Calculation Of Stability Constants Research Articles

Determination of stability constants of Cu(II)2-bistren cascade complexes by cellmetry method

Cu(II)2-bistren cascade complexes were studied by cellmetry methodology where by choosing appropriate cell sizes of the box the logK values can be calculated by a plane wave DFT method. Different types of anions were chosen to study the effect of the size, shape, and bite length of the donor atoms on the stability constants. It was found that the ligand strain needs to be taken into account to calculate reasonable logK values. Correction factors were determined regarding the energy of the anions and the length of the bistren ligands which resulted in accurate calculated stability constants for all types of anions.

Investigating the Suitability of Various Silver(I) Complexes for Use in a Cyanide-Free Silver Electrolyte

The suitability of various nitrogen, sulfur, oxygen, and phosphorus compounds as complexing agents in a silver electrolyte was examined by using potentiometric titration under practical conditions. The setup consisted of three electrodes to measure the pH and the activity of the silver ions simultaneously. Different ratios of silver to complexing agent from 1:10 to 1:1 at a constant ionic strength of 0.2 mol/L were investigated. The type of the complexes and their corresponding critical stability constants were evaluated by fitting the measured data using a self-developed algorithm. The pH and Nernst potential curve were calculated for the assumed complexes based on the law of mass action to find the best approximation. The correct definition of the occurring species is challenging and can lead to significant changes in the calculation of stability constants. For this reason, the measured silver potential curves were primarily used for the rating of the complexing agents. An evaluation of the measurements shows that the donor atom of the complexing agent and its ligand field strongly affected the stability and type of the complexes. Only a few complexing agents were found to be suitable for use in the cyanide-free silver electrolyte.

PH-metric titration technique for the study of metal-complexes of substituted 2- Oxo-2H-Chromene-3-Carbohydrazide derivatives in solution: calculation of stability constants

Background: In coordination chemistry, the stability of complexes is expressed in terms of the formation constant of complexes. In coordination complexes, the temperature is very important. It plays an important role in complex formation reaction. Temperature affects metal-ligand stability constant (log K) and proton-ligand stability constant (pK). The metal ion Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures form complexes with 4-sulfamethoxazoleazo-3-methyl-2-pyrazolin-5-one are reported. The metal-ligand stability constant (logK) and proton-ligand stability constant (pK) of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with organic ligand n-[2-hydroxy-1-napthalydene]-2-methylanilline at 0.1 M ionic strength in 60% dioxane-water medium is studied. The study of thermodynamic parameters and stability constant of complexes of substituted thiazole Schiff bases with rare earth metal ions in mixed solvent is reported. Objective: The study of coordination compounds and a lot of work has been done on metal-ligand stability constant. The same transition metal ion form complexes with substituted pyrazole for this metal-ligand stability constant are determined. Method: Pointwise Calculation Method Half Integral Method. Result: The values of logK1 and logK2 are determined from the metal-ligand formation curve at formation numbers 0.5 and 1.5. In all cases, logK1 is greater than logK2. The ratio logK1/logK2 is positive and greater than one in all systems. This implies that there is little or no steric hindrance to the addition of the secondary ligand molecules. The difference between logK1 - logK2 is usually positive. If the difference between logK1 and logK2 is less than 2.5, simultaneous formation of 1:1 and 1:2 complexes occurs and if it is more than 2.5, then stepwise complex formation occurs. In the present case, in all systems, it is less than 2.5. This indicates the simultaneous formation of 1:1 and 1:2 complexes takes place. Conclusion: A pH-metric study of Substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), and Mn(II) occurs. The graphical representation of the curve shows that the acid + ligand curve is separated from the corresponding acid + ligand + metal curve in this system. The formation of a complex is indicated. Half integral method and pointwise calculation method give nearly similar results. The values of stability constants for all systems indicate that the complexes formed in these processes are stable.

Formulation of inclusion complex of Abiraterone acetate with 2-Hydroxypropyl-Beta-Cyclodextrin: physiochemical characterization, molecular docking and bioavailability evaluation

Abiraterone acetate is a steroid-based anti-androgen molecule approved in the year of 2011 for the therapy of patients suffering from metastatic prostate cancer. However, its physicochemical properties and therapeutic applications are limited by its lipophilic nature and low aqueous solubility. One of the most favourable and well-established methods of cyclodextrins (CDs) assisted inclusion complex was chosen to elevate the solubility-related pitfalls, chemical stability, and associated bioavailability issues of Abiraterone acetate (ABT). Several preparative methods like grinding, kneading, and freeze-drying were employed to fabricate the inclusion complex of ABT/2-hydroxypropyl-β-cyclodextrin (ABT-HP-β-CD). The freeze-drying assisted inclusion complex showed better physicochemical properties, which were investigated using DSC, TGA, PXRD, ATR-FTIR, FESEM, phase solubility, and molecular docking studies. All the above-said characterization studies performed exhibited the emergence of ABT-HP-β-CD. The inclusion complex existed in the stoichiometric ratio of 1:1 with the calculated stability constant (Ks) of 2385 M−1. The solubility of ABT was enhanced to 39-fold after complexation with HP-β-CD. Moreover, a molecular docking study confirmed that ABT was towards the core of HP-β-CD. The in vivo plasma pharmacokinetic studies demonstrated a higher solubility, absorption rate and 2.25-fold improved bioavailability than the free ABT group. This existing study revealed that HP-β-CD can be a notable molecule to fabricate a feasible and cost-effective inclusion complex for elevating the aqueous solubility, stability and in vivo pharmacokinetics of ABT.

Recovery Process for Critical Metals: Selective Adsorption of Nickel(II) from Cobalt(II) at Acidic Condition and Elevated Temperature

Effective and sustainable separation processes for critical metals, especially for the physicochemically similar elements nickel and cobalt in battery recycling, are of great interest in the future. Selective adsorption represents a highly potential process for this purpose. In this publication, a silica adsorbent functionalized with an amino-polycarboxylate derivate (HSU331) was investigated regarding the selective adsorption of Ni(II) in the presence of Co(II) in acidic solution (pH range at equilibrium 1.8–2.3) at elevated temperature. Comparable maximum equilibrium loadings ([Formula: see text]) for Ni(II) and Co(II) of 0.59 μmol(Ni(II)) · μmol(Ligand)-1 (18.3 mg(Ni(II)) · g(Adsorbent)-1), and 0.52 μmol(Co(II)) · μmol(Ligand)-1 (16.0 mg(Co(II)) · g(Adsorbent)-1), respectively, were achieved at T = 50°C in single-component experiments. Under competitive conditions, the Ni(II) loading remained constant at 0.60 μmol(Ni(II)) · μmol(Ligand)-1 (18.4 mg(Ni(II)) · g(Adsorbent)-1), while the Co(II) loading drastically decreased to 0.09 μmol(Co(II)) · μmol(Ligand)-1 (2.7 mg(Co(II)) · g(Adsorbent)-1) in an equimolar dual-component system. Calculated stability constants of 3 · 103 and 0.7 · 103 L · mol-1, respectively, for the formed metal ion complexes of Ni(II) and Co(II) onto the adsorbent HSU331, clarify the clear selectivity of the adsorbent towards Ni(II) in the presence of Co(II) even at elevated temperature ( T = 50°C).

A molecular dynamics investigation of La3+ and Lu3+-ligand speciation in aqueous solution

Ion-pair association of rare earth elements (REE) with ligands is important for its mobilization, enrichment, and fractionation during hydrothermal transport process, which is of great significance to study REE ore genesis, weathering process, the origin and evolution of earth and other related geoscience issues. However, reliable experimental data are limited to a specific system or ambient conditions, which hampered our understanding of the geochemical behavior of REE. In the present study, classical molecular dynamics simulations were carried out to calculate the potential of mean force (PMF) between La3+/Lu3+ and ligands of Cl−, F−, OH−, HCO3−, CO32− and SO42− in dilute aqueous solutions from ambient to supercritical thermodynamic conditions. Stability constants were calculated from the PMFs and compared with literature reported and thermodynamic calculated data. The analyses of the PMFs and stability constants suggest smaller or highly charged ions are easier to form stable complexes. For both La3+ and Lu3+ containing systems, the stability of ion pair decreases in the order of CO32− > OH− > SO42− > F− > HCO3− > Cl−. The smaller Lu3+ is to form more stable aqueous complexes at all thermodynamic conditions and these stability difference may lead to significant fractionation between La (light) and Lu (heavy). The trends of PMFs calculated stability constants are consistent with thermodynamic calculated values and provide association constants of ligands for which no experimental data exist.

Copper-binding properties of microplastic-derived dissolved organic matter revealed by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Despite numerous studies on microplastics (MPs), little attention has been paid to the dissolved organic substances leached from MPs and their environmental fate. In this study, we explored the copper-binding characteristics of MP-derived dissolved organic matter (MP-DOM) leached from several MP types, including commercial polypropylene, polyvinylchloride, and expanded polystyrene, under dark and UV irradiation conditions. The copper-binding affinity of MP-DOM was examined using fluorescence quenching method based on different fluorophores identified via the excitation emission matrix-parallel factor analysis (EEM-PARAFAC). The heterogeneous distribution of binding sites across the functional groups of MP-DOM was further elucidated by utilizing two-dimensional correlation spectroscopy (2D-COS) based on Fourier transform infrared spectroscopy (FTIR). Phenol/protein-like fluorescence prevailed in all MP-DOM samples, whereas humic-like fluorescence was more pronounced in the irradiated MP-DOM. For all tested plastic types, two plastic-derived fluorescent components (C2 and C3) exhibited substantial fluorescence quenching with increasing copper concentrations. The calculated stability constants showed larger differences between the two leaching conditions than between the three MP types with higher log KM values for the UV-irradiated (4.08–5.36) than dark-treated MP-DOM (1.05–3.60). The binding constants were comparable to those of natural organic matter with aquatic/terrestrial origins. The 2D-COS results further revealed that the oxygen-containing structures in MP-DOM generated by UV irradiation might be responsible for the higher binding affinity of the irradiated MP-DOM. This is the first study demonstrating the environmental reactivity of MP-DOM towards metal binding, highlighting the importance of leaching conditions for the metal-binding behavior of MP-DOM.

Prediction of stability constants of Cu2+ complexes with organic fluorescent ligands using thermodynamic cycle in combination with DFT theory and SMD solvent model

Accurately predicting the stability constant ( ) of the Cu2+ complex with organic fluorescent ligands provides an important basis to design molecular fluorescent sensors for selective detection of Cu2+. With appropriate reference complexes, the calculated stability constants are in good agreement with experimental values. The values of the predicted stability constants of Cu2+ complexes with Calcein blue (H3Cb) and FluoZin-1 (H2Fz) are 13.33 (exp. 14.27) and 6.59 (exp. 6.01), respectively. More importantly, the results could be applied to the investigation of complexes.

Corona Charged Aerosol Detector in studying retention and β-cyclodextrin complex stability using RP-HPLC

Binding between cyclodextrin (CD) cavity and guest molecule in Reversed Phase High-Performance Liquid Chromatography (RP-HPLC) is dynamic process. In general, increasing CD concentration is inducing inclusion complex formation, leading to reduction of analyte’s retention time. Consequently, the shortness in retention time is a measure of complex stability in HPLC. However, under certain experimental conditions, the retention of some analytes could be prolonged even when concentration of CD in the mobile phase is increased. In order to reveal the cause of this unexpected retention behavior, the present study was carried on. The model mixture consisted of risperidone, olanzapine and their related impurities, while β-CD was selected among CDs, as in the previous study. In order to achieve fast equilibrium between free analyte and β-CD-analyte complex, β-CD was not added to the mobile phase, but only to the sample. Detection was performed with Corona Charged Aerosol Detector (CAD), suitable for non-chromophoric β-CD. When analyzing olanzapine impurity B-β-CD sample, three peaks were detected, namely free β-CD, β-CD-analyte complex and free analyte. The complex stability constant was calculated employing a modification of the Benesi-Hildebrandt equation and CAD has proven to be useful in complex stability constants assessment if retention of free analyte and β-CD-analyte complex is distinguished. For all other analytes only two peaks could be detected, because free analyte and formed complex are eluting at the same retention time. Under such circumstances, the authors proposed the methodology for calculating stability constants and confirmed its applicability to studied model mixture.

Evaluation of Stoichiometry, Stability Constants and Gibbs Free Energies of Acetaminophen-Zn (II) complex at Different Temperatures

Acetaminophen also known as paracetamol, is a drug used in the treatment of pain and fever. It is essentially used for the relief of mild to moderate pain. The presence of phenol and carbonyl oxygen atom enables acetaminophen to behave as a bidentate ligand. The stoichiometry, stability constants and Gibbs free energies of acetaminophen-Zn (II) were determined colorimetrically at 25 and 40 oC using continuous variation and mole ratio methods. The formation of Zn (II) complex with acetaminophen was studied colorimetrically at an absorption maximum of 630 nm at different temperatures. The data showed that Zn (II) and acetaminophen combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 2.70 x 103 and 2.20 x 103 using continuous variation method and 7.21 x 103 and 7.21 x 103 using mole ratio methods at 25 and 40 oC respectively. Calculated ΔGƟ for the complex were - 1.96 x 104 and -1.98 x 104 J using continuous variation method and -2.2 x 104 J and - 2.31 x 104 J using mole ratio method at 25 and 40 oC respectively. The stability constant and Gibbs free energy results suggested that acetaminophen used in the study is a good chelating agent and can be an efficient antidote in the therapy of Zn (II) overload or poisoning.
 Keywords: Acetaminophen, Zinc, complex, stability constant, Gibbs free energy.

Colorimetric Determination of Stability Constant of Sulfamethoxazole-Cu(II) Complex at Different Temperatures by Continuous Variation Method

Sulfamethoxazole is an antibiotic that is used for the treatment of bacterial infections such as prostatitis, bronchitis and urinary tract infections. It is effective against gram negative and gram positive bacteria. Classical equation has been used in the calculation of stability constant of SulfamethoxazoleCu(II) complex depending on the theoretical explanation of the stoichiometry. The formation of Cu(II) complex with sulfamethoxazole was studied colorimetrically at an absorption maximum of 430 nm at 25, 30, 35 and 40 oC. The data showed that Cu(II) and sulfamethoxazole combine in the molar ratio of 1:2 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 4.02 x 106 , 2.93 x 106 , 1.37 x 106 and 9.21 x 105 using continuous variation method. Calculated ∆GƟ for the complex were -3.77 x 104 , -3.75 x 104 , -3.62 x 104 and - 3.57 x 104 . The stoichiometry, stability constant and Gibbs free energy results suggested that sulfamethoxazole used in the study is a good chelating agent and can be an efficient antidote in the therapy of Cu(II) overload or poisoning

Development and validation of spectrophotometric methods for the sensitive and selective determination of lamotrigine in pharmaceuticals using bromocresol purple

Three simple, selective and sensitive methods have been developed and validated for the determination of lamotrigine (LMT) in pure drug and in tablets. The first method (method A) is based on the formation of ion-pair complex between LMT and the dye, bromocresol purple (BCP) at pH 2.40±0.01 which was extracted into dichloromethane (DCM) and the absorbance of yellow ion-pair complex was measured at 410 nm. In the second and third methods (method B and method C), the drug-dye ion-pair was dissolved either in ethanol and the resulting acid form of the dye was measured at 410 nm or in ethanolic potassium hydroxide and the resulting base form of the dye was measured at 600 nm. Under the optimized conditions, Beer's law was obeyed over 2.0-20.0 μg/mL, 150-1500 ng/mL and 50-600 ng/mL for method A, method B and method C, respectively, and the corresponding molar absorptivity values were 1.018×104, 1.43×105 and 4.21×105 L/mol/cm. The Sandell sensitivity values of 0.0252, 0.0018 and 0.0006 μg/cm2 for method A, method B and method C, respectively, and the corresponding values for limits of detection and quantification were also reported for all three methods. The molar ratio of the formed ion-pair complex was found to be 1: 1 as deduced by Job's method for method A, and the calculated stability constant was also reported. Over the linear ranges applicable, the accuracy and precision of the methods were evaluated on intra-day and inter-day basis; the reported mean accuracy values are 99.50±1.09%, 99.99±1.11% and 100.72±0.62% for method A, method B, and method C, respectively; the relative error (RE) was ≤ 2.57% and the relative standard deviation (RSD) was ≤ 2.01%. Application of the proposed methods to bulk powder and commercial pharmaceutical tablets are also presented.

Formation of ionic associates with pyrogallol complexes of antimony (III) and their application for spectrophotometric determination of antimony

The possibility of using water soluble pyrogallol red (PRWS) as a photometric reagent for the quantitative determination of antimony (III) in real objects has been studied. Formation of a colored product is observed in acidic solutions (pH 3.8 - 4.5) with a weak oxidizing agent (iodine) present for preliminary oxidation of SbHg to salts of Sb (III). The excess iodine is eliminated through introduction of sodium thiosulfate solution after obtaining the photometric form. The maximum analytical signal of the colored form is observed at 378 nm (e = 5.936 x 103). A decrease in the acidity of the solution (pH > 7) is accompanied by the formation of sodium salts of the reagent which prevents further complexation, whereas the only one maximum in the absorbance within the recommended pH range directly indicates to the formation of the the only one ionic associate (AI). The ionic associate thus formed appeared low stability in time. Unfortunately, change in the dielectric constant of the solution failed to give a positive effect and measurements of the absorbance of the colored compound were limited to 3 minutes. Determination of the composition and possible mechanism of the ionic associate formation was carried out on using the methods of molar ratios and isomolar series. After stripping of stibine into the absorption system, an ionic associate of the composition M:R = 1:1 is formed with a calculated stability constant of 4.01 x 105. The obtained results are used to develop a spectrophotometric (SP) method for antimony determination with the limits of detection and quantitative determination of the element 1.30 and 4.32 pg/ml, respectively. The developed method is valid in terms of the specificity, linearity, precision and accuracy, and, therefore, can be recommended for determination of the antimony content in any control and analytical laboratory.

Thermodynamic Study on the Interaction of Nicotinic Acid with H+, Na+, Ca2+ and Mg2+ at Different Temperatures and Ionic Strengths

Protonation of nicotinic acid has been investigated by means of potentiometric titrations at different temperatures 283.15 ≤ T (K) ≤ 383.15 and ionic strengths of NaCl(aq), 0.12 ≤ I (mol·kg−1) ≤ 4.84 and mixed NaCl with MgCl2 or CaCl2. Stability constants of the CaL+ and MgL+ species were obtained by means of the ΔpK method. Different models (e.g. Debye–Huckel type equation, Specific Ion Interaction Theory, Pitzer and van’t Hoff) were applied to account for the ionic strength and temperature dependences, in order to obtain data in a standard state and parameters to calculate stability constants in any point of our experimental domain. Speciation studies were performed simulating the conditions of natural fluids. Literature data were investigated for comparison with the experimental results here obtained.

The Role for the Weak Interaction on the Stabilization of Copper-Containing Complex: DFT Investigation of Noncovalent Interactions in Ternary-Cu(II) (DA)(AA) Complexes (DA = Diamine and AA = Amino Acids) as a Model of Metalloprotein

Abstract In view of the key roles played by noncovalent or weak interactions in biological processes, it is important to understand them at the molecular level. Based on the results of the thermodynamic, spectroscopic and X-ray structural studies on ternary Cu(II) complexes, as platform molecules for ligand-ligand interactions, the presence of π-π interactions between aromatic rings (phenyl, phenol and indole) of amino acids and aromatic rings of imidazole, diamines have been shown. We carried out systematic theoretical studies using different DFT functionals (pure-GGA, meta-GGA, hybrid-GGA and meta-hybrid-GGA) with triple-ζ (def2TZVP) basis set for the experimentally determined structure of [Cu(hista)(Phe)]ClO4, to obtain the most suitable method. We gained reliable insight into the geometry, electronic structure and noncovalent interactions for different ternary complexes, [Cu(hista)(AA)]ClO4 (AA = Phe, Tyr, Trp, Leu, Ile, Ala, Met, Val) by applying the most accurate method (PW91/def2TZVP/CPCM). The calculated stability constants (logK) were in good agreement with the experimental results. We obtained knowledge of the differences in noncovalent interactions and excited states among the ternary Cu(II) complexes containing Phe, Tyr, and Trp by the Non-Covalent Interaction (NCI) and TDDFT methods.

Spectrophotometric study of complexation of cobalt (II) with HEDP in aqueous solutions

The complexation of cobalt(II) with HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) in aqueous solutions was studied by spectrophotometry over a wide range of pH values, including strongly acidic and strongly alkaline solutions. The formation of 2:1, 1:1, 1:2 and 1:3 Co(II)–HEDP complexes was proved by decomposing the electronic absorption spectra recorded in strongly alkaline solutions into individual bands using Gaussian functions and plotting changes in absorbance against the metal:ligand mole ratio at increasing values of the ligand concentrations. Species composition dynamics in the 1:4 Co(II)–HEDP system in alkaline solutions was determined by the change in the metal:ligand mole ratio with time. A decrease in the amount of bis- and the predominant formation of tris-phosphonate species with preservation of the amount of the 2:1 and 1:1 complexes was observed after three months. The modeling of complexation in the Co(II)–HEDP system and the calculation of stability constants (β) were carried out on the basis of experimental dependences of the absorbance of the solutions on pH. High thermodynamic stability was found for the binuclear chelates [Co2HHEDP], [Co2HEDP]−, [Co2(OH)2H2HEDP]−, [Co2(OH)2HHEDP]2−, log β are equal 18.90, 7.11, 23.85 and 31.45, respectively. Speciation diagrams of complexes in the 1:1 and 1:4 Co(II)–HEDP systems were calculated for freshly prepared solutions.

Thermochromic behaviour and thermodynamics of cobalt(II) chloride complexes in ammonium nitrate + N-methylformamide mixture

In this paper thermochromic features of cobalt(II) were investigated in the binary mixture containing inorganic salt (ammonium nitrate) and molecular solvent (N-methylformamide) in order to find responsive thermochromic medium for possible application in a greenhouses for auto-regulated shading and solar protection. Absorption spectra of cobalt(II) in the NH4NO3 + zNMF (z = 3, 4, 5, 6 and 20) binary mixtures were recorded in the visible wavelength range in the presence of different cobalt(II) and chloride concentrations at five selected temperatures: 308.15; 318.15; 328.15; 338.15 and 348.15 K. From the obtained spectra, geometry, composition and speciation of the complexes were discussed. Influences of the temperature and mixture composition on the absorption spectra were also analysed. From an analysis of the spectra using two computer programs, it was concluded that the following complexes were formed: [Co(NO3)4(NMF)2]2−, [CoCl3(NO3)(NMF)2]2−and [CoCl4]2−. For these complexes stability constants were determined at all temperatures. Thermodynamic parameters were also calculated using the temperature dependence of calculated stability constants.

Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes

Stability constants are central to the multiscale modeling of the thermodynamic speciation, cycling, and transport of mercury (Hg) and other contaminants in aquatic environments. However, for Hg, experimental values for many relevant complexes are not available, and for others can span ranges in excess of 10 log units. The missing data and large uncertainties lead to significant knowledge gaps in predictions of thermodynamic speciation. As an alternative to experimental measurements, thermodynamic quantities can be calculated with quantum chemical methods. Among these, density functional theory (DFT) with a polarizable continuum solvent combines accuracy with practicability. Here, we present an accurate and quick approach in which we use DFT with continuum solvation to calculate stability constants of Hg complexes with inorganic and low molecular-weight organic ligands in aqueous solution. Specifically, we use the M06/[SDD]6-31+G(d,p) level of theory in combination with a modified version of the SMD solve...

Computational Tools for Calculating log β Values of Geochemically Relevant Uranium Organometallic Complexes.

Uranium (UVI) interacts with organic ligands, subsequently controlling its aqueous chemistry. It is therefore imperative to assess the binding ability of natural organic molecules. We evidence that density functional theory (DFT) can be used as a practical protocol for predicting the stability of UVI organic ligand complexes, allowing for the development of a relative stability series for organic complexes with limited experimental data. Solvation methods and DFT settings were benchmarked to suggest a suitable off-the-shelf solution. The results indicate that the IEFPCM solvation method should be employed. A mixed solvation approach improves the accuracy of the calculated stability constant (log β); however, the calculated log β are approximately five times more favorable than experimental data. Different basis sets, functionals, and effective core potentials were tested to check that there were no major changes in molecular geometries and Δr G. The recommended method employed is the B3LYP functional, aug-cc-pVDZ basis set for ligands, MDF60 ECP and basis set for UVI, and the IEFPCM solvation model. Using the fitting approach employed in the literature with these updated DFT settings allows fitting of 1:1 UVI complexes with root-mean-square deviation of 1.38 log β units. Fitting multiple bound carboxylate ligands indicates a second, separate fitting for 1:2 and 1:3 complexes.

Selective fluorometric sensing of Hg2+ in aqueous solution by the inhibition of PET from dithia-15-crown-5 ether receptor conjugated to 4-amino-1,8-naphthalimide fluorophore

Two novel derivatives of 4-amino-1,8-naphthalimide bearing N-phenylaza-15-crown-5 (NI1) and benzodithia-15-crown-5 (NI2) ether receptor as N-aryl substituent attached to the N-imide nitrogen of the naphthalimide ring were evaluated as fluorescent probes for the detection of mercury (II) ions in aqueous solutions containing 40 vol. % MeOH. Both molecules were configured as fluorophore–space–receptor systems in which binding with a cation would trigger the fluorescence between «OFF» and «ON» states due to inhibition of the photoinduced electron transfer process (PET) in the excited state. The results of spectroscopic studies as well as quantum-chemical calculations have demonstrated that only compound NI1 is able to switch the emission signal. Upon addition of Hg2+ to the solution of NI1 at pH 4.7, the fluorescence intensity increases in a linear fashion covering the range from 0.1 μM to 1.2 μM; the detection limit is 25 nM. Based on the fluorometric titration data, the calculated stability constant of (NI1)·Hg2+ complex is found to be 5.74 ± 0.01. Competition studies have shown that the other metal ions including Ca2+, Mg2+, Zn2+, Ni2+, Fe2+, Cd2+ don’t interfere the emission of mercury (II) complex, however Cu2+ and to a lesser extent Pb2+ have a little effect. Thus, the proposed sensor NI1 can be applied to selective detection of Hg2+ in aquatic media.