Self‐Pillared,Single‐Unit‐Cell Sn‐MFI Zeolite Nanosheets and Their Use for Glucose and Lactose Isomerization

Single‐unit‐cell Sn‐MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single‐step, synthesis is based on repetitive branching caused by rotational intergrowths of single‐unit‐cell lamellae. The self‐pillared, meso‐ and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated.     

Controlling Aedes aegypti populations by limited Wolbachia‐based strategies in a seasonal environment

In this work, the linear feedback limited control strategy is proposed to indicate how the Wolbachia‐infected mosquitoes should be introduced in the seasonal environment to reduce the non‐Wolbachia mosquito population. The numerical simulations show that the proposed strategy reduces the population level of non‐Wolbachia mosquitos, avoiding mosquito spread and, consequently, reducing the number of cases of vector‐borne diseases.     

Antimicrobial activities of the CH2Cl2-CH3OH (1:1) extracts and compounds from the roots and fruits of Pycnanthus angolensis (Myristicaceae)

This study was designed at evaluating the antimycobacterial, antibacterial and antifungal activities of the CH2Cl2-CH3OH (1:1) extracts and isolated compounds, namely 3,4-dimethoxy-3',4'-methylenedioxy-7,7'-epoxylignan (1), genkwainin (2), pycnanthulignene C (3), 4,5-dimethoxy-3',4'-methylenedioxy-2,7'-cycloligna-7,7'-diene (4), pycnanthulignene A (5) from the roots, and calycosin (6), biochanin A (7) and prunetin (8), from the fruits of Pycnanthus angolensis. The microplate alamar blue assay and the broth microdilution method were used to determine the minimal inhibitory concentration (MIC) and minimal microbicidal concentration of the samples. The H+-ATPase-mediated proton pumping assay was used to evaluate one of the possible mechanisms of action of the extracts and isolated compounds. The results of MIC determinations showed that the extract from roots was able to prevent the growth of all the studied organisms, including mycobacteria, fungi, and Gram-positive and Gram-negative bacteria. All tested compounds showed antimicrobial activities to different extents, compound 1 and 8 exhibiting the best antimicrobial spectrum, with 92.3% of the tested organisms being sensitive. The results obtained in this study also showed that the extracts as well as most of the compounds were able to inhibit the H(+)-ATPase activity. The overall results provided evidence that P. angolensis and some of its components might be potential sources of antimicrobial drugs against tuberculosis, bacterial and fungal diseases.     

Structural evolution of larger gold clusters

The preferred structures of larger gold clusters comprised of 100 to 1000 atoms (1.4–C3.0 nm equivalent diameter) have been determined theoretically via exhaustive search and energy-minimization methods and experimentally by synchrotron x-ray diffraction analysis of purified powder samples of small gold nanocrystals passivated by alkylthiol(ate) self-assembled monolayers. Theory predicts a persistent, close competition, across the entire size-range, among three structure-types: Marks-type decahedral (Dh) structures, monocrystals of a particular (TO+) truncated-octahedral (or ‘Wulffi’) morphology, and symmetrically twin-faulted variants (t-TO+) of the second; all other forms are much less stable. Quantitative comparison of the experimental diffraction patterns with patterns calculated from the structures provides clear evidence for a high abundance of the Dh and t-TO+ forms, but also reveals a definite transition from the former to the latter structures in the 1.7 to 2.0 nm range (~ 200 atoms). Further, the observed (mean) lattice contraction is only about half that predicted, suggesting that the surfactant monolayer acts to reduce the surface energy of the clusters. Taken together, these results suggest that the surfactant monolayer may play a small but important role in differentially stabilizing the higher energy {100}-type facets present to a greater extent in the TO-type structures.     

Experimental umbilic diabolos in random optical fields

The intensity of a random optical field consists of bright speckle spots (maxima) separated from dark areas (minima and optical vortices) by saddle points. We show that hidden in this complicated landscape are umbilic points--singular points at which the eigenvalues Lambda (+/-) of the Hessian matrix that measure the curvature of the landscape become degenerate. Although not observed previously in random optical fields, umbilic points are the most numerous of all special points, outnumbering maxima, minima, saddle points, and vortices. We show experimentally that the directions of principal curvature, the eigenvectors Psi (+/-), rotate about intensity umbilic points with positive or negative half-integer winding number, in accord with theory, and that Lambda (+) and Lambda (-) generate a double cone known as a diabolo. At optical vortices the curvature of the amplitude is singular, and we show from both theory and experiment that for this landscape Psi (+/-) rotate about vortex centers with a positive integer winding number. Diabolos can be classified as elliptic or hyperbolic, and we present initial results for the measured fractions of these two different types of umbilic diabolos.     

Structure and dynamics of the hydration shells of the Al3+ ion

First principles simulations of the hydration shells surrounding Al3+ ions are reported for temperatures near 300 degrees C. The predicted six water molecules in the octahedral first hydration shell were found to be trigonally coordinated via hydrogen bonds to 12 s shell water molecules in agreement with the putative structure used to analyze the x-ray data, but in disagreement with the results reported from conventional molecular dynamics using two-and three-body potentials. Bond lengths and angles of the water molecules in the first and second hydration shells and the average radii of these shells also agreed very well with the results of the x-ray analysis. Water transfers into and out of the second solvation shell were observed to occur on a picosecond time scale via a dissociative mechanism. Beyond the second shell the bonding pattern substantially returned to the tetrahedral structure of bulk water. Most of the simulations were done with 64 solvating water molecules (20 ps). Limited simulations with 128 water molecules (7 ps) were also carried out. Results agreed as to the general structure of the solvation region and were essentially the same for the first and second shell. However, there were differences in hydrogen bonding and Al-O radial distribution function in the region just beyond the second shell. At the end of the second shell a nearly zero minimum in the Al-O radial distribution was found for the 128 water system. This minimum is less pronounced minimum found for the 64 water system, which may indicate that sizes larger than 64 may be required to reliably predict behavior in this region.