Benesi-Hildebrand Plot Research Articles

Lab-on-Paper Strip Chemical Sensor: Reversible Visible Sensor for Detection of Acids Using Naphthalenediimide Derivative

Naphthalenediimide derivatives have shown applications in the area of chemical sensors for anions due to their special optical and electrical properties. In the current work, NDI derivative having phenyl amine end group (PPD-NDI) has been synthesized and tested for sensitivity towards trifluoroacetic acid (TFA), hydrochloric acid (HCl), nitric acid (HNO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and sulfuric acid (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) for 1-65 mM concentrations. PPD-NDI displays reversible optical and visible sensitivity for detection of acids, specially, for HCl and TFA. PPD-NDI shows charge transfer band in the range of 500-600 nm in absorption spectra along with color change in presence of acid. To understand the mechanism of sensitivity, an exclusion method has been applied by analyzing other reference NDI molecules with different end groups and linkers. PPD-NDI shows selective sensitivity for TFA present in low concentration (1 mM) and HCl at all other concentrations. Binding constants for the association between PPD-NDI and acids are obtained from the Benesi Hildebrand plot and highest value is observed in case of TFA. The sensitivity of NDI derivatives can be very helpful in detection of acids in various industrial effluents from cloth, paper, refineries and in smelting industries. We have demonstrated the reversible lab-on paper strip testing experiment for detection of HCl acid by naked eye in low and high concentrations without need of any excitation light source.

A Schiff base luminescent chemosensor for selective detection of Zn2+ in aqueous medium

Luminescent chemosensors based on Schiff bases have drawn tremendous research interest owing to their easy synthesis, enriched photophysical properties, and potential applications in biology and materials science. A dinitrophenyl-based Schiff base molecular probe (L) was synthesized and characterized to estimate its selective detection of Zn2+. The probe L exhibits weak emission in the DMSO-H2O solvent mixture due to excited-state intramolecular proton transfer (ESIPT). Interestingly, fluorescence is enhanced with the addition of Zn2+ to the DMSO-H2O solution of L, whereas the emission remains unchanged with the addition of other ions. This specifies that probe L acts as a selective chemosensor for Zn2+. The binding stoichiometry for the L: Zn2+ complex is 1:1, which was calculated using the Benesi-Hildebrand plot from fluorescence data. Furthermore, the binding modes are also supported by density functional theory (DFT) calculation. The binding constant and detection limits are 6.35 × 107 M−1 and 1.1 × 10−8 M, respectively. The L-Zn2+ complex formation is reversible upon the addition of a strong chelating EDTA ligand. In addition, L is also used to detect Zn2+ in living Hela cells and selective sensing of Zn2+ in the solid phase.

Studies on the characterisation of thiophene substituted 1,3,4-oxadiazole derivative for the highly selective and sensitive detection of picric acid

A novel thiophene substituted 1,3,4-oxadiazole based chemosensor namely 2-(4-(5-(5-hexylthiophen-2-yl) thiophen-2-yl)phenyl) -5-(5-(5-(5-hexylthiophen-2-yl) thiophen-2-yl)thiophen-2-yl)-1,3,4-oxadiazole [TKO] has been characterised for the efficient detection of picric acid (PA) based on fluorescence quenching mechanism. In this regard, the electronic absorption spectra, fluorescence spectra, and fluorescence lifetime of TKO are recorded in the presence of different nitroaromatic compounds (NACs) in ethanol at room temperature. The absorption studies exhibited a blue shift in the absorption maxima with the increase in the concentration of PA. In the fluorescence titration studies, TKO shows a remarkable fluorescence quenching with picric acid as compared to other nitroaromatic compounds. Using the Benesi-Hildebrand plot, the binding constant value of PA with TKO is determined and is of the order of 6.467 × 104 M−1. Job's plot analysis confirms the 1:1 binding stoichiometry ratio between TKO and PA and is supported by the 1H NMR studies. The detection limit is determined and is of the order of 10.08 µM. The competitive studies revealed that TKO is highly selective for recognizing PA without the interference of other NACs. The theoretical studies were also carried out to understand the binding mechanisms of PA with TKO. The fluorescence quenching of TKO by PA may be attributed to photo induced electron transfer (PET). Overall, the experimental findings suggest that, the novel probe TKO may be used as a highly selective and sensitive chemosensor for the detection of explosives like picric acid.

DNA Binding and Cleavage Study of Novel Ruthenium (II)-Polypyridine-5-(3-pyridyl)-4H-1,2,4-Triazole-3-Thiol Complex on Escherichia Coli Genomic DNA

Background: Transition metal complexes especially Ruthenium-Polypyridyl complexes interact with multidentate ligands considered as a new therapeutic agent to make the possible DNA probes and conformers due to several interests owing to their potential applications. The aim of the present work is to concentrate on the binding and cleavage activity of [Ru(bpy)2(pytrzSH)2]2+ (complex 1) and [Ru(phen)2(pytrzSH)2]2+ (complex 2) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, pytrzSH = 5-(3-pyridyl)-4H-1,2,4-triazole-3-thiol) on Escherichia coli genomic DNA (gDNA). Materials and Methods: DNA binding and cleavage activity is carried out using ultraviolet-Visible spectral technique and Agarose gel electrophoresis method at three different concentrations against the standard genomic DNA isolated from E. coli bacteria. Results: The changes in the absorbance and wavelength upon incremental addition of the complexes on gDNA clearly depict the binding nature of complexes. The binding constant values for ligand centered and metal to ligand charge transfer transitions obtained from the Benesi Hildebrand plots are found to be 1.560 × 104 and 9.586 × 104 M−1 for complex 1 and 3.594 × 104 and 9.801 × 105 M−1 for complex 2. The results revealed that complex 2 shows better binding property than complex 1 on E. coli gDNA. The extent of DNA cleavage activity of the synthesized complexes on E. coli gDNA is determined from the band intensities, complex 2 shows full cleavage in all the three concentrations, whereas complex 1 exhibits full cleavage at 100 μg/mL. The cleaving ability depends on the nature of the ligands present in the complexes. Conclusion: The synthesized [Ru(bpy)2(pytrzSH)2]2+ (complex 1) and [Ru(phen)2(pytrzSH)2]2+ (complex 2) bind with the E. coli gDNA through electrostatic and intercalative modes. The [Ru(phen)2(pytrzSH)2]2+ complex 2 shows better cleavage activity than [Ru(bpy)2(pytrzSH)2]2+ complex 1.

Host-guest inclusion complexes of sulfabenzamide with β- and methyl-β-cyclodextrins: Characterization, antioxidant activity and DFT calculation

The inclusion complexation behavior, characterization and binding ability of sulfabenzamide (SBZ) with β-cyclodextrin (β-CD) and methyl-β-cyclodextrin (Mβ-CD) have been investigated both in solution and solid state by different experimental techniques. Sulfabenzamide drug having poor water solubility and slow dissolution. In order to improve its water solubility and thus dissolution, cyclodextrin complexation technique was followed. The spectral shifts revealed that part of aniline ring of SBZ is entrapped in the CD cavity. The association constants were determined by Benesi-Hildebrand plots and spectroscopic studies. The phase solubility studies were carried using two different types of cyclodextrins viz., β, methyl-β cyclodextrins. The phase solubility profiles with all the two cyclodextrins were classified as AL-type, indicating the formation of 1:1 stoichiometric inclusion complexes. Inclusion complexes exhibited higher rates of dissolution than the corresponding physical mixtures and pure drug. Characterization of inclusion complexes was done by solubility studies, in vitro dissolution studies, FTIR, 1HNMR, XRD and SEM studies. We investigated the interaction of the host–guest Mβ-CD/SBZ complex by means of molecular dynamics simulation using a density functional based tight-binding code (DFT).

Valorisation of bio-derived fluorescent carbon dots for metal sensing, DNA binding and bioimaging

Carbon dots are quasi-spherical and zero dimensional nanomaterials with unique optical and electronic properties. In this work, a facile and sustainable strategy was employed to synthesise nitrogen doped carbon dots from Terminalia chebula via hydrothermal treatment with a quantum yield of 19.9%. The structural and optical properties of nitrogen doped carbon dots (N-CDs) were studied by UV–Visible absorption and fluorescence spectroscopy. The surface functional groups, average particle size and elemental analysis were assessed with the help of Fourier Transform Infra Red spectroscopy, High Resolution Transmission Electron Microscopy and Energy Dispersive X-ray analysis respectively. The N-CDs exhibited excitation dependent emission upon irradiation with UV light, pH stability over neutral range and excellent photostability. The average particle size of the synthesised N-CDs was found to be 3.56 nm. The fluorescence intensity of the N-CDs quenched linearly with increase in concentration of Fe3+ ions. The limit of detection (LOD) of N-CDs with Fe3+ ions was calculated to be 4.5 nM using Stern-Volmer plot. The fluorescence was restored by addition of EDTA to Fe3+ coordinated N-CD system. Further, the synthesised N-CDs interacted with ct-DNA through intercalative mode and the binding constant calculated using the Benesi Hildebrand plot was 1.78 × 108 mg/mL. The cytotoxicity of N-CDs was evaluated using MTT assay. The excellent biocompatible and less toxic nature of N-CDs was extrapolated to serve as fluorescent probes for imaging E.coli and SKMEL cells. From the results of this work, it is evident that the synthesised N-CDs can be used to develop efficient fluorescent metal sensors. The fluorescent property of N-CDs enables it to find extension as a potential curative drug, an efficient patterning agent and an effective biomarker to image biological cells causing no damage to normal cells.

A new benzeneacetic acid derivative-based sensor for assessing thorium (IV) in aqueous solution based on aggregation caused quenching (ACQ) and aggregation induced emission (AIE)

Herein a new benzeneacetic acid derivative-based luminescence sensor (2-[(2,6-dichlorophenyl)amino] benzeneacetic acid, monopotassium salt) (BA) for assessing Thorium (IV) [Th4+] in aqueous solution is introduced. In the presence of various metal ions, the BA sensor exhibits good selectivity for Th4+ ions that ranged from 0.01 µM to 0.2 µM, with a detection limit of 0.0104 µM in EtOH:H2O (v/v = 3:7) solution. The stoichiometry and the binding ability of BA ligand with Th4+ ions were studied by Job's, Hill's and modified Benesi–Hildebrand plots. The binding mode of BA ligand with Th4+ ions is 2:1. Interaction properties and the fluorescent mechanism between the BA ligand and Th4+ ions were investigated by 1HNMR, MS, FTIR and density functional theory (DFT). Furthermore, this study showed that combining the photophysical effects of aggregation caused quenching (ACQ) and aggregation induced emission (AIE) might give the benefits of reduced noise and increased signal when developing a simple luminescent sensor in aqueous environment.

Tannic acid as a chemosensor for colorimetric detection of Fe(II) and Au(III) ions in environmental water samples

AbstractA simple and efficient method to detect and quantify Fe(II) and Au(III) cations in environmental water samples was developed. The detection principle is based on the 1:1 mol‐ratio complex formation between the probe molecule (tannic acid, TA) and Fe(II)/or Au(III), which yields visual color change and strong light absorbance at 518 nm and 534 nm, respectively. The association constant Ka for Fe(II) and Au(III) cations 4.01 × 104 and 4.13 × 104 M−1, respectively, was determined from Benesi–Hildebrand plot, indicating strong interactions between TA and target ions. This TA probe performed well in 50 mM phosphate buffer (PB, pH 9.0) solution and demonstrated an outstanding selectivity over 16 potential interfering metal ions and a good selectivity over Fe(III). The linear range in this study for Fe(II) and Au(III) cations was 0.25–100 μM and 1.0–100 μM, respectively. The detection limit of the TA probe for Fe(II) and Au(III) cations was found to be 0.080 and 0.50 μM, respectively. The spike recovery for both metal ions in three environmental aqueous samples (spring water and pond water) was ranged 90.2%–117.2%. This study demonstrated that the TA probe is a simple and convenient detection method for analyzing water samples obtained from fresh water sources.

Spectroscopic and DFT studies of the charge transfer complexation of iodine with aniline and its derivatives in carbon tetrachloride medium

The charge-transfer (CT) complex formation of iodine with aniline and derivatives of aniline in CCl4 at numerous temperatures (293.15–308.15 K) has been investigated by UV–Visible spectroscopy and density functional theory (DFT) methods. The formation constant (KCT) of the CT complexation was determined by using the Benesi-Hildebrand plot. The KCT values of CT complexes amid iodine and aniline/aniline derivatives were found to be changed with temperature variation and the change of the structure of donor molecules. Thermodynamic parameters such as ΔG0, ΔH0, and ΔS0 of CT complexes were calculated from the standard thermodynamic equations. The ΔG0 values are negative, which indicates the spontaneous nature of CT complexation. The ΔH0 and ΔS0 values for the iodine-aniline/ derivatives of aniline indicated that the CT complexation is happened due to hydrophobic and exothermic interactions. The additional CT band has appeared in the UV spectra from experimental and DFT studies. Besides, the interaction between the I2 and aniline/ derivatives of aniline was detected by the elongation of bond length of I2 acceptors. Also, other parameters associated with the CT complexes have been evaluated and described in detail.

A highly selective fluorescence and absorption sensor for rapid recognition and detection of Cu2+ ions in aqueous solution and film.

A fluorescence and absorption chemosensor (SAAT) based on 5-(hydroxymethyl)-salicylaldehyde (SA) and o-aminothiophenol (AT) was designed and synthesized. SAAT in DMSO-HEPES (20.0 mM, v/v, 1:99, pH = 7.0) solution shows a highly selective and sensitive absorption and an 'on-off' fluorescence response to Cu2+ ions in aqueous solutions over all other competitive metal ions including Na+ , Ag+ , Ba2+ , Ca2+ , Cd2+ , Mg2+ , Zn2+ , Cr3+ , Al3+ , Hg2+ , K+ , Mn2+ , Ni2+ , Sr2+ , Tb3+ and Co2+ . SAAT exhibits ratiometric absorption sensing ability for Cu2+ ions. Importantly, SAAT also can sense Cu2+ ions using fluorescence quenching, the fluorescence intensity of SAAT showed a good linear relationship with Cu2+ concentration, and the detection limit of Cu2+ was 0.34 μM. The results of Job's plot, Benesi-Hildebrand plot, mass spectra, and density functional theory calculations confirmed that the selective absorption and fluorescence response were attributed to the formation of a 1:1 complex between SAAT and Cu2+ . SAAT in test film could identify Cu2+ in water samples using the intuitive fluorescence colour change under a UV lamp. SAAT has great application value as a selective and sensitive chemosensor to discriminate and detect Cu2+ ions.

Antipyrine-based Schiff base as fluorogenic chemosensor for recognition of Zn2+, Cu2+ and H2PO4− in aqueous media by comparator, half subtractor and integrated logic circuits

A new dual colorimetric and fluorescent receptor L, antipyrine-based chemosensor, was synthesized and characterized by UV–Vis absorption and fluorescence spectroscopic studies. The binding behavior of the chemosensor L toward Cu2+ and Zn2+ ions in an aqueous medium was investigated by UV–Vis absorption, 1HNMR and fluorescence spectroscopic studies. Benesi-Hildebrand plot is used to calculate the binding affinity. Based on the UV–Vis titration of receptor L, the 1:1 stoichiometry between L and M2+ (M2+= Cu2+ or Zn2+) is obtained. The detection limits (obtained by the 3σ method) of compound L are 4.23 × 10−6 mol L−1 for Cu2+ and 2.41 × 10−6 mol L−1 for Zn2+. The receptor L-Zn2+ can act as a highly selective sensor for H2PO4− ions over other anionic species (F−, Cl−, Br−, I−, NO3−, CN−, HSO4−, ClO4− and OAC−) in an aqueous medium. According to the changes in absorption and emission wavelengths and visual color changes with two sequential ionic inputs (Cu2+ and Zn2+), it is clear that the receptor behavior can mimic the arithmetic functions of XOR, INH1, INH2, XNOR, OR, NOR and IMP logic gates and complex logic circuits such as comparator and half subtractor with a single molecule. The ‘novel’ dinuclear Zn(II) complex could be used as a colorimetric fluorescent H2PO4− (Pi) chemosensor. By utilizing Cu2+, Zn2+ and H2PO4− ions as the inputs, a new combinational logic circuit with three different logic gates (OR, NOT, and AND) has been constructed.

Microwave-assisted one-pot multicomponent synthesis of indole derived fluorometric probe for detection of Co2+ ions

Cobalt (Co2+) is an essential constituent in the human body while excessive exposure leads to severe systemic toxic reactions which highlight the importance of developing effective methods to detect Co2+ ions. A simple and highly efficient fluorescence enhanced turn OFF-ON chemosensor was synthesized to detect the paramagnetic Co2+. The ligand, N-((1H-indol-3-yl)(phenyl)methyl)aniline (L), was synthesized in 92% yield by means of hydrated ferric chloride catalyzed one -pot multicomponent microwave irradiation in the presence of Indole, benzaldehyde, and aniline as reactants. The major green principles of waste prevention, high atom economy (94.3%), green solvent, higher energy efficiency, and catalysis were the highlights of the ligand synthesis. The ligand exhibited remarkable fluorescence enhancement with Co2+ and a turn ON ratio of over 160-fold in MeOH/H2O (at pH 3.5) solution at an excitation wavelength of 369 nm in the Ultra-Violet range. The detection limit of L- Co2+ was 2.2 μM. The excitation and the emission spectra indicated stoke’s shift of 93 nm which supports the fluorescence enhancement observed in L- Co2+ with respect to the free ligand. The Job’s plot indicated fluorometric sensing of Co2+ ascribed to the complex formation with a stoichiometric ratio of 2:1 (L- Co2+). Furthermore, the high linearity (r2 =0.992) observed in the Benesi Hildebrand plot in a wide concentration range of 0.5−80 μM confirmed the above stoichiometric ratio. The association constant (Ka) for the L-Co2+ was determined to be 8.382 ×1 04 M−1 ± 5.8 ×103M−1.The prepared Co2+ fluorometric probe indicated long-term stability in −18 ℃ up to 45 days. Furthermore, the presence of Fe2+ and Fe3+ in the medium with Co2+ exhibited an interference effect in the fluorescence intensities. Upon further concentration studies, it was evident that the interference of Fe2+ and Fe3+ starts around 10.00 μM and rises exponentially.&#x0D; Keywords: MCR, Green synthesis, Fluorescent Chemo-sensor, Turn OFF-ON, Cobalt (II), indole derivatives

Fluorene-Based Fluorometric and Colorimetric Conjugated Polymers for Sensitive Detection of 2,4,6-Trinitrophenol Explosive in Aqueous Medium.

Nitroaromatic explosives are a class of compounds that are responsible for various health hazards and terrorist outrages. Among these, sensitive detection of 2,4,6-trinitrophenol (TNP) explosive has always been highly desirable considering public health and national security. In this regard, three fluorene-based conjugated polymers (CP 1, CP 2, and CP 3) were synthesized through the Suzuki–Miyaura coupling reaction and were found to be highly sensitive for fluorescence detection of TNP with detection limits of 3.2, 5.7, and 6.1 pM, respectively. Excellent selectivity of CPs toward TNP was attributed to their unique π-π interactions based on fluorescence studies and density functional theory (DFT) calculations. The high sensitivity of CPs to TNP was attributed to the static quenching mechanism based on the photoinduced electron transfer process and was evaluated by fluorescence, UV–visible absorption, dynamic light scattering, Job’s plots, the Benesi–Hildebrand plots, and DFT calculations. CPs were also used for colorimetric and real-water sample analysis for the detection of TNP explosive. Meanwhile, sensor-coated test strips were fabricated for on-site detection of TNP, which makes them convenient solid-supported sensors.

Detection to trace aluminum ion of pharmaceutical wastewater using synthesis of Schiff-based chemosensor

Background: The aim of this research was to develop a fluorogenic sensor for Al3+ions, which have been identified as a possible food and drinking water pollutant by the WHO and considered to be harmful to human health. Methods: The sensing mechanism was based on excited-state intramolecular proton transfer, with the intramolecular rotation restriction occurring after binding with the analyte. The probe attaches Al3+selectively and emits strong emission in 4:1 H2 O/MeOH (v/v) solution while irradiated at 400 nm in the presence of a wide number of cations, acting as a "turn-on" fluorescence chemosensor. The range of detection for Al3+is 3.3 nM (3 method), which is more than 200 times more responsive than the WHO suggested limit of 7.4 mM (3σ method). Mass spectra, job plot, and Benesi-Hildebrand plot were used to determine the formation of the 1:1 metal-to-ligand complex. Results: Aluminum (Al) ion content in effluent obtained from the pharmaceutical sector is 0.381 mM, which is a trace amount. A separate in vitro experiment indicates that the probe can precisely perceive Al3+ions in a cell line. The sensor-based method is developed to detect 3.3 nM of Al3+ions, which is significantly less than the WHO max. Conclusion: The probe to detect Al3+ions in live cells. HL becomes a flexible sensor for recognizing intracellular Al3+in human liver cancer cell line Hep G2 and human lung fibroblast cell lines by fluorescence cell imaging procedures, and the probe’s non-toxicity has been proven by MTT tests up to 100M.

Synthesis, characterization, theoretical investigations and fluorescent sensing behavior of oligomeric azine-based Fe3+Chemosensors

Three azine oligomeric esters were synthesized, characterized by IR, UV, 1H, 13C{1H} and GPC technique, and applied to chemosensor application. The sensitivity response of the oligomers towards the metal ion was evaluated for a metal ion series. The results have shown selective and sensitive “turn off” fluorescence response towards Fe3+ ion in DMF/H2O (1:1, pH: 7.4, fluorophore: 5 μM) solution. The binding stoichiometry and binding constant of the fluorophores were calculated using the Stern–Volmer equation and Benesi–Hildebrand plots, respectively. The quenching of fluorophores on the addition of Fe3+ ion indicates the capability of fluorophore towards quantitative analysis of Fe3+. The dimer of oligomers was theoretically studied using DFT, B3LYP/6-311G level basic set to support and explain the quenching mechanism of LMCT, PET process and to explain the DC, AC electrical studies results. The electrical conductivity measurements of solid-state, I2 doped and undoped oligomers were carried out and the conductivity gradually increases with increase in iodine vapor contact time of oligomers. The electrical conductivity was related with band gap and charge density values of imine nitrogen obtained by Huckel calculations. The dielectric measurements at different temperatures and frequencies were made by two probe method. Among the oligomers, EBHAP has recorded a high dielectric constant at the low applied frequency of 50 Hz at 373 K due to loosely attached π bonds resulting good polarization.

Fluorene based fluorescent and colorimetric chemosensors for selective detection of cyanide ions in aqueous medium and application of logic gate

Rising detrimental effects of cyanide due to its frequent large-scale utilization demand rapid and sensitive detection of cyanide ions. Herein, two new fluorene based chemosensors 1 and 2 have been developed through the Suzuki–Miyaura coupling reaction for fluorescence enhancement based selective detection of cyanide with sensitivity levels down to 0.2 ppb and 0.4 ppb, respectively. The plausible sensing mechanism is based on Michael type adduct formation due to the reaction of cyanide with chemosensors and was confirmed by 1H NMR titration, Job’s plot, dynamic light scattering (DLS), and density functional theory (DFT) calculations. Chemosensors 1 and 2 showed excellent linear response towards CN¯ ions (0–100 nM) in the Benesi–Hildebrand plot with association constants (Ka) 1.61 × 106 and 7.1 × 105 M¯1, respectively that corresponds to their favorable chemical reaction. Excellent selectivity of chemosensors for cyanide in the presence of other interferences was investigated through fluorescence emission, UV–Visible, and DFT analysis. Surprisingly, an immediate reversible colorimetric change upon alternate shaking and steadiness of chemosensor − CN¯ solution was noticed indicating that chemosensors can act as promising recyclable sensors for colorimetric on-site detection of CN¯. Meanwhile, chemosensors 1 and 2 displayed highly selective colorimetric detection of CN¯ under daylight and UV radiations (365 nm). Further, cyanide responsive test kits were fabricated that provided a low-cost and portable method for on-site detection of CN¯ ions in an aqueous medium. Finally, chemosensors were successfully applied for designing logic gates, and detection of cyanide in industrial waste and food samples.

An efficient naphthalimide based receptor for selective detection of Hg2+and Pb2+ions

Naphthalimide based receptor 1 with N-substituted benzothiazole and pyrrolidine subunit is designed, synthesized, and characterized using FT-IR, 1 H and 13 C NMR spectroscopy and mass spectrometry techniques. The receptor 1 exhibits prominent optical response for Hg 2+ and Pb 2+ ions allowing the detection of these ions in acetonitrile (ACN). The formation of the receptor 1 :cation complexes have been investigated using UV-Vis and fluorescence emission titration. Further, the selectivity of the receptor 1 towards Hg 2+ and Pb 2+ ions on the presence of various interfering cations such as Mg 2+ , Ba 2+ , Ni 2+ , Co 2+ , Cu 2+ , Ag 2+ , Fe 2+ , Fe 3+ and Cr 3+ has been confirmed by UV-Vis and fluorescence spectroscopy. The binding constant between receptor 1 and Hg 2+ and Pb 2+ was estimated by Benesi-Hildebrand plot and equations. The binding constants have been found to be K a = 3.43286 ´ 10 −6 and K a = 2.84079 ´ 10 −6 M for Hg 2+ and Pb 2+ , respectively. The limit of detection (LOD) for Hg 2+ and Pb 2+ by receptor 1 are down to 7.44 ´ 10 −10 M and 1.26 ´ 10 −9 M, respectively. In addition, Job’s plot analysis reveals 1:2 binding stoichiometry between the receptor 1 and Pb 2+ and Hg 2+ cations.

Naphthalimide appended isoquinoline fluorescent probe for specific detection of Al3+ ions and its application in living cell imaging

Herein, a novel Schiff base fluorescent probe NIQ based on naphthalimide and iso-quinoline units has been readily prepared for the selective detection of Al3+ ions. The obviously visible color changes and prominent fluorescence enhancement were observed upon the addition of Al3+ to NIQ, which could be attributed to the complexation of NIQ with Al3+ and thus leading to the inhibition of photo-induced electron transfer (PET) and the chelation-enhanced fluorescence (CHEF) progress. The limit of detection (LOD) was 52 nM that was far below the standard recommended by the WHO. Binding ratio (1:1) of NIQ with Al3+ ions was supported by Job’s plot. The binding constant of NIQ for Al3+ were calculated to be 3.27 × 105 M−1 on the basis of benesi-Hildebrand plot. The plausible binding mechanism for NIQ towards Al3+ ions was evidenced by the density functional theory (DFT) and 1H NMR titration experiment. Furthermore, this “turn-on” probe NIQ has been successfully applied as a biomarker for imaging the Al3+ ions in living cells.

2-((E)-1-((E)-(2-methoxybenzylidene)hydrazono)ethyl)phenol based cost-effective sensor for the selective detection of Eu3+ ions

The detection of lanthanides has emerged as an attractive field of research due to potential applications in biomedical sciences. Here we design a simple and cost-effective ligand 2-((E)-1-((E)-(2-methoxybenzylidene)hydrazono)ethyl)phenol (MHEP) that acts as a rapid selective sensor for Eu3+ ions with a blue shift in UV–visible, ratiometric enhancement in fluorescence intensity and significant redox potential changes in cyclic voltammetric graph among various metal ions in the CH3OH:H2O (1:1, v/v) solvent system. The UV–visible titrations are used to determine the limit of detection 1.2 × 10−7 M, the limit of quantitation 41 × 10−7 M and linear range 22 × 10−6 M−1 to 124 × 10−6 M−1 are determined. The binding stoichiometry is determined by Job’s plot, mole ratio method and Benesi-Hildebrand plot that is found 1:1 (MHEP:Eu3+) with association constant 2.360 × 105 M−1. The IR spectroscopy reveals the role of imine functionalities for the Eu3+ ions detection.

Lysozyme-AuNPs Interactions: Determination of Binding Free Energy.

Investigation and optimization of lysozyme (Lys) adsorption onto gold nanoparticles, AuNPs, were carried out. The purpose of this study is to determine the magnitude of the AuNPs–lysozyme interaction in aqueous media by simple spectrophotometric means, and to obtain the free energy of binding of the system for the first time. In order to explore the possibilities of gold nanoparticles for sensing lysozyme in aqueous media, the stability of the samples and the influence of the gold and nanoparticle concentrations in the detection limit were studied. ζ potential measurements and the shift of the surface plasmon band showed a state of saturation with an average number of 55 Lys per gold nanoparticle. Lysozyme–AuNPs interactions induce aggregation of citrate-stabilized AuNPs at low concentrations by neutering the negative charges of citrate anions; from those aggregation data, the magnitude of the interactions has been measured by using Benesi–Hildebrand plots. However, at higher protein concentrations aggregation has been found to decrease. Although the nanocluster morphology remains unchanged in the presence of Lys, slight conformational changes of the protein occur. The influence of the size of the nanoclusters was also investigated for 5, 10, and 20 nm AuNPs, and 10 nm AuNPs was found the most appropriate.