Artificial DNA Directed toward Synthetic Metallofoldamers - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 314

9.4.2 Analytical Characterization in Solution
Several analytical methods are routinely applied for the characterization of metal base
pair containing DNA double-strands, while the application of other methods, such as
NMR and EPR, have only been demonstrated in a few cases so far.
One of the most useful analytical techniques in the characterization of DNA modifica-
tions is the UV-based melting curve analysis (also termed a thermal de- and renaturation
study) [36]. The aim of this method is the determination of the so-called melting point
( T M ) of the DNA double strand under investigation, which is defined as the temperature
at the transition point in the melting curve (absorption against temperature). It is a mea-
sure for the characteristic temperature at which a specific double strand under given con-
ditions (concentration, pH, ionic strength) dehybridizes to yield a solution containing
the corresponding single strands (Figure 9.8a). The basis for obtaining a temperature-
dependent change in UV absorption (usually measured at the absorption maximum of
DNA at 260 nm) can be found in the different molar absorptivity of double-stranded
DNA compared to the absorbance sum of the corresponding two single strands. Whereas
double-stranded DNA has a relatively low molar absorptivity due to quenching effects in
the duplex structure, the corresponding single strands have a higher extinction (an
effect termed “hyperchromicity”) which can be monitored in order to follow the thermal
denaturation of double to single strands and vice versa. Different DNA sequences of the
Figure 9.8 (a) Typical DNA melting curves for (b) metal-containing ligand-modified DNA; (c)
the same strand in the absence of metal ions and (d) the same sequence containing a G-C base
pair instead of the ligands.