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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1446-1452 
    ISSN: 0947-6539
    Keywords: hydrogen bonds ; LFER ; molecular recognition ; NMR spectroscopy ; nucleobases ; thermodynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Association energies ΔGt in chloroform, in part also in carbon tetrachloride, were determined by NMR titrations of suitably substituted nucleosides and several synthetic analogues. Based on these and on many literature data, two simple free energy increments were derived describing the ΔGt values of 58 complexes within 1.8 kJ mol-1. With chloroform as solvent the increment for the primary interaction between donor and acceptor is 7.9 kJ mol-1, for the secondary one 2.9 kJ mol-1, irrespective of whether the latter is attractive or repulsive. Addition of only 1% methanol to CCl4 led to a decrease in association constants by a factor of 25. Calorimetric titrations of G-C nucleoside derivatives in CCl4 showed substantial contributions from G dimers, in line with NMR titrations, and surprisingly small decreases in entropy. Preliminary NOE measurements allowed us to single out some of the possible association modes; they are also in line with expected self- and triple-association modes of the nucleobases. These modes are generally in accord with nucleobase associations predicted by MM calculations in the literature, which in turn agree with predictions based solely on the increments derived in the present work.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0952-3499
    Keywords: supramolecular complexes ; enzyme analogues ; hydrogen bonds ; salt bridges ; catalysis ; linear free energy relation ; artificial nucleases ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Strategies and results for the extraction of biologically important non-covalent binding increments from studies of synthetic host-guest complexes are described with selected examples. Systematic analyses of association constants and the corresponding complex conformations in solution allows us to assign specific values to different pairwise interactions, including salt bridges, amide-type hydrogen bonds, van der Waals effects, and metal ion interactions. A comparison of association constants between selected flexible and rigid ion pairs shows few differences, indicating that different entropy contributions either are small, or cancel with corresponding enthalpy changes, at least in weakly bound complexes. The supramolecular design of enzyme-analogous catalysts is illustrated with complexes containing, e.g. strongly bound yet still active Ln3+ ions, e.g. in an azacrown ether, and groups which support association with nucleic acids and can serve as nucleophiles. The experimentally observed hydrolysis rate enhancements with such artificial nucleases amount to 106 and more, both with phenyl phosphates and with ds-DNA.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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