Roymon Joseph

Lower rim 1,3-di{bis(2-picolyl)}amide derivative of calix[4]arene (l) as ratiometric primary sensor toward Ag+ and the complex of Ag+ as secondary sensor toward Cys: experimental, computational, and microscopy studies and INHIBIT logic gate properties of L.

A structurally characterized lower rim 1,3-di{bis(2-picolyl)}amide derivative of calix[4]arene (L) exhibits high selectivity toward Ag(+) by forming a 1:1 complex, among nine other biologically important metal ions, viz., Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), and Zn(2+), as studied by fluorescence, absorption, and (1)H NMR spectroscopy. The 1:1 complex formed between L and Ag(+) has been further proven on the basis of ESI mass spectrometry and has been shown to have an association constant, K(a), of 11,117 +/- 190 M(-1) based on fluorescence data. L acts as a primary ratiometric sensor toward Ag(+) by switch-on fluorescence and exhibits a lowest detectable concentration of 450 ppb. DFT computational studies carried out in mimicking the formation of a 1:1 complex between L and Ag(+) resulted in a tetrahedral complex wherein the nitrogens of all four pyridyl moieties present on both arms are being coordinated. Whereas these pyridyls are located farther apart in the crystal structure, appropriate dihedral changes are induced in the arms in the presence of silver ion in order to form a coordination complex. Even the nanostructural features obtained in TEM clearly differentiates L from its Ag(+) complex. The in situ prepared silver complex of L detects Cys ratiometrically among the naturally occurring amino acids to a lowest concentration of 514 ppb by releasing L from the complex followed by formation of the cysteine complex of Ag(+). These were demonstrated on the basis of emission, absorption, (1)H NMR, and ESI mass spectra. The INH logic gate has also been generated by choosing Ag(+) and Cys as input and by monitoring the output signal at 445 nm that originates from the excimer emission of L in the presence of Ag(+). Thus L is a potential primary sensor toward Ag(+) and is a secondary sensor toward Cys.

Lower Rim 1,3-Diderivative of Calix[4]arene-Appended Salicylidene Imine (H2L): Experimental and Computational Studies of the Selective Recognition of H2L toward Zn2+ and Sensing Phosphate and Amino Acid by [ZnL]

A new 1,3-diderivative of calix[4]arene appended with hydroxymethyl salicylyl imine has been synthesized and its ion recognition toward biologically relevant M(n+) ions studied. The receptor H(2)L showed selectivity toward Zn(2+) by switch-on fluorescence among the 12 metal ions studied with a detection limit of 192 ppb. The interaction of Zn(2+) with H(2)L has been further supported by absorption studies, and the stoichiometry of the complex formed (1:1) has been established on the basis of absorption and ESI MS. Competitive ion titrations carried out reveal that the Zn(2+) can be detected even in the presence of other metal ions of bioimportance. The mode of interaction of Zn(2+) with conjugate has been established by a fleet of computational calculations carried out in a cascade manner, either on the ligand or on the complex, wherein the final optimizations were carried out by the density functional theory (DFT) and found that the Zn(2+) and Cd(2+) indeed bind differently. In situ prepared [ZnL] complex responds to both inorganic phosphate as well as AMP, ADP, and ATP with a minimum detection limit of 426 ppb wherein the Zn(2+) from the complex is detached and recomplexed by the added phosphate moiety. It has been possible to build an INHIBIT logic gate for the conjugate using Zn(2+) and HPO(4)(2-) as inputs by monitoring the fluorescence emission band at 444 nm as output. The amino acid sensing abilities of [ZnL] have been explored by fluorescence and absorbance spectroscopy where it showed selectivity toward Cys, Asp, and His through the formation of the Zn(2+) complex of these amino acids by chelating through their side chain moieties. Thus, while H(2)L is selective for Zn(2+) among a number of cations, the [ZnL] is selective toward phosphate among a number of anions and also toward Asp, Cys, and His among the naturally occurring amino acids.

Experimental and Computational Studies of Selective Recognition of Hg2+ by Amide Linked Lower Rim 1,3-Dibenzimidazole Derivative of Calix[4]arene: Species Characterization in Solution and that in the Isolated Complex, Including the Delineation of the Nanostructures

Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg(2+) in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg(2+) has been shown among 11 M(2+) ions, viz., Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ca(2+), and Mg(2+) studied, including those of the mercury group and none of these ions impede the recognition of Hg(2+) by L. Role of the solvent on the recognition of Hg(2+) has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg(2+) by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg(2+) with L has been further established based on (1)H and (13)C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg(2+) have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg(2+) toward L have been established based on the DFT computational calculations.

Calix[4]arene-Based 1,3-Diconjugate of Salicylyl Imine Having Dibenzyl Amine Moiety (L): Synthesis, Characterization, Receptor Properties toward Fe2+, Cu2+, and Zn2+, Crystal Structures of Its Zn2+ and Cu2+ Complexes, and Selective Phosphate Sensing by the [ZnL]

A calix[4]arene conjugate bearing salicylyl imine having dibenzyl moiety (L) has been synthesized and characterized, and its ability to recognize three most important essential elements of human system, viz., iron, copper, and zinc, has been addressed by colorimetry and fluorescence techniques. L acts as a sensor for Cu(2+) and Fe(2+) by exhibiting visual color change and for Zn(2+) based on fluorescence spectroscopy. L shows a minimum detection limit of 3.96 ± 0.42 and 4.51 ± 0.53 ppm and 45 ± 4 ppb, respectively, toward Fe(2+), Cu(2+), and Zn(2+). The in situ prepared [ZnL] exhibits phosphate sensing among 14 anions studied with a detection limit of 247 ± 25 ppb. The complexes of Zn(2+), Cu(2+), and Fe(2+) of L have been synthesized and characterized by different techniques. The crystalline nature of the zinc and copper complexes and the noncrystalline nature of simple L and its iron complex have been demonstrated by powder XRD. The structures of Cu(2+) and Zn(2+) complexes have been established by single crystal XRD wherein these were found to be 1:1 monomeric and 2:2 dimeric, respectively, using N(2)O(2) as binding core. The geometries exhibited by the Zn(2+) and the Cu(2+) complexes were found to be distorted tetrahedral and distorted square planar, respectively. The iron complex of L exists in 1:1 stoichiometry as evident from the mass spectrometry and elemental analysis.