Walter M. Müller

Novel Amide‐Based Molecular Knots: Complete Enantiomeric Separation, Chiroptical Properties, and Absolute Configuration

By comparison of experimental and theoretical CD curves the absolute configurations of chromatographically baseline-separated enantiomers of new trefoil molecular knots could be determined. From the results of syntheses with differently substituted starting materials, conclusions can be drawn about the knot-formation mechanism.

Dendrimers with a 4,4′-bipyridinium core and electron-donor branches. Electrochemical and spectroscopic properties

The synthesis, characterization, and electrochemical and spectroscopic properties of a new family of dendrimers comprising a 4,4′-bipyridinium core and 1,3-dimethyleneoxybenzene-type dendrons are described. The electrochemical results show that there is no significant inhibition of electron transfer involving the dendrimer core by the dendrons. The strong fluorescence of the 1,3-dimethyleneoxybenzene units of the branches is completely quenched as a result of charge-transfer interactions with the core.

Surface and bulk interactions of organic molecules with calixarene layers

Modified calixarenes can be used as model compounds to study molecular recognition since their molecular cavities reversibly incorporate small organic molecules. This effect has been used in chemical sensors with bulk and surface acoustic wave devices, coated with thin calixarene layers. These devices sensitively convert the mass changes during molecule/calixarene interactions into electronic signals. Thin films of modified calixarenes were prepared with various side groups and various sizes by Knudsen sublimation under well-defined, ultra-high-vacuum conditions. The interaction with perchloroethylene, chloroform, benzene, and toluene at constant temperatures, T, and partial pressures, pi, was studied systematically for different film thicknesses, d, by means of mass changes Δm=f(T,pi,d). From the thickness dependence of values, Δmeq, obtained under thermodynamic equilibrium conditions, surface and bulk effects during molecule calixarene interactions were separated. Pronounced excesses of surface concentrations of organic molecules have been found. Activation energies for molecular desorption from surface sites and for diffusion to subsurface sites were determined from mass spectroscopic results of thermal desorption behaviour. Experimental data of adsorption and desorption energies were confirmed by theoretical force field calculations.

Chiral Amide Rotaxanes with Glucose Stoppers – Synthesis, Chiroptical Properties and Wheel-Axle Interactions

In this paper we report on amide rotaxanes with tetrabenzoylglucose stoppers. When acetyl groups are used instead of benzoyl groups, merely a pseudo-rotaxane 5 is obtained. The circular dichroism measurements of the rotaxanes 6a and 6b differ significantly from that one of the free axle 7. Similarly, the Cotton effects of the mixtures of achiral wheels 2a and 2b and chiral axle indicate intermolecular host-guest interactions, likewise. After an addition of a solution of NaOMe the wheel is slipping off immediately and quantitatively by hydrolysis, as the benzoylglucose stoppers decrease in size by hydrolysis.

Cyclodextrine und synthetische Wirthohlräume — Vergleich der Komplexierungseigenschaften

It is shown that the synthetic host compounds described in this study possess higher complexation constants versus 1,8-ANS than β-or γ-cyclodextrin. The attachment of side chains to β-cyclodextrin increases the complex formation, whereas the value of γ-cyclodextrin is not reached. The quaternary ammonium nitrogens of the synthetic hosts may be replaced by amide groups without diminution of the association constants. Bicyclic compounds in general bind more strongly than monocyclic hosts due to tighter inclusion and increased hydrophobic interaction. The influence of side chains attached to synthetic host compounds on the complexation constants is difficult to predict.

Synthesis of highly phenylene substituted p-phenylene oligomers from pyrylium salts

A transition metal free route to phenyl substituted oligophenylenes that tolerates halogens is described.

Selective inclusion and orientation of chloroform in the molecular cavity of a 30-membered hexalactam host

X-Ray structural studies reveal that one chloroform guest molecule is embedded in molecular cavity formed by the synthetic large-ring host molecule (1) and is orientated in an unique Key–lock-type arrangement in such a way that the hydrogen atom of the chloroform projects into the centre of the macro-ring.

Pentamacrocyclic tris-crown hosts: selective binding of cationic, anionic, and neutral guests

The tris-crown host compounds (1)–(4) were synthesized and the structures of (2) and of the 3:1 potassium complex of (1)(with the SCN- anion projecting inside the cavity) were studied by X-ray analyses; specific organic guest molecules like β-naphthol and naphthalene diols are selectively bound inside the fitting cavities of the hosts (2) and (3)[but not (1) and (4)] in acidic water solution.

Salts of 4-Substituted Dipicolinic Acid Derivatives − Very Low Molecular Mass Gelators of Aqueous DMSO

This study reports on the gelation behaviour of a well-known family of dipicolinic acid derivatives that lack any long aliphatic chain as substituent. The mechanism of gelation is likely to arise from the base-assisted deprotonation of the carboxylic functionality which leads to the formation of the

Host:guest chemistry of diaza-18-crown-6: selective precipitation from mixtures of oligohydroxy phenols and the structures of five host: guest complexes

Diaza-18-crown-6 (1,4,10,13-tetraoxa-7,16-diaza-cyclo-octadecane) selectively precipitates as a 1,4-dihydroxybenzene-complex from a mixture of isomeric phenols and as a 2,6-dihydroxynapthalene-complex from mixtures of isomeric diols. These selective precipitations are discussed in terms of structure and solubility of the host-guest complexes and phenol acidity. The crystal structures of diaza-18-crown-6 with guestsp-nitrophenol (2: 1), 2,4-dinitroaniline (2: 1), 5,5-diethylbarbituric acid (2: 1), salicylaldoxime (2: 1) and 1,4-dihydroxybut-2-yne (1: 1) are reported.