Projects / Programmes
Solvation and ion specific effects in biological systems
| Code |
Science |
Field |
Subfield |
| 1.04.01 |
Natural sciences and mathematics |
Chemistry |
Phyisical chemistry |
| Code |
Science |
Field |
| P400 |
Natural sciences and mathematics |
Physical chemistry |
| Code |
Science |
Field |
| 1.04 |
Natural Sciences |
Chemical sciences |
Ionic hydration, hydrophobic effect, ion-specific effect, polyelectrolytes, proteins, aliphatic ionenes, molecular dynamics simulation
Researchers (27)
Organisations (3)
Abstract
Hydrated ions are a common component of nearly all biological systems. A key challenge relevant to these systems is how to handle the interaction depending on the chemical nature of ions in particular if hydrophobic groups are present. The ion–specific effects (ISE) occur in aqueous solutions of biopolyelectrolytes, in self–assembled amphiphilic structures and at charged interfaces. They are reflected in variations (Hofmeister series) of measurable properties with the nature of salt present in the system. We plan to obtain experimental data for well-defined systems, where we can vary the charge/hydrophobicity ratio of the molecules and composition of the solution. The data will than be analyzed by appropriate theories and generalized to more complex systems. The goal is to rationalize ISE in aqueous solutions and relate them to the solubility of proteins as reflected in ordering in the Hofmeister series. We hope also propose improvements of the force fields commonly used in simulations. We will attack the problem from different perspectives. (a) Experimental – we will measure electrical transport, solubility, heats of mixing, heat capacity, and structural properties, obtained via SANS, SAXS and DLS measurements. (b) Theoretical – we will continue developing integral equation theory for associated systems (associated mean spherical approximation, AMSA), which allows calculation of thermodynamic quantities with an explicit account of the solvent molecules. (c) Simulational – we will perform the explicit solvent molecular dynamics (MD) studies of the biologically interesting molecules and ions. (i) x,y–ionene salts are ideal molecules for studying the balance between hydrophobic and charge effects. We will continue experimental studies of these polyelectrolytes; we will examine the effect of the counterion variation from strong kosmotrope (F–) to chaotrope (I–). The properties such as heat capacity, heats of mixing, SANS and SAXS spectra, etc, will be examined. Our preliminary measurements show clear ion–specific effects. We will continue with explicit water MD simulations of ionenes and will utilize our own theoretical approach (AMSA) to calculate the properties we measure. (ii) We plan to study solution of model protein (lysozyme) in mixture with alkali halides in water. We will vary the salt in a mixture; from both ions being chaotropes or kosmotropes to chaotrope–kosmotrope combinations. We have already obtained important information about the salt and individual ion behaviour in relation with this model, additional info can be found in literature. We will assume that electrostatic potential is arising from “patches” of active groups on the protein surface. To obtain measurable properties AMSA, developed with coworkers in Lviv, will be applied. The osmotic coefficient will be calculated; this quantity is well correlated with the solubility of proteins and contains information about the ability of a particular salt to crystallize the protein. We have our own data of lysozyme solubility in ternary systems, which we plan to complement with measurements for other proteins. (iii) The process when two ions approach each other in water may be connected with a partial desolvation of one or both ions. The isothermal reversible work needed to transfer two ions from infinity to the some distance (PMF) is the quantity of principal interest. In MD studies, we plan to explore correlation between the measured osmotic pressure and calculated PMFs for various water and ion models in order to find the force fields providing consistent results. Another important goal is to separately evaluate the enthalpy and entropy contributions to PMF between the ions in water. The latter quantity is a fingerprint of the ISE. Knowledge obtained for well–defined systems can be than usefully applied to more complex molecules (and systems) and/or to critically evaluate (improve) the force fields commonly used in biophysical simulations.
Significance for science
Focusing on two different polyelectrolytes, one cationic and one anionic, we showed that besides the nature of the group on the polyion its immediate environment may play an important role. If the group is embedded in the hydrophobic environment (an example of 12,12-ionenes) the interaction between this group and the salt ions in water may be substantially modified. One consequence is that the sequence of ions in the Hofmeister series describing certain property (the latter not fully explained though its discovery dates to 19. century), reverses its ordering. This fact is of importance for understanding the protein precipitation under influence of of addition of salts. The project which we report on here is of the fundamental nature: on the well defined polyelectrolyte systems we studied an interplay of ionic and hydrophobic effects. The articles were published in important Journals from this field of Science.
Significance for the country
Physical chemistry group of FCCT, University of Ljubljana, is the only group in Slovenia whose research is mainly devoted to aqueous solutions of electrolytes, polyelectrolytes, biopolymers (DNA, proteins), and similar systems. Because the solutions in water are ecologically acceptable, there was some interest for our work expressed also from the side of industry; Vodna kemija za barvno industrijo : HELIOS, Tovarna barv, lakov in umetnih smol Količevo, d.o.o., Domžale, 24. 4. 2013]. [2013]. [COBISS.SI-ID 36864517]. The reports of our studies were published in important Journals from the field of physical chemistry and the work reported in form of lectures in several international conferences and foreign Universities.
Most important scientific results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
