Recognition at the Electrochemical Interface

The cyt. c redox can be promoted also by the SAMs of 2-amino-6-purinethiol and 6-amino-8-purinethiol. The cyt c redox on the 6-amino-8-purinethiol SAM is largely suppressed by the addition of thymidine, a derivative of thiamine, into the solution, while it is not suppressed on the 2-amino-6-purinethiol SAM [101, 

IR spectroscopy is one of the useful methods to study the hydrogen-bonded pairing between the bases. The measurements are generally carried out in aptotic solvents and the hydrogen-bonded pairing is discussed from the shift of v(NH) and v(C=0). Unfortunately, this approach cannot be used for the studies at the solid/water interface, because both adenine moiety of the SAM and thymidine are hydrated in water and the distinction between hydrogen bonds between the complementary base pair and those between the bases and water is practically impossible from the v(NH) and v(C=0) modes only. The interaction between the surface-confined 6-amino-8-purinethiol and thymidine was discussed from the potential dependence of the band intensities of the v(OH) mode of water and some modes of adenine moiety in this study. 

In the absence of thymidine in the solution (Fig. 8.18a), the 1700- and 1680-cm bands are assigned to the 5 (N H2) modes of the protonated and unprotonated adenine moieties (at Nl), respectively. The decrease and increase in the intensities of the 1700 and 1680 cm bands, respectively, on the positive potential scan indicate the shift of the acid-base equihbrium towards the unprotonated form. The pKa value for the adenine moiety at open circuit potential was evaluated to be 6 from the SEIRA spectra, which is much larger than those for adenine 

From these observations, it was concluded that an A-T type hydrogen bond pair is formed between the surface-confined adenine moiety and thymidine in 

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