Hydroxid-halogenid-verbindungen des di-t-butyl-substituierten zinns

The di-t-butyltin hydroxide halides t-Bu₂Sn(OH)X (X = F, Cl or Br) have been prepared starting from the dihalides t-Bu₂SnX₂ or the oxide (t-Bu₂SnO)₃. X-Ray analysis of the three compounds shows dimeric molecules: two 5-coordinated tin atoms and the oxygen atoms of the hydroxyl groups are linked to a four-membered ring. As confirmed by the IR spectra, the molecules in the crystal are held together by OH?X hydrogen bonds. These are strong in the hydroxide fluoride but are weak in the analogous chloride and bromide.     

Über den Einfluß der Substituenten im (R3Si)2(P–Si)R2Cl auf Bildung und Eigenschaften der Hexasila-tetraphosphadantane und deren 31P-NMR-Spektren

The Effect of the Substituents in (R₃Si)₂P–SiR₂Cl on the Formation and the Properties of the Hexasilatetraphospha-adamantanes and their ³¹P-NMR Spectra The thermolysis of (Me₃Si)₂P–SiEt₂Cl 4 at 300°C leads to the silylphosphanes with adamantane structure (Et₂Si)_x(Me₂Si)_6–x (x = 0–6), aside of (Me₃Si)₃P, (Et₂MeSi) (Me₃Si)₂P, (Et₂MeSi)₂(Me₃Si)P and Me₃SiCl, Et₂SiCl, Et₂MeSiCl. Due to the different positions of the Et₂Si-bridges in the adamantane cage the compounds featuring x = 2–4, form isomers. The thermolysis of (Me₃Si)₂P–SiEtMeCl 14 occurs analogously and leads to the adamantanes (EtMeSi)_x (Me₂Si)_6–xP₄ (x = 0–6). The introduction of the SiEtMe group causes the existence of chiralic isomers of the compounds featuring x = 2–6. From (Et₃Si)₂P–SiEt₂Cl 24 (Et₂Si)₆P₄ is obtained. The thermolyses of (Me₃Si)₂P–SiPh₂Cl 25 and [(Me₃Si)P–SiPh₂]₂ do not enable the formation of adamantanes with SiPh₂-bridges. They rather lead to Me- and Ph-substituted trisilylphosphanes. The syntheses of the starting compounds 4, 14, 24 , and 25 are reported. The ³¹P-NMR spectra of silylphosphanes with adamantane structure show, that the linear increase of the ³¹P-chemical shift values as dependent on the rising number of Et groups, which is observed in partially Et-substituted methyltrisilylphosphanes, allows the prediction of the δ³¹P values of the specific P atoms in an adamantane cage, heeding both the position and the direction of the SiEt groups in the particular molecule.     

Estimation of aqueous solubility of organic molecules by the group contribution approach. Application to the study of biodegradation.

A reliable and generally applicable aqueous solubility estimation method for organic compounds based on a group contribution approach has been developed. Two models have been established based on two different sets of parameters. One has a higher accuracy, while the other has a more general applicability. The prediction potentials of these two models have been evaluated through cross-validation experiments. For model I, the mean cross-validated r2 and SD for 10 such cross-validation experiments were 0.946 and 0.503 log units, respectively. While for model II, they were 0.953 and 0.546 log units, respectively. Applying our models to estimate the water solubility values for the compounds in an independent test set, we found that model I can be applied to 13 out of 21 compounds with a SD equal to 0.58 log unit and model II can be applied to all the 21 compounds with a SD equal to 1.25 log units. Our models compare favorably to all the current available water estimation methods. A program based on this approach has been written in FORTRAN77 and is currently running on a VAX/VMS system. The program can be applied to estimate the water solubility of the water solubility of any organic chemical with a good or fairly good accuracy except for except for electrolytes. Applying our aqueous solubility estimation models to biodegradation studies, we found that although the water solubility was not the sole factor controlling the rate of biodegradation, ring compounds with greater solubilities were more likely to biodegrade at a faster rate. The significance of the relationship between water solubility and biodegradation activity has been illustrated by predicting the biodegradation activity of 27 new chemicals based solely on their estimated solubility values.     

The regioisomeric 1H(2H)‐pyrazolo[3,4‐d]pyrimidine N1‐ and N2‐(2′‐deoxy‐β‐D‐ribofuranosides)

In the title regioisomeric nucleosides, alternatively called 1‐(2‐deoxy‐β‐d ‐erythro‐furan­osyl)‐1H‐pyrazolo­[3,4‐d]­pyrimidine, C₁₀H₁₂N₄O₃, (II), and 2‐(2‐deoxy‐β‐d ‐erythro‐furan­osyl)‐2H‐pyrazolo­[3,4‐d]pyrimidine, C₁₀H₁₂N₄O₃, (III), the conformations of the gly­cosyl­ic bonds are anti [?100.4 (2)° for (II) and 15.0 (2)° for (III)]. Both nucleosides adopt an S‐type sugar pucker, which is C2′‐endo‐C3′‐exo (²T₃) for (II) and 3′‐exo (between ₃E and ⁴T₃) for (III).     

2‐Amino‐7‐chloro‐2′‐deoxy­tubercidin

In 4‐chloro‐7‐(2‐de­oxy‐β‐d ‐erythro‐pento­furanos­yl)‐7H‐pyr­rolo­[2,3‐d]­pyrimidine‐2,4‐diamine, C₁₁H₁₄ClN₅O₃, the conformation of the N‐glycosylic bond is between anti and high‐anti [χ = −102.5 (6)°]. The 2′‐deoxy­ribofuranosyl unit adopts the C3′‐endo‐C4′‐exo (³T₄) sugar pucker (N‐type) with P = 19.6° and τ_m = 32.9° [terminology: Saenger (1989). Landolt‐Börnstein New Series, Vol. 1, Nucleic Acids, Subvol. a, edited by O. Madelung, pp. 1–21. Berlin: Springer‐Verlag]. The orientation of the exocyclic C4′—C5′ bond is +ap (trans) with a torsion angle γ = 171.5 (4)°. The compound forms a three‐dimensional network that is stabilized by four inter­molecular hydrogen bonds (N—H⋯O and O—H⋯N) and one intra­molecular hydrogen bond (N—H⋯Cl).     

The elusive oxidant species of cytochrome P450 enzymes: characterization by combined quantum mechanical/molecular mechanical (QM/MM) calculations

The primary oxidant of cytochrome P450 enzymes, Compound I, is hard to detect experimentally; in the case of cytochrome P450(cam), this intermediate does not accumulate in solution during the catalytic cycle even at temperatures as low as 200 K (ref 4). Theory can play an important role in characterizing such elusive species. We present here combined quantum mechanical/molecular mechanical (QM/MM) calculations of Compound I of cytochrome P450(cam) in the full enzyme environment as well as density functional studies of the isolated QM region. The calculations assign the ground state of the species, quantify the effect of polarization and hydrogen bonding on its properties, and show that the protein environment and its specific hydrogen bonding to the cysteinate ligand are crucial for sustaining the Fe-S bond and for preventing the full oxidation of the sulfur.     

Ueber physikalisch-chemische Eigenschaften des Chloralhydrats und deren Verwerthung in pharmaceutischer Richtung

Ohne Zusammenfassung     

Frequency-dependent C(V) spectroscopy of the hole system in InAs quantum dots

The hole system in InAs quantum dots was investigated by frequency-dependent capacitance–voltage spectroscopy. Up to eight distinct charging peaks could be observed and the energy difference between the individual peaks could be estimated. All charging peaks decrease with increasing measurement frequency; however, the lower the energy of the hole level the stronger the decrease. A comparison with the results of the electron system in similar quantum dots yields that for all hole levels the effective mass in the barrier is much larger than in the electron system.     

Fast vacuum slag analysis in a steel works by laser-induced breakdown spectroscopy

Samples taken from the liquid slag layer in a vacuum degasser station of a steel works are analyzed after solidification by laser-induced breakdown spectroscopy (LIBS) without any further sample preparation. The mass fractions of the major components of the vacuum slags are in the range of 50–60% for CaO, 0.5–12% for SiO₂ and 20–40% for Al₂O₃. The species are distributed heterogeneously in the solid samples having diameters of 35 mm. Furthermore the color and structure of the samples is varying significantly. A fast spatial averaging of representative sample areas is realized by spatial laser beam shaping. Multivariate calibration and its validation is carried out with calibration and validation sets of production samples which are analyzed by X-ray fluorescence measurements or as borate beads for reference. The laser-induced breakdown spectroscopy instrument is installed in the steel works at a distance of about 10 m from the vacuum degasser. The laser-induced breakdown spectroscopy analysis runs automatically after the sample placement and it takes 80 s including data transfer to the host computer of the steel works. Operational tests are carried out to demonstrate the feasibility of a fast slag analysis in the harsh environment of the vacuum degasser plant.