Biocatalytic asymmetric hydroxylation of hydrocarbons with the topsoil-microorganism Bacillus megaterium

A Bacillus megaterium strain was isolated from topsoil by a selective screening procedure with allylbenzene as a xenobiotic substrate. This strain performed the hydroxylation chemoselectively (no arene oxidation and overoxidized products) and enantioselectively (up to 99% ee) in the benzylic and nonbenzylic positions of a variety of unfunctionalized arylalkanes. Salycilate and phenobarbital, which are potent inducers of cytochrome P-450 activity, changed the regioselectivity of the microbial CH insertion, without an effect on the enantioselectivity. The biotransformation conditions were optimized in regard to product yield and enantioselectivity by variation of the oxygen-gas supply and the time of the substrate addition. The different product distributions (alpha- versus beta-hydroxylated product) that are obtained on induction of cytochrome P-450 enzyme activity demonstrate the involvement of two or more hydroxylating enzymes with distinct regioselectivities in this biotransformation. An oxygen-rebound mechanism is assumed for the cytochrome P-450-type monooxygenase activity, in which steric interactions between the substrate and the enzyme determine the preferred face of the hydroxy-group transfer to the radical intermediate.     

SPOCC-194, a new high functional group density PEG-based resin for solid-phase organic synthesis

A novel polymer matrix for solid-phase synthesis, SPOCC(194) resin (1), was designed featuring a backbone of homogeneous tetraethylene glycol (TEG(194)) macromonomer linked by quaternary carbon junctions and terminating in primary alcohol functionality. Beaded SPOCC(194) resin was effectively prepared by suspension polymerization of oxetanylated TEG macromonomer 5 in stirred silicon oil. Mechanically stable and inert to a diverse range of reaction conditions, SPOCC(194) possessed a high hydroxyl group loading (0.9-1.2 mmol/g) for substrate attachment and swelled effectively ( approximately 2-4 mL/g) in a variety of organic and aqueous solvents. Developed for solid-phase synthesis at high reactant concentrations for driving organic and aqueous reactions to completion, SPOCC(194) exhibited high functional group density (mmol/mL) similar to that of low-loaded aminomethylated polystyrene-divinylbenzene copolymer (PS-1%DVB) yet significantly higher than that of PEGA(1900), SPOCC(1500), and TentaGel S. High-resolution MAS NMR spectra of Fmoc-derivatized SPOCC(194) indicate that monitoring of functional group transformation is possible. Moreover, by employment of a nonaromatic resin-linker combination, electrophilic chemistry, such as Lewis acid catalyzed glycosylation and Friedel-Crafts acylation, was selectively performed on substrate bound to SPOCC(194) resin. Such properties make SPOCC(194) resin a promising new polymer matrix for the support-bound construction of small organic molecules by parallel and combinatorial synthesis and the scavenging of solution-phase reactants or byproducts.     

Conversion of sodium lactate to lactic acid with water-splitting electrodialysis

The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.     

Chiral auxiliary based approach toward the synthesis of C-glycosylated amino acids

[reaction in text] In a chiral auxiliary based method C-glycosylated amino acids can be obtained by a 1,3-dipolar cycloaddition of a chiral glycine equivalent and C-1 allyl- or vinyl-derived carbohydrate building blocks as the key step. The products are formed regio- and diastereoselectively. Reductive cleavage of the N-O bond of the isoxazolidine and of the chiral auxiliary leads to C-glycosylated amino acids. The use of (-)-menthone to (+)-menthone as the auxiliary leads to the corresponding diastereomers.     

The stability of gold iodides in the gas phase and the solid state

The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.     

Investigation of the hyperfine structure of Ta I-lines (III)

By investigating the hyperfine structure of 41 Ta I lines we could determine the magnetic hyperfine interaction constants A and the electric quadrupole interaction constants B of 25 even parity levels and 32 odd parity levels. Additionally, we could classify one line. With 78 dipole allowed transitions which we tried to excite by laser light we obtained neither optogalvanic nor fluorescence signals. Therefore we conclude that some of the Ta I levels, listed in commonly used tables [e.g. Moore, Ch.: Atomic energy levels. Vol. III. Natl. Bur. Stand. (U.S.) Circ. No. 467. Washington, D.C.: U.S. GPO 1949], do not exist.     

Eine neue photometrische bestimmung für nickel mit aethylendiamintetraessigsäure

It is possible to determine very high concentrations of nickel photometrically by means of ethylenediaminetetra-acetic acid, by working at a pH between 4.55 and 6.82. The absorption curves obtained for this complex are very reproducible; for these measurements an Elko II apparatus with filter S57E is used. High concentrations of ammoniacal salts hinder the measurement. The formation of the complex is not influenced by the anion of the compound of nickel used. The Lambert-Beer law is followed for strengths of nickel of 40 — 5000 mg/100 ml. This procedure is convenient for alloys rich in nickel.     

Accurate time-resolved laser spectroscopy on silver atoms

The lifetimes of the silver 5p ² P states have been measured with high accuracy by time-resolved laser spectroscopy using the delayed coincidence technique. Also, the hyperfine structure of¹⁰⁷Ag and¹⁰⁹Ag in these two states has been studied by observing quantum beats.