Voltage and concentration gradients across membraneless interface generated next to hydrogels: relation to glycocalyx

Next to many hydrophilic surfaces, including those of biological cells and tissues, a layer of water that effectively excludes solutes and particles can be generated. This interfacial water is the subject of research aiming for practical applications such as removal of salts, pathogens or manipulation of biomolecules. Yet, the exact mechanism of its creation is still elusive, because its persistence and extension contradict hydrogen-bond dynamics and electric double layer predictions. The experimentally recorded negative voltage of this interfacial water remains to be properly explained. Even less is known about the nature of such water layers in biological systems. We present experimental evidence for ion and particle exclusion as a result of separation of ionic charges with distinct diffusion rates across a liquid junction at the gel/water interface and the subsequent repulsion of ions of a given sign by a like-charged gel surface. Gels represent features of biological interfaces (in terms of functional groups and porosity) and are subject to biologically relevant chemical triggers. Our results show that gels with –OSO3- and –COO- groups can effectively generate ion- and particle-depleted regions of water reaching over 100 μm and having negative voltage up to - 30 mV. Exclusion distance and electric potential depend on the liquid junction potential at the gel/water interface and on the concentration gradient at the depleted region/bulk interface, respectively. The voltage and extension of these ion- and particle-depleted water layers can be effectively modified by CO2 (respiratory gas) or KH2PO4 (cell metabolite). Possible implications pertain to biological unstirred water layers and a cell’s bioenergetics.Published in Soft Matter, 19, 7528–7540, 2023</p

Effect of Infrared Light on Protein Behavior in Contact with Solid Surface

Adsorption of proteins at a solid surface affects characteristics of the surface (e.g. its biocompatibility) and functionality of the immobilized biomacromolecules. The latter is defined by the type of binding sites, protein conformation and its structural flexibility that enable functional motions to occur. Protein motions are only possible at certain level of hydration. Furthermore, water molecules act as lubricant facilitating sliding along solid surface. In this work we explore the potential of a remote physical trigger –a non-ionizing infrared radiation (IR) to affect protein-surface interactions. We report on IR-induced changes of hydrophilicity of the protein coatings on silica nanoparticles, impact of IR on monitored in-situ dynamic adsorption of proteins on silica surface and effect of IR on conformational state of adsorbed proteins. Our results indicate that IR can protect proteins from surface denaturation depending on the presence of strongly hydrated amino acid residues. Preservation of native fold results in protein coatings of higher hydrophilicity. IR can also facilitate displacement of surface activespecies that became adsorbed to protein apolar compartments and couldotherwise promote denaturation. Apart from supporting native conformation, their removalincreases protein-water interfacial tension and therefore promotes aggregation (hydrophobic attraction) of the protein-coated nanoparticles. By its ability to affect protein conformational state and interfacial characteristics (such as effective protein-water affinity) IR radiation can therefore modulate protein interactions

Effect of Infrared Light on Protein Behavior in Contact with Solid Surface

Adsorption of proteins at a solid surface affects characteristics of the surface (e.g. its biocompatibility) and functionality of the immobilized biomacromolecules. The latter is defined by the type of binding sites, protein conformation and its structural flexibility that enable functional motions to occur. Protein motions are only possible at certain level of hydration. Furthermore, water molecules act as lubricant facilitating sliding along solid surface. In this work we explore the potential of a remote physical trigger –a non-ionizing infrared radiation (IR) to affect protein-surface interactions. We report on IR-induced changes of hydrophilicity of the protein coatings on silica nanoparticles, impact of IR on monitored in-situ dynamic adsorption of proteins on silica surface and effect of IR on conformational state of adsorbed proteins. Our results indicate that IR can protect proteins from surface denaturation depending on the presence of strongly hydrated amino acid residues. Preservation of native fold results in protein coatings of higher hydrophilicity. IR can also facilitate displacement of surface activespecies that became adsorbed to protein apolar compartments and couldotherwise promote denaturation. Apart from supporting native conformation, their removalincreases protein-water interfacial tension and therefore promotes aggregation (hydrophobic attraction) of the protein-coated nanoparticles. By its ability to affect protein conformational state and interfacial characteristics (such as effective protein-water affinity) IR radiation can therefore modulate protein interactions

Kinetics of crystal nucleation in ionic solutions: Electrostatics and hydration forces

The heat of precipitation, the mean crystal size and the broadness of crystal size distribution of barium sulfate precipitating in aqueous solutions of different background electrolytes (KCl, NaCl, LiCl, NaBr or NaF), was shown to vary at constant thermodynamic driving force (supersaturation) and constant ionic strength depending on the salt present in solution. The relative inversion in the effect of respective background ions on the characteristics of barite precipitate was observed between two studied supersaturation (O) and ionic strength (IS) conditions. The crystal size variance (ß2) increased in the presence of background electrolytes in the order LiCl &lt; NaCl &lt; KCl at O = 103.33 and IS = 0.03 M and KCl &lt; NaCl &lt; LiCl at O = 103.77 and IS = 0.09 M. At a given O and IS the respective size of barite crystals decreased with increasing ß2 in chloride salts of different cations and remained constant in sodium salts of different anions. We suggest that ionic salts affect the kinetics of barite nucleation and growth due to their influence on water of solvation and bulk solvent structure. This idea is consistent with the hypothesis that the kinetic barrier for barium sulfate nucleation depends on the frequency of water exchange around respective building units that can be modified by additives present in solution. In electrolyte solution the relative switchover between long range electrostatic interactions and short range hydration forces, which influence the dynamics of solvent exchange between an ion solvation shell and bulk fluid, results in the observed inversion in the effect of differently hydrated salts on nucleation rates and the resulting precipitate characteristics. © 2009 Elsevier Ltd. All rights reserved