Maryna G. Gorbunova

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 amino-functionalized 1,3-alternate calix[4]arene bis- and mono-(benzo-crown-6 ethers) for pH-switched cesium nitrate extraction

Four calix[4]arene benzo-crown-6 ethers functionalized with primary amine groups in various positions have been synthesized. The cesium extraction behavior under alkaline and acidic conditions has been measured for these compounds and compared with that of non-amine containing analogs. Extraction strength when the amine group is neutral is not affected by the amino substituent, but protonation causes a marked decrease in extraction strength, permitting pH-switched back-extraction.

pH‐Switchable Cesium Nitrate Extraction with Calix[4]arene Mono and bis(Benzo‐crown‐6) Ethers Bearing Amino Functionalities

Abstract Results obtained in this work show that four calix[4]arene mono and bis(benzo‐crown‐6) ethers functionalized with primary amine groups feature markedly enhanced cesium stripping under acidic conditions compared with nonfunctionalized analogs. The four amine‐derivatized calixarenes were surveyed in nitrobenzene diluent at 25°C, demonstrating the effect under controlled conditions, where it was seen that the amino functionalization entailed at most a mild sacrifice of cesium extraction strength or selectivity. Limited solubility of the protonated forms of the extractants appears to be a potential issue for future development, however. In the best case, calix[4]arene bis[4‐(2‐ethylhexyl)benzo‐crown‐6], possessing an aminomethyl group on the upper rim, (AMBEHB) exhibited a cesium extraction strength comparable to that of a control system containing calix[4]arene bis(tert‐octylbenzo‐crown‐6) (BOB) under alkaline conditions, whereas stripping of the cesium from AMBEHB was 56‐fold more effective than BOB. A proof‐of‐principle extraction, scrubbing, and stripping (ESS) cycle using AMBEHB in Isopar L modified with 0.75 M 1‐(2,2,3,3‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol (Cs‐7SB) showed that a greater than three‐fold more efficient stripping may be obtained with AMBEHB vs. its nonfunctionalized control BEHB. A slope analysis of systematic extraction data under caustic and acidic conditions confirmed that the extraction of cesium nitrate by AMBEHB in dodecane modified by 0.5 M Cs‐7SB involves the formation of a 1:1:1 metal:ligand:nitrate organic species.

Protonation-assisted spontaneous resolution: formation of a homochiral 2D interpenetrated hydrogen-bonded network from 4,4′-binicotinic acid under highly acidic conditions

The conformationally chiral 4,4′-bipyridine-2,2′-dicarboxylic acid (herein called 4,4′-binicotinic acid, BNA) forms racemic crystals either from neutral water as the free base, or from dilute hydrochloric acid (1 M) as the monohydrochloride salt, as determined by single crystal X-ray analysis. Crystallization from more concentrated hydrochloric acid (6 M), on the other hand, yields the dihydrochloride salt of BNA, which was found to segregate into conglomerates with the chiral space group C2. In this structure, the BNA·2HCl forms a homochiral (4,4) net, with BNA molecules of the same chirality linked via COOH⋯Cl⋯HN hydrogen bonds. The resulting low-density framework self-penetrates to generate a two-fold 2D interwoven homochiral layer. Stacking of layers of the same handedness generates an enantiomorphous crystal. The increased contribution of ionic and hydrogen bonding in this crystal appears to be responsible for the observed spontaneous resolution.

Novel fluorogenic calix[4]arene-bis(crown-6-ether) for selective recognition of thallium(I)

A new fluorogenic, dansyl group-containing derivative of 1,3-alternate calix[4]arene-bis(crown-6-ether) provides optical recognition of Tl+ with selectivity over many other metal cations, including Na+, K+, Ca2+, Ag+, Hg2+ and Pb2+, and embodies the first example of a calixarene-based fluorescent Tl+-chemosensor.

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.