  In this review we focus on the idea of establishing connections between the
mechanical properties of DNAligand complexes and the physical chemistry of
DNA-ligand interactions. This type of connection is interesting because it
opens the possibility of performing a robust characterization of such
interactions by using only one experimental technique: single molecule
stretching. Furthermore, it also opens new possibilities in comparing results
obtained by very different approaches, in special when comparing single
molecule techniques to ensemble-averaging techniques. We start the manuscript
reviewing important concepts of the DNA mechanics, from the basic mechanical
properties to the Worm-Like Chain model. Next we review the basic concepts of
the physical chemistry of DNA-ligand interactions, revisiting the most
important models used to analyze the binding data and discussing their binding
isotherms. Then, we discuss the basic features of the single molecule
techniques most used to stretch the DNA-ligand complexes and to obtain force x
extension data, from which the mechanical properties of the complexes can be
determined. We also discuss the characteristics of the main types of
interactions that can occur between DNA and ligands, from covalent binding to
simple electrostatic driven interactions. Finally, we present a historical
survey on the attempts to connect mechanics to physical chemistry for
DNA-ligand systems, emphasizing a recently developed fitting approach useful to
connect the persistence length of the DNA-ligand complexes to the
physicochemical properties of the interaction. Such approach in principle can
be used for any type of ligand, from drugs to proteins, even if multiple
binding modes are present.
