Substrate binding to vanadate-dependent bromoperoxidase from Ascophyllum nodosum: a vanadium K-edge XAS approach

The EXAFS region of vanadium K-edge XAS spectra of native vanadate-dependent bromoperoxidase (isoenzyme I) from Ascophyllum nodosum in the presence of the substrate bromide can be fitted to three shells (at 1.62, 1.73-1.78 and 1.99-2.07 A) in the first coordination sphere of vanadium plus two more distant shells at 4.1A, possibly corresponding to bromide, and 4.7 A due to light scatterers stemming from the protein pocket. Bromide does not directly bind to the vanadium centre. The XANES and the EXAFS features for the enzyme are essentially reproduced by model complexes of the general composition [VO(H(2)O)(n)(ONO)] (n= 1 or 2) where ONO is the dianion of a Schiff base from bromosalicylaldehydes (Brsal; with the Br substituent in the position 3, 4, 5 or 6) and amino acids. The 3-Brsal derivatives exhibit an outer sphere shell at 3.8 A, which is traced back to intermolecular contacts. The data obtained from EXAFS are compared to those obtained from single crystal X-ray diffraction of [VO(H(2)O)(2)(4-Brsal-gly)] and [VO(H(2)O)(2)(6-Brsal-gly)] (gly = glycinate). In the complex [VOBr(2)(ONO)']] ((ONO)' is the Schiff base from o-anisole and o-hydroxyaniline), the V-Br distance is 2.44 A.     

Chemistry in microstructured reactors

The application of microstructured reactors in the chemical process industry has gained significant importance in recent years. Companies that offer not only microstructured reactors, but also entire chemical process plants and services relating to them, are already in existence. In addition, many institutes and universities are active within this field, and process-engineering-oriented reviews and a specialized book are available. Microstructured systems can be applied with particular success in the investigation of highly exothermic and fast reactions. Often the presence of temperature-induced side reactions can be significantly reduced through isothermal operations. Although microstructured reaction techniques have been shown to optimize many synthetic procedures, they have not yet received the attention they deserve in organic chemistry. For this reason, this Review aims to address this by providing an overview of the chemistry in microstructured reactors, grouped into liquid-phase, gas-phase, and gas-liquid reactions.     

Slopes of vector bundles on projective curves and applications to tight closure problems

We study different notions of slope of a vector bundle over a smooth projective curve with respect to ampleness and affineness in order to apply this to tight closure problems. This method gives new degree estimates from above and from below for the tight closure of a homogeneous -primary ideal in a two-dimensional normal standard-graded algebra in terms of the minimal and the maximal slope of the sheaf of relations for some ideal generators. If moreover this sheaf of relations is semistable, then both degree estimates coincide and we get a vanishing type theorem.

     

Directional synthesis of a dye-linked conducting homopolymer

We report a new synthesis of a 10,20-diphenyl-5,15-bis(4-cyanophenyl)porphyrin (1) and its reduction to give 10,20-diphenyl-5,15-bis(4-formylphenyl)porphyrin (2). When the conducting polymer poly(2',5'-dioctyl-4,4' '-terphenylenecyanovinylene) was prepared in the presence of 2, we obtained a three-domain structure, compound 3, consisting of two homopolymer blocks (J domains) with the porphyrin dye molecule (P domain) in the middle. The JPJ assembly was subjected to photophysical studies where we showed that the J domain could serve as a light-harvesting antenna for the P domain.     

Synthetic studies and structural aspects of novel metallacyclic compoundsof titanium(IV) incorporating nitrogen,oxygen and sulphur: 1. Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV) with alkoxyalkanols and the crystal structure of a new modification: di-μ-oxo-bis[diacetylacetonatotitanium(IV)]

Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)₂Ti(OR)₂] (R = Et, Pr ⁱ ) with alkoxyalkanols (ROCH₂CH₂OH) (R = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)₂Ti(OR)_2–n (OCH₂CH₂OR) _n ] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (¹H- and ¹³C-) spectral studies, a cis-octahedral environment around Ti^IV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)₂Ti(OEt)(OCH₂CH₂OBu)] for 2 weeks, orange yellow crystals of [(acac)₂TiO]₂ were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)₂TiO]₂.     

Toward Transition-Metal-Templated Construction of Arylated B4 Chains by Dihydroborane Dehydrocoupling

The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH₂] (Dur=2,3,5,6-Me₄C₆H) and [(Me₃Si)₂NBH₂] led to the formation of bridging borylene complexes of the form [(Cp*RuH)₂BR] (Cp*=C₅Me₅; 1 a : R=Dur; 1 b : R=N(SiMe₃)₂) through oxidative addition of the B−H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF₃)₂-C₆H₃BH₂] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)₄[(Cp*Ru)₂B₄H₅(3,5-(CF₃)₂C₆H₃)₄] ( 4 ), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp*Ru)₂(μ-H)B₄H₉] ( I ) indicates that there appear to be no classical σ-bonds between the boron atoms in complex I , whereas in the case of 4 the B₄ chain better resembles a network of three B−B σ bonds, the central bond being significantly weaker than the other two.     

An apparatus for the determination of speeds of sound in fluids

An apparatus for accurate measurements of the sound velocity in fluids is described, which is based on the pulse-echo technique, and operates up to 30 MPa in the temperature range between (250 and 350) K. The expanded uncertainties (k = 2) in the speed of sound measurements are 0.006%, 6 mK in the temperature, 2.1 hPa in the pressure up to 3 MPa, and 23.9 hPa above this value. Measurements of the speed of sound for nitrogen from (250 to 350) K and for water at temperatures between (303.15 and 323.15) K are presented at pressures up to 30 MPa to validate the new apparatus. The expanded overall uncertainty of the measurements on nitrogen and water were estimated to be 0.011% and 0.006%, respectively. The speed of sound of both fluids was compared with literature sources showing an excellent agreement among them, with relative deviations lower than 0.01% in nitrogen and 0.006% in water.