Synthese und Struktur von γ-Halogenpropyl-octa(silasesquioxanen)

Synthesis and Structures of γ-Halopropyl-octa(silasesquioxanes) As a more rapid and versatile synthetic approach, we have studied the FeCl₃-catalyzed hydrolytic polycondensation of suited trichlorosilanes in a biphasic system which yields e.g. the new octa(silasesquioxane) (BrCH₂CH₂CH₂)₈Si₈O₁₂.     

Resolution enhancement in multidimensional solid-state NMR spectroscopy of proteins using spin-state selection

We show that the resolution of homonuclear multidimensional solid-state NMR correlation experiments can be significantly improved using transition selection and spin-state-selective polarization transfer techniques. The selection and transfer of single states allow the removal of the J-coupling contribution from the line width in both the direct and indirect spectral dimensions. This is demonstrated with a new spin-state-selective CO-Calpha correlation experiment, applied to a microcrystalline 85-residue protein. With this new sequence, all four components of the CO-Calpha cross-peaks are separated into different spectra, obtained by linear combination of four recorded data sets. Line narrowing of up to 44% was obtained on the protein sample for the spin-state-selective CO-Calpha spectrum compared to a standard spin-diffusion experiment. The new technique also allows an easy distinction between "direct" and "relayed" transfer cross-peaks.     

Metallation des halogenures d'aryle par le tributylstannyllithium dans le tetrahydrofuranne

The metallation of aryl halides with tributylstannyllithium in THF proceeds via at least three different mechanisms whose relative rates depend on the nature of the halogen, the substrate and the experimental conditions. In the case of aryl bromides, a halogenmetal exchange (major process) is competing with a radical mechanism. With aryl chlorides, an arynic process, a halogenmetal exchange and a radical mechanism are involved. Finally, with aryl fluorides, the arynic process is usual, but it may be strongly competed by a radical mechanism whenever suitable experimental conditions are arranged.     

Synthesis of an unsymmetrically doubly bridged calix[4]arene in the 1,3-alternate conformation

We report the synthesis of the first calix[4]arene constrained to a 1,3-alternate conformation by one crown ether and one di-aza-benzo crown ether bridgings. Preliminary binding properties are also given.     

Towards clustered carbonyl cations [M3(CO)14]2+ (M = Ru,Os): the need for innocent deelectronation

To access the hitherto almost unknown class of clustered transition metal carbonyl cations, the trimetal dodecacarbonyls M₃(CO)₁₂ (M = Ru, Os) were reacted with the oxidant Ag⁺[WCA]⁻, but yielded the silver complexes [Ag{M₃(CO)₁₂}₂]⁺[WCA]⁻ (WCA = [Al(OR^F)₄]⁻, [F{Al(OR^F)₃}₂]⁻; R^F = –OC(CF₃)₃). Addition of further diiodine I₂ to increase the redox potential led for M = Ru non-specifically to divalent mixed iodo-Ru^II-carbonyl cations. With [NO]⁺, even the N–O bond was cleaved and led to the butterfly carbonyl complex cation [Ru₄N(CO)₁₃]⁺ in low yield. Obviously, ionization of M₃(CO)₁₂ with retention of its pseudo-binary composition including only M and CO is difficult and the inorganic reagents did react non-innocently. Yet, the radical cation of the commercially available perhalogenated anthracene derivative 9,10-dichlorooctafluoroanthracene (anthracene^Hal) is a straightforward accessible innocent deelectronator with a half-wave potential E_1/2 of 1.42 V vs. Fc^0/+. It deelectronates M₃(CO)₁₂ under a CO atmosphere and leads to the structurally characterized cluster salts [M₃(CO)₁₄]²⁺([WCA]⁻)₂ including a linear M₃ chain. The structural characterization as well as vibrational and NMR spectroscopies indicate the presence of three electronically independent sets of carbonyl ligands, which almost mimic M(CO)₅, free CO and even [M(CO)₆]²⁺ in one and the same cation.

Trimeric M₃(CO)₁₂ (M = Ru, Os) reacts with typical inorganic oxidants to unwanted side products. Yet, the 9,10-dichlorooctafluoroanthracene radical cation deelectronates these under CO pressure to give the first homotrimetallic [M₃(CO)₁₄]²⁺ salts.     

Nanomolar hydrogen peroxide detection using horseradish peroxidase covalently linked to undoped nanocrystalline diamond surfaces

In this article, we report on the low-level detection of hydrogen peroxide, a key player in the redox signaling pathway and a toxic product in the cellular system, using a colorimetric solution assay. Amine-terminated undoped nanocrystalline diamond thin films were grown on glass using a linear-antenna microwave plasma CVD process. The diamond surface consists mainly of -NH(2) termination. The aminated diamond surface was decorated with horseradish peroxidase (HRP) enzyme using carbodiimide coupling chemistry. The success of the HRP immobilization was confirmed by X-ray photoelectron spectroscopy (XPS). The enzymatic activity of immobilized HRP was determined with a colorimetric test based on the HRP-catalyzed oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sufonic acid (ABTS) in the presence of hydrogen peroxide. The surface coverage of active HRP was estimated to be Γ = 7.3 × 10(13) molecules cm(-2). The use of the functionalized diamond surface as an optical sensor for the detection of hydrogen peroxide with a detection limit of 35 nM was demonstrated.     

Observation of an Organic Acid Mediated Spin State Transition in a Co(II)-Schiff Base Complex: An EPR, HYSCORE, and DFT Study

The interactions of a weak organic acid (acetic acid, HOAc) with a toluene solution of the Co(II)-Schiff base type complex, (R,R')-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II) (labeled [Co(1)]), was investigated using EPR, HYSCORE, and DFT computations. This activated [Co(II)(1)] system is extremely important within the context of asymmetric catalysts (notably the hydrolytic kinetic resolution of epoxides) despite the lack of detailed structural information about the nature of the paramagnetic species present. Under anaerobic conditions, the LS [Co(II)(1)] complex with a |yz, (2)A(2)? ground state is converted into a low-spin (LS) and a high-spin (HS) complex in the presence of the acid. The newly formed LS state is assigned to the coordinated [Co(II)(1)]-(HOAc) complex, possessing a |z(2), (2)A(1)? ground state (species A; g(x) = 2.42, g(y) = 2.28, g(z) = 2.02, A(x) = 100, A(y) = 120, A(z) = 310 MHz). The newly formed HS state is assigned to an acetate coordinated [Co(II)(1)]-(OAc(-)) complex, possessing an S = (3)/(2) spin ground state (species B, responsible for a broad EPR signal with g ≈ 4.6). These spin ground states were confirmed with DFT calculations using the hybrid BP86 and B3LYP functionals. Under aerobic conditions, the LS and HS complexes (species A and B) are not observed; instead, a new HS complex (species C) is formed. This complex is tentatively assigned to a paramagnetic superoxo bridged dimer (AcO(-))[Co(II)(1)···O(2)(-)Co(III)(1)](HOAc), as distinct from the more common diamagnetic peroxo bridged dimers. Species C is characterized by a very broad HS EPR signal (g(x) = 5.1, g(y) = 3.9, g(z) = 2.1) and is reversibly formed by oxygenation of the LS [Co(II)(1)]-(HOAc) complex to the superoxo complex [Co(III)(1)O(2)(-)](HOAc), which subsequently forms the association complex C by interaction with the HS [Co(II)(1)](OAc(-)) species. The LS and HS complexes were also identified using other organic acids (benzoic and propanoic acid). Thermal annealing-quenching experiments revealed the additional presence of [Co(III)(1)O(2)(-)](HOAc) adducts, corroborating the presence of species C and the presence of diamagnetic dimer complexes in the solution, such as the EPR silent (HOAc)[Co(III)(1)(O(2)(2-))Co(III)(1)](HOAc). Overall, it appears that a facile interconversion of the [Co(1)] complex, possessing a LS ground state, occurs in the presence of acetic acid, producing both HS and LS Co(II) states, prior to formation of the oxidized active form of the catalyst, [Co(III)(1)](OAc(-)).     

Novel beta-lactam antibiotics synthesized by amination of catechols using fungal laccase

Novel cephalosporins, penicillins, and carbacephems were synthesized by amination of catechols with amino-beta-lactams like cefadroxil, amoxicillin, ampicillin and the structurally related carbacephem loracarbef using laccase from Trametes sp. All isolated monoaminated products inhibited the growth of several Gram positive bacterial strains in the agar diffusion assay, among them methicillin-resistant Staphylococcus aureus strains and vancomycin-resistant Enterococci. Observed differences in the cytotoxicity and in vivo activity in a "Staphylococcus-infected, immune suppressed mouse" model are discussed.     

Acoustic Radiation from a Finite Length Cylindrical Shell Excited by an Internal Acoustic Source: Solution Based on a Boundary Element Method and a Matched Asymptotic Expansion

This paper deals with acoustic radiation by a thin elastic shell, closed by two perfectly rigid discs, immersed in water and filled with air. The system is driven by an internal acoustic source. The shell has a length L, is clamped along one of its boundaries and is freely supported along the other boundary. Using the infinite domain Green's function, the radiated acoustic pressure is modeled by a hybrid layer potential (linear combination with nonreal coefficient of a simple layer and a double layer). Using Green's tensor of the in vacuo shell operator, the shell displacement is expressed as the sum of the field generated by the acoustic pressures and that due to boundary sources. Finally, the Green's function of the interior Neumann problem is used to express the acoustic pressure inside the shell in terms of the acoustic source and shell normal displacement: this representation fails for any frequency equal to one of the resonance frequencies of the shell interior. To overcome this, a light fluid approximation, which is allowed because the inner fluid is a gas, is adopted. Around each resonance frequency, an inner approximation is defined which matches the classical outer approximation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probing the substrate specificity of the catalytically self-sufficient cytochrome P450 RhF from a Rhodococcus sp

Analysis of the substrate specificity of the self-sufficient cytochrome P450 RhF revealed that the enzyme tends to catalyse the dealkylation of substituted alkyl-aryl ethers with shorter alkyl moieties more readily than equivalent compounds with longer alkyl groups.