Franz Effenberger

Anion-exchange membranes with improved alkaline stability

Abstract With the increasing use of electrodialysis in the chemical and biochemical process industry and for the treatment of industrial waste waters, the demand for ion-exchange membranes which provide good stability in strong acid or alkaline solutions has drastically increased. Cation-exchange membranes with adequate chemical stability are available today. However, all commercial anion-exchanges are unsatisfactory as far as their alkaline stability is concerned. In this paper the development of anion-exchange membranes with low electrical resistance, high selectivity and good long-term stability in strong alkaline solutions is described.

Photoactivated Preparation and Patterning of Self-Assembled Monolayers with 1-Alkenes and Aldehydes on Silicon Hydride Surfaces

Direct lateral patterning in the formation of self-assembled monolayers (SAMs) on silicon was achieved by the photoinduced reaction of aldehydes with Si(111)-H surfaces by using the usual masking techniques (see the schematic illustration; on the right-hand side is a microscopy image of a patterned SAM formed from octadecanal).

Enzyme-catalyzed synthesis of (S)-cyanohydrins and subsequent hydrolysis to (S)-α-hydroxy-carboxylic acids

(S)-Cyanohydrins 2 are obtained with high enantioselectivity from aromatic aldehydes and HCN in the presence of (S)-oxynitrilase (E.C.4.1.2.11). Acid-catalyzed hydrolysis of the cyanohydrins 2 affords the corresponding (S)-α-hydroxy carboxylic acids 3 without racemization.

Fulgides as switches for intramolecular energy transfer

In a molecular unit which is a donor-fulgimide-acceptor triade, the possibility of an intramolecular energy transfer from donor to acceptor depends upon the isomer configuration of the photochromic fulgimide. It is shown that a switching on and off of this intramolecular energy transfer is possible by photoinduced shifting of the fulgimide levels between a trap and an antitrap function.

Anthryloligothienylporphyrins: Energy Transfer and Light‐Harvesting Systems

In the new trichromophoric supermolecule 1, a quantitative intramolecular energy transfer (>98 %) occurs from the anthracene donor to the emitting porphyrin acceptor through the oligothiophene chain after selective UV excitation of anthracene. Energy-transfer properties and fluorescence quantum yields are independent of the oligothiophene chain length. Attachment of further anthrylquinquethienyl chromophores to the porphyrin ring results in an increase in the intensity of characteristic absorption and fluorescence bands.

Oxidative phosphonylation of aromatic compounds

Aryl phosphonates can be prepared in good yield from the respective arenes and tri- or dialkyphosphites by either chemical or anodic oxidation. The anodic oxidation proceeds either via phosphinium radical cations, which then attack the arenes electrophilically, or via arene radical cations, which add the trialkylphosphite as nucleophile. Aryl phosphonates are also obtained in good yield by chemical oxidation with peroxodisulfate/AgNO3 in acetonitrile/water or glacial acetic acid. The diethylphosphinium radical cation, formed from diethylphosphite by oxidation with Ag(II), is supposed to be the reactive species in this process. Raising the silver salt concentration leads to an increase in polyphosphonylation. Selectivity ratios were determined for the oxidative phosphonylation process.

Hydroxynitrile lyases in stereoselective catalysis

(R)- as well as (S)-cyanohydrins are now easily available as a result of the excellent accessibility, the relatively high stability and the easy handling of hydroxynitrile lyases (HNLs). The optimization of reaction conditions (solvent, temperature, and using site-directed mutagenesis, etc.) has enabled HNL-catalyzed preparations of optically active cyanohydrins on a technical scale. The enantioselectivity of chiral metal-complex-catalyzed additions of trimethylsilyl cyanide to aldehydes has been improved, but is, by far, not yet competitive with the HNL-catalyzed reactions.

Second-order polarizability of donor-acceptor substituted oligothiophenes : substituent variation and conjugation length dependence

Abstract Second-order polarizabilities and excited state dipole moments of a number of donor—acceptor substituted α-oligothiophenes have been investigated by use of electric field induced second harmonic generation (EFISH), solvatochromism and electrooptical absorption measurements (EOAM). The experimental results reveal that oligothiophenes are very effective conjugation units offering substantial enhancement of the second-order polarizability with increasing chain length.

Enzyme-catalyzed synthesis of (R)-ketone-cyanohydrins and their hydrolysis to (R)-α-hydroxy-α-methyl-carboxylic acids

(R)-Ketone-cyanohydrins (R)-2 are obtained with high enantioselectivity from aliphatic ketones 1 and HCN in organic solvents using (R)-oxynitrilase (EC 4.1.2.10) as catalyst. Acid catalyzed hydrolysis of the cyanohydrins (R)-2 affords the corresponding (R)-α-hydroxy-α-methyl-carboxylic acids (R)-3 without measurable racemization.

A novel convenient preparation of dihydroxyacetone phosphate and its use in enzymatic aldol reactions

A new preparation of the stable barium salt of 2,5-bis(phosphonooxymethyl)-2,5-diethoxy-1,4-dioxane Ba-2 is described, which by treatment with DOWEX 50 H+ gives dihydroxyacetone phosphate (DHAP in high yield. DHAP prepared by this method was used for aldolase-catalyzed condensations.