Association Constant Values Research Articles

Click‐Generated Triazole‐Based Silanes: A Potent Chemosensor for Dihydrogen Phosphate

AbstractOver the years, ground and surface water has been reported to be contaminated with phosphates. These phosphates are known to cause various diseases and if present in excess can lead to eutrophication. The known silane chemistry has not been thoroughly investigated for the sensing of anions. In the current study four new triazole based silanes have been prepared by the renowned Click Chemistry for the selective and sensitive detection of dihydrogen phosphate. The synthesized compounds were well characterized by various spectroscopic techniques and their absorptive and emissive responses were investigated for the recognition of dihydrogen phosphate ions. The binding ratio between triazole based silane chemosensor and dihydrogen phosphate has been discovered from Job's plot and was also confirmed by non‐linear fitting method. The value of association constant was found to be 571.18 M−1. The limit of detection (LOD) and limit of quantitation (LOQ) were calculated by fluorescence spectroscopy. The results obtained clearly illustrated that triazole based silane could be used as a potent chemosensor for selective and sensitive recognition of dihydrogen phosphate. Further, the possible binding site of chemosensor for dihydrogen phosphate has been identified from 1H NMR studies and DFT calculations. At last real sample analysis was performed to check the practical applicability of chemosensor.

Modulation of aluminum sensing properties of a sulphone group containing chemosensor and its biological applications

A chemosensor with two binding pockets facilitates binding of one metal ion in either of the pockets providing a better chance for the interaction and hence recognition of the cation. We report here a chemosensor, namely 2,2′-(1E)-(5,5′-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H4L-naph), for selective sensing of Al3+ in DMF- HEPES buffer (1:4, v/v, pH 7.4). It shows almost 100-fold fluorescence enhancement at 532 nm (λex = 482 nm) in the presence of Al3+. Its quantum yield and excited state lifetime enhances significantly with the cations. H4L-naph forms a 1:2 complex with Al3+ with an association constant value of 2.18 × 104 M−2. Fluorescence enhancement may be attributed to CHEFF mechanism and restriction of >CN isomerization. Effect of the presence of naphthyl rings instead phenyl ring of a previously reported probe has resulted shifting of excitation/emission peak towards longer wavelength. The probe has been applied to image Al3+ in L6 cells with no significant cytotoxicity.

The theory of oxygen hemoglobin association

We develop a theory of oxygen hemoglobin association and derive the oxygen hemoglobin association equation and determine the values of the four association constants by curve fitting four commonly accepted data points that relate oxygen saturation and oxygen partial pressure (PO2) in the blood using mathematical reasoning and chemical kinetics. The four association constants come from the progression of oxygen binding to each of the four subunits on the hemoglobin molecule in a cooperative manner. The binding of oxygen alters the affinity of subsequent binding of additional oxygen molecules, which is reflected in changing magnitudes of the association constants. We also demonstrate rather surprisingly that the value of the third association constant is significantly smaller than all other association constants and offer some conjecture about this puzzling finding. With our equation, we can compute the distributions of all five oxyhemoglobin species at various PO2 levels that are published for the first time in the history of hemoglobin research. After examining the distributions, we find the triply bound oxyhemoglobin exists in very low concentration, consistent with the small third association constant. In addition, we present the oxygen levels where maximal concentrations of various oxyhemoglobin species occur, another unexpected finding that was never published before. Finally, we determine the inflection point of the hemoglobin association curve, a defining property to a specific sigmoid curve, representing the steepest portion of the curve.

‘Click’-synthesized PET based fluorescent sensor for Hg(II), Pb(II) and Cr(III) recognition: DFT and docking studies

In this study, a novel photoinduced electron transfer (PET) based 1,2,3-triazole appended chemosensor probe (PRT) for the recognition of toxic heavy metal ions has been developed via Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC), a quintessential example of ‘click chemistry’ for which the 2022 Nobel prize in chemistry was awarded to Prof. K.B. Sharpless, Prof. M. Meldal and Prof. C. Bertozzi. The synthesized probe was successfully characterized via IR spectroscopy, NMR (1H and 13C) spectroscopy, and mass spectrometry; and additionally demonstrated to selectively sense the highly toxic Hg(II), Pb(II), and the biologically essential Cr(III) ions via absorption and fluorescence spectroscopy. The Job plot of PRT suggested the stoichiometric ratio of 1:1 with the sensed metal ions, whereas the association constant values determined through Benesi-Hildebrand (B-H) equation indicated the strongest binding of PRT with Cr(III) followed by Pb(II) and Hg(II) respectively, even though the competitive metal ion titration revealed the selectivity of PRT for Pb(II) over the other metal ions. The density functional theory (DFT) approach as implemented in the Gaussian 09 package with B3LYP/6-311G++(d,p) and B3LYP/LANL2DZ was used to perform geometry optimization and quantum chemical computations. Above and beyond, PRT was also docked with Interleukin (IL)-6 protein, thereby providing glimpses of its anti-inflammatory potential.

Selective recognition of Pb(II) and Cr(III) by novel maleic hydrazide-based 1,2,3-triazole linked derivatives

The present report describes the application of versatile and stereospecific Copper(I) catalyzed alkyne-azide cycloaddition (CuAAC) reaction to synthesize two novel maleic hydrazide appended 1,2,3-triazole based chemosensors (5 and 6) as selective probes for Pb(II) and Cr(III) recognition. Maleic hydrazide is a plant growth regulator known to prevent cell division. The probes were characterized via IR, NMR (1H and 13C) spectroscopy and mass spectrometry; and subsequently explored for their ion sensing behavior in DMSO as solvent media via UV–Vis spectroscopy. The probe 5 displayed peak at 312 nm accompanied by a smaller peak at 258 nm; whereas the probe 6 exhibited peaks at 274 nm, 284 nm and 294 nm. Furthermore, the association constants for probe 5 were determined to be 0.61×105M−1 and 0.20×106M−1 for Pb(II) and Cr(III) respectively; and for probe 6 the association constant values for Pb(II) and Cr(III) were 0.46×106M−1 and 0.76×106M−1 respectively. Structural optimization of both the probes was carried out using DFT with hybrid density functional (B3LYP)/6–311G++(d,p)basis set of theory and LANL2DZ basis set was utilized to optimize the representative 5+metal complex . Subsequent docking analysis of 5 and 6 was carried out with leukotriene b4 via AutoDock Vina to get perceptions about their potential anti-inflammatory properties, wherein the binding energies of the probes 5 and 6 were observed to be -8.3 and -9.6 kcal/mol respectively.

The physicochemical properties of selected imidazolium chloride ionic liquids in tetraethylene glycol: Experimental and computational approach

In this work, the influence of the side chain length of five ionic liquids (ILs) containing N3-substituted 1-methylimidazolium chloride ionic liquids, [Cnmim][Cl] (n = 0, 1, 2, 4, 6) on the interactions with tetraethylene glycol (TEG) was studied. Measuring the density and electrical conductivity of the IL + TEG mixtures in the temperature range (278.15–313.15) K, the values of physicochemical properties, such as apparent molar volume, apparent molar volume at infinite dilution, Masson’s interaction coefficient, limiting apparent molar expansibilities, Heppler’s coefficient, ion association constants, thermodynamic parameters of ion-pair formation, as well as diffusion coefficient were calculated. The results obtained from these experiments were supported by molecular dynamics (MD) simulations. In comparation with systems containing ethylene–glycol (IL + EG), the calculated free volumes in TEG are about three times higher than in EG. Therefore, assuming that the packing effect is responsible for the lower apparent molar volume at infinite dilution, values in the TEG seem reasonable. The values of ion association constants in TEG are lower than in EG. The ion association process is spontaneous for all investigated ILs in TEG solutions and entropy-driven.

Synthesis of bis-1, 2, 3-triazole tweezer with BINOL backbone and amide subunits: An efficient sensor for iodide and magnesium ions

The synthesis of novel S-BINOL-based 1, 2, 3-triazoles were carried out by using efficient synthetic protocol with high yields from S-BINOL (1) as the backbone and amide subunits. Selective sensing of iodide and magnesium was observed due to nonbonding interaction of the ions with BINOL-based 1, 2, 3-triazoles tweezers (6). Significantly strong association constant, 1.897 × 105 M−1, was observed for interaction of host with iodide ions and 0.974 × 105 M−1 with magnesium ions. The recorded association constant value for iodide sensing and magnesium sensing is among the best reported so far and this is attributed to tweezer arms with helical BINOL backbone, 1,2,3-Triazoles with acidic proton and electron rich nitrogen atoms, a structural feature suitable for binding with cations and anions. The stronger binding is also attributed to involvement of amide units in bringing the two tweezer arms closer and involvement of the amide unit in binding with ions.

Ninhydrin and isatin appended 2-Hydrazinobenzothiazole based simple Schiff bases for colorimetric selective detection of Cr3+ and Pb2+ ions

A simple and easily synthesizable chromogenic small molecules probe L4(2-(2-(benzo[d]thiazol-2-yl)hydrazono)-1H-indene-1,3(2H)-dione) and L5 (2-(2-(benzo[d]thiazol-2-yl)hydrazono)indolin-3-one) have been synthesized and characterized by various spectroscopy techniques such as FT-IR, NMR, and HRMS. The colorimetric naked eye detection of probe L4 showed a color change towards Cr3+ from orange color to pale yellow, whereas in case of L5 Pb2+ yellow to orange color was witnessed. The jobs plot analyses indicate the 1:1 binding stoichiometric for Cr3+ and 1:2 binding stoichiometric for Pb2+ ions with probes L4 and L5 respectively. The binding association constant (ka) values for L4 and L5 were found to be 6.651 × 10-5 M for Cr3+ and 6.493 × 10-5 M for Pb2+ ions. The limit of detection was found to be for Cr3+ (1.69 × 10−7 M) and Pb2+ (1.208 × 10−7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Finally, the designed probes were applied for visible colorimetric test kits and real samples for rapid detection of Cr3+ and Pb2+ for all practical purposes, indicating their potential use in environmental samples.

Emulsion liquid membrane in the selective extraction of Dy

Due to comparable ionic radii, lanthanoids are known to have similar physical and chemical properties. Separation of lanthanoids from one another is therefore a challenging task. Such crucial separation chemistry could be performed with the help of solvent extraction technique. In order to overcome the associated problems based on solvent extractions, the emulsion liquid membrane based method has been applied to do the selective and efficient extraction of the lanthanoid Dy. This work describes the role of emulsion liquid membranes for the selective extraction of Dy(III) ion with the help of aniline yellow dye at pH 3 medium. The emulsion was prepared using different oils viz, mustard oil, coconut oil and palm oil as the organic phase. The complexation of the lanthanoids (La(III), Ce(III), Ce(IV), Pr(III), Gd(III), Sm(III) and Dy(III)) with aniline yellow (AY) and benzene azo naphthylamine (BAN) dye was studied using UV-Vis spectrophotometer at three different pH (pH 1, pH 3 and pH 5) conditions. The complexation was observed at pH 3 and 5 for only Pr(III) and Dy(III) with both the dyes having high association constant values (∼106 M-1). The emulsion liquid membrane (ELM) prepared with mustard oil, coconut oil and palm oil at pH 3 showed zeta potential value − 30.60 mV, − 27.00 mV and − 35.90 mV respectively. Selective extraction of the Dy-AY complex was obtained for the ELM prepared with mustard oil at pH 3 medium (90%). After extraction of the Dy-AY complex, the zeta potential decreased to − 41.80 mV for the ELM. The effect of stirring time, pH of the medium and the concentrations of the feed solutions have positive correlations towards the extraction process. After the extraction process, the oil reach phase was demulsified using a mixture of organic solvents and the extracted metal ion was back-extracted with the help of cation exchange resin. 88% of the extracted Dy could be back extracted upon demulsification.

Electrochemically deposited cobalt bis(dicarbollide) derivative and the detection of neuroblastoma markers on the electrode surface

A cobalt bis(dicarbollide) derivative deposited onto the surface of a graphite electrode through an electrochemically oxidized o-phenylenediamine unit (pCB-oPD) is proposed for the detection of catecholamine metabolites, namely homovanillic acid (HVA) and vanillylmandelic acid (VMA). These metabolites are diagnostic markers of neuroblastoma. The set of electrochemical techniques, electrochemical impedance spectroscopy (EIS), potentiometry, and differential pulse voltammetry (DPV), makes it possible to evaluate the options of the individual and simultaneous detection of metabolites. The values of association constants that were found between the pCB-oPD attached to the electrode surface and the metabolites showed a high affinity to HVA (2.5 × 105) compared to VMA (4.3 × 104). The binding of the metabolites to the pCB-oPD-modified electrode allows the differentiation of VMA and HVA in the mixture, which can be of practical interest.

Efficient and Original Technique for the Optimization and Intensification of Membrane Processes Relating to the Treatment and Recovery of Discharges Loaded with the Emerging Pollutant Paracetamol

Paracetamol (acetaminophen) is one of the most commonly used pain relievers and fever reducers due to the high stability, solubility, and hydrophilicity; it is mainly detected in pharmaceutical releases. Its presence in aquatic systems is a serious ecological concern. The pharmaceutical industries are using several technologies for separation, extraction, and control such as membrane processes because of their numerous advantages. In the present work, a polymer inclusion membrane containing Tween 20 (TW20) as an extractive agent was fabricated for the treatment and recovery of effluents loaded with emerging pollutants (paracetamol). After characterization of the morphology and porosity, the membrane was adopted to carry out the extraction and recovery processes of paracetamol, assisted by activated carbon. Kinetic and thermodynamic models were applied to determine the values of permeability (P), initial flux (J0), association constant (Kass), and diffusion apparent coefficient (D*) parameters. Subsequently, activation parameters energy (Ea), association and dissociation enthalpies (ΔH#ass and ΔH#dis, respectively), and entropy (ΔS#) were measured. For this original technique, the effects of activated carbon on the evolution of processes carried out across the membrane have been investigated and indicate a significant optimization and intensification of the membrane performance and total paracetamol extraction rate. In addition, this technique is clean and does not affect the structure or the stability of the membrane.

Imidazole-Based Monomer as Functional Unit for the Specific Detection of Paraxanthine in Aqueous Environments

In the context of personalized medicine, the paraxanthine-to-caffeine ratio is an accepted standard for the optimization of the dose-response effect of many pharmaceuticals in individual patients. There is a strong drive towards the development of cheaper and portable devices for the detection of biomarkers, including paraxanthine and caffeine, which requires materials with high binding efficiency and specificity. We designed a recognition unit specific for paraxanthine which can discriminate molecules with small structural differences and can be used to increase the sensitivity of sensors. A number of functional units were screened by nuclear magnetic resonance for their ability to form specific binding interactions with paraxanthine in water and negligible interactions with its structural analogue caffeine. Imidazole was identified as the unit showing the most promising results and its two polymerizable derivatives were evaluated by isothermal titration calorimetry to identify the best monomer. The data suggested that 4-vinylimidazole was the most promising unit forming specific and strong binding interaction with paraxanthine. The calorimetry experiments allowed also the determination of the thermodynamic parameters of all interactions and the association constant values. Optimization of polymerization protocols in water, achieving high monomer conversions and chemical yields, demonstrate the suitability of the selected functional monomer for polymer preparations, targeting the detection of paraxanthine in aqueous environments.

A chromone-based colorimetric fluorescence sensor for selective detection of Cu2+ions, and its application for in-situ imaging

A chromone-based chemosensor Probe 1 was synthesized, and characterized by FTIR, UV-vis, 1H NMR, 13C NMR, and mass spectrometric studies. Probe 1 exhibited high selectivity and sensitivity for the Cu2+ions over various metal ions (Al3+, Cr3+, Co2+, Cd2+, Mn2+, Fe3+, Ni2+, Zn2+) that was investigated by colorimetric, absorption, and fluorescence titrations. The binding mode of Probe 1 with the Cu2+ ion was derived from Job's plot measurements, and it showed 2:1 stoichiometry. Probe 1 revealed an association constant value of 8.48 × 108 M−2 as determined by employing non-linear least square fit data. The detection limit of Probe 1 for the Cu2+ion was found to be 0.273 × 10−6 mol L−1. Furthermore, Probe 1 was implemented to detect Cu2+ ions in different tissues of the liver fluke, infected and non-infected bovine liver. DFT studies were performed to support the sensing mechanism. The results of these experiments demonstrate that Probe 1 could be a promising chemosensor for the instant naked eye and fluorescence detection of Cu2+ ions in different biological samples.

Designing of thiosemicarbazone-triazole linked organotriethoxysilane as UV-Visible and fluorescence sensor for the selective detection of Hg2+ ions and their cytotoxic evaluation

In this manuscript, a new series of thiosemicarbazone-triazole linked organotriethoxysilanes (6a-6 g) have been synthesized using Cu (I) catalyzed click reaction and characterized by spectroscopic techniques including IR, 1H and 13C NMR, TGA and ESI-QTOF mass spectrometry. The compound 6a was screened for its photophysical properties using UV-Visible and fluorescence spectroscopy which showed the selective detection of Hg2+ ion without any significant interference from different metal cations. The chemosensor 6a binds in 1:1 stoichiometry with Hg2+ confirmed by Job's-plot and with high binding affinity as determined from association constant values 0.3747 × 106 M−1 and 0.3134 × 107 M−1 obtained from BH-plot and Stern-Volmer plot respectively. The LOD values for Hg2+ obtained from absorption and emission spectroscopy were 0.3122 × 10−6 M and 0.3928 × 10−7 M respectively. The binding interactions between 6a and Hg2+ion were also examined by conducting DFT calculations on Gaussian 03 software. Furthermore, all the synthesized organosilanes were tested for their use in the biological field by evaluating their pharmacokinetic profile and cytotoxicity using PreADMET, molinspiration software and PLHC-1 cell line. The chemosensor 6a with lowest cytotoxicity could be applied to monitor Hg2+ ions in living cells.

Volumetric properties, conductivity and computation analysis of selected imidazolium chloride ionic liquids in ethylene glycol

In this paper, the influence of the side chain length of five ionic liquids (ILs): 1-methylimidazolium chloride ([C0mim][Cl]), 1,3-dimethylimidazolium chloride (([C1mim][Cl]), 1-ethyl-3-methylimidazolium chloride (([C2mim][Cl]), 1-butyl-3-methylimidazolium chloride (([C4mim][Cl]) and 1-hexyl-3-methylimidazolium chloride (([C6mim][Cl]) on the interactions with ethylene glycol (EG) was studied. Based on the measurement of density and electrical conductivity of the ionic liquid + EG mixture in the temperature range (278.15–313.15) K, the values of apparent molar volume, standard partial molar volumes, apparent molar volume at infinite dilution, Masson’s interaction coefficient, thermal expansion coefficient, limiting apparent molar expansibilities, Heppler’s coefficient, ion association constants, thermodynamic parameters of ion-pair formation as well as diffusion coefficient was calculated. Experimental results were supported by molecular dynamic simulations. With the increase of the side chain length, from C0mim+ to C6mim+ cation, ion–dipole interactions on the solvation process decrease, and the influence of solvophobic solvation increases. Ionic liquids [C0mim][Cl] and [C1mim][Cl] show structure-breaker properties, [C4mim][Cl] and [C6mim][Cl] structure-making properties in EG solutions, while [C2mim][Cl] is borderline. The values of ion association constants in EG are higher than in water. The ion association process is spontaneous for all ionic liquids and entropy-driven.

Association of rhodamine cations with tetraphenylborate-anion in aqueous solution: structural properties of ions and stability of associates

The ability of rhodamine cations to form cation-anionic associates with tetraphenylborate-anion in an aqueous solution has been studied. The thermodynamic values of the equilibrium association constants Kasт were determined spectrophotometrically. The values of a number of properties of dye molecules (surface area, effective volume, hydrophobicity index log P, standard enthalpy of hydration ΔНohydr) were calculated using the QSAR model. The possibility of dependence of the value of Kasт on these factors has been reviewed. It was shown that changes in lg Kasт in the series of rhodamine associates are consistent with changes in the parameters log P and ΔНohydr.

Benzene-1,3-disulfonate capped gold nanoparticles: DFT computations in support of particles-capping agent and nano-sensing interactions

We have successfully synthesized water-dispersible gold (Au) nanoparticles (NPs) using benzene disulfonate anions (BDS2−) as a capping agent and applied them for the colorimetric recognition of Pb2+ and Cu2+ ions in aqueous solutions. The synthetic method for the BDS-AuNPs is very simple, one-pot and rapid. The particles are stable in a wide pH range of 5 to 10 over a month and are small in size (dTEM=8.9nm and dDLS=17nm). They selectively bind Pb2+ and Cu2+ ions over 14 other metal ions. This makes the particles an efficient optical dual-nanosensor. The limit of detection (LOD) values for Pb2+(0.469 μM) and Cu2+ (0.645 μM) ions are quite low. The association constant values for the Pb2+----BDS-AuNPs and Cu2+-----BDS-AuNPs complexes are found to be 1.612 × 106 M−1 (R2 adj. 0.9603) and 8.12 × 105 M−1 (R2 adj 0.9947), respectively, indicating strong interactions between the particles and the metal ions. A DFT computational study reveals that the binding affinity of BDS to the Aun cluster increases with the increase of Au atoms in the Aun cluster, supporting the experimental findings. The practical acceptance of the sensor was tested with real samples, where the sensor showed excellent recovery results. So, the BDS-AuNPs could be treated as an easy-to-develop dual-nanosensor for Pb2+ and Cu2+ metal ions.

Описание концентрационной зависимости теплоемкости спиртовых (изопропиловый спирт) и водно-спиртовых растворов соли-электролита иодида натрия

The paper considers using a high-sensitivity calorimeter with an isothermal jacket to measure heat capacities of electrolyte salt solutions at the temperature of 298.15 K, the salt being sodium iodide NaI dissolved in isopropyl alcohol and in mixtures of isopropyl alcohol with water containing 10, 20, and 40 % water by mass, at various molalities of the electrolyte salt. We processed the apparent heat capacity values computed for the electrolyte salt by means of the ion association model, which assumes that there exists an equilibrium between ions and ion pairs of the same type in a solution. The association constant values obtained make it possible to predict the heat capacity values not measured empirically, which lie within the margin of error of the experimental values. The investigation shows that the apparent heat capacity of the electrolyte salt as a function of concentration is adequately described by the ion association model in a wide range of solution molalities

Thiourea Organocatalysts as Emerging Chiral Pollutants: En Route to Porphyrin-Based (Chir)Optical Sensing

Environmental pollution with chiral organic compounds is an emerging problem requiring innovative sensing methods. Amino-functionalized thioureas, such as 2-(dimethylamino)cyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea (Takemoto’s catalyst), are widely used organocatalysts with virtually unknown environmental safety data. Ecotoxicity studies based on the Vibrio fischeri luminescence inhibition test reveal significant toxicity of Takemoto’s catalyst (EC50 = 7.9 mg/L) and its NH2-substituted analog (EC50 = 7.2–7.4 mg/L). The observed toxic effect was pronounced by the influence of the trifluoromethyl moiety. En route to the porphyrin-based chemosensing of Takemoto-type thioureas, their supramolecular binding to a series of zinc porphyrins was studied with UV-Vis and circular dichroism (CD) spectroscopy, computational analysis and single crystal X-ray diffraction. The association constant values generally increased with the increasing electron-withdrawing properties of the porphyrins and electron-donating ability of the thioureas, a result of the predominant Zn⋯N cation–dipole (Lewis acid–base) interaction. The binding event induced a CD signal in the Soret band region of the porphyrin hosts—a crucial property for chirality sensing of Takemoto-type thioureas.

Conductometric studies of 1, 3, 5 –triazinothiocarbamide at different concentration and temperature

Conductivity plays vital role in drug diffusion. Thermodynamic parameters affected by substituents of drug. Thermodynamic parameters of 1, 3, 5 –triazinothiocarbamide (1a) have been investigated by using conductometrically carried out at different molar concentrations. This work highlights investigation of G, K and µ values. The thermodynamic parameters viz. ΔH, ΔS and ∆G for ion pair formation determine from the value of ion association constant. This technique is suitable and accurate to study of pharmokinetics and pharmodynamics parameters.