There are no net charges in (bio)colloid world. All of them result from the dissociation of chargeable groups, as in e.g., proteins from dissociable amino acid moieties. How do charging equilibria, aka charge regulation, then affect electrostatic interactions? This is a fundamental problem in biophysics, important for our understanding of interactions between the proteins and proteinaceous aggregates such as viral capsids, but also in the general colloid context, often built on the fictional foundation of fixed charges. Recent advances in the theoretical formulation and analysis of charge regulated systems lead to some far reaching conclusions about electrostatic interactions in colloidal systems, conclusions that often differ fundamentally from the accepted wisdom. I will present examples of both novel behavior and of new understanding of known behavior specifically connected with the response of the charging equilibrium on (bio)colloidal surfaces to the local bathing solution conditions.

Prof. Podgornik started his career in Slovenia as a theoretical physicist working on molecular interactions and the physics of colloids. In the mid-80s, he joined NIH, moved into biophysics to study the phase diagram of DNA in aqueous solutions, a hot topic at the time. He discovered the line-hexatic phase of DNA, which is relevant for the organization of viral capsids and has become since an important topic of physical virology. At about the same time Prof. Podgornik also started working on the problem of electrostatic interactions in Coulomb fluids. He formulated a functional integral approach to the classical partition function. This approach later led to formulations of the strong coupling theory of highly-charged Coulomb systems. For the past ten years, Prof. Podgornik worked on interactions between materials with anisotropic dielectric response. This led to a series of remarkable results. This work, coupled to very detailed ab initio calculations of optical spectra, produced detailed predictions about van der Waals torques, which were experimentally confirmed this year. Prof. Podgornik has published more than 250 papers in international journals, totaling more than 6000 citations for an h-index of 43 (Clarivate Analytics). In 1999, he received the highly prestigious Slovenian Zois award. He is also a recipient of the important Sackler Scholar Award from the Sackler Institute of Advanced Studies in Tel Aviv. He is now a professor at the University of the Chinese Academy of Sciences in Beijing.