Biomedical subjects

W Lohmann

Publications and source records attributed to W Lohmann.

At least 73 records · Page 4Linked to original sources

PubMed1976

ESR and optical absorption studies on the copper (II) interaction with aromatic amino acids.

Electron spin resonance and optical absorption studies have been done in order to investigate the interaction between Cu2+ and aromatic amino acids in aqueous solution at 77 K and at room temperature as well. Depending on the concentration each aromatic amino acid can form two different kinds of complexes with Cu2+ which can be characterized by its ESR pattern. Additional information was obtained from optical d-d and CT transitions.

Amino Acids↗

PubMed1976

Self-association and binding sites of some psychotomimetic tryptamine derivatives and related compounds: nuclear magnetic resonance investigations.

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Binding Sites↗

PubMed1975

Stacking interactions of nucleobases: NMR-investigations. II. Self-association of purine-and pyrimidine-derivatives.

The self-association of various purine- and pyrimidine-derivatives in D2O has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model. Among the nucleobases investigated, the adenine-derivatives were found to be most suitable for quantitative determination. A comparison of methylated adenine-derivatives and the pH-dependence of the self-association lead to the conlcusion, that the stacking associates are stabilized by special van der Waals interactions based, essentially, on the polarizability of the pi-electron-system of the assciated molecules.

Adenine↗

PubMed1975

Association of sexual hormones with nucleobases in water: NMR-investigations.

The mixed association of testosterone-sulfate and estradiol-sulfate with several derivatives of nucleobases in D2O has been investigated by means of nuclear magnetic resonnance spectroscopy. From the differences among the chemical shifts of the hormone-protons it is concluded, that the nucleobases in the complexes are located above the center of the steroid molecule. The beta-side of the steroid which is characterized by the axial methyl-groups is directed towards the bases. The enthalpies of mixed association of the hormones with a certain nucleobase of the same order of magnitude as the enthalpy of selfassociation of this nucleobase (Schimmack et al., to be published). It is suggested that the complexes are stabilized by van-der-Waals forces. This stacking-like interaction is not specific for the male or female sex hormones: no qualitative or quantitative differences have been observed among the complexes of the two hormone-sulfates with the nucleobases.

Adenine↗

PubMed1975

Stacking interactions of nucleobases: NMR-investigations. I. Self association of N6, N9-dimethyladenine and N6-dimethyl-N9-ethyladenine.

The selfassociation of N6,N9-dimethyladenine and N6-dimethyl-N9-ethyladenine has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model with three NMR parameters (the monomer shift deltaM and two complex shifts delta2 and delta3). The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of deltaM and its temperature dependence. Calculations with delta3 = 2 - delta2 and deltaM taken independently of temperature result in an average entropy deltaS = - 17.9 +/- 1.8 e.u. for N6,N9-dimethyladenine and deltaS = - 16.7 +/- 1.7 e.u. for N6-dimethyl-N9-ethyladenine and in an average enthalpy deltaH = - 7.2 +/- 0.6 kcal - mol-1 for both substances investigated.

Adenine↗

PubMed1975

Charge-transfer interactions between metal ions and some uracil derivatives.

The interaction between Cu2+ and a few uracil derivatives has been investigated by means of electron spin resonance and optical absorption studies. It could be shown that a charge transfer interaction occurs. Its strength depends upon the electron attracting or releasing properties of the substitutents of the nucleobase.

Copper↗

PubMed1974