i-Motif DNA structures may be formed in regions rich in 2'-deoxyCytidine. Especially at acidic pH, these structures could be described as C-Quadruplexes with two parallel stranded sequences also held together in an antiparallel orientation by cytosine-cytosine base pairs. Since these structures are stable at acidic pH, they can act as nanoswitches by change in pH. As they were not considered to be stable at physiological pH, they were not initially considered to be relevant to biological systems. However, the stability of the cytosine-cytosine base pair is enhanced by intercallating ligands and so a variety of i-Motif structures are now considered to be biologically significant.