Chiral and fractal: from simple design rules to complex supramolecular constructs.

Using theoretical modeling, we demonstrate the self-assembly of functional organic molecules into 2D fractal aggregates resembling the Sierpinski triangle (ST). It is shown for the first time that the fractal self-assembly can be realized in one-component systems comprising K- and A-shaped tectons whose arms meet to form chiral nodes with directional intermolecular bonds.

Simulation of the self-assembly of simple molecular bricks into Sierpinski triangles.

The canonical lattice Monte Carlo simulation was used to demonstrate the surface-confined mixed self-assembly of 120° ditopic organic tectons and metal atoms into ordered hierarchical structures resembling the mathematical fractal set called the Sierpinski triangle.

Kinetic adsorption energy distributions of rough surfaces: a computational study.

The adsorption energy distribution usually refers to localized monolayers of adsorbate at thermodynamic equilibrium. Many papers have been published that analyze its influence on adsorption isotherms, heats of adsorption, and adsorption kinetics. However, the adsorption energy distribution, in its classical thermodynamic equilibrium sense, may be not as useful as expected. This is because many important processes involving adsorption have dynamic character and reactant particles have a finite time for penetration of the adsorbent. The above suggests that some adsorption centers located in less accessible fragments of the surface can be invisible in a dynamic process. However, under conditions allowing the thermodynamic equilibrium such adsorption centers could noticeably contribute to the adsorption energy distribution. The aim of this work is to measure the adsorption energy distributions of special rough surfaces using a dynamic method. This method is based on the molecular dynamics simulation of an ideal gas flowing over a sample surface. The ideal gas particles penetrate the surface, and at the moment of collision of a gas particle with the surface the Lennard-Jones potential energy is calculated. This energy can be identified with the adsorption energy at a given point on the surface. The surfaces used in the calculations have been created using two surface growth models (i.e., random deposition and ballistic deposition). The application of these highly disordered surfaces enables us to draw some general conclusions about the properties of real surfaces that are usually far from any deterministic geometry.

Study of proton adsorption at heterogeneous oxide/electrolyte interface. Prediction of the surface potential using Monte Carlo simulations and 1-pK approach.

Adsorption of protons on a heterogeneous solid surface is modeled using the Monte Carlo (MC) simulation method. The surface of an oxide is assumed to consist of adsorption sites with pK assigned according to a quasi-Gaussian distribution. The influence of the electrostatic interactions combined with the energetic heterogeneity of the surface is examined and the MC results are compared with the predictions of the analytical 1-pK approach. The surface potential behavior is examined using both "experimental" MC results and "theoretical" results obtained from the application of 1-pK model. The results are compared qualitatively with experimental determination of the surface potential of metal oxide surfaces. They confirm that the relation between the surface potential and the pH of bulk solution should not be described by the Nernst equation but by the equation with the parameter linearly reducing Nerstian potential. The values of this parameter are examined with respect to degree of surface energetic heterogeneity and site density of the surface.

Experimental studies of pressure/temperature dependence of protein adsorption equilibrium in reversed-phase high-performance liquid chromatography.

The effect of the average pressure and temperature of the column on the adsorption equilibrium of insulin variants on a C8 bonded silica was studied in isocratic reversed-phase HPLC. Analytical injections of samples of four different insulins (bovine, porcine. Lys-Pro and human recombinant) were carried out at constant flow-rate but under increased average pressure. The temperature dependence of the retention parameters over the range 25-50 degrees C was studied under two different average column pressures (47 and 147 bar). Substantial increases of the retention time (up to 300%) were observed when the pressure and/or the temperature were increased. Similar adsorption-induced changes in the partial molar volume at constant temperature (deltaVm approximately 102 ml/mol) were found for all the variants studied. Furthermore, deltaVm was revealed to be practically independent of the temperature, which suggests that the temperature has no or very little influence on the mechanism of the pressure induced perturbations in the molecular structure of the solute. This conclusion was also derived from the observed temperature dependence of the logarithm of the retention factor (k) measured under different pressures. The relation between the temperature and In k was nonlinear with a parabolic shape. Moreover, the shapes of the plots corresponding to the low and high pressures were found to be exactly the same, except that the curves were vertically shifted, due to the difference between the two average column pressures. These results indicate that pressure and temperature affect the retention behavior of insulins in a different and separate way.

Modeling of the separation of the enantiomers of 1-phenyl-1-propanol on cellulose tribenzoate.

The competitive adsorption isotherms of rac-1-phenyl-1-propanol on cellulose tribenzoate were measured by competitive frontal analysis. The experimental data were fitted to four different isotherm models: Langmuir, Bilangmuir, Langmuir-Freundlich, and Tóth. The fittings of the experimental data to all four models were satisfactory. It was excellent in the case of the Langmuir-Freundlich and the Tóth models. Overloaded elution profiles calculated with the Tóth isotherm were in good agreement with the experimental profiles in all the different experimental conditions investigated. This work extends to the case of binary mixtures the equivalence between the general rate and the lumped pore diffusion models already demonstrated for pure compounds when the ratio between the Stanton and the Biot numbers exceeds 5. The adsorption energy distribution for the Tóth isotherm was also calculated.