Thymidine proflavine • poly

Hydrogen Bonding The thymidine H-3 Watson-Crick proton can be readily detected in the proflavine poly(dA-dT) complex,... 

The dissociation of the proflavine poly(dA-dT) complex can be followed by monitoring the temperature dependent chemical shift or the line width as demonstrated by shift data on the thymidine CH3-5 resonance (Figure 18A) and width data on the adenosine H-8 resonance (Figure 18B). The proton resonances shift as average peaks during the dissociation of the complex, indicative of fast exchange ( dissociation 10 sec l at the transition midpoint) between the complex and its dissociated components on the NMR time scale. 

Figure 16. The temperature dependence of the thymidine H-3 resonance in poly(dA-dT) (O) and the proflavine poly(dA-dT) complex Nuc/D = 8(0) in /M NaCl, lOmM cacodylate, ImM EDTA, HtO at pH 6.53, and pH 7.1...

Nucleic Acid Base Resonances The chemical shifts of the nonexchangeable protons in poly(dA-dT), the Nuc/D = 24 complex and the Nuc/D = 8 complex in 1 M NaCl solution are plotted as a function of temperature in Figure 19. The nucleic acid nonexchangeable proton chemical shifts in the duplex state are either unperturbed (adenosine H-8, H-2, and thymidine CH3-5) or shift slightly upfield (thymidine H-6) on complex formation (Figure 19). By contrast, the thymidine H-3 exchangeable proton located in the center of the duplex resonates 0.35 ppm to higher field in the Nuc/D = 8 proflavine complex compared to its position in the... 

In the center of the duplex shifts upfield by 0.15 ppm (Table VI, Figure 25) and the thymidine CH3-5 which Is directed towards the major groove shifts upfield by 0.1 ppm (Figure 29). It should be noted that such an upfield shift of the thymidine CH3-5 group was not observed in the intercalation complexes of ethidium (11), proflavine (25), terpyridylplatinum II (11) and nitroaniline dication with poly(dA-dT). The results require that at least one thymidine CH3-5 group project onto the periphery of the anthra-cycline ring system at the intercalation site. 

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