Magnetic anisotropy of cyclopropane and epoxide rings

MO LCAO results are presented for the interatomic contribution to the anisotropy of the diamagnetic susceptibility; values of _d=–23.5 · 10^–6 and _d=–13.8 · 10^–6 cm³/mole are obtained for the cyclopropane and epoxide ring systems, respectively. The results are used to interpret PMR spectra in terms of the configuration and conformation of the and forms of caran-4-ol and two stereoisomers of caranone.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Summary. Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

Electrochemical Determination of 4-Nitrophenol Using a Single-Wall Carbon Nanotube Film-Coated Glassy Carbon Electrode

A single-wall carbon nanotubes (SWNT) film coated glassy carbon electrode (GCE) was fabricated for the direct determination of 4-nitrophenol (4-NP). The electrochemical behaviors of 4-NP at the SWNT-film coated GCE were examined. In 0.1M phosphate buffer with a pH of 5.0, 4-NP yields a very sensitive and well-defined reduction peak at the SWNT-modified GCE. It is found that the SWNT film exhibits obvious electrocatalytic activity towards the reduction of 4-NP since it not only increases the reduction peak current but also lowers the reduction overpotential. Based on this, an electrochemical method was proposed for the direct determination of 4-NP. The reduction peak current varies linearly with the concentration of 4-NP ranging from 1×10^–8 to 5×10^–6M, and the detection limit is 2.5×10^–9M after 3min of open-circuit accumulation. The relative standard deviation at 2×10^–7M 4-NP was about 6% (n=10), suggesting excellent reproducibility. This new method was successfully employed to determine 4-NP in several lake water samples.     

Cardiac glycosides of theCheiranthus allioni. XII

The seeds ofCheiranthus allioni hort. have yielded three new cardenolides the structures of which have been established and which have been named as 4-dehydrosarmentogenin (II), 4-dehydrosarmentogenin rhamnoside (I), and 4-dehydrosarmentogenin rhamnoglucoside (IV). (II) — C₂₃H₃₂O₅. m.p. 296–302°, [] _D ²⁰ +26.2±3° (in pyridine) is 3,11,14-trihydroxy-14-card-4,20(22)-dienolide. (I) C₂₉-H₄₂O₉, m.p. 268–275°, [] _D ²⁰ –38.2±3° (chloroform-ethanol) is 11,14-dihydroxy-3--L-rhamnopyranosyloxy-14-card-4,20(22)-dienolide.(IV) C₃₅H₅₂O₁₄, [] _D ^20D –44.1±3° (methanol), is 3-(4-O--D-glucopyranosyl--L-rhamnopyranosyloxy)-14-card-4, 20(22)-dienolide. An independent synthesis of 4-dehydrosarmentogenin (II) has been carried out, starting from 3,5,11,14-tetrahydroxy-5,14-card-20(22)-enolide, which has confirmed its structure.For Communication XI, see [1].All-Union Scientific-Research Drug Institute, Kharkov. Kharkov State Pharmaceutical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 119–125, January–February, 1987.     

Zum Spingleichgewicht5T2−1A1 in Fe(II)py 2 phen(NCS) 2

Zusammenfassung Die magnetischen, spektralen und strukturellen Eigenschaften des gemischten Amminkomplexes [Fe(II)py ₂ phen(NCS)₂] werden diskutiert. Der Orbitalparamter liegt mit 11 700 cm^–1 nahe der Spinpaarungsenergie für den mittleren kovalenten Fall 11 000 bis 12 000 cm^–1 und erlaubt so ein Spingleichgewicht zwischen den Spektralzuständen⁵T₂–¹A₁. Dieses Gleichgewicht wird durch magnetische Messungen bei verschiedenen Temperaturen nachgewiesen.

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On the spin equilibrium⁵T₂–¹A₁ in [Fe(II)py₂phen(NCS)₂]

The magnetic, spectral and structural properties of the mixed ammine [Fe(II)py ₂ phen(NCS)₂] are discussed. The orbital parameter of about 11 700 cm^–1 near to the spin-pairing energy for the mean covalent case 11 000 to 12 000 cm^–1 allows a spin equilibrium between the spectral states⁵T₂–¹A₁, put in evidence by the magnetic measurements at different temperatures.

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Mit 3 Abbildungen

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Photorefractive Composites Based on Nanocrystalline Carbocyanine Dye J-Aggregates with a Fast Response Time

The use of carbocyanine dye J-aggregates as sensitizers of photoelectric sensitivity and chromophores with the third-order nonlinear optical polarizability made it possible, by the action of two intersecting He–Ne laser (633 nm) beams and an applied electric field, to obtain photorefractive spatial modulation of the refractive index in a nonplasticized polymer layer having the glass transition temperature of about 230°C with a short (20 ms) time of response to this action. A fairly high two-beam-coupling gain coefficient was obtained, which reached a value of = 218 cm^–1 at an applied field of E ₀ = 50 V/m. The net internal gain (difference between the beam-coupling gain coefficient and the absorption coefficient ) was – = 143 cm^–1 under these conditions.     

Fluorescence Quenching Studies of Curcumin by Hydrogen Peroxide in Acetonitrile Solution

Summary. Steady state quenching studies of curcumin, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, fluorescence by hydrogen peroxide were conducted in acetonitrile solution. A quenching rate constant, k_q, of 1.05×10¹⁰M^–1·s^–1 was obtained with a short fluorescence lifetime of 347ps. The reaction rate constant, which is within the diffusion-limited regime, is activation-controlled. The rate constant of deactivation of the thermally excited curcumin was 1.2 orders of magnitude more nonradiative (2.67×10⁹s^–1) than radiative (2.16×10⁸s^–1). The reaction was exothermic with a G° of –1.97eV and solvent reorganization energy of 1.37eV. These values indicate that the electron transfer reaction is solvent-mediated with electron transfer rate constant, k_ET, of 2.16×10¹⁰s^–1.     

Characterization of airborne particulates by laser microprobe mass analysis

Summary Laser microprobe mass analysis (LAMMA) was applied to characterize aerosol particles collected and separated from 16m to 0.06m by a low pressure cascade impactor. Positive ion LAMMA spectra showed characteristic molecular peaks such as PbCl⁺, a series of Si₂O⁺–Si₂O₄ ⁺ and NaAl₂Si₂O₂ ⁺–NaAl₂Si₂O₅ ⁺, and TiO⁺ in 0.06–0.12m, 0.5–1m and 4–8m fraction, respectively. In the negative ion LAMMA spectra, it was observed that the fragment peaks of sulfate ions were deficient above 2m and those of nitrate ions were deficient under 2m. LAMMA allows remarkable insights into the chemical nature of aerosol particles.

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Charakterisierung luftgetragener Teilchen durch Laser-Microprobe-Massenspektrometrie

Zusammenfassung Laser-Microprobe-Spektrometrie (LAMMS) wurde zur Analyse atmosphärischen Aerosols herangezogen, welches im Korngrößenbereich zwischen 16m und 0.06m mit einem Niederdruckkaskadenimpaktor fraktioniert gesammelt wurde. Positive LAMMS-Spektren zeigten charakteristische molekulare Peaks, wie etwa PbCl⁺, eine Serie von Si₂O⁺–Si₂O₄ ⁺ und NaAl₂Si₂O₂ ⁺–NaAl₂Si₂O₅ ⁺, sowie TiO⁺ in der 0,06–0,12-m,- 0,5–1–m- bzw. 4–8-m-Fraktion. In den negativen LAMMS-Spektren konnten über 2m keine Fragmentpeaks für Sulfationen, unter 2m. keine für Nitrationen beobachtet werden. LAMMS ermöglicht eine bemerkenswerte Einsicht in die chemische Natur von Aerosolteilchen.

     

Configurations of the [Pd(NO2)4]2- Complex Anion: Crystal Structure of Ag4A2[M(NO2)4]3 (M = Pd, Pt; A = K, Rb)

An integrated Xray diffraction study was performed on polycrystals and single crystals of three new isostructural phases with general formula Ag₄A₂[M(NO₂)₄]₃ (M = Pd, Pt; A = K, Rb). Data on the crystal structure solution (CAD4 diffractometer, MoK radiation, graphite monochromator = 2–30° are presented. In one crystallographically independent [M(NO₂)₄]^2- complex anion, the planar square coordination of the central atom is completed to 4 + 2 by two oxygen atoms at a distance of 3.02–3.12 in the other anion, it is completed to 4 + 1 + 1 by an oxygen atom at a distance of 3.12–3.30 and an Ag⁺ cation at a distance of 3.04–3.11 . Part of the Ag⁺ cations form Ag - Ag dimers with a distance of 3.03–3.07. Crystalchemical analysis of known structures containing [Pd(NO₂)₄]^2- complex anions was performed. It has been established that in none of the cases do any of the possible limiting configurations occur.     

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).     

Kinetics and mechanism of isothermal dehydration of LiKC4H4O6 · H2O single-crystals

The kinetics of isothermal dehydration of LiKC₄H₄O₆.H₂O single-crystals was investigated in the [001] crystallographic direction under a dynamic vacuum of 6.7×10^–5 Pa with a quartz crystal microbalance. The removal of H₂O molecules may be described by a diffusion equation for a semi-infinite medium. The diffusion coefficients vary from 2.13×10^–11 cm² s^–1 at 391.7 K to 9.9×10^–9 cm² s^–1 at 453.2 K. The scanning electron microscope data provide some evidence that the dehydration is not a topochemical reaction. From the experimental data it is concluded that the anhydrous product is in the state of premelting. This explains the anomalous diffusion energyE _D=37±1 kcal mol^–1 and preexponential factorD ₀=5×10⁹ cm² s^–1.

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Zusammenfassung Die Kinetik der Entwässerung von LiKC₄H₄O₆.H₂O in [001] — Richtung unter dynamischem Vakuum wurde mit einer Quarzkristall-Mikrowaage verfolgt. Die Abgabe von Wasser kann mit einer Diffusionsgleichung für ein halb-unendliches Medium beschrieben werden, die Diffusionskoeffizienten variieren von 2, 13 · 10^–11 cm²s^–1 bei 391,7 K bis 9,9 · 10^–9 cm² s^–1 bei 453,2 K. Rasterelektronenmikroskopische Aufnahmen zeigen, daß die Entwässerung nicht topochemisch abläuft. Nach dem experimentellen Ergebnis befindet sich das entwässerte Produkt in einem Vorschmelz-Stadium. Daraus erklären sich die anomalen Werte für die DiffusionsenergieE _D=(37±1) kcal mol–1 und den präexponentiellen FaktorD ₀=5 · 10⁹ cm² s^–1.

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6,7 · 10. LiKC₄H₄O₆.H₂O [001]. . 2,13·10^{–11 2 –1} 391,7 9,9·10^{–9 2 –1} 453,2 . , . , «», E =37±1 ·^{– 1} ₀=5·10⁹²·^–1.

     

Path of “dry” electrons before localization in liquid hydrocarbons

Conclusions On the basis of measurements of values of in liquid hydrocarbons, it has been shown that the path length before localization of a photoliberated electron increases with increasing mobility of the excess electron, from approximately 40 Å (methylcyclohexane) to 200 Å (isooctane). In a liquid with10^–2 cm²/V·sec (methylcyclohexane, hexane), the localization takes place before or immediately after thermalization of the electron. In a liquid with>10^–1 cm²/V·sec, the electron passes through the main part of its path before localization, being in thermal equilibrium with the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2198–2203, October, 1985.     

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.     

Heat capacity of indium from 300 to 1000 K

The heat capacity of high-purity indium has been determined by adiabatic-shield calorimetry in the range 300 to 1000 K. Values of thermodynamic functions have been calculated andC _p (1000 K), [H° (1000 K)–H° (298.15 K)], and [S° (1000 K)–S° (298.15 K)] are (27.11±0.15) J K^–1 mole^–1, (22873±70) J mole^–1, and (41.567 ±0.125) J K^–1 mole^–1, respectively. The enthalpy of fusion is (3283±7) J mole^–1 and the melting temperature (429.77±0.01) K. The premelting heat capacity is compatible with the presence of a mole fractionx 1·10^–6 of a liquid-soluble/solidinsoluble impurity in the sample.

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Zusammenfassung Die Wärmekapazität von hochreinem Indium wurde im Bereich von 300 bis 1000 K durch adiabatische Schildkalorimetrie bestimmt. Die Berechnungen der thermodynamischen Funktionen:C _p (1000 K), [H° (1000 K)–H° (298.15 K)] und [S° (1000 K–S° (298.15 K)] ergab 27.11±0.15 J K^–1 Mol^–1, (22 875±70) J Mol^–1, bzw. (41.567±0.125) J K^–1 Mol^–1. Die Schmelzenthalpie beträgt (3283±7) J Mol^–1 und die Schmelztemperatur (429.77±0.01) K. Die Vorschmelz-Wärmekapazität ist mit der Gegenwart einer Molfraktionx1×10^–6 einer flüssig-löslich/fest-unlöslichen Verunreinigung in der Probe vereinbar.

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Résumé La chaleur spécifique de l'indium de haute pureté a été déterminée entre 300 et 1000 K par calorimétrie adiabatique. Les valeurs des fonctions thermodynamiques suivantes ont été calculées:C _p (1000 K)=(27.11±0.15) J K^–1mol^–1, [H° (1000 K)–H° (298.15 K)]= (22 875±70) J mol^–1 et [S° (1000 K)–S° (298.15 K)]=(41.567±0.125) J K^–1 mol^–1. L'enthalpie de fusion est (3283±7) J mol^–1 et la température de fusion (429.77±0.01) K. La chaleur spécifique de pré-fusion est compatible avec la présence d'une fraction molairex1×10^–6 d'une impureté dans l'échantillon, soluble dans le liquide, insoluble dans le solide.

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C - 300 1000 . : _p(1000 ), [ (1000 ) — H (298,15 )] [S (1000 ) — S (298.15 )], : 27.11±0.15 . ^–1. ^–1, 2 2875±70 . ^–1 41.567±0.125 . ^{– 1–1}. 3283±7 .^–1, – 429.77±0,01 . - / 1.10^–6.

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The assistance of Bjørn Lyng Nielsen with the experimental work is recognized with thanks.     

Determination of Trace Proteins by Rayleigh Light Scattering Technique with Indophenol Blue

The interaction of indophenol blue (IPB) with proteins in aqueous solution has been studied by optical absorption and Rayleigh light scattering (RLS) spectroscopy. At pH 3.8, the weak RLS of IPB is enhanced by proteins. Based on this phenomenon, a novel method for the determination of proteins at nanogram levels using the RLS technique is developed. The method is simple, practical and sensitive. The linear range is 0.25–20.9µgmL^–1 for BSA, and 0.25–17.6µgmL^–1 for HSA. The detection limits (S/N=3) are 23ngmL^–1 for BSA and 22ngmL^–1 for HAS. The results for the determination of proteins in human serum samples are very close to those obtained by an established clinical method. There is very little interference from amino acids, metal ions or other coexisting compounds.     

Synthesis,spectroscopic studies and magnetic properties of binuclear complexes of the first transition series cations bridged by 2,2′-bipyrimidine

Binuclear complexes [M₂Cl₄(-bpym)], where M = VO²⁺, Fe^II, Co^II or Cu^II and bpym = 2,2-bipyrimidine, and [M₂(hfacac)₄(-bpym)] complexes, where hfacac = hexafluoroacetylacetonate and M = Fe^II, Ni^II or Co^II have been synthesized and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r spectroscopies and by magnetic susceptibility measurements (in the 4.2–291K range). Co^II and Fe^II are in a high spin state. [(VO)₂Cl₄(-bpym)] is paramagnetic, without significant interactions. [Fe₂Cl₄(-bpym)] shows a singular behaviour explained by an antiferromagnetic intradimer exchange and a ferromagnetic interdimer interaction. All other complexes are antiferromagnetic, with an intramolecular exchange parameter, J, varying from –3.3 cm^–1 for Co^II/math> to –109 cm^–1 for Cu^II.     

A Simple Sensitive Spectrophotometric Method for the Determination of Ce4+ Using Variamine Blue as a Chromogenic Reagent

A rapid and sensitive spectrophotometric method is described for the determination of trace amounts of cerium using Variamine Blue (VB) as a chromogenic reagent. The proposed method is based on the reaction of cerium with potassium iodide in acidic medium to liberate iodine, which oxidizes Variamine Blue to give a violet colored species with an absorption maximum at 560nm. Beers law was obeyed in the range 2–10µg mL^–1 of cerium. The molar absorptivity and Sandells sensitivity are found to be 1.65×10⁴L mol^–1cm^–1 and 8.48×10^–3µgcm^–2, respectively. The proposed method has been successfully applied to the determination of cerium in alloy and synthetic mixtures.     

Rate constants and mechanism of the reactions of N(4S) atoms with methane and ethane

The channel for the reaction of nitrogen atoms and methane yielding hydrogen atoms does not exceed 10% at 20C. The rate constant for the reaction of nitrogen atoms and ethane at 20C is (4 ± 2)·10^–16 cm³/sec.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 705–706, March, 1990.     

Gamma radiolysis of Methyl Red solution and reaction induced by γ-irradiated NaCl in Methyl Red

The -radiolysis of Methyl Red solution in HCl medium at pH=2 has been studied along with energy transfer reaction brought about byF and hole centers of -irradiated NaCl. The G-values for degradation of the azo dye indicator by radiolysis and -irradiated salt were determined as 9·10^–1 and 4.8·10^–3, respectively. The kinetic rate constants (k) of degradation are evaluated as 2·10^–5 rad^–1 in the case of direct radiolysis, while for the irradiated salt it is 2·10^–7 rad^–1. The extent of degradation by direct -radiolysis is 100–200 times greater as compared to that by the -irradiated salt. The same mechanism is proposed for radiolysis as well as the reaction induced by -irradiated sodium chloride.     

Triterpene glycosides ofHedera taurica XV. Structures of glycosides St-I3, St-I4a, St-I4b, and St-I5 from the stems of Crimean ivy

From the stems of Crimean ivyHedera taurica Carr. (fam. Araliaceae) we have isolated the new triterpene glycosides St-I₃, St-I₅, and St-I_4a, which are, respectively, the 3–0--D-glucopyranoside 28-O-[O--L-rhamnopyranosyl-(14)-O-(6-O-acetyl--D-glucopyranosyl)-(16)-O--D-glucopyranosides] of oleanolic acid and of hederagenin and the 3-O--D-glucopyranuronoside 28-O--gentiobioside of oleanolic acid, and also the previously known 3-O-[O--D-galactopyranosyl-(12)--D-glucopyranuronoside 28-O--D-glucopyranoside] of oleanolic acid (glycoside Rb-4).Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 404–410, May–June, 1997.