Figure 6.

Acceptor numbers for A–T base pairs in DNA duplexes. A plot of the solvent’s Gutmann H-bond acceptor number (AN) vs the observed TC2=O stretching. Values for ¹³C2-labeled duplexes, the Hoogsteen crystal, and the isolated matrix N1-methylthymine were calculated based on the regression line derived from the observed values for the T base in water, dimethylformamide (DMF), and d₆-dimethyl sulfoxide (d₆-DMSO). The isolated matrix value is from N1-methylthymine in the study by Person and co-workers.¹¹²