MgO films grown on yttria-stabilized zirconia by molecular beam epitaxy

MgO films were grown on (0 0 1) yttria-stabilized zirconia (YSZ) substrates by molecular beam epitaxy (MBE). The crystalline structures of these films were investigated using X-ray diffraction and transmission electron microscopy. Growth temperature was varied from 350 to 550 °C, with crystalline quality being improved at higher temperatures. The MgO films had a domain structure: (1 1 1)[1 1 2¯]_MgO(0 0 1)[1 0 0]_YSZ with four twin variants related by a 90° in-plane rotation about the [1 1 1]_MgO axis. The observed epitaxial orientation was compared to previous reports of films grown by pulsed laser deposition and sputtering and explained as resulting in the lowest interface energy.     

Automated sample cleanup in HPLC using column-switching techniques

Sample pretreatment has often been the rate limiting step in analyses by HPLC. Multicolumn or column switching techniques now available have made efficient automated cleanup procedures possible, with high sample throughput and analytical precision.     

Direct optical detection of singlet oxygen from a single cell

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1deltag --> X3sigmag-) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.     

Salvinicins A and B, new neoclerodane diterpenes from Salvia divinorum

[reaction: see text] Two new neoclerodane diterpenes, salvinicins A (4) and B (5), were isolated from the dried leaves of Salvia divinorum. The structures of these compounds were elucidated by spectroscopic techniques, including (1)H and (13)C NMR, NOESY, HMQC, and HMBC. The absolute stereochemistry of these compounds was assigned on the basis of single-crystal X-ray crystallographic analysis of salvinicin A (4) and a 3,4-dichlorobenzoate derivative of salvinorin B.     

A stereoelectronic effect on turn formation due to proline substitution in elastin-mimetic polypeptides

Stereoelectronic effects have been identified as contributing factors to the conformational stability of collagen-mimetic peptide sequences. To assess the relevance of these factors within other protein structural contexts, three polypeptide sequences were prepared in which the sequences were derived from the canonical repeat unit (Val-Pro-Gly-Val-Gly) of the protein material elastin. These elastin-mimetic polypeptides, elastin-1, elastin-2, and elastin-3, incorporate (2S)-proline, (2S,4S)-4-fluoroproline, and (2S,4R)-4-fluoroproline, respectively, at the second position of the elastin repeat. Calorimetric and spectroscopic investigations of these three polypeptides indicate that the incorporation of the substituted proline residues had a dramatic effect upon the self-assembly of the corresponding elastin peptide. The presence of (2S,4R)-4-fluoroproline in elastin-3 lowered the temperature of the phase transition and increased the type II beta-turn population with respect to the parent polypeptide, while the presence of (2S,4S)-4-fluoroproline in elastin-2 had the opposite effect. These results suggest that stereoelectronic effects could either enhance or hinder the self-assembly of elastin-mimetic polypeptides, depending on the influence of the proline analogue on the energetics of the beta-turn conformation that develops within the pentapeptide structural repeats above the phase transition. Density functional theory (DFT) was employed to model three possible turn types (betaI-, betaII-, and inverse gamma-turns) derived from model peptide segments (MeCO-Xaa-Gly-NHMe) (Xaa = Pro, 4S-F-Pro, or 4R-F-Pro) corresponding to the turn-forming residues of the elastin repeat unit (Val-Pro-Gly-Val-Gly). The results of the these calculations suggested a similar outcome to the experimental data for the elastin-mimetic polypeptides, in that type II beta-turn structures were stabilized for peptide segments containing (2S,4R)-fluoroproline and destabilized for segments containing (2S,4S)-fluoroproline relative to the canonical proline residue.     

Assignment of π → 3d rydberg transitions in ethylene around 9 eV using MCD and synchrotron radiation

Magnetic circular dichroism measurements on ethylene are reported over the region of the 3R₀₀ and 4R₀₀^? origins around 9 eV. The results show conclusively that each origin is a composite of two electronic transitions. The 3R₀₀ origin is assigned to the Rydberg transitions, ^tA₁ → ¹B₂(3dδ) + ¹B₃(3dδ). 4R₀₀^? is assigned as ¹A₁ → 3R₀₀ + ν₃(u).     

Fluoroalkyl-s-triazines

A series of symmetrically and asymmetrically substituted s-triazines was synthesized by condensation of fluorocarbon nitriles (Scheme II, compounds 1a-c ) and by cyclodehydration of a fluorocarbon imidoylamidine utilizing a fluorocarbon anhydride (Scheme III, compounds 2a-e ). Among the new nitriles prepared for incorporation in these reaction paths were 11-H-4,9-dioxahexadecylfluoroundecanenitrile ( 3 ) and 6-chloro-6-H-4-oxaheptafluorohexanenitrile ( 4 ), prepared by Scheme 1.