Synthesis, structures and reactivity of macrocyclic imidazolylboranes

New macrocyclic imidazolylboranes [imidazolylB(R¹)₂]_n, where selected carbon atoms of imidazolyl rings may bear substituents other than hydrogen, and where n=4 or 5, are obtained from 1-trimethysilylimidazoles and haloboranes XB(R¹)₂ by boron/silicon exchange using 2-bromoimidazole and benzimidazole. These macrocycles are formally zwitterionic and contain imidazolyl rings linked through their nitrogen atoms by BH₂, B(R¹)₂ or BR¹X units. Despite the sterical demand of these derivatives tetrameric macrocycles are formed. A new synthetic strategy to macrocyclic imidazolylboranes includes the preparation and cyclization of bis(imidazolyl)boronium chlorides. In addition dihaloboranes have been tested for cyclization to yield halogen-containing macrocycles. The new compounds are spectroscopically characterized and X-ray structure analyses of tetrameric- (2a) and pentameric 1-imidazolylborane (2a′), tetrameric 1-imidazolyldimethylborane (2b), tetrameric 1-(2-bromo)imidazolylborane (2d) and bis(2-bromoimidazolyl)boronium chloride (3d) are reported.     

Die Cardenolide der Samen von Mansonia altissima A. CHEV. 2. Mitteilung Die Struktur von Mansonin und Strophothevosid Glykoside und Aglykone, 287. Mitteilung

Mansonin is the 2,3-di-O-methyl-6-deoxy-β-D-glucopyranoside of strophanthidin, and strophothevoside the corresponding 3-O-methyl-6-deoxy-β-D-glucopyranoside.     

Thermal enhancement of the quantum decay rate in a dissipative system

The quantum decay of a metastable system which interacts with an environment at temperatureT is considered. A general formula for the decay rate at finite temperatures is obtained by a method which is based on the framework recently described by Caldeira and Leggett. The thermal enhancement of the tunnelling rate at low temperatures is discussed for arbitrary metastable potentials, and it is found that the exponent of the rate obeys a power law in a dissipative system. The power law exponent is shown to be a characteristic feature of the dissipative mechanism. Finally, a universally valid formula for the thermal enhancement factor is given, where the form of the potential enters only through the frequency of small oscillations about the metastable minimum and the length of the zero temperature bounce trajectory.     

Die Cardenolide und Pregnan-Glykoside der Wurzeln von Asclepias lilacina WEIMARCK. I. Isolierungen Glykoside und Aglykone, 290. Mitteilung

The dried roots of Asclepias lilacina contain ca. 14% glykosides, in which both cardenolides and ester glycosides of pregnane derivatives are present, the latter predominating. Uzarigenin, coroglaucigenin, and their corresponding glycosides ascleposide and frugoside, resp., were shown to be present; of these four, uzarigenin was isolated in crystalline form. The ester glycosides, some of which could be isolated in a crystalline state, are predominantly composed of the aglycones 20-O-acetyl-12-O-benzoyl-sarcostin and 12,20-di-O-benzoyl-sarcostin, besides which esters of desacetyl-metaplexigenin, lineolon, and dihydrosarcostin are also present. These aglycones are mostly attached to various trisaccharides which are composed of at least two 2-deoxy-sugar residues. Mild acid hydrolysis gave, besides the genins, 7 sugars, namely cymarose, oleandrose, digitoxose, 3-O-methyl-6-deoxy-D-allose (U3), as well as 3 unknown sugars U1, U2 and U5 which are probably disaccharides. U1 and U2 were isolated in crystalline form; they are isomeric and have been named asclepobiose and lilacinobiose; they are probably composed of units similar to those in the isomeric pachybiose.     

Der zweistufige Carbanion-Mechanismus der Fragmentierung von 3-Aminopropylbenzoaten. Fragmentierungs-Reaktionen. 25. Mitteilung

The unsubstituted and p-substituted benzoates 2b – 2e of 3-dimethylamino-2,2bis(p-nitrophenyl)-propanol ( 2a ) undergo quantitative fragmentation in 80% ethanol yielding 1,1-bis(p-nitrophenyl)-ethylene ( 5 ) besides formaldehyde and dimethylamine, the hydrolysis products of the imonium ion 3 . The corresponding alcohol 2a , however, yields 2,2-bis(p-nitrophenyl)-ethanol ( 9 ) in addition to fragmentation products. Conversely, no fragmentation is observed with the benzoates 6b – 6e of 3-dimethylamino-2,2-diphenylpropanol ( 6a ) which lack electronwithdrawing substituents in the β-phenyl groups. These results are in agreement with a two-step carbanion mechanism (Scheme 2) involving the ionization of the aminoalkohol 2a and its esters 2b – 2e to the imonium ion 3 and the carbanions 4a – 4e . The latter undergo competitive cleavage, recombination and protonation to 5 , 2 and 9 , respectively, depending on the nucleofugal activity of –X. These conclusions are supported by the first-order rate constants for the benzoates 2b – 2e which differ merely by a factor of three. Since the p-substituents in the benzoate groups have only a minor effect on the reaction rate the bonds to the nucleofugal groups are not appreciably broken in the rate determining step.     

Metall-Schwefelstickstoff-Verbindungen. 22. S4N3Cl als Ausgangsprodukt zur Herstellung von Komplexen mit dem S3N−-Liganden Die Komplexe [Ph6P2N][Cu3(S3N)2(CN)2]und [Ph4As][(CuS3N)2(CN)]

The reaction of S₄N₃Cl with metal salts leads to complexes containing the S₃N^?chelating ligand, a reaction which proceeds smoothly especially in an alkaline medium. Thus we were able to prepare, by the reaction of CuCN with S₄N₃Cl and [Ph₆P₂N]OH (Ph = phenyl), the salt [Ph₆P₂N][Cu₃(S₃N)₂(CN)₂], a compound in which the anions build a bidimensional network through supplementary Cu - S contact interactions. The salt is monoclinic, space group C2/c, a = 18.960, b = 14.651 and c = 15.400 Å, β = 101.03° and Z = 4. Metal Sulfur Nitrogen Compounds. 22. S₄N₃Cl as a Starting Compound for the Preparation of Complexes Containing the S₃N^? Ligand. Complexes [Ph₆P₂N] [Cu₃(S₃N)₂ (CN)₂] and [Ph₄As] [(CuS₃N)₂ (CN)] In contrast, the reaction of CuN with S₄N₃Cl and [Ph₄As]OH led to the compound [Ph₄As][(CuS₃N)₂(CN)], monoclinic, space group C2/c, a = 18.478, b = 6.405, c = 27.051 Å, β = 119.50°, Z = 4. In the centrosymmetric anion the two Cu(S₃N) groups are linked together by disordered CN^? groups. An additional linkage results from Cu - Cu contact interactions, with d = 2.84 Å.     

In situ investigations on organic foam films using neutron and synchrotron radiation

We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of foam films stabilized by sodium dodecyl sulfate. Previous measurements on dry foams (Axelos, M. A. V.; Boue, B. Langmuir 2003, 19, 6598) have shown the presence of spikes in the two-dimensional scattering data which suggest that the incident beam is reflected on some film surfaces. The latter interpretation is confirmed by new neutron studies performed on ordered ("bamboo") foams which allow selection of single films. In the first case, we show that the spikes of the scattered intensity can be obtained by reflection on two parts of the foam, namely, the films and the Plateau borders. With synchrotron radiation, first observations of distinct interference fringes have allowed an accurate determination of the film thickness. A comparison with X-ray and neutron data is made, opening a general discussion about the capabilities of small-angle scattering techniques for studying the microscopic properties of foam films.     

Qualitative and quantitative changes in barley seed protein patterns during the malting process analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with respect to malting quality.

Seeds of two barley cultivars, similar in total protein content and malt extract yield but different in their final attenuation values, were malted. Samples taken at daily intervals during the malting process were extracted sequentially with Tris-HCl buffer, aqueous 2-propanol, aqueous 2-propanol containing 0.5% dithiothreitol, and 4 M urea, containing 0.5% dithiothreitol and 1% Nonidet P-40. The protein composition of these extracts was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and computer densitometry to determine whether differences observed in the rate or extent of protein modification are related to the malting quality character final attenuation. It was found that, common to both cultivars, the albumin and globulin proteins were relatively resistant to proteolysis, whereas the hordeins suffered a dramatic breakdown during malting, with the D hordein being degraded most rapidly, followed by the B and C hordeins. Besides these similarities, differences between both cultivars were observed in the relative rates of D hordein degradation, as this rate was considerably higher in the cultivar with high malting quality. Similar, but much less distinct kinetics were seen with certain B hordeins. Since a possible relationship might exist between the rate of proteolysis of the D hordeins and the character final attenuation, we analyzed a larger number of barley cultivars with different final attenuation values with a simplified technique. For the ten cultivars examined, differences during germination were again seen in the rates of modification of the D hordeins. However, significant correlations between the D hordein breakdown and final attenuation values were not obtained, so that we propose that there exists at best a loose correlation between the relative rate of proteolysis of these proteins and the malting quality character final attenuation.     

Übergangsmetallkomplexe der Pyrazin-2,6-dicarbonsäure und der Pyridin-2,6-dicarbonsäure: Synthesen und Elektrochemie. Die Kristallstruktur von NH4[RuCl2(dipicH)2]

Transition Metal Complexes Containing the Ligands Pyrazine-2, 6-dicarboxylate and Pyridine-2, 6-dicarboxylate: Syntheses and Electrochemistry. Crystal Structure of NH₄[RuCl₂(dipicH)₂] The coordination chemistry of the tridentate ligand pyrazine-2, 6-dicarboxylate (pyraz-2,6 = L) with transition metals in aqueous solution has been investigated. The reaction of the ligand with metal aqua ions (1:1) affords insoluble precipitates [M^IIL(OH₂)₂] (M = Mn, Fe, Co, Ni, Cu, Zn, Cd). [TiOL(OH₂)₂], [VOL(H₂O)₂] and [UO₂L(H₂O)] were also prepared. [M^IIIL₂]^? complexes (M^III ? Fe^III, Co^III) were isolated as NH₄⁺ and P(C₆H₅)₄⁺ salts; they are strong one electron oxidants (E_1/2 = +0.602 V and +0.795 V vs. NHE, respectively). Redox potentials of analogous complexes containing pyridine- 2, 6-dicarboxylate (L′) ligands have been determined by cyclic voltammetry: [ML′₂]^1-/2?: M = V^III: -0.591 V; Cr^III: -0.712 V. It is shown that pymzine-2,6-dicarboxylate as compared to pyridine-2,6-dicarboxylate stabilizes metal complexes in low oxidation states (+II). The reaction of RuCl₃ · nH₂O with pyridine-2,6-dicarboxylic acid in aqueous solution affords the yellow-green anion [RuCl₂(L′H)₂]^?. The crystal structure of NH₄[RuCl₂(L′H)₂] has been determined. It crystallizes in the monoclinic space group P2₁/c with a = 8.812(2) Å b = 10.551(2) Å, c = 10.068(2) Å, β = 110.03(6)°, Z = 2; 2507 independent reflections; R = 0.032. The ruthenium centers are in an octahedral environment of two Cl^? ligands (trans) and two bidentate pyridine-2, 6-hydrogendicarboxylate ligands which possess each one protonated, uncoordinated carboxylic group.     

THE INFLUENCE OF SMECTIC PHASES OF PERFLUORODECYL DECANE ON THE PHOTOREACTIONS OF PERFLUOROHEPTYL OCTYL KETONE. AN EXAMPLE OF MICROSCOPIC DISORDER IN HIGHLY ORDERED LAYERED PHASES*

The consequences of solvent order, imposed by the two smectic phases of 1,1,1,2,2,3,3,4, 4,5,5,6,6,7,7,8,8,9,9,10,10-heneicosylfluoroeicosane (F10H10, a “diblock” molecule) on the photochemistry of 1,1,1,2,2,3,3,4,4,5,5.6,6,7,7-pentadecylfluoro-8-hexadecanone (F7COH8) were investigated. Results from irradiations of F7COH8 in smectic F10H10 are compared to those obtained in hexane, perfluorohexane, and the isotropic phase of F10H10. They are complemented by ²H-NMR experiments on F10H10 solutions of F7COH8 deuterated at the methylene alpha to the carbonyl, and differential scanning calorimetry thermograms. More than 85% of the photoproducts are derived from carbonyl reduction and Norrish II processes. Based upon the ²H-NMR spectra and Norrish II photoproduct ratios, the microscopic environment experienced by the locus of reaction of F7COH8 in smectic F10H10 is not very restrictive towards the solute shape changes that must occur. This conclusion was not anticipated because the macroscopic order of the smectic phases of F10H10 is high.