Single-gas and mixed-gas permeation of N2/CH4 in thermally-rearranged TR-PBO membranes and their 6FDA-bisAPAF polyimide precursor studied by molecular dynamics simulations.

High-performance polymers with polybenzoxazole (PBO) structures, formed via thermal rearrangement (TR) of aromatic polyimide precursors, have been developed for gas separation applications. The present work compares the transport of N2 and CH4 in a 6FDA-bisAPAF polyimide precursor and in its TR-PBO derivative using molecular dynamics (MD) simulations. The modelling closely mimicked the experimental approach by transforming a 6FDA-bisAPAF atomistic model into its corresponding TR-PBO structure via a specific algorithm. The densities and void spaces of both precursor and TR polymers were found to compare well to experimental data. An iterative technique was used to obtain the single-gas sorption isotherms of N2 and CH4 at 338.5 K in both polymers over a range of feed pressures up to and exceeding 65 bar. CH4 was systematically found to be more soluble than N2. Solubilities in both matrices were quite similar with those in TR-PBO being slightly higher due to its larger fraction of significant volume. Volume dilation analyses confirmed a higher resistance to plasticization for TR-PBO. Extended single-gas N2 and CH4 simulations and 2 : 1 binary CH4/N2 mixed-gas simulations were then conducted in both matrices at 338.5 K and at a pressure of ∼65 bar corresponding to natural gas processing conditions. Mixed-gas sorption was modelled using a modification of the aforementioned iterative method, which fixed the pressure and iterated to convergence the number of molecules of each type of penetrant. The gas diffusion coefficients were estimated using the Trajectory-Extending Kinetic Monte Carlo (TEKMC) procedure. As found experimentally, significantly higher diffusivities and permeabilities were observed in the TR polymer, which led to a slightly lower ideal N2/CH4 permselectivity for TR-PBO (∼2.6) when compared to its 6FDA-bisAPAF precursor (∼3.8). However, both models showed a reduced N2/CH4 separation efficiency under 2 : 1 binary CH4/N2 mixed-gas conditions bordering on the loss of selectivity. For 6FDA-bisAPAF, both permeabilities decreased in the mixed-gas case, but more for N2 than for CH4. For TR-PBO, the permeability of the faster N2 decreased while the permeability of the slower CH4 increased under mixed-gas conditions. This confirms that single-gas simulations are not sufficient for the prediction of the actual mixed-gas permselectivity behaviour in such polymers.

A Molecular Dynamics Study of Single-Gas and Mixed-Gas N2 and CH4 Transport in Triptycene-Based Polyimide Membranes.

Fluorinated polyimides incorporated with triptycene units have gained growing attention over the last decade since they present potentially interesting selectivities and a higher free volume with respect to their triptycene-free counterparts. This work examines the transport of single-gas and mixed-gas N2 and CH4 in the triptycene-based 6FDA-BAPT homopolyimide and in a block 15,000 g mol-1/15,000 g mol-1 6FDA-mPDA/BAPT copolyimide by using molecular dynamics (MD) simulations. The void-space analyses reveal that, while the free volume consists of small-to-medium holes in the 6FDA-BAPT homopolyimide, there are more medium-to-large holes in the 6FDA-mPDA/BAPT copolyimide. The single-gas sorption isotherms for N2 and CH4 over the 0-70 bar range at 338.5 K show that both gases are more soluble in the block copolyimide, with a higher affinity for methane. CH4 favours sites with the most favourable energetic interactions, while N2 probes more sites in the matrices. The volume swellings remain limited since neither N2 nor CH4 plasticise penetrants. The transport of a binary-gas 2:1 CH4/N2 mixture is also examined in both polyimides under operating conditions similar to those used in current natural gas processing, i.e., at 65.5 bar and 338.5 K. In the mixed-gas simulations, the solubility selectivities in favour of CH4 are enhanced similarly in both matrices. Although diffusion is higher in 6FDA-BAPT/6FDA-mPDA, the diffusion selectivities are also close. Both triptycene-based polyimides under study favour, to a similar extent, the transport of methane over that of nitrogen under the conditions studied.

Copper transporter 2 content is lower in liver and heart of copper-deficient rats.

Copper (Cu) transporter 2 (Ctr2) is a transmembrane protein that transports Cu across cell membranes and increases cytosolic Cu levels. Experiments using cell lines have suggested that Ctr2 expression is regulated by Cu status. The importance of changes in Ctr2 expression is underscored by recent studies demonstrating that lower Ctr2 content in cells increases the cellular uptake of platinum-containing cancer drugs and toxicity to the drugs. In this study, we examined whether Ctr2 expression is altered by a nutritional Cu deficiency in vivo. Ctr2 mRNA and protein in liver and heart from rats fed a normal (Cu-N), moderately deficient (Cu-M) or deficient (Cu-D) Cu diet was measured. Rats fed the Cu-deficient diets showed a dose-dependent decrease in liver Ctr2 protein compared to Cu-N rats. Ctr2 protein was 42% and 85% lower in Cu-M and Cu-D rats, respectively. Liver Ctr2 mRNA was 50% lower in Cu-D rats and unaffected in Cu-M rats. In heart, Ctr2 protein was only lower in Cu-D rats (46% lower). These data show that Cu deficiency decreases Ctr2 content in vivo.

[Edema and protein-losing enteropathy complicating chronic constrictive pericarditis associated with an ascending aortic aneurysm]. / Oedèmes et entéropathie exsudative compliquant une péricardite chronique constrictive associée à un anévrisme de l'aorte ascendante.

INTRODUCTION: Chronic constrictive pericarditis is suspected on clinical and echocardiographic grounds. Its treatment is surgical. CASE: We report here the case of a 45-year-old man, admitted for edema characteristic of lymphatic obstruction. Examination revealed ascending aorta ectasia, associated with chronic constrictive pericarditis. Measurement of alpha-1 antitrypsin clearance confirmed protein-losing enteropathy. Total recovery followed pericardectomy and aneurysm resection. DISCUSSION: The clinical edema in this case was due to several phenomena: protein-losing enteropathy from a functional lymphatic overload, induced by chronic constrictive pericarditis and by compression of the right atrium and vena cava by an aortic aneurysm. The hypoalbuminemia induced by protein loss may also magnify edema. An association between chronic constrictive pericarditis and ascending aortic aneurysm is uncommon. No cause for this association was found.

Comparison of operator radiation exposure with optimized radiation protection devices during coronary angiograms and ad hoc percutaneous coronary interventions by radial and femoral routes.

AIMS: Although underestimated by interventional cardiologists for a long time, radiation exposure of operators and patients is currently a major concern. The objective of the present operator-blinded registry was to compare related-peripheral arterial route radiation exposure of operators. METHODS AND RESULTS: During 420 consecutive coronary angiograms (CAs) and percutaneous coronary interventions (PCIs), four interventional cardiologists were blindly screened. Radiation exposures were assessed using electronic personal dosimeters. Protection of operator was ensured using a lead apron, low leaded flaps, and leaded glass. Radiation exposure of operators was significantly higher using the radial route when compared with the femoral route for both CAs and CAs followed by ad hoc PCIs: 29.0 [1.0-195.0] microSv vs. 13.0 [1.0-164.0] microSv; P < 0.0001 and 69.5 [4.0-531.0] microSv vs. 41.0 [2.0-360.0] microSv; P = 0.018, respectively. Similarly, radiation exposure of patients was significantly higher using the radial route when compared with the femoral route for both CAs and CAs followed by ad hoc PCIs. Moreover, procedural durations and fluoroscopy times were significantly higher throughout the radial route. CONCLUSIONS: Although the radial route decreases peripheral arterial complication rates, increased radiation exposure of operators despite extensive use of specific protection devices is currently a growing problem for the interventional cardiologist health. Radial route indication should be promptly reconsidered in the light of the present findings.