Calix(n)arene-quinone interactions: Molecular recognition of 2,6-naphthoquinone by 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexahydroxycalix(6)arene

Determination of association constant of host-guest supramolecular complex (molecular recognition of carbamazepine, antiseizure drug, with calix(4)arene)

The thermodynamic property of the host-guest, inclusion complex formed between p-t-butyl calix(4)arene which is a supramolecule, and the antiseizure drug, carbamazepine was studied. p-t-Butyl calix(4)arene has been used as a host molecule and carbamazepine as a guest molecule. Optical absorption spectral studies were carried out to investigate the molecular recognition properties of p-t-butyl calix(4)arene with carbamazepine. The stochiometry of the host-guest complexes formed and the association constant were determined. An interesting 1:2 stochiometric host-guest complex was formed. Job's continuous method of variation and Benesi-Hildebrand expression were used for the determination of binding constant and the stochiometry of the host-guest complex formed. Molecular dimension of the host molecule plays a vital role in the formation of the host-guest stochiometric complexes.

Selective functionalization of methylene bridges of calix[6]arenes. Isolation and identification of stable conformers of methyl ether of p-tert-butylcalix[6]arene

Direct disubstitution at the methylene bridges of p-tert-butylcalix[6]arenemethyl ether has been achieved for the first time using a lithiation-substitution protocol. Two stable conformers have been isolated using column chromatography, and their structures have been unambiguously confirmed from 1D, 2D and variable temperature NMR studies and single crystal X-ray structure analysis.

Molecular recognition study of Carbamazepine, antiseizure drug, by p-t-butyl calix(8)arene

The formation of inclusion complex of Carbamazepine, a antiseizure drug molecule, with the supra molecule, p-t-butyl calix(8)arene was studied. p-t-Butyl calix(8)arene was the host molecule and Carbamazepine was the guest molecule. Optical absorption spectral studies were carried out to study the molecular recognition properties of p-t-butyl calix(8)arene with Carbamazepine. The stochiometry of the host-guest complex and the binding constant were determined.

Molecular recognition of 1,5 diamino anthraquinone by p-tert-butyl-calix(8)arene

The molecular recognition properties of p-tert-butyl-calix(8)arene with 1,5 -diamino anthraquinone (1,5 DAAQ) were studied by using UV-Visible and Fluorescence spectroscopic techniques. The binding constant was determined by using the Benesi-Hilde brand expression. It was found that the host-guest complex was formed between 1,5 DAAQ and p-tert-butyl- calix(8)arene in the 1:2 Stoichiometry ratio.

Solvatochromism, Preferential Solvation of 2,3-Bis(Chloromethyl)-1,4-Anthraquinone in Binary Mixtures and the Molecular Recognition Towards p-Tert-Butyl-Calix[4]arene

Optical absorption and fluorescence emission spectra of 2,3-bis(chloromethyl)-1,4-anthraquinone (DCMAQ) in single solvents namely, carbon tetrachloride, acetonitrile, chloroform, propan-2-ol and its binary mixtures [carbon tetrachloride/chloroform, chloroform/acetonitrile, chloroform/propan-2-ol] have been investigated. The preferential solvation of DCMAQ in above mixtures has been studied by monitoring the absorption and fluorescence spectra of DCMAQ. The spectral features indicate that DCMAQ is preferentially solvated by CHCl(3) in the above mixtures. This can be elucidated from the local mole fraction, non-linearity in transition energy plot, preferential solvation index (delta (s2)) and (f2/f1) values. Molecular recognition properties of p-tert-butylcalix[4]arene (tBC) to DCMAQ via hydrogen bonding and pi-pi interaction were sensed successfully on the basis of absorption and fluorescence emission spectroscopies, by which the stoichiometry ratio and the binding constant of the tBC-DCMAQ complex were determined.

Spectral investigations on 2,3-bis(chloromethyl)-1,4- anthraquinone: solvent effects and host–guest interactions

Solvent effects on 2,3-bis(chloromethyl)-1,4-anthraquinone (DCMAQ) and the molecular recognition of DCMAQ in calix[8]arene were investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra show n-->pi(*) band in 350-500 nm region. It also indicates that the dipole-dipole interaction and solvent reorganization energies are responsible for the observed features in different solvents. The observed quantum yield of DCMAQ in different solvents is due to the formation of intermolecular hydrogen bond and reorientation of solvent molecule in the excited state of DCMAQ. Excited state dipole moment of DCMAQ is calculated by solvatochromic data and it shows a higher excited state dipole moment than ground state dipole moment. Optical absorption and fluorescence studies of DCMAQ in calix[8]arene elucidate the evidence for the formation of complex between DCMAQ and calix[8]arene. The inclusion ratios and inclusion constant of the host-guest complexes are also determined.

Light-induced electron transfer in porphyrin–calixarene conjugates

The fluorescence from a set of porphyrin-calixarene complexes is quenched upon addition of benzo-1,4-quinone (BQ) in fluid solution. In N,N-dimethylformamide solution, fluorescence quenching involves both static and dynamic interactions but there are no obvious differences between porphyrins with or without the appended calixarene. Under such conditions, the static quenching behaviour is attributed to pi-complexation between the reactants and it is concluded that the calixarene cavity does not bind BQ. An additional static component is apparent in dichloromethane solution. This latter effect involves partial fluorescence quenching, for which the intramolecular rate constant can be obtained by time-resolved fluorescence spectroscopy. The derived rate constants depend on molecular structure in a manner consistent with fluorescence quenching being due to electron transfer. In all cases, however, the dominant quenching step involves diffusional contact between the porphyrin nucleus and a non-bound molecule of BQ.