Towards the understanding of the spectroscopic behaviour of the C–H oscillator in C–HO hydrogen bonds: the effect of solvent polarity

The effect of solvent polarity versus specific C–HO contacts on the vibrational νC–H mode is studied using CHCl₃ as a model system. Ab initio SCI–PCM calculations show that the overall shift of the νC–H band, sometimes ascribed to the C–HO hydrogen bonding, can in fact be explained by the electrostatic interaction with a dielectric environment. The presence of a new νC–H band – assigned to the C–HO bonded forms – remains as the most reliable evidence of C–HO hydrogen bonding.     

Radioisotope excited EDXRF analysis of sediment core samples from the southern part of the Black Sea +

In all 43 sediment samples were collected as gravity cores in depthfrom 70 to 150 cm, from the 20 sampling sites of the continental slope ofthe southern part of the Black Sea, during 1978. The samples were quantitativelyanalyzed by radioisotope excited energy dispersive X-ray fluorescence spectrometry(EDXRF) using fundamental parameter technique (FTP). The investigated sedimentsamples were the organic rich-mud components of the core samples, which wereknown as rich in metals. The metal concentration ranges were as follows: Ca(3.1–12.9%), Ti (1000–2000 µg/g), V (40–150 µg/g),Cr (30–200 µg/g), Mn (200–1500 µg/g), Ni (25–100µg/g), Cu (20–70 µg/g), Zn (20–50 µg/g), Br(15–670 µg/g), Rb (5–90 µg/g), Sr (80–700 µg/g),Y (10–20 µg/g), Mo (10–111 µg/g), Zr (20–190µg/g), Cd ( <1–5 µg/g), Sb ( <1–5 µg/g),I (10–430 µg/g), Ba (100–1650 µg/g), La (5–18µg/g), Ce (12–38 µg/g) and Nd (6–17 µg/g). Thesediment cores systematically collected in 1978 by Mineral Research and ExplorationInstitute of Turkey (MTA) are the oldest available sediment samples from theTurkish coastline of the Black Sea. Therefore, the results may be used asreferences for monitoring possible future metal pollution.     

Effect of temperature on the selectivity of the extraction of lanthanides with dibutylphosphoric acid from thiocyanate solution

Extraction coefficients and separation factors of all lanthanides were determined in the system: dibutylphosphoric acid /HDBP/ - 3M NH₄NCS, in the temperature range of 15–50 °C. The values for the separation factors for such pairs as: Gd–Tb and Er–Tm, are higher than 4, those for the pair of Tb–Dy are higher than 3, and those for the La–Ce, Pm–Sm, Dy–Ho, Ho–Er and Tm–Yb pairs are higher than 2. The influence of temperature on the separation factors of light /La–Gd/ and heavy /Gd–Lu/ lanthanides is discussed and compared with that observed for the extraction from the nitric acid solutions. The results are also discussed in the light of the double-double effect and outer-, vs. inner-sphere complexation in the lanthanide series.     

A New Predictive Equation for the Surface Tensions of Aqueous Mixed Ionic Solutions Conforming to the Linear Isopiestic Relation

The linear isopiestic relation has been used, together with the fundamental Butler equations, to establish a new simple predictive equation for the surface tensions of the mixed ionic solutions. This newly proposed equation can provide the surface tensions of multicomponent solutions using only the data of the corresponding binary subsystems of equal water activity. No binary interaction parameters are required. The predictive capability of the equation has been tested by comparing with the experimental data of the surface tensions for the systems HCl–LiCl–H₂O, HCl–NaClO₄–H₂O, HCl–CaCl₂–H₂O, HCl–SrCl₂–H₂O, HCl–BaCl₂–H₂O, LiCl–NaCl–H₂O, LiCl–KCl–H₂O, NaCl–KCl–H₂O, KNO₃–NH₄NO₃–H₂O, and LiCl–NaCl–KCl–H₂O at 298.15 K; KNO₃–NH₄Cl–H₂O, KBr–Sr(NO₃)₂–H₂O, NaNO₃–Sr(NO₃)₂–H₂O, NaNO₃ –(NH₄)₂SO₄–H₂O, KNO₃–Sr(NO₃)₂– H₂O, NH₄Cl–Sr(NO₃)₂–H₂O, NH₄Cl– (NH₄)₂SO₄–H₂O, KBr–KCl–H₂O, KBr–KCl–NH₄Cl–H₂O, KBr–KNO₃– Sr(NO₃)₂–H₂O, KBr–NH₄Cl–Sr(NO₃)₂–H₂O, KNO₃–NH₄Cl–Sr(NO₃)₂–H₂O, and NH₄Cl–(NH₄)₂SO₄–NaNO₃–H₂O at 291.15 K; and KBr–NaBr–H₂O at temperatures from 283.15 to 308.15 K. The agreement is generally quite good.     

Spectroscopic studies of the behaviour of the AgNO3−HNO3 — Tetrabutyl dithiopyrophosphate extraction system

A very efficient extraction of silver with tetrabutyl dithiopyrophosphate (TBDTPP) is followed by dramatic changes in the structure of the extractant molecule. The IR and NMR spectroscopic studies have revealed that in the presence of Ag⁺ and NO ₃ ^– ions the TBDTPP molecule rearranges first into a molecule containing a P–S–P bridge and one P=O group instead of P–O–P and P=S, respectively, and then into a molecule containing two P–S–C and two P=O groups at a P–O–P bridge.     

A study of the potential surface of LiOB by the method of diatomic fragments in molecules

Conclusion The results of the calculations by the DFM method provide evidence that the minimum on the potential surface of LiOB in the state¹A corresponds to the linear structure Li–O–B. Estimates of the dissociation energy with respect to various decomposition channels show that the molecule is stable. The qualitative behavior of the section of the potential surface corresponding to the minimum energy path for the intramolecular rearrangement Li–O–BO–B–Li is independent of the adjustable parameters of the method—the coefficients of the mixing of the diatomic states of identical symmetry. The lack of agreement between the difference in the energies of the linear forms Li–O–B and O–B–Li and the results of nonempirical calculations indicates that the model of the molecule chosen within the framework of the DFM approach requires further refinement. In particular, the addition to the set of MBF of functions constructed with allowance for the excited state⁴P of the boron atom will make it possible to decrease this energy difference. It will then be necessary, however, to take into account the much larger number of states from the fragments BO and BLi.M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 24, No. 3, pp. 13–17, May–June, 1983.     

The nature of the splitting of the bands in the infrared spectra of phosphorus dithioacids

Conclusions The IR spectra of a series of phosphorus dithioacids were studied under different conditions. The splitting of bands in the regions 490–550 and 2500–2600 cm^–1 is explained by rotational isomerism.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 672–673, March, 1968.     

Study of the Influence of the Preparation Method on the Formation of the Phase Composition and Structure of V–Ti–O and W–Ti–O Catalysts for Selective Catalytic Reduction of NO by NH3

The influence of the preparation method on the structure and phase composition of V–Ti–O and W–Ti–O catalysts for selective catalytic reduction of NO by NH₃ was studied. The preparation conditions were found to insignificantly affect the structure of the resulting V–Ti–O catalysts, whereas in the case of W–Ti–O catalysts, such an influence was distinctly observed. The introduction of tungsten ions into the lattice of titanium dioxide leads to the formation of both local defects (solid solutions of the substitution type) and extended, so-called Wadsley's defects in the framework of TiO₂. The concentrations of the defects of both types depend on the catalyst preparation conditions.     

A study of the chemiluminescence behavior of myoglobin with luminol and its analytical applications

A chemiluminescence signal at 425 nm was observed when ferric state myoglobin was mixed with luminol in alkaline medium. Because the signal was remarkably enhanced in the presence of Fe(CN)₆ ^4–, analytical applications were investigated in a flow-injection system. The increase in chemiluminescence was linearly dependent on myoglobin concentration in the range 0.1 to 100 nmol L^–1, and the limit of detection was 0.04 nmol L^–1 with relative standard deviation 3.2% (3). It was also found that binding of Mb with the ligands CN^–, SCN^–, and F^– significantly inhibited the chemiluminescence reaction. The linear dynamic ranges for the ligands were 1.0–300.0, 0.1–3.0, and 0.5–100.0 nmol L^–1, and the limits of detection (S/N=3) 0.4, 0.04, and 0.2 nmol L^–1, for F^–, CN^–, and SCN^–, respectively. The relative standard deviations were 5.32%, 6.13%, and 3.38% for 0.1 nmol L^–1 CN^–, 0.5 nmol L^–1 SCN^–, and 1.0 nmol L^–1 F^–, respectively. At a flow rate of 2.0 mL min^–1 the assay could be accomplished in 1 min, including sampling and washing. The method has been successfully applied to the determination of myoglobin in human urine and F^– in water samples. A possible mechanism of chemiluminescence production by myoglobin and luminol is presented.     

Zirconium-Containing Compositions with a Component Ratio Characteristic of the Garnet Structure: Physicochemical and Catalytic Properties

The possibility for the formation of garnet structures in the Mn–Fe–Zr–O and Ca–Sm–Zr–O systems obtained by the precipitation of the corresponding salts is studied. It is shown that, in the Mn–Fe–Zr–O system, garnet is crystallized at 860–920°C, for which probable cation distribution is estimated to be {Zr_2.5 ⁴⁺Mn_0.5 ²⁺}[Mn₂ ²⁺](Fe_2.5 ³⁺Mn_0.5 ³⁺)O₁₂. In the Ca–Sm–Zr–O system, the perovskite CaZrO₃, pyrochlore Sm₂Zr₂O₇, and CaO are formed at 900–1200°C, but compounds with garnet structures are not found. The reported systems are characterized by surface areas of 300–450 m²/g at 450°C, and they have the polydisperse distribution of pores over sizes. The introduction of surfactants at the stage of component mixing enables an increase in the overall pore volume and mechanical strength of these systems. The Mn–Fe–Zr and Ca–Sm–Zr compositions are active catalysts for the complete oxidation of hydrocarbons.     

Conformational features of peptide fragments of the C-end of histone H1

The conformational possibilities of four synthesized oligopeptides with the amino acid sequences 165–172, 173–184, 152–172, and 152–184 of the C-end of histone H1 of calf thymus above been studied in solution under various conditions by the method of circular dichroism.V. I. Nikitin Institute of Chemistry, Academy of Sciences of the Tadchik SSR, Dushanbe. Institute of Cytology, Academy of Sciences of the USSR, Leningrad. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 793–798, November–December, 1990.     

Sizes and Conformation of the Molecules of DNA–Surfactant Complexes in Dilute Solutions and on the Atomic Smooth Substrates

The conformations of the molecules of DNA–surfactant complexes in dilute solutions and on the atomic smooth surfaces of mica and highly oriented pyrolytic graphite were comparatively studied by the methods of isothermal diffusion, electric birefringence, and atomic force microscopy. The DNA–surfactant complexes were deposited onto the substrates from a chloroform solution. The number of particles of the DNA–surfactant complex on the substrate was changed by varying the concentration of the initial solution within three orders of magnitude. The particles of a shape close to ellipsoidal, 25–70 nm in diameter and 2–4 nm high, were observed at the lowest concentration of DNA–surfactant solution on the mica substrate. The shape and size of these particles correspond to those of a single DNA–surfactant complex, calculated from its translational diffusion coefficient and the time of orientational relaxation in dilute solutions. An increase in the number of molecules deposited onto the substrate leads to an increase in the characteristic sizes of DNA–surfactant complex particles observed by the atomic force microscopy. This may be associated with the aggregation of DNA–surfactant complexes.     

In situ study on the effects of Ni and Mo on the passive film formed on Fe–20Cr alloys by photoelectrochemical and Mott–Schottky techniques

Effects of alloying elements (Ni and Mo) on the structure of passive film formed on Fe–20Cr alloys in pH 8.5 buffer solution were explored by analyzing the in situ electronic properties measured using the photoelectrochemical technique and Mott–Schottky analysis. The passive film formed on Fe–20Cr–10Ni was found to be mainly composed of Cr-substituted γ-Fe₂O₃ from similarities in photocurrent response for the passive films formed on the alloy and Fe–20Cr. On the other hand, the photocurrent spectra for the passive films of Fe–20Cr–15Ni–(0, 4)Mo alloys exhibited the spectral components associated with NiO and Mo oxide (MoO₂ and/or MoO₃) in addition to that induced by Cr-substituted γ-Fe₂O₃. Mott–Schottky plots for the passive films formed on Fe–20Cr–(10, 15)Ni and Fe–20Cr–15Ni–4Mo confirmed that the passive films on Fe–20Cr–(10, 15)Ni–(0, 4)Mo alloys have a base structure of Cr-substituted γ-Fe₂O₃ with variation of densities of shallow and deep donors depending on the Ni and Mo contents in the alloys. We suggest that the passive film formed on Fe–20Cr–(10, 15)Ni and Fe–20Cr–15Ni–4Mo alloys are composed of (Cr, Ni, Mo)-substituted γ-Fe₂O₃ when the concentrations of Ni and Mo are below critical values. However, NiO and Mo oxide (MoO₂ and/or MoO₃) would be precipitated in the passive films when the concentrations of Ni and Mo exceed critical values.     

Solvent extraction and separation of some lanthanides and americium by extraction chromatography in the system Aliquat-336 — LiNO3 and HNO3

Summary The liquid-liquid extraction of Nd, Eu, Ho, and Am nitrates by means of the radiotracer method in the system tri-caprylmonomethyl ammonium nitrate /Aliquat-336/ — lithium nitrate and nitric acid was investigated.The mixture of tracer quantities of Eu–Am, Nd–Pr, Sm–Pm, Gd–Eu, Er–Ho, Tm–Er, Yb–Tm, and Lu–Tm were separated by column partition chromatography.

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Lösungsmittelextraktion und Trennung einiger Lanthanide und Americium durch Extraktions-chromatographie im System Aliquat-336 — LiNO₃ und HNO₃

Zusammenfassung Es wurde die Flüssig-Flüssig-Extraktion von Nd-, Eu-, Ho- und Am-Nitraten mit Hilfe radioaktiver Markierung im System Tri-caprylmonomethyl-ammoniumnitrat-/Aliquat-336/-Lithiumnitrat und Salpetersäure untersucht.Die Markierungsgemische von Eu–Am, Nd–Pr, Sm–Pm, Gd–Eu, Er–Ho, Tm–Er, Yb–Tm und Lu–Tm wurden durch Säulen-Verteilungs-Chromatographie getrennt.

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Extraction par solvant et separation de quelques lanthanides et d'americium par chromatographie d'éxtraction dans le système «Aliquat-336, LiNO₃, HNO₃»

Sommaire On a étudié, au moyen de la méthode des radiotraceurs, l'éxtraction liquide-liquide de nitrates de Nd, Eu, Ho et Am dans le système «nitrate de tri-caprylmonométhyl ammonium [Aliquat-336], nitrate de lithium, acide nitrique».Les mélanges de Eu–Am, Nd–Pr, Sm–Pm, Gd–Eu, Er–Ho, Tm–Er, Yb–Tm et Lu–Tm à la dose des traceurs radioactifs, ont été résolus en leurs composants chromatographie de partage sur colonne.

     

Extraction characteristics of pertechnetate with tetraphenylarsonium in the presence of chloride,nitrate and perchlorate anions

Selected extraction systems of TcO ₄ ^– –(H,Na)A–H₂O/R(TcO₄,A)–CHCl₃, C₆H₅NO₂ type, where A=Cl^–, NO ₃ ^– , ClO ₄ ^– , R=(C₆H₅)₄As⁺, were studied. The solvent extraction of sub- and super-stoichiometric ratio of TcR was performed. The solubility of (C₆H₅)₄AsTcO₄ in water, chloroform and nitrobenzene were determined too. The results of the extractions are presented in the form of TcO ₄ ^– distribution dependencies on the phase composition and the extraction constants of individual TcO ₄ ^– , Cl^–, NO ₃ ^– , ClO ₄ ^– anions and TcO ₄ ^– -Cl^–, TcO ₄ ^– –NO ₃ ^– , TcO ₄ ^– –ClO ₄ ^– ion pairs.     

Characteristic frequencies in the infrared spectra of pyrazolines

Pyrazolines are characterized by valence vibrations at the following frequencies: C=N (1580–1627 cm^–1), H-C³=N (3040–3063 cm^–1), H-N (3270–3305 cm^–1) and CH₃-N (2780–2805 cm^–1). Lowering of the frequencies of the valence vibrations of C=N in pyrazolines, when compared with the magnitudes characteristic of alkyledene amines and oximes, is regarded as a consequence of coupling with the unshared electron pair of the neighboring nitrogen atom. By means of the IR spectra, it is possible to determine the position of the double bonds in the pyrazoline ring, to distinguish between pyrazolines substituted and nonsubstituted in positions 1 and 3, and to establish the presence of geminate (twin) methyl groups and methyl groups in position 1.     

The effect of pressure on the dissociation constant of hydrofluoric acid and the association constant of the NaF ion pair at 25°C

The effect of pressure on the dissociation constant of hydrofluoric acid was determined by using the indicator technique at 25°C at an ionic strength of 0.1m over a pressure range of 1 to 2000 atm. A value of 3.14 for pK _a ^* at I =0 was obtained by extrapolation to zero ionic strength at 1 atm. The pressure dependence yielded a partial molar volume change of –9.6 cm³-mol^–1 and a compressibility change of — 35×10^–3 cm³-mol^–1 –atm^–1 for the dissociation. The dependence of ionic strength on the association constant K _A ^* of NaF was studied at 25°C and 1 atm. Extrapolation to I=0 yielded a pK _A ^* of –0.78. The pressure dependence of K _A ^* gave a change of volume of 3.26 cm³-mol^–1 and a change in compressibility of 6×10^–3 cm³-mol^–1-atm^–1 for the formation of the ion pair.     

Mechanism of the Effect of Thermal Treatment on the Formation of Strong Acid Sites in the Surface Layers of Sulfated Metal Oxides

Strong acid catalysts were synthesized by the impregnation of hydrated ZrO₂ and TiO₂ with sulfuric acid followed by thermal treatment at different temperatures. The surface acidity and crystallochemical characteristics of the catalysts were studied by potentiometry and X-ray diffraction analysis, respectively. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 350 to 600°C for SO^2– ₄/ZrO₂ or to 200°C for SO^2– ₄/TiO₂; this increase correlated with the degrees of crystallinity of the samples. A hypothesis was proposed to explain the gradual accumulation of acid sites in the surface layer in the course of thermal treatment. It was assumed that, because of crystallographic changes that caused the weakening or even rupture of Zr–O–S and Ti–O–S bonds in modified surface layers, these layers exhibited an enhanced reactivity in contact with water vapor. Subsequently, this resulted in the formation of strongly acidic grafted M–O–SO₃–H⁺ groups.     

Influence of oxidative strength of stable cation radicals of para-substituted triphenylamines on the process of pyrrole polymerization and on the properties of the polymeric products

A study has been made of the influence of the oxidative strength of stable cation radicals (CRs) of parasubstituted triphenylamines on the process of pyrrole polymerization and on the physicochemical characteristics of the resulting polymer. The triphenylamines had the general formula (X-C₆H₄)₃ N ^{+ ·} A, where X=–OCH₃ and A^–=SbCl₆ ^– (I); X=–CH₃ and A^–=SbCl₆ ^– (II); X=–Br and A^–=SbCl ₆ ^– (III); or X=–OCH₃ and A^–=BF₄ ^– (IV). For the CRs I, II, and IV, polypyrrole formation was observed, the product being soluble in organic solvents, specifically in CH₃CN. With increasing oxidative strength of the CR in the series I相似文献