Thermodynamic parameters of the formation of deprotonated single-ligand complexes in the Cu(II)−triglycine system in aqueous solutions

Heat effects arising from interactions between triglycine solutions and Cu(NO₃)₂ solutions are studied at 298.15 K and ionic strengths of 0.2 to 1.0 (KNO₃) via isothermal calorimetry. Using experimental data, enthalpies of formation are calculated for species CuH_?1L, CuH_?2L^?, and CuH_?3L^2?, along with Δ_rH°, Δ_rG°, and Δ_rS° of the complexation process. A relationship is revealed between the structures of deprotonated single-ligand triglycine complexes of Cu(II) and the thermodynamic parameters of their formation.     

NMR and luminescence spectroscopy study of the formation of mixed europium β-diketonate complexes with trifluoroacetic acid in nonaqueous solutions

The ligand substitution in Eu(AA)₃ · Phen-CDCl₃-TFA systems, where AA is acetylacetone, Phen is 1,10-phenanthroline, and TFA is trifluoroacetic acid was studied at various molar ratios (m) of competing ligands (m = TFA/AA) using NMR (¹H, ¹⁹F) and luminescence spectroscopy. The formation of mixed Eu(AA)₂(TFA) · Phen and Eu(AA)(TFA)₂ · Phen complexes in the resultant solutions was attested. The luminescence spectra were studied. The competitive capacity of TFA was ascertained to be higher than that of AA. Depending on the m value, the substitution of acido ligands was shown to occur successively according equations Eu(AA)₃ · Phen + (TFA) _n = Eu(AA)_{3 − n} (TFA) _n · Phen + (AA) _n (n = 1, 2, 3).     

Transformations of ortho-quinones in the γ-radiolysis of their solutions in cyclohexane

The transformations of 4-tert-butyl-1,2-benzoquinone (I), 3,5-di-tert-butyl-1,2-benzoquinone (II), and 4-methoxy-5-tert-butyl-1,2-benzoquinone (III) in deaerated cyclohexane solutions under exposure to γ-radiation were studied. It was found by chromatography-mass spectrometry and ¹H and ¹³C NMR spectroscopy that the addition of cyclohexyl radicals at the C=O bond in compounds I–III resulted in monoalkyl ethers, whereas cyclic ketal XXI was also formed in the case of compound II. Moreover, quinone I afforded mixed O-and C-alkylation products, and the adduct of cyclohexyl radicals and quinone II at the C=C bond was the source of dimeric products.     

Photoproduction and determination of hydroxyl radicals in aqueous solutions of Fe(III)–tartrate complexes: a quantitative assessment

Benzene has been used as a probe to determine the photogeneration of ^·OH radicals in aqueous solutions containing Fe(III) and tartrate (Tar) when they are irradiated (λ?≥?313?nm, 250?W). Products were determined by HPLC. Results show that tartrate has a positive effect on the photogeneration of ^·OH. The influence of pH, temperature, and concentrations of Fe(III) and Tar were systematically investigated. Production of ^·OH radicals was greatest at pH 3.0. Concentrations of ^·OH increased with increasing Fe(III) and tartrate concentrations, but at a certain ratio they decreased. The quantum yield of ^·OH radicals at 328?K was nearly twice that at 298?K.     

Luminescence determination of praseodymium in solutions of its β-diketonates

With the aim of a search for new analytical forms for the determination of praseodymium(III), its 4f luminescence was studied in solutions of mixed-ligand complexes with fluorinated β-diketones and donoractive ligands (1,10-phenanthroline, neocuproine, diantipyrylmethane, diantipyrylpropylmethane, and trioctylphosphine oxide). It was found that the luminescence intensity of praseodymium(III) depends on both the character of the fluoroalkyl substituent in the β-diketone molecule and the nature of the second ligand. The complex of praseodymium(III) with thenoyltrifluoroacetone and diantipyrylpropylmethane was used for the determination of praseodymium in some optical materials. The lower determination limit of praseodymium was 0.01 μg/mL.     

Thermodynamics of the formation of Sm3+-ethylenediamine-N,N′-disuccinic acid complexes in aqueous solutions at 298.15 K

The thermodynamic parameters of the formation of the complexes of ethylenediamine-N,N′-disuccinic acid (H₄Y) with Sm³⁺ ion are determined by means of calorimetry and measuring pH at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO₃). The values of logK, Δ _r G, Δ _r H, and Δ _r S are calculated for the formation of SmY^? and SmHY complexes at fixed and zero values of ionic strength. The resulting values are interpreted.     

Thiourea complexes in synthesis of Cd1 ? xZnxS solid solutions

Solid solutions of the CdS-ZnS system deposited as polycrystalline films by aerosol pyrolysis from aqueous solutions of cadmium and zinc thiourea complexes have been studied. The phase composition and solid-phase solubility are dictated by the nature of initial complexes. From solutions of [M(thio)₂(CH₃COO)₂] complexes, sphalerite sulfides are precipitated, which form a continuous solid solution s-Cd_1−x Zn _x S, whereas the use of the [M(thio)₂Cl₂] precursor leads to crystallization of the wurtzite w-Cd_1−x Zn _x S solid solution based on CdS (the homogeneity range 0–20 mol % ZnS) and the s-Cd_1−x Zn _x S solid solution based on zinc sulfide (50–100 mol % ZnS). The structure of the solid phase in the sulfide system is attributed to the specific features of the stereochemistry of complex precursors.     

Structure of hydrated complexes formed by metal ions of Groups I—III of the Periodic Table in aqueous electrolyte solutions under ambient conditions

Published and authors" experimental data on the structures of aqueous electrolyte solutions under ambient conditions are considered. The hydrated metal complexes formed in aqueous solutions are described systematically depending on the size of the cation, the charge, and the structure of the outer electron shell.     

Kinetics and mechanism of oxidation of some nickel(II)–imine–oxime complexes by peroxodisulfate in aqueous acidic solutions

The kinetics of the oxidation of [Ni(II)(H₂L¹)](ClO₄)₂, (H₂L¹ = 3,8-dimethyl-4,7-diaza-3,7-decadiene-2,9-dione dioxime) and [Ni(II)(HL²)]ClO₄, (H₂L² = 3,9-dimethyl-4,8-diaza-3,8-undecadiene-2,10-dione dioxime) by peroxodisulfate anion (PDS) in aqueous media at 298.0 K have been studied. The kinetics of oxidation of both Ni(II) complexes was found to be first order in the complex concentration. The dependence of the pseudo-first-order rate constant, k _obs, for both complexes showed first-order dependence on PDS concentration. The kinetics of oxidation of [Ni(II)(H₂L¹)]²⁺ complex showed a complex dependence on [H⁺] over the pH range of 4.98–7.50, whereas that of [Ni(II)(HL²)]⁺ is independent of pH over the pH range of 5.02–7.76. The value of k _obs, for both complexes, decreased with increasing ionic strength consistent with the involvement of oppositely charged ions in the rate-determining step. The effect of ionic strength is more pronounced for [Ni(II)(H₂L¹)]²⁺–PDS reaction than for [Ni(II)(HL²)]⁺–PDS reaction, confirming the higher charges of the latter.     

Long-lived phosphorescence of aqueous solutions of β-cyclodextrin complexes with naphthalene and its derivatives at room temperature

A long-lived phosphorescence at room temperature (lifetime>1 s) of aqueous solutions of β-cyclodextrin complexes with naphthalene and its derivatives was found. The phosphorescence isobserved for aggregated complexes that form in water a light-scattering suspension, and its low intensity is due to predomination of 2∶2 complexes with efficient excimer fluorescence. Complexes containing isolated aromatic molecules are assumed to be the centers of fluorescence. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2022–2024, October, 1999.     

Formation of chitosan—surfactant complexes in aqueous-alcohol media

Russian Chemical Bulletin - The complexation of chitosan and anionic surfactant, sodium dodecyl sulfate (DDS), in aqueous-alcohol media with a variable content of an organic cosolvent (methanol,...     

Structure and catalytic activity of α-chymotrypsin in solutions of gemini surfactants

The regulatory effect of gemini alkylammonium surfactants (GSurf) with the hexamethylene spacer varying in the length of alkyl radicals on the structure and catalytic activity of a-chymotrypsin was studied. A correlation between the activity of a-chymotrypsin and the length of the alkyl radical of GSurf was found. Gemini surfactants enhance the enzyme activity below the critical micelle concentration (CMC) and inhibit that above the CMC. The results of IR spectroscopy and the data on tryptophan fluorescence show that the interaction of GSurf with a-chymotrypsin induces changes in the protein structure differed in intensity. The most probable enzyme complexes with GSurf were characterized by the molecular docking method.     

The role of π electrons in the formation of benzene-containing lithium-bonded complexes

The intermolecular interactions in C₆H₆???LiX (X=OH, NH₂, F, Cl, Br, NC, CN) complexes are investigated by using second‐order Møller–Plesset perturbation theory (MP2) calculations and quantum theory of “atoms in molecules” (QTAIM) studies, and the role of π electrons is studied in the formation of these benzene‐containing lithium‐bonded complexes. The molecular electrostatic potentials of benzene and LiX determine the geometries of the lithium‐bonded complexes. The electron densities at the lithium bond critical points in the πC₆H₆???LiX complexes are obviously stronger than those in the σC₆H₆???LiX complexes, which indicates that the intermolecular interactions in the C₆H₆???LiX complexes are mainly attributable to π‐type interaction. The topological and energy properties at the lithium bond critical points in both the C₆H₆???LiX and πC₆H₆???LiX complexes are linear with the interaction energies, thereby showing the crucial role of the π electrons in the formation of these complexes. Electron localization function (ELF) analysis indicates that the formation of the lithium bonds leads to the reduction of the ELF π‐electron density and volume, and the reduction of the π‐electron volume is linear with the interaction energies with the correction coefficient 0.9949.     

Thermodynamics of oxygen solutions in titanium-containing Fe–Co melts

Performed for the first time, the thermodynamic analysis of oxygen solutions in titanium-containing Fe–Co melts showed that the deoxidizing power of titanium with increasing cobalt content of the melt first decreases, reaches a minimum at a cobalt content of 20%, and then increases. The titanium contents [%Ti]* at equilibrium points between the oxide phases TiO₂, Ti₃O₅, and Ti₂O₃ were determined. The curves of the oxygen solubility in titanium-containing iron–cobalt melts pass through a minimum, which shifts toward lower titanium contents with increasing cobalt content of the melt. Further alloying with titanium leads to an increase in the oxygen concentration of the melt so that the higher cobalt content of the melt, the steeper the increase in the oxygen content after the minimum as titanium is added to the melt.     

Persistent π-arene interactions in bulky formamidinate complexes of potassium

The reaction of potassium hexamethyldisilazide (K-HMDS) with 1 equiv. of the bulky formamidine N(Diep)C(H)NH(Diep) (DiepFormH, Diep = 2,6-Et₂C₆H₃) in THF yields the half deprotonated compound [K(DiepForm)(DiepFormH)] (1), which exhibits suppressed reactivity with the hexamethyldisilazide anion. Reaction of 1 with n-BuLi gives the polymer [{Li(THF)₂K(DiepForm)₂}_n] (2). Preparation of 1 in the presence of the chelating solvents 1,2-dimethoxyethane (DME) or N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) gives the fully deprotonated species [{K₃(DiepForm)₃(DME)₃}_n] (3) and [{K(PMDETA)K(DiepForm)₂}_n] (6). The syntheses of compounds 1-3, 6 and related compounds, e.g. [{K₃{N(Dimp)C(H)N(Dimp)}₃(DME)₃}_n] (4) (Dimp = 2,6-Me₂C₆H₃), are described.     

Inclusion complexes ofγ-cyclodextrin with coronene in aqueous methanol

Coronene has been found to form an inclusion complex with -cyclodextrin (-CD) in methanol-H₂O (6:4 v/v). The inclusion complex, which has a 2 : 1 stoichiometry of -CD to coronene, tends to bind methanol. Upon addition of 1-adamantanol or adamantane to a solution of -CD and coronene, the absorption spectrum of coronene underwent changes in a manner similar to that observed when the -CD concentration was increased in a coronene solution, indicating the formation of a ternary complex composed of -CD, coronene, and 1-adamantanol or adamantane. The complex-forming equilibrium was investigated on the basis of fluorescence measurements.     

Density and viscosity of α-amino acids in aqueous solutions of cetyltrimethylammonium bromide

The densities and viscosities of aqueous solution of cetyltrimethylammonium bromide (0.01 mol kg⁻¹) (CTAB) and solutions of CTAB containing amino acids, viz., glycine, l-serine, and l-valine (0.01–0.05 mol kg⁻¹), were determined in the temperature range 298.15—313.15 K. Apparent molar volumes of the amino acids were calculated from the density and viscosity values. The calculated apparent molar volumes were used to calculate standard partial molar volumes (-V ₂⁰) and standard partial molar volumes of transfer of amino acids from water to an aqueous solution of CTAB. The viscosity values were used for the calculation of the viscosity coefficients A and B in the Jones—Dole equation. The linear dependences of -V ₂⁰ and B on the number of carbon atoms in the alkyl chains of the amino acids were found. The results obtained were used in analysis of hydrophilic-hydrophilic, hydrophilic-hydrophobic, and hydrophobic-hydrophobic interactions that occur during dissolution of amino acids in an aqueous solution of CTAB.     

Spectrochemistry of solutions—XVIII. Infrared spectroscopy of solutions of electrolytes in liquid ammonia: A new pressure cell and its use in the quantitative determination of thiocyanate

A cell and solution handling system is described which enables i.r. spectra to be obtained for solutions in liquid ammonia, or other condensed gases, at pressures in excess of atmospheric at ambient temperature. Its use, together with a ratio-recording spectrometer, in obtaining quantitative spectroscopic data from dilute solutions of sodium thiocyanate in liquid ammonia by computer subtractions of solution and solvent spectra is illustrated. The applicability of the procedure to high quality determinations of the concentrations of dissolved solutes is demonstrated.     

Selective colorimetric sensing of cysteine in aqueous solutions using silver nanoparticles in the presence of Cr³+

We here in report an extensive study on the development of a highly facile, selective and sensitive colorimetric probe for cysteine detection using silver nanoparticles (Ag NPs). The efficacy of the process relies upon the surface plasmon resonance properties of Ag NPs and the interaction of Ag-cysteine complex with chromium ions (Cr³⁺) in a ratio of 2:1. In the presence of Cr³⁺, cysteine was able to induce the aggregation of Ag NPs thereby resulting in a change in yellow colour of the Ag colloid to purple. The reported probe has a limit of detection down to 1 nM which is to the best of our knowledge the lowest ever reported for the colorimetric detection of cysteine. Furthermore, a remarkable feature of this method is that it involves a simple technique exhibiting high selectivity to cysteine over other tested amino acids.