Search results for "PHASE"

1985

Structures, properties and miscibility behaviour of liquid crystalline polycatenar tetrone derivatives

1995

Abstract The tetrones represent an interesting new mesogenic building block. The results of this study show that they can be incorporated into a variety of mesophases. A smectic phase was observed in the polycatenar compound with four terminal chains as expected. The phase exhibits a tilted structure (Sc phase) to prevent void formation. The compound with six pendant chains forms a columnar phase. In spite of their structural similarity, the tetrones studied tended not to be completely miscible. However, complete miscibility with a semi-discoid phenylhydrazone was observed. When this hydrazone, which forms a columnar ‘Dho phase’, was mixed with tetrone which forms a columnar ‘Dhd phase’ a c…

Experimental and estimated saturated vapour pressures of aroma compounds

1999

Abstract The saturated vapour pressure of d-linalool, 2-nonanone, d-limonene and isoamyl acetate were measured using a static method at different temperatures from 223 to 468 K. From the experimental values, Antoine's constants were determined to enable the calculations of the saturated vapour pressures at a given temperature. The saturated vapour pressure of the four aroma compounds at 298 K were respectively 27, 59, 200 and 733 Pa. These results were compared with those obtained using different estimation methods (Antoine–Grain, Watson, Lee–Kesler, Gomez–Thodos, Grain and Mackay). Gomez–Thodos' model was found to be the most accurate method for the estimation of the saturated vapour press…

Improvement of biphasic polymerization by application of binary ionic liquid mixture

2013

Abstract The mixture of two ionic liquids, 1- n -butyl-3-methylimidazolium and 1-(2-phenylethyl)-3-methylimidazolium chloroaluminates, [C 4 -mim][AlCl 4 ] and [PhC 2 -mim][AlCl 4 ], were applied as a medium to immobilize the Cp 2 TiCl 2 titanocene catalyst for biphasic ionic liquid/hexane ethylene polymerization. The system makes possible to perform the reaction at lower temperatures, below the melting temperature of the aralkyl ionic liquid. A better separation of the ionic liquid phase was observed and an easier mass transfer of the polymer product from the ionic liquid to the hexane phase was obtained. The polyethylene reveals bimodal distribution of molecular weight. It is characterized…

ChemInform Abstract: Solution and Fluorous Phase Synthesis of β,β-Difluorinated 1-Amino-1-cyclopentane Carboxylic Acid Derivatives.

2009

An efficient protocol for the preparation of β,β-difluorinated 1-amino-1-cyclopentane carboxylic acid derivatives was developed. 2,2-Difluro-4-phenyl-3-butenoic acid 6 was used as substrate for the preparation of the starting vinyl difluoro imino esters 8. The key steps of this methodology rely on the chemo- and diastereoselective addition of allylzinc bromides over the iminic functionality of 8 and subsequent RCM reaction. This synthetic sequence was successfully applied to fluorous synthesis.

Relationship between Auxin-Dependent Proton Extrusion and Plasmalemma Redox System in Maize Coleoptile Segments

1988

Abraded coleoptile segments reduce ferricyanide utilizing endogenous substrates. The kinetics of ferricyanide reduction shows an initial rapid rate followed by a slow rate of reduction. The duration of the initial phase is about 5 minutes. The slow phase is observed for more than 30 minutes. A Lineweaver-Burk plot of the slow phase was linear and revealed maximum velocity of the reaction of 42 nmols ferricyanide reduced/hour*coleoptile segment and an apparent Km (ferri) of 2.25mM.

Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

1997

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity s…

QENS from polymeric micelles in supercritical CO[sub 2]

2000

We report QENS measurements from PS-b-PFOA aggregates in supercritical CO2. These consist of dense cores of CO2-insoluble polystyrene surrounded by a ‘corona’ of PFOA surfactant molecules whose CO2-philic groups interface with supercritical CO2. Lineshapes are dominated by localized diffusive modes and segmental dynamics of the anchored, finite-length PFOA chains. For Q∼0.6 A−1, we obtain effective diffusion coefficients of ≈0.8×10−6 cm2/sec. At higher Q, a single component is not sufficient as shown by excess intensity on the flanks. For Q>1.5 A−1, the wings reflect contributions due to a distribution of faster, more localized chain modes.

Solid State NMR Structure Analysis of the Antimicrobial Peptide Gramicidin S in Lipid Membranes: Concentration-Dependent Re-alignment and Self-Assemb…

2008

Antimicrobial peptides can kill bacteria by permeabilizing their cell membrane, as these amphiphilicmolecules interact favourably with lipid bilayers. This mechanism of action is attributed eitherto the formation of a peptide “carpet” on the membrane surface, or to a transmembranepore. However, the structure of such a pore has not yet been resolved under relevant conditions.Gramicidin S is a symmetrical cyclic β-sheet decapeptide, which has been previouslyshown by solid state NMR to lie flat on the membrane surface at low peptide:lipid ratios (≤ 1:80).Using highly sensitive 19F-NMR, supported by 15N-labelling,we found that gramicidin S can flip into an upright transmembrane alignment at hig…

Über die polymerisation bei der sublimation des trioxans. 17. Mitt. Über polyoxymethylene

1962

Bei der Sublimation von gereinigtem Trioxan und bei seiner Kristallisation aus der Schmelze erfolgt in der kristallinen Phase eine langsame Polymerisation zu hochmolekularem Polyoxymethylen. Die Ausbeuten an Polymeren sind um so hoher, je trockener das Trioxan ist und je geringer der Fremdgasdruck bei der Sublimation ist. Es wurde festgestellt, das diese Polymerisation durch Spuren von monomerem Formaldehyd ausgelost wird; wenn letzterer durch Silberoxyd zerstort wird, kann Trioxan unverandert sublimiert und kristallisiert werden. Wahrend der Polymerisation wird monomerer Formaldehyd von den wachsenden Polyoxymethylenketten abgespalten und so der Polymerisationskatalysator regeneriert. Desh…