Vladimir S. Talanov

A Calixarene-Based Fluorogenic Reagent for Selective Mercury(II) Recognition.

The first calixarene-based fluorogenic Hg(II)-selective extractant, 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-bis(N-(5-dimethylaminonaphthalene-1-sulfonyl)carbamoylmethoxy)-26,28-dimethoxycalix[4]arene (2), is reported. In solvent extraction from aqueous acidic solutions (HNO(3)), 2 exhibits excellent selectivity for Hg(II) over a wide range of transition, alkali, and alkaline earth metal cations. Quenching of its fluorescence due to Hg(II) coordination is unaffected by the presence of 100-fold excesses of alkali metal cations, alkaline earth metal cations, Ag(I), Tl(I), Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Pd(II), Zn(II), or Fe(III).

New Fluorogenic Dansyl-Containing Calix[4]arene in the Partial Cone Conformation for Highly Sensitive and Selective Recognition of Lead(II)

A new efficient and highly selective fluorescent chemosensor for determination of Pb (2+) has been obtained by covalent attachment of two pendent proton-ionizable dansylcarboxamide groups to the calix[4]arene preorganized in the partial cone conformation. This geometry of the calixarene moiety was chosen on the basis of the prior (1)H NMR study of conformations adopted by the flexible dansyl-containing prototype upon complexation with lead ion. In acidic MeCN-H2O (1:1 v/v) solutions, the partial cone fluoroionophore allowed for detection of Pb (2+) at the levels as low as 2.5 ppb, which is totally compatible with the regulations of the U.S. Environmental Protection Agency and the World Health Organization on the limiting content of this hazardous pollutant in drinking water.

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.

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.

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.

Effect of upper rim para-alkyl substituents on extraction of alkali and alkaline earth metal cations by di-ionizable calix[4]arenes

A series of new di-ionizable calix[4]arene N-(X-sulfonyl)carboxamides (X = CF3, Me, Ph and C6H4-4-NO2) and carboxylic acids with partially and completely removed upper rim p-tert-butyl groups was synthesized and utilized for competitive solvent extractions of alkali and alkaline earth metal cations. Removal of the para-alkyl substituents changes significantly both the efficiency and selectivity of metal ion separations by the carboxamide calix[4]arene extractants, while no such effect is observed for corresponding carboxylic acids.

Highly selective preparation of conformationally rigid stereoisomeric calix[4]arenes with two carboxymethoxy groups

Highly selective formation of the 1,3-alternate and partial cone conformational isomers of p-tert-butylcalix[4]arene diesters 5 with two butoxy and two methoxycarbonylmethoxy groups was achieved by alkylations of disubstituted calix[4]arenes 3 and 4, respectively, with KH as the base in THF. The potassium diphenoxide form of 3 was shown by NMR spectroscopy to adopt a 1,3-alternate conformation which provides strong evidence for a template effect of potassium cations on the conformation of the calix[4]arene reactant. Alkylation with subsequent hydrolysis of the diesters provides an effective route for the preparation of the 1,3-alternate and partial cone isomers of p-tert-butylcalix[4]arenedicarboxylic acids 6.

New mono-ionizable, Li+-selective calix[4]arenes

A series of new mono-ionizable cone calix[4]arenes, with either a pendent carboxylic acid or a N-(X-sulfonyl)carboxamide group, is synthesized and their alkali metal cation extraction behavior determined and compared with that for conformationally mobile analogues. These new proton-ionizable, cone calixarenes exhibit good (for the sulfonylcarboxamides) to excellent (for the carboxylic acid) Li+-selectivity. Surprisingly, the Li+-selectivity decreases on going from the conformationally flexible to the cone ionophores due to enhanced Na+ binding by the latter. During the ligand synthesis, unusual behavior of cone tributoxy-N-(trifluoromethylsulfonyl)carbamoylmethoxy-p-tert-butylcalix[4]arene suggests a strong tendency for molecular association.

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.

Improved Preparation of 24-Crown-8

Abstract An improved method for the preparation of 24-crown-8 is described. Cyclization at room temperature and purification of the crude product via an acetonitrile complex provides a much higher yield than those reported in the literature.