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The zinc boron complex formation was studied as a function of temperature (25, 50 and 70 °C) in boric acid solutions of various concentration (0.25, 0.50 and 0.68 mol·kg−1). pH was monitored during zinc ion addition by galvanostatic dissolution of a zinc metal electrode, in a solution of boric acid. The determination of the complex formation showed the importance of an accurate model of the polyborate speciation, recalculated for this work based on the previous literature data mainly potentiometric measurements completed by Raman spectroscopy and Ab Initio calculations. Modelling of our experimental results, considering various scenarios of boric acid speciation, was performed using R and PhreeqC, suggesting the formation of an aqueous triborate-zinc (II) complex, ZnB 3 O 3 (OH) 4 (aq) + , according to the reaction: Zn 2 + + 3 B (OH) 3 ⇌ ZnB 3 O 3 (OH) 4 (aq) + + 2 H 2 O + H + . The nature and structure of this aqueous complex disagrees with the results reported previously in the literature. Three formation constants of the triborate-zinc (II) complex were determined at 25, 50 and 70 °C as log 10 K ZnB = − 4.73 ± 0.10, − 4.21 ± 0.16 and − 4.94 ± 0.12, respectively. The evolution of zinc boron complex formation as a function of temperature (between 25 and 70 °C) provides information on the effect of the polyborate predominance in the solution on the complexation of zinc. [ABSTRACT FROM AUTHOR]

In the present study, we have explored the binding abilities of powerful dipodal chelator ligand N1,N3-bis(2-(((Z)-2,3-dihydroxybenzylidene)amino)ethyl)malonamide (MEC) to trivalent metal ions. We have investigated the coordination behavior of the dipodal ligand MEC with the trivalent metal ions Al3+, Fe3+, and Cr3+ in aqueous media ranging from pH 2 to 11, employing potentiometry and spectrophotometry techniques. Results shows the higher binding ability of Cr+3 metal ion among all metal ions with largest formation constant value, log ß = 28.56. [ABSTRACT FROM AUTHOR]

An aqueous Cu2+ and Zn2+ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm's thermal phase transition from hydrophobic globule to hydrophilic open coil. As a basis for sensing the metal-binding, the dansyl fluorescence emission spectra provide a signal at ca. 530 nm and a signal at 500 nm for the hydrophobic and hydrophilic environment, respectively, that are ratiometrically interpreted. The synthesis of the title pyridylethyl-pyridylmethyl-amine ligand (acronym PEPMA) with a 3-carbon linker to the copolymerizable group, aminopropylacrylamide (PEPMA-C3-acrylamide), is reported, along with a nonpolymerizable model ligand derivative. The response of the polymer is validated by increasing temperature from 25 °C to 49 °C, which causes a shift in maximum emission wavelength from 536 nm to 505 nm, along with an increase in the ratio of emission intensity of 505 nm/536 nm from 0.77 to 1.22 (λex = 330 nm) as the polymer releases water. The addition of divalent Cu or Zn to the indicator resulted in a dansyl emission shift of 10 nm to a longer wavelength, accompanied by fluorescence quenching in the case of Cu2+. The addition of EDTA to the Cu2+-loaded indicator reversed the fluorescence shift at 25 °C to 35 °C. The affinities of Cu2+ and Zn2+ for the PEPMA derivatives are log Kf = 11.85 and log Kf = 5.67, respectively, as determined by potentiometric titration. The single-crystal X-ray structure of the Cu2+-PEPMA derivative is five-coordinate, of-geometry intermediate between square-pyramidal and trigonal-bipyramidal, and is comparable to that of Cu2+ complexes with similar formation constants. [ABSTRACT FROM AUTHOR]

Using affinity capillary electrophoresis, the stability constants of inclusion complexes of a number of betulin ester derivatives with randomly methylated β-cyclodextrin in 0.0100 M sodium tetraborate (pH 9.18, ionic strength 0.0200 M) at 25°С were determined for the first time. The decimal logarithms of the stability constants of 1 : 1 complexes of betulin 3,28-diphthalate, betulin 3,28-disulfate, and betulin 3,28-disuccinate in a 95% confidence interval were 4.64 ± 0.05, 4.78 ± 0.02, and 4.94 ± 0.02, respectively. The logarithms of the stability constants of 1 : 2 complexes of betulin 3,28-diphthalate and betulin 3,28-disulfate were 7.91 (6.66–8.19) and 8.02 (7.63–8.23), respectively. It was determined that betulin 3,28-disuccinate forms only 1 : 1 complex. The obtained stability constants of 1 : 1 complexes are generally higher than those of the complexes of the same compounds with β-cyclodextrin (β-CD) and lower than those for dimethyl-β-CD, γ-CD, and (2-hydroxypropyl)-γ-CD complexes. [ABSTRACT FROM AUTHOR]

For lump and nanocobalt sulfate (CoSO4) in pure water, the affiliation and thermodynamic association characteristics were measured at 298.15, 303.15, 308.15, and 313.15 K. Based on the bulk and nano CoSO4 molar conductance, estimates were made for the parameters of the solvation, such as the activity coefficient, free energy of association, enthalpy of association, association constant, and entropy of association. We discussed about each of these solvation parameters. Two stoichiometric complexes were formed by the interaction of bulk and nano CoSO4.7H2O with fuchsin acid: 1:1 and 1:2 In the case of 1:1 (CoSO4.7H2O/fuchsin acid) compared to 1:2 (fuchsin acid in pure water as solvent), the complex Kf and ΔGf are higher, indicating simpler complex formation. The temperature increase resulted in a drop in the formation constants. The complexation's negative ΔGf values demonstrate that the process of complex synthesis was spontaneous and that the temperature improved the spontaneity. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a flexible tripodal ligand 2,2′,2″-((1E,1′E,1″E)-(cyclohexane-1,3,5-triyltris(azanylylidene))tris(methanylylidene))tris(quinolin-8-ol), TACH2OX, containing three 8-hydroxyquinoline units joined to a cyclohexane‐1,3,5‐triamine skeleton has been described. The protonation equilibria and formation constants of the ligand and its complexes with iron (III), aluminum (III), and gallium (III) are explored by potentiometric and absorption spectrophotometric studies. Six protonation constants with log K values ranging from 1.22 to 9.91 were evaluated, substantiating three nitrogen atoms of the 8-hydroxyquinoline ring and three phenolate groups. The ligand formed [FeL], [FeLH], [FeLH2], [FeLH3] complexes for iron, [AlL], [AlLH2], [AlLH3] complexes for aluminum and [GaLH3], [GaL] complexes for gallium. TACH2OX and its complexes exhibited a variation in the absorption and emission spectral behavior when measured in different pH. It exhibited an enhancement in emission at 400 nm at neutral pH 7.0, while in acidic and basic pH, the fluorescence is quenched with bathochromic shift implying its utility as an OFF-ON-OFF type pH molecular sensor in an aqueous solution. Interestingly, the fluorescence of TACH2OX showed more significant enhancement in the presence of Ga3+ as compared to Al3+, while a reverse phenomenon was observed for Fe3+, indicating that the ligand can behave as a metal sensor for the metal ions, one as "ON" type and the other as "OFF" type. Density functional theory with GGA-BLYP-D functional and TZ2P basis set was employed for the prediction of molecular geometry and spectral nature of all species of the ligand and its metal complexes. The nature of bonding and electronic transitions of the ligand and its complexes were assessed by EDA-NOCV, NBO, APO, and FMO studies. [ABSTRACT FROM AUTHOR]

Three proton‐transfer salts of diphenylphosphinic acid (DPPA) with 2‐amino‐5‐(X)‐pyridine (AMPY, X = Cl, CN or CH3), namely, 2‐amino‐5‐chloropyridinium diphenylphosphinate, C5H6ClN2+·C12H10O2P− (1, X = Cl), 2‐amino‐5‐cyanopyridinium diphenylphosphinate, C6H6N3+·C12H10O2P− (2, X = CN), and 2‐amino‐5‐methylpyridinium diphenylphosphinate, C6H9N2+·C12H10O2P− (3, X = CH3), have been synthesized and characterized by FT–IR and 1H NMR spectroscopy, and X‐ray crystallography. The crystal structures of compounds 1–3 were determined in the space group P for 1 and 2, and C2/c for 3. All three compounds contain N—H...O hydrogen‐bonding interactions due to proton transfer from the O=P—OH group of DPPA as donor to the pyridine N atom of AMPY as acceptor. The proton transfer of compounds 1–3 was also verified by 1H NMR and FT–IR spectroscopy. The stoichiometry of all three proton‐transfer salts was determined to be 1:1 and the Benesi–Hildebrand equation was applied to determine the formation constant (KCT) and the molar extinction coefficient (ϵCT) in each case. Theoretical density functional theory (DFT) calculations were performed to investigate the optimized geometries, the molecular electrostatic potentials (MEP) and the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of all three proton‐transfer salts. The results showed good agreement between the experimental data and the DFT computational analysis. [ABSTRACT FROM AUTHOR]

Host–guest complexation of betulin 3,28-diphthalate (DPhB), that is poorly soluble in water and is an amphiphilic compound, with β-cyclodextrin (β-CD) was studied by spectrophotometry in 10 mM sodium tetraborate solution at pH 9.18 (ionic strength of 20 mM). This interaction was found to lead to a bathochromic shift of the DPhB absorption bands and an increase in absorption. Using the first derivative spectra of solutions with a fixed concentration of DPhB (0.01 mM) and a variable concentration of β-CD (0–10 mM), the logarithms of binding constants for 1:1 and 1:2 complexes of DPhB with β-CD were determined with 95% confidence intervals at 25 °C: 4.13 (4.03–4.20) and 6.30 (4.72–6.59). To eliminate systematic errors, the assumption that the equilibrium CD concentration in solution was equal to its total concentration was not used in this study. The obtained value for the 1:1 complex is consistent with the value determined earlier by affinity capillary electrophoresis (ACE), while the constant for the 1:2 complex is slightly lower than that from ACE, which can be explained by a higher concentration of DPhB; however, the use of this concentration is reasonable to reduce the measurement error. DPhB was found to form micelles at pH 9.18 and the critical micelle concentration (CMC) measured was 0.13 mM. This is a possible reason why the experimental points obtained at higher concentrations of DPhB than CMC are not described within the framework of theories that take into account the formation of 1:1 or both 1:1 and 1:2 complexes. [ABSTRACT FROM AUTHOR]

Cancer chemotherapeutics usually have serious side effects. Targeting the special properties of cancer and activation of the anticancer drug in the tumor microenvironment in situ may decrease the intensity of the side effects and improve the efficacy of therapy. In this study, half-sandwich Rh complexes are introduced, which may be activated at the acidic, extracellular pH of the tumor tissue. The synthesis and aqueous stability of mixed-ligand complexes with a general formula of [Rh(η5-Cp*)(N,N/O)(N)]2+/+ are reported, where (N,N/O) indicates bidentate 8-quinolate, ethylenediamine and 1,10-phenanthroline and (N) represents the releasable monodentate ligand with a nitrogen donor atom. UV-visible spectrophotometry, 1H NMR, and pH-potentiometry were used to determine the protonation constants of the monodentate ligands, the proton dissociation constants of the coordinated water molecules in the aqua complexes, and the formation constants of the mixed-ligand complexes. The obtained data were compared to those of the analogous Ru(η6-p-cymene) complexes. The developed mixed-ligand complexes were tested in drug-sensitive and resistant colon cancer cell lines (Colo205 and Colo320, respectively) and in four bacterial strains (Gram-positive and Gram-negative, drug-sensitive, and resistant) at different pH values (5–8). The mixed-ligand complexes with 1-methylimidazole displayed sufficient stability at pH 7.4, and their activation was found in cancer cells with decreasing pH; moreover, the mixed-ligand complexes demonstrated antimicrobial activity in Gram-positive and Gram-negative bacteria, including the resistant MRSA strain. This study proved the viability of incorporating releasable monodentate ligands into mixed-ligand half-sandwich complexes, which is supported by the biological assays. [ABSTRACT FROM AUTHOR]

Salen ligands are essential for coordinating a diverse group of metals in their respective oxidation states. This creates significant complexes of salen metals that are used in different fields. Condensation of ehylenediamine (en) with p-methoxybenzaldehyde (L1) or o-hydroxyacetophenone (L2) with a ratio 1: 2 (en: p-methoxybenzaldehyde or o-hydroxyacetophenone) or by the interaction of o-phenylenediamine (phen) with o-hydroxybenzaldehyde (L3) or p-hydroxybenzaldehyde (L4) with a ratio 1: 2 (phen: o-hydroxybenzaldehyde or p-hydroxybenzaldehyde) has been used to prepare four symmetrical Schiff bases (L1-L4). The UV–vis spectroscopy has been used to investigate the diverse electronic transitions associated with the Schiff bases molecules as well as how these transitions are impacted by diverse polarities of solvents. Elemental analysis, FT-IR, UV–vis spectra, molar conductivity, and 1H NMR have been used to characterise all the compounds obtained in this process. The continuous variation applied alongside molar ratio spectral methods showed the formation of different complexes arising from the reaction of the ligand (L1-L4) with the metal ions Mn(II), Fe(III) and Cu(II) is 1: 1 and/ or 1: 2 (M: L). A series of universal buffer solutions (20 % ethanol v/v) with varying pH values were used in spectrophotometry to determine the acid dissociation constants of the L2 and L4 ligands. Gamma radiation was applied to examine the compounds’ irradiation stability. Additionally, the absorptions of the main functional groups were screened using FT-IR spectra before and after Gamma irradiation. The results show that all the compounds are stable after irradiation process; therefore, it could be used as enhancing agents in cancer therapy.

Background: Stigmasterol possesses numerous physiological effects and is used as food supplements and behaves as a pharmaceutical agent. It exhibits anticancer effects against various cancers. The usefulness of the stigmasterol is restricted due to its poor solubility. To overcome this and enhance the solubility and bioavailability of this phytosterol, molecular encapsulation is utilized to augment the desirable properties of stigmasterol. This research work aims to investigate the interaction between stigmasterol and alpha-cyclodextrin (α-CD) in aqueous solution as well as in solid state and experimentally examined by spectral techniques. Methods: The liquid complexes are characterized by ultraviolet (UV)-visible spectroscopy and solid inclusion complexes are characterized by Fourier transformer infrared resonance and 1H nuclear magnetic resonance spectroscopy. The thermal behavior of the complex is analyzed by differential scanning calorimeter. Phase solubility studies are done to learn the solubility of the newly synthesized complex. Results: Formation constant from UV-visible analysis is found to be 569 M−1 by Benesi–Hildebrand equation. The solubility constant is calculated to be 52 M−1. The results obtained prove the inclusion which is confirmed through molecular docking studies. Conclusion: The newly synthesized inclusion complex is a potent pharmaceutical agent in drug formulation as stigmasterol solubility is enhanced when included in the cavity of α-CD.

An aqueous Cu2+ and Zn2+ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm’s thermal phase transition from hydrophobic globule to hydrophilic open coil. As a basis for sensing the metal-binding, the dansyl fluorescence emission spectra provide a signal at ca. 530 nm and a signal at 500 nm for the hydrophobic and hydrophilic environment, respectively, that are ratiometrically interpreted. The synthesis of the title pyridylethyl-pyridylmethyl-amine ligand (acronym PEPMA) with a 3-carbon linker to the copolymerizable group, aminopropylacrylamide (PEPMA-C3-acrylamide), is reported, along with a nonpolymerizable model ligand derivative. The response of the polymer is validated by increasing temperature from 25 °C to 49 °C, which causes a shift in maximum emission wavelength from 536 nm to 505 nm, along with an increase in the ratio of emission intensity of 505 nm/536 nm from 0.77 to 1.22 (λex = 330 nm) as the polymer releases water. The addition of divalent Cu or Zn to the indicator resulted in a dansyl emission shift of 10 nm to a longer wavelength, accompanied by fluorescence quenching in the case of Cu2+. The addition of EDTA to the Cu2+-loaded indicator reversed the fluorescence shift at 25 °C to 35 °C. The affinities of Cu2+ and Zn2+ for the PEPMA derivatives are log Kf = 11.85 and log Kf = 5.67, respectively, as determined by potentiometric titration. The single-crystal X-ray structure of the Cu2+-PEPMA derivative is five-coordinate, of-geometry intermediate between square-pyramidal and trigonal-bipyramidal, and is comparable to that of Cu2+ complexes with similar formation constants.

A simple and easily synthesized fluorescent sensor, Schiff base sensor (SBS), produced by condensation reaction of equal amounts of anthranilic acid and salicyladehyde. It was synthesized and characterized systemically. Both UV-vis and fluorescence spectroscopic studies indicated that the SBS sensor showed good selectivity toward the studied ions: Na+, K+, Cu2+, Co2+, Fe3+, Al3+ and Cr3+. Whereas, chromium (III) and copper (II) exhibited the largest fluorescence enhancement over the other investigated ions. Chelation-enhanced fluorescence were shown upon the interaction of SBS sensor with some metal ions studied forming inclusion complexes. The fluorescent sensor in aqueous ethanolic solution exhibited high selectivity towards Cu2+ and Cr3+ ions, forming 2 : 1 (L : M) complex as determined by Job’s plot. The formation constants of the inclusion complexes (Mn+/SBS) were measured via spectrofluorometric method applying Benesi-Hildebrand equation. [ABSTRACT FROM AUTHOR]

Background: Stigmasterol possesses numerous physiological effects and is used as food supplements and behaves as a pharmaceutical agent. It exhibits anticancer effects against various cancers. The usefulness of the stigmasterol is restricted due to its poor solubility. To overcome this and enhance the solubility and bioavailability of this phytosterol, molecular encapsulation is utilized to augment the desirable properties of stigmasterol. This research work aims to investigate the interaction between stigmasterol and alpha-cyclodextrin (α-CD) in aqueous solution as well as in solid state and experimentally examined by spectral techniques. Methods: The liquid complexes are characterized by ultraviolet (UV)-visible spectroscopy and solid inclusion complexes are characterized by Fourier transformer infrared resonance and 1H nuclear magnetic resonance spectroscopy. The thermal behavior of the complex is analyzed by differential scanning calorimeter. Phase solubility studies are done to learn the solubility of the newly synthesized complex. Results: Formation constant from UV-visible analysis is found to be 569 M−1 by Benesi–Hildebrand equation. The solubility constant is calculated to be 52 M−1. The results obtained prove the inclusion which is confirmed through molecular docking studies. Conclusion: The newly synthesized inclusion complex is a potent pharmaceutical agent in drug formulation as stigmasterol solubility is enhanced when included in the cavity of α-CD. [ABSTRACT FROM AUTHOR]

Cancer chemotherapeutics usually have serious side effects. Targeting the special properties of cancer and activation of the anticancer drug in the tumor microenvironment in situ may decrease the intensity of the side effects and improve the efficacy of therapy. In this study, half-sandwich Rh complexes are introduced, which may be activated at the acidic, extracellular pH of the tumor tissue. The synthesis and aqueous stability of mixed-ligand complexes with a general formula of [Rh(η5-Cp*)(N,N/O)(N)]2+/+ are reported, where (N,N/O) indicates bidentate 8-quinolate, ethylenediamine and 1,10-phenanthroline and (N) represents the releasable monodentate ligand with a nitrogen donor atom. UV-visible spectrophotometry, 1H NMR, and pH-potentiometry were used to determine the protonation constants of the monodentate ligands, the proton dissociation constants of the coordinated water molecules in the aqua complexes, and the formation constants of the mixed-ligand complexes. The obtained data were compared to those of the analogous Ru(η6-p-cymene) complexes. The developed mixed-ligand complexes were tested in drug-sensitive and resistant colon cancer cell lines (Colo205 and Colo320, respectively) and in four bacterial strains (Gram-positive and Gram-negative, drug-sensitive, and resistant) at different pH values (5–8). The mixed-ligand complexes with 1-methylimidazole displayed sufficient stability at pH 7.4, and their activation was found in cancer cells with decreasing pH; moreover, the mixed-ligand complexes demonstrated antimicrobial activity in Gram-positive and Gram-negative bacteria, including the resistant MRSA strain. This study proved the viability of incorporating releasable monodentate ligands into mixed-ligand half-sandwich complexes, which is supported by the biological assays.

Ivabradine hydrochloride (IVR) is a medically important drug because of its ability to lower the heart rate. Techniques reported for IVR determination were expensive, laborious, besides being of poor selectivity. In this study, iron oxide @ carbon nanotube (Fe2O3@MWCNTs) nanocomposite and molecularly imprinted polymer (MIP) were synthesized and used in the fabrication of carbon paste electrodes (CPEs) for the potentiometric detection of IVR in biological and pharmaceutical samples. CPEs of the best sensor were formulated from graphite (41 wt%) as a carbon source, MIP (3 wt.%) as an ionophore, Fe2O3@MWCNTs (5 wt%) as a modifier, and nitrophenyl octyl ether (NPOE, 51 wt.%) as a conductive oil so-called plasticizer. The best sensor exhibits a Nernstian slope (response) of 56 mV decade–1 within the IVR concentration range from 1.0 × 10–3 M to 9.8 × 10–8 M with high selectivity against interfering species (ascorbic, maltose, glucose, lactose, dopamine, glycine) over those reported earlier. The use of Fe2O3@MWCNTs together with MIP in the electrode formulation was found to improve the limit of detection (LOD) from 630 to 98 nM along with high reversibility, a short response time of 30 s, and a good lifetime of more than 2 weeks. The sandwich membrane (SMM) method was used to quantify the H-bonding complexing strength of the MIP binding sites for IVR with Log βILn = 11.33. The constructed sensors were successfully applied for the IVR determination in blood serum, urine, and commercial formulations (Savapran®) with high sensitivity.

The complexation reaction between some heavy metal ions such as: Ag+, Co2+, Hg2+, Zn2+, Ni2+, Cu2+, Cd2+, Mn2+, Cr3+, Fe3+ and Pb2+ with 2,3-dimethyl-1,2-dihydro-8H-pyrazolo[5,1-a]isoindol-8-one, ligand in acetonitrile as nonaqueous solvents at 25 ºC were investigated by spectrophotometric and conductometric methods. The formation constants (kf) of the 1:1 (metal ion to ligand) complexes were calculated by computer fitting of the absorbance-mole ratio data, and molar conductance-mole ratio data at 25 ºC using the KINFIT program, and found that complexes to vary in acetonitrile solvent in the order of Zn2+> Ag+> Cr3+> Ni2+> Hg2+> Fe3+> Cu2+> Cd2+> Co2+> Mn2+> Pb2+. DOI: http://dx.doi.org/10.17807/orbital.v10i6.1141

Two novel copper(II) Schiff base complexes were synthesized and characterized by various physico-chemical and spectroscopic methods, revealing a distorted square planar geometry around the copper atom. The analytical data confirmed the 1:1 metal to ligand stoichiometry of the complexes. B3LYP/(LANL2DZ/6-311G**) density functional theory (DFT) were used to investigate structural and electronic properties of the synthesized compounds in gas phase. The computational results support the conclusion obtained by the experimental studies. Thermodynamic study of complex formation in solution was carried out spectrophotometrically at 25°C. These compounds were also subjected to study in vitro antibacterial screening against some bacteria. Also, click reaction was investigated for its catalytic properties. The synthesized Schiff base copper complexes catalyzed 1,3-dipolar Huisgen cycloaddition of different functionalized β-azido alcohols and alkynes in the presence of ascorbic acid in a solution of THF/H2O (2:1, V/V) at room temperature.

Metal ions play a key role in living systems and are used to perform different physiological activities in our body. Complexation of drugs with metal ions is known to influence the bioavailability and other pharmacokinetic properties of drugs. In the present work, complexation of two essential cations, Mg2+ and Ca2+ with zidovudine (AZT), the first approved antiretroviral drug for human immunodeficiency virus (HIV) has been studied by conductometry and spectrophotometry. The plots of molar conductance versus the mole ratio of [AZT]/[M2+], Job’s method of continuous variation and mole ratio method showed the stoichiometry to be 1:1 (M2+:AZT) for both the cations. The metal ion-AZT complexes formed through the nitrogen of the azide group were further ascertained by liquid chromatography-mass spectrometric analysis. The formation constants of the complexes as evaluated by the conductance method and the Rose-Drago method were in good agreement. The values of thermodynamic parameters (∆H and ∆S) for the formation of complexes were obtained from the Van’t Hoff plots. The results revealed that both the complexation reactions were spontaneous, endothermic and entropy stabilized.

Formation constant (Kf) values of Schiff base ligand, L = methyl-2-{[1-methyl-2-(aceton)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate, with Co(II), Ni(II), Cu(II) and Zn(II) ions has been determined spectrophotometrically for 1:1 complex formation at constant ionic strength 0.01 M (NaClO4), and at various temperatures in DMF solvent. Thermodynamic studies of the complexes have been carried out and their stability were found in the order CoL > CuL > NiL > ZnL. The enthalpy, entropy and Gibbs free energy changes of the complexation reaction have been evaluated from the temperature dependence of the formation constant. Our experimental results revealed that the complexation process is spontaneous, exothermic and entropically unfavorable. Also, B3LYP/(LANL2DZ and 6-311G٭٭) level density functional theory is applied on the structure and stability of Schiff base ligand and their complexes. HOMO-LUMO and binding energies were calculated to obtained stability of the complexes. The theoretical results are compared with experimental data.

The nano-silicon tetrachloride was prepared by an effective and environmentally friendly ball milling technique. The protonation constants of 2-oxo-N-(pyridine-2-yl)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)acetamide (H2L) and the stability constants of its nano silicon complexes were estimated by the potentiometric technique at different temperatures 298, 308 & 318°K. [ABSTRACT FROM AUTHOR]

A silver selective electrode based on TEPQA‐MCM‐41 material was developed and used for the selective determination of Ag+ ion in various samples. The effect of various plasticizers i. e. dimethyl phthalate (DMP), Tris(ethylhexyl)phosphate (TEP), bis‐(2‐ethylhexyl)sebacate (BEHS), bis‐(2‐ethylhexyl)adipate (BEHA) was investigated. The electrode of the composition of 2 : 1 : 77 : 12 : 8 (w/w, %) of TEPQA‐MCM‐41 : NaTPB : Graphite powder : paraffin oil : DMP respectively, works satisfactorily in a wide concentration range of 1.3×10−9 M–1.0×10−1 M for Ag+ ion with a lower detection limit (LOD) of 1.0×10−9 M and has Nernstian slope of 63.4± 1 mV/decay. The electrode can be used in a pH range of 2.3 to 6.7 for a period of 3 months without any divergence in potential response. The selectivity coefficient calculated by fixed interference method indicates the high selectivity of the electrode towards Ag+ ion over other tested cations. [ABSTRACT FROM AUTHOR]

There is a growing interest for aromatic and biological properties of essential oils as alternatives to synthetic chemicals and drugs. However, essential oils and their components are poorly soluble in aqueous systems and are highly sensitive to degradation and evaporation. These drawbacks can be overcome by encapsulation into cyclodextrins, which are non-toxic cyclic oligosaccharides obtained from the enzymatic degradation of starch. Cyclodextrins inclusion complexes offer solutions to many limitations of the use of essential oils in the food, pharmaceutical and cosmetic industries. This article reviews essential oils encapsulation in cyclodextrins. The strength of binding between cyclodextrins and essential oils components covers a wide range of formation constants with values ranging from 13 to 166,338 M−1. The encapsulation in cyclodextrins can increase the aqueous solubility of essential oils up to 16-fold and reduce their photodegradation rates up to 44-fold, while ensuring a gradual release. We also discuss the effect of encapsulation on biological activities, such as antimicrobial and antioxidant properties of essential oils. Finally, we present novel cyclodextrin-based approaches in the sectors of textiles and nanofibres. [ABSTRACT FROM AUTHOR]

Headspace technology is a sampling method of a gas, which has been previously in contact with a liquid or a solid matrix from which volatiles were released into the gaseous phase. It is generally coupled to a subsequent gas chromatography analysis. The headspace analysis can be carried out either as a one-step extraction (static or equilibrium headspace) or as a continuous extraction (dynamic headspace). The static headspace gas chromatography (SH-GC) is gaining an increasing interest for the study of cyclodextrin (CD) inclusion complexes with volatile compounds. CDs are natural supermolecular hosts able to encapsulate volatile compounds and improve their functionalities (e.g. solubility, stability, retention, controlled release). Herein, the application of the SH-GC in the CD field will be reviewed. This paper will focus on the characterization of the inclusion complexes via the SH-GC, mainly aiming at the determination of formation constant (Kf) and encapsulation efficiency (EE%) values. Moreover, it will review the application of the SH-GC to monitor the properties of volatile compounds upon encapsulation (e.g. retention, controlled release). [ABSTRACT FROM AUTHOR]

Carvacrol and thymol have been widely studied for their ability to control food spoilage and to extend shelf-life of food products due to their antimicrobial and antioxidant activities. However, they suffer from poor aqueous solubility and pronounced flavoring ability that limit their application in food systems. These drawbacks could be surpassed by encapsulation in cyclodextrins (CDs). Applications of their inclusion complexes with CDs were reported without investigating the inclusion phenomenon in deep. In this study, inclusion complexes were characterized in terms of formation constants (Kf), complexation efficiency (CE), CD:guest molar ratio and increase in bulk formulation by using an UV–visible competitive method, phase solubility studies as well as 1H and DOSY 1H NMR titration experiments. For the first time, a new algorithmic treatment that combines the chemical shifts and diffusion coefficients variations for all guest protons was applied to calculate Kf. The position of the hydroxy group in carvacrol and thymol did not affect the stoichiometry of the inclusion complexes but led to a different binding stability with CDs. 2D ROESY NMR experiments were also performed to prove the encapsulation and illustrate the stable 3D conformation of the inclusion complexes. The structural investigation was accomplished with molecular modeling studies. Finally, the radical scavenging activity of carvacrol and thymol was evaluated by the ABTS radical scavenging assay. An improvement of this activity was observed upon encapsulation. Taken together, these results evidence that the encapsulation in CDs could be valuable for applications of carvacrol and thymol in food.

Complex formation between uranyl ion, UO22+, and a hydrophilic anionic form of SO3-Ph-BTP4- ligand, L4-, in water was studied by liquid-liquid extraction experiments performed over a range of the ligand and HNO3 concentrations in the aqueous phase, at a constant concentration of nitrate anions at 25°C . The competition for UO22+ ions between the lipophilic TODGA extractant and the hydrophilic L4- ligand leads to the decrease in the uranyl distribution ratios, D, with an increasing L4- concentration. The model of the solvent extraction process used accounts - apart from uranyl complexation by TODGA and SO3-Ph-BTP4- - also for uranyl complexation by nitrates and for the decrease in the concentration of the free L4- ligand in the aqueous phase, due to its protonation, bonding in the uranyl complex and the distribution between the two liquid phases. The unusually strong dependence of the D values on the acidity, found in the experiment, could hardly be explained as due to L4- protonation merely. Three hypotheses were experimentally tested, striving to interpret the data in terms of additional extraction to the organic phase of ion associates of protonated TODGA cation with either partly protonated anionic L4- ligands or anionic UO22+ complexes with NO3 - or L4-. None of them has been confirmed. The analysis of the results, based on the formal correction of free ligand concentrations, points to the formation of 1 : 1 and 1 : 2 uranyl - SO3-Ph-BTP complexes in the aqueous phase. The conditional formation constant of the 1:1 complex has been determined, logßL,1 = 2.95 ± 0.15.

The association parameters of both bulk and nano-CuSO4 salts in (EtOH-H2O) mixed solvents were estimated at room temperature (293.15K) using conductivity method by applying Fuoss-Shedlovsky calculation. The association parameters of nano-CuSO4 was greater than bulk CuSO4 salt. The interaction between the cation (Cu2+) with ligand (ciprofloxacin, CFL) in (EtOH-H2O) mixed solvents at room temperature (293.15K) was determined by the conduct metric method. The formation Gibbs free energies change (ΔGf) and transfer Gibbs free energies change (ΔGt) were increased in negative signs with increasing in EtOH content in the binary solvent. Two stoichiometric complexes 1:2 and 1:1 (M:L) are formed and the formation constant and Gibbs free energy of the formed complexes follow the order: Kf (1:1) > Kf (1:2) and ΔGf (1:1) > ΔGf (1:2) for (M:L) (in negative values), which indicate more favorable formation of (1:1) complex compared with (1:2) complex. Also there are a decrease in values of Kf and ΔGf in case of using nano-CuSO4 than that of using bulk-CuSO4 but in small difference due to the more solvation effect in case of using nanoparticles. [ABSTRACT FROM AUTHOR]

Potentiometeric investigation on the complex formation equilibria involving Co(II), Ni(II), Cu(II) & Zn(II) with ethylenediaamine-N,N,N1,N1-tetraacetic acid and melonic acid have been made in solution at three different temps viz. (15±10, 35±10, 45±10C). Important thermodynamic parameters namely, change in Gibb's free energy (ΔG0), change in enthalpy (ΔH0) and change in entropy (DS0) and stability constant have been determined potentiometrically at ionic strength of 0.1 M (KNO3). [ABSTRACT FROM AUTHOR]

Abstract Physicochemical behaviour of n – hexane solutions containing benzyl amine (BA) and alicyclic ethers in the concentration range 0.02M–0.20 M is extensively studied through acoustical (experimental) and Density Functional Theory (DFT) methods and the nature of non-covalent molecular interactions existing in these ternary liquid mixtures have been investigated. Two structurally different ethers, namely, tetrahydrofuran (THF) and 1,4-dioxane (DIOX) are used. Ultrasonic velocity (u) at 2 MHz frequency, density (ρ) and viscosity (η) are measured for the ternary liquid systems at different concentrations andat 303.15 K. The existence of strong BA – ether non-covalent interaction and formation of hydrogen bonded complexes is identified in both the systems through the variations in acoustical and excess thermo-acoustical parameters with concentration. The influence of structure of ether on the strength of molecular interaction has been analysed through the calculation of formation constants of these complexes computed using Kannappan equation. An attempt has been made using meta hybrid density functional theory to confirm the existence of hydrogen bonded complexes in these two systems through the computed interaction energies and hydrogen bonding parameters. Computational investigation shows CH---π dispersive interactions in these complexes in addition to the classical hydrogen bonding. Graphical abstract Image 1 Highlights • Acoustical study was done on ternary systems of benzyl amine and alicyclic ethers. • Formation constants of H- bonded complexes are reported. • DFT study shows CH---π interaction in addition to classical H – bonding. • Interaction parameters are used to assess the strength of various interactions. • The structural dependence of ethers on the stability of complexes is discussed. [ABSTRACT FROM AUTHOR]

The complexation reaction between some heavy metal ions such as: Ag+, Co2+, Hg2+, Zn2+, Ni2+, Cu2+, Cd2+, Mn2+, Cr3+, Fe3+ and Pb2+ with 2,3-dimethyl-1,2-dihydro-8H-pyrazolo[5,1-a]isoindol-8-one, ligand in acetonitrile as nonaqueous solvents at 25 °C were investigated by spectrophotometric and conductometric methods. The formation constants (kf) of the 1:1 (metal ion to ligand) complexes were calculated by computer fitting of the absorbance-mole ratio data, and molar conductance-mole ratio data at 25 °C using the KINFIT program, and found that complexes to vary in acetonitrile solvent in the order of Zn2+> Ag+> Cr3+> Ni2+> Hg2+> Fe3+> Cu2+> Cd2+> Co2+> Mn2+> Pb2+. [ABSTRACT FROM AUTHOR]

Two novel copper(II) Schiff base complexes were synthesized and characterized by various physico-chemical and spectroscopic methods, revealing a distorted square planar geometry around the copper atom. The analytical data confirmed the 1:1 metal to ligand stoichiometry of the complexes. B3LYP/(LANL2DZ/6-311G**) density functional theory (DFT) were used to investigate structural and electronic properties of the synthesized compounds in gas phase. The computational results support the conclusion obtained by the experimental studies. Thermodynamic study of complex formation in solution was carried out spectrophotometrically at 25 °C. These compounds were also subjected to study in vitro antibacterial screening against some bacteria. Also, click reaction was investigated for its catalytic properties. The synthesized Schiff base copper complexes catalyzed 1,3-dipolar Huisgen cycloaddition of different functionalized β-azido alcohols and alkynes in the presence of ascorbic acid in a solution of THF/H2O (2:1, V/V) at room temperature. [ABSTRACT FROM AUTHOR]

The charge transfer complex of benzhydryl piperazine as donor with the π-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone has been studied spectrophotometrically in acetonitrile medium at different temperatures. On mixing the donor with acceptor, a reddish brown colored charge transfer complex is formed. Electronic absorption spectra of the complex show charge transfer bands at 587, 546 and 457 nm. The molecular composition of the complex was studied by applying Job’s continuous variation and spectrophotometric titration methods. These results support the formation of the complex in a 1:2 ratio. The Benesi-Hildebrand equation has been applied to compute the formation constant and molecular extinction coefficient. Thermodynamic parameters of the charge transfer complexation reaction (standard entropy, standard enthalpy and standard Gibbs free energy) have been calculated. The results of the spectrophotometric study demonstrated that the charge transfer complex formation is endothermic. The computational studies of the charge transfer complex were performed by using the Gaussian 09 W package of programs. The bond lengths, bond angles, dihedral angles, Mulliken atomic charges, molecular electrostatic potential maps and characterization of the highest occupied molecular orbital and lowest unoccupied molecular orbital surfaces of charge transfer complex were computed. [ABSTRACT FROM AUTHOR]

Abstract: Bicinchoninic acid (BCA) is widely used for determining the valence state of copper in biological systems and quantification of the total protein concentration (BCA assay). Despite its well‐known high selectivity of Cu(I) over Cu(II), the exact formation constants for Cu(I)(BCA)23− and Cu(II)(BCA)22− complexes remain uncertain. These uncertainties, affect the correct interpretations of the roles of copper in biological processes and the BCA assay data. By studying the voltammetric behaviors of Cu(I)(BCA)23− and Cu(II)(BCA)22−, we demonstrate that the apparent lack of redox reaction reversibility is caused by an adsorption wave of Cu(II)(BCA)22−. With the adsorption wave identified, we found that the Cu(I)/Cu(II) selectivity of BCA is essentially identical to another popular ligand, bathocuproinedisulfonic acid (BCS). Density functional theory calculation on the geometries of Cu(I)(BCA)23− and Cu(II)(BCA)22− rationalizes the preferential Cu(I) binding by BCA and the strong adsorption of the Cu(II)(BCA)22− complex at the glassy carbon electrode. Based on the shift in the standard reduction potential of free Cu(II)/Cu(I) upon binding to BCA, we affirm that the formation constants for Cu(I)(BCA)23− and Cu(II)(BCA)22− are 1017.2 and 108.9, respectively. Therefore, BCA can be chosen among various ligands for effective and reliable studies of the copper binding affinities of different biomolecules. [ABSTRACT FROM AUTHOR]

The core of aluminium electrolytic capacitors anode foil is the pit distribution of etched foils and the specific capacitance of formed foils, there is still no well-developed system to evaluate both at once. In this study, a pit anodizing model and a method to simulate the CV value of high-voltage etched aluminium foil is proposed. The model processes scanning electron microscopy photographs of high-voltage etched aluminium foils, models the growth of alumina in the 200–600 V ranges, takes into account the pit clogging phenomenon of the anodic oxidation process by image processing, corrects and specifies the formation constants and dielectric constants of alumina at different formation voltages. The model can reflect the growth pattern of alumina in the standard process. With the model proposed in this work, the CV values of aluminium foils at each formation voltage are simulated. The simulated results have a mean deviation of 1.4% from the actual experimental values, which can accurately simulate the real performance of the etched foil. This simulation method can evaluate the performance of aluminium foil after anodizing by considering both the pit distribution and the anodizing environment. It can also be used to compare the applicable working voltage ranges of different etched foils. This can help factories and laboratories with etching foil selection, greatly reducing material and time consumption. [Display omitted] [ABSTRACT FROM AUTHOR]

We have carried out thermodynamic study on the ion-selective electrode for Al(III) ions based on (1E,2E) N1,N2-dihydroxy N1,N2 bis (4-hydroxyphenyl) oxalimidamide that was previously prepared by our team. In the recent work, the electrolyte behavior was studied in the mixed solvents such as “water–ethanol” and “water–dioxane”. The electrode exhibited a good response at the temperature range of 20–50 °C. The Nernstian slope of the electrode was 19.2 ± 0.6 mV per decade. In addition the standard electrode potentials were determined at different temperatures and the results were used to calculate the temperature coefficient of the cell and the other thermodynamic functions. The temperature coefficients of the cell and the electrode are 9.99 × 10−4 V/°C and 3.93 × 10−4 V/°C respectively. The formation constant of the ionophore – Al(III) complex was calculated at 25 °C (logKf = 6.1 ± 1.1).

The complexation abilities of five cyclodextrins (CDs) with seven phenylpropanoids (PPs) were evaluated by UV–visible spectroscopy, phase solubility studies and molecular modeling. Formation constants (Kf), complexation efficiency (CE), PP:CD molar ratio, increase in formulation bulk and complexation energy were assessed. All complexes exhibited a 1:1 stoichiometry but their stability was influenced by the nature and the position of the phenyl ring substituents. A relationship between the intrinsic solubility of guests (S0) and the solubilizing potential of CD was proposed. Molecular modeling was used to investigate the complementarities between host and guest. Finally, the antioxidant activity of encapsulated PPs was evaluated by scavenging of the stable DPPH radical.

A new ligand (L), N,N′-bis(2-hydroxybenzyl)-1,2-diaminoethane, was synthesized and characterized. The sensing behavior of L toward various metal ions was investigated by spectrofluorometric and UV-Vis spectrophotometric methods. The sensor displayed selective and sensitive recognition toward Fe and Fe in acetonitrile. The fluorescence of L was quenched mainly by Fe, and a considerable enhancement of fluorescence was observed in the presence of Zn. Using multivariate hard modeling and stoichiometry, the concentration, spectral profiles, and formation constants of the studied complexes were calculated. [ABSTRACT FROM AUTHOR]