9-Ethyladenine , association constants

Shea et al. have prepared an imprinted polymer (a matrix of polymethacrylate) using 9-ethyladenine (9-EA) as a template (Figure 62) [85], They have shown that the average association constant for this substrate is of the order of... 

The association constants K for hydrogen-bonded dimer formation in chloroform solution by 9-ethyladenine and by 1-cyclohexyluracil, as well as for the formation of the 1 1 hydrogen-bonded complex of the two bases, were measured by infrared methods at 4 to 58°C. At 25°C, for the mixed dimer was 30 times larger than Kaa for the 9-ethyladenine dimer and 15 times larger than for the 1-cyclo-hexyluracil dimer. From the temperature dependence of association constants, A// for association was calculated to be — 4.3 0.4kcal/mole of dimer for cyclo-hexyluracil, —4.0 0.8kcal for ethyladenine, and —6.2 + 0.6kcal for the mixed dimer. The entropy differences AS° were —11.0 + 1, —11.4 2, and —11.8 1.2 e.u., respectively. The method used for the calculations was based on work by Lord and Porro (1960). 

A plot of this chemical shift versus the reciprocal of the concentration (Figure 2.10) allowed us to calculate the interassociation equilibrium constant (K = 534 M ). We transformed the value of from the model compound into Ky by dividing by the molar volume of the VBA repeat unit (0.1125 L moH at 25°C) [24], providing a value for the interassociation equilibrium constant K, of 4750. Likewise, we determined that the self-association equilibrium constant (Kg) of adenine was 32, after dividing the value of Kj, of 3 M for the model compoimd 2-ethyladenine by the molar volume of the VBA repeat unit [70]. 

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