High-resolution solid-state NMR structure of Alanyl-Prolyl-Glycine

We present a de novo high-resolution structure of the peptide Alanyl-Prolyl-Glycine using a combination of sensitive solid-state NMR techniques that each yield precise structural constraints. High-quality ¹³C–¹³C distance constraints are extracted by fitting rotational resonance width (R²W) experiments using Multimode Multipole Floquet Theory and experimental chemical shift anisotropy (CSA) orientations. In this strategy, a structure is first calculated using DANTE-REDOR and torsion angle measurements and the resulting relative CSA orientations are used as an input parameter in the ¹³C–¹³C distance calculations. Finally, a refined structure is calculated using all the constraints. We investigate the effect of different structural constraints on structure quality, as determined by comparison to the crystal structure and also self-consistency of the calculated structures. Inclusion of all or subsets of these constraints into CNS calculations resulted in high-quality structures (0.02 Å backbone RMSD using all 11 constraints).     

Soft spin wave near nu=1: evidence for a magnetic instability in Skyrmion systems

The ground state of the two-dimensional electron gas near nu=1 is investigated by inelastic light scattering measurements carried down to very low temperatures. Away from nu=1, the ferromagnetic spin wave collapses and a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave shows soft behavior as its energy increases with temperature and reaches the Zeeman energy for temperatures above 2 K. The observed softening indicates an instability of the two-dimensional electron gas towards a magnetic order that breaks spin rotational symmetry. We discuss our findings in light of the possible existence of a Skyrme crystal.     

Fabrication and microscopic characterization of a single quantum-wire laser with high uniformity

A T-shaped single quantum-wire laser with high spatial uniformity has been fabricated by a cleaved-edge overgrowth method with molecular beam epitaxy and a growth-interrupt annealing technique. Using micro-photoluminescence imaging and spectroscopy, we confirmed the formation of a spatially uniform quantum wire over 20 μm long without hetero-interface roughness. By optical pumping, we achieved single-mode lasing from the ground state of the single quantum wire at a threshold excitation power as low as 5 mW at 5 K.     

Lanthanum: Thermodynamic properties,chemical equilibria,and standard potentials

We have gathered, critically evaluated, calculated, and tabulated thermodynamic properties and related equilibrium constants and standard potentials for inorganic compounds and aqueous species of lanthanum. We have been explicit about sources of data and our calculations so that interested readers can check the steps leading to tabulated thermodynamic quantities and thus form their own opinions about reliability and accuracy.     

Densities,excess molar volumes,and partial molar volumes for binary mixtures of water with monoethanolamine,diethanolamine, and triethanolamine from 25 to 80°C

We have measured densities of binary mixtures of water with monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) over the full range of compositions and over the temperature range from 25 to 80°C. Results of these measurements have been used in calculating excess molar volumes and partial molar volumes. Knowledge of the volumetric properties of these mixtures is useful in connection with industrial treatment of acidic gases; derived excess molar volumes and partial molar volumes can be used as a basis for understanding some of the molecular interactions in water-organic mixtures.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Synthesis of achiral and racemic catenanes based on terpyridine and a directionalized terpyridine mimic, pyridyl-phenanthroline

Concatenated macrocycles containing manisyl-substituted tridentate ligands 2,2':6',2'-terpyridine and 2-pyridin-2-yl-1,10-phenanthroline (simply referred to as terpyridine and pyridyl-phenanthroline herein) have been prepared via dual cyclization procedures. The manisyl derivative (manisyl = 4-methoxy-2,6-dimethylphenyl) was chosen for its ability to improve solubility while simultaneously incorporating functionality. Deprotection of the methoxy groups provided a soluble ligand that was re-alkylated with an array of terminal alkyne and alkene linkers. The tridentate coordinating ability of these ligands enabled complexation with Ru(ii) and Fe(ii), generating achiral and racemic octahedral complexes for terpyridine and pyridyl-phenanthroline, respectively. Subsequent macrocyclization via olefin metathesis or copper-mediated alkyne coupling afforded the corresponding catenanes, and in some cases a figure-eight macrocycle. The difference in symmetry and the presence of the manisyl group allowed the distinction between the catenane and the undesired figure-eight to be made directly by (1)H NMR. Metal-free achiral and racemic catenanes were obtained by liberating Fe(ii) from the octahedral bound title ligands by treatment with hydrogen peroxide.     

The microwave spectrum and structure of allyl alcohol

The microwave spectrum of the normal species of the gauche, gauche isomer of allyl alcohol has been reassigned and rotational and centrifugal distortion constants have been determined. Rotational constants of nine deuterated species three carbon-13 species and the oxygen-18 species have also been obtained. These data were used to estimate structural parameters by least-squares fitting of the effective moments of inertia. Good agreement with an earlier electron diffraction and ab initio study was obtained. Unassigned transitions from another isomer were observed, presumably the cis, gauche conformer.     

Thermal and volumetric properties of chloroform + triethylamine mixtures and the ideal associated solution model of complex formation

In the ideal associated solution model, activity coefficients of all species (labelled A, B, and AB here) are taken to be unity at all mole fractions and all temperatures, with several derivative consequences that have not previously been investigated. We have applied this model to an analysis of the thermodynamic properties (vapor pressures, excess volumes, excess enthalpies, partial molar enthalpies of solution, and excess heat capacities) of the chloroform + triethylamine system in terms of K, V, H, and C _p for the equilibrium represented by A+B=AB. It is shown that there is good consistency between the relatively simple chemical ideal associated solution model and all available thermodynamic data except heat capacities, for which the consistency between model and data is less good. Some limitation of the ideal associated solution model are discussed, along with the relationship of this model to hydrogen bonding in the AB complex and to spectroscopic investigations. New thermal (partial molar enthalpies of solution and excess heat capacities) and volumetric data are presented.     

The meyer-schuster rearrangement and hydrohalide addition of 3-alkynyl-3-hydroxy-1H-isoindol-1-ones

Treatment of N-methyl and N-phenylphthalimide with appropiate lithium acetylides in tetrahydrofuran obtained the acetylenic alcohols 2a through 2h . These compounds, when subjected to mildly acidic hydrolysis conditions in aqueous organic solvents, underwent Meyer-Schuster rearrangement to yield the α,β-unsaturated carbonyl compounds 4a through 4h which were determined to have the E configuration. The phenyl ethynyl analogs of series 4 underwent hydrohalide addition when treated with hydrogen halides in water solution.