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Rotational Isomerization about C−C Single Bond in a Novel ICT Probe Facilitates Naked‐Eye, Colorimetric and Ratiometric Detection of Cobalt in Aqueous Samples **
Author(s) -
Divya Dhakshinamurthy,
Thennarasu Sathiah
Publication year - 2021
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.202101089
Subject(s) - bathochromic shift , isomerization , chemistry , naked eye , detection limit , metal ions in aqueous solution , aqueous solution , cobalt , ion , analytical chemistry (journal) , stoichiometry , transition metal , photochemistry , inorganic chemistry , fluorescence , organic chemistry , catalysis , chromatography , physics , quantum mechanics
A new UV‐active indole‐pyrazole extended π‐system (probe A ) that displays a large bathochromic shift (∼325 nm) when it interacts only with Co 2+ and not with other transition metal ions, is presented. The increase in the intensity of new transitions at 592 and 684 nm due to A−Co 2+ −Cl 2 .H 2 O complex formation occurs at the expense of the transition at 358 nm arising from the probe A , and thereby offers a ratiometric method for detection of Co 2+ present in aqueous samples. The ratiometric method sets the detection limit for Co 2+ at 0.404×10 −6 M and 0.337×10 −6 M, when calculated for the transitions at 592 and 684 nm, respectively. The corresponding association constants are 4.041×10 5 M −1 at 592 nm, and 3.617×10 5 M −1 at 684 nm. Job plot and ESI‐MS data confirmed the 1 : 1 stoichiometry of A−Co 2+ −Cl 2 .H 2 O complex. The mode of interaction between the probe A and Co 2+ is explained in terms of conformational isomerization and chelation, using 1 H NMR method and DFT calculations. Other metal ions commonly found in the environment do not seem to interfere in the selective determination of Co 2+ ions. Suitability of probe A in the detection of Co 2+ at concentrations less than 1.7 μM (recommended level of Co 2+ ions by US‐EPA) is also demonstrated using water samples collected from the environment. Test kits suitable for routine on‐site analysis are also developed.