Modulation of the interactions at the biointerface: Specific buffer effects

This thesis aims to investigate specific buffer effects on the physico-chemical properties of biomolecules and consequently their interaction with other biomolecules or with surfaces generating a biointerface. In biochemical systems, the pH of the bulk solution is usually regulated by a buffer composed of a weak electrolyte and its conjugate species. The same bulk pH can be obtained with different buffer species provided that the pKa of the weak electrolyte is close to the pH (= pKa ± 1) of interest to the biochemical experiment. It is usually assumed that different buffers support the same interfacial interactions when providing the same bulk pH. However, this assumption is too simplistic and may lead to unreproducible results if different buffer species, even at the same pH, are used. Here, to highlight the impact of buffer specificity, biomolecules and biointerfaces have been chosen as model systems having relevant interest in biotechnology and biomedical applications. Through a combination of experimental techniques, the effect of buffers on i) protein adsorption on nanoparticles, ii) the interaction between DNA and supported lipid bilayer, iii) the thermal stability of DNA and iv) the interaction of drugs with DNA are investigated in this thesis. It is found that buffers affect specifically and significantly the interactions occurring at biointerfaces even at the low buffer concentrations (10 - 50 mM) usually used in these kinds of studies. Even at fixed ionic strength, buffer specificity plays a relevant role which is not solely related to the charge of buffer ions and cannot be explained with classic electrostatic theories. Furthermore, the specific buffer effect is observed in addition to the specific ion effect coming from the dissociation of strong electrolytes, commonly used in conventional "Hofmeister series" studies.