Electrostatic interactions between positively charged porphyrins and nucleotides or amides: buffer-dependent dramatic changes of binding affinities and modes

The association strength of positively charged porphyrins with anionic species can be orders of magnitude higher than reported in the literature, depending on the chosen buffer; the buffer also determines the dominating interaction mechanism, leading to stronger stacking contributions at higher salt concentrations; even electroneutral amides show a hitherto not recognized interaction between the negatively charged carbonyl oxygen and the positively charged pi-surface of the porphyrin system.