Adsorption of trace thorium(IV) from aqueous solution by mono-modified β-cyclodextrin polyrotaxane using response surface methodology (RSM)

The adsorption of thorium(IV) was studied using a novel supramolecular polyrotaxane based on β-cyclodextrin derivatives. The effects of pH, contact time, Th(IV) initial concentration and adsorbents dosage on the adsorption of thorium(IV) by polyrotaxane were optimized using Box–Behnken design of response surface methodology. Analysis of variance and correlation coefficients showed that the predicted model was consistent with the experimental data well. The adsorption best fitted to the Langmuir model indicated that the adsorption process happened on homogeneous surface. The thermodynamic parameters (?G ⁰ < 0, ?H ⁰ > 0, ?S ⁰ > 0) demonstrated that the adsorption of Th(IV) ions onto polyrotaxane was spontaneous and endothermic.     

Planar or nonplanar: what is the structure of urea in aqueous solution?

A combined quantum chemical statistical mechanical method has been used to study the solvation of urea in water, with emphasis on the structure of urea. The model system consists of three parts: a Hartree-Fock quantum chemical core, 99 water molecules described with a polarizable force-field, and a dielectric continuum. A free-energy profile along the transition of urea from planar to a nonplanar structure is calculated. This mode in aqueous solution is found to be floppy. That is, the structure of urea in water is not well-defined because the planar to nonplanar transition requires an energy of the order of the thermal energy at room temperature. We discuss the implications of this finding for simulation studies of urea in polar environments like water and proteins.     

Interaction studies of styrene—ethylene oxide block copolymers with ionic surfactants in aqueous solution

The interaction of styrene—ethylene oxide block copolymers with four anionic surfactants (sodium dodecyl sulfate, sodium dodecanoate, sodium dodecylbenzenesulfonate, and sodium dodecanoyl sarcosinate), and two cationic surfactants (tetradecyl- and hexadecyl-trimethylammonium bromide), was studied and each surfactant showed a distinct interaction with the copolymer in aqueous solution. Usually two transitions, one below and one above the critical micelle concentration, CMC, of the surfactants, were observed from conductance, surface tension, and dye solubilization measurements. These transitions indicate the beginning and completion of polymer—surfactant interaction. The viscometric results showed the formation of a polyelectrolyte complex. The interaction between copolymer and sodium dodecyl sulfate was also examined by ¹H NMR. The influence of the molecular characteristics of the block copolymers, the nature and type of surfactants, temperature and added salt on the interaction is described. A possible mechanism for such an interaction is proposed.     

Adsorption of thorium(IV) from aqueous solutions by poly(cyclotriphosphazene-co-4,4′-diaminodiphenyl ether) microspheres

Journal of Radioanalytical and Nuclear Chemistry - Poly(cyclotriphosphazene-co-4,4′-diaminodiphenyl ether) microspheres (PZA) was based on hexachlorocyclotriphosphazene (HCCP) and...     

Complexation of β-cyclodextrin with carborane derivatives in aqueous solution

β-Cyclodextrin formed the most robust complexes with o-carboranols 1b and 1c in aqueous solution, and the association constants estimated from NMR titration studies indicated K_a >1 × 10⁶ M⁻¹ and K_a = 6 × 10⁵ M⁻¹, respectively.     

Liquid–liquid extraction of thorium(IV) with N-n-heptylaniline from acid media

The extraction behavior of thorium(IV) from sulphuric acid medium with N-n-heptylaniline in xylene. Various parameters like reagent concentration, acid concentration, equilibration time, diverse ions and effect of diluents were studied. Thorium(IV) was selectively extracted and separated from many metal ions. The nature of the extracted species was determined. Thorium(IV) was analyzed from monazite ore and gas mantle.

     

Study of complexation of gliclazide with β-cyclodextrin in solution by nmr techniques

The study of complexation between GL and -CD in liquid medium has been carried out by phase-solubility,¹H and¹³C NMR studies. A formation complex is observed from the phase solubility diagram, being the average association constant of 1094 M^–1, The NMR studies revealed the preferent complexation of the aliphatic moiety of GL. The aromatic moiety is also entrapped, but in minor extent, by the CD molecules.     

What drives the precipitation of long-chain calcium carboxylates (soaps) in aqueous solution?

The interaction of sodium octanoate, decanoate or dodecanoate with calcium(ii) in aqueous solutions has been studied using turbidity, conductivity and potentiometric measurements. These show a marked alkyl chain length dependence on the behaviour. At the calcium concentration used (1.0 mM), there is little interaction with the octanoate, the decanoate shows initially formation of a 1:1 complex, followed by precipitation, while the dodecanoate precipitates at low surfactant concentrations. The solid calcium carboxylates were prepared, and show lamellar, bilayer structures with planes of calcium(II) ions coordinated to carboxylate groups through bidentate chelate linkages. Thermogravimetry and elemental analyses indicate the presence of coordinated water with the calcium decanoate but not with longer chain carboxylates. The results of both the solution and solid state studies suggest that precipitation of long-chain carboxylates depends on a balance between hydration effects and hydrophobic (largely van der Waals') interactions. Electrostatic effects make little energetic contribution but play the important structural role of ordering the carboxylate anions before precipitation. Differences are observed in the interactions between calcium(II) and long chain alkylcarboxylates and alkylsulfates, and are interpreted in terms of stronger binding to the metal of the carboxylate group. A general mechanism is proposed for calcium carboxylate precipitation from aqueous solution based on this and previous studies.     

Anation reactions involving bidentate ligands—II: The effect of nitrate ion on the kinetics of the reaction between oxalate and diaquatetraamminecobalt(III) ion in aqueous solution

The title anation reaction was studied at 73.4°C in the presence of added nitrate ion. The nitrate ion accelerated the reaction by an amount which was dependent on the pH of the solution. This is interpreted in terms of the effect of nitrate ion on ion-pair formation.     

The effect of σ-donation on the interactions of cis-diaqua(2-aminomethylpiperidine)platinum(II) complex with biomolecules in aqueous medium: synthesis,kinetic and mechanistic study

The kinetics of the interaction of dl-penicillamine with cis-[Pt(pipen)(OH₂)₂]²⁺ (pipen = 2-aminomethylpiperidine) have been investigated under pseudo-first-order conditions as a function of concentration and temperature at pH 4.0 in aqueous solution of 0.10 M NaClO₄ using UV–Vis spectrophotometry. The kinetic study has been supported by isolation and characterization of the product by IR and ESI–MS spectroscopic analysis. Thermodynamic and kinetic parameters for the reaction have been evaluated. The DNA-binding properties, pKa values and substitution rates of such complexes can be tuned through the σ-donation properties of the spectator ligand, which leads to potential applications in cancer therapy.     

Molecular recognition studies on supramolecular systems (XXIV)——Conformations and complexation abilities of chemically modified cyclodextrins in aqueous solution

Circular dichroism spectral and fluorescence decay methods have been employed to determine the conformations of mono[6-(p-tolylseleno)-6-deoxy]-p-CD(1), mono(6-anilino-6-deoxy) β -CD (2) and mono[6-(L-tryptophan)-6-deoxy]-β-CD (3) in phosphate buffer solution (pH 7.2, 0.1 mol dm-3) at 298.15 K. The results indicate that compounds 2 and 3 formed self-inclusion complexes in aqueous buffer solution, while the substituent of compound 1 was not included into cyclodextrin cavity at all. Furthermore, the complex stability constant (logKs) and Gibbs free energy change (-ΔG° ) of these three cylcodextrin derivatives with several cycloalkanols have been determined by circular dichroism spectral titration in phosphate buffer solution at 298.15 K. It is found that the location of the substituent affects the stability of host-guest complex in aqueous solution.     

Interactions of some α-l-glutamic acid oligomers and polymers with Cu(II) in aqueous solution

The interactions between copper ions and various α-l-glutamic polyacids (DP 6,27,50,300) has been studied, in aqueous solution with an external salt NaClO₄ 0.1 M at 25°C. Both measurements of pH and pCu allow, according to Bjerrum's and Marinsky's methods, the display of MA and MA₂ species and the calculation of their formation constants. These last are depending on the DP and, concerning DP 300, the formation constants vary with the respective metallic and polyacid concentrations. The formation of polynuclear species has been demonstrated for this DP only.     

Degradation of trichloroethylene in aqueous solution by persulfate activated with Fe(III)–EDDS complex

In this study, an environmentally friendly complexing agent, S,S′-ethylenediamine-N,N′-disuccinic acid (EDDS), was applied in Fe(III)-mediated activation of persulfate (PS), and the degradation performance of trichloroethylene (TCE) was investigated. The effects of PS concentration, Fe(III)/EDDS molar ratio, and inorganic anions on TCE degradation were evaluated, and the generated reactive oxygen species responsible for TCE removal were identified. The results showed that nearly complete TCE degradation was achieved with PS of 15.0 mM and a molar ratio of Fe(III)/EDDS of 4:1. An increase in PS concentration or Fe(III)/EDDS molar ratio to a certain value resulted in enhanced TCE degradation. All of the anions (Cl^?, HCO₃ ^?, SO₄ ^2?, and NO ₃ ^? ) at tested concentrations had negative effects on TCE removal. In addition, investigations using radical probe compounds and radical scavengers revealed that sulfate radicals (SO ₄ ^·? ), hydroxyl radicals (^·OH), and superoxide radical anions (O ₂ ^·? ) were all generated in the Fe(III)–EDDS/PS system, and ^·OH was the primary radical responsible for TCE degradation. In conclusion, the Fe(III)–EDDS-activated PS process is a promising technique for TCE-contaminated groundwater remediation.     

Complex formation of hexakis(2,6-di-O-methyl)-α-cyclodextrin with substituted benzenes in aqueous solution

The host-guest interaction of hexakis(2,6-di-O-methyl)--cyclodextrin (DM--CDx) with substituted benzenes in aqueous solution has been investigated by circular dichroism spectra. From the resemblance of the spectra, it is concluded that the guest molecules are included in the DM--CDx ring in a manner similar to that of corresponding -cyclodextrin complexes. Thermodynamic parameters of the complex formation were determined on the basis of the temperature dependent intensity change of the spectra. In spite of the considerable variation in H and AS values, the free energy does not change much among complexes because of the strong compensation effect. The compensation temperature was 309 ± 11K. Negative values of H and S, suggesting that the complex formation is not governed by the hydrophobic interaction, can be interpreted in terms of the tight binding of the guest molecule within the host cavity.     

Complexation of the antibiotic daunomycin with desoxytetraribonucleoside triphosphate 5’-d(CpGpCpG) in aqueous solution

This paper presents the results of our study of the complexation of the antibiotic daunomycin with desoxytetranucleotide 5’-d(CpGpCpG) in aqueous salt solution by one- and two-dimensional (2D-TOCSY and 2D-NOESY)¹H NMR spectroscopy (500 MHz). The concentration and temperature dependences of the proton chemical shifts of molecules were measured and used to calculate the equilibrium reaction constants, the relative contents of different types of complex as functions of concentration and temperature, the limiting values of the proton chemical shifts of daunomycin in various complexes, and the thermodynamic parameters of complexation δH and δS. It is concluded that the triplet nucleotide sequences are the preferable sites at which daunomycin is attached. The binding of the second daunomycin molecule to both single-stranded and duplex forms of tetramer is markedly anticooperative. This is explained by the presence in the antibiotic of a positively charged amino sugar residue creating steric hindrances for the attachment of the second antibiotic molecule to the short tetranucleotide sequence. The most plausible spatial structure of the 1:2 complex of antibiotic with desoxytetranucleotide is constructed using the calculated values of the induced proton chemical shifts of daunomycin and 2D-NOE data. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 276–286, March–April, 1999.     

Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the salicylato(2–) type: Syntheses and structural characterization in the solid state and in solution

Reaction of tetramethoxysilane or tetramethoxygermane with salicylic acid and morpholine (molar ratio 1:3:2) in tetrahydrofuran yielded morpholiniummer-tris[salicylato(2–)-O¹,O³]silicate(mer -5) and morpholiniummer-tris[salicylato(2–)-O¹,O³]germanate (mer-8), respectively. Treatment of tetramethoxysilane with 5-chlorosalicylic acid and piperidine (molar ratio 1:3:2) in tetrahydrofuran afforded piperidinium mer-tris[5-chlorosalicylato(2–)-O¹,O³]silicate–ditetrahydrofuran (mer-6·2THF). Triethylammonium mer-tris[3-methylsalicylato(2–)-O¹,O³]silicate (mer-7) was obtained analogously by reaction of tetramethoxysilane with three molar equivalents of 3-methylsalicylic acid and two molar equivalents of triethylamine in dichloromethane/diethyl ether. The racemic compounds mer-5, mer-6· 2THF,mer-7, and mer-8 were characterized by elemental analyses (C, H, N), single-crystal X-ray diffraction, as well as solid-state (²⁹Si) and solution(¹H, ¹³C, ²⁹Si) NMR studies. The structural characterizationwas complemented by computational studies (HF studies, TZVP level) of thefac- and mer-tris[salicylato(2–)-O¹,O³]silicatedianion. In addition, the behavior of mer-7 in solution was studied by VT ¹HNMR experiments.     

Preparation and characterization of tetrakis (β-ketophosphonato) thorium(IV) complexes

Tetrakis (β-ketosphonato) thorium(IV) complexes have been prepared using a liquid—liquid extraction method. They have been well characterized by i.r., Raman, ¹H, ¹³C and ³¹P NMR spectroscopies. β-ketophosphonates act as anionic chelating ligands and are coordinated by the PO and CO oxygen atoms. An asymmetric repartition of the negative charge on the chelate ring is observed. A stabilities order of the studied β-ketophosphonato-thorium complexes has been established.     

Multinuclear NMR study of lanthanide(Ⅲ)complexes of 1,2-PDTA in aqueous solution

The complexation oflanthanide(Ⅲ) cations with 1,2-propanediaminetetraacetate (1,2-PDTA)in aqueous solution has been investigated by ~(23)Na,~(35)Cl,~2H and ~(17)O NMR shift measurements.It hasbeen shown that the contact shifts are dominant for ~(17)O,~(35)Cl and ~2H (only for the heavier lanthanideseries) and the pseudocontact shifts are dominant for ~(23)Na.It is suggested that the 1,2-PDTA ligandis bound pentadentately via the two nitrogens and the three carboxylates for the lighter lanthanidecomplexes,hexdentately via the two nitrogens and the four carboxylates for the heavier ones.Thenumbers of the water coordinated were determined.The small amount of chloride anion in innercoordination sphere was observed.     

Thermodynamics of interaction of L-α-phenylalanine with urea and dimethylformamide in aqueous solution

The thermal effects of solution of L-phenylalanine in aqueous solutions of urea and dimethylformamide (DMF) at 25°C were determined. The solubility of L-phenylalanine in water and aqueous DMF solutions was measured. The standard enthalpies, free energies, and entropies of solution of the amino acid in aqueous solutions of amides were calculated. The parameters of pair and ternary amino acid-amide interactions were determined within the framework of the McMillan-Mayer theory. The amino acid-amide pair interaction is accompanied by a decrease in the Gibbs free energy, controlled by the entropy term with DMF and by the enthalpy term with urea. The interaction of L-phenylalanine with two amide molecules is repulsive, which in the case of DMF leads to an increase in the standard free energies of solution of the amino acid at the amide mole fraction X ₂ > 0.05.     

Interaction of tris(2,2′-bipyrazine)ruthenium(2+) ion with radiolytically-generated radicals in aqueous solution. Reactivity of Ru(bpz)+3 toward electron relays

The one-electron reduction of Ru(bpz)²⁺₃ by (CH₃)₂ḢOH is rapid (k = 3.5 × 10⁹ M^-1 s^-1) and quantitative. The product of the reaction, which possesses a ligand-radical coordinated to a Ru(II) center, can be written generically as Ru(bpz)⁺₃, and represented as Ru(bpz)₂(^.bpz^-)⁺ in alkaline solution and its conjugate acid [Ru(bpz)₂(^.bpzH)²⁺; pK_a = 7.1] in acidic solution. The reaction of Ru(bpz)²⁺₃ with ^.OH (k = 5.5 × 10⁹ M^-1 s^-1) yields the OH-adduct to the ring system of the ligands; Ru(bpz)₂(^.bpzOH)²⁺ is unstable toward bimolecular decay (k ∼4× 10⁸ M^-1 s^-1). Reaction with H^. (k = 3 × 10⁹ M^-1 s^-1) results in hydrogenation at a ring-carbon; this product is unstable in the time frame of seconds. No reaction is observed between Ru(bpz)²⁺₃ and Cl^-.₂. Ru(bpz)₂(^.bpz^-)⁺ reduces Co(sep)³⁺ (k = 3.3 × 10⁵ M^-1 s^-1) at pH 10, but there is no reaction at pH 4. However, Ru(bpz)₂(^.bpzH)²⁺ establishes an electron-transfer equilibrium (K_eq = 7) with Cr(bpy)³⁺₃ at pH 3.