Specific effects of the sodium salts of m and phydroxybenzoates (mHB and pHB) on the aggregation process of dodecyltrimethylammonium chloride (DTAC) have been investigated by isothermal titration calorimetry, electrical conductivity measurements and 1H NMR spectroscopy. Results were compared with already reported data for the sodium salt of ohydroxybenzoate (oHB). For pHB, it has been found that the spherical DTAC micelles are formed at all pHB concentrations. On the other side, the situation is more complex for oHB, where two distinct states of aggregation can be involved: at high salt concentration, rodlike micelles of DTAC are formed, whereas at lower concentration spherical aggregates are predominant. The transition from the cylinder to the sphere increases the mobility of the surfactant because the core of the rodlike micelles is more closely packed due to the expulsion of water from the interior of the aggregate. mHB exhibits an intermediate behavior between these two extreme situations. Thus, the position of hydrophilic substituents (hydroxyl group) on the aromatic ring influences the insertion of the hydroxybenzoate anion in the micellar aggregate of DTAC crucially.
COBISS.SI-ID: 36610565
Interactions of isotactic, syndiotactic, and atactic poly(methacrylic acid) with trivalent lanthanide ions was studied by luminescence, NMR and binding isotherms measurements. Fluorescence data suggest carboxylate binds in a bidentate fashion. This is accompanied by the loss of 5-6 hydration water molecules. The behavior depends on pH and polyelectrolyte stereoregularity. Binding of surfactant to poly(methacrylate) in the presence of lanthanides is noncooperative.
COBISS.SI-ID: 1656879
Monte Carlo simulations and integral equation theory were used to study the thermodynamics and structure of particles interacting through the smooth version of Stell Hemmer interaction. We showed that a potential with two characteristic distances is sufficient for the system to exhibit water-like behavior and anomalies, including the famous density maximum. We also showed that some versions of the integral equation theory completely fail to predict structure of such system, while others only predict it qualitatively.
COBISS.SI-ID: 1647663
Many separation processes are related to the behavior of ions close to charged surfaces. In this work, we examine uranyl ions, which can be considered as rod-like molecular ions with a spatially distributed charge, embedded in a system of like charged planar surfaces. The model system is based on an approximate mean-field theory and canonical Monte Carlo computer simulations. Results show that close to the charged surface the uranyl ions are oriented parallel to the surface, whereas at distances greater than half of the ion length, they are randomly oriented. For large surface charge densities, the force between like charged surfaces becomes attractive, as a result of charge correlations. The theoretical results are in good agreement with the Monte Carlo simulation data.
COBISS.SI-ID: 4593003
Intrinsically disordered proteins (IDPs) have only recently been recognized as a large and important group of proteins and their studyhas become a fast growing field in protein science. Proteins without a defined three dimensional structure play important roles in many cellular processes, including those that lead to widespread diseases such as Alzheimer's or cancer. We present, to the best of our knowledge, the first detailed description of the molecular driving forces of a process exhibiting folding upon binding of an IDP. We demonstrate that the disorder need not result in fuzzy or weak binding and that the structure IDPs assume on binding may already be encoded in their amino acid sequence. Therefore, we believe our work represents an important step in the molecular understanding of IDP functioning.
COBISS.SI-ID: 36496133