ABSTRACT
We have studied the structure of salt-free lysozyme at 293 K and pH 7.8 using molecular simulations and experimental SAXS effective potentials between proteins at three volume fractions, Ï=0.012, 0.033, and 0.12. We found that the structure of lysozyme near physiological conditions strongly depends on the volume fraction of proteins. The studied lysozyme solutions are dominated by monomers only for Ï≤0.012; for the strong dilution 70% of proteins are in a form of monomers. For Ï=0.033 only 20% of proteins do not belong to a cluster. The clusters are mainly elongated. For Ï=0.12 almost no individual particles exits, and branched, irregular clusters of large extent appear. Our simulation study provides new insight into the formation of equilibrium clusters in charged protein solutions near physiological conditions.
Subject(s)
Muramidase/chemistry , Hydrogen-Ion Concentration , Models, Molecular , Solutions , TemperatureABSTRACT
We present a new determination method of the porosity created by the adsorption space between closed multiwalled carbon nanotubes. Using the grand canonical Monte Carlo (GCMC) simulation of nitrogen adsorption at 77 K and applying the "Karolina" algorithm, local isotherms were simulated for different distances between parallel nanotubes and finally the equation of the global adsorption isotherm was solved. This methodology leads to a satisfactory description of the experimental nitrogen adsorption data showing that the distance between nanotubes is in the range between 4 and 14 nm.
ABSTRACT
The paper investigates the changes in porosity (i.e., in the accessible adsorption capacity of carbonaceous adsorbents for pollutants during filter bed maturation) of three activated carbons applied in a filter bed pilot operation. The results of this investigation may help to reduce operating costs, increase granular activated carbon bed life, maximize the useful life of biofilters, and understand the mechanism of water purification by carbon adsorbents. The analysis of the pore structure was limited to the first year of service of the beds, since this was when the largest decrease in the available pore capacity occurred. Low-temperature nitrogen adsorption isotherms were used to evaluate the structural parameters and pore size distributions (PSDs) of carbon samples (virgin (reference) and mature adsorbents for different periods of water treatment) on the basis of the Nguyen and Do (ND) method and density functional theory (DFT). These results were compared with small-angle X-ray scattering (SAXS) investigations (PSDs calculated by Glatter's indirect transformation method (ITP)). The results show that in general, the ND and ITP methods lead to almost the same qualitative distribution curve behavior. Moreover, the enthalpy of immersion in water, mercury porosimetry, densities (true and apparent), and the analysis of ash are reported and compared to explain the decrease in adsorptive capacity of the carbons investigated. On the other hand, the efficacy of TOC (total organic carbon, i.e., a quantity describing the complex matrix of organic material present in natural waters) removal and the bacteria count were analyzed to explain the role of adsorption in the elimination of contaminants from water. Finally, a mechanism of organic matter removal was suggested on the basis of the above-mentioned experimental data and compared with mechanisms reported by other authors.
ABSTRACT
A new Determining Horvath-Kawazoe (DHK) program for the evaluation of pore-size distribution curve based on the HK method (J. Chem. Eng. Jpn. 16 (1983) 470) is described. The standard bisection procedure (Gerald, C.F., 1977. Applied Numerical Analysis, 2nd ed. Addison-Wesley, CA) is used as a kernel in the proposed algorithm. The calculation of the effective pore-size distribution and the comparative analysis with the previous data published by Horvath and co-workers (J. Chem. Eng. Jpn. 16 (1983) 470; Fraissard, J., Conner, C.W., 1997. Physical Adsorption: Experiment, Theory and Applications. Kluwer Academic, London) and recalculated by Do (Do, D.D., 1998. Adsorption Analysis: Equilibria and Kinetics. Imperial College Press, London) were done.
ABSTRACT
The paper presents a new simple adsorption genetic algorithm (SAGA) which is based on the genetic theory of natural selection and rivalry. This algorithm is utilized to estimate the parameters of the Dubinin-Rhadushkevich equation. The obtained results are compared with these achieved from the classical optimization methods. The analysis of the error of fitting of the DR model to experimental data is discussed. It is shown that the proposed SAGA, contrary to the other methods, makes it possible to calculate the parameters of the DR equation not only very precisely but also very quickly. Copyright 2001 Academic Press.
