Molecular simulation of low temperature argon adsorption in several models of IRMOF-1 with defects and structural disorder.

Defects and inclusions in metal-organic frameworks (MOFs) have captured the attention of the scientific community as a possible new source of interesting functionalities. Currently, little is known about how the presence of defects and guest molecules affects adsorptive, catalytic, mechanical and other properties of a MOF crystal and there is a clear need for a comprehensive theoretical framework. In this article we offer several conceptual models of IRMOF-1 with defects and guest molecules and explore properties of these models using computational structure characterization methods and molecular simulation of argon adsorption at 78 K.

Structure and phase transformations of DPPC lipid bilayers in the presence of nanoparticles: insights from coarse-grained molecular dynamics simulations.

In this article, we investigate fluid-gel transformations of a DPPC lipid bilayer in the presence of nanoparticles, using coarse-grained molecular dynamics. Two types of nanoparticles are considered, specifically a 3 nm hydrophobic nanoparticle located in the core of the bilayer and a 6 nm charged nanoparticle located at the interface between the bilayer and water phase. Both negatively and positively charged nanoparticles at the bilayer interface are investigated. We demonstrate that the presence of all types of nanoparticles induces disorder effects in the structure of the lipid bilayer. These effects are characterized using computer visualization of the gel phase in the presence of nanoparticles, radial distribution functions, and order parameters. The 3 nm hydrophobic nanoparticle immersed in the bilayer core and the positively charged nanoparticle at the bilayer surface have no effect on the temperature of the fluid-gel transformation, compared to the bulk case. Interestingly, a negatively charged hydrophobic nanoparticle located at the surface of the bilayer causes slight shift of the fluid-gel transformation to a lower temperature, compared to the bulk bilayer case.

Spontaneous formation of a barrel-stave pore in a coarse-grained model of the synthetic LS3 peptide and a DPPC lipid bilayer.

We perform long-time-scale coarse-grained molecular dynamics simulations of the synthetic amphiphilic LS3 peptide interacting with a DPPC lipid bilayer. Our studies show that within several microseconds, the peptide assembles in a trans-membrane barrel-stave pore. The pore consists of six peptides and has an inner diameter of about 5.2 A, which is comparable to earlier experimental and more detailed atomistic studies. Other structures such as three-, four-, and five-member bundles are also observed.

Lattice model of adsorption in disordered porous materials: mean-field density functional theory and Monte Carlo simulations.

We present mean-field density functional theory calculations and Monte Carlo simulations for a lattice model of a fluid confined in a disordered porous material. The model is obtained by a coarse graining of an off-lattice model of adsorption of simple molecules in silica xerogels. In some of our calculations a model of a porous glass is also considered. The lattice models exhibit behavior that is qualitatively similar to that of their off-lattice counterparts but the computations required are much more tractable and this makes it feasible to investigate the effects of porous material microstructure at longer length scales. We focus on exploring in detail the behavior in the adsorption/desorption hysteresis region for these models. In agreement with recent results for a model that uses a random distribution of solid sites on the lattice [Kierlik et al., Phys. Rev. Lett. 87, 055701 (2001)] we show that the disorder of the solid matrix induces multiple metastable states within the hysteresis region, which are evident in both the mean-field theory calculations and the Monte Carlo simulations. These multiple metastable states can be connected by scanning curves that are very similar to those seen in experimental studies of adsorption hysteresis. The results from mean-field theory predict that while there is hysteresis in the adsorption/desorption isotherms it is not possible to locate a condition of phase equilibrium that satisfies thermodynamic consistency. A wider significance of these results is discussed.

Capillary condensation in disordered porous materials: hysteresis versus equilibrium behavior.

We study the interplay between hysteresis and equilibrium behavior in capillary condensation of fluids in mesoporous disordered materials via a mean-field density functional theory of a disordered lattice-gas model. The approach reproduces all major features observed experimentally. We show that the simple van der Waals picture of metastability fails due to the appearance of a complex free-energy landscape with a large number of metastable states. In particular, hysteresis can occur both with and without an underlying equilibrium transition, and thermodynamic consistency is not satisfied along the hysteresis loop.

Computer simulations of phase equilibrium for a fluid confined in a disordered porous structure.

We present calculations of the phase diagrams of a Lennard-Jones 12-6 fluid confined in a disordered porous structure made up of a dispersion of spherical particles, following up on an earlier work on the same system. In particular we present additional calculations using more realizations of the matrix and we investigate the applicability of the Gibbs-Duhem integration method to the calculation of phase equilibrium in these systems. The essential picture of disordered and inhomogeneous coexisting vapor and liquid phases, which emerged in the earlier work, is confirmed by the new calculations. However, a second phase transition associated with the wetting of the porous material by the fluid is found to be more sensitive to variations of the matrix realization. While for the present model this transition appears for particular realizations of the matrix, it does not seem to survive averaging over realizations.

[RNA synthesis in the polymorphonuclear leukocytes of a suppurative wound]. / Sintez RNK v polimorfnoiadernykh leikotsitakh gnoinoi rany.

RNA synthesis in biopsy specimens of burn or traumatic wounds and in blood leukocytes was investigated in 11 patients by electron microscopic radioautography. Experiments with leukocytes were carried out in two variants: 1) incubation with 3H-uridine; 2) incubation with 3H-uridine in the presence of Staphylococcus aureus of Staphylococcus epidermidis suspensions. It was detected that neutrophils incubated without bacteria did not contain the label. Neutrophils incubated with bacteria and phagocytizing them could incorporate 3H-uridine. The label was insignificant in this case and the number of labeled cells did not exceed 18%. The majority of neutrophils (70-90%) in pus accumulations from burn and traumatic wounds contained the label in a higher concentration than neutrophils that phagocytize bacteria in test-tubes.