Cardiac glycosides ofAcokanthera venenata

Six cardenolides have been isolated from the leaves ofAcokanthera venenata G. Don: AV-1, mp 252–255°C, [] _D ²⁰ +39.4° (MeOH); AV-2, mp 199–208°C, [] _D ²⁰ -59.3° (MeOH); AV-3, mp 269–275°C/300–304°C, [] _D ²¹ –69.8° (MeOH); AV-4, mp 279–289°C; AV-5, mp 222–225°, [] _D ²⁰ -64.3° (MeOH); and AV-6, mp 193–196°C [] _D ²⁰ –23.8° (MeOH — CHCl₃). AV-5 has been identified as acovenoside A. AV-3 is a new cardiac glycoside: it is 1-acetoxy-3-(4-O--D-glucosyl-3-O-methyl--L-talomethylosyloxy)-14-hydroxy-5, 14-card-20(22)-enolide (glucoacovenoside B).Khar'kov State Pharmaceutical Institute. All-Union Scientific Research Institute of Drug, Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 372–376, May–June, 1987.     

Reactions of pennogenin and related compounds. IV. Formation of (25R,22′R,25′R)-3β,3′β-diacetoxy-26,22′-epoxy-16,16′-bifurosta-5,20(22),5′,17′(20′)-tetraen-26′-ol from pennogenin diacetate under the action of BF3·Et2O

A new direction of the reaction of pennogenin diacetate with BF₃·Et₂O has been discovered in which a previously unknown dimeric steroid is formed — (25R,22R,25R)-3,3-diacetoxy-26,22-epoxy-16,16-bifurosta-5,20(22), 5,17(20)-tetraen-26-ol, the structure of which has been established as the result of an analysis of IR, UV,¹H and¹³C NMR, and mass spectra. A probable mechanism for the formation of the title compound from pennogenin diacetate is suggested.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Institute of Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 202–208, March–April, 1990.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Iron Catalysis of SO2 Oxidation in the Atmosphere

The mechanisms of SO₂ oxidation catalyzed by iron ions in the droplet phase of the convective cloud in the lower atmosphere were examined. The relations of the catalytic SO₂ decrease to the concentration of the iron ions and to the intensity of fluxes to the droplet of the OH _(g) and HO _2(g) radicals were characterized. The determining role of the replacement of the low-reactive HO _2(g)(O^– _2(aq)) radical by the reactive SO^– _5(aq) radical in the sulfite medium during daytime was revealed. This process occurred due to the coupling of the decay of the radicals and their regeneration in the liquid-phase reactions O^– _2(aq) + FeOH²⁺ _(aq) Fe²⁺ _(aq) + OH^– _(aq) + O_2(aq), HSO^– _5(aq) + Fe²⁺ _(aq) FeOH²⁺ _(aq) + SO^– _4(aq)HSO ₃ ^- _(aq),O_{2 (aq)} SO^– _5(aq).     

Transference numbers of aqueous HCl up to 15 mol-kg−1 at 25°C: A systematization and reassessment

Ion-transfer parameters of aqueous hydrochloric acid over a wide molality range have been re-investigated taking the concurrent solventtransfer into due account. In this context, the transference numbers for the hydrogen ion _H and for water _w have been determined from 10^–2 to 15 mol-kg^–1, together with the corresponding infinite-dilution values _H ^o and _w ^o , by processing a set of nearly a hundred emf measurements (some twenty of them new for this work) on HCl concentration cells with transference with both cation-reversible and anion-reversible electrode pairs.     

Crystal Structures of Two New Holmium Polysulfides in the Series of Rare-Earth Polychalcogenides

The crystal structures of two polysulfide phases HoS_1.885(5) (I) and HoS_1.863(8) (II) were determined; the integer stoichiometric ratio was found to be Ho₈S₁₅. The data were collected on an Enraf-Nonius CAD-4 automatic diffractometer using the standard procedure (MoK, graphite monochromator, an absorption correction applied based on -scan data). Crystal I: space group P4/nmm, a = 3.820(1), c = 7.840(3) , V = 114.40(6) ³, Z = 2 for the composition HoS_1.885(5), d _calc = 6.542 g/cm³, R = 0.0520 for 184 unique reflections with I_hkl > 2 _I; crystal II: space group P2₁/m, a = 10.961(2), b = 11.465(2), c = 10.984(2) , = 91.27(3)°, V = 1380.0(4) ³, Z = 24 for the composition HoS_1.863(8), d _calc = 6.486 g/cm³, R = 0.0596 for 5354 unique reflections with I_hkl > 2 _I. In both compounds, the Ho atoms are surrounded by 9 (8+1 for three atoms in II) S atoms forming monocapped square antiprisms. The Ho–S distances vary from 2.717 to 3.067 irrespective of the type of ion [S^2– or (S₂)^2–]; the maximal distance to the atoms completing the coordination is 3.684 . The compounds have PbFCl type structures composed of ...(S₂)^2–...Ho³⁺...S^2–...S^2–...Ho³⁺...(S₂)^2–... layer packets differently oriented in space relative to the unit cell axes. The S^2–...S^2– and S^2–...(S₂)^2– interlayer distances are mostly shorter than the sum of the ionic radii and vary within the limits of 3.331-3.558 and 3.029-3.784 for the first and second types, respectively. For I, the calculated site occupancies and densities are given depending on the composition Ho-S_2-x (x = 0.25-0); for II, the most probable formulas of rational compositions in the same range of x are presented.     

Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

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Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

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Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

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(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Minimum energy path equation for A+BC→AB+C type hydrogen atom abstraction reactions

The equation L₁X_AB+ln(L₁X_AB)=–L₂X_BC–ln(L₂X_BC) is suggested to predict the minimum energy path for A+BCAB+C type reactions. X=R–R^o, where R^o denotes the equilibrium bond length. Parameters L₁ and L₂ are assumed to depend on the properties of the bonds formed and cleaved, respectively.

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L₁X_AB+ln(L₁X_AB+ln(L₁X_AB)=–L₂X_BC–ln(L₂X_BC) A+BAB+C. X=R–R^o, R^o . , L₁ L₂ .

     

Quadrupole hyperfine interaction in iron(III) dicarboxylic acid complexes

Mössbauer and infrared spectroscopic studies of a series of iron(III) complexes of dicarboxylic acids, maleic, malonic, succinic, glutaric, adipic, pimelic, suberic, azealic and sebacic have been carried out at room temperature. All complexes exhibit a quadrupole doublet with isomer shift () values in the range of 0.62 –0.72 mm·s^–1 (with respect to SNP) and quadrupole splitting, E_Q=0.53–0.74 mm· s^–1. It is observed that tris complexes are formed up to pimelic acid, while bis complexes are formed those for the other three acids. Isomer shift () values do not vary significantly but E_Q values show a somewhat regular trend. Magnetic moment data indicate high spin Fe(III) in octahedral geometry.     

Femtosecond dynamics of relaxation of photoexcited meso-tetraferrocenylporphyrin in the nonprotonated and diprotonated forms (Fc4PH2 and Fc4PH42+)

The relaxation of the Q¹(—*) excited state of the nonprotonated Fc₄PH₂ and diprotonated Fc₄PH₄ ²⁺ forms of meso-tetraferrocenylporphyrin was studied by femtosecond laser absorption spectroscopy. Transition from the Q¹(—*) state to the charge-transfer state was shown to occur within 208±10 fs for Fc₄PH₂ and 9±3 ps for Fc₄PH₄ ²⁺. A fast vibrational relaxation with a characteristic time of 120—140 fs was found for both forms. The relaxation time of Fc⁺—P^– charge-transfer state for Fc₄PH₂ was 17±4 ps.     

Catalytic oxidative hydrolysis of H2PO2? anions in the presence of RhCl3

Kinetics of H₂ evolution in the RhCl₃–NaH₂PO₂–HCl–H₂O system has been studied. As found by³¹P NMR, Rh(I) complexes with the Rh–P(OH)₂O^– bond are formed and play the role of catalysts in the subsequent H₂ evolution reaction.

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H₂ RhCl₃–NaH₂PO₂–HCl–H₂O. ³¹P Rh(I) Rh–P(OH)₂O^–, H₂.

     

Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

The thermodynamic characterization of the weakly complexed model system Sm³⁺-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm³⁺ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm³⁺ and the complexing site of xylitol in water is characterized by: K = 8.1, _rG^o = –5.2 kJ-mol^–1, _rH^o = –13.7 kJ-mol^–1, T_rS^o = –8.5 kJ-mol^–1, _rV^o = 8.8 cm³-mol^–1 and _rC _p ^o = 51 J-K^–1-mol^–1.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

Spectroscopic manifestation of the accidental degeneracy of π=Δ electronic adiabatic terms of linear triatomic systems

The semiclassical form of the absorption band of a linear triatomic system which corresponds to an electronic transition from the -ground state term to the excited intersection and terms was calculated. The analysis was carried for negligibly small defect of frequencies and in the absence of a shift of the equilibrium position on excitation. The experimentally observed CuCl₂ absorption spectrum was interpreted qualitatively as a , gS transition on the existence of a point of = accidental degeneracy. The 7000–24000 cm^–1 energy interval in the spectrum was analyzed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 222–225, March–April, 1988.     

Some remarks on the periodical change of the stability constants of the lanthanide complexes

The correlations between the values of the lgK (K = stability constant of the lanthanide complex) and the reciprocal of the ionic radius 1/r or the sum of the ionization potentials ₁ ³ I for the lanthanide ions were reviewed for different ligands. A straight-line relationship (lgK – lgK)/lgK vs. (1/r – 1/r)/(1/r) or vs. ( ₁ ³ I – ₁ ³ I)/ ₁ ³ I was found within the tetrads La-Nd, Gd-Ho, and Er-Lu.

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Bemerkungen zum periodischen Wechsel der Stabilitätskonstanten von Lanthaniden-Komplexen

Zusammenfassung Es wurde eine Übersicht der Korrelationen zwischen den Werten von logK (K = Stabilitätskonstante der Lanthanidenkomplexe) und den reziproken Ionenradien 1/r oder der Summe der Ionisierungspotentiale ₁ ³ I für die Lanthanidenionen für verschiedene Liganden gegeben. Dabei wurde eine lineare Korrelation für (lgK – lgK)/lgK gegen (1/r – 1/r)/(1/r) oder gegen ( ₁ ³ I – ₁ ³ I)/_1/3 I innerhalb der Tetraden La-Nd, Gd-Ho und Er-Lu aufgefunden.

     

Determination of Aqueous Nickel-Carbonate and Nickel-Oxalate Complexation Constants

An ion-exchange method was used to determine complexation constants for the Ni-oxalate and Ni-carbonate systems in a NaClO₄ background electrolyte. The Ni-oxalate data were interpreted in terms of a single Niox(aq) complex having log K ₁ values for Ni²⁺ + ox^2– Niox(aq) of 3.9 ± 0.1 (I.S. = 0.5 mol-L^–1 p[H] = 7.1) and 4.4 ± 0.1 (I.S. = 0.1 mol-L^–1 p[H] = 8.6) at 22 ± 1C. Specific ion-interaction theory (SIT) was used to obtain log K ₁ = 5.17 ± 0.05 (95% confidence level and = –0.23 ± 0.15) at I.S. = 0. The Ni-carbonate studies were carried out at p[H] values of 7.5, 8.5, and 9.6 in 0.5 mol-L^–1 NaClO₄/NaHCO₃ solutions. The NiCO₃(aq) species was the dominant complex in the [CO₃ ^2–] concentration ranges studied at all three p[H] values. A log K ₁ value for Ni²⁺ + CO₃ ^2– NiCO₃(aq) of 2.9 ± 0.3 was deduced at I.S. = 0.5 mol-L^–1. Extrapolating this value to zero ionic strength using the SIT approach yielded log K ₁ = 4.2 ± 0.3 (95% confidence level and = –0.26 ± 0.04). The data allowed upper bound values for the complexation constants for NiHCO₃ ⁺ and Ni(CO₃)₂ ^2– to be estimated, i.e., log K < 1.4 for Ni²⁺ + HCO₃ ^– NiHCO₃ ⁺, and log K ₂ < 2 for NiCO₃(aq) + CO₃ ^2– Ni(CO₃)₂ ^2–, respectively.     

IR-Untersuchungen an B-Tris (dimethylamino) boroxin und B-Tris[dimethylamino (d6)] boroxin

Zusammenfassung In B-Tri(dimethylamino)boroxin zeigt — im Gegensatz zum B-Trimethoxyboroxin — die B–O-Hauptbande nur geringe Kopplung mit CH₃-Deformationsschwingungen. Die B–N-Valenzbande tritt hingegen mit _sCH₃ in Wechselwirkung, wodurch Banden mit gemischtem Schwingungscharakter entstehen. In der deuterierten Verbindung liegt BN verkoppelt mit BO bei 1461 cm^–1

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In B-Tri(dimethylamino)boroxin coupling between the B–O ring stretching main-band and CH₃ is weak in contrast to B-trimethoxyboroxine. Interference between BN and CH₃ leads to bands of mixed character, one of them is above 1500 cm^–1. In [(CD₃)₂NBO] BN coupled with BO is at 1461 cm^–1.

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Mit 2 Abbildungen     

Solvent extraction and spectrophotometric including graphite furnace atomic absorption determination of molybdenum in the environment

A selective and sensitive method for the extraction and microgram determination of molybdenum (VI) with hydroxamic acid as yellow molybdenum-hydroxamate complex from acidic medium is described. The molybdenum-PCPPSAHA complex has _max 388 nm, molar absorptivity 5.0 × 10³l mol^–1 cm^–1. The system obeys Beer's law in the range of 1–28 g/ml of molybdenum(VI). Sandell's sensitivity is 0.0192 g cm² and stoichiometry of the complex is 12, molybdenum: PCPPSAHA while mixed complex molybdenum-PCPPSAHA-morin has _max 400 nm and molar absorptivity 5.9 × 10³lmo1^–1 cm^–1 and stoichiometry of the complex is 121.The molybdenum is determined by graphite furnace atomic absorption spectrophotometry after directly pipetted the extract into the furnace which increases the sensitivity 20 fold.     

Temperature-programmed reduction of CuO?NiO/Al2O3 catalysts

Reducibility of NiO/Al₂O₃ and CuO–NiO/Al₂O₃ catalysts has been studied by the TPR method within the temperature range 293–873 K. The results suggest that the copper content essentially does not influence the reducibility of NiO/Al₂O₃.

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NiO/Al₂O₃ CuO–NiO/Al₂O₃ TPR 293–873 . , NiO/Al₂O₃.

     

Extraction of sodium picrate into nitrobenzene in the presence of dicyclohexyl-18-crown-6

From extraction experiments and -activity measurements, the extraction constant corresponding to the equilibrium Na⁺(aq)+A^–(aq)+L(nb)NaL⁺(nb)+A^–(nb) taking place in the two-phase water-nitrobenzene system (A^–=picrate, L= dicyclohexyl-18-crown-6; aq-aqueous phase, nb=nitrobenzene phase) was evaluated as logK _ex(NaL⁺, A^–)=2.6.Further, the stability constant of the dicyclohexyl-18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: _nb(NaL⁺)=7.8.