Quantitative determination of the total flavonols inAlhagi pseudoalhagi

The optimum conditions for extracting flavonols fromAlhagi pseudoalhagi has been determined. A method for the UV-spectrometric identification of the total alkaloids has been developed which permits reliable reproducible results to be obtained. The relative error of the determination does not exceed ±1.7%.Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 664–667, September–October, 1993.     

Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25°C

Potentiometric titrations of uranyl(VI) solutions were conducted using a standard glasslcalomel electrode combination over the pH range 3 to 12 at 0.1 molkg^–1 ionic strength with tetramethylammonium trifluoromethanesulfonate as the supporting electrolyte. The electrodes were calibrated directly on the hydrogen ion concentration scale during the initial stage of each titration. The species, UO ₂ ²⁺ , (UO₂)₂(OH) ₂ ²⁺ , (UO₂)₃(OH) ₅ ⁺ , (UO₂)₃(OH) ₇ ^– , (UO₂)₃(OH) ₈ ^2– , and (UO₂)₃(OH) ₁₀ ^4– identified in an earlier Raman study were compatible with the analysis of the titration data. Based on this analysis and application of the extended Debye-Hückel treatment, the polynuclear species indicated above were assigned overall formation constants at 25°C and at infinite dilution of –5.51±0.04, –15.3±0.1, –27.77±0.09, –37.65±0.14, and –62.4±0.3, respectively. The results are discussed in reference to hydrolysis quotients reported in the literature for the first three species. Formation quotients for the last two species have not been reported previously.     

Measuring the solubilities of ionic liquids in water using ion-selective electrodes

Polyvinyl chloride-plasticized membrane ion-selective electrodes (ISE) based on conventional ion-exchangers have been proposed as a cheap universal tool to measure the solubilities of ionic liquids (ILs) in water. They are applicable for ILs with a wide range of solubilities in water, since the linear range of a potentiometric response spans several orders of magnitude. As an example, we have fabricated and tested ISEs for widely used alkylimidazolium ionic liquids. The aqueous solubilities of four typical ILs have been determined at 21 °C: 0.075±0.001 mol l^–1 (1-butyl-3-methylimidazolium, BMIm, hexafluorophosphate); 0.018±0.001 mol l^–1 (BMIm bis(triflylimide)); 0.054±0.007 mol l^–1 (1-butyl-2,3-dimethylimidazolium, BDMIm, hexafluorophosphate); 0.014±0.001 mol l^–1 (BDMIm bis(triflylimide)).     

Thermochemistry of Amines: Experimental Standard Molar Enthalpies of Formation of N-Alkylated Piperidines

The standard molar enthalpies of formation _f H _m ^° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization _l ^g H ^{m °} of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol^–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.     

Rate Constant for the Reaction of the OH-Radical with CH2F2

The rate constant value of k ₁ = (6.05 ± 0.20)×10⁹ cm³ mol^–1 s^–1 (with ± 1 error) has been determined for the reaction OH + CH₂F₂ (1) by applying the discharge-flow/resonance-fluorescence method at 298 K.     

Viscosimetric Study of Some Cyclic Ethers with Benzene, Toluene, or Halobenzene

Experimental viscosities and the corresponding viscosity deviations for the binary mixtures of a cyclic ether (tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, or 2,5-dimethyltetrahydrofuran) with benzene, toluene, fluorobenzene, or chlorobenzene are given at 25°C. The kinematic viscosities and the corresponding densities were measured with an uncertainty of ±10^{– 4} mm²-s^{– 1} and ±(5×10^{– 3}) kg-m^{– 3}, respectively. The viscosity data were correlated by the equations of Grunberg–Nissan, McAllister, and Heric. On the other hand, the results have been compared to the predictions, by the method proposed by Asfour.     

Far infrared spectrum,conformational stability,barriers to internal rotation,vibrational assignment,and ab initio calculations of 2-chloro-3-fluoropropene

The far infrared spectrum (375 to 30 cm^–1) of gaseous 2-chloro-3-fluoropropene, CH₂=C(CH₂F)CI, has been recorded at a resolution of 0.10 cm^–1. The fundamental asymmetric torsional mode is observed at 117.5 cm^–1 with ten excited states falling to low frequency for thes-cis (fluorine atom eclipsing the double bond) conformer. For the higher energy gauche conformer, the asymmetric torsion is estimated to be at 94 cm^–1. From these data the asymmetric torsional potential function has been calculated. The potential function coefficients are calculated to be in cm^–1):V ₁=803±21,V ₂=–94±21,V ₃= 1025±10,V ₄=95±10, andV ₆=2±1, with an enthalpy difference between the more stables-cis and gauche conformera of 550±100 cm^–1 (1.57±0.29 kcal/mol). This function gives values of 1227±50cm^–1(3.51±0.14kcal/mol), 1266±200 cm^–1 (3.62±0.57 kcal/mol), and 665±100 cm^–1 (1.90±0.29 kcal/mol), for thes-cis to gauche, gauche to gauche, and gauche tos-cis barriers, respectively. From the relative intensities of the Raman lines of the gas at 652 cm^–1 (gauche) and 731 cm^–1 (s-cis) as a function temperature, the enthalpy difference is found to be 565±96 cm^–1 (1.62±0.27 kcal/mol). However, the more polar gauche conformer remains in the crystalline solid. The Raman spectrum of the gas has been recorded from 3500 to 70 cm^–1 and, utilizing these data and the previously reported infrared data, a complete vibrational analysis is proposed for both conformers. The conformational stability, barriers to internal rotation, fundamental vibrational frequencies, and structural parameters that have been determined experimentally are compared to those obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21 G^* and 6–31G^* basis sets and to the corresponding quantities for some similar molecules.     

Kinetics and mechanism of the reaction between bis 4-(2-pyridylazo)resorcinol ferrate(III) complex and cyanide ion

Summary Kinetics and mechanism of formation of a 113 mixed cyano-complex from [Fe^III (Par)₂]^– (where Par represents 4-(2-pyridylazo)resorcional) and cyanide ion has been studied spectrophotometrically at 720 nm [_max=Fe^(III)(Par) ₂ ^– ], pH=10.0±0.02, temp=25±0.1°C and 1=0.1 M (NaClO₄). The order with respect to cyanidevaries from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k₁=10.8±0.6×10^–2 M^–1 s^–1, k₂=7.7±0.5 M^–2 s^–1. The reverse reaction does not occur at a measurable rate even in presence of large excess of par. These observations suggest that Fe^III (Par) ₂ ^– forms a mixed complex, [FePar(CN)₃]^2-, in presence of an excess of cyanide ions. A three-step mechanism consistent with these results is proposed. The activation parameters for the reaction have been derived and used to support the proposed mechanism. The effect of ionic strength lends further support to the mechanism.     

Rapid method for the quantitative determination of sanguiritrine in the herbsMacleaya cordata andMacleaya microcarpa

For analyzing the herb plume poppy a spectrophotometric method has been developed which is distinguished by a high productivity thanks to the absence of a stage of chromatographically separating the combined alkaloids. The error of a single determination is ±5.07%.All-Union Scientific-Research Institute of Medicinal Plants, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 619–621, September–October, 1981.     

The dissociation of phosphoric acid in NaCl and NaMgCl solutions at 25°C

The pK ₁ ^* , pK ₁ ^* and pK ₃ ^* for the dissociation of H₃PO₄ have been measured in NaCl solutions from 0.5 to 6m at 25°C. The results have been used to evaluate Pitzer interaction parameters (NaClH₂PO₄)=–0.028±0.005, (NaH₃PO₄)=–0.075±0.025, (HPO₄Cl)=0.105±0.009, (PO₄Cl)=–0.59±0.02 and (NaClHPO₄)=–0.003±0.004, (PO₄NaClH)=0.110±0.008. These parameters yield values of pK ₁ ^* , pK ₂ ^* and pK ₃ ^* in NaCl that agree with the measured values with average deviations of ±0.04, ±0.03 and ±0.05 in pK ₁ ^* . Measurements of pK ₁ ^* and pK ₂ ^* were also made in NaMgCl solutions. These results have been used to evaluate ^(O)(MgH ₂ PO ₄)=–3.55±0.07,⁽¹⁾(MgH ₂ PO ₄=–16.9±0.03, ^(O)(MgH ₂ PO ₄=–17.5±0.03 and ⁽¹⁾(MgH ₂ PO ₄)=27.4±0.8 at 25°C. The results for pK ₂ ^* in NaMg–Cl solutions were also used to calculate log K _MX ^* =3.2±0.1 for the formation of the ion pair MgHPO ₄ ^o .     

An NMR study of proton exchange in the system p-nitrosophenol—p-quinone monooxime

The solvent used was dimethylformamide at neutral and alkaline pH. The equilibrium constants are determined by spectrophotometry. The rate of proton exchange has been measured as a function of temperature and concentration. The rate constants and activation energies have been measured; for uncatalyzed exchange k_n=(1.5±0.5) ·· 10³ M^–1 sec^–1, E=8±1 kcal/mole, while base-catalyzed exchange has k=(0.3±0.1) · 10⁶ M^–1 sec^–1 and E=6±1 kcal/mole.We are indebted to A. I. Brodskii for assistance in this work, and to V. I. Oshkaderov and L. A. Kichakova for recording the NMR spectra.     

Vibrational spectra,conformational stability,barriers to internal rotation,r0 structural parameters and ab initio calculations of fluoromethyl methyl ether

The far-infrared spectrum of gaseous fluoromethyl methyl ether, FCH₂OCH₃, along with three of the deuterium isotopes, has been recorded at a resolution of 0.10 cm^–1 in the 350 to 50 cm^–1 region. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 182 and 132 cm^–1, respectively, for the stablegauche conformer with the lower frequency band having several excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one-dimensional model the barrier to internal rotation of the methyl moiety is determined to be 527±9 cm^–1 (1.51±0.03 kcal/mol). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500 to 50 cm^–1) spectra of the gas and solid and from the Raman (3200 to 10 cm^–1) spectra of the gas, liquid, and solid is proposed. No evidence could be found in any of the spectra for the high-energytrans conformer. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G and 6-31G* basis sets along with the 6-31G* basis set with electron correlation at the MP2 level. Additionally, completer ₀ geometries have been determined from the previously reported microwave data and carbon-hydrogen distances determined from infrared studies. The heavy-atom structural parameters (distances in Å, angles in degrees) arer(C₁-F) = 1.395 ± 0.005;r(C₁-O) = 1.368 ± 0.007;r(C₂-O) = 1.426 ±0.003; FC₁O = 111.33 ± 0.25; C₁OC₂ = 113.50 ± 0.18 and dih FC₁OC₂ = 69.12 ± 0.26. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

Homolytic dissociation in hydrogen-bonding liquids: energetics of the phenol O–H bond in methanol and the water O–H bond in water

The energetics of the phenol O–H bond in methanol and the water O–H bond in liquid water were investigated by microsolvation modelling and statistical mechanics Monte Carlo simulations. The microsolvation approach was based on density functional theory calculations. Optimised structures for clusters of phenol and the phenoxy radical with one and two methanol molecules are reported. By analysing the differential solvation of phenol and the phenoxy radical in methanol, we predict that the phenol O–H homolytic bond dissociation enthalpy in solution is 24.3±11 kJ/mol above the gas-phase value. The analysis of the water O–H bond dissociation by microsolvation was based on optimised structures of OH–(H₂O)_1–6 and –(H₂O)_1–7 clusters. Microsolvation modelling and statistical mechanics simulations predict that the HO–H bond dissociation enthalpies in the gas phase and in liquid water are very similar. Our results stress the importance of estimating the differences between the solvation enthalpies of the radical species and the parent molecule and the limitations of local models based on microsolvation.Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

New synthesis of [8-arginine] vasopressin and its de-9-glycine analogs

A unified scheme is proposed for the synthesis of [8-arginine]vasopressin (I), de-9-glycine[8-arginine]vasopressin (II), and de-9-glycinamide[8-arginine]vasopressin (III) which has been developed on the basis of the tetrapeptide Gln-Asn-Cys(Bzl)-Pro and other homologous fragments of neurohypophyseal hormones as common initial and intermediate compounds. The free dithiols obtained by the reduction of protected derivatives of (I)–(III) by sodium in liquid ammonia have been oxidized to the corresponding cyclic disulfides (I)–(III) with the aid of 1 M H₂O₂ at 0–5°C and pH 8.5. The vasopressor activities of (I)–(III) are, respectively 470 ± 20, 1.7, and 0.5 IU/mg (rat, in vivo).Institute of Organic Synthesis, Latvian SSR Academy of Sciences, Riga. Translated from Khimiya Prirodnykh Soedinenii, No.3, pp. 433–439, May–June, 1988.     

Preparation and Thermochemistry of Complexes of Zinc Nitrate with Threonine

The solubility property of Zn(NO₃)₂–Thr–H₂O system (Thr—threonine) at 25°C in the entire concentration range has been investigated by the phase equilibrium semimicromethod. The corresponding phase diagram and refractive index diagram were constructed. From the phase equilibrium results, the incongruently soluble compounds of Zn(Thr)(NO₃)₂ · 2H₂O, Zn(Thr)₂(NO₃)₂ · H₂O, and Zn(Thr)₃(NO₃)₂ · H₂O were synthesized and characterized by IR, XRD, TG–DTG, chemical and elemental analyses. The constant-volume combustion energies of the compounds, _c E, determined by precision rotating bomb calorimeter at 298.15 K, were –6266.88 ± 3.72, –9263.28 ± 2.23, and –11 423.11 ± 6.81 J/g, respectively. The standard enthalpies of combustion for these compounds, _c H _m ^° (complex, s., 298.15 K), were calculated as –2147.40 ± 1.28, –4120.83 ± 0.99, and –6444.68 ± 3.85 kJ/mol and the standard enthalpies of formation, _f H _m ^° (complex, s., 298.15 K), are –1632.82 ± 1.43, –1885.55 ± 1.50, and –2770.25 ± 4.21 kJ/mol. The enthalpies of dissolution of the complexes in a medium of simulated human gastric juice (37°C, pH 1, in the solution of hydrochloric acid), _dis H _m ^° (complex, s., 310 K), which were also measured by a microcalorimeter to be 13.36 ± 0.06, 15.53 ± 0.06, and 17.04 ± 0.05 kJ/mol, respectively.     

Study of the structure of molecular complexes

A cluster of 200 molecules of water containing one of the LiF, LiCl, NaF, NaCl, KF or KCl ion pairs has been studied at the temperature T= 298°K using Monte Carlo techniques. The anion-cation internuclear separations considered in this work for any of the above pairs are 6.0 Å, 8.0 Å and 10.0 Å. The water-water potential is obtained from quantum-mechanical Hartree-Fock type computations corrected by inclusion of dispersion forces; the ion-water potentials have been obtained from Hartree-Fock type computations on the single ion-water complex. The computed radii for the first hydration shell are 2.7±0.1 Å, 3.4±0.3 Å, 4.0±0.3 Å, 3.0±0.5 Å, and 3.9±0.4 Å, for Li⁺, Na⁺, K⁺, F^– and Cl^–, respectively. The computed coordination numbers are 5.4±0.7,6.0±1.1, 7.2±1.2,4.5±0.6 and 5.1±0.8 for the same ions, respectively. The range of the coordination number obtained from compressibility, enthalpy, NMR spectroscopy and other experimental methods is much larger than the error ranges above given. Therefore the Monte Carlo simulation provides reliable information on the cluster shape, cluster structure and on the coordination numbers and hydration shell radii for the cations and anions, when both are present in a water cluster.     

A constitutional diagram of the system VC0.88−HfC0.98−WC

The system VC_0.88–HfC_0.98–WC was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction and metallographic techniques on hot pressed and heat treated as well as melted alloy specimens and a complete constitutional diagram from 1500°C through the melting range established.The phase behaviour within VC_0.88–HfC_0.98–WC is characterized by the presence of a large (binary) miscibility gap within VC–HfC (T _crit.,hypo.=3000°C). Additions of WC decrease the miscibility gap in the ternary. Interaction of the solvus (boundary of the cubic-B1 monocarbide solution) and the ternary miscibility gap was established at 2075°C and (VC)_0.17(HfC)_0.37(WC)_0.46: On cooling below 2075°C alloys of this composition enter a decomposition reaction into two isotypic cubic B1 phases and hexagonal WC.Solid state and melting behaviour was established within the isopleths VC_0.88–WC and VC_0.88–HfC_0.98 as well as within (V_0.8W_0.2)C–(Hf_0.8W_0.2)C and WC–(V_0.38Hf_0.62)C. The isopleth VC_0.88–HfC_0.98 intersects the four phase plane of the ternary V–Hf–C euctetic [2580±10°C, (VC)_0.78(HfC)_0.22]. Originating at the VC–HfC binary this eutetic trough proceeds into the VC–HfC–WC ternary with raising temperatures connecting the maximum critical point of the disappearing miscibility gap [(VC)_0.35(HfC)_0.51(WC)_0.14] by a limiting tie line (2830±20°C).Isothermal sections have been calculated assuming regular solutions.With 9 Figures     

Comparison of GC-ICP-MS and HPLC-ICP-MS for species-specific isotope dilution analysis of tributyltin in sediment after accelerated solvent extraction

This study describes a direct comparison of GC and HPLC hyphenated to ICP–MS determination of tributyltin (TBT) in sediment by species-specific isotope dilution analysis (SS-IDMS). The certified reference sediment PACS-2 (NRC, Canada) and a candidate reference sediment (P-18/HIPA-1) were extracted using an accelerated solvent extraction (ASE) procedure. For comparison of GC and LC methods an older bottle of PACS-2 was used, whilst a fresh bottle was taken for demonstration of the accuracy of the methods. The data obtained show good agreement between both methods for both the PACS-2 sediment (LC–ICP–IDMS 828±87 ng g^–1 TBT as Sn, GC–ICP–IDMS 848±39 ng g^–1 TBT as Sn) and the P-18/ HIPA-1 sediment (LC–ICP–IDMS 78.0±9.7 ng g^–1 TBT as Sn, GC–ICP–IDMS 79.2±3.8 ng g^–1 TBT as Sn). The analysis by GC–ICP–IDMS offers a greater signal-to-noise ratio and hence a superior detection limit of 0.03 pg TBT as Sn, in the sediment extracts compared to HPLC–ICP–IDMS (3 pg TBT as Sn). A comparison of the uncertainties associated with both methods indicates superior precision of the GC approach. This is related to the better reproducibility of the peak integration, which affects the isotope ratio measurements used for IDMS. The accuracy of the ASE method combined with HPLC–ICP–IDMS was demonstrated during the international interlaboratory comparison P-18 organised by the Comité Consultatif pour la Quantité de Matière (CCQM). The results obtained by GC–ICP–IDMS for a newly opened bottle of PACS-2 were 1087±77 ng g^–1 Sn for DBT and 876±51 ng g^–1 Sn for TBT (expanded uncertainties with a coverage factor of 2), which are in good agreement with the certified values of 1090±150 ng g^–1 Sn and 980±130 ng g^–1 Sn, respectively.     

Quantum-chemical calculations of O-O bond strengths in organic hydrotrioxides

The O-O bond strengths in ten organic hydrotrioxides have been calculated by semiempirical MNDO and AMI methods. The RO-OOH bond strength is independent of the nature of substituent R and is equal to 20.4±1.1 kcal mol^–1 (AM1). The influence of the inductive effect of substituent R on the value ofD(ROO-OH) has been established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1129–1131, May, 1996.