Hildebrand Plot Research Articles

Transglutaminase–mucin binding dynamics in gastrointestinal mucus: Interfacial behaviour, thermodynamics and gelation mechanism

Transglutaminase, an enzyme present in epithelial cells and as a residual component in processed foods, is hypothesised to interact with gastrointestinal mucus, impacting its structure and function. To test the physical validity of this phenomenon, this study investigates the binding kinetics and thermodynamics between porcine gastric mucin (PGM) and microbial transglumatinse (TGM) in a model gastrointestinal mucus, followed by the rheological analysis of the resulting systems. At pH 7, TGM exhibited pronounced binding with the PGM interface, characterised by a high surface density (55.34 ± 1.86 µg/m−2) and a low dissociation constant (KD ∼ 4.03 ± 0.10 μM) as determined by surface plasma resonance (SPR). Conversely, at pH 3, TGM showed weak adhesion onto PGM, resulting in a less stable binding, reflected by a lower surface density (10.94 ± 0.67 µg/m−2) and a higher dissociation constant (KD ∼ 6.24 ± 0.22 μM). Regardless of the nature of interaction, the Hill coefficients (nH ≥ 1) indicated that the binding sites were markedly denser at pH 7 (1383.38 ± 46.47 pmol/m−2), than at pH 3 (273.68 ± 16.84 pmol/m−2). Fluorimetry analysis suggested temperature-dependent dynamic binding between PGM and TGM. The resulting Benesi – Hildebrand plots illustrated a linear correlation between PGM and increasing TGM concentration, suggesting a single-step interaction mechanism. The calculated thermodynamic parameters indicated spontaneous interaction between PGM and TGM (ΔG < 0) via endothermic (entropic) interactions (ΔH > 0). Notably, hydrophobic forces played a significant role in the network stabilisation of PGM−TGM complex (ΔS > 0). Rheometry analysis elucidates that the interaction maxima within TGM−PGM systems substantially elevate both shear viscosity (η), and the melting point (Tm), shifting from 6.75 ± 0.28 to 70.94 ± 2.21 (×10−3) Pa s (at 1 s−1), and 36.80 ± 0.80 to 48.20 ± 0.11 °C, respectively. Furthermore, the coexistence of these two macromolecular species results in a 3- to 4-fold dramatic increase in the viscoelastic moduli of the binary complex. These findings build a strong physicochemical basis for the interaction between TGM and PGM, with profound effects on the rhological behaviour of the latter; it also highlights the need to examine the biochemical/enzymatic aspects of said interactions, and their potential effects on mucosa and human physiology.

Formation of Inclusion Complexes of 2-Hydroxypropyl β-Cyclodextrin with 2-Hydroxychalcone: Experimental and Theoretical Study

The formation of inclusion complexes of 2-hydroxypropyl-β-cyclodextrin (HP β-CD) with 2-hydroxychalcone (2HOCH) in solution and solid state was investigated using UV–Visible, fluorescence, Fourier transform-infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscope (SEM) techniques. The results obtained confirmed that 2HOCH formed the stable inclusion complex with HP β-CD. Moreover, the spectral data and Benesi–Hildebrand plots results indicated that the stoichiometry of the inclusion complex was 1:1. Theoretically, the structure of the inclusion complexes and the physical parameters such as complexation energy, highest occupied molecular orbital–lowest unoccupied molecular orbital, and energy gap were obtained using the DFT/B3LYP/6-311G method. It was found that the complexation energy for orientation B was lower than that for orientation A as evidenced by the theoretical calculations. Moreover, the carbonyl group of molecules was located outside of the cyclodextrin cavity while the hydroxyl group was located inside the cavity. The antioxidant capacity and antibacterial responses of the inclusion complexes and, for comparison, the parent compounds were also carried out.

Rhodamine 6G salicylaldehyde hydrazone-Zn complex: Synthesis, characterization, photochromism, understanding, and application

Zinc complex-based photochromic materials are gaining significant interest from their applications in various consumer products such as toys, cosmetic products, photochromic inks (for security marking), data storage, erasable optical memory media, etc. Here, the rhodamine 6G salicylaldehyde hydrazone-Zn complex was synthesized, characterized, and understood to develop a molecular device. The crystal structure analysis (CCDC number 2260405) confirms the synthesis of a new photo-ligand, rhodamine 6G salicylaldehyde hydrazone. The NMR, ESI-Mass, FT-IR, UV–Vis spectra (Job's and Benesi Hildebrand plots), chelation-enhanced fluorescence spectra (CHEF), and geometry optimization confirm the synthesis of the Zn-complex. We have studied photochromic behavior with absorption, emission, fatigue resistance, role of solvents, thermal bleaching kinetics, FMO computation, and vibrational analysis. The vibrational analysis has rationalized excited state intramolecular proton transfer (ESIPT) involved in photochromism. An attempt has been made to construct photochromic devices.

Enhancing solubilization of Nebivolol hydrochloride through tuning pluronic F-127 with ionic Surfactants: An experimental and theoretical investigation

In the present work, the interaction of the antihypertensive drug Nebivolol hydrochloride (NBL) with nonionic surfactant pluronic F-127 (F-127) is investigated in an aqueous medium. Two ionic surfactants, viz., cationic, cetyl trimethyl ammonium bromide (CTAB) and anionic, sodium tetradecyl sulphate (STS) were added to F-127 to improve the physicochemical properties of the single micellar medium. The characterization techniques employed were, FTIR, UV–visible spectroscopy, dynamic light scattering, zeta potential, antioxidant, conductivity, and FESEM studies. The critical micellar concentration (CMC) of CTAB and STS are estimated from the conductivity experiments which is lowered due to the addition of F-127 and NBL. The lowering of CMC is attributed to the solubilization of NBL in the binary micellar mediums. The extent of binding of NBL in F-127, F-127 + CTAB, and F-127 + STS were quantified by determining the binding constant values using the Benesi–Hildebrand (B-H) plot from UV absorbance data. They were, 838.2 M−1 for F-127 1100.7 M−1 for F-127 + CTAB and 1836.5 M−1 for F-127 + STS systems. There was an increase in the size of the micelle due to the encapsulation of the drug in both binary micellar systems. The zeta potential (ZP) values displayed enhanced stability of the drug in binary micellar systems. The radical scavenging activity (RSA %) of NBL was estimated to be 16.5 % in F-127, 24.7 % in F-127 + CTAB, and 44.9 % in F-127 + STS systems. The encapsulation efficiency (EE %) for the above three systems were 14.7 %, 16.4 % and 18.5 %, respectively. The surface parameters and the interactions were verified through molecular docking studies. The results suggest that the properties of F-127 can be improved by tuning with ionic surfactants to solubilize NBL. To our knowledge, this is the first report of NBL solubilization in mixed micellar systems. Similar studies with other drug systems can be applied to get improved results.

Synthesis of carbohydrate based polythiophene graft poly(N,N-dimethylaminoethyl methacrylate)-co-poly(GLU-HEM) copolymer for lectin sensing

Sensing of lectins are utmost necessary for its inflammatory, digestive disorder, gut pains and toxicity to human beings and for this purpose we have chosen polythiophene (PT) for its exciting optoelectronic properties. Because of precise carbohydrate specificities of lectin and to make PT water soluble for sensing of lectin, we have synthesized polythiophene-g-poly(N,N-dimethylaminoethyl methacrylate) -co-poly(glucose-hydroxyethyl methacrylate) (PT-g-pDMAEMA-co-pGLU-HEM), [PTDG]) from polythiophene macroinitiator (PTI) by copolymerizing DMAEMA and GLU-HEM monomers mixture with CuCl/HMTETA catalyst/ligand followed by hydrolysis using alcoholic NaOMe solution. The Mn of PTI was 38000, polydispersity 2.5, head-tail (H-T) regioregularity 70 mol % and Mn of unhydrolyzed PTDG is 98,900. The UV-Vis spectra of PTDG solution shows two absorption peaks at 430 and 462 nm but it shows a sharp emission peak at 544 nm which quenches with increasing pH. Concanavalin A (ConA) shows an absorbance peak at 278 nm and with addition of PTDG solution absorbance intensity increases showing hypochromic effect. Benesi–Hildebrand plot of reciprocal molar extinction coefficients with concentration suggests 1:1 complex formation between PTDG and ConA. With addition of ConA fluorescence quenching of PTDG solution occurred and using the fluorescence intensity ratio vs concentration plot the limit of detection (LOD) of Con A lectin is found to be 57 µg/L and storing the polymer solution for two months exhibits good durability. The morphology of PTDG changes from vesicle to compound micellar aggregate on addition of Con A lectin.

Rationally designed novel phenazine based chemosensor with real time Hg2+ sensing application

Phenazine derivatives have been explored in the selective detection of ions due to their binding ability with analytes. In this context, C-6 sulfenylated benzo[a]phenazine-5-ols (3a-d)have been synthesied and explored in sensing application. Initially, the molecules were designed by utilizing benzo[a]phenazin-5-ol as a core structure variably substituted with electronically diverse aryl thiols to investigate the substituent effect on their electrostatic properties. The ground state geometry of all the designed molecules was optimized with DFT using B3LYP/6-311G+(d,p) level of theory. Energy gap between FMOs was observed to be minimum and maximum for electron rich and deficient frameworks, respectively. The LUMO electron density in all the designed molecules except for compound bearing nitro group (3c) lies on the phenazine unit. This exceptional behavior enthusiased us to explore their photophysical properties. The compounds were synthesized and characterized using FT-IR, NMR and mass spectrometric techniques. In an attempt to examine their spectral behavior in different solvents, their absorption and emission spectra were recorded. The compounds exhibited absorptions maxima ranging between 475-514 nm, which shifted to longer wavelength while changing solvent polarity from CHCl3 to DMSO thus depicting positive solvatochromism. Similarly, the emission maxima was observed in a range of 570–685 nm with a maximum stokes shift of 6454 cm−1 for 3c. The compound 3c was further explored in the sensing application using DMSO:Water (60:40, v/v) mixture. A blue shift of 30 nm with nearly 7 fold increase in the emission intensity was observed upon addition of Hg2+ into 3c solution. Moreover, LOD of 21.9 nM and binding stoichiometry of 2:1 as determined by Benesi–Hildebrand and Job's plot establish the robust response of developed probe towards Hg2+ ion. The mechanism of complex formation was predicted by 1H NMR titration and DFT studies. Finally, the developed probe has been successfully utilized for sensing Hg2+ in real water samples.

Nitrogen doped fluorescent carbon dots from Delonix regia for Fe(III) and cysteine sensing, DNA binding and bioimaging

The current work primarily deals with the synthesis of nitrogen rich carbon dots from Delonix regia along with characterisation using several analytical techniques for fluorescent sensing of Fe(III) and cysteine, electrochemical sensing of hydrogen peroxide and DNA binding. The average particle size of the spherical N-CDs is calculated to be 2.23 nm with a quantum yield of 33.5%. The SAED pattern from HR-TEM confirms the slight graphitisation of the N-CDs along with the amorphous carbon core. The synthesised N-CDs served as an efficient turn off sensor for Fe(III) with a detection limit of 5.76 × 10-7 M and turn on sensor for L-Cysteine with a detection limit of 3.76 × 10-4 M. The nature and extent of binding of the N-CDs with ctDNA was evaluated and the binding constant from the Benesi Hildebrand plot is calculated to be 6.49 (mg/mL)-1. The limit of detection was found to be 71 µM for electrochemical sensing of hydrogen peroxide. The less cytotoxic and excellent biocompatible nature of the N-CDs have been taken advantage to image L6 cells and SKMEL cells.

Synthesis and Characterization of Newly Designed and Highly Solvatochromic Double Squaraine Dye for Sensitive and Selective Recognition towards Cu2.

Synthesis and characterization of a novel and zwitterionic double squaraine dye (DSQ) with a unique D-A-A-D structure is being reported. Contrary to the conventional mono and bis-squaraine dyes with D-A-D and D-A-D-A molecular frameworks reported so far, DSQ dye demonstrated strong solvatochromism allowing for the multiple ion sensing using a single probe by judicious selection of the suitable solvent system. The DSQ dye exhibited a large solvatochromic shift of about 200 nm with color changes from the visible to NIR region with metal ion sensitivity. Utilization of a binary solvent consisted of dimethylformamide and acetonitrile (1:99, v/v), highly selective detection of Cu2+ ions with the linearity range from 50 μM to 1 nM and a detection limit of 6.5 × 10−10 M has been successfully demonstrated. Results of the Benesi–Hildebrand and Jobs plot analysis revealed that DSQ and Cu2+ ions interact in the 2:1 molecular stoichiometry with appreciably good association constant of 2.32 × 104 M−1. Considering the allowed limit of Cu2+ ions intake by human body as recommended by WHO to be 30 μM, the proposed dye can be conveniently used for the simple and naked eye colorimetric monitoring of the drinking water quality.

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.

Benzothiazole azo derivatives as colorimetric probes for optical recognition of different metal ions and anions

In this study, we report on novel optical chemosensors containing benzothiazole moeity, namely, 2‐(6‐chloro‐benzothiazol‐2‐yl azo)‐4‐methyl‐phenol (CBAMP) and 1‐(6‐chloro‐benzothiazol‐2‐yl azo)‐naphthalen‐2‐ol (CBAN), which were synthesized and characterized by Fourier transform infrared spectroscopy (FT‐IR), 1H‐NMR, 13C‐NMR, and mass spectrometry. The solvatochromic behavior was explored in different solvents of various polarities to explore the active fluorescent tautomer, and the photophysical parameters have been measured. The naked eyes, as well as ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, were used to study the colorimetric and optical sensing properties of CBAMP and CBAN toward various metal ions and anions. These chemosensors have a strong detecting ability, with excellent sensitivity and selectivity for certain of the metal ions investigated, as well as CO32− and CN− over other anions. The Benesi–Hildebrand and Job's plots were used to determine the binding constants and stoichiometry of the formed metal ions–sensor complexes, respectively. Co2+ and Cu2+ ions have lower detection limits in CBAMP and CBAN than other metal ions (6.4 × 10−7 and 8.4 × 10−7 M, respectively). Furthermore, fluorescent imaging investigations for Co2+ and Cu2+ ions in living cells reveal CBAMP and CBAN's promise for biological chemosensing.

Chiral separation of catechin and epicatechin by reversed phase high-performance liquid chromatography with β-cyclodextrin stepwise and linear gradient elution modes

Catechin and epicatechin were enantioseparated by high-performance liquid chromatography (HPLC) with a phenyl column and aqueous mobile phases containing 0.05% (w/v) and 0.6% (w/v) of β-cyclodextrin for catechin and epicatechin, respectively. β-Cyclodextrin was found to be scarcely retained on a phenyl column. Consequently, it was suggested that catechin, which was eluted earlier than epicatechin, formed more stable inclusion complex with β-cyclodextrin than epicatechin and earlier eluted enantiomers, (−)-catechin and (+)-epicatechin, formed more stable diastereomer complexes with β-cyclodextrin than the respective enantiomers. This was confirmed by β-cyclodextrin-modified micellar electrokinetic chromatography and Benesi−Hildebrand plots by fluorescence spectrophotometry. Effect of sugars (D-sucrose, D-glucose, and D-fructose) on the epimerization of (+)-catechin and (+)-epicatechin by heating was investigated by HPLC with a β-cyclodextrin stepwise elution mode, in which two kinds of aqueous eluents containing different concentrations of β-cyclodextrin were used by turns. The epimerization of the two enantiomers was suppressed only when D-fructose was added. Separation of ten kinds of catechins including catechin and epicatechin enantiomers was investigated by a β-cyclodextrin linear gradient HPLC elution mode without using organic solvents, where two kinds of aqueous eluents containing different concentrations of β-cyclodextrin were used with changing their ratio gradually. These catechins in a green tea infusion could be separated successfully by this method.

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.

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

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.

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.

Designing of chalcone functionalized 1,2,3-triazole allied bis-organosilanes as potent antioxidants and optical sensor for recognition of Sn2+ and Hg2+ ions

This article presents the design, synthesis and characterization of a series of new acetylenic bis-chalcones (5a-5c) and chalcone functionalized 1,2,3-triazole allied bis-organosilanes (6a-6c) using aldol condensation followed by the Cu(I) catalyzed click strategy. The absorption studies of the designed compounds 5a and 6a were examined towards various metal ions that exhibit their high selectivity and sensitivity towards the recognition of Sn2+ and Hg2+ ions. The sensors show reversible nature upon the addition of disodium salt of ethylenediaminetetraacetic acid. Furthermore, the obtained detection limit with sensors 5a and 6a by plotting calibration curve was 0.34 µM and 0.64 µM for Sn2+ ion and 0.31 µM and 0.15 µM for Hg2+ ion respectively. The association constant value calculated for chemosensors 5a and 6a using the Benesi and Hildebrand plot method was 0.69 × 105 M−1 and 0.18 × 105 M−1 towards Sn2+ ion and 0.67 × 106 M−1 and 0.54 × 106 M−1 towards Hg2+ ion respectively. Moreover, the synthesized compounds 5a and 6a were investigated for their biological application by evaluating their cytotoxicity and antioxidant activity.

Label-Free Creatinine Optical Sensing Using Molecularly Imprinted Titanium Dioxide-Polycarboxylic Acid Hybrid Thin Films: A Preliminary Study for Urine Sample Analysis

Creatinine (CR) is a representative metabolic byproduct of muscles, and its sensitive and selective detection has become critical in the diagnosis of kidney diseases. In this study, poly(acrylic acid) (PAA)-assisted molecularly imprinted (MI) TiO2 nanothin films fabricated via liquid phase deposition (LPD) were employed for CR detection. The molecular recognition properties of the fabricated films were evaluated using fiber optic long period grating (LPG) and quartz crystal microbalance sensors. Imprinting effects were examined compared with nonimprinted (NI) pure TiO2 and PAA-assisted TiO2 films fabricated similarly without a template. In addition, the surface modification of the optical fiber section containing the LPG with a mesoporous base coating of silica nanoparticles, which was conducted before LPD-based TiO2 film deposition, contributed to the improvement of the sensitivity of the MI LPG sensor. The sensitivity and selectivity of LPGs coated with MI films were tested using CR solutions dissolved in different pH waters and artificial urine (near pH 7). The CR binding constants of the MI and NI films, which were calculated from the Benesi–Hildebrand plots of the wavelength shifts of the second LPG band recorded in water at pH 4.6, were estimated to be 67 and 7.8 M−1, respectively, showing an almost ninefold higher sensitivity in the MI film. The mechanism of the interaction between the template and the TiO2 matrix and the film composition was investigated via ultraviolet–visible and attenuated total reflectance Fourier-transform infrared spectroscopy along with X-ray photoelectron spectroscopy analysis. In addition, morphological studies using a scanning electron microscope and atomic force microscope were conducted. The proposed system has the potential for practical use to determine CR levels in urine samples. This LPG-based label-free CR biosensor is innovative and expected to be a new tool to identify complex biomolecules in terms of its easy fabrication and simplicity in methodology.