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Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by 1H NMR, 13C NMR, HRMS, and single crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn2+, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co2+ or Cu2+ ions present in aqueous acetonitrile medium. 13C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co2+ or Cu2+ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10–7 M, probe 1/Zn2+; 0.420 × 10–7 M, probe 2/Co2+ and 0.304 × 10–7 M, probe 2/Cu2+). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn2+, Co2+ or Cu2+, and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using 13C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn2+, Co2+ and Cu2+ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn2+, Co2+ or Cu2+ ions in onion epidermal cells. [ABSTRACT FROM AUTHOR]

Density functional theoretical calculations predicted non‐coplanar twisted geometry for two new imidazo[1,2‐a]pyridine derivatives, Imp and ImBt. Analysis of single‐crystal of Imp asserted the non‐coplanar twisted geometry, which is implicated in aggregation induced emission (AIE) of small aromatic molecules. Universal quenching by water was observed in aqueous THF solutions of Imp and ImBt, but they showed AIE effect when the water content was more than 80 %. Non‐fluorescent solutions of Imp and ImBt in THF‐water (7 : 3 v/v) mixture turned fluorescent on addition of specific metal ions prompting their potential to be explored for turn‐on sensor applications. While ImBt showed AIE response to Cd2+, Hg2+ and Al3+, Imp displayed AIE effect only to Cd2+ ions, under identical conditions. Absence of interference from common metal ions (including Hg2+ and Al3+) led to selective formation of Imp‐CdCl2 (1 : 1) complex, which offered the limit of detection of Cd2+ to be 19.2 μM. The observed selectivity for Cd2+ permitted the use of Imp in the imaging of live Rhizoctonia oryze contaminated with Cd2+ ions. [ABSTRACT FROM AUTHOR]

A new UV‐active indole‐pyrazole extended π‐system (probe A) that displays a large bathochromic shift (∼325 nm) when it interacts only with Co2+ 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−Co2+−Cl2.H2O 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 Co2+ present in aqueous samples. The ratiometric method sets the detection limit for Co2+ 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 4.041×105 M−1 at 592 nm, and 3.617×105 M−1 at 684 nm. Job plot and ESI‐MS data confirmed the 1 : 1 stoichiometry of A−Co2+−Cl2.H2O complex. The mode of interaction between the probe A and Co2+ is explained in terms of conformational isomerization and chelation, using 1H NMR method and DFT calculations. Other metal ions commonly found in the environment do not seem to interfere in the selective determination of Co2+ ions. Suitability of probe A in the detection of Co2+ at concentrations less than 1.7 μM (recommended level of Co2+ 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. [ABSTRACT FROM AUTHOR]

Two new rhodamine–indole conjugates 1 and 2 were synthesized for studying their ability to probe specific metal ions at physiological pH in the presence of other competing metal ions. In non-aqueous medium, probe 1 predominantly binds Cu2+ ions with considerable interference from Fe3+ and Ni2+ ions. However, in aqueous medium, 1 exhibits a higher degree of selectivity for Cu2+ ions with little interference from Fe3+ ions, and no interference from Ni2+ ions. The probe 2, obtained by tethering a triazole moiety with probe 1, selectively binds Cu2+ ions in aqueous medium even in the presence of other metal ions including Fe3+ ions. The sensitivity of probe 2 to pH variation and interaction with various amino acids were also investigated. The excellent stability of 2 in physiological pH conditions, non-toxicity, non-interference of amino acids in the detection process, and the remarkable selectivity for Cu2+ ions in aqueous medium allowed the use of 2 in the imaging of live fibroblast cells treated with Cu2+. [ABSTRACT FROM AUTHOR]

Abstract: A bis-rhodamine based fluorescent chemosensor for naked-eye detection of Cu2+ with enhanced sensitivity as compared to mono-rhodamine derivative has been synthesized, and its selectivity for Cu2+ in the presence of other competitive metal ions (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, and Pb2+), and application in bio-imaging are demonstrated. [Copyright &y& Elsevier]

[Display omitted] • A simple single step multicomponent ugi type reaction was carried out to yield N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2- a ]pyridine-3-amine (TBFIPA). • The synthesized TBFIPA was characterized using 1H NMR, 13C NMR and HRMS spectroscopic methods. • The selective & sensitive detection was identified using hypsochromic shift (lab : 335nm → 285nm) & fluorescence quenching. • The proposed mechanism is evident from Job plot, 1H NMR titration, ESI-MS data and theoretical DFT calculation. • The Cr3+ ion-selective TBFIPA was successfully applied in the design of a user-friendly silica-based portable test kits. • Also, the fluorescence quenching ability of TBFIPA in presence of Cr3+ ions are validated by imaging onion epidermal cells. • Real samples contaminated with Cr3+ ions were identified using TBFIPA with an appropriated relative error percentage. A simple single step one pot multicomponent reaction was performed to synthesize N-(tert -butyl)-2-(furan-2-yl)imidazo[1,2- a ]pyridine-3-amine (TBFIPA). The synthesized TBFIPA was subjected to library of cations to study its ability for selective and sensitive detection of specific metal ions. Selective detection of chromium ions by TBFIPA were found from the significant hypsochromic shift (335 nm → 285 nm) in the UV–Visible spectra. The fluorescent TBFIPA displays complete quenching of fluorescence under UV lamp (365 nm) only in the presence of chromium without the interference of common metal ions. Binding constant (k a) obtained from Benesi-Hildebrand plot is 0.21 × 105 M−1, limit of detection (LOD) and limit of quantification (LOQ) of TBFIPA toward Cr3+ ions are 4.70 × 10−7 M and 1.56 × 10−7 M, respectively. The mechanism proposed during complex formation were supported by stoichiometric Job continuous variation plot, 1H NMR titration and ESI-MS spectroscopic data. All the experimental confirmation for complex formation were corroborated with theoretical DFT studies optimized using RB3LYP/6-31G(d) basis set. The selectivity and sensitivity of TBFIPA toward Cr3+ ions are found suitable to design a user-friendly silica based portable test kit. Alongside, TBFIPA was successfully utilized for imaging onion epidermal cells. Furthermore, the results obtained for biological, environmental, and industrial samples provided solid evidence to estimate chromium ions using TBFIPA in these real samples. [ABSTRACT FROM AUTHOR]

A novel fluorescein-rhodamine dyad probe has been synthesized and its chemosensory applications are explored. Anion and cation specific responses of the probe permit ratiometric detection of Hg 2+ and fluoride ions, individually and collectively, with different fluorescence outputs. The presence of other commonly coexistent ions does not affect the Hg 2+ and fluoride ion detection ability of the probe. The probe is highly sensitive to Hg 2+ and fluoride ions and it can detect Hg 2+ and fluoride ions even at ppb level concentrations. The probe is non-toxic under the experimental conditions, cell permeable and useful for the imaging of intracellular Hg 2+ and fluoride ions. [ABSTRACT FROM AUTHOR]

Synthesis and chelation induced fluorescence emission from two imidazo[1,2- a ]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al3+, Fe3+ and Cr3+, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn2+ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi3+ and In3+) and common divalent metal ions (including Hg2+ and Cd2+) fail to form any complex with 1 or 2 , and they do not interfere in the detection of Zn2+, Al3+, Fe3+ or Cr3+ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn2+, Al3+, Fe3+ or Cr3+ ions. Two structurally related bidentate nonplanar nonfluorescent molecules attain coplanarity through selective interactions with divalent Zn2+ and trivalent Al3+, Fe3+ and Cr3+ ions and emit fluorescence, permitting the detection of these metal ions. Unlabelled Image • Two imidazo[1,2- a ]pyridine based bidentate nonfluorescent molecules 1 and 2 form, respectively, a 1:1 complex with divalent Zn2+ and trivalent Fe3+, Al3+ and Cr3+ ions, adopt coplanar conformation, and show chelation induced fluorescence enhancement. [ABSTRACT FROM AUTHOR]