Debdeep Maity

Colorimetric detection of Cu2+ and Pb2+ ions using calix[4]arene functionalized gold nanoparticles

Abstract.Calixarene functionalized gold nanoparticles (CFAuNPs) have been prepared and characterized by spectroscopic and microscopic (TEM) techniques. To use this material as potential colorimetric sensor, the binding property of this new material has been investigated with a large number of metal ions. It exhibited sharp colour change from dark brown to green and blue, detectable by naked-eye, in the presence of Cu2+ and Pb2+ ions, respectively. It has also triggered substantial change in surface plasmon resonance (SPR) band of the functionalized gold nanoparticles, which in case of Pb(II) is due to the inter particle plasmon coupling arising from the metal-induced aggregation of the nanoparticles and for Cu(II), it is because of the formation of AuCu alloy due to anti-galvanic exchange. The size and aggregation of the nanoparticles are confirmed from HRTEM images, elemental analysis and the line profiling for both the metal ions have been done by STEM-EDX analysis. Graphical AbstractCalixarene functionalized gold nanoparticles have been prepared, which detect Cu2+ and Pb2+ ions with visible colour change. For Pb(II), the colour change is due to metal-induced aggregation of the nanoparticles and for Cu(II), it is due to formation of Au–Cu alloy.

Calixarenes: Versatile molecules as molecular sensors for ion recognition study

AbstractThis article presents a brief account on designing of calixarene-based molecular sensor for recognition of various metal ions and anions and also different analytical techniques to monitor the recognition event. This review focuses only on calix[4]arene derivatives, in which mainly the lower rim is modified incorporating either crown moiety to make calix–crown hybrid ionophore to encapsulate metal ions or some fluoregenic inorganic and organic moieties to use it as signalling unit. In order to investigate effect of conformation of the calixarene unit and steric crowding on ion selectivity, designing of these molecules have been made using both the cone and 1,3-alternate conformations of the calixarene unit and also incorporating bulky ter-butyl group in few cases to impose controlled steric crowding. Among various ions, here focuses are mainly on biologically and commercially important alkali metal ion such as K + , toxic metal ions such as Hg2 + , Pb2 + , Cd2 + , important transition metal ion such as Cu2 +  and toxic anion like F − . The techniques used to monitor the recognition event and also to determine binding constants with strongly interacting ions are fluorescence, UV-vis and 1H NMR spectroscopy. Most of the ionophores reported in this review have been characterized crystallographically, however no structural information (except one case) are incorporated in this article, as it will occupy space without significant enhancement of chemistry part. Different factors such as size of the ionophore cavity, size of metal ion, coordination sites/donor atoms, steric crowding and solvents, which determine selectivity have been discussed. Response of ion recognition process to different analytical techniques is another interesting factor discussed in this article. Graphical AbstractIon-recognition property of a large variety of calix[4]arenes incorporating crown moiety to make hybrid ionophore, substituents to impose steric crowding and fluoregenic moieties as signalling unit has been reported. This report demonstrates how factors such as sizes of the ionophore and metal ions, donor atoms, steric crowding and solvents, influence ion-selectivity.

Effect of steric crowding on ion selectivity for calix-crown hybrid ionophores: experimental, molecular modeling and crystallographic studies

A number of calix[4]arene-azacrowns with variation in ring size and substituents at the upper and lower rims have been synthesized to investigate the effect of steric crowding towards ion selectivity. The structural elucidation of these ionophores has been carried out mainly by 1H NMR and ES-MS in solution and by single crystal X-ray study in the solid state. Interaction of these ionophores with a large number of cations has been investigated by NMR studies. The ionophore with tert-butyl at the upper rim (3) exhibits selectivity towards Na+ only whereas an ionophore of the same size but without tert-butyl at the upper rim (1) shows selectivity towards both Na+ and K+. An ionophore of the same size but with three tosyl substituents at the lower rim (4) exhibits no complexation with any cation. The ionophore with the larger crown ring and without tert-butyl at the upper rim (2) exhibits complexation with K+, Rb+, Ba2+ and weak interaction with Na+. Binding constants with these metal ions have been determined by NMR titration. Molecular modeling studies performed by a molecular mechanics force field (MMFF94) using the Monte Carlo search method and DFT calculations predicted the observed higher selectivity for sterically crowded receptor.

Detection of NaCN in aqueous media using a calixarene-based fluoroionophore containing ruthenium(II)-bipyridine as the fluorogenic unit

A new molecular sensor containing calixarene and ruthenium(II)-bipyridine as the fluorophore bridged by an amide moiety has been synthesised and characterized, and its anion binding properties have been investigated. It selectively detected cyanide in 95 : 5 water : acetonitrile when sodium salts of various anions such as F−, Cl−, Br−, I−, PO42−, IO4−, BO3−, CH3COO−, CN− and SO42− were investigated. The recognition event was monitored by fluorescence spectroscopy and the lower detection limit found was 70 ppb. However, when tetrabutylammonium salts of the same anions were used then, in addition to CN−, CH3COO− was also detected under similar experimental conditions. Interestingly, CN− exhibited substantial quenching, whereas CH3COO− showed an enhancement in emission intensity. The interaction of anions with the fluoroionophore was also monitored by electrochemical technique and the result obtained is consistent to that found by fluorogenic method. Binding constants were determined from emission titration, composition of the anion-complexes formed were determined from mass and emission titration data, mechanistic aspects of the interaction have been discussed with the aid of NMR data and the role of cations in the contrast fluorescent off and on behaviour has also been discussed. This sensor has also been used to estimate cyanide in real samples and the result obtained is satisfactory.

Functionalized calix[4]arene as a colorimetric dual sensor for Cu(II) and cysteine in aqueous media: experimental and computational study

A family of calix[4]arenes with variation in steric crowding at the upper rim and incorporating pyridine and amide moieties at two of the four OH groups located in the lower rim have been synthesized and their performance as sensors for metal ions has been investigated. Two of the compounds exhibited selective interaction with Cu2+ ions with sharp colour change, observed by the naked eye. Spectroscopic and computational studies revealed that two of the compounds form 1 : 2 complexes, in which one of the Cu2+ ions interacts strongly with the phenolic OH, resulting in a colour change due to strong absorption (ICT) in the visible region. For the third compound, the Cu2+ ions coordinate with the pyridine and amide nitrogen atoms, and the Cu2+ ion could not enter inside to interact with the OH group due to restricted flexibility at the lower rim because of the bulky groups at the upper rim. The Cu2+ complexes thus formed have been used for sensing of amino acids and interestingly, one of the complexes exhibits interactions selectively with cysteine out of eighteen amino acids tested with a sharp colour change in aqueous media. The formation of the Cu2+–cysteine complex is confirmed from mass data, and the surface morphology of the complex before and after the addition of cysteine is investigated by SEM study.

Effect of conformation, flexibility and intramolecular interaction on ion selectivity of calix[4]arene-based anion sensors: experimental and computational studies

Abstract A number of calix[4]arene-based molecules were designed incorporating amide moiety with variation in conformation, rigidity at the binding sites and steric crowding at the upper rim to investigate the anion sensing property of this series of ionophores. These compounds were synthesised and characterised, molecular structures of two of the compounds were established by single-crystal X-ray study. Anion binding property of these ionophores, investigated with the aid of 1H NMR and UV–vis spectroscopy, revealed that three (1–3) out of four ionophores strongly interact with F−, in addition, ionophore 2 interacts with CN− and , ionophore 3 interacts with CH3COO− and and ionophore 4 does not interact with any anions. NMR titration was carried out to determine binding constant with strongly interacting anions. Crystal structure analysis revealed that strong intramolecular interaction in 4 prevented the anions to interact with the N–H protons of the amide moiety. Interestingly, 2 with F− and CN− exhibits sharp colour change in acetonitrile–chloroform. Apparently, conformation of the calix moiety, flexibility of the binding sites and intramolecular H-bonding played critical role towards determination of selectivity. Computational study was performed to investigate the interaction site(s) and also to corroborate some of the experimental results. Anion binding study of functionalised calix[4]arenes revealed that conformation, flexibility and intramolecular interaction in calix moiety play critical role to determine ion selectivity. One of the receptors performs as sensitive colorimetric sensor for F− and CN−, computational study also corroborates most of the experimental results.