1. Departament de Fisicoquímica, Facultat de Farmàcia, and Departament de Bioquímica i Biologia Molecular, Facultat de Química, Universitat de Barcelona, Avgda Diagonal s/n, 08028 Barcelona, Spain, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejökova 3, 182 23 Prague, Czech Republic, and Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 612 65 Brno, Czech Republic