Exploring Colorimetric Real-Time Sensing Behavior of a Newly Designed CT Complex toward Nitrobenzene and Co2+: Spectrophotometric, DFT/TD-DFT, and Mechanistic Insights.
ABSTRACT: An exceptionally unique, easy-to-prepare, and economic charge transfer complex (CTC), [(IMH)+(PA)-], was synthesized as a highly selective real-time colorimetric chemosensor material for nitro explosive nitrobenzene (NB) and Co2+ ion. Co2+ and NB are highly potential toxic and hazardous beyond the exposure limits and also classified as carcinogens (group 2B) by IARS and United States Environmental Protection Agency. Unusual sensing ability with appreciatively low detection limits of 0.114 and 0.589 ppb for NB and Co2+ ion, respectively, in the aqueous medium of dimethyl sulfoxide has been reported for the first time among this class of complexes reported so far. The mechanism of the tremendous sensing behavior of this material as chemosensor was ascertained by static quenching mechanism, Dexter electron transfer, and Forster resonance energy transfer dynamic quenching mechanism, which was supported by spectral overlapping and density functional theory (DFT) (B-3LYP/def2-SVP) calculations. Real-time colorimetric sensing behavior of chemosensor was demonstrated by the naked eye test and prestained paper Co2+ strip test. Job's plot and comparative Fourier transform infrared (FTIR) study between CTC and CTC-Co2+ complex revealed the coordination mode between CTC and Co2+ ion and 2:1 stoichiometry. This sensing material [(IMH)+(PA)-] was synthesized with donor imidazole (IM) and acceptor picric acid (PA), and its characterization was achieved by experimental (single-crystal X-ray diffraction, thermal gravimetric analysis-differential thermal analysis, FTIR, and UV-vis studies) and theoretical methods [DFT/TD-DFT calculations, comparing experimental-theoretical data and obtaining MEP map along with electronic energy gap of HOMO ? LUMO (?E = 3.545 eV) and Hirshfeld surfaces analysis]. The SC-XRD confirms the composition and bonding features, which show hydrogen bond via N+-H···O- between IM and PA. This N+-H···O- interaction plays a significant role in Co2+ binding, proving this method of synthesizing CTC as a chemosensor to be a novel approach.
Project description:One of the greatest challenges in using fluorescent chemosensors for highly selective and sensitive transition-metal ions is finding an efficient and simple method for its synthesis. In this study, a highly efficient fluorescence chemosensor for Zn<sup>II</sup> was developed from <i>N</i>-Boc-<i>L-</i>proline modified 1,8-naphthyridine. The fluorescence intensity of the chemosensor was increased significantly only in the presence of Zn<sup>II</sup> ion which provided a perceived color change for rapid visual sensing, while other metal ions showed fluorescence quenching or little changes. It was worth noting that the chemosensor <b>L</b> distinguished Zn<sup>II</sup> from Cd<sup>II</sup> commonly having similar properties. The solvent effect and possible bonding mode for fluorescence enhancement have been also discussed. Results of this study indicated that the Boc-group in <i>l</i>-proline significantly improved the sensitivity and selectivity for Zn<sup>II</sup> detection performance, as confirmed by comparison experiments and time dependent-density functional theory (TD-DFT) calculations.
Project description:The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F(-) Cl(-), Br(-), AcO(-), and H(2)PO(4) (-)) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F(-) is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only.
Project description:Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.
Project description:A bisthiocarbonohydrazone-based chemosensor molecule (R1) containing a tetrahydro-8-hydroxyquinolizine-9-carboxaldehyde moiety has been synthesized and characterized as a new ratiometric fluorescent probe for picric acid (PA). The ratiometric probe R1 is a highly selective and sensitive colorimetric chemosensor for PA. The association between the chemosensor and PA and the ratiometric performance enabled by the key role of excited state intramolecular proton transfer in the detection process are demonstrated. Selectivity experiments proved that R1 has excellent selectivity to PA over other nitroaromatic chemicals. Importantly, the ratiometric probe exhibited a noteworthy change in both colorimetric and emission color, and this key feature enables R1 to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe R1 has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of R1 and its PA complex have been measured by a field emission scanning electron microscope, and it clearly proves that their morphological features differ dramatically both in shape and size. Density function theory and time-dependent density function theory calculations were performed to establish the sensing mechanism and the electronic properties of probe R1. Furthermore, we have demonstrated the utility of probe R1 for the detection of PA in live Vero cells for ratiometric fluorescence imaging.
Project description:The <i>exo</i>⇔<i>endo</i> isomerization of 2,5-dimethoxybenzaldehyde was theoretically studied by density functional theory (DFT) to examine its favored conformers via sp<sup>2</sup>-sp<sup>2</sup> single rotation. Both isomers were docked against 1BNA DNA to elucidate their binding ability, and the DFT-computed structural parameters results were matched with the X-ray diffraction (XRD) crystallographic parameters. XRD analysis showed that the <i>exo</i>-isomer was structurally favored and was also considered as the kinetically preferred isomer, while several hydrogen-bonding interactions detected in the crystal lattice by XRD were in good agreement with the Hirshfeld surface analysis calculations. The molecular electrostatic potential, Mulliken and natural population analysis charges, frontier molecular orbitals (HOMO/LUMO), and global reactivity descriptors quantum parameters were also determined at the B3LYP/6-311G(d,p) level of theory. The computed electronic calculations, i.e., TD-SCF/DFT, B3LYP-IR, NMR-DB, and GIAO-NMR, were compared to the experimental UV-Vis., optical energy gap, FTIR, and <sup>1</sup>H-NMR, respectively. The thermal behavior of 2,5-dimethoxybenzaldehyde was also evaluated in an open atmosphere by a thermogravimetric-derivative thermogravimetric analysis, indicating its stability up to 95 °C.
Project description:A simple S-S (disulfide)-bridged dimeric Schiff base probe, L, has been designed, synthesized, and successfully characterized for the specific recognition of Al3+ and Fe2+ ions as fluorometric and colorimetric "turn-on" responses in a dimethylformamide (DMF)-H2O solvent mixture, respectively. The probe L and each metal ion bind through a 1:1 complex stoichiometry, and the plausible sensing mechanism is proposed based on the inhibition of the photoinduced electron transfer process (PET). The reversible chemosensor L showed high sensitivity toward Al3+ and Fe2+ ions, which was analyzed by fluorescence and UV-vis spectroscopy techniques up to nanomolar detection limits, 38.26 × 10-9 and 17.54 × 10-9 M, respectively. These experimental details were advocated by density functional theory (DFT) calculations. The practical utility of the chemosensor L was further demonstrated in electrochemical sensing, in vitro antimicrobial activity, molecular logic gate function, and quantification of the trace amount of Al3+ and Fe2+ ions in real water samples.
Project description:A novel colorimetric sensor based on the TiO<sub>2</sub>/poly(acrylamide-<i>co</i>-methylene bis acrylamide-<i>co</i>-2-(3-(4-nitro-phenyl)thioureido)ethyl methacrylate) nanocomposite was synthesized via a surface modification strategy; methacryloxypropyltrimethoxysilane was used to provide reactive vinyl groups on the surface of TiO<sub>2</sub> nanoparticles for the successful surface polymerization of Am (acrylamide), MBA (methylenbisacrylamide), and NPhM (2-(3-(4-nitrophenyl)thioureido)ethyl methacrylate) components. The successful preparation of nanocomposites was confirmed using Fourier transform infrared, <sup>1</sup>H NMR, <sup>13</sup>C NMR, scanning electron microscopy, transmission electron microscopy, thermogravimetry analysis, and X-ray diffraction methods, and the sensing ability of the probe toward fluoride ions was investigated using naked-eye detection and UV-vis measurement. The interaction of the prepared polymeric nanocomposite with fluoride ions elicited a significant visible change in color from pale yellow to orange and was further affirmed by a clean interconversion of the two absorption bands at 330 and 485 nm. The selective binding ability of the polymeric nanocomposite towards fluoride over other anions, such as I<sup>-</sup>, Cl<sup>-</sup>, Br<sup>-</sup>, AcO<sup>-</sup>, H<sub>2</sub>PO<sub>4</sub> <sup>-</sup>, and H<sub>2</sub>SO<sub>4</sub> <sup>-</sup> was further explored; the prepared chemosensor could detect fluoride ions in acetonitrile with a detection limit of 3 ?M.
Project description:We prepared the monomer <b>PCDA-HP</b> composed of 5-hydroxy-<i>N</i> <sup>1</sup>,<i>N</i> <sup>3</sup>-bis(pyridin-2-ylmethyl)isophthalamide (<b>HP</b>) as a cadmium ion tweezer and then polymerized them to form a polydiacetylene (PDA)-based sensor (<b>PDA-HP</b>), which displayed selective and sensitive colorimetric and fluorometric change upon addition of a cadmium ion (Cd<sup>2+</sup>) at both pH 7.4 and 6.8. The <b>PDA-HP</b> polymer was highly selective for Cd<sup>2+</sup> over other metal ions with colorimetric change. In addition, the <b>PDA-HP</b> chemosensor also showed a red fluorescence change in the presence of Cd<sup>2+</sup> at both pH 7.4 and 6.8. Naked-eye detection of Cd<sup>2+</sup> was accomplished in an aqueous solution through a PDA-based sensor system. Finally, the lowest energy structure of an HP chelator was obtained by the crystal structure and density functional theory (DFT) calculations.
Project description:We reported an experimental and theoretical spectroscopic studies of (2Z,5Z)-5-(4-nitrobenzylidene)-3-N (2-methoxyphenyl)-2-N' (2-methoxyphenylimino) thiazolidin-4-one (C<sub>24</sub>H<sub>19</sub>N<sub>3</sub>O<sub>5</sub>S) molecule, using FT-IR, NMR spectroscopy, and density functional theory (DFT) via time-dependent schema (TD-DFT) respectively. The molecular inter-contacts were explored using Hirshfeld surfaces (HS) analysis method. Vibrational frequencies, gauge-independent atomic orbital (GIAO)<sup>1</sup>H and<sup>13</sup>C NMR chemical shift values and frontier molecular orbitals (FMOs) have been calculated from the optimized structure of the molecule by DFT/B3LYP functional with 6-31G(d, p) basis set. Our theoretical results show a good agreement with the experimental data. The calculated UV-visible spectrum employing TD-DFT shows electronic transitions at 388 nm and 495 nm. To get insight on the charge interaction happening inside the molecule, HOMO and LUMO were scrutinized and their calculated energy gap was found to be 2.96 eV. The molecular docking was analyzed via interplay study ofacetyl cholinesterase, and Butyrylcholinesterase using molecular docking methodology.
Project description:A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxybenzothieno[3,2-b]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many-body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of ?5 cm<sup>-1</sup> (?0.6 meV). Due to the high accuracy of the simulations, they can be used to unambiguously identify different polymorphs and to characterize the nature of the lattice vibrations and their relationship to the structural properties. More generally, this work implies that DFT-MBD-vdW is a promising method to describe also other physical properties that depend on lattice dynamics like charge transport.