Direct Electron Transfer and Bioelectrocatalysis by a Hexameric,Heme Protein at Nanostructured Electrodes

A nanohybrid consisting of poly(3‐aminobenzenesulfonic acid‐co‐aniline) and multiwalled carbon nanotubes [MWCNT‐P(ABS‐A)]) on a gold electrode was used to immobilize the hexameric tyrosine‐coordinated heme protein (HTHP). The enzyme showed direct electron transfer between the heme group of the protein and the nanostructured surface. Desorption of the noncovalently bound heme from the protein could be excluded by control measurements with adsorbed hemin on aminohexanthiol‐modified electrodes. The nanostructuring and the optimised charge characteristics resulted in a higher protein coverage as compared with MUA/MU modified electrodes. The adsorbed enzyme shows catalytic activity for the cathodic H₂O₂ reduction and oxidation of NADH.     

Surface‐Tuned Electron Transfer and Electrocatalysis of Hexameric Tyrosine‐Coordinated Heme Protein

Molecular modeling, electrochemical methods, and quartz crystal microbalance were used to characterize immobilized hexameric tyrosine‐coordinated heme protein (HTHP) on bare carbon or on gold electrodes modified with positively and negatively charged self‐assembled monolayers (SAMs), respectively. HTHP binds to the positively charged surface but no direct electron transfer (DET) is found due to the long distance of the active sites from the electrode surfaces. At carboxyl‐terminated surfaces, the neutrally charged bottom of HTHP can bind to the SAM. For this “disc” orientation all six hemes are close to the electrode and their direct electron transfer should be efficient. HTHP on all negatively charged SAMs showed a quasi‐reversible redox behavior with rate constant k_s values between 0.93 and 2.86 s^?1 and apparent formal potentials ${E{{0{^{\prime }}\hfill \atop {\rm app}\hfill}}}$ between ‐131.1 and ‐249.1 mV. On the MUA/MU‐modified electrode, the maximum surface concentration corresponds to a complete monolayer of the hexameric HTHP in the disc orientation. HTHP electrostatically immobilized on negatively charged SAMs shows electrocatalysis of peroxide reduction and enzymatic oxidation of NADH.     

The Structure and Conformation of (CH3)3CSNO

The gas‐phase molecular structure of (CH₃)₃CSNO was investigated by using electron diffraction, allowing the first experimental geometrical parameters for an S‐nitrosothiol species to be elucidated. Depending on the orientation of the ?SNO group, two conformers (anti and syn) are identified in the vapor of (CH₃)₃CSNO at room temperature, the syn conformer being less abundant. The conformational landscape is further scrutinized by using vibrational spectroscopy techniques, including gas‐phase and matrix‐isolation IR spectroscopy, resulting in a contribution of ca. 80:20 for the anti:syn abundance ratio, in good agreement with the computed value at the MP2(full)/cc‐pVTZ level of approximation. The UV/Vis and resonance Raman spectra also show the occurrence of the conformational equilibrium in the liquid phase, with a moderate post‐resonance Raman signature associated with the 350 nm electronic absorption.     

A Neutral Germanium/Phosphorus Frustrated Lewis Pair and Its Contrasting Reactivity Compared to Its Silicon Analogue

Chlorogermane (C₂F₅)₃GeCl with very electronegative pentafluoroethyl groups was converted with LiCH₂P(tBu)₂ to obtain the intramolecular frustrated Lewis pair (FLP) (C₂F₅)₃GeCH₂P(tBu)₂, a neutral, germanium-based FLP. Its reactivity was compared to its silicon homologue (C₂F₅)₃SiCH₂P(tBu)₂. Both FLPs cleave NO but give cyclic (Si) and open-chain oxides (Ge). In reactions with HCl both FLPs gave the same adduct type in the solid state, while the proton seems more mobile in solution in the germanium case. Reactions with PhCNO and Me₃SiCHN₂ result in ring-type adducts. The structures of (C₂F₅)₃GeCH₂P(tBu)₂ and of five adducts with substrates were elucidated by X-ray diffraction. The study clearly showed the germanium compound to have a more moderate Lewis acidity compared to the silicon analogue.     

Universality of the automorphism group of the real line

We discuss the question, whether each automorphism group (of cardinality at most ) of a linear order is embeddable into the automorphism group of the real line. We show that the answer to this question is independent of the axioms of ZFC: the answer is positive, if we assume < and Souslin's hypothesis; the answer is negative, if we assume orV=L.     

5-Organyl-5-phosphaspiro[4.4]nonanes: a contribution to the structural chemistry of spirocyclic tetraalkylphosphonium salts and pentaalkylphosphoranes

Spirocyclic phosphonium salts of the type [(CH(2))(4)P(CH(2))(4)](+) X(-) with X = I(3) (1a), I (1b), picrate (1c), benzoate (1d), and Cl (1e) were prepared from 1,4-diiodobutane and elemental phosphorus followed by metathesis reactions. The crystal structures of 1b and 1c and of 1d(H(2)O) have been determined by X-ray diffraction methods. In the cations of these salts the phosphorus atoms are shared by two five-membered rings in envelop conformations. In the picrate 1c the cations show an unsymmetrical ring folding pattern (point group C(1)), while the geometry of the cations of the iodide 1b and the benzoate hydrate [1d(H(2)O)] approaches the symmetry of point group C(2). These structures can be taken as models for the as yet unknown molecular geometries of the corresponding hydrocarbon (CH(2))(4)C(CH(2))(4) and silane (CH(2))(4)Si(CH(2))(4). Treatment of 1e with organolithium reagents RLi affords spirocyclic pentaorganophosphoranes RP[(CH(2))(4)](2) with R = Me, Et, n-Bu, Vi, and Ph (2a-e) in good (R = Me, Et, n-Bu) to low yields (R = Vi, Ph). The products are isolated as colorless liquids, of which only 2a, 2b, and 2d can be distilled without decomposition. Single crystals of 2a were obtained by low-temperature in situ crystal growth. The molecule has a trigonal bipyramidal configuration with the methyl group in an equatorial position and the two five-membered rings spanning axial/equatorial positions of the polyhedron. Deviations from the standard trigonal bipyramidal geometry are small. The compounds 2a-e are fluctional in solution as demonstrated by NMR spectroscopy.     

Nucleosides, 45.-Assignment of glycosylation sites in o-hexopyranosyl-ribonucleosides by 13C-NMR

Evidence is presented that glycosylation of a ribose-OH group in nucleosides results in a significant downfield shift for the appended ¹³C nucleus and smaller upfield displacements for the adjacent carbons, providing an efficient tool for differentiating between 2′-$\text{o}$-, 3′-$\text{o}$- and 5′-$\text{o}$-glycosyl-ribonucleosides. Therewith, the products formed on enzymatic galactosylation of uridine, inosine, and adenosine are unequivocally assigned β(1→3)-glycosidic linkages ($\text{3a}$ – $\text{3c}$).     

Differences Between Gas-Phase and Solid-State Molecular Structures of the Simplest Phosphonium Ylide,Me3P=CH2

Clearly different from local C ₃ symmetric is the heavy-atom core of Me₃P=CH₂, the simplest phosphonium ylide. The geometry obtained by reanalysis of gas-electron-diffraction data from 1977 is now consistent with theoretical calculations, but different from the molecular structure in the solid state. The picture shows the structure of Me₃P=CH₂ in the gas phase (a) and in the crystal (c) together with the calculated transition state (b) (viewed along the P=C bond).     

A convenient access to the 1,5-anhydro forms of d-tagatose,l-rhamnulose and d-xylulose via 2-hydroxyglycal esters

Zemplén methanolysis or a three-step protocol comprising hydroxylaminolysis, de-O-acetylation and deoximination smoothly and efficiently convert the benzoylated 2-hydroxy-d-glycals of d-galactose, l-rhamnose and d-xylose into their configurationally related 1,5-anhydro-ketoses, thereby providing convenient access to the 1,5-anhydro forms of d-tagatose, l-rhamnulose and d-xylulose. Invariably obtained as amorphous solids, they are best characterized through their highly crystalline oximes.