Investigations on purine and pyrimidine bases stacking associations in aqueous solutions by the fluorescence quenching method: I. Autoassociation of 2-aminopurine |
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Authors: | Andrzej Bierzynski Hanna Kozlowska KL Wierzchowski |
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Institution: | Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Rakowiecka 36, 02-532 Warszawa, Poland |
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Abstract: | A general equation was derived, describing fluorescence quantum yield and lifetime of an autoassociating compound in liquid solutions. The autoassociation of 2-aminopurine in aqueous solution was examined within the range from 0 to 90°C. The compound seemed to associate cooperatively. The thermodynamic parameters of polymerization change with temperature, so that its free enthalpy ΔG = ?0.0797 T2 + 45.4 T ?7893. The dimerization enthalpy and entropy are approximately temperature-independent (ΔH2 = ?4.17 , ΔS2 = ?10.9 e.u.), although the function: ΔG2 = ?0.0308 T2 + 30.3 T - 7213 fits experimental points better. The observed dependences can be explained by the increasing role of the hydrophobic effect with temperature and size of the aggregates. The association rate constants were determined, and a two-step reaction mechanism was demonstrated. The first step is diffusion-controlled. The second is characterized by an activation energy of ~2 and an encounter distance of ~8.3 Å. |
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