Merocyanine dye based fluorescent organic compound has been synthesized for the detection of glutamine. The probe showed remarkable fluorescent intensity with glutamine through ICT (Intermolecular Charge Transfer Mechanism). Hence, it is tested for the detection of glutamine using colorimetric and fluorimetric techniques in physiological and neutral pH (7.2). Under optimized experimental conditions, the probe detects glutamine selectively among other interfering biomolecules. The probe has showed a LOD (lower limit of detection) of 9.6?×?10–8 mol/L at the linear range 0–180 µM towards glutamine. The practical application of the probe is successfully tested in human biofluids.
Graphical abstractFluorescent carbon dots (CDs) have acquired growing interest from different areas over decades. Their fascinating property of tunable fluorescence by changing the excitation wavelength has attracted researchers worldwide. Understanding the mechanisms behind fluorescence is of great importance, as they help with the synthesis and applications, significantly when narrowed down to applications with color-tunable mechanisms. But, due to a lack of practical and theoretical information, the fluorescence mechanisms of CDs remain unknown, preventing the production of CDs with desired optical qualities. This review focuses on the PL mechanisms of carbon dots. The quantum confinement effect determined the carbon core, the surface and edge states determined by various surface defects and the connected functional/chemical groups on the surface/edges, the molecular state solely determined the fluorophores in the interior or surface of the CDs, and the Crosslink Enhanced Emission Effect are the currently confirmed PL mechanisms.
Graphic AbstractA series of amino acid-based Schiff bases have been synthesized using a facile condensation between benzil (a diketone) and amino acid in the presence of a base. The formation of Schiff base compounds has been ensured by elemental analysis, FT-IR, 1H-NMR, 13C-NMR and UV–Vis. spectra. Density Functional Theory (DFT) calculations have been explored in order to get intuition into the molecular structure and chemical reactivity of the compounds. The DFT, optimized structure of the compounds, has been used to attain the molecular docking studies with DNA structure to find the favorable mode of interaction. In silico ADME/Tox profile of the compounds has been predicted using pkCSM web tools, exhibiting suitable values of absorption, distribution, and metabolism. These obtained parameters are connected to bioavailability. In addition, toxicity, skin sensitization and cardiotoxicity (hERG) analysis have been performed for evaluating the drug-like character of the prepared Schiff bases. The findings obtained from this study may find applications in the field focusing on the production of efficient and harmless pharmacological drugs.
Graphical abstractA novel nitrogen doped and surface functionalized fluorescent CDs (T1) was synthesized by one-step and green hydrothermal method, which exhibits a satisfactory fluorescence quantum yield and a series of admirable features such as good aqueous solubility, narrow particle size distribution, resistance to photobleaching as well as excitation-dependent behavior. Benefitting from above merits, T1 can be employed to serve as an outstanding sensing platform for sensitive and accurate detection of ClO– by remarkable fluorescence “on–off” process with rapid and anti-interference. More notably, the good biocompatibility and photostability can ensure enormous bioimaging potential and successful application of T1 in monitoring of exogenous ClO– in MG-63 cells. Meanwhile, T1 can also be regarded as a filter paper sensor providing a convenient and efficient analyzing technology for monitoring of free residual chlorine in practical environmental samples. All these results demonstrate that there exists promising possibility for practical applications of T1 in bioimaging systems and environmental monitoring.
Graphical abstractNonionic surfactant vesicles (Niosomes) were prepared using polyoxyethylene alkyl ether (Brij 58).The impact of variation of the Brij: cholesterol molar ratio on the niosomal structure was studied. Fluorescence studies performed with the membrane probe 1,6-Diphenyl-1,3,5-triene (DPH) gave important insight on the bilayer integrity of the niosomes in response to environmental perturbations. The aim of the work being assessment of the efficacy of the niosomes as “drug release vehicles”, release studies were performed with a xanthene dye Carboxyfluorescein (CF). Further, the vesicles were used as nanoreactors for the synthesis of gold nanoparticles (GNPs) as it is often useful to house nanoparticles in biological /biomimicking environments. Stable, spherical GNPs of diameter 6–10 nm were formed in these vesicles. As the vesicular bilayer mimics the cell membrane, the present work is relevant to the use of the GNPs for diagnostic and therapeutic purpose. It has also been established that fluorescence resonance energy transfer (FRET) effectively occurs between DPH and CF in the niosomes. The FRET studies provide important insight on the location of dyes within the vesicles thus indicating the prospective applications of this fluorescence technique for tracking the location of probes in biomimicking systems which maybe extrapolated to in vivo biological systems in future.
Graphical AbstractRapid and onsite detection of nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is very crucial for the safety and security of human life as well as for the environment. In this present work, we demonstrate the feasibility for employing Folic Acid (FA) as a fluorescent as well as a colorimetric probe for the detection of TNT. This probe was synthesized by a simple one-step process. The developed probe shows an emission maximum at 490 nm upon excitation at 420 nm. On adding TNT, the fluorescence of the FA probe is quenched. Also, it shows a good selectivity towards TNT over other similar organic compounds such as 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP) and picric acid (PA). The limit of detection (LoD) of TNT was found to be 1.9398 µM. Colorimetric detection was conducted and paper strip assay was developed for the practical applications.
Graphical AbstractThe present study aimed to develop a carbon dots-based fluorescence (FL) sensor that can detect more than one pollutant simultaneously in the same aqueous solution. The carbon dots-based FL sensor has been prepared by employing a facile hydrothermal method using citric acid and ethylenediamine as precursors. The as-synthesized CDs displayed excellent hydrophilicity, good photostability and blue fluorescence under UV light. They have been used as an efficient “turn-off” FL sensor for dual sensing of Fe3+ and Hg2+ ions in an aqueous medium with high sensitivity and selectivity through a static quenching mechanism. The lowest limit of detection (LOD) for Fe3+ and Hg2+ ions was found to be 0.406 µM and 0.934 µM, respectively over the concentration range of 0-50 µM. Therefore, the present work provides an effective strategy to monitor the concentration of Fe3+ and Hg2+ ions simultaneously in an aqueous medium using environment-friendly CDs.
Graphical AbstractA simple fluorescent chemosensor 5-(4-methylphenyl)-3-(5-methylfuran-2-yl)-1-phenyl-4, 5-dihydro-1H-pyrazole (PY) has been synthesized for the detection of Cd2+ ion.The fluorescent probe PY shows high selectivity for Cd2+in the presence of othermetal ions (Co2+, Cu2+, Hg2+, Mn2+, Zn2+, Fe3+, Pb2+, Ni2+, and Al3+). The fluorescence intensity of the PY has been strongly quenched with increasing concentration of Cd2+ (0–0.9 μM)via photoinduced electron transfer mechanism. The binding constant of Cd2+ to PY for the 1:1 complex isfound to be 5.3?×?105 M?1with a detection limit of 0.09 μM. The chemosensor was successfully applied for determination of Cd2+ in different water samples (tap, river, and bottled water) showing good recovery values in the range of 94.8–101.7% with RSD less than 3%. Density functional theory (DFT) calculations were also performed to investigate electronic and spectral characteristics which are quite agreeable with the experimental value. The results show that the synthesized fluorescent chemosensor shows good selectivity towards Cd2+ and can be readily applied for the detection of Cd2+ in real samples including water samples.
Graphical AbstractThe bioreductive enzymes typically upregulated in hypoxic tumor cells can be targeted for developing diagnostic and drug delivery applications. In this study, a new fluorescent probe 4?(6?nitro?1,3?dioxo?1H?benzo[de]isoquinolin?2(3H)?yl)benzaldehyde (NIB) based on a nitronaphthalimide skeleton that could respond to nitroreductase (NTR) overexpressed in hypoxic tumors is designed and its application in imaging tumor hypoxia is demonstrated. The docking studies revealed favourable interactions of NIB with the binding pocket of NTR-Escherichia coli. NIB, which is synthesized through a simple and single step imidation of 4?nitro?1,8?naphthalic anhydride displayed excellent reducible capacity under hypoxic conditions as evidenced from cyclic voltammetry investigations. The fluorescence measurements confirmed the formation of identical products (NIB-red) during chemical as well as NTR?aided enzymatic reduction in the presence of NADH. The potential fluorescence imaging of hypoxia based on NTR-mediated reduction of NIB is confirmed using in-vitro cell culture experiments using human breast cancer (MCF?7) cells, which displayed a significant change in the fluorescence colour and intensity at low NIB concentration within a short incubation period in hypoxic conditions.
Graphical abstractWe have demonstrated a unique approach to alter the aqueous pool size of an AOT/n-heptane/water reverse micellar system. A positively charged dye Rhodamine B (RhB) and negatively charged Rose Bengal (RB) were incorporated in the reverse micellar pool to investigate the effect of electrostatic interactions and stacking effects among the dye molecules on the AOT/n-heptane/water interface. Dynamic light scattering revealed increase in reverse micellar pool size in presence of positively charged dye aggregates at the oil–water interface. However, less expansion was observed in presence of negatively charged dye aggregates (RB). This confirms the role of electrostatic interaction in modulating the hydrodynamic radius. A head-to-tail type of stacking of RhB molecules at the interface favors this expansion. The differences in stacking of the two dyes inside the reverse micelles and their torsional mobility indicated the role of the reverse micellar interface and H-bonding ability of the microenvironment on dye aggregation. Conductivity measurements demonstrated a significant drop in percolation temperature of the reverse micellar system in presence of dye aggregates. This confirms the effect of dye aggregation and electrostatic interaction on such expansion. This strategy can be exploited for solubilizing greater amounts and a wider variety of drug molecules in microemulsions.
Graphical abstractA triplet diphenylcarbene, bis[3-bromo-5-(trifluoromethyl)[1,1'-biphenyl]-4-yl]methylidene (B3B), with exceptional stability was discovered by chemists from Japan's Mie University. To investigate its different quantum chemical features, a theoretical analysis was predicated on Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) based technique. According to the findings, the singlet–triplet energy gap (ES-T), as well as HOMO–LUMO energy bandgap (EH-L), was found to be diminished when nucleophilicity (N) rose. We looked at the geometrical dimensions, molecular orbitals (MOs), electronic spectra, electrostatic potential, molecular surfaces, reactivity characteristics, and thermodynamics features of the title carbene (B3B). Its electronic spectra in different solvents were calculated using TD-DFT and Polarizable Continuum Model (PCM) framework. The estimated absorption maxima of B3B were seen between 327 and 340 nm, relying on the solvents, and were attributed to the S0?→?S1 transition. Estimated fluorescence spectral peaks were found around 389 and 407 nm with the S1 and S0 transitions being identified. Its fluorescence/absorption intensities revealed a blue shift change when the solvent polarity was increased. The least exciting state has been discovered to be the π?→?π* charge-transfer (CT) phase. According to the Natural Bonding Orbital (NBO) exploration, ICT offers a significant role in chemical system destabilization. Furthermore, several hybrid features were used to determine the NLO (nonlinear optical) features (polarizability, first-order hyperpolarizability, and dipole moment). The calculated values suggest that B3B is a promising candidate for further research into nonlinear optical properties.
Graphical AbstractMultidentate 1,3,5-benzenetricarboxylic acid (organic linker), Zn (II) based Zn-BTC has been synthesized via electrochemical method. Quantitative and Qualitative analyses of synthesized metal–organic framework (MOF) have been done using Fourier Transform Infrared (FTIR) Spectroscopy, Energy Dispersive X- Ray Spectroscopy (EDS), and Photoluminescence (PL). Powder X-Ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM) have been used for crystallographic and morphological & topographical analyses, respectively. Crystallographic studies confirm the formation of face-centered cubic (fcc) crystal structure with good crystallinity. Photo-catalytic activity of synthesized MOF has been tested using Methylene Blue (MB) dye as a test contaminant in aqueous media under sunlight irradiation. Recorded results reveal that the synthesized MOF efficiently degrade MB dye upto 96% under sunlight exposure after 270 min. Photoluminescence studies indicate that Zn-BTC could be used as an efficient material for sensing of nitroaromatic compounds (NACs): 4-Nitroaniline (4-NA), 2-Nitroaniline (2-NA), 3- Nitroaniline (3-NA), 2,4-Dinitrotoulene (2,4-DNT), 4-Nitrotoulene (4-NT) in N,N’-Dimethylformamide (DMF) by fluorescence quenching and shows maximum quenching efficiency towards 3-NA (72.80%). Notably, the variation in luminescence intensity of 3-NA@Zn-BTC shows a linear relationship over its different concentrations from 0–1000 ppb range with KSV?=?2.7?×?104 M?1 and R2?=?0.9924 with limit of detection 0.889 ppb (6.43 µM) (LOD). The possible ways of luminescence quenching are successfully explained by the combination of Photoinduced Electron Transfer (PET) and Resonance Energy Transfer (RET) mechanisms. Additionally, the Density Functional Theory (DFT) calculations have been employed to support the experimental results. Zn-BTC fully demonstrates the power of a multi component MOF, which provides a feasible pathway for the design of novel material towards fast responding luminescence sensing and photocatalytic degradation of pollutants.
Graphical AbstractMicrocystin-LR (MC-LR) is widely distributed in natural lakes and could strongly inhibit protein phosphatase activity; it is also a potent liver tumor promoter. Over the last two decades, tremendous efforts have been devoted to enhance the detection of MC-LR in water samples. However, the traditional method is complex and costly, and achieving the fast, sensitive, and accurate determination of MC-LR in the cells and natural lakes by using fluorescence signal changes is fairly difficult. Our work explores novel fluorescent probes that are capable of concurrently analyzing and detecting MC-LR in the cells and water. In this study, we introduce, for the first time, 5-AF and 6-AF as small-molecule fluorescent probes suitable for MC-LR detection in the cells and water samples based on fluorescence signal changes. We titrated 5-AF and 6-AF with MC-LR in pure water, scanned the fluorescence of the sample, and then obtained the equation the fluorescence intensity versus MC-LR concentration curve. MC-LR in lake water samples was crudely purified, and then 5-AF was added to measure its fluorescence peak. The fluorescence intensity of 5-AF is significantly enhanced with increasing MC-LR concentration. This enhancement trend is stable and could be mathematically modeled. We also comprehensively analyzed the mechanism and recognition principle of the probe response to MC-LR in natural lake water. Moreover, we believe that 5-AF may be capable of detecting exogenous MC-LR in cells. The results of this study reveal that these unique fluorescent probes may be applied to construct near-infrared fluorescent probes that could detect MC-LR levels in vivo.
Graphical AbstractOptimization and re-optimization of bioactive molecules using in silico methods have found application in the design of more active ones. Herein, we applied a pharmacophore modeling approach to screen potent dual inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) aimed at Alzheimer's disease (AD) treatment. The investigation entails molecular dynamics simulation, docking, pharmacophore modeling, drug-like screening, and binding energy analysis. We prepared a pharmacophore model from approved inhibitors of AChE and BuChE to predict the crucial moieties required for optimum molecular interaction with these proteins. The obtained pharmacophore model, used for database screening via some critical criteria, showed 229 hit molecules. Further analyses showed 42 likely dual inhibitors of AChE/BuChE with drug-like and pharmacokinetics properties the same as the approved cholinesterase inhibitors. Finally, we identified 14 dual molecules with improved potentials over the existing inhibitors and simulated ZINC92385797 bound to human AChE and BuChE structure after noticing that these 14 molecules are similar. The selected compound maintained relative stability at the active sites of both proteins over 120 ns simulation. Our integrated protocols showed the pertinent recipes of anti-AD drug design through the in silico pipeline.
Graphical abstractA novel multicomponent one-pot expeditious synthesis of highly functionalized and pharmaceutically fascinated pyranopyrazoles has been developed. This reaction occurs via tandem Knoevenagel condensation reaction of methyl aryl derivatives, 3-methyl pyrazolone and malononitrile in the presence of urea hydrogen peroxide under the physical grinding method. The present methodology offers several benefits such as available green and cheap starting materials, solvent-free, mild reaction conditions, high atom economy, eco-friendly standards, excellent yields and easy isolation of the products without column chromatographic separation.
Graphic abstractFukuyama reaction for the synthesis of multifunctional aldehydes, secondary amines and ketones has gained considerable importance in synthetic organic chemistry because of mild reaction conditions. The use of thioesters in both Fukuyama aldehydes and ketones synthesis is highly attractive for organic chemists as they are easily accessible from corresponding carboxylic acids. Fukuyama–Mitsunobu reaction utilizes 2-nitrobenzenesulfonyl (Ns) for the protection/activation/deprotection of primary amines to afford secondary amines in good yields and high enantioselectivities. This review presents recent synthetic developments and applications of Fukuyama reaction for the synthesis of aldehydes, secondary amines and ketones.
Graphic abstractThe azomethine ylides are generally used in 1,3-dipolar cycloadditions with various dipolarophiles. In this work, a new and diverse route has been developed for the azomethine ylides, for synthesis of novel pyrrole derivatives. The azomethine ylide, produced via C–H activation of unreactive C(sp3)–H bond of 2-methylquinoline, by molecular iodine, in the presence of pyridine. Herein, we represent novel pyrrole derivatives, synthesized from the reaction of pyridinium ylide with olefins, which formed via a reaction of isatin, dialkyl acetylenedicarboxylate derivatives and pyridine as a base in moderate to excellent yields. Various features of this cyclization, discussed.
Graphic abstractMultifunctional Cu (II)-based Metal Organic Framework (MOF) [Cu3(BTC)2] has been synthesized by a facile electrochemical method. Crystallographic and morphological characterizations of synthesized MOF have been done using Powder X-ray Diffractometer and Scanning Electron Microscope (SEM), respectively, whereas Fourier Transform Infrared Spectroscopy (FT-IR), Energy Dispersive X-ray Spectroscopy (EDS), UV–Vis Absorption Spectroscopy and Energy Resolved Luminescence Spectroscopic studies have been used for the detailed qualitative, quantitative as well as optical analyses. Sharp PXRD peaks indicate the formation of highly crystalline MOF with face centered cubic (fcc) structure. Flakes (average length?=?0.71 µm and width?=?0.10 µm) and rods (average aspect ratio?=?((0.1:8.3) µm) like morphologies have been observed in SEM micrographs. The presence of C, O and Cu has been confirmed by EDS analysis. Photocatalytic activity potential of the synthesized MOF has been tested using methylene blue dye (MB) as a test contaminant in aqueous media under sunlight irradiation. Selective and sensitive fluorescent sensing of different Nitroaromatic compounds (NACs) like 4-Nitroaniline (4-NA), 2-Nitroaniline (2-NA), 3-Nitroaniline (3-NA), 4-Nitrotoulene (4-NT), 2,4-Dinitrotoulene (2,4-DNT), 1,3-Dinitrobenzene (1,3-DNB), 2,6- Dinitrotoulene (2,6-DNT) has been done by exploring the photoluminescent behaviour of chemically stable Cu3(BTC)2. Synthesized MOF is extremely sensitive towards 4-NA, which is having PL quenching efficiency of 82.61% with highest quenching rate till reported. Indeed, a large quenching coefficient KSV?=?34.02?×?10–7 M?1 and correlation coefficient R2?=?0.9962 in KSV plot have been elucidated with limit of detection (LOD)?=?0.7544 ppb. The possible ways of luminescence quenching are successfully explained by the combination of Photoinduced Electron Transfer (PET) and Resonance Energy Transfer (RET) mechanisms. Additionally, the Density Functional Theory (DFT) calculations have been employed to support the experimental results. Cu3(BTC)2 fully demonstrates the power of a multi component MOF, which provides a feasible pathway for the design of novel material towards fast responding luminescence sensing and photocatalytic degradation of pollutants.
Graphical AbstractIn this work, we introduce a highly selective and sensitive fluorescent sensor based on pyrene derivative for Fe(III) ion sensing in DMSO/water media. 2-(pyrene-2-yl)-1-(pyrene-2-ylmethyl)-1H-benzo[d]imidazole (PEBD) receptor was synthesized via simple condensation reaction and confirmed by spectroscopic techniques. The receptor exhibits fluorescence quenching in the presence of Fe(III) ions at 440 nm. ESI–MS and Job’s method were used to confirm the 1:1 molar binding ratio of the receptor PEBD to Fe(III) ions. Using the Benesi-Hildebrand equation the binding constant value was determined as 8.485?×?103 M?1. Furthermore, the limit of detection (LOD, 3σ/K) value was found to be 1.81 µM in DMSO/water (95/5, v/v) media. According to the Environmental Protection Agency (EPA) of the United States, it is lower than the acceptable value of Fe3+ in drinking water (0.3 mg/L). The presence of 14 other metal ions such Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Pb2+, K+, Ni2+, Mg2+, Cd2+, Ca2+, Mn2+, Al3+, and Zn2+ did not interfere with the detection of Fe(III) ions. The fluorescence life-time of the receptor PEBD with and without Fe3+ ion was found to be 1.097?×?10?9 s and 0.9202?×?10?9 s respectively. Similarly, the quantum yield of the receptor PEBD with Fe3+ and without Fe3+ ion was calculated, and found as 0.05 and 0.25 respectively. Computational studies of the receptor PEBD were carried out with density functional theory (DFT) using B3LYP/ 6-311G (d, p), LANL2DZ level of theory.
Graphical AbstractThe c-Met tyrosine kinase plays an important role in human cancers. Preclinical studies demonstrated that c-Met is over-expressed, mutated and amplified in a variety of human tumor types and design of more potent c-Met inhibitors is a priority. In this study, 14 molecular dynamics simulations of potent type II c-Met inhibitors were run to resolve the critical interactions responsible for high affinity of ligands towards c-Met considering the essential flexibility of protein–ligand interactions. Residues Phe1223 and Tyr1159, involved in pi-pi interactions were recognized as the most effective residues in the ligand binding in terms of binding free energies. Hydrogen bond interaction with Met1160 was also found necessary for effective type II ligand binding to c-Met.
Graphic abstract