  The phenomenon of hysteresis is commonly observed in many UV thermal
experiments involving unmodified or modified nucleic acids. In presence of
hysteresis, the thermal curves are irreversible and demand a significant effort
to produce the reaction-specific kinetic and thermodynamic parameters. In this
article, we describe a unified statistical procedure to analyze such thermal
curves. Our method applies to experiments with intramolecular as well as
intermolecular reactions. More specifically, the proposed method allows one to
handle the thermal curves for the formation of duplexes, triplexes, and various
quadruplexes in exactly the same way. The proposed method uses a local
polynomial regression for finding the smoothed thermal curves and calculating
their slopes. This method is more flexible and easy to implement than the least
squares polynomial smoothing which is currently almost universally used for
such purposes. Full analyses of the curves including computation of kinetic and
thermodynamic parameters can be done using freely available statistical
software. In the end, we illustrate our method by analyzing irreversible curves
encountered in the formations of a G-quadruplex and an LNA-modified parallel
duplex.
