DNA structure, called the i-motif can be formed from sequences containing stretches of cytosine (C) residues. In this structure protonated C forms a noncanonical base pair with anunprotonated C. A pH titration of the formation of the i-motiffolded structure shows a sharp transition around pH 6.5. Draw the C-C base pairs found in i- motif. Explain the structural change at pH 6.5.