Har Mohindra Chawla

A new class of functionalized calix[4]arenes as neutral receptors for colorimetric detection of fluoride ions

A new class of functionalized calix[4]arenes have been synthesized and evaluated for colorimetric detection of fluoride ions. The molecular receptor 4b selectively recognizes fluoride ions via H-bonds and subsequent deprotonation to elicit a distinct colour change from yellow to dark purple.

Synthesis of selectively formylated calixarene ethers

coworkers10 have successfully used dichloromethylmethyl ether and titanium tetrachloride for formylation of tetrakis(2-ethoxyethyl)calix[4]arene but they have not examined the case of other calixarenes and conformational selectivity. The outcome of reaction under different parameters has also not been elaborated so far. Since we required selectively formylated calix[«]arene ethers and esters with long alkyl chains, we had to optimize the reaction parameters to achieve desired derivatives since reported reaction conditions were not useful. During the execution of present work, characterization of products and conformational analysis was achieved by well-document ed NMR methods. Direct comparison with authentic samples prepared by known routes confirmed the identity of products. New information gathered on the formylation of calixarenes is given in the ensuing discussion.

A CONVENIENT ONE POT ONE STEP SYNTHESIS OF p-NITROCALIXARENES VIA IPSONITRATION

An efficient one step one pot synthesis of p-nitrocalix(n)arenes by ipsonitration of p-tert-butylcalix(n)arenes is described.

One step facile synthesis of bromo calix[n]arenes

Bromination of p-tert-butyl calix[n]arenes under different reaction conditions can provide either methylene bridge or ring substituted calix[n]arenes that are usually only amenable through long circuitous routes.

A convenient single step synthesis of p-thiomethylmethylcalixarenes and metal ion extraction studies

A facile synthesis of p-thiomethylmethylcalixarenes through a [2,5] sigmatropic rearrangement and extraction of soft heavy metal ions using the prepared calix[4]arene derivative is reported here.

A one-step, one-pot synthesis of p-acyl calix[n]arenes

A one-step, one-pot procedure for conversion of p-tert-butylcalix[n]arenes to their p-acyl derivatives has been achieved.

Simultaneous quantitative estimation of oxybenzone and 2-ethylhexyl-4-methoxycinnamate in sunscreen formulations by second order derivative spectrophotometry

Simultaneous determination of 2-ethylhexyl-4-methoxycinnamate (OMC) and oxybenzone (OB) in commercial sunscreen formulations has been achieved by using second order derivative spectrophotometry. The analytical methodology described does not require elaborate pretreatment of samples. The results obtained could be validated by reverse phase HPLC assay by using isocratic methanol: water (88: 12) solvent system. The sensitivity of the developed derivative spectrophotometry method was determined to be 9.0 × 10−3 L/mg for OB and 9.56 × 10−3 L/mg for OMC. The limit of instrumental detection (LOD) was determined to be 0.6 mg/L for OB and 1.38 mg/L for OMC with relative standard deviation of 0.001 and 0.004 for OB and OMC respectively. The method developed can be used for quick assay of commercial sunscreens.

Sensitive recognition of cyanide through supramolecularly complexed new calix[4]arenes

Two new calix[4]arene based fluorescence sensors (L1 and L2) have been synthesized and characterized. L1 was found to selectively quench fluorescence intensity upon addition of Cu2+ ions through host–guest complexation and display “on–off” behavior while L2 was not that efficient. The in situ generated L1·Cu2+ complex could further recognize CN− from the anionic broth with a distinct “off–on” behavior in the fluorescence titration.

A new calix[4]arene based molecular probe for selective and sensitive detection of CN− ions in aqueous media

A calix[4]arene based molecular probe, 4, has been proposed as a diagnostic probe for CN− ions in aqueous media. The investigation promises the development of disposable filter paper strips for field applications.

Novel colorimetric anion sensors based on N-acetylglyoxylic amides containing nitrophenyl signalling units.

N-acetylglyoxylic amides 4 and 5 bearing pendant 4-nitrophenyl and 2,4-dinitrophenyl groups respectively were synthesized and evaluated as anion sensors. A crystal structure of 4 was obtained by X-ray crystallography. Compounds 4 and 5 behaved as colorimetric sensors for CN(-) and F(-), and exhibited naked eye-detectable color changes upon the addition of these anions. The chromogenic properties of 4 and 5 were assessed by UV-Vis and (1)H NMR spectroscopy.