Proton-ionizable Group Research Articles

Sterically congested, geminal aryl-substituted, proton-ionizable sym-dibenzo-16-crown-5 lariat ethers: synthesis and alkali metal cation extraction

Three series of proton-ionizable sym-dibenzo-16-crown-5 ethers with sterically demanding 1- naphthyl, 2-naphthyl, and 9-phenanthryl geminal groups are synthesized and characterized. Variation of the proton-ionizable group includes oxyacetic acid and N-(X)sulfonyl oxyacetamide units with X = Me, Ph, C6H4-4-NO2, and CF3. For the latter series, variation of X provides 'tunable' acidity of the ligand. The metal ion-complexing properties of the proton-ionizable sym- (aryl)dibenzo-16-crown-5 compounds are probed by competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform.

ChemInform Abstract: New Lariat Ether Carboxylic and Hydroxamic Acids: Synthesis and Lanthanide Ion Complexation.

Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The 1H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation.

Aminopyridyl derivative of thiacalix[4]arene-carboxylic acid as ionizable highly selective Ag+ ionophore

A novel mono-ionizable receptor 2 possessing three aminopyridyl and one carboxylic group in 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. For competitive solvent extraction of alkali metal (Na+, K+ and Cs+) and some transition metal (Cu2+, Zn2+, TI+, Ag+) cations from aqueous solutions into chloroform, it was found that the introduction of proton-ionizable group (carboxylic acid moiety) into the aminopyridyl-thiacalix[4]arene derivative could further improve its Ag+ extractability with high selectivity.

Mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations: synthesis, structure and silver(I) extraction

Two series of novel mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations are synthesized. In one series, the proton-ionizable group (PIG) is attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether ring cavity. In the other series, the PIG is a substituent on the benzo group in the polyether ring. This orients the PIG away from the crown ether cavity. In addition to carboxylic acid functions, the PIGs include N-(X)sulfonyl carboxamide groups. With X group variation from methyl to phenyl to 4-nitrophenyl to trifluoromethyl, the acidity of the PIG is ‘tuned’. Solvent extraction of Ag+ from aqueous solutions into chloroform is used to probe the influence of structural variation within the mono-ionizable calixcrown ligand on metal ion extraction efficiency, including the identity and acidity of the PIG and its orientation with respect to the polyether ring.

Chromogenic betaine lariates for highly selective calcium ion sensing in aqueous environment

This paper describes the design, synthesis, and the characterization of the two new chromogenic crown ethers 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-methyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-001) and the lipophilic derivative 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-dodecyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-002). A merocyanine dye that forms a betainic structure upon intramolecular charge transfer and shows solvent polarity dependent spectral sensitivity was selected as the chromophore system to develop the new chromoionophores. This approach allows the design of overall electrically neutral ligands bearing charged groups without the need of external counter ions. A proton ionizable group in the dye moiety acts as a charged ion-binding site and is an integral part of a lariat crown ether ionophore. A chromoionophore for calcium ion sensing has been developed, which combines the size-selective binding character of a crown ether with strong electrostatic attraction between the positively charged calcium ion and two negatively charged lariat side arms in the overall neutral compound. This water-soluble dye selectively responds to the presence of calcium ions in water at pH 8.5 with a dynamic response range between 10 μM and 10 mM. The binding event can be monitored both by absorption spectrometry and by fluorescence spectrometry. No cross-sensitivity was found for the physiologically important cations Mg2+, Li+, Na+, and K+ up to concentrations of 0.1 M under the same experimental conditions. In contrast to the water-soluble reagent KBC-001, the lipophilized derivative KBC-002 having two long alkyl chains was successfully applied to ion-exchange type optode membranes made from plasticized poly(vinyl chloride) (PVC). The dynamic response range of the optode at pH 9.0 was between 10 μM and 10 mM while retaining the high calcium selectivity.

Calix[4]arene-bis(dibenzocrown-6-ethers) with one proton-ionizable group

Abstract Two 1,3-alternate calix[4]arene-biscrowns with one proton-ionizable group and two dibenzocrown-6-ether units are synthesized. The compounds exhibit high Cs + extraction efficiency and selectivity. Cs + /Na + and Cs + /K + selectivities for the new N -(trifluoromethylsulfonyl)carbamoyl-substituted calix[4]arene-bis(dibenzocrown-6) are found to be higher than those for an analog with no benzo group substituents in the crown ether units.

Novel caesium-selective, 1,3-alternate calix[4]arene-bis(crown-6-ethers) with proton-ionizable groups for enhanced extraction efficiencyElectronic supplementary information (ESI) available: HSQC spectra for Na+ and Cs+ complexes of ionized 7, and graphs for Cs+ extraction. See http://www.rsc.org/suppdata/p2/b1/b109638a/

Synthesis of a series of novel 1,3-alternate calix[4]arene-bis(crown-6-ethers) with a proton-ionizable group (PIG) located in front of one crown ether cavity is reported. Variation of the X group in the N-(X-sulfonyl)carbamoyl substituent on the calixbiscrowns provides variation of acidity of the PIG. NMR spectroscopic studies demonstrate that the position of the PIG within the molecule allows it to participate in cooperative metal ion coordination by the ligand. In solvent extraction of alkali metal cations from aqueous solutions of varying pH into chloroform, the novel ionophores possess enhanced efficiency relative to a non-ionizable analog, while retaining high Cs+ selectivity. The Cs+ extraction constants of the proton-ionizable calixbiscrowns are proportional to their acidities. Under the conditions employed, 1 ∶ 1 complexes of the ionized calixbiscrowns with Cs+ are the dominant species extracted into the organic phase.

Unusual conformational control of mobile mono- and diionizable calix[4]arene ligands by alkali metal cations† ‡

Conformations adopted in CDCl3 solution by alkali metal salts of mobile calix[4]arene ligands with one and two pendent proton-ionizable groups have been studied by NMR spectroscopy. For a series of the ligands with two N-(R-sulfonyl)carbamoylmethoxy substituents, there is no significant change in the conformational preferences of the calix[4]arene unit upon variation of the NSO2R substituents. Systematic changes of the preferred conformation(s) for the calix[4]arene moiety from cone to partial cone to 1,3-alternate are observed for all five of the ligands as the alkali metal cation is varied from Li+ to Na+ to K+ to Rb+ to Cs+. For ligands with one proton-ionizable group [carboxylic acid or N-(trifluoromethylsulfonyl)carboxamide] the conformational preferences of the calix[4]arene unit are also controlled by the identity of the complexed metal ion. The Li+ salts prefer the cone conformation, while for the Na+ and K+ salts more than two significantly populated conformations are evident. Remarkably, Cs+ and Rb+ salts prefer a partial cone conformation, which provides the possibility for the metal ion to have three π-interactions with the arene units of the calix[4]arene moiety and a coulombic interaction with the ionized group.

New proton-ionizable, cesium-selective calix[4]arene-bis(crown-6-ethers) with markedly enhanced extraction efficiency

The first 1,3-alternate calix[4]arene-bis(crown-6-ethers) with a proton-ionizable group located in front of one crown ether cavity are synthesized. Compared with an analog that has no proton-ionizable group, the two new ligands possess markedly higher Cs+ extraction efficiency.

Metal ion extraction by lariat ethers with ‘tunable’ proton-ionizable groups

Abstract

Sorption of lead(II) by proton-ionizable polyether resins

Novel ion-exchange resins have been prepared by condensation polymerization with formaldehyde of dibeozo acyclic and cyclic polyethers bearing a pendent acidic function (carboxylic acid, phosphonic acid monoethyl ester, phosphonic acid, or sulfonic acid). Such resins possess both ion-exchange and polyether-binding sites for metal-ion complexation. The efficiency of Ph2+ sorption and selectivity relative to Zn2+ sorption are assessed as a function of: (1) the acyclic, pseudocyclic, or cyclic nature of the polyether unit; (2) the identity of the proton-ionizable group; (3) the length of the spacer which joins the proton-ionizable group to the polyether framework; and (4) for the proton-ionizable crown ether resins, the atom or group which is geminal to the functional side arm.

Lariat ethers with a novel proton-ionizable group. Synthesis and solvent extraction of alkali metal cations

V. J. Huber, S. N. Ivy, J. Lu and R. A. Bartsch, Chem. Commun., 1997, 1499 DOI: 10.1039/A703106H

Einhorn Reaction for the Synthesis of Aromatic Building Blocks for Macrocyclization.

The present study concerns the synthesis of bis(α-haloacetamidomethyl) and benzyldiamine sythons 1−3 (Scheme 1) through amidomethylation and their application for the preparation of benzoazamacroheterocycles. These synthons are useful as rigid building blocks containing the chromophoric NO_2 group. The methoxy function could be converted to the phenolic OH after ring closure, providing a proton-ionizable group in the macrocyclic cavity. We show three synthetic routes to prepare benzoazamacrocycles using synthons 1−3.