Nanoscale structure intercrystalline interactions in fat crystal networks

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated that the formation of such a fat crystal network starts with the association of nanoplatelets at the lowest constitutional level. These nanoplatelets interact and aggregate via van der Waals's forces into larger fractal structures, which eventually form a 3-dimensional network responsible for the solid-like characteristics of the material. The purpose of this review is to summarize recent efforts in the characterization and quantification of these recently discovered crystalline nanoplatelets and to discuss the role of van der Waals interactions between them. In addition a brief discussion of previous fractal model will be presented. The new experimental findings on the nanostructural level will then be used to validate our fractal structural–mechanical model of fats (Marangoni, 2000). These new insights will contribute to our knowledge of the nature of fat crystal network in plastic fats at different length scales and the relationship of these structural characteristics to the function and properties of fats.     

Thickness measurement in composite materials using Lamb waves

Pulse propagation in plate elements is investigated with the identification of Lamb modes in the range 40–150 kHz. The possibilities of the application of this technique in the measurement of thickness in composites and coarse materials are evaluated, particularly in ferrocement materials.     

Molar and partial molar excess volumes of di-n-butylamine with chloroalkanes at 25°C

Molar excess volumes and partial molar excess volumes are reported for binary mixtures of dibutylamine+dichloromethane, trichloromethane and tetrachloromethane at 25°C, over the whole concentration range. A comparative study is made between the primary and secondary amines and their mixtures with chloroalkanes. The applicability of the so-called ERAS model for predicting thermodynamic excess properties is tested here for excess molar volumes; the calculated values agree quite well with experimental data.     

The calculation of electric dipole vibronic intensities in centrosymmetric coordination compounds using the crystal field-closure-ligand polarization model

Equations are derived for the evaluation of the contribution to the electric dipole vibronic intensity of d-d and f-f transitions in octahedral complex ions. Expressions for the evaluation of the crystal-field and ligand polarization terms and the cross term between are presented in symmetry adapted form and tables of the required coupling constants are given.     

Solvent effects and mechanism for a nucleophilic aromatic substitution from QM/MM simulations

The nucleophilic aromatic substitution (SNAr) reaction between azide ion and 4-fluoronitrobenzene has been investigated using QM/MM and DFT/PCM calculations in protic and dipolar aprotic solvents. The effects of solvation on the transition structures, the intermediate Meisenheimer complex, and the rate of reaction are elucidated. The large rate increases in proceeding from protic to dipolar aprotic solvents are only reproduced by the QM/MM methodology.     

Turbulent statistical characteristics associated to the north wind phenomenon in southern Brazil with application to turbulent diffusion

A parameterization for the transport processes in a shear driven planetary boundary layer (PBL) has been established employing turbulent statistical quantities measured during the north wind phenomenon in southern Brazil. Therefore, observed one-dimensional turbulent energy spectra are compared with a spectral model based on the Kolmogorov arguments. The good agreement obtained from this comparison leads to well defined formulations for the turbulent velocity variance, local decorrelation time scale and eddy diffusivity. Furthermore, for vertical regions in which the wind shear forcing is relevant, the eddy diffusivity derived from the north wind data presents a similar profile to those obtained from the non-extensive statistical mechanics theory. Finally, a validation for the present parameterization has been accomplished, using a Lagrangian stochastic dispersion model. The Prairie Grass data set, which presents high mean wind speed, is simulated. The analysis developed in this study shows that the turbulence parameterization constructed from wind data for north wind flow cases is able to describe the diffusion in a high wind speed, shear-dominated PBL.     

New triterpenoids from the orchids Scaphyglottis livida and Nidema boothii

Two new triterpenoids, nidemin (1), a modified lanostane, and 9,19-cyclolanosta-24,24-dimethyl-25-en-3beta-yl trans-p-hydroxycinnamate (2) have been isolated from the orchids Nidema boothii and Scaphyglottis livida, respectively. The isolates were characterized by spectral methods. The structure of nidemin (1) was unambiguously confirmed by X-ray analysis.     

The effect of solvent on a Lewis acid catalyzed Diels-Alder reaction,using computed and experimental kinetic isotope effects

A new transition structure for the Diels-Alder reaction between isoprene and acrolein catalyzed by Et(2)AlCl is found to reconcile reported discrepancies between computed and observed secondary kinetic isotope effects (KIEs). Including the effect of solvent realigns the computed results with experiment demonstrating the importance of nonbond interactions at transition structures. Comparison of experimental and newly predicted KIE data reaffirms the ability of theory and experiment to probe the mechanism and transition structure geometry of organic reactions.     

Densities, Refractive Indexes, and Excess Properties of Mixing of the n-Hexanol + Ethanenitrile + Dichloromethane Ternary System at 25°C

Excess molar volumes and excess refractive indexes of the n-hexanol + ethanenitrile + dichloromethane system and the three corresponding binary mixtures have been determined at 25°C, by measuring densities and refractive indexes. Different expressions exist in the literature to predict these excess properties from binary data. The empirical correlation of Cibulka is shown to be the best in this system. An estimation of excess molar volumes is also evaluated using a modified Heller equation, which depends on the refractive indexes of the mixtures. Comparison of the predictions by different methods with the experimental values of the physical properties has been made.