Enhanced ternary 1:2 host–guest complexation of amino-γ-cyclodextrins with 2-anthracenecarboxylic acid

The complexation behavior of 6-amino-6-deoxy-γ-cyclodextrin (CD), 6^A,6^X-diamino-6^A,6^X-deoxy-γ-CDs and 3^A-amino-3^A-deoxy-altro-γ-CD with 2-anthracenecarboxylic acid (AC) was studied by NMR, UV–vis and circular dichroism spectroscopy. These modified γ-CD derivatives were found to form stable 1:2 host-guest ternary complexes with AC in aqueous solution. Compared with native γ-CD, the primary-face-aminated γ-CDs exhibited remarkably enhanced overall association constants as a result of the additional electrostatic interactions between the oppositely charged host and guest. In contrast, the ternary complex formation of the secondary-face-aminated γ-CD with AC was hindered.     

Inclusion complexation of diclofenac with natural and modified cyclodextrins explored through phase solubility, 1H-NMR and molecular modeling studies

Guest–host interactions were examined for neutral diclofenac (Diclo) and Diclofenac sodium (Diclo sodium) with each of the cyclodextrin (CD) derivatives: α-CD, β-CD, γ-CD and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), all in 0.05 M aqueous phosphate buffer solution adjusted to 0.2 M ionic strength with NaCl at 20 °C, and with β-CD at different pHs and temperatures. The pH solubility profiles were measured to obtain the acid–base ionization constants (pK _as) for Diclo in the presence and absence of β-CD. Phase solubility diagrams (PSDs) were also measured and analyzed through rigorous procedures to obtain estimates of the complex formation constants for Diclo/CD and Diclo sodium/CD complexation in aqueous solutions. The results indicate that both Diclo and Diclo sodium form soluble 1:1 complexes with α-, β-, and HP-β-CD. In contrast, Diclo forms soluble 1:1 Diclo/γ-CD complexes, while Diclo sodium forms 1:1 and 2:1 Diclo/γ-CD, but the 1:1 complex saturates at 5.8 mM γ-CD with a solubility product constant (pK _sp = 5.5). Therefore, though overall complex stabilities were found to follow the decreasing order: γ-CD > HP-β-CD > β-CD > α-CD, some complex precipitation problems may be faced with aqueous formulations of Diclo sodium with γ-CD, where the overall concentration of the latter exceeds 5.8 mM γ-CD. Both ¹H-NMR spectroscopic and molecular mechanical modeling (MM⁺) studies of Diclo/β-CD indicate the possible formation of soluble isomeric 1:1 complexes in water.     

Inclusion complexes of spin-labeled indoles with cyclodextrins in aqueous solutions

Guest-host complexes of β- and γ-cyclodextrins (CDs) with two spin-labeled indole derivatives having the same molecular weights but different structures were studied by EPR spectroscopy in aqueous solutions and semiempirical quantum-chemical calculations of these systems were carried out. In the presence of CD the polarity of the NO group environment decreases and the rotational correlation time (τ) of guest molecules increases. Both indole derivatives form 1 : 1 complexes with γ-CD, the binding constants of the complexes being different more than twice. Simulation of EPR spectra made it possible to determine the indole ring orientation relative to the plane of the host molecule (at angles in the range 30–60°) and the rotational diffusion coefficients of the complexes, which corresponded to the hydrodynamic volume of one γ-CD molecule. In contrast to the complexes with γ-CD the rotational correlation times, τ, of the complexes with β-CD correspond to a hydrodynamic volume which much exceeds the volume of a single β-CD molecule. The complexes with β-CD are also characterized by more hydrophobic environment for guest molecules and absence of spin exchange with Ni²⁺ ions in the aqueous solution. There results are consistent with a dimeric structure of β-CD in the complex and with the orientation of the long axis of the guest molecule along the dimer axis. The energies and geometric parameters were calculated for all complexes by the PM3 method with a conventional set of parameters. The optimized energetically stable structures of the 1 : 1 complexes with γ-CD and of the 1 : 2 complexes with β-CD are consistent with experimental data. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1139–1147, May, 2005.     

Comparative Study on Triclosan Interactions in Solution and in the Solid State with Natural and Chemically Modified Cyclodextrins

The aim of this study was to investigate the interactions of triclosan (TRI), a poorly water-soluble antimicrobial drug, with natural crystalline cyclodextrins (α-, β- and γ-Cd) and the corresponding hydroxypropylated amorphous derivatives (HPα-, HPβ-, and HPγ-Cd) and evaluate their effectiveness as complexing and solubilizing agents towards the drug. Equimolar solid systems were prepared using different techniques (physical mixing (PM), kneading (KN) and coevaporation (COE)) in order to evaluate the influence of the preparation method on the performance of the end products. Drug–carrier interactions were investigated both in aqueous solution, using phase-solubility analysis, fluorescence and circular dichroism (CD) techniques, and in the solid state, using differential scanning calorimetry (DSC) supported by thermograumetric analysis (TGA), X-ray powder diffractometry (XRPD) and scanning electron microscopy (SEM) analysis. Among the native cyclodextrins, β-Cd seemed to have the most suitable cavity to fit the drug molecule, whereas the α-Cd cavity was too small and the γ-Cd cavity too large to establish stable interactions with the guest. However, due to the B _S -type phase solubility diagram, its solubilizing efficiency was very limited. The presence of the hydroxypropylic substituents improved, in all cases, Cd solubilizing and complexing efficacies towards the drug. This was particularly evident in the case of HPγ-Cd, whose stability constant was about 200-fold higher than that of the native γ-Cd. HPβ-Cd was the most effective carrier for TRI, showing a solubilizing power about 20 times higher than the corresponding native Cd and about 2-fold that of the other hydroxypropyl derivatives. Moreover, a clear influence of the preparation method on the properties of the final products was observed. The COE method with hydroxypropylated cyclodextrins seemed the most suitable technique in achieving the complete drug amorphization and/or inclusion complexation. Received in final form: 24 January 2005     

A neutron induced prompt gamma-ray spectroscopy system using a 252Cf neutron source for quantitative analysis of aqueous samples

A neutron induced prompt γ -ray spectrometry (NIPS) facility has been developed at the Nuclear Chemistry Research Division, of the Korea Atomic Energy Research Institute (KAERI) with the aim of analyzing the major components of various elements in aqueous samples. The facility is equipped with a ²⁵²Cf neutron source and a γ-γ coincidence setup with two n-type coaxial HPGe detectors based on NIM spectrometric modules in association with data acquisition and spectral analysis systems. The development of the system, its set-up and the calibration of detection efficiency up to 8 MeV using a set of radionuclides and the (n,γ) reactions of chlorine are described in the paper. This revised version was published online in July 2006 with corrections to the Cover Date.     

Host–Guest Complexation of <Emphasis Type="Italic">β</Emphasis>-, <Emphasis Type="Italic">γ</Emphasis>-Cyclodextrin with Alkyl Trimethyl Ammonium Bromides in Aqueous Solution

As a continuation of our previous investigation, interactions between cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and alkyl trimethylammonium bromides in aqueous solutions have been studied with titration calorimetry and ¹H NMR at 298.15 K. The results are discussed in terms of the amphiphilic interaction of CD with surfactants and the iceberg structure formed by water molecules existing around the hydrophobic tail of surfactant molecules. The stoichiometry of the β-CD–surfactant system is 1:1 whereas that of the γ-CD–surfactant system is 1:2. The corresponding formation enthalpy (negative) of the complexes of the two systems decreases with an increase in the number of carbon atoms (n) in hydrophobic chain of surfactant molecule, C _n H_2n+1, whereas the entropy increases with the enlargement of n.     

Amperometric determination of xanthine in tea,coffee, and fish meat with graphite rod bound xanthine oxidase

A method is described for construction of an amperometric xanthine biosensor based on graphite rod modified through adsorption of xanthine oxidase. Enzymatically produced H₂O₂ from xanthine was split into 2H⁺ + O₂ + 2^e− at 0.6 V and the current was measured, which was directly proportional to xanthine concentration ranging from 1 ° 10⁻⁷ to 6 ° 10⁻⁷ M with a detection limit of 1 ° 10⁻⁷ M. The biosensor exhibited optimum response within 35 sec at pH 7.0 and 35°C. It was employed for determination of xanthine in tea leaves (0.9 ° 10⁻⁵−2.5 ° 10⁻⁵ mmol/g), coffee powder (3.2 μmol/g) and fish meat (90 mmol/g). The content of xanthine in fish meat increased 6.5 times with its storage at room temperature during 15 days. The enzyme electrode could be reused 200 times during the span of 30 days, when stored in reaction buffer at 4°C.     

Ion-specific swelling behavior of poly(vinyl alcohol) gel prepared by γ-ray irradiation

Poly(vinyl alcohol) gel was prepared by γ-ray irradiation of an aqueous solution of the polymer and its swelling behavior in solutions of the alkali-metal and alkaline-earth-metal salts was investigated. The gel deswelled in solutions containing strongly hydrated anions and swelled in solutions containing strongly hydrated cations. The degree of swelling of the gel was in the following order: SO₄ ²⁻<Cl⁻<Br⁻ ≅ NO₃ ⁻<I⁻ for the anions and K⁺<Na⁺<Li⁺ and Sr²⁺<Ca²⁺<Mg²⁺ for the cations. These results were interpreted in terms of interactions between the polymer and the ions through the hydration layers. Received: 6 November 2000 Accepted: 24 May 2001     

The Structure of the VOx Oxo complexes on the surface of the Al2O3 of various structural modifications

The structure of the surface VO_x oxo complexes prepared by deposition from aqueous solutions on alumina in various modifications (γ, η, χ, θ, and δ) is studied using⁵¹V and¹H NMR. The crystal structure and acidic properties of the surface of the starting phases of A1₂O₃ do not substantially affect the structure of the surface VO_x compounds. This is explained by the reconstruction of the surface layer of the support and a change in its acidic properties caused by the action of impregnating aqueous solutions.     

Cyclodextrins Binding to Paeonol and Two of Its Isomers in Aqueous Solution. Isothermal Titration Calorimetry and 1H NMR Investigations of Molecular Recognition

Interactions between CDs with three substituted phenols, paeonol (Pae), acetovanillone (Ace) and 2-hydroxyl-5-methoxy-acetophone (Hma), which are isomers, have been determined by isothermal titration calorimetry (ITC) and ¹H NMR in aqueous solution at 298.2 K. Both the binding thermodynamics and ¹H NMR spectra show that the interaction between α-cyclodextrin (α-CD) molecule and each guest molecule is extremely weak. The thermodynamic parameters indicate that the binding processes of β-cyclodextrin (β-CD) with the isomers are mainly entropy driven and that β-CD binds with Pae or Ace in 1:1 stoichiometry, whereas with Hma binds in 1:1 and 2:1 stoichiometries. The thermodynamic parameters also suggest that γ-cyclodextrin (γ-CD) binds each isomer in the same 1:1 stoichiometry. The binding processes of Pae and Hma with γ-CD are enthalpy driven whereas Ace with γ-CD is predominantly driven by entropy. The ¹H NMR spectra reveal that the three isomers were trapped into the torus cavity of the β-CD molecule from the narrow side during the binding process. Pae penetrates into the γ-CD cavity from the primary rim of the macrocycle whereas Ace does so from the secondary rim, but Hma appears not interact with the internal cavity of γ-CD at all.     

Can cyclodextrins really improve the selectivity of extraction of BTEX compounds?

Solubility of BTEX compounds was determined in aqueous solutions of natural CDs (α-, β-, γCD) as well as of some industrial βCD derivatives (RAMEB, HPBCD, AcβCD) measured by UV photometry. From the phase solubility diagrams the complex association constants were determined. The βCD derivatives increased the solubility of individual monoaromatic compounds, depending on the structure of the guest molecule. We have found that RAMEB (randomly methylated βCD) and AcβCD (partially acetylated βCD) are the most effective solubilizers while the effect of natural CDs is not significant because the complexes precipitate from the solutions. Extraction experiments were performed to see how the complexation of components influences the extraction using a mixture modeling the composition of these pollutants in soil. We have found that although the soluble CD derivatives are not as selective as expected based on complex association constants, they increased the efficacy of extraction by 4–6 times. The reason of the low selectivity is that the concentration ratio of certain BTEX compounds in CD solutions is smaller than in water. CD derivatives seem to have an equalizing effect: the solubility of the least soluble p-xylene is improved in the highest extent, but that of benzene the least. This result, however, is an advantage in the application of these CD derivatives in soil remediation (the availability of each BTEX compounds will be enhanced).     

Radiolysis of DEHPA-CCL4 solvent mixture in the presence of aqueous solutions

In order to clarify the effect of carbon tetrachloride on the radiolysis of di(2-ethylhexyl)phosphoric acid(DEHPA), DEHPA diluted with carbon tetrachloride was exposed to⁶⁰Co γ-rays in the presence or absence of aqueous solution and the yields of degradation products of DEHPA and hydrogen chloride were determined. Radiolysis of DEHPA is enhanced by carbon tetrachloride, most intensively in the stirred system of DEHPA−CCl₄ and an aqueous solution. Carbon tetrachloride also corroded stainless steel immersed in it during γ-irradiation owing to the formation of hydrogen chloride. Yield of hydrogen chloride increased in the presence of the aqueous solution, most effectively upon stirring, and corrosion became significant.     

Hydrophobic Interactions of Methylureas in Aqueous Solutions Estimated with Density, Molal Volume, Viscosity and Surface Tension from 293.15 to 303.15 K

Density (ρ), viscosity (η), and surface tension (γ) for 0.005–0.25 mol ⋅ kg⁻¹ solutions of urea, 1-methylurea, and 1,3-dimethylurea solutions have been measured at intervals of 0.005 mol ⋅ kg⁻¹. Apparent molal volume (V _o, cm³ ⋅ mol⁻¹) and intrinsic viscosity coefficients (B and D) are calculated from the ρ and η values, respectively. Primary data were regressed and extrapolated to zero concentration for the limiting density (ρ ⁰), apparent molal volume (V _φ ⁰), viscosity (η ⁰), and surface tension (γ ⁰) values for solute–solvent interactions. The –CH₃ (methyl) groups of N-methylureas weaken hydrophilic interactions and enhance hydrophobic interactions, and the values of the ρ ⁰ and V _φ ^o reflect the intermolecular forces due to electrostatic charge, whereas the η ⁰ and γ ⁰ values reflect the frictional and surface forces. The B values depict the size of hydrodynamic sphere due to heteromolecular forces whereas D shows the effect of concentration. The molar surface energy (ΔE _m/sur) for dropwise flow was calculated from the γ values and decreases with concentration and temperature, but increases with –CH₃ weakening of the hydrophilic interactions and strengthening the hydrophobic interactions.     

Electron paramagnetic resonance (EPR) study of γ-radiation-induced radicals in 1,3,5-trithiane and its derivatives

Radicals formed in γ-irradiated 1,3,5-trithiane (TT) and its three derivatives, α- and β-2,4,6-trimethyl-1,3,5-trithiane (α-TMT and β-TMT), and 2,4,6-trimethyl-2,4,6-triphenyl-1,3,5-trithiane (TMTPT), were studied by the electron paramagnetic resonance (EPR) method in the solid state. The sulfur radical cations (>S^+•) were identified in all compounds at 77 K. In TT and its two derivatives, α-TMT and β-TMT, the >S^+• decay via deprotonation-forming C-centered radicals. Further increase of temperature up to 293 K results in the appearance of thiyl-type radicals (RS^•). In TMTPT, the >S^+• are stable up to 250 K. They formed the intermolecularly three-electron-bonded dimeric radical cations (S∴S)⁺ while RS^• radicals were not observed. Some of the radical assignments and their EPR parameters (g and a hyperfine splittings) obtained support from the DFT calculations.     

Isotope dilution quantification of ultratrace gamma-glutamyl-Se-methylselenocysteine species using HPLC with enhanced ICP–MS detection by ultrasonic nebulisation or carbon-loaded plasma

A method for the accurate determination of ultratrace selenium species of relevance to cancer research, such as gamma-glutamyl-Se-methylselenocysteine (γ-glutamyl-SeMC), using species-specific double isotope dilution analysis (IDA) with HPLC–ICP–MS is reported for the first time. The ⁷⁷Se-enriched γ-glutamyl-SeMC spike was produced in-house by collecting the fraction at the retention time of the γ-glutamyl-SeMC peak from a chromatographed aqueous extract of ⁷⁷Se-enriched yeast, pooling the collected fractions and freeze-drying the homogenate. The Se content of this spike was characterised using reverse isotope dilution mass spectrometry (IDMS) and the isotopic composition of this spike was checked prior to quantification of the natural abundance dipeptide species in garlic using speciated IDA. The extraction of the γ-glutamyl-SeMC species in water was performed in a sonication bath for 2 h after adding an appropriate quantity of ⁷⁷Se-enriched γ-glutamyl-SeMC to 50 mg of garlic to give optimal ⁷⁸Se/⁷⁷Se and ⁸²Se/⁷⁷Se ratios of 1.5 and 0.6, respectively. The effect of ultrasonic nebulisation, in comparison with the loading of the ICP with carbon (through the addition of methane gas on-line), on the detection of Se associated with γ-glutamyl-SeMC using collision/reaction cell ICP–MS with hydrogen as collision gas was investigated. Sensitivity enhancements of approximately fourfold and twofold were achieved using USN and methane mixed plasma, respectively, in comparison with conventional nebulisation and conventional Ar ICP–MS. However, an approximately twofold improvement in the detection limit was achieved using both approaches (42 ng kg⁻¹ for ⁷⁸Se using peak height measurements). The use of species-specific IDMS enabled quantification of the dipeptide species at ng g⁻¹ levels (603 ng g⁻¹ Se) in the complex food matrix with a relative standard deviation (RSD, n = 4) of 4.5%, which was approximately half that obtained using standard addition as a confirmatory technique. Furthermore, good agreement was found between the γ-glutamyl-SeMC species concentrations obtained using both calibration methods.     

Study on the Inclusion Compounds of Eugenol with α-, β-, γ- and Heptakis (2,6-di-O-methyl)-β-cyclodextrins

Several host–guest inclusion compounds of eugenol as a guest molecule and cyclodextrins (α-,β-,γ-CD) and heptakis (2,6-di-O-methyl)-β-cyclodextrin (DMβ-CD) as hosts were investigated in the solid state and in aqueous solution. The one-to-one solid inclusion compounds of eugenol and β-CD or γ-CD were prepared, but those of eugenol with α- or DMβ-CD were not obtained under the same condition. However, the UV-visible absorption spectroscopy data indicated that the liquid guest could form a 1:1 inclusion compound with all four hosts respectively in aqueous solution. The two solid inclusion compounds were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The association constants (K), calculated from the modified Benesi–Hidebrand equation, of eugenol with α-, β-, γ- and DMβ-CD is 4.95 × 10⁴, 3.96 × 10⁵, 1.47 × 10⁵ and 9.33 × 10⁴ mol⁻¹ dm³, respectively.     

Complexation of Aliphatic Alcohols by α- and β-Cyclodextrins and their Partial Methylated Derivatives in Aqueous Solution

The complexation of aliphatic alcohols by α- and β-cyclodextrins and their partially methylated derivatives has been studied by means of calorimetric titrations in aqueous solution. The methyl substituents have no pronounced influence upon the complex formation. α-Cyclodextrin and the partially methylated derivative form with only few exceptions more stable than β-cyclodextrin. With increasing chain length of the alcohols the values of the stability constants and reaction enthalpies increase in case of the complex formation with α-cyclodextrin and partially methylated α-cyclodextrin. In contrast the complex formation becomes disfavoured by the reaction entropy with an increasing number of methylene groups. The values of the reaction enthalpies with the β-cyclodextrins are close to zero. Thus the complexation is only favoured by entropic contributions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Characterization of Semiconductor Nanomaterials and Micromaterials via Gamma-irradiation Route

In this review, we reported our recent studies on controlled growth of sulfide and oxide semiconductor nano-and micro-structures via gamma-irradiation route. NiS and PbS uniform hollow microspheres (∼500 nm) have been successfully synthesized by γ-irradiating PMMA-CS₂-ethanol aqueous solution that contains Ni²⁺ or Pb²⁺ at room temperature, respectively. Large-scale single-crystalline ZnO hexangular prisms were successfully prepared through a simple γ-irradiation approach at room temperature and under ambient pressure. CdSe hollow structures and hollow nanospheres (40∼50 nm), compass-shaped (80 nm in middle width and 200 nm in length) Mn₃O₄ (hausmannite) and monodisperse ZnS nanoballs etc. had been successfully synthesized through γ-irradiation route with different surfactant-assisted systems at room temperature. Those successful synthesis approaches in large scale and under mild conditions could be of interest for both applications and fundamental studies.     

Sorption of radiocobalt on a novel γ-MnO2 hollow structure: effects of pH, ionic strength, humic substances and temperature

A novel γ-MnO₂ hollow structure has been synthesized using a simple chemical reaction between MnSO₄ and KMnO₄ in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, γ-MnO₂ hollow structure was used as adsorbent in radionuclide ⁶⁰Co(II) treatment, and showed an excellent ability. The effect of pH, contact time, ionic strength, humic acid (HA)/fulvic acid (FA), and temperature was investigated using batch techniques. The results indicated that the sorption of ⁶⁰Co(II) on γ-MnO₂ was obviously dependent on pH values but independent of ionic strength. The presence of HA/FA enhanced the sorption of ⁶⁰Co(II) on γ-MnO₂ at low pH, whereas reduced ⁶⁰Co(II) sorption on γ-MnO₂ at high pH. The kinetic sorption of ⁶⁰Co(II) on γ-MnO₂ can be well fitted by the pseudo-second-order rate equation. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) were also calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption of ⁶⁰Co(II) on γ-MnO₂ was a spontaneous and endothermic process. The sorption of ⁶⁰Co(II) on γ-MnO₂ was attributed to surface complexation rather than ion exchange.     

Sorption behavior of γ-irradiated α-Al2O3

Irradiation of α-Al₂O₃ (Corundum) was carried out in contact with acidic media and with different doses (100-to-2500 kGy) and dose-rates (0.9, 2.6 and 6.1 kGy·h⁻¹) of γ-rays. Simultaneously parallel experiments were carried out using the same procedure, but preheated at 150°C for two days and then irradiated without acidic media. The solid thus obtained was used to determine the effect of γ-irradiation on the sorption capacities of microamounts of fission products from strongly alkaline aqueous solutions of uranium. The results revealed that the effect of γ-irradiation of α-Al₂O₃ and the acidic media in which it is immersed, is associated with a stable matrix resistant to significant changes in the composition of the surface layer; whilst it seems that the effect of γ-irradiation of preheated α-Al₂O₃, is connected with changes of surface-OH groups strongly affected by heat treatment and irradiation dose.