Phase transitions in diglyceride monolayers studied by computer simulations,pressure-area isotherms and X-ray diffraction

Summary 1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found between the simulations and experiments. The Langmuir film undergoes two phase transitions occurring at 38.3 and 39.8 ?²/molecule. The transition at low surface density is associated with a tilt of ≈14° in the direction close to nearest neighbour. The first transition is unique for the diglyceride molecules and has not been observed for other amphiphilic molecules. It is driven by a competition of hydrophobic/hydrophilic and intra/intermolecular forces and can be pictured as a ?seesaw? mechanism. Due to the close packing of the chains at high surface pressure, thesn-1 ester group aligns with the alkyl chain, and only thesn-2 ester group is favoured to lay at the aqueous interface. Hydrophilic forces attract thesn-1 ester group, but its motion towards the aqueous subphase is hindered by intra- and intermolecular chain interactions. On expansion, the intermolecular interaction decreases, and at the first transition, the intramolecular interaction between the two chains is strong enough to cause a ?swelling? of the molecules. The diffraction pattern determined in the different mesophases reveals that the layer maintains its hexagonal structure up to the second phase. Concomitant with the tilt, the structure relaxed from a hexagonal to a distorted hexagonal lattice. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Stratospheric temperature profile from balloon-borne measurements of the 10.4-μm band of CO2

The technique of nonlinear least squares spectral curve fitting has been used to derive the stratospheric vertical temperature profile from balloon-borne measurements of the 10.4-μm band of CO₂. The spectral data were obtained at sunset with the ?0.02 cm^-1 resolution University of Denver interferometer system from a float altitude of 33.5 km near Alamogordo, New Mexico, on 23 March 1981. The r.m.s. deviation between the retrieved temperature profile and correlative radiosonde measurements is 2.2 K.     

High-pressure liquid chromatography of irradiated nuclear fuel: Separation of neodymium for burn-up determination

Neodymium is separated from solutions of spent nuclear fuel by high-pressure liquid chromatography in methanol-nitric acid-water media using an anion-exchange column. Chromatograms obtained by monitoring at 280 nm, illustrate the difficulties especially with the fission product ruthenium in nuclear chemistry. Preseparation of the rare earths and trivalent actinides using a di(2-ethylhexyl)phosphoric acid/kieselguhr column is described.     

Photoemission from valence bands of GaAs(001) grown by molecular beam epitaxy

Angle-resolved photoemission measurements for GaAs(001) prepared by MBE have been carried out using synchroton radiation. Observed bulk features in the spectra can be explained by a direct transition model using free-electron-like final states down to energies as low as 16 eV above the top of the valence bands. Spectral bulk valence band features can be distinguished from surface features by an appropriate choice of photon energies and polar angles. This is demonstrated using calculated valence bands.     

Asymmetric Pt(II)-catalyzed ene reactions: counterion-dependent additive and diphosphine electronic effects

[reaction: see text]. Catalysis of the glyoxylate-ene reaction by dicationic P2Pt(II) complexes is subject to anion-dependent additive effects. For [((S)-MeOBiphep)Pt](OTf)2 catalysts, acidic phenols such as 3-CF3-C6H3OH or C6F5OH provide substantial rate increases but do not affect the more active SbF6-based catalysts. Enantioselectivity and reactivity also increased with diphosphine basicity, with 4-t-Bu-substituted MeOBiphep ligands yielding the highest enantioselectivities.     

The electrical properties of coal slag

The inorganic constituents of coal remaining after high temperature combustion in a MHD (Magnetohydrodynamic) power plant combustor form an iron-rich, “dirty” glass whose electrical properties are important in the operation of the MHD generator. In particular, alkali “seed” (K₂CO₃) is added to enhance the conductivity of the plasma so the slag layer which coats the walls and electrodes of the generator is rich in K₂O. We present results of a systematic study of the electrical conductivity of a Rosebud coal ash with graded amounts of K₂CO₃ added. At high temperatures, the conductivity curves are smooth with many ions contributing. At lower temperatures the curves become more complex with the presence of crystalline phases in the glass.     

Hydrogen-bonded OH stretching modes of methanol clusters: a combined IR and Raman isotopomer study

A comprehensive study of the OH and OD stretching fundamentals in clusters of methanol and its isotopomers CH(3)OD, CD(3)OH, and CD(3)OD provides detailed insights into the hydrogen-bond mediated coupling as a function of cluster size. The combination of infrared and Raman supersonic jet spectroscopy enables the observation and assignment of all hydrogen-bonded OH stretching modes of isolated methanol trimer and methanol tetramer. A consistent explanation for the spectral complexity observed more than a decade ago in methanol trimer in terms of low-frequency methyl umbrella motions is provided. Previous explanations based on cluster isomerism or anharmonic resonances are ruled out by dedicated jet experiments. The first experimental lower bound for concerted quadruple proton transfer in S(4) symmetric methanol tetramer is derived and compared with theoretical predictions. The observed isotope effects offer insights into the anharmonicity of the localized OH bond. The performance of harmonic B3LYP and MP2 calculations in predicting hydrogen-bond-induced spectral shifts and couplings is investigated.     

Synthesis and structure of phosphatidylinositol dimannoside

(R)-tuberculostearic acid (2) was synthesized in seven steps from (S)-citronellol (5). The carbon chain of 2 was assembled by copper-catalyzed cross coupling of (S)-citronellol tosylate (6) and hexylmagnesium bromide; subsequent ozonolysis and reaction with 6-benzyloxyhexylmagnesium bromide furnished alcohol 10. Functional group manipulation afforded (R)-2 in 49% overall yield from 5. DCC coupling of (R)-2 with 3-O-benzyl-1-O-palmitoyl-sn-glycerol (16), followed by hydrogenolytic removal of the benzyl group and treatment with benzyl bis(diisopropyl)phosphoramidite, afforded phosphoramidite 20. Tetrazole-mediated coupling of 20 with PIM1 head group 21 gave 22, and subsequent debenzylation afforded phosphatidylinositol mono-mannoside, PIM1 (23). Similarly, coupling of 20 and 24 and removal of the benzyl protecting groups gave PIM2 (1c). Both 23 and 1c have a clearly defined acylation pattern, which was confirmed by mass spectrometry, with sn-1 palmitoyl and sn-2 tuberculostearoyl groups on the glycerol moiety. Both 23 and 1c were shown to modulate the release of the pro-inflammatory cytokine, IL-12, in a dendritic cell assay.     

Power supply–demand balance in a Smart Grid: An information sharing model for a market mechanism

In the future, global energy balance of a Smart Grid system can be achieved by its agents deciding on their own power demand and production (locally) and the exchange of these decisions. In this paper, we develop a network model that describes how the information of power imbalance of individual agents can be exchanged in the system. Compared to existing network models with hierarchical structures, our developed model, together with a market mechanism, achieve the power balance in the system in a completely distributed way. Additionally, dynamics, constraints and forecasts of each agent can be conveniently involved.