title: Lower rim 1,3-diderivative of calix[4]arene-appended salicylidene imine (H(2)L): experimental and computational studies of the selective recognition of H(2)L toward Zn(2+) and sensing phosphate and amino acid by [ZnL].
abstract: 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.
authors.affiliation: Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India.
authors.forename: Roymon
authors.initials: R
authors.lastname: Joseph
authors.forename: Jugun Prakash
authors.initials: JP
authors.lastname: Chinta
authors.forename: Chebrolu P
authors.initials: CP
authors.lastname: Rao
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D047250:Calixarenes / Q000737:chemistry*; D003198:Computer Simulation; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D012459:Salicylates / Q000737:chemistry*; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D010710:Phosphates; D012459:Salicylates; C121325:calix(4)arene; D047250:Calixarenes; D015032:Zinc