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  • 1
    Electronic Resource
    Electronic Resource
    Stacking Interactions of nucleobases: NMR-Investigations I. Selfassociation of N6,N9-Dimethyladenine and N6-Dimethyl-N9-Ethyladenine (1975)
    Springer
    European biophysics journal 1 (1975), S. 113-120 
    Details
    ISSN: 1432-1017
    Keywords: Stacking ; selfassociation ; NMR ; Isodesmic Model ; Enthalpy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract 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 δM and two complex shifts δ 2 and δ 3). The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of δ M and its temperature dependence. Calculations with δ 3=2·δ 2 and δ M taken independently of temperature result in an average entropy δ S =−17.9±1.8 e.u. for N6,N9-dimethyladenine and δ S =−16.7±1.7 e.u. for N6-dimethyl-N9-ethyladenine and in an average enthalpy δH=−7.2±0.6 kcal· mol−1 for both substances investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539773
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  • 2
    Electronic Resource
    Electronic Resource
    Stacking interactions of nucleobases: NMR-Investigations II. Selfassociation of purine- and pyrimidine-derivatives (1975)
    Springer
    European biophysics journal 1 (1975), S. 311-318 
    Details
    ISSN: 1432-1017
    Keywords: Stacking ; Selfassociation ; NMR ; Nucleobases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The selfassociation 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 selfassociation lead to the conclusion, that the stacking associates are stabilized by special van der Waals interactions based, essentially, on the polarizability of the π-electron-system of the associated molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537644
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of ascorbic acid and its biological function (1983)
    Springer
    European biophysics journal 10 (1983), S. 197-204 
    Details
    ISSN: 1432-1017
    Keywords: Ascorbic acid ; ESR ; Na+ ; K+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract ESR investigations on lyophilized systems have shown that the signal at g = 2.005 can be explained by an interaction between Na+ or K+ and the anionic ascorbyl radical. The unpaired electron is probably localized near the C(4) region and is produced by a cleavage of an H atom belonging to a water molecule bound tightly to C(4). Experiments on aqueous samples revealed that ascorbic acid in its radical configuration and in its highest concentration exists only at physiological pH and temperature. An additional splitting is obtained by the ring formation between C(3) and C(6)-OH. The coupling constants of the triplets produced by the CH2-6 protons differ between ascorbic acid and isoascorbic acid. Thus, the ESR technique can be applied for an easy distinction between these two epimers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00535548
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  • 4
    Electronic Resource
    Electronic Resource
    Charge-transfer interactions between metal ions and some uracil derivatives (1975)
    Springer
    European biophysics journal 1 (1975), S. 147-152 
    Details
    ISSN: 1432-1017
    Keywords: CT-Interactions ; Metal Ions ; Uracil Derivatives ; ESR ; Optical Absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract 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 substituents of the nucleobase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539776
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  • 5
    Electronic Resource
    Electronic Resource
    Redox properties of paramagnetic “Platinum Uracil Blues” (1980)
    Springer
    European biophysics journal 6 (1980), S. 56-56 
    Details
    ISSN: 1432-1017
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647529
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  • 6
    Electronic Resource
    Electronic Resource
    Stacking interaction of nucleobases: NMR investigations (1978)
    Springer
    European biophysics journal 4 (1978), S. 327-335 
    Details
    ISSN: 1432-1017
    Keywords: Stacking ; Solvent-mixtures ; 6-methylpurine ; Self-association
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The stacking interaction between nucleic acid bases has been investigated by the determination of the self-association of 6-methylpurine in various mixtures of water and nonaqueous solvents in order to elucidate the solvent effect. The parameters of stacking association as well as of local solvent-solute interactions have been measured by means of NMR technique. The influences of local hydration and of solvent-solvent interactions on the stacking ability are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537615
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  • 7
    Electronic Resource
    Electronic Resource
    Investigations on the viscosity of fixed erythrocytes (1981)
    Springer
    European biophysics journal 7 (1981), S. 309-309 
    Details
    ISSN: 1432-1017
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02425440
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  • 8
    Electronic Resource
    Electronic Resource
    Association of sexual hormones with nucleobases in water: NMR-Investigations (1975)
    Springer
    European biophysics journal 1 (1975), S. 319-328 
    Details
    ISSN: 1432-1017
    Keywords: Sexual Hormones ; Nucleobases ; NMR ; Stacking ; Enthalpies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The mixed association of testosterone-sulfate and estradiol-sulfate with several derivatives of nucleobases in D2O has been investigated by means of nuclear magnetic resonance 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 Β-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 are 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537645
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  • 9
    Electronic Resource
    Electronic Resource
    structure of ascorbic acid and its biological function (1983)
    Springer
    European biophysics journal 10 (1983), S. 205-210 
    Details
    ISSN: 1432-1017
    Keywords: Ascorbic acid ; Na+/K+-transport ; ESR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Ascorbic acid/isoascorbic acid are present as radicals at physiological pH with the unpaired electron located in the C(4) region. Since a distinction can be made between both types of radicals, the electron spin resonance technique can be used for discrimination between the epimers of vitamin C. The radical has a cyclic side-chain structure which is formed by the hydrogen bond C(3)-O− ... HO-C(6) (≈ 2.7 kJ) and which engulfs Na+ or K+ in the case of the ascorbyl or the isoascorbyl radical, respectively. The radicals Na-ASC and K-Iso-ASC are electroneutral. Red. glutathione affects both types of radicals by restoring the original electronic configuration at C(4) without changing the electroneutral bicyclic structure. In this way, the mobile carriers Na-ASC and K-Iso-ASC can transport Na+ and K+ across membranes. Its highest efficiency is around 37
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00535549
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  • 10
    Electronic Resource
    Electronic Resource
    The effect of some transition metal ions on the ascorbate radical observed in blood of patients with acute lymphatic leukemia (1981)
    Springer
    European biophysics journal 7 (1981), S. 264-264 
    Details
    ISSN: 1432-1017
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02425395
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