Shahabuddin Memon

Synthesis and study of allosteric effects on extraction behavior of novel calixarene-based dichromate anion receptors

Abstract In this study the selective derivatization of p-tert-butylcalix[4]arene was carried out and two new calix[4]arene-based azacrown ionophores, 5,17-di-tert-butyl-11, 23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,26,27,28-tetrahydroxycalix[4]arene ( 6 ), and 5,17-di-tert-butyl-11,23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,27-diethoxyformyl-methoxy-26,28-dihydroxycalix[4]arene ( 7 ) have been synthesized. Treatment of 5,17-di-tert-butyl-11,23-diformylcalix[4]arene-25,26,27,28-tetrol ( 5 ) with 1,8-diamino-3,6-dioxaoctane gave the ionophore 6 which was converted to its diester derivative 7 by reaction with ethylbromoacetate in the presence of potassium carbonate. In the synthesis, the upper and lower rims of p-tert-butylcalix[4]arene were modified in order to acquire binding sites for the recognition of metal cations and dichromate anions. It was observed that receptor 7 is a better extractant for Cr2O72− anions than receptor 6 . The protonated alkylinium form of 7 is an effective extractant for transferring the Cr2O72− anions from aqueous into a dichloromethane layer and failed in transferring Na+ cations due to the allosteric effect produced by the crown part of the calix moiety present at the p-position.

Synthesis and Extraction Studies of a Versatile Calix[4]arene-Based “Proton-Switchable Extractant” for Toxic Metals and Dichromate Anions

The article describes the syntheses and extraction properties of a new calixarenebased extractant 5, which has been synthesized from5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene(4) by treatment with isoniazid (isonicotinic acid hydrazide) in the presence ofpyridine. The compound 5 was converted to its methyl iodide salt (6) by refluxing 5 with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr2O7-/Cr2O72- anions. The complexing properties of 5 toward selected alkali/transition metal cationsand HCr2O7-/Cr2O72- anions are reported. It has been observed that receptor 5 does not extract alkali metal cations but shows an excellent selectivity toward transition metals. The protonated pyridinium form of 5 is an effective formfor transferring the HCr2O7-/Cr2O72- anions from an aqueous into adichloromethane layer.

Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a p-tert-butylcalix[4]arene-oxacrown-4.

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using p-tert-butylcalix[4]arene-oxacrown-4 as ionophore. Apart from the ionophore, plasticisers and lipophilic anions were blended, in various proportions, with PVC in tetrahydrofurane and mixtures so prepared were poured onto glass surfaces to form the membrane. 2-Nitrophenylpentylether has proved to be the best alternative as plasticiser and the lipophilic anions tried have turned out to have an adverse effect on the pH response. The electrode of the optimum characteristics had a composition of 2% p-tert-butylcalix[4]arene-oxacrown-4, 68.3% o-NPPE and 29.7% PVC. The electrode showed an apparent Nernstian response in the pH range 2-11 with a slope of 54.2+/-0.4mVpH(-1) at 20+/-1 degrees C. It has a rapid potential-response to changes of pH, high ion selectivity towards lithium, sodium and potassium, and other characteristics comparable to those reported for the conventional pH glass membrane electrode. It appears to be a suitable potentiometric indicator electrode specifically for hydrofluoric acid solutions.

Polymer Supported Calix[4]Arene Derivatives for the Extraction of Metals and Dichromate Anions

Three newly synthesized polymer supported calix[4]arene ionophores (7–9) were synthesized, and their ion binding properties toward selected alkali (Li+, Na+, K+, Cs+) and transition metal (Hg2+, Ni2+, Cu2+, Co2+, Cd2+, and Pb2+) cations were investigated. It has been observed that these ionophores are not selective toward a particular metal cation but show better ion binding property as compared to monomeric calixarene derivatives (2 and 6). Ionophore 6 and its supported polymer were also employed in dichromate anion extraction experiments. The polymeric ionophore (9) was found an effective extractant for dichromate anion even at pH 7.

A complimentary study of calixarene based bifunctional receptors for alkali or transition metal cations and Cr2O72−anions

Abstract The article describes the syntheses and extraction properties of two new calixarene based receptors ( 3 and 4 ); the receptor 3 was synthesized from 25,27-diacetonyloxy-26,28-dihydroxy-5,11,17,23-tetra- tert -butylcalix[4]arene 2 by treatment with tetraethylene glycol ditosylate and then the compound 3 was converted to its Schiff base derivative 4 by refluxing 3 with 1,8-diamino-3,6-dioxaoctane. In the synthesis, the lower rim of p - tert -butylcalix[4]arene has been modified in order to acquire soft and hard binding sites for the recognition of metal cations and Cr 2 O 7 2− anions. The complexing properties of 3 and 4 toward selected alkali, transition metal cations and Cr 2 O 7 2− anions are reported. It has been observed that receptor 4 is a better extractant for all metal cations, but not selective as compared to the receptor 3 . The protonated alkylinium form of 4 is an effective extractant for transferring the Cr 2 O 7 2− anions from an aqueous into a dichloromethane layer.

A Convenient Approach towards the Synthesis of a “Proton Switchable” Chromium(VI) Extractant Based on Calix[4]arene

A convenient synthesis and Cr(VI) extraction properties of a new calix[4]arene-based receptor (5), which has been synthesized from 5,17-diformyl-25,27-dimethoxycarbonylmethoxycalix[4]arene (4) by treatment with 3-aminomethylpyridine in one step, are described. The receptor 5 contains four pyridinyl groups, two on each rim. Two of them are joined by an amide linkage onto the lower rim, and other two are linked by an imine-type linkage onto the upper rim of the calix[4]arene moiety. Receptor 5 is very soluble in water at low pH (<2.5). Calixarene 5 also represents a good extractant for Thus, the partially protonated form of 5 is an effective extractant for transferring ions from an aqueous into a chloroform layer. Deprotonation of 5 results in a reversal, with migrating back into the aqueous layer.

Synthesis and binding properties of polymeric calix[4]arene nitriles

Abstract Two new polymers containing pendant calix[4]arene units with nitrile functionalities at their lower rim have been synthesized via radical initiated reactions involving a vinylic monomer 6 {5,11,17,23-tetra- tert -butyl-25,26,27- tris (cyanomethoxy)-28-(2-acryloyloxy) ethoxycalix[4]arene} and with styrene. A five atom spacer group was incorporated between the bulky calixarene core and the acrylate moiety in order to minimize steric interactions which proved to impede the polymerization. The complexation studies were made by using liquid–liquid extraction procedures. It has been deduced from the observations that both polymers show a good selectivity towards Hg 2+ like their precursor 5,11,17,23-tetra- tert -butyl-25,26,27-tricyanomethoxy-28-(2-hydroxy)ethoxycalix[4]arene 5 , which supports their utility as adsorbents or potential candidate materials for fabricating membranes and sensors, which can separate or detect Hg 2+ metal ions in a high selectivity.

Syntheses and binding properties of polymeric calix[4]crown-4

Abstract Three new polymers containing pendant calix[4]crown-4 units have been synthesized via radical initiated reactions involving a vinylic monomer 7 (5,7,11,23-tetra- tert -butyl-25-[2-(Acryloxy)ethoxy]-27-methoxycalix[4]arene-crown-4) and with styrene. A five atom spacer group was incorporated between the bulky calixarene core and the acrylate moiety in order to minimize steric interactions which proved to impede the polymerization. The complexation studies were made by using liquid–liquid and solid–liquid extraction procedures. It has been deduced from the observations that the precursor 5 (5,7,11,23-tetra- tert -butyl-25-hydroxy-27-methoxycalix[4]arene-crown-4) is selective for Hg 2+ , whereas the polymers are not selective but better extractants for all used metal cations. The extraction data support the conformational change of the calix[4]crown from cone to the other various conformations of calixarene moiety.

Synthesis and complexation studies of 1,3-dialkylated p-tert-butylcalix[4]arene telomers

Abstract A series of cone structured lower rim dialkylated p-tert-butylcalix[4]arene (2a–5a) and their relative telomers (2b–5b) have been synthesized to estimate extraction of alkali and transition metal cations from an aqueous phase to an organic phase (dichloromethane). The complexation studies were made by using a liquid–liquid extraction procedure. It has been deduced from the observations that the monomers 2a, 3a and 5a are selective for Hg2+, whereas 4a is not selective but showed higher affinity towards transition metals than the alkali metal cations. The telomer 2b showed more affinity toward Cu2+, Hg2+ and Pb2+, but the telomer 3b is effective for Hg2+ and Pb2+. The telomers 4b and 5b are not selective but they are efficient extractants for the selected transition metal cations. The results indicate that the ligand groups circularly arranged on the lower rim of calixarene cavity form novel binding sites for transition metal cations.

Selective Complexation of Hg2+ by Biscalix[4]arene Nitriles

Ionophoric biscalix[4]arenyl nitriles in which the lower rims are linked via a single site on each calixarene were synthesized. Their complexing abilities were studied by the liquid–liquid extraction of alkali (Li+, Na+, K+, and Cs+) and selected transition metal (Cu2+, Co2+, Cd2+, Ni2+, and Hg2+) cations. We found a novel selectivity of these compounds toward Hg+2 cations through examination of the extraction.