Binding of an acetic acid ligand to adenosine: a low-temperature NMR study |
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Authors: | Basílio Janke Eline M Limbach Hans-Heinrich Weisz Klaus |
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Affiliation: | Institut für Chemie, Freie Universit?t Berlin, Takustrasse 3, D-14195 Berlin, Germany. |
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Abstract: | Binding of an acetic acid (HAc) ligand to adenosine (A) was studied by (1)H NMR spectroscopic techniques. Using a low-melting deuterated Freon mixture as solvent, liquid-state measurements could be performed in the slow exchange regime and allowed a detailed characterization of the formed associates. Thus, at 128 K, trimolecular complexes A.HAc(2) and A(2).HAc with both Watson-Crick and Hoogsteen sites of the central adenine base occupied coexist in various amounts depending on the adenosine:acetic acid molar ratio. Whereas the carboxylic acid OH proton is located closer to the acid for all hydrogen bonds formed, a more deshielded proton at the Watson-Crick site is evidence for a stronger hydrogen bond as compared to the Hoogsteen interaction. For the binding of acetic acid to an adenosine-thymidine base pair in either a Watson-Crick or a Hoogsteen configuration, hydrogen bonds to the available adenine binding site are strengthened as compared to the corresponding hydrogen bonds in the A.HAc(2) complex. |
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