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To mimic the process of gibbsite nucleation on sodium oxalate crystals and their intergrowth in alumina Bayer process, such a coprecipitation process has been broken down into three distinct stages and studied by in situ AFM and ex situ SEM under static conditions. In the first stage, a solution saturated in aluminate and supersaturated in oxalate has been used for investigating the oxalate growth on its {110} face, which is controlled by a layer-by-layer mechanism. In the second stage, in a solution saturated in oxalate and supersaturated in aluminate, gibbsite secondary nucleation was preferred along macrosteps of sodium oxalate {110} faces and appeared as two-dimensional (2D) islands with pisolitic shapes. There does not appear to be a preferred epitaxial relationship at the heterointerface between gibbsite crystals and sodium oxalate substrates, indicating that the magnitude of the surface free energy for nucleation is greater than that associated with strain energy caused by lattice mismatch. In the ...

Although internal features of a crystal play key roles in crystal growth, the relationship between crystal struc- ture and crystal shape is still an unresolved problem. In this paper, we constructed a correlation between crystallographic structure, morphological evolution, and resultant final shape of noble metal nanocrystals. The minimal stable crystal was predicted to consist of 27 unit cells, which facilitates the growth of the crystal matrix into different shapes. During the parallel grouping process, anisotropic nanocrystal with thermodynami- callyunfavorableshapeswasobservedviathesymmetryaxisand symmetry facet. The results indicate that the formation of isotropic shapes with single or multiple twinned crystal structures are still governed by the internal order of crystal structure.

This study demonstrates that the morphology of boehmite (AlOOH) nanoparticles can be controlled over a short timespan by supercritical hydrothermal treatment in the presence of alkyl carboxylic acids including hexanoic, octanoic, decanoic, tetradecanoic, and octadecanoic acids. Boehmite nanoparticles were treated with carboxylic acid in supercritical water at 400 °C and at a water density of 0.35 g/cm3 in a batch-type reactor. When the carboxylic acid was not added, the particles were shaped as rhombic plates. However, the addition of carboxylic acid changed the crystal morphology to hexagonal plates. The aspect ratio (i.e., [length along the a-axis]/[length along the c-axis]) of the rhombic plates increased with a treatment time of 2–30 min, which is a much shorter timespan than that used for conventional hydrothermal crystallization. The aspect ratio of the hexagonal plates increased with increasing concentration of alkyl carboxylic acids. These results clearly indicate that carboxylic acids enhance the...

Comparison of the crystal structures of compounds we have designated “bridge-flipped isomers,” which on the molecular level differ only in the orientation of a bridge of atoms connecting two larger parts of the molecule, offers a useful context for the examination and evaluation of intermolecular interactions and their robustness as supramolecular synthons. Intermolecular interactions in the crystal structures of five pairs of bridge-flipped isomeric benzylideneanilines are examined here, including interactions between nitrile groups and ring hydrogen atoms, between halogen atoms, and between nitrile groups and halogen atoms. Of these, only the halogen−nitrile interaction in which the halogen is iodine is present in both bridge-flipped isomers of the pair, although its influence on the molecular packing arrangement is insufficient to compel the two isomers to assume identical packing arrangements. Pairwise analysis of crystal structures of bridge-flipped isomers thus provides a perspective beyond that pro...

The effects of cocoa butter (CB) origin, tempering procedure, and structure on oil migration kinetics were studied using a flatbed scanner followed by image processing and analysis. The migration rate (OMR) and migration distance (I10) of stained oil were determined in tempered and nontempered CBs. Tempered matrices had 10 to 50 times lower OMRs than nontempered CBs. In addition, the lag phase observed before significant oil migration was also significantly longer in tempered CBs (12 days vs 2 days in nontempered butters). Moreover, cocoa butter origin had a strong effect on OMR. Brazilian and Nigerian CBs had the highest OMR in both tempered and nontempered samples. Malaysian CB had the third highest OMR, but this effect was only significant in untempered samples. Finally, the lowest OMRs were found in Chinese, Ecuadorian, and Ivorian cocoa butters. The amount of oleic acid and triunsaturated triglycerides (UUU) was strongly correlated to OMR (the higher the UUU concentration, the lower the resistance to...

The ideal strength of methane hydrate and ice Ih was investigated and quantified from first-principles calculations. Using density functional theory, methane hydrate was studied under uniaxial, tri...

The crystal structures of nine compounds (1-9) bearing the 4-aminofuran-2(5H)-one scaffold (commonly known as tetronamide, C4H5NO2) and two decorating aromatic/heteroaromatic moieties with two stereocenters have been determined. Tetronamides bearing at the 5-position a phenyl moiety (1 and 2, 3-chloro derivatives with either a 4-p-tolylamino or 4-p-bromophenylamino substituent), an o-bromopyridyl moiety (3, a 3-bromo-4-p-tolylamino derivative), or an o-tolyl moiety (4, a 3-bromo-4-p-tolylamino derivative) adopt a U-shaped conformation. This conformation is stabilized by an intramolecular contact involving either the phenyl o-CH moiety (1 and 2) or the substituent at the ortho position (3 and 4) and the π system of the N-phenyl ring. The other five tetronamides (5-9) are not present with such an intramolecular contact. In fact, these last five compounds are not U-shaped and feature the presence at the 5-position of a p-biphenyl moiety (5 and 7, 3-bromo-4-p-tolylamino diastereomers differing as 5R and 5S), a p-methoxyphenyl moiety (6, a 3-chloro-4-p-bromophenylamino derivative), or a 5-chlorofuran-2-yl moiety (8 and 9, 3-chloro-4-p-tolylamino diastereomers differing as 5R and 5S). Crystal structures of a 5,5-disubstituted tetronamide bearing m-nitrophenyl moieties (10) and a parent tetronamide without a substituent at the 5-position (11d) reinforce the conformational trend found in 1-9. Furthermore, OH···O centrosymmetric dimers are formed only in the crystal structures of the U-shaped tetronamides. Chain motifs assembled through OH···O and NH···O hydrogen bonds are preferred in the line-shaped tetronamides. Furthermore, the conformer energies were calculated in both the gas and solution phases (B3LYP/6-31G∗). The lowest-energy conformations feature an intramolecular N-H···O hydrogen bond as in the crystal structure of 7. In the U-shaped tetronamides, the crystal structure conformations are similar to the third or fourth energetically ranked stable calculated conformer. Therefore, it is concluded that the substitution pattern in the U-shaped tetronamides allows for accessible secondary minimum-energy conformations that are easily adopted in the crystal structure as a result of their compatibility with the robust centrosymmetric O-H···O dimer formation. Fil: Karak, Milandip. Universidade Federal de Minas Gerais; Brasil. Universidade Federal de Viçosa; Brasil Fil: Acosta, Jaime A. M.. Universidade Federal de Minas Gerais; Brasil Fil: Barbosa, Luiz C. A.. Universidade Federal de Minas Gerais; Brasil. Universidade Federal de Viçosa; Brasil Fil: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Da Silva, Cameron C.. Universidade Federal de Goiás; Brasil Fil: Boukouvalas, John. Universite Laval; Francia Fil: Martins, Felipe T.. Universidade Federal de Goiás; Brasil

A combined crystallographic and optical properties study offers a simple model for the dichroic behavior of crystalline azobenzene chromophores, leading to a cocrystallization strategy to manipulate their solid-state arrangement and, therewith, dichroic behavior. This supramolecular strategy represents the first entry of crystal engineering into the design of dichroism in organic crystals.

The Gewald reaction was used to make a 2,5-diaminothiphonene that was functionalized with two styrene monomers. It was condensed with 2,5-thiophene dicarboxaldehyde to afford a conjugated azomethin...

We demonstrate a design for halogen-bonded metal–organic cocrystals involving coordinatively unsaturated square-planar Cu(II) and Ni(II) centers, by utilizing a Schiff base ligand whose pendant acetyl group enables halogen bonding. The robustness of this design is evident by the assembly of a large family of eight cocrystals based on zero-, one-, and two-dimensional halogen bonded architectures involving mono- or ditopic halogen bond donors based on iodine or bromine.