Suban K. Sahoo

An aqueous friendly chemosensor derived from vitamin B6 cofactor for colorimetric sensing of Cu2 + and fluorescent turn-off sensing of Fe3 +

Chemosensor L derived from vitamin B6 cofactor pyridoxal-5-phosphate was investigated for the selective detection of Cu(2+) and Fe(3+) in aqueous medium. Sensor L formed a 1:1 complex with Cu(2+) and displays a perceptible color change from colorless to yellow brown with the appearance of a new charge transfer band at ~450 nm. In contrast, the fluorescence of L was quenched selectively in the presence of Fe(3+) without any interference from other metal ions including Cu(2+).

Design, synthesis and 1H NMR study of C3v-symmetric anion receptors with urethane-NH as recognition group

C3v-Symmetric anion receptors 3 and 4 with urethane groups were synthesized by using trindane triol as tripodal molecular framework. In (1)H NMR titration study, the receptors showed noticeable downfield shift/disappearance of the urethane-NH peak in presence of H2PO4(-) and F(-) due to the host-guest complexation occurred through multiple hydrogen bonding and/or the deprotonation of urethane-NH groups. Other tested anions such as Cl(-), Br(-), HSO4(-), and NO3(-) showed either no or negligible chemical shift of the urethane groups. The deprotonation event in 4 allowed selective detection of F(-) by perceptible color change from colorless to yellowish-red with the appearance of a new charge transfer absorption band at 450 nm.

C 3v -symmetric anion receptors with guanidine recognition motifs for ratiometric sensing of fluoride

Two new tripodal receptors 3 and 4 derived from a trindane framework having guanidine groups acting as hydrogen bond acceptors are synthesized and characterized for the selective recognition of anions. The anion recognition ability of the receptors was evaluated by UV-vis absorption, fluorescence and 1H NMR methods. Both the receptors showed F− selective ratiometric chromogenic and fluorogenic responses among the tested anions due to the host–guest complexation followed by the abstraction of the amide-NH protons supported by the 1H NMR titration study. Receptor 4 with the naphthalene fluorophore units showed higher F− selectively than the receptor 3 by giving visually detectable blue fluorescence and significant turn-on fluorescence at 410 nm which can be switched back and forth by successive addition of F− and H+. Further, the reversible and reproducible fluorescence state of 4 can be applied to design a molecular-scale sequential memory unit displaying “Write–Read–Erase–Read” functions in the form of binary logic.