In recent experiments, the "local pH" near polyelectrolyte chains was determined from the shift in the effective acidity constant of fluorescent pH indicators attached to the macromolecules. This indirect determination raises the question if the analyzed quantity was indeed the "local pH" and what this term actually means. In this study, we combined experiments and simulations to demonstrate that the shift in ionization constant is slightly lower than the difference between the pH and the "local pH". This offset is caused by correlations between fluctuations in chain conformation, small-ion distribution, and fluorophore ionization.

Department of Physical and Macromolecular Chemistry Charles University Hlavova 8 128 43 Prague 2 Czech Republic

Institute of Macromolecular Chemistry AS CR Heyrovský square 2 162 06 Prague 6 Czech Republic

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Charge Regulation Triggers Condensation of Short Oligopeptides to Polyelectrolytes