Here we develop a theoretical model for reversible protein protein aggregation in salt solutions. We treat proteins as hard spheres having square-well-energy binding sites, using Wertheim's thermodynamic perturbation theory. The model gives accurate liquid-liquid coexistence curves for lysozyme and γIIIa-crystallin solutions in respective buffers. It provides good fits to the cloud-point curves of lysozyme in buffer salt mixtures as a function of the type and concentration of salt. It than predicts full coexistence curves, and second virial coefficients under such conditions.
COBISS.SI-ID: 1536295363
The double helix is not the only physiologically important form of deoxyribonucleic acid (DNA). The guanine-rich DNA, for example, is able to form G-quadruplex structures, which can play an important role in regulating normal and disease-related (cancer, Alzheimer's disease, diabetes, genetic diseases, ...) cellular processes. Understanding them is closely linked to the questions as how quadruplexes fold and convert from one form to another and why this happens in a specific way. To answer these questions, the authors built a conceptual framework based on thermodynamic analysis of spectroscopic and calorimetric data which leads to the description of the conformational space of a phase (phase diagram) of guanine-rich DNA sequences derived from the human telomere sequence. This framework explains the forces driving the conformational changes of DNA in solution at different temperatures and concentrations of solutes and shows that the DNA conformational phase space can be similarly complex than that of RNA and proteins.
COBISS.SI-ID: 1537063107
Article describes driving forces of binding of ligands to the human telomeric DNA sequence folded into G-quadruplex structures in relation with structural characteristics of ligands, DNA and DNA-ligand complexes, and shows how to explore the predictive power of thermodynamics for better understanding of DNA recognition of G-quadruplexes by aromatic ligands.
COBISS.SI-ID: 1536627907
The interaction between hyaluronate anion (HA) and the lysine derived biocompatible cationic surfactant (MKM) was investigated in aqueous solutions by potentiometry and fluorescence spectroscopy. The critical micelle concentration in pure surfactant solutions and the critical association concentration in the presence of HA were determined in dependence on NaCl concentration. The equilibrium between the protonated and deprotonated forms of MKM is proposed to explain anomalous binding isotherms. The explanation is supported by the theoretical model calculations of the micellar equilibrium and the competitive binding of the two forms to the surface of the electrode membrane. The paper was chosen for graphical presentation on the Langmuir cover (volume 31, issue 48, December 8, 2015).
COBISS.SI-ID: 19020310
During this research it was found that alkali-metal counterions (Li+, Na+, Cs+) are bound to the poly(thiophen-3-ylacetate) non-specifically i.e. they are bound by the attractive Coulombic forces. None of these counterions shows preferential binding towards other alkali-metal counterions nor exhibit specific influence on the conformation of the polyion. This finding confirmed our previous assumptions that the considerable (usually even the predominant one) portion of heat effects observed during mixing polyelectrolyte and simple salt solutions stems from changed extent of hydration of counterions. The latter one is the consequence of the changed environment of the counterions. Contrary to the case of alkali-metal counterions, fraction of bound counterions strongly depends on the kind of tetraalkylammonium counterion and increases with the length of alkyl chain. The deviation from the value predicted by electrostatic theories is the larger the longer the alkyl chains are. Most probably, lengthening of alkyl groups contributes to additional (non-Coulombic) attractive forces between tetraalkylammonium counterions and polyanion, what increases charge neutralization of the polyanion and provokes more coiled conformation of polyanions. The outcomes of this research, which is one of the rare systematic studies of this kind, enable more profound understanding of interactions between the given kind of counterions and polyions as well as of their consequences. New knowledge about hydration in polyelectrolyte systems will help us in further studies of solutions.
COBISS.SI-ID: 1537121475