Beiträge zur Chemie des Schwefels. 108. Schmelzwärme und spezifische Wärme des flüssigen Schwefels. Einfluß von Verunreinigungen

Using an adiabatic calorimeter, the heat of transition S_α ? S_β, the heat of fusion of S_β and the specific heat of the liquid had been determined on sulfur samples refined by zone melting and samples doped with chlorine, bromine and iodine. The data obtained from pure sulfur (heat of fusion: 1608 ± 8 J/Tom, specific heat of the liquid at 120°C: 29,4 J/Tom.°C) are about 10% lower than comparable values of other authors. Apparently they represent heat of fusion and specific heat of the pure cyclooctasulfur. The measurements on doped samples (δH_S = 1736 ± 10 J/Tom) are in agreement with the data reported in literature and include a portion of enthalpy from the transition reaction of cycloocta-sulfur (S_λ) to catenaocta-sulfur (S_π), requiring extremly long equilibrium times in pure sulfur. The influence of impurity on the caloric properties of the liquid sulfur is also indicated by the increasing width and decreasing highness of the C_p-maximum at 159°C with increasing amount of halogens. For the heat of transition S_α → S_β, independent of the amount of impurity, the literature data could be confirmed. At the samples doped with iodine there was observed a previously unreported transition near 65,9°C.     

Advanced system for separation of rare-earth fission products

A microprocessor-controlled radiochemical separation system, which has been developed at the INEL, has been further advanced to separate individual rare-earth elements from mixed fission products in times of a few minutes. The system was composed of an automated chemistry system fed by two ∼300μg²⁵²Cf sources coupled directly by a He-jet to transport the fission products. Chemical separations were performed using two high performance liquid chromatography columns coupled in series. The first column separated the rare-earth group by extraction chromatography using dihexyldiethylcarbamoylmethylphosphonate (DHDECMP) adsorbed on Vydac C₈ resin. The second column isolated the individual rare-earth elements by cation exchange chromatography using Aminex A-9 resin with α-hydroxyisobutyric acid (α-HIBA) as the eluent. Significant results, which have been obtained to date with this advanced system, are the identification of several new neutron-rich rare-earth isotopes including¹⁵⁵Pm (T=48±4 s) and¹⁶³Gd (T=68±3 s). In addition a half-life of 41±4 s is reported for¹⁶⁰Eu. Work supported by the U.S. Department of Energy under DOE Contract No. De-ACO7-76IDO-1570.     

Oscillatory reactions of sakhalin oil oxidation

After light irradiation of oil films on water surface the autoxidation process has been found to be of nonsteady auto-oscillatory character, which can be observed in rate oscillations of O₂ absorption. Also recorded have been intensity oscillations of the EPR signal from the radical counter added into an oil sample. Complex dynamics of autoxidation can be due to an autocatalytic process involving the participation of peroxides accumulated in oil during photooxidation., , , , O₂. , , . , , .     

Low-temperature vibrational spectra of cis-dichloro-(meso-2,3-diaminobutane)palladium(II) and platinum(II)

IR and Raman spectra of MCl₂(meso-2,3-diaminobutane), (M = Pd, Pt), have been recorded down to liquid nitrogen temperature or lower. It is shown that correlation coupling occurs between closely spaced hydrogen-bonded pairs of molecules, which form a “super molecule,” but not between all eight molecules in the unit cell. The lattice mode region is also understood in outline on the basis of motions of the “super molecules” Methyl torsional modes appear to be near 140 cm^?1.     

Preparation and sedimentation behavior in magnetic fields of magnetite-covered clay particles

This work is devoted to the preparation of magnetite-covered clay particles in aqueous medium. For this purpose, magnetite nanoparticles were synthesized by a coprecipitation method. These magnetic particles are adhered to sodium montmorillonite (NaMt) particles in aqueous suspensions of both materials, by appropriate control of the electrolyte concentrations. The best condition to produce such heteroaggregation corresponds to acid pH and approximately 1 mol/L ionic strength, when the electrokinetic potentials (zeta-potential) of both NaMt and Fe3O4 particles have high enough and opposite sign, as demonstrated from electrophoresis measurements. When a layer of magnetite re-covers the clay particles, the application of an external magnetic field induces a magnetic moment in clay-magnetite particles parallel to the external magnetic flux density. The sedimentation behavior of such magnetic particles is studied in the absence or presence of an external magnetic field in a vertical direction. The whole sedimentation behavior is also strongly affected by the formation of big flocculi in the suspensions under the action of internal colloidal interactions. van der Waals and dipole-dipole magnetic attractions between magnetite-covered clay particles dominate the flocculation processes. The different relative orientation of the clay-magnetite particles (edge-to-edge, face-to-edge, and face-to-face) are discussed in order to predict the most favored flocculi configuration.     

Isotachophoretic zone formation of serum albumin in different free fluid electrophoresis instruments

The isotachophoretic behavior of a model protein, serum albumin, was examined (i) by computer simulation, (ii) by capillary isotachophoresis in HPE 100 and Tachophor 2127, (iii) by continuous flow isotachophoresis in Elphor VaP 22 and the BIO-STREAM Separator and (iv) by recycling isotachophoresis in an apparatus of our own design. Variations in monitored zone shapes can be explained by differences in engineering aspects and fluid stabilization principles of the instruments.     

Triacylglycerols of the seeds and fruit flesh ofMandragora turcomanica

The triacylglycerols (TAGs) of the seeds and fruit flesh ofManagora turcomanica have been investigated for the first time using the methods of mass spectrometry and enzymolysis. It has been found that in the TAGs of the seeds the 182 acids undergo specific esterification in the sn-2 position, while in the TAGs of the flesh this position is acylated by 181 and 182 acids. For both parts of the fruit the main TAG species is sn-1(3)-oleoyldilinoleate, and the main types are represented by triunsaturated and monounsaturated-diunsaturated glycerides.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 322–326, May–June, 1999.     

Autocollimation spectroscopy for fast hydrogenic ions

We propose a new experimental method (Autocollimation Spectroscopy), which provides a strong suppression of systematic error contributions in the laser resonance spectroscopy of broad resonances. Using a bidirectional laser beam with a fixed wavelength in connection with high current pulsed ion beams an accuracy ofΔE _Exp/Γ≈5·10^?5 (Γ: resonance width) for the resonance energy seems to be achievable. Applying this technique to 2S-Lamb shift (LS) measurements on medium heavy ions would yield a precision ofΔE _Exp/E _LS≈1·10^?5, i.e. an improvement by a factor up to 100 as compared to present experiments.     

Stericaliy Congested Molecules: 2,2′-[(Biaryldiyl)bis(oxy)]bis[1,3,2-oxazaphospholidines]

The original suggestion that a through-space mechanism was operative in the seven-bond J(P, P) coupling constant of 30.3 Hz observed for 3.3′-bis(1,1-dimethylethyl)-2,2′-[3,3′,5,5′-tetrakis(1,1-dimethylethyl)-1,1′-biphenyl-2,2′-diyl]bis(oxy)}bis[1,3,2-oxazaphospholidine] ( 1a )) was investigated. In the solid-state CP-MAS ³¹PNMR spectrum of 1a , two nonequivalent P -atoms were observed; sufficient resolution could not be obtained to determine whether P, P coupling was present. The preparation and spectral data of the N-methyl analogue 1b and of the acyclic N-isopropyl analogue 6 (Scheme 1) provided evidence that a) the essentially exclusive formation (R*, R*,S*)- 1a in the reaction of the disodium biphenyldiolate 3a with the phosphorochloridite 4a is the result of significant differences in the free energy of activation (ΔG*) for the formation of the various diastereoisomers due to the steric congestion within the molecule and that b) the magnitude of the observed P,P coupling is dependent upon the degree of conformational freedom within the molecule. In the ³¹P-NMR spectrum of the P-sulfide 7 , which was prepared by the reaction of la with sulfur, 2s resonances were observed that strongly suggested that the lone electrons pair on P are involved in the mechanism for the transmission of coupling data. The (4S,5R) -12 and (4R, 5S) -12 of la were prepared in a three-step reaction sequence starting from the corresponding enantiomerically pure norephredine 8 (Scheme 2). Both (4S, 5R)- and (4R, 5S) -12 were obtained as a diastereoisomer mixture that differ by the configuration of the axis of chirality, i.e., (R*R*,R*)- and (R*,S*,R*) -12 were obtained. The major diastereoisomer was obtained upon recrystallization, and the atropisomers were observed to equilibrate in solution by monitoring the H? C(5) resonance in the ¹H-NMR with time (ΔG° = 0.4 kcal/mol; Fig. 2). The process observed corresponds to the restricted rotation about the central single bond of the biphenyl system. The isolation of an atropisomer with only a single ortho substituent on each aryl ring is quite rare. In the ¹³C-NMR spectrum of both (R*,R*,R*)- and (R*,S*,R*) -12 , C(5) is two-bond-coupled to the oxazaphospholidine P-atom (²J(C(5),P((2)) = 8.5 Hz) that is further virtually coupled to the P-atom of the other oxazaphospholidine ring (7J(P(2),P(2′)) = 30 Hz; ⁹J(C(5),P(2′)) = 0 Hz; δ(P(2)) = δ(P(2′)) = 136 ppm. In the ³¹P-NMR spectrum of (R*,R*,S*) -12 , which was prepared from the racemic chloridite (mixture of three diastereoisomers was obtained), a ⁷J(P(2),P(2′) of 36 Hz was observed. These observations provide strong evidence that seven-bond P,P coupling occurs in all three diastereoisomers of 12 . The observed P,P coupling is both independent of the configuration of the chiral axis and the configuration of the asymmetric P-centers. This independence of P,P coupling upon the configuration on P implies also the independence of the observed coupling upon the orientation of the lone-pair of electrons on P provided that the conformations of the diastereoisomers are similar in solution. The X-ray crystal structure of the complex formed from 1a and dichloro(cycloocta-1,5-diene)platinum(II) was obtained and the solid-state structure discussed. The major diastereoisomer of (4S,5R) -12 was used as a chiral ligand in asymmetric hydrosilylation and hydrogenation reactions (Scheme 3).     

Laser-Induced Electron-Transfer Processes in a Pyrene–β-Cyclodextrin Complex in Titanosilicate Systems

We have used fluorescent spectroscopy and laser flash photolysis to investigate the photonics of pyrene molecules in a pyrene–-cyclodextrin inclusion complex in various media. We have observed a protective effect of -cyclodextrin relative to solubilized pyrene molecules during quenching of fluorescence by Ti ions (or titanium dioxide particles) in mixed colloids. In the presence of a precursor of silica (a TEOS solution), the pyrene molecules react with the colloidal silica particles formed, and the reaction is accompanied by decomposition of the pyrene–-cyclodextrin inclusion complex and efficient photoionization of pyrene.