Phenylpropanoid and phenylethanoid derivatives from Kigelia pinnata DC. fruits

Further phytochemical investigation of the fruits of Kigelia pinnata DC. has yielded a new phenylpropanoid derivative identified as 6-p-coumaroyl-sucrose (1) together with ten known phenylpropanoid and phenylethanoid derivatives (2-11) and a flavonoid glycoside (12). The structures of the isolated compounds were elucidated using various techniques of NMR and MS spectral analysis.     

Morphology and nanomechanics of conducting plastic crystals.

We present a temperature-controlled scanning probe microscopy characterisation of morphology and mechanical behaviour of conducting N,N'-cyclized pyrazolium salts. These salts are plastic crystals belonging to the pyrazolium trifluoromethanesulfonimide family. Going from a five-membered to a seven-membered ring, and adding a methyl group in alpha to either the five-membered or six-membered rings, allows modulation of the temperature of the phase transitions. Before and after the transitions, the materials' Young moduli, hardnesses and surface roughnesses change. We attribute these macroscopic modifications to specific states: brittle, elastoplastic and viscoplastic, corresponding to variations in the extent of the dislocations present in the crystal lattice planes of the compounds.     

Ab Initio calculations of the stabilization energies of the conformational and the structural isomers of C(3)H(7)X where X = F,Cl, and Br

HF, MP2, and B3LYP calculations with different basis sets have been used in the computation of the stabilization energies of C(3)H(7)X isomers, where X is F, Cl, and Br. The experimental stabilization energies of the structural isomers of C(3)H(7)Cl and C(3)H(7)Br have been reproduced via B3LYP calculations. However, the calculated stabilization energies of fluoropropane isomers from their reported enthalpies of formation have been reproduced in all methods of calculations in present work. The experimental relative stabilities of the gauche conformers of 1-fluoro-, 1-chloro-, and 1-bromopropanes have been also reproduced via some of the used calculations in the present work. The effect of the geminal interactions on X atomic charges and on the C-X and C-C bond lengths in halopropane isomers are also discussed.     

Development and validation of a separation method for the diastereomers and enantiomers of aziridine-type protease inhibitors

Aziridine derivatives are attracting pharmacological interest as protease inhibitors. Due to their two centers of chirality, the aziridines studied here are mixtures of two diastereomers and corresponding enantiomers. Applying cyclodextrin-modified capillary electrophoresis resulted in a baseline separation of the four isomers. The most robust separation was obtained by means of 2 mM sulfated beta-cyclodextrin in 50 mM phosphate buffer of pH 2.5. Using this method, 0.25% of the trans-diastereomers aziridine could be precisely and accurately quantified in the presence of 99.75% of the cis-isomers. The corrected peak-area ratios, migration times, and resolutions were found to be robust with respect to small variations of voltage, buffer concentrations, pH, temperature, chiral selector concentration, and different lots.     

Acetic acid effects on enhancement of growth rate and reduction of amorphous carbon deposition on CNT arrays along a growth window in a floating catalyst reactor

The mm-long carbon nanotube (CNT) arrays were grown in a floating catalyst reactor, using xylene-ferrocene and a small amount of acetic acid as the feed. The CNT arrays deposited on a quartz substrate at several positions along the reactor were extensively characterized using Raman spectroscopy, scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, and optical microscopy. Various characterization methods consistently reveal that the acetic acid additive to the feed alleviates deposition of amorphous carbon layer, which gradually thickens CNTs along the reactor. The acetic acid also resulted in a higher growth rate along the so-called growth window, where CNT arrays are deposited on the quartz substrate. High-performance liquid chromatography of extracted byproducts (PAHs) confirmed the presence of some polycyclic aromatic hydrocarbons. The solid weight of PAHs decreased upon addition of ferrocene as the catalyst precursor, as well as of acetic acid to xylene feed. The results suggest that primary light products of xylene pyrolysis can be competitive reactants for both catalytic and subsequent pyrolytic reactions. They may also be more efficient feeds for CNT growth than xylene itself.     

Quantification of Density-Driven Natural Convection for Dissolution Mechanism in CO<Subscript>2</Subscript> Sequestration

Dissolution of CO₂ into brine causes the density of the mixture to increase. The density gradient induces natural convection in the liquid phase, which is a favorable process of practical interest for CO₂ storage. Correct estimation of the dissolution rate is important because the time scale for dissolution corresponds to the time scale over which free phase CO₂ has a chance to leak out. However, for this estimation, the challenging simulation on the basis of convection–diffusion equation must be done. In this study, pseudo-diffusion coefficient is introduced which accounts for the rate of mass transferring by both convection and diffusion mechanisms. Experimental tests in fluid continuum and porous media were performed to measure the real rate of dissolution of CO₂ into water during the time. The pseudo diffusion coefficient of CO₂ into water was evaluated by the theory of pressure decay and this coefficient is used as a key parameter to quantify the natural convection and its effect on mass transfer of CO₂. For each experiment, fraction of ultimate dissolution is calculated from measured pressure data and the results are compared with predicted values from analytical solution. Measured CO₂ mass transfer rate from experiments are in reasonable agreement with values calculated from diffusion equation performed on the basis of pseudo-diffusion coefficient. It is suggested that solving diffusion equation with pseudo diffusion coefficient herein could be used as a simple and rapid tool to calculate the rate of mass transfer of CO₂ in CCS projects.     

Groove geometry effects on turbulent heat transfer and fluid flow

The present work represents a two-dimensional numerical prediction of forced turbulent flow heat transfer through a grooved tube. Four geometric groove shapes (circular, rectangular, trapezoidal and triangular) were selected to perform the study, as well as two aspect ratios of groove-depth to tube diameter (e/D = 0.1 and 0.2). The study focuses on the influence of the geometrical shapes of grooves and groove-depth on heat transfer and fluid flow characteristics for Reynolds number ranging from 10,000 to 20,000. The characteristics of Nusselt number, friction factor and entropy generation are studied numerically by the aid of the computational fluid dynamics (CFD) commercial code of FLUENT. It is observed that the best performance occurs with the lower depth-groove ratio, whereas it is found that the grooved tube provides a considerable increase in heat transfer at about 64.4 % over the smooth tube and a maximum gain of 1.52 on thermal performance factor is obtained for the triangular groove with (e/D = 0.1).     

The final state of gravitational collapse in Eddington‐inspired Born‐Infeld theory

In this paper, we address the implications when a homogeneous dust model is considered for a scenario of gravitational collapse in the context of Eddington‐inspired Born‐Infeld (EiBI) theory. In order to describe the dynamical evolution of the collapse, we present an effective equation, which constitutes the first order corrections, in EiBI coupling parameter κ, to Einstein's field equations. The geometry outside the collapsing object is derived by imposing the standard Darmois‐Israel junction conditions at the boundary surface of the dust. This induces an effective matter source in the outer region which gives rise to a non‐singular, non‐Schwarzschild geometry at the final state of the collapse. For this exterior geometry, we find the threshold of mass for the formation of the black hole. This provides a cut‐off over κ as .