Stabilization vs. destabilization of G-quadruplex superstructures: the role of the porphyrin derivative having spermine arms

The interaction of the porphyrin derivative H(2)TCPPSpm4, having spermine pendants in the four meso positions, with the G-quadruplex (GQ) structure formed by the DNA aptamer TGGGAG has been investigated by means of UV, electronic circular dichroism and PAGE studies. The results reported here demonstrate that the porphyrin derivative is capable of stabilizing or destabilizing the higher-ordered structures of parallel GQs, depending on the method used to reach their relative stoichiometry (titration vs. single addition). Noteworthily, when two equivalents of H(2)TCPPSpm4 were mixed directly with one equivalent of the (TGGGAG)(4) GQ to reach a 2 : 1 H(2)TCPPSpm4: GQ ratio T-1/2 higher than 80 degrees C was also observed confirming the presence of higher-ordered GQ structures.