Colorimetric and fluorescence sensing of Zn2+ ion and its bio-imaging applications based on macrocyclic "tet a" derivative.

We report on the synthesis and characterization of trans N, N'-di-substituted macrocyclic "tet a" probe (L) for metal ion sensing. Both the colorimetric and fluorescent titration studies are performed with different metal ions. The results have suggested that the probe L is very selective and sensitive towards Zn2+ ions with significant changes in color. The pendant armed macrocyclic "tet a" probe has exhibited 1.28× 105 M-1 binding constant and virtuous selectivity for Zn2+ ion than other common metal ions. The detection limit of the probe towards Zn2+ ion is 0.027 nM. The selective sensing of Zn2+ ion is efficiently reversible with EDTA, which is demonstrated for five cycles without losing sensitivity. The time-resolved single-photon counting (TCSPC) studies have determined the average lifetime value for the probe L and L+ Zn2+ ion of 1.29 and 2.96 ns, respectively. The theoretical DFT studies have well supported the experimental outcomes. The practical application of the probe in visualizing intracellular Zn2+ ion distribution in live Artemia salina has proved the low cytotoxicity and cell membrane permeability of probe, which makes it capable of sensing Zn2+ ion in HeLa cells. Thus, the probe L can act as a selective recognition of Zn2+ ion in living cell applications.

Macrocyclic "tet a" derived colorimetric sensor for the detection of mercury cations and hydrogen sulphate anions and its bio-imaging in living cells.

A mono-N-substituted probe L containing a bromosalicylaldehyde pendant arm attached to a tetraazamacrocyclic "tet a" moiety was synthesized via straight forward reaction. The probe L crystallizes in a monoclinic P21/n space group. The probe L displayed quick sensitivity and selectivity towards Hg2+ ions due to its hopeful Chelation Enhancement Quenching (CHEQ) feature. Interestingly, the probe L exhibits turn-off fluorescence response to Hg2+ ion and turn-on fluorescence signals to HSO4- ions. When the probe L was complexed with HSO4- in 1:1 mode (L + HSO4- formation), improved turn-on fluorescence emission was detected due to the chelation enhanced fluorescence effect through sensor complex. The macrocyclic "tet a" probe L exhibited a binding constant value of 3.89 × 106 M-1 and 5.58 × 105 M-1 for Hg2+ and HSO4-, respectively. Probe L exhibited good selectivity to Hg2+ rather than other common metal ions and HSO4- over other common anions. The limit of detection (LOD) of Hg2+ and HSO4- were found to be 1 nM and 7 µM, respectively. The time-resolved fluorescence emission single-photon counting study was used to determine the average lifetime value for the probe L and L + HSO4- ions as 0.47 and 1.02 ns, respectively. The practical application of the probe in visualizing intracellular Hg2+ and HSO4- ions distribution in live Artemia salina was demonstrated. Furthermore, the probe L with Hg2+cations was found to be cytotoxic against breast cancer cells in nature and can be delivered as an anticancer agent. Besides the probe L with HSO4- exhibit strong fluorescence emission with low cytotoxicity, and it can be recommended for live-cell imaging.

Theoretical study on cyclophane amide molecular receptors and its complexation behavior with TCNQ.

Complexation behavior of cyclophane amide molecular receptors towards 7,7,8,8-tetracyanoquinodimethane (TCNQ) studied. TD-B3LYP/6-31 + G(d,p) based density functional theory was employed to investigate the photophysical characteristics of the complexes obtained. Syn isomers of cyclophane amide molecular hosts show preferred conformation over other conformations. Molecular Orbital analysis indicates the electronic structure change, which reflects in the absorption spectra of the cyclophane amide-1@TCNQ, and cyclophane amide-2@TCNQ charge-transfer (CT) complexes. Binding energy studies with B3LYP-D3/6-31 + G (d,p) theory demonstrated that the more effective binding of the pyridine-2,6-dicarboxamide macrocycles than for their isophthalamide analogs. Both the CT complexes show intermolecular bifurcated hydrogen bonding (N-H(host)···N(guest)···H-N(host)) interactions (2.06 to 2.08 Å), and π(host)···π(guest) interactions (3.2 to 3.4 Å). Calculated BSSE corrected complexation energy (ΔE) be associated with the formation of the inclusion complexes in the range - 28 to -37 kJ mol-1, indicating spontaneity of host-guest complex formation in both the cases. From the calculated vibrational spectra of these complexes, the formation of inclusion complexes via N - H(host)···N(guest) and π(host)···π(guest) intermolecular interactions established by the frequency shift in the N - H vibrations. Mulliken population analysis performed to recognize the CT process and the variation in charges between the free and complex TCNQ molecules suggests the intermolecular charge transfer. This study indicates that these cyclophane amides can be a decent CT complexation host for the guests like TCNQ.

Nitrogen-doped carbon quantum dots embedded Co3O4 with multiwall carbon nanotubes: An efficient probe for the simultaneous determination of anticancer and antibiotic drugs.

The simultaneous determination of anticancer and antibiotic drugs in biological samples with fast and sensitive methods is an essential task for the effective monitoring of drug therapy. A novel electrochemical sensor for the simultaneous determination of anticancer drug Flutamide (FLU) and antibiotic drug Nitrofurantoin (NF) was developed based on the glassy carbon electrode (GCE) modified with N-CQD@Co3O4/MWCNTs hybrid nanocomposite. The electro-kinetics of the developed sensor was studied using cyclic voltammetry (CV). The electrochemical performance of FLU and NF on the N-CQD@Co3O4/MWCNTs/GCE surface was examined using CV and differential pulse voltammetry (DPV) techniques. At an optimized condition, the developed sensor exhibits excellent performance in simultaneous determination of FLU and NF with a linear range of 0.05-590 µM and 0.05-1220 µM and detection limit of 0.0169 µM and 0.044 µM respectively. Furthermore, the developed sensor exhibits satisfactory results in the real sample analysis.

Electrochemical synthesis of nitrogen-doped carbon quantum dots decorated copper oxide for the sensitive and selective detection of non-steroidal anti-inflammatory drug in berries.

We report a sensitive non-steroidal anti-inflammatory drug aspirin (ASA) sensor studies using the nitrogen-doped carbon quantum dots (N-CQD) decorated copper oxide (Cu2O). A simplistic approach of electrochemical deposition method has been used to prepare the N-CQD incorporated with copper oxide (N-CQD/Cu2O) and the resulting composite has characterized by analytical techniques. Modified glassy carbon electrode of N-CQD/Cu2O/GCE is developed and is used for the sensor studies of aspirin. The modified N-CQD/Cu2O/GCE has exhibited a higher current (Ipa) response to the oxidation process when compared to N-CQD/GCE, Cu2O/GCE and bare GCE. Furthermore, it has shown a good linear range of 1-907 µM with a limit of detection (LOD) ∼0.002 µM and sensitivity ∼21.87 µA µM-1 cm-2. The developed sensor has displayed outstanding repeatability, stability and accumulation time along with better electro-catalytic response in berries for real-life application.