Quantitative Structure—Retention Relationship Modeling of the Retention Behavior of Selected Antipsychotic Drugs in Normal-Phase Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC -     

Effect of composition and drying method on glass transition temperature,water sorption characteristics and surface morphology of newly designed β-lactoglobulin/retinyl palmitate/disaccharides systems

Epoxy-based nanocomposites containing different concentrations (0–3%) of surface-modified graphene nanosheets (GNS) with 3-aminopropyltriethoxysilane were prepared and their thermal and mechanical properties including dynamic mechanical analysis, tensile strength, hardness, and abrasion tests were evaluated in order to have a database for thermo-mechanical properties of epoxy nanocomposites. The main aim of this study was to understand the optimum percentage of GNS which would perform the best reinforcing influence on mechanical and physical performance of an epoxy nanocomposite. The results explain how applying the analysis of variance (ANOVA) method as a useful tool in optimization of GNS concentration in preparation of high-performance epoxy-based nanocomposites.     

Analysis of flammability and smoke emission of rigid polyurethane foams modified with nanoparticles and halogen-free fire retardants

Using one-step method, rigid polyurethane foams were made, modified with developed fire retardant systems containing halogen-free flame retardants and nanofillers in the form of multi-walled carbon nanotubes or nanoscale titanium dioxide. The materials were subjected to a test using a cone calorimeter and smoke-generating chamber, and selected samples were further analyzed via thermogravimetry and oxygen index. Moreover, the products of thermal degradation of selected samples were identified using gas chromatography with mass spectrometer. Conducted flammability tests confirmed the presence of a synergistic effect between the used nanofillers and halogen-free flame retardants. It has been observed that the carbonized layer, the formation of which favored the presence of nanoadditives, inhibits the combustion process. Furthermore, nanofillers influenced favorably reduction in the amount and the number of occurring products of thermal degradation.     

A rugged landscape model for self-organization and emergent leadership in creative problem solving and production groups

The process by which an initially leaderless group differentiates into one containing leadership and secondary role structures was examined using the swallowtail catastrophe model and principles of selforganization. The objectives were to identify the control variables in the process of leadership emergence in creative problem solving groups and production groups. In the first of two experiments, groups of university students (total N = 114) played a creative problem solving game. Participants later rated each other on leadership behavior, styles, and variables related to the process of conversation. A performance quality measure was included also. Control parameters in the swallowtail catastrophe model were identified through a combination of factor analysis and nonlinear regression. Leaders displayed a broad spectrum of behaviors in the general categories of Controlling the Conversation and Creativity in their role-play. In the second experiment, groups of university students (total N = 197) engaged in a laboratory work experiment that had a substantial production goal component. The same system of ratings and modeling strategy was used along with a work production measure. Leaders in the production task emerged to the extent that they exhibited control over both the creative and production aspects of the task, they could keep tension low, and the externally imposed production goals were realistic.     

Brownian dynamics simulations on CPU and GPU with BD_BOX

There has been growing interest in simulating biological processes under in vivo conditions due to recent advances in experimental techniques dedicated to study single particle behavior in crowded environments. We have developed a software package, BD_BOX, for multiscale Brownian dynamics simulations. BD_BOX can simulate either single molecules or multicomponent systems of diverse, interacting molecular species using flexible, coarse-grained bead models. BD_BOX is written in C and employs modern computer architectures and technologies; these include MPI for distributed-memory architectures, OpenMP for shared-memory platforms, NVIDIA CUDA framework for GPGPU, and SSE vectorization for CPU.     

Stimuli-responsive electrospun fibers and their applications

Stimuli-responsive electrospun nanofibers are gaining considerable attention as highly versatile tools which offer great potential in the biomedical field. In this critical review, an overview is given on recent advances made in the development and application of stimuli-responsive fibers. The specific features of these electrospun fibers are highlighted and discussed in view of the properties required for the diverse applications. Furthermore, several novel biomedical applications are discussed and the respective advantages and shortcomings inherent to stimuli-responsive electrospun fibers are addressed (136 references).     

Oxidation of phenothiazine dyes by manganese(III) in sulfuric acid solution

Manganese(III) sulfato complexes cause the oxidative degradation of methylene blue and its partially and fully N-demethylated derivatives, azure B and thionine dyes, respectively, in sulfuric acid media. The reaction proceeds through a colored reactive organic radical generated in the first stage via one-electron oxidation of the starting material, leading to a mixture of N-demethylated and/or deaminated species. The rates of formation of the methylene blue and azure B radicals are much higher than those of their further decomposition, whereas the generation of the thionine radical is much slower than its immeasurably fast decay. The kinetics of decomposition of all three dyes and the methylene blue and azure B radicals were studied spectrophotometrically under isolation conditions at 298 K. The first stage of each reaction proceeds according to a second-order rate expression, being first order in the dyes and in the manganese(III) concentrations. Dependence of the pseudo-first-order rate constants on the oxidant concentration for the second stage exhibits a saturation effect under the applied conditions. It is postulated that electron transfer takes place between the [Mn(SO₄)₃]³⁻ complex and the protonated form of the dye. The reactivity order of the dyes as determined from the second-order rate constants for the first reaction stage corresponds to the order of their HOMO energies.     

A mechanistic study on the disproportionation and oxidative degradation of phenothiazine derivatives by manganese(III) complexes in phosphate acidic media

The oxidative degradation of phenothiazine derivatives (PTZ) by manganese(III) was studied in the presence of a large excess of manganese(III)-pyrophosphate (P₂O₇ ²⁻), phosphate (PO₄ ³⁻), and H⁺ ions using UV–vis. spectroscopy. The first irreversible step is a fast reaction between phenothiazine and manganese pyrophosphate leading to the complete conversion to a stable phenothiazine radical. In the second step, the cation radical is oxidized by manganese to a dication, which subsequently hydrolyzes to phenothiazine 5-oxide. The reaction rate is controlled by the coordination and stability of manganese(III) ion influenced by the reduction potential of these ions and their strong ability to oxidize many reducing agents. The cation radical might also be transformed to the final product in another competing reaction. The final product, phenothiazine 5-oxide, is also formed via a disproportionation reaction. The kinetics of the second step of the oxidative degradation could be studied in acidic phosphate media due to the large difference in the rates of the first and further processes. Linear dependences of the pseudo-first-order rate constants (k _obs) on [Mn^III] with a significant non-zero intercept were established for the degradation of phenothiazine radicals. The rate is dependent on [H⁺] and independent of [PTZ] within the excess concentration range of the manganese(III) complexes used in the isolation method. The kinetics of the disproportionation of the phenothiazine radical have been studied independently from the further oxidative degradation process in acidic sulphate media. The rate is inversely dependent on [PTZ^+.], dependent on [H⁺], and increases slightly with decreasing H⁺ concentration. Mechanistic consequences of all these results are discussed.     

Freeze-fracture TEM imaging of robust order in swollen phases of amphiphilic diblock copolymers

We report on the structures exhibited by two different diblock poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) copolymers in water, a selective solvent. Using a combination of X-ray scattering and freeze fracture-transmission electron microscopy (FF-TEM), we show that these structures can be widely swollen while retaining their initial morphology and a high degree of long-range order. The analysis of the FF-TEM pictures also evidences the presence of water crystallites of regular size and shape within the confined water domains. We relate the growth of these crystallites to the high local ionic strength of the water swelling the PAA brushes. Moreover, the confinement of the crystallites growth shows that the swollen phases have a very robust structure, potentially useful for confining colloidal particles.