Study of PEGylated lipid layers as a model for PEGylated liposome surfaces: molecular dynamics simulation and Langmuir monolayer studies

We have combined Langmuir monolayer film experiments and all-atom molecular dynamics (MD) simulation of a bilayer to study the surface structure of a PEGylated liposome and its interaction with the ionic environment present under physiological conditions. Lipids that form both gel and liquid-crystalline membranes have been used in our study. By varying the salt concentration in the Langmuir film experiment and including salt at the physiological level in the simulation, we have studied the effect of salt ions present in the blood plasma on the structure of the poly(ethylene glycol) (PEG) layer. We have also studied the interaction between the PEG layer and the lipid bilayer in both the liquid-crystalline and gel states. The MD simulation shows two clear results: (a) The Na(+) ions form close interactions with the PEG oxygens, with the PEG chains forming loops around them and (b) PEG penetrates the lipid core of the membrane for the case of a liquid-crystalline membrane but is excluded from the tighter structure of the gel membrane. The Langmuir monolayer results indicate that the salt concentration affects the PEGylated lipid system, and these results can be interpreted in a fashion that is in agreement with the results of our MD simulation. We conclude that the currently accepted picture of the PEG surface layer acting as a generic neutral hydrophilic polymer entirely outside the membrane, with its effect explained through steric interactions, is not sufficient. The phenomena we have observed may affect both the interaction between the liposome and bloodstream proteins and the liquid-crystalline-gel transition and is thus relevant to nanotechnological drug delivery device design.     

All-integer column generation for set partitioning: Basic principles and extensions

Column generation, combined with an appropriate integer programming technique, has shown to be a powerful tool for solving huge integer programmes arising in various applications. In these column generation approaches, the master problem is often of a set partitioning type.     

Palladium(II) chemically bonded to silica surface applied to the separation and identification of polycyclic aromatic sulfur heterocycles in heavy oil

Separation of polycyclic aromatic sulfur heterocycles among themselves and also from interferents in petrochemical matrices is a challenging task because of their low concentration, matrix complexity, and also due to the presence of polyaromatic hydrocarbons, as they present similar physico‐chemical properties. Therefore, the objective of this work was preparation, characterization, and application of a stationary phase for separation of these compounds in a heavy gas oil sample and their identification by comprehensive two‐dimensional gas chromatography. The stationary phase was prepared by grafting mercaptopropyltrimethoxisilane onto a silica surface, followed by palladium(II) chloride immobilization. Elemental analysis, thermogravimetry, nitrogen adsorption‐desorption isotherms, infrared analysis, and scanning electron microscopy were performed to characterize this solid phase. Sulfur compounds were separated in an open column packed with the stationary phase and analyzed by comprehensive two‐dimensional gas chromatography coupled to time‐of‐flight mass spectrometric detection. The number of compounds tentatively identified was 314 and their classes were thiophenes, benzotiophenes, dibenzothiophenes, naphthothiophenes, benzonaphthothiophenes, and dinaphthothiophenes. Separation among sulfur compounds and polyaromatic hydrocarbons was successful, which is a difficult goal to achieve with the traditionally employed solid phases. Some recalcitrant compounds (dibenzothiophenes with substituents of two and four carbons) were fully separated and tentatively identified.     

Weighted generalized functions and hyperbolic Riesz B‐potential

The paper is devoted to the study of the fractional integral operator, which is a negative real power of the singular wave operator generated by Bessel operator using weighted generalized functions. We give conditions for this operator to be bounded in appropriate spaces, obtain formula for the Hankel transform of this operator, and get formula of connection between this operator and natural degree of singular wave operator generated by Bessel operator.     

Copper-cobalt ferrites as catalysts for methanol decomposition

Copper-cobalt ferrites with composition Cu_1?xCo_xFe₂O₄, where x= 0.2 and 0.8 were prepared by thermal treatment of co-precipitated precursor. The obtained materials were characterized by TG-DSC, XRD, Transmission and Conversion Electron Mössbauer spectroscopy and temperature programmed reduction with hydrogen. The catalytic properties of ferrites were tested in methanol decomposition to CO and hydrogen.      

Column generation in the integral simplex method

The integral simplex method for set partitioning problems allows only pivots-on-one to be made, which results in a primal all-integer method. In this technical note we outline how to tailor the column generation principle to this method. Because of the restriction to pivots-on-one, only local optimality can be guaranteed, and to ensure global optimality we consider the use of implicit enumeration.     

Stability of quasiminimizers of the p-Dirichlet integral with varying p on metric spaces

We prove a stability result, with respect to the varying exponentp, for a family of quasiminimizers of the p-Dirichlet energyfunctional on a doubling metric measure space. In addition,we prove global higher integrability for upper gradients ofquasiminimizers with fixed boundary data, provided that theboundary data belong to a slightly better Newtonian space.     

Alkyl and 2-hydroxy derivatives of imidazo]4,5-b]pyrazine and their N-oxides

N-Monoxides and N,N-dioxides of some alkyl and hydroxy derivatives of imidazo[4,5-b]pyrazine were synthesized. It was proved that the nitrogen atoms of the pyrazine ring are oxidized; alkylation of N₁ sterically hinders oxidation of N₇. The hydrolytic cleavage of imidazo[4,5-b]pyrazines and their N-oxides was studied.     

Applications of comprehensive two-dimensional gas chromatography to the characterization of petrochemical and related samples

This article discusses the application of comprehensive two-dimensional gas chromatography (GC x GC) to samples derived from petrochemicals. The use of GC x GC for characterization of petroleum and petroleum derivatives, through group type analysis, such as benzene, toluene, ethylbenzene, xylenes (BTEX), total aromatic hydrocarbons, polyaromatic hydrocarbons, and heteroatomic sulfur-, oxygen-, and nitrogen-containing compounds is presented. The capability of GC x GC to provide additional chemical-specific information regarding petroleum-processing steps, such as linear alkanes dehydrogenation, Fischer-Tropsch process, hydrogenation and oligomerization, is also described. In addition, GC x GC analyses of petrochemical biomarkers and environmental petrochemical-derived pollutants are reported. The role of comparison of samples through use of simple fingerprint approaches is highlighted.