Wie steuert man die Koordination in Zinkkomplexen?? Untersuchungen mit Hydridotris(3-phenylpyrazolyl)borat als Ligand

How to Steer the Coordination of Zinc Complexes? Investigations with Hydridotris(3-phenylpyrazolyl)borate as a Ligand The crystal structure analyses of the zinc complexes L_PhZnCl ( A ) and Zn(L_Ph)₂ ( B ) of the potentially tridentate nitrogen ligand L_Ph^? = HB(3-Phpz)₃^? Phpz = 3-Phenylpyrazolyl) unexpectedly show tetrahedral coordination of the metal ion in both cases. The bisligand zinc complex B is formed by decomposition of unstable hydroxy and alkoxy complexes of the formula L_PhZnOR. As a further product of that reaction a complex of the formula [η³B(3-Phpz)₃Zn(3-PhpzH)]⁺ClO₄^? could be identified which is a first example for the cationic species L_PhZn(neutral ligand)⁺. A crystallizes in the trigonal system with lattice constants of a = 11.449(2) and c=11.365(2) Å, space group P3 , Z = 2, d_calc. = 1.365mg/mm³. B crystallizes in the orthorhombic system with a = 22.675(3), b = 10.797(2), and c = 19.699(3) Å, space group Pbcn; Z = 4, d_calc. = 1.306 mg/mm³. The crystal structures were determined from 1 687 ( A ) and 2 341 ( B ) observed X-ray data and refined to R = 0.03 and 0.04, respectively. A was characterized as a chlorotripod complex with symmetry 3-C₃ and a distorted tetrahedral coordination of the Zn atom (angle Cl? Zn? N 122.9(1)° and N? Zn? N′ 93.3(1)°), while B was identified as a bisligand complex with symmetry 2-C₂ and again a distorted tetrahedral coordination of the Zn atom (angles N? Zn? N 101.5(1) up to 118.9(1)°).     

Stereochemical studies. 81. Saturated heterocycles. 69 . Preparation of methylene-bridged 3,1-benzoxazines, 3,1-benzoxazin-2-ones and 3,1-benzoxazine-2-thiones

3-exo-Aminobicyclo[2.2.1]hept-5-ene-2-exo-carboxylic acid and ethyl 3-endo-aminobicyclo[2.2.1]heptane-2-endo-carboxylate ( 6 ) were reduced with lithium aluminum hydride to the corresponding bicyclic aminoalcohols 3 and 4 . These and the saturated endo-endo and exo-exo N-methylaminoalcohols 16 and 22 , respectively, were converted to methylene-bridged tetrahydro- ( 11 ) and hexahydro-3,1-benzoxazin-2-ones 12, 17, 23 and 3,1-benzoxazin-2-thiones 13, 14, 18, 24 . The exo-exo 3 and endo-endo 4 aminoalcohols were cyclized by means of ethyl arylimidates to tricyclic dihydro-1,3-oxazines 7a-d, 8a-d . The structures were confirmed by ir, ¹H and ¹³C nmr spectroscopy.     

Production of nisin by Lactococcus lactis in media with skimmed milk

Nisin is a bacteriocin that inhibits the germination and growth of Gram-positive bacteria. With nisin expression related to growth conditions of Lactococcus lactis subsp. lactis, the effects of growth parameters, media components, and incubation time were studied to optimize expression. L. lactis ATCC 11454 was grown (100 rpm at 30°C for 36 h) in both M17 and MRS standard broth media (pH 6.0–7.0) supplemented with sucrose (1.0–12.5 g/L), potassium phosphate (0.13 g/L), asparagine (0.5 g/L), and sucrose (0.24 g/L), and diluted 1:1 with liquid nonfat milk. Liquid nonfat milk, undiluted, was also used as another medium (9% total solids, pH 6.5). Nisin production was assayed by agar diffusion using Lactobacillus sake ATCC 15521 (30°C for 24 h) as the sensitive test organism. The titers of nisin expressed and released in culture media were quantified and expressed in arbitrary units (AU/L of medium) and converted into known concentrations of “standard nisin” (Nisaplin®, g/L). The detection of nisin activity was <0.01 AU/L in M17 and MRS broths, and 7.5 AU/L in M17 with 0.14% sucrose or 0.13% other supplements, and the activity increased to 142.5 AU/L in M17 diluted with liquid nonfat milk (1:1). The 25% milk added to either 25% M17 or 25% MRS provided the highest levels of nisin assayed.     

Sol–Gel Chemistry for Ba2+ Sensors to Allow Oil Production Engineered Nanometrically

Work on the development of a Ba^{2 +}-sensitive sol–gel based optical fiber (OF) for use in oil wells is described. The optical fiber (OF) has on its surface a Ba^{2 +} chelating ligand (L) immobilized at a 2–16 wt% loading immobilized in a porous SiO₂ sol–gel host. The authors report sol–gel routes to these SiO₂ and L/SiO₂ nanocomposites and describe their characterization by XPS, fluorescence, NMR, UV-vis and BET methods. They also report on the sol–gel coating and its selectivity to Ba^{2 +}_(aq).     

Ti2: accurate determination of the dissociation energy from matrix resonance Raman spectra and chemical interaction with noble gases

UV-visible and resonance Raman spectra of Ti(2) isolated in Ar, Kr, and Xe matrices at temperatures of 10 K were measured by using the 514 nm line of an Ar ion laser. The data show that the Ti(2) molecule interacts strongly with Xe, leading to a significant weakening of the Ti[bond]Ti bond strength. The f(Ti[bond]Ti) force constant decreases in the series Ar>Kr>Xe, from 232.8 Nm(-1) in Ar and 225.5 Nm(-1) in Kr to 199.7 Nm(-1) in Xe. Additional experiments in an Ar matrix containing 2 % of Xe indicate the formation of a molecule of the formula Ti(2)Xe. Our spectra for Ti(2) in an Ar matrix give evidence for several previously not observed members of the Stokes progression. The sum of experimental data allows for an improved estimation of the dissociation energy on the basis of a LeRoy-Bernstein-Lam analysis. A dissociation energy of 1.18 eV was derived from this analysis. The UV-visible data give evidence of the vibrational levels of an excited state of Ti(2).     

Conversion of aquifex aeolicus 3-deoxy-d-manno-octulosonate 8-phosphate synthase, a metalloenzyme, into a nonmetalloenzyme

The Aquifex aeolicus 3-deoxy-d-manno-octulosonate 8-phosphate synthase (KDO8PS), a class II metalloenzyme, is converted into an active nonmetalloenzyme by a single amino acid mutation, namely, C11N. The result may provide insight into the evolutionary link between the two KDO8PS classes as well as the potential role of the metal and/or asparagine in the catalytic mechanism.     

On the acylation of 1,3-benzoxathiole systems

The acylation on 1,3-benzoxathiole systems, as well as the effect of the stoichiometry of the catalyst on the yields of ketones and of breaking products of the O C S bonds is here described.     

CdSe Quantum Dot Doped Amine-Functionalized Ormosils

Nanosized phenyl-capped CdSe particles (quantum dots) were isolated, after preparation inside reversed micelles present in AOT/H2 O/heptane, and then successfully redispersed in amine-functionalized ormosils derived from 3-aminopropyl(trimethoxy)silane (i.e., SA). Doped ormosils were formed into films of a few m thickness or small bulk samples. Host ormosils were structurally characterized by means of absorption spectroscopy, in the near- and mid-infrared ranges, and by 29Si and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Doped ormosils were prepared and investigated via visible spectroscopy. The size of CdSe particles dispersed into the amino-ormosil hosts was calculated using the Effective Mass Model.     

Gliadin effect on fluctuation properties of phospholipid giant vesicles

Gliadin is a fraction of wheat gluten, a protein supramolecular complex known for its remarkable and biotechnologically relevant viscoelastic properties. Very high molecular mass characterise these systems, thus hindering high-resolution structural investigations. It is known, however, that these proteins comprise rather extended, extensively interassociated structures, which respond for their peculiar mechanical behaviour. Besides these properties, some of gluten's fractions, such as gliadin, are also known to be involved in a nutritionally relevant pathology of auto-immune character, the celiac disease, supposedly related to some unusual structural features of the protein. Despite its medical relevance, however, the role played by gliadin in the etiology of the celiac disease is not sufficiently understood to date. In this work, we investigated the role of gliadin on mechanical properties of a membrane model of dioleoylphosphatidylcholine (DOPC) giant unilamellar vesicles. The technique of micropipette aspiration, coupled to videomicroscopy, was applied. The microvesicles, produced by electric field pulsing over metal-covered plates, were suctioned into the micropipettes under varying applied pressures. A significant increase in the values of the bilayer curvature constant, k(c), was observed, with a saturation effect being verified at around 0.02-0.03 gliadin/DOPC mass ratio, indicating that the membrane becomes less elastic in the presence of the protein. Possible correlations between the observed membrane fluctuation properties and the celiac disease etiology are suggested and discussed.