Experimental and theoretical study on propylene absorption by using PVDF hollow fiber membrane contactors with various membrane structures

Five kinds of asymmetric poly(vinylidene fluoride) (PVDF) hollow fiber membranes with considerable different porosities at the inner and outer surfaces of the membrane were prepared via thermally induced phase separation (TIPS) method and applied for propylene absorption as gas–liquid membrane contactors. A commercial microporous poly(tetrafluoroethylene) (PTFE) hollow fiber membrane was also used as a highly hydrophobic membrane. Experiments on the absorption of pure propylene into silver nitrate solutions were performed and the effects of membrane structure, inner diameter, silver nitrate concentration and absorbent liquid flow rate were investigated at 298 K. PVDF membranes prepared by using nitrogen as bore fluid had lower inner surface porosity than the membranes prepared with solvent as bore fluid. Except the membrane with a skin layer at the outer surface, propylene absorption flux was inversely proportional to the inner diameter of the hollow fiber membrane, and propylene absorption rate per fiber was almost the same. Propylene flux increased with increasing the silver nitrate concentration and also with increasing the absorbent flow rate.A mathematical model for pure propylene absorption in a membrane contactor, which assumes that the membrane resistance is negligibly small and the total membrane area is effective for gas absorption, was proposed to simulate propylene absorption rates. Experimental results were satisfactorily simulated by the model except for the membrane having a skin layer. The model also suggested that propylene is absorbed in silver nitrate solutions accompanied by the instantaneous reversible reaction. This paper may be the first experimental and theoretical study on propylene absorption in membrane contactors.     

In situ structural analysis of crystalline Fe-Mo-C nanoparticle catalysts during the growth of carbon nanotubes

We show that image simulation is invaluable for the interpretation of time-dependent environmental transmission electron microscopy (ETEM) images. Experimental ETEM images of a crystalline nanoparticle catalyst (NPC) during the growth of carbon nanotubes were compared with simulated images of the Fe(21)Mo(2)C(6) structure that was observed along various directions. Lattice images that appear in the NPC at different times can be accounted for by considering only the Fe(21)Mo(2)C(6) structure.     

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy**

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C−H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.     

Conformational features and chemical behavior of 5H, 7H-dibenzo[B,g][1,5] dithiocin oxides: 1,5-Oxygen shift via a dithiodication intermediate

Some 5H,7H-dibenzo[b,g][1,5]dithiocin oxides ( 4–8 ) and their related compounds 9–13 were prepared and the assignment of the most favorable conformation was carried out on the basis of the characteristic ¹H NMR spectral data. Only a single conformer (BC: boatchair form) exists for 4 , 5 , and 8–13 , while two conformers (BC and TB: twist-boat form) are apparent for 6 and 7 . Oxidation and methylation of 4 gave exclusively a single geometrical isomer ( 8 and 13 , respectively). These results are interpreted as a sterically preferential attack of electrophiles on the BC conformer of the starting material. A 1,5-oxygen shift of 4 occurred smoothly to give 6 in the presence of trifluoroacetic acid in CDCl₃ solution. The mechanistic investigation is described briefly. Differences in chemical behavior between dibenzodithiocin 12-oxide 4 and dibenzothiazocine 12-oxide 2 are also discussed on the basis of the conformational features.     

Novel results obtained by freezing berry pseudorotation of phosphoranes (10‐P‐5)

By freezing Berry pseudorotation of spirophosphoranes with recourse to the rigidity of the Martin bidentate ligand, we successfully prepared configurationally stable enantiomeric pairs of optically active phosphoranes, and could isolate “anti‐apicophilic” C‐apical O‐equatorial (O‐cis) phosphoranes. The effect of σ*_{P O} orbital of the O‐cis phosphorane was investigated both experimentally and theoretically. O‐cis phosphoranes were revealed to be much more electrophilic at the phosphorus atom than O‐trans isomers by experimental studies. The acidity of the α‐proton of an O‐cis benzylphosphorane was found to be higher than that of the corresponding O‐trans isomer. By the reaction of the α‐carbanion of an O‐cis benzylphosphorane with PhCHO, we succeeded in the first isolation and full structural characterization of a 12‐P‐6 phosphate bearing an oxaphosphetane ring, the intermediate in the Wittig type reaction using a 10‐P‐5 phosphorane. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:390–396, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10072