Carotenoids of the Carotenoprotein Asteriarubin. Optical Purity of Asterinic Acid

The carotenoid composition of the carotenoprotein asteriarubin ex the starfish Asterias rubens, determined by HPLC, comprised canthaxanthin ( 6 , 3% of total), all-trans-astaxanthin ( 1 , 14%), all-trans-7,8-didehydroastaxanthin ( 2 , 24%), all-trans-7,8,7′,8′-tetradehydroastaxanthin ( 3 , 43%) and 4-oxomytiloxanthin ( 7 , 10%). The previously unknown 4-oxomytiloxanthin was tentatively identified by the UV./VIS., 'H-NMR. spectra and MS. data. The optical purity was determined by HPLC. of the di-(?)-camphanates, by comparison with those of synthetic standards: 7,8,7′, 8′-tetradehydroastaxanthin (92% (3S, 3′S), 2% meso), 7,8-didehydroastaxanthin (89% (3S,3′S), 2% meso?), and astaxanthin (78% (3S,3′S), 14% (3R,3′S), and 5% (3R,3′R)). It is concluded that the acetylenic derivatives of astaxanthin in contrast to astaxanthin from marine animal sources are essentially pure (3S, 3′S)-isomers. This might reflect their probable metabolic formation by 4-oxo modification of acetylenic (3R,3′R)-carotenols ex Mytilus edulis in their diet.     

On the existence of ordered organic adlayers at the Cu(111)/electrolyte interface

We have reinvestigated the behavior of a Cu(111) electrode in pure and cinchonidine containing aqueous 0.1 M HClO4 solution by cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (STM). In contrast to previous publications by Wan et al. (Langmuir 2000, 19, 1958-1962 and references cited therein) on Cu(111) in pure 0.1 M HClO4 which claimed an adsorbate-free Cu(111) surface in the entire potential range, we have found a highly ordered hexagonal adsorbate structure with a (4 x 4) unit cell, which is stable in the potential range from hydrogen evolution at -350 to -150 mV (RHE). The adsorbate-free (1 x 1) Cu(111) surface is only visible in a fairly small potential range from -150 to +50 mV. A disordered surface structure is formed at more positive potentials which is interpreted by adsorption of an oxygen-containing species. Furthermore, the formation of a highly ordered cinchonidine adlayer on Cu(111) in 0.1 M HClO4 as reported by Wan et al. (J. Am. Chem. Soc. 2002, 124, 14300-14301) could not be reproduced here. In fact, the similarity of all structures reported by Wan et al. for a great variety of different organic adlayers on Cu(111) in HClO4 solution including cinchonidine with the (4 x 4) superstructure found here already in pure HClO4 solution (i.e., without organic solute) casts serious doubts on the validity of those previous results by Wan et al. in general.     

Colorimetrische pH-Bestimmung

Ohne Zusammenfassung     

Planar Chirality: Synthesis and Transannular Reactions of Unsaturated Optically Active Azoninones Bearing E-Olefins

The zwitterionic aza-Claisen rearrangement of optically active trans 4-silyloxy-2-vinylpyrrolidines and carboxylic acid fluoride generated nine-membered ring lactams with high yields. The reaction proceeded with an almost complete 1,4-chirality transfer and the exclusive generation of the E-double bond in the medium sized rings to cause additional planar chiral information. The initially formed azoninones were characterized by a pS-arrangement of the olefin with respect to the ring. The rather kinetically stable conformation underwent a flipping of the double bond to give the pR-azoninones as the thermodynamically stable products. The planar diastereomers were subjected to regio- and diastereoselective transannular ring contractions to give indolizidinones. The stereochemical outcome was strongly dependent from the planar chiral information of the double bond and the lactam unit. The so-formed optically active bicycles bearing a defined substitution pattern should serve as versatile building blocks in alkaloid synthesis.     

Phototransformation of monovinyl and divinyl protochlorophyllide by NADPH:Protochlorophyllide oxidoreductase of barley expressed in Escherichia coli

The chlorophyll precursors monovinyl protochlorophyllide (MV-PChlide) and divinyl protochlorophyllide (DV-PChlide) were extracted from mutant C-2A' of the unicellular green alga Scenedesmus obliquus which accumulates both protochlorophyllide derivatives in the dark. The two pigments were characterized by absorption and fluorescence spectroscopy and by plasma desorption mass spectrometry. The molecular masses of MV-PChlide and DV-PChlide were determined as 612 and 610 atomic mass units (amu) respectively. Both MV-PChlide and DV-PChlide were accepted as substrates and photoconverted to chlorophyllides in vitro by NADPH:protochlorophyllide oxidoreductase of barley expressed in Escherichia coli.     

The synthesis,vibrational spectra,and molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF - the first structurally characterized salt with a tripositive,homoleptic metal carbonyl cation and the first example of a tetrahedral hydrogen-bonded (HF)(4) cluster

The reductive carbonylation of IrF(6) in a dilute solution of SbF(5) in anhydrous HF (1:6 by volume) produces surprisingly at 25 degrees C and 1.5 atm CO the complex salt [Ir(CO)(6)][SbF(6)](3).4HF, while [Ir(CO)(6)][Sb(2)F(11)](3) is obtained in liquid SbF(5) under similar conditions. Vibrational spectra in the CO stretching range for both salts and [Ir(CO)(6)](3+)((solv)) are identical within error limits, and nu(CO)(av) is with 2269 cm(-1) the highest average stretching frequency so far observed for octahedral metal carbonyl cations. A vibrational assignment supported by DFT calculations is presented, and the vibrational fundamentals are compared to those of [Os(CO)(6)](2+). The molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF is determined by single-crystal X-ray diffraction. Crystal data for [Ir(CO)(6)][SbF(6)](3).4HF: rhombohedral, R3c (No. 161), a = 14.630(4) A, c = 18.377(7) A, V = 3406.4(18) A(3), Z = 6, T = 150 K, R(1) = 0.0338 [I > 2sigma (I)], wR(2) = 0.0797). The average Ir-C bond length in the octahedral [Ir(CO)(6)](3+) cation is with 2.029(10) the longest observed for iridium carbonyl derivatives, consistent with the absence of Ir --> CO pi-back-bonding. The four solvate HF molecules form a tetrahedron via long, asymmetric, and partly delocalized hydrogen bonds with F-F edge lengths of 2.857 (3x) and 2.914 (3x) A. There is no precedent for a polyhedral (HF)(n) cluster in the gas, liquid, or solid phase. The four F atoms of the (HF)(4) cluster are coordinated to the C atoms of the six CO ligands of the cation, which again is without precedent. The coordination of one of the F atoms to three C atoms in a iso-tridentate mode with contact distances C-F(8) of 2.641(10) A is most unusual. The observed tight C-F coordination in [Ir(CO)(6)][SbF(6)](3).4HF provides conclusive evidence for the presence of electrophilic carbon in the cation and illustrates how superelectrophilic cations such as [Ir(CO)(6)](3+) are solvent stabilized in the conjugate Br?nsted-Lewis superacid HF-SbF(5).     

Structure and dynamics of micelles and cubic phase structures with ethoxylated phytosterol surfactant in water

The self-assembly of a sterol ethoxylate surfactant with 30 oxyethylene units in water was studied by 1H NMR self-diffusion measurements in a wide concentration range in the micellar region (0-25 wt %). The data showed that the surfactant aggregates do not interact by hard sphere interactions but rather a strong concentration dependence of the diffusion coefficient was noted which was explained by polymer scaling theory. In the cubic phase (30-65 wt %), the self-diffusion data from water, from surfactant, and from free polyoxyethylene suggest spherical micelles, although water diffusion was much restricted due to binding to the surfactant headgroup. From X-ray measurements in the cubic phase, the unit cell size was calculated, and together with surfactant self-diffusion measurements the exchange dynamics between free and aggregated surfactant was obtained.     

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses,vibrational spectra,NMR studies,and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.     

Molecular modelling studies on the ORL1-receptor and ORL1-agonists

The ORLI (opioid receptor like 1)- receptor is a member of the family of rhodopsin-like G protein-coupled receptors (GPCR) and represents an interesting new therapeutical target since it is involved in a variety of biomedical important processes, such as anxiety, nociception, feeding, and memory. In order to shed light on the molecular basis of the interactions of the GPCR with its ligands, the receptor protein and a dataset of specific agonists were examined using molecular modelling methods. For that purpose, the conformational space of a very potent non-peptide ORL1-receptor agonist (Ro 64-6198) with a small number of rotatable bonds was analysed in order to derive a pharmacophoric arrangement. The conformational analyses yielded a conformation that served as template for the superposition of a set of related analogues. Structural superposition was achieved by employing the program FlexS. Using the experimental binding data and the superposition of the ligands, a 3D-QSAR analysis applying the GRID/GOLPE method was carried out. After the ligand-based modelling approach, a 3D model of the ORL1-receptor has been constructed using homology modelling methods based on the crystal structure of bovine rhodopsin. A representative structure of the model taken from molecular dynamics simulations was used for a manual docking procedure. Asp-130 and Thr-305 within the ORL1-receptor model served as important hydrophilic interaction partners. Furthermore, a hydrophobic cavity was identified stabilizing the agonists within their binding site. The manual docking results were supported using FlexX, which identified the same protein-ligand interaction points.     

An Anti‐angiogenic Reverse Thermal Gel as a Drug‐Delivery System for Age‐Related Wet Macular Degeneration

Reverse thermal gels have numerous biomedical implications, as they undergo physical gelation upon temperature increases and can incorporate biomolecules to promote tissue repair. Such a material is developed for the sustained release of bevacizumab (Avastin), a drug used to treat age‐related macular degeneration. The polymer, poly(ethylene glycol)‐poly(serinol hexamethylene urethane) (ESHU), forms a physical gel when heated to 37 °C and shows good cytocompatibility with ocular cells. ESHU is capable of sustaining bevacizumab release over 17 weeks in vitro, and the release kinetics can be altered by changing the drug dose and the ESHU concentration. These results suggest that ESHU is biologically safe, and suitable for ocular drug delivery.