TF and neoplasm: As for the latter observation, the protonation of cytosines in N3 positions of the TF-PNA1K, clearly favoured under the acid conditions mimicking the tumour microenvironment, increases Hoogsteen base-pairing with bcl2midG4-ds [27] thus being responsible for the 12 °C enhancement of the melting temperature value corresponding to the dissociation of the PNA strand from the triplex complex.