Fluid Dynamics at Connections in Paediatric Cardiac Surgery*

The modified Blalock-Taussig shunt is a connection created between the systemic and pulmonary arterial circulations to improve pulmonary perfusion in children with congenital heart diseases. Survival of these patients is critically dependent on blood flow distribution between the pulmonary and systemic circulations, that in turn depends upon the fluid dynamic behaviour of the shunt. Computational fluid dynamics, structural analyses as well as in vitro experiments were carried out to derive a quantitative relationship between the shunt flow and the corresponding pressure drop. While computational fluid dynamics simulations were based on the assumption of rigid wall for the shunt and the arteries, proper distensible conduits were used in the in vitro study and the structural analysis of the anastomosis deformation. The results indicated that the internal pressure combined with wall distensibility modifies the cross-sectional area of the distal anastomosis (between the shunt and the pulmonary artery). This fact affects the pressure drop across the shunt, especially at low pressures. Based on the results from the computational analyses and the in vitro experiments, a relationship between pressure drop and flow in the shunt was obtained, which matches data from clinical measurements.     

Azelaic acid in model membranes: A thermodynamical and structural study

Summary We report a thermodynamical and structural investigation on the effect of a dicarboxylic acid, the azelaic acid, on a synthetic phosophatidylcholine in excess water condition. The results indicate that the drug interacts with the lipid headgroup region, near to the hydrocarbon chains: in particular, at higher concentrations investigated, an interdigitated ?gel phase?, with rigid chains, stiff and perpendicular to the lamellar planes, is induced. The experimental electron density profiles, obtained for samples containing low and high quantity of azelaic acid, support the proposed interaction. Moreover, step electron density models, used to confirm the selected sign combination of the observed structure factors, show the best agreement with the experimental data when the chain terminal methyl groups are frozen in fixed position. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.     

Investigation of the Cholesteryl Oleate Mesophases by X-Ray Diffraction

The following phase transitions occurring in the cholesteryl oleate were investigated by X-ray diffraction: solid-isotropic liquid, isotropic liquid-cholesteric, cholesteric-smectic.

The sample purity was 98%. Strong pretransitional effects were observed at the solid-isotropic liquid phase transition and at the cholesteric-smectic phase transition.

At this last transition the longitudinal coherence length ξ_∥ appears to diverge as the critical temperature is approached in the cholesteric phase, whereas the transversal coherence length ξ_τ increases at the critical temperature in the smectic phase in an abrupt way. It seems from the temperature dependence analysis of the angular position of the low angle peak that the smectic phase is a smectic A phase and that a progressive melting of chains occurs at the temperature increases.     

Structural modifications in the distearoyl phosphatidyl choline liposomes induced by variable cholesterol concentration

Summary Liposomes of distearoyl phosphatidyl choline (DSPC) in excess water and containing different quantities of cholesterol were studied by using X-ray diffraction and differential scanning calorimetry techniques. A phase diagram was obtained with phases not occurring in the absence of cholesterol. Coexistences of phases were also detected. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.     

Terpenoids Derived from Linalyl Oxide,Part 4. The oxidation of davanone. Isolation and synthesis of the davana ethers,sesquiterpenes of Artemisia Pallens

The photosensitized oxygenation of the β,γ-unsaturated ketonic sesquiterpene, davanone, is described. Treatment of davanone epoxide with an acid ion exchange resin yields a stereoisomeric mixture of the davana ethers, sesquiterpenoids containing two reduced furan rings.     

Structural analysis of the Γ phase in cholesterol-distearoylphosphatidylcholine multilamellar vesicles

Summary The interaction of cholesterol with membranes is particularly interesting as the cholesterol concentration influences membrane stability and permeability by inducing changes in the structure and dynamics of the constituent lipid molecules. On the other hand, cholesterol is present in the atherosclerotic plaques and in some skin diseases, like xanthomas and xantelasmas. An investigation was performed on the Γ phase in a cholesterol-distearoyl phosphatidyl choline (DSPC) mixture by using X-ray diffraction and differential scanning calorimetry. The cholesterol/DSPC molar ratio was 35/65 and DSPC-to-water weight ratio was 1/3. The Γ phase appears at sufficiently high concentration of cholesterol and it is characterized by interchain positional order considerably lower than in theL _β′ andP _β′ phases but higher than in theL _∝ liquid crystalline phase of pure lecithin in excess water. The results suggest that a lateral phase separation exists in the temperature range of existence of the Γ phase. The other phase Γ′ appears to be richer in cholesterol. The (Γ+Γ′) toL _∝ phase transition was investigated and the temperature dependence of the in-plane correlation length in the Γ phase was determined. A very weak enthalpy peak was observed at the chain melting transition, confirming the highly disordered nature of phases Γ and Γ′. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.     

X-ray diffraction study of cholesterol-cholesteryl oleate binary mixtures

Summary The phase transitions for binary mixtures of cholesteryl oleate (CO) and cholesterol (CH) have been investigated by X-ray diffraction, differential scanning calorimetry and optical microscopy. The phase diagrams on heating, involving the solid-solid and solid-isotropic liquid transitions, and on cooling, involving the cholesteric and smectic mesophases, have been derived. In particular, a strong supercooling effect of liquid cholesterol and a progressive decrease of the isotropic liquid-cholesteric and cholesteric-smectic transition temperatures were observed. Moreover, some structural modifications induced in the smecticA and in the cholesteric phase by the presence of CH in CO were detected. Finally the dependence of intermolecular distance in the isotropic liquid phase was studied as a function of temperature and mixture composition.

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Riassunto Mediante diffrazione dei raggi X, calorimetria differenziale e microscopia ottica sono state studiate le transizioni di fase per miscele binarie di colesteril oleato (CO) e colesterolo (CH). Sono stati ricavati in riscaldamento il diagramma di fase per le transizioni solido-solido e solido-liquido isotropo ed in raffreddamento un diagramma di fase comprendente le mesofasi colesterica e smettica. In particolare sono stati osservati un marcato effetto di sovraraffreddamento del liquido del colesterolo ed una progressiva diminuzione delle temperature di transizione delle fasi liquido-isotropo colesterico e colestericosmettico. Inoltre sono state trovate alcune modificazioni strutturali indotte nella fase smetticaA ed in quella colesterica dalla presenza del CH nel CO. Infine è stata studiata la dipendenza della distanza intermolecolare nella fase liquido isotropo in funzione della temperatura e della composizione della miscela.

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Резюме Исследуются фазовые переходы в бинарных смесях олеата холестерила (CO) и холестерола (CH) с помощью дифракции рентгеновских лучей, дифференциальной сканирующей калориметрии и оптической микроскопии. Получаются при нагревании фазовые диаграммы, вклюьающие переходы твердое тело-твердое тело и твердое тело-изотропная жидкость, а при охлаждении фазовая диаграмма, включающая холестерическую и смектическую мезофазы. В частности, наблюдается сильные эффект сверхохлаждения дия жидкого холестерола и постепенное уменьшение температур фазовых переходов изотропная жидкость-холестерик и холестерик-смектик. Кроме того, определяются структурные модификации, индуцированные в фазе смектикаА и в фазе холестерика наличием CH и CO. В эаключение, исследуется эависимость расстояния между молекулами в фазе изотропной жидкости, как функция температуры и состава смеси.

     

Terpenoids Derived from Linalyl Oxide. Part 3. The isolation,structure, absolute configuration and synthesis of the davanafurans,nor-sesquiterpenes isolated from Artemisia Pallens

The novel nor-sesquiterpenoids, the davanafurans, have been isolated from the oil of Artemisia pallens, the principal component being the cis, threo-isomer ( 1a ). The absolute configuration of this isomer, and the relative stereochemistry of the other isomers, have been established by synthesis from linalool oxides of known configuration.     

The [2,3] Sigmatropic Reaction of Acetonyl Allyl Ethers,a new method for preparing certain 2-hydroxyketones

A new [2] [3] sigmatropic rearrangement is described, enabling the conversion of acetonyl allyl ethers to 3-hydroxy-5-en-2-ones.     

Effects of cholesterol and azelaic acid in lecithin liposomes exposed to ELF fields: A thermodynamic and structural study

Summary In the present work some thermodynamic and structural aspects of electric-, magnetic- and electromagnetic-field interaction at 50 Hz with lecithin liposomes mixed with azelaic acid or cholesterol have been investigated by using differential scanning calorimetry and X-ray diffraction. Calorimetric scans and X-ray diffraction patterns show that no significant modifications of the two mixtures occur, except a little increase of the freezing temperature of the free water after exposure to electromagnetic field.