Crystal structure and theoretical calculations of Julocrotine,a natural product with antileishmanial activity

Julocrotine, N‐(2,6‐dioxo‐1‐phenethyl‐piperidin‐3‐yl)‐2‐methyl‐butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X‐ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6‐311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Synthesis of alkyl α‐aminomethyl‐phenylphosphinates and N,N‐bis(alkoxyphenylphosphinylmethyl)amines by the microwave‐assisted Kabachnik–Fields reaction

As a novel extension, the Kabachnik–Fields reaction was applied to the synthesis of alkyl α‐aminomethyl‐phenylphosphinates, and the double phospha‐Mannich reaction was utilized in the preparation of bis(alkoxyphenylphosphinylmethyl)amines. A total of 27 new aminophosphinate derivatives were synthesized by the microwave‐assisted solvent‐free condensation of alkyl phenyl‐H‐phosphinates, paraformaldehyde, and primary or secondary amines. The starting P‐species were also prepared under microwave conditions. The formation of the N‐methylated aminomethyl‐phenylphosphinate by‐products was also investigated.     

A facile approach for assembling lipid bilayer membranes on template-stripped gold

Lipid vesicles are designed with functional chemical groups to promote vesicle fusion on template-stripped gold (TS Au) surfaces that does not spontaneously occur on unfunctionalized Au surfaces. Three types of vesicles were exposed to TS Au surfaces: (1) vesicles composed of only 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipids; (2) vesicles composed of lipid mixtures of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP) and 97.5 mol % of POPC; and (3) vesicles composed of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG) and 97.5 mol % POPC. Atomic force microscopy (AFM) topography and force spectroscopy measurements acquired in a fluid environment confirmed tethered lipid bilayer membrane (tLBM) formation only for vesicles composed of 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC, thus indicating that the sulfur-containing PDP group is necessary to achieve tLBM formation on TS Au via Au-thiolate bonds. Analysis of force-distance curves for 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC tLBMs on TS Au yielded a breakthrough distance of 4.8 ± 0.4 nm, which is about 1.7 nm thicker than that of POPC lipid bilayer membrane formed on mica. Thus, the PEG group serves as a spacer layer between the tLBM and the TS Au surface. Fluorescence microscopy results indicate that these tLBMs also have greater mechanical stability than solid-supported lipid bilayer membranes made from the same vesicles on mica. The described process for assembling stable tLBMs on Au surfaces is compatible with microdispensing used in array fabrication.     

The influence of the nature of a nanoparticle and polymer matrix on the morphological characteristics of polymeric nanostructures

Comparative studies of the morphological characteristics of selenium- and platinum-containing nanostructures were performed by molecular optics methods. The nanostructures were based on an ionogenic polymeric stabilizer, poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate, and a non-ionogenic polymeric stabilizer, oxyethylcellulose. Studies were performed in aqueous solutions at a fixed ratio between components. The adsorption of a considerable number of polymer macromolecules on nanoparticles with the formation of superhigh-molecular-weight nanostructures with shapes close to spherical was observed for all the nanosystems studied. The thermodynamic state of nanosystems was characterized. Certain morphological characteristics of nanostructures were substantially influenced by the nature of both nanoparticles and polymer matrix.     

Self‐assembled Monolayers of Alkylphosphonic Acids on Aluminum Oxide Surfaces – A Theoretical Study

Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al₂O₃ (0001), bayerite β‐Al(OH)₃ (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting.     

Structured polyphenylenes as carriers of palladium nanoparticles used as selective hydrogenation catalysts

Structured polyphenylenes that are used as matrices for immobilization of palladium nanoparticles are synthesized through the cyclocondensation of acetylaromatic compounds followed by structuring at different temperatures and, as a result, different crosslink densities. The relationship between the structure and structuring temperature of the polymers is investigated. It is shown that the sizes of palladium nanoparticles immobilized in polyphenylene matrices depend on the conditions of polymer structuring. The resulting catalytic systems are examined for the selective hydrogenation of triple bonds in acetylene alcohols.     

Dipolar drag in bilayer harmonically trapped gases

We consider two separated pancake-shaped trapped gases interacting with a dipolar (either magnetic or electric) force. We study how the center of mass motion propagates from one cloud to the other as a consequence of the long-range nature of the interaction. The corresponding dynamics is fixed by the frequency difference between the in-phase and the out-of-phase center of mass modes of the two clouds, whose dependence on the dipolar interaction strength and the cloud separation is explicitly investigated. We discuss Fermi gases in the degenerate as well as in the classical limit and comment on the case of Bose-Einstein condensed gases.     

Ultrastructural architecture of colonies of different morphologies produced by phenotypic switching of a clinical strain of Candida tropicalis and biofilm formation by variant phenotypes

Candida tropicalis has been identified as one of the most prevalent pathogenic yeast species of the Candida-non-albicans (CNA) group. Study of switching in C. tropicalis has not been the subject of extensive research. Therefore, we investigated switching event and characterized the ultrastructural architecture of different phenotypes and biofilm produced in a C. tropicalis clinical strain. Cells switched heritably, reversibly, and at a high frequency between four phenotypes readily distinguishable by the shape of colonies formed on agar at 25°C. SEM analysis was used to verify the architecture of whole Candida colonies at ultrastructural level. The smooth phenotype (parental phenotype) colony showed a hemispherical shape character, while the semi-smooth was characterized by the presence of shallow marginal depressions. The ring and rough phenotypes exhibited more complex architecture and were characterized by the presence of deep central and peripheral depressions areas. The biofilm-forming ability varied among the switch phenotypes. After 12h incubation, the smooth phenotype formed less biofilm compared to the other phenotypes (P<0.05). The electron microscopy analysis revealed that filamentation (pseudohyphae) was associated with ring and rough colonies. The ultrastructural analysis allowed the observation of the arrangement of individual cells within the colonies. At the deep central and peripheral depressions areas of the ring and rough colonies extracellular material was seen in different arrangements. The data presented here open new avenues to study a possible role for extracellular material in the formation and maintenance of the architecture of switch phenotypes in C. tropicalis. It is therefore essential that more strains be investigated to determine the biological significance of extracellular material in C. tropicalis phenotypic switching phenomenon.     

A Phase Field Approach for Martensitic Transformations and Crystal Plasticity

This work is motivated by cryogenic turning which allows end shape machining and simultaneously attaining a hardened surface due to deformation induced martensitic transformations. To study the process on the microscale, a multivariant phase field model for martensitic transformations in conjunction with a crystal plastic material model is introduced. The evolution of microstructure is assumed to follow a time-dependent Ginzburg-Landau equation. To solve the field equations the finite element method is used. Time integration is performed with Euler backward schemes, on the global level for the evolution equation of the phase field, and on the element level for the crystal plastic material law. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A phase field approach for multivariant martensitic transformations of stable and metastable phases

A phase field model approach for multivariant martensitic transformations of stable and metastable phases is introduced. The evolution of the microstructure is examined with respect to elastic energy minimization in which one or two martensitic orientation variants are considered. In this context, the martensitic nucleation behavior is simulated for different activation barriers. Furthermore, the influence of time-dependent external loads on the formation of the different phases is studied. The numerical implementation is performed with finite elements and an implicit time integration scheme.