Refined Insight in Stereochemical and Directional Features of the FeI-Mediated Dehydrogenation of Tetralin

Experimental results demonstrate that, in the course of gas-phase Fe⁺-mediated dehydrogenation of tetralin, the metal ion sticks to the same plane of the hydrocarbon surface. The study of 5-substituted, labeled tetralin analogues reveal the operation of an interesting substituent effect: Steric hindrance imposed by a CH₃ group at C(5) deflects the metal to the more easily accessible region of C(1)/C(2); in contrast, a CH₃O substituent at C(5) directs the metal ion to the more congested C(3)/C(4) region which clearly points to a coordination of Fe⁺ to the MeO group in the course of the haptotropic migration.     

Fibronectin displacement at polymer surfaces

The interactions of fibronectin with thin polymer films are studied in displacement experiments using human serum albumin. Fibronectin adsorption and exchange on two different maleic anhydride copolymer surfaces differing in hydrophobicity and surface charge density have been analyzed by quartz crystal microbalance and laser scanning microscopy with respect to adsorbed amounts, viscoelastic properties, and conformation. Fibronectin is concluded to become attached onto hydrophilic surfaces as a "softer", less rigid protein layer, in contrast to the more rigid, densely packed layer on hydrophobic surfaces. As a result, the fibronectin conformation is more distorted on the hydrophobic substrates together with remarkably different displacement characteristics in dependence on the adsorbed fibronectin surface concentration and the displacing albumin solution concentration. While the displacement kinetic remains constant for the strongly interacting surface, an acceleration in fibronectin exchange is observed for the weakly interacting surface with increasing fibronectin coverage. For displaced amounts, no change is determined for the hydrophobic substrate, in contrast to the hydrophilic substrate with a decrease of fibronectin exchange with decreasing coverage leading finally to a constant nondisplaceable amount of adsorbed proteins. Furthermore, the variation of the albumin exchange concentration reveals a stronger dependence of the kinetic for the weakly interacting substrate with higher rates at higher albumin concentrations.     

The detection of UV-induced membrane damages by a combination of two biosensor techniques

Ketoprofen is an important anti-inflammatory drug, but its dermal application is limited because of the photosensitizing properties causing phototoxic reactions of the skin when exposed to UV light. We have recently investigated the peroxide formation of ketoprofen in solutions of linoleic acid during UV irradiation. To continue these studies and focus on UV-induced changes in membrane integrity and barrier function we established an in vitro model using two biosensor techniques simultaneously. Support-fixed bilayers were irradiated with different doses of UV-B up to damaging intensities with or without ketoprofen. Cyclic voltammetry was carried out to detect alterations in membrane permeability; quartz crystal microbalance (QCM) measurements were helpful in analyzing whether a permeability increase was caused by depletion of membrane components. In absence of ketoprofen, increasing UV-B doses induce membrane permeabilities of both unsaturated and saturated bilayers. QCM measurements could not reveal a significant loss of membrane components as a reason for the permeability. In contrast, 0.3 mM ketoprofen induced a dose-dependent increase in membrane permeability. QCM results indicated a mass loss. Although this model does not explain all molecular mechanisms of membrane damage by ketoprofen, the combined application of both QCM and CV is a novel and powerful tool to investigate functional mechanisms of UV-induced membrane damages.     

Decreasing the ring size of a cyclic nonribosomal peptide antibiotic by in-frame module deletion in the biosynthetic genes

Many natural products of therapeutical and biotechnological importance are nonribosomally synthesized peptides. Structural hallmarks of this class of compounds are the occurrence of unusual amino acids, mostly cyclic peptide backbones, and numerous further modifications such as acylation, heterocyclic ring formation, and glycosylation. Because of their structural complexity, chemical synthesis is usually an unattractive route to these molecules. In contrast, genetic engineering of the biosynthesis genes emerges as a potentially powerful approach to the combinatorial biosynthesis of useful analogues of the lead compounds. Nonribosomal peptide synthetases (NRPSs) carry out a sequential multistep assembly and modification of the peptides in a thiotemplate process described by the multiple carrier model. The modular architecture of NRPSs suggests straightforward methods for the reprogramming of these enzymes by exchange of catalytic subunits. However, many of the reported engineering attempts faced low product yields or even inactive hybrid enzymes. Using a new approach to obtain hybrid NRPSs, we show here that the deletion of an entire module in an NRPS assembly line caused the secretion of the predicted peptide antibiotic variant with a decreased ring size. Furthermore, a module exchange resulted in a significantly higher product yield than that observed in previous studies.     

Cobalt(II) complexes bearing 2-imino-1,10-phenanthroline ligands: synthesis, characterization and ethylene oligomerization

A series of cobalt(II) complexes containing 2-imino-1,10-phenanthrolines have been synthesized and characterized by elemental and spectroscopic analysis. The molecular structures of complexes 2, 3, 8 and 14 were confirmed by X-ray diffraction analysis. On treatment with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), these cobalt(II) complexes show moderate to high catalytic activities for ethylene oligomerization and butene predominates among the oligomers produced. The parameters of the reaction conditions and the effects of the ligands environment were investigated. To cite this article: S. Jie et al. C. R. Chimie 9 (2006).     

Weitere Oxochlorotitanate LnTiO3Cl der Seltenen Erden (LnSm?Lu) - Präparation,Kristallstruktur, elektronenmikroskopische Untersuchung

New Rare Earth Oxochlorotitanates LnTiO₃Cl (Ln?Sm? Lu) - Preparation, Structure and Electron Microscopic Investigations After the preparation of SmTiO₃Cl we made the attempt to prepare analogous compounds with the heavier rare earth elements. We present 2 methods to prepare powders of LnTiO₃Cl (Ln = Sm? Lu) together with a new method to prepare the rare earth oxychlorides LnOCl (Ln = Tm? Lu). There will be also presented 2 methods to get single crystals of these compounds via chemical vapour transport. The new rare earth oxochlorotitanates LnTiO₃Cl (Ln = Eu? Lu) are isotypic to SmTiO₃Cl. They crystallize in the monoclinic space group: C2/m (No. 12). The lattice parameters (Å) are between a = 9.716(3), b = 3.942(2), c = 10.100(4) (SmTiO₃Cl) and a = 9.748(1), b = 3.8454(5), c = 9.625(2) (LuTiO₃Cl), Z = 4. We observed a permanent decay of the cell volume with the decay of the radii of the cations. The structure of EuTiO₃Cl and DyTiO₃Cl was refined to R = 3.4% and R = 5.8% respectively. The crystal structure which has a certain similarity to brannerite can be described in a simplified way by saying that the rare earth and chlorine particles are located between walls of Ti? O-double-octahedra.     

Darstellung und Röntgenstrukturanalyse von 26 Thiomolybdato- bzw. Thiowolframato-und eines Selenowolframato-Komplexes

Summary The preparation and characterization by X-ray structure analysis of the following chalcogenometalato complexes are reported: 1: [(Ph ₃P)₂N]₂(NEt ₄)[Fe(WS₄)₂]·2MeCN; 2: [(Ph ₃P)₂N]₂(NEt ₄)[Cu(WS₄)₂]·2MeCN; 3: [(Ph ₃P)₂N]₂(NEt ₄)[Ag(MoS₄)₂]·MeCN; 4: [(Ph ₃P)₂N]₂(NEt ₄)[Ag(WS₄)₂]·MeCN; 5: (PPh ₄)₂[Hg(WS₄)₂]; 6: (PPh ₄)₂[Au₂(WOS₃)₂]; 7: (PPh ₄)₄[Pb₂(MoS₄)₄]; 8: (PPh ₄)₄[Pb₂(WS₄)₄]; 9: (NEt ₄)₂[Fe(WS₄)₂(H₂O)₂]; 10: [Fe(DMSO)₆][Cl₂Fe(MoS₄)]; 11: [Fe(DMSO)₆][Cl₂Fe(MoOS₃)]; 12: (PPh ₄)(NMe ₃CH₂ Ph)[Cl₂Fe(WS₄)]; 13: [Fe(DMF)₆][Cl₂Fe(WS₄)]; 14: (PPh ₄)₂[Cl₂Fe(WS₄)]; 15: (PPh ₄)₂[Cl₂Fe(WS₄)]·2 CH₂Cl₂; 16: (PPh ₄)₂[NCCu(MoS₄)]; 17: (PPh ₄)₂[NCAg(MoS₄)]; 18: (PPh ₄)₂[NCAg(WS₄)]; 19: (PPh ₄)₂[Cu₃Cl₃(MoOS₃)]; 20: (PPh ₄)₂[Cu₃Br₃(MoS₄)]·MeCN; 21: (PPh ₃)₃Cu₂(MoOS₃)·0.8 CH₂Cl₂; 22: (PPh ₃)₃Cu₂(WOS₃)·0.8 CH₂Cl₂; 23: {Cu₃MoS₃Br}(PPh ₃)₃O·0.5Me ₂CO; 24: (PPh ₃)₃Ag₂(WSe₄)·0.8 CH₂Cl₂; 25: [(Ph ₃P)₂N]₂(NEt ₄)₂[Fe₂S₂(WS₄)₂]·3MeCN; 26: (PPh ₄)₂[MoO(MoS₄)₂]; 27: (PPh ₄)₂[Br₂Fe(WOS₄)]·DMF.

     

Bis-chelated imine-alkoxytitanium complexes: novel chiral dopants with high helical twisting power in liquid crystals

Enantiomerically and diastereomerically pure bis-chelated imine-alkoxytitanium complexes 6 and 7 have been synthesized and used as chiral dopants for converting nematic into cholesteric phases. The dopants were tested in mainly commercially available nematic liquid crystalline compounds or mixtures: LC1 (BASF), ZLI-1695 and ZLI-1840 (Merck), as well as N-(4-methoxybenzylidene)-4'-butylaniline (MBBA). The values of the helical twisting power (HTP) were determined by the Grandjean-Cano method. Exceptionally high helical twisting powers were obtained. Thus, the titanium complex 6 h displayed a HTP value of 740 microm(-1) in MBBA, the highest HTP value reported. The helical twisting power has been found to depend strongly on the structure of the nematic phase and the substitution pattern of the chiral ligand in the titanium complexes 6 and 7. Crystal structure analysis of 6 f confirmed the A,R,R configuration of the metal complex. The chiral imine ligands 4 and 5 were derived from the regioisomeric amino alcohols 1 and 2.     

Gas phase structure of Ruppert's reagent, CF3SiMe3

CF3SiMe3 (Ruppert's reagent) has been investigated by gas phase electron diffraction, microwave spectroscopy and quantum chemical methods, deriving structural parameters and the barrier height for the methyl torsion. The bond length of the Si-CF3 bond, 1.941(3) A, is the longest Si-C bond observed so far in the gas phase. The V3 barrier for the methyl group torsion (V3= 5.71 kJ/mol) is only slightly lower than barriers determined for other trimethylsilane compounds.     

Biosynthesis of the antitumor agent chartreusin involves the oxidative rearrangement of an anthracyclic polyketide

Chartreusin is a potent antitumor agent with a mixed polyketide-carbohydrate structure produced by Streptomyces chartreusis. Three type II polyketide synthase (PKS) gene clusters were identified from an S. chartreusis HKI-249 genomic cosmid library, one of which encodes chartreusin (cha) biosynthesis, as confirmed by heterologous expression of the entire cha gene cluster in Streptomyces albus. Molecular analysis of the approximately 37 kb locus and structure elucidation of a linear pathway intermediate from an engineered mutant reveal that the unusual bis-lactone aglycone chartarin is derived from an anthracycline-type polyketide. A revised biosynthetic model involving an oxidative rearrangement is presented.