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Abstract: A new molecular fluorescent sensor (L) for Cu2+ has been synthesized by derivatizing the lower rim of calix[4]arene with benzothiazole moiety, through amide linkage to result in 1,3-di-derivative. The receptor molecule, L exhibited fluorescence quenching towards Cu2+ among eleven divalent ions, viz., Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Ca2+, Mg2+ and Pb2+, studied. The 1:1 stoichiometry of the complex formed between L and Cu2+ has been demonstrated by electronic absorption and ESI-MS. The role of calix[4]arene for the selective sensing of Cu2+ has been established by comparing the data with that obtained for an appropriate control molecule. The minimum concentration at which L can detect Cu2+ has been found to be 403ppb. The computations carried out at DFT level have provided the coordination and structural features of the Cu2+ complex of L as species of recognition. The Cu2+ complex thus formed recognizes iodide by bringing change in the color, among the 14 anions studied. [ABSTRACT FROM AUTHOR]

A new 1,3-diderivative of calix[4]arene appended with hydroxymethyl salicylyl irnine has been synthesized and its ion recognition toward biologically relevant Mn+ ions studied. The receptor H2L showed selectivity toward Zn2+ by switch-on fluorescence among the 12 metal ions studied with a detection limit of 192 ppb. The interaction of Zn2+ with H2L has been further supported by absorption studies, and the stoichiometiy 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 Zn2+ can be detected even tn the presence of other metal ions of bioimportance. The mode of interaction of Zn2+ 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 Zn2+ and Cd2+ 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 Zn2+ 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 Zn2+ and HPO42- as inputs by monitoring the fluorescence emission band at 444 nm as output. The amino acid senstng 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 Zn2+ complex of these amino acids by chelating through their side chain moieties. Thus, while H2L is selective for Zn2+ 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. [ABSTRACT FROM AUTHOR]

A structurally characterized lower rim 1,3-di(bis(2-picolyl))amide derivative of calix[4larene (L) exhibits high selectivity toward Ag+ by fonning a 1:1 complex, among nine other biologically important metal ions, viz., Na+, K+, Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, and Zn2+, as studied by fluorescence, absorption, and 1H NMR spectroscopy. The 1:1 complex formed between Land Ag+ has been further proven on the basis of ESI mass spectrometry and has been shown to have an association constant, Ka, of 11117 ± 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 11 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, 1HNMR, 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 rim that originates from the excimer emission of L in the presence of Ag+. Thus Lisa potential primary sensor toward Ag+ and is a secondary sensor toward Cys. [ABSTRACT FROM AUTHOR]

Abstract: A highly selective fluorescence switch on sensor, L for detecting Cu2+ has been synthesized by introducing a bis-(2-picolyl)amine moiety at the lower rim of a calix[4]arene platform via amide linkage. Binding properties of L toward ten different biologically relevant Mn+ ions have been studied by fluorescence and absorption spectroscopy in methanol and aqueous methanol. L was found to detect Cu2+ selectively down to a concentration of 196 and 341ppb, respectively, in methanol and 1:1 aqueous methanol even in the presence of other metal ions. The composition of the complex has been found to be 1:1 based on the Job plot and is further confirmed by ESI MS. The role of calix[4]arene platform as well as the pre-organized binding core in the selective recognition of Cu2+ has been demonstrated by studying appropriate reference molecules. The possible modes of binding of L with Cu2+ have been modeled by computational calculations. L and its Cu2+ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM. [Copyright &y& Elsevier]

Abstract: The bis-{N-(2-hydroxynaphthyl-1-methylimine)} anchored 1,3-di-derivative of lower rim p-tert-butyl-calix[4]arene possessing a N2O2, N2O4 or N2O6 binding core was found to be selective for Zn(II) ions even at ⩽60ppb by eliciting fluorescence-on behaviour while the other ions, viz., Ti4+, VO2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Mg2+, Cd2+ and Hg2+ caused no change in the fluorescence. The reaction between 1 and Zn2+ was found to be stoichiometric with the formation of a 1:1 complex; while H+ quenched the fluorescence of the complex, OH− restored it. The studies of the 1:1 isolated complexes of Zn2+, Ni2+ and Cu2+ augmented the results. [Copyright &y& Elsevier]

A quinoline functionalized pillar[5]arene, QPA has been prepared and its interaction with biologically relevant ions and molecules in aqueous solution has been demonstrated. The sensor molecule, QPA has shown selectivity towards Fe3+ among eleven metal ions studied. The Fe3+ complex of QPA (FeQPA) selectively interacts with F− among halides by ∼4 fold fluorescence enhancement. Further, FeQPA has shown selectivity towards arginine and lysine among twenty naturally occurring amino acids. The binding of QPA with Fe3+ has been confirmed by MALDI-TOF and 1H NMR titrations. Unlabelled Image • Selective sensing of Fe3+ by novel pillar[5]arene derivative, QPA • Fe3+ complex of QPA (FeQPA) detects F− among all halides. • FeQPA selectively detects arginine and lysine among twenty amino acids. [ABSTRACT FROM AUTHOR]