Charged Species in Bulk and at Interfaces: Mobility and Motility of Macromolecular Systems
There is a multitude of experiments and simulations, using very different methods to study a large variety of phenomena (from the polarization of single macromolecules, field-induced self-assembly, biological processes, to filtration processes).
A number of new experiments have been carried out in the last few years on the self-assembly of charged species of superstructures of biologically friendly amphiphilic proteins, electrostatically-induced attractive patchy protein-protein aggregates [1,2], charged-receptors and ion channeling of sodium ions and physiological membrane voltages for signal transduction , as well as nerve agents immobilized biocatalysts in cellulose fibers . Optically-driven micro-rods [5, 6], and hydrogel-based circuits and biomimetic devices are used to probe ion transport [7-8]. Not only the mobility of the particles, but also their motility (as a short-ranged functionality), play an important role in cells and in biological interfaces. For the effective functioning of bio-interfaces, proton migration along membranes is of vital relevance, such as in cellular energy homeostasis and various proton-coupled transport processes . The visualization of protein interactions of macromolecules with a heterogeneous charge distribution is used to predict the electric polarizability [10-11]. Molten salts and ionic liquids are found to exhibit ion-pairing in external electric fields [12-14], while the phase behavior of lactoferritin is affected by hydrophobic interactions . Super-resolution human brain tractography , magneto-encephalography signal sensing of brain activities , and magneto-rheological dampers [18, 19] have been of recent interest.
Simulations and Theory:
In this workshop, simulations and theoretical concepts will be developed for the electric-double layer of antagonic salts, ionization at a solid-water interface, and charge-regulations in electric-fields [20, 21]. Drug penetration relating to the diffusivity and diffusive-convective transitions during non-equilibrium charging of an electric double-layer are studied in Refs. [22, 23]. Charge effects also play an important role in micro-filtration , and counterion-induced osmotic swelling of ionic microgels/microcapsules . A numerical sampling method is developed to solve problems related to the standard Poisson–Boltzmann approach . Proton migration along the membrane and ion permeation though membrane channels have been studied [9, 27]. The behavior of synthetic charged colloids in bulk and near an oil-water interfaces  and inverse patchy systems of heterogeneously charged particles  are shown to exhibit layer formation. Simulations and theory have been performed in case of anisotropic macromolecules, where considerable ion-condensation occurs which plays role for the electric polarizability of DNA fragments as well as their structure [30-32]. The electric-field induced dissociation/association of condensed ions of highly charged DNA viruses, leading to dynamical states , the formation of stable aggregates of polymorphic amyloid fibrils in Alzheimer’s decease , the combined hydrophilic and hydrophobic interactions, ion-hydration, as well as the structural changes of ion channels  have been of recent interest. Relevant for neuro-degenerative diseases are molecular dynamics simulations of trans membrane ion channels, anion selectivity, and ion permeation along different possible pathways . Mobility of nanoparticles in bijel formation and dynamic assembly of magnetic colloidal vortices and 2d patterns in shear-flow [37, 38] are to be newly included.
One of the objectives of this workshop is to bring together scientists from the various disciplines where charge interactions play a major role, but who have been acting, so far, independently.. The various ideas, concepts, and methods that have been used in these different fields are planned to be presented and discussed during this meeting. The exchange of ideas and expertise will thus lead to cross-fertilization among the communities and will boost the physics-based understanding that is necessary for the future development of smart soft-materials and to quantify biological processes.
Charge interactions play a central role in many different phenomena and processes: they are omnipresent in daily life and are of high relevance in a wide range of scientific research areas and technological processes. Thus there are scientific communities where charge interactions play a key role. However, these communities are often working independently, like those concerned with fundamental theoretical and simulation problems in macromolecular systems, electrostatics in various biological processes, and the assembly and transport in complex synthetic soft-matter functional materials, to name a few. One of the motivations of this workshop is to bring scientists from these different communities together and to achieve an efficient and beneficial cross-fertilization: for instance, analytical approaches and simulation algorithms that are specific for the specialized problems at hand in the different disciplines could very well be highly valuable to make progress in another discipline. In addition, our motivation to organize this workshop is to review the progress made within these separate disciplines.
As will be discussed in the section “Objectives”, three different emerging overarching themes have been distilled from the previous workshop:
• Fundamental theoretical and simulation problems in macromolecular electrostatics.
• The role of electrostatics in biological processes/systems.
• Self assembly and transport in complex synthetic charged macromolecules, used to create soft-matter functional materials.
The present meeting focuses on these currently developing themes, which involves the participation and cooperation of simulators, analytical theoreticians, and experimentalists. This workshop thus creates an interdisciplinary approach towards various types of charged systems, aiming at a long-term continuing exchange of ideas. With this meeting we thus aim to overcome the major drawbacks induced by the current separation between the different disciplines and to create a synergy between them. During this workshop, we aim to define the common features in an effort to enable cross-fertilization between the various scientific disciplines.
In view of the three identified overarching themes defined during the previous workshop, speakers were invited to address the following topics:
• Field-induced ionic polarizability and charge-condensation
• Charge interaction of bio-macromolecules (like proteins and DNA)
• Atomistic simulation of ion-channels
• Field-driven ion-diffusivity and ion-penetration of membranes
• Functionalization of synthetic, charged particles
• Filtration of charge-stabilized particles
• Hydrogel-ionic devices and soft-matter biomimetic actuators
• Charge transport in ion channels and proton diffusion
• Coarse-grained dynamics of assemblies of charged-particle aggregates
• Protein structure determination with Cryo-EM
• Magneto-encephalography (MEG) signal sensing of the brain activities
• Nanobio-photonics: bio-sensing displays and interfacial panels
• Tunable magneto-rheological vehicle dampers.
Gerhard Kahl (Institut für Theoretische Physik, TU Wien) - Organiser
Jan Dhont (Forschungszentrum Juelich) - Organiser
Kyongok Kang (Forschungszentrum Juelich) - Organiser