in the series to Sm(III). The significance of this result is that MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am(III) and Ln(III) ions in the treatment of nuclear waste, and (2) Am(III) is very close in M−N bond lengths to Pm(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca(II), which has the most appropriate M−N lengths. The structures of DPP complexes of Zn(II) and Bi(III), as representative of a small and of a large metal ion respectively, are reported. [Zn(DPP) 2 ](ClO 4 ) 2 (triclinic, P1, R = 0.0507) has a six-coordinate Zn(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be π-stacked on the central aromatic ring of the other DPP ligand. [Bi(DPP)(H 2 O) 2 (ClO 4 ) 2 ](ClO 4 ) (triclinic, P1, R = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln(tpy)(H 2 O) n ] 3+ and [Ln(DPP)(H 2 O) 5 ] 3+ complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln(tpy)(H 2 O) n ] 3+ with Ln = La and n = 6, and Ln = Lu with n = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln(DPP)(H 2 O) 5 ] 3+ complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln(III) ions. The effect that such short O--O nonbonded distances has on thermodynamic complex stability and coordination number is then discussed.