Gas and vapor transport properties of amorphous perfluorinated copolymer membranes based on 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole/tetrafluoroethylene

Teflon AF 2400 (Du Pont) is an amorphous, glassy perfluorinated copolymer containing 87 mol% 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole and 13 mol% tetrafluoroethylene. The polymer has an extremely high fractional free volume of 0.327. Permeability coefficients for helium, hydrogen, carbon dioxide, oxygen, nitrogen, methane, ethane, propane, and chlorodifluoromethane (Freon 22) were determined at temperatures from 25 to 60°C and pressures from 20 to 120 psig. Permeation properties were also determined at a feed pressure of 200 psig at 25°C with a 2 mol% n-butane/98 mol% methane mixture. Permeabilities of permanent gases in Teflon AF 2400 are among the highest of all known polymers; the oxygen permeability coefficient at 25°C is 1600 × 10⁻¹⁰ cm³ (STP) cm/cm² s cmHg and the nitrogen permeability coefficient is 780 × 10⁻¹⁰ cm³ (STP) cm/cm² s cmHg. The permeabilities of organic vapors increase up to 20-fold as the vapor activity increases from 0.1 to unity, indicating that Teflon AF 2400 is easily plasticized. Although Teflon AF 2400 is an ultrahigh-free-volume polymer like poly(1-trimethylsilyl-1-propyne) [PTMSP], their gas permeation properties differ significantly. Teflon AF 2400 shows gas transport behavior similar to that of conventional, low-free-volume glassy polymers. PTMSP, on the other hand, acts more like a nanoporous carbon than a conventional glassy polymer.     

An experimental approach for direct observation of the interaction of polyanions with sphingosine-containing giant vesicles

A new approach for direct optical microscopy observation of polyanion interactions with bilayers of giant cationic liposomes (GUVs) was suggested. Polyanions as DNA, dextran sulfate (DS), heparin (H) and polyacrylic acids (PA) were locally delivered by a micropipette to a part of a giant unilamellar vesicle membrane. The phenomena were directly observed under optical microscope. GUVs, about 100 micro m in diameter, formed of phosphatidylcholines and up to 33 mol% of the natural bioactive cationic amphiphile sphingosine (Sph), were prepared by electroformation. The effects of water-soluble molecules with high negative linear charge density as dextran sulfate (DS), heparin (H) polyacrylic acids (PA) and adenosine-5'-triphosphoric acid (ATP) were compared with those of DNAs. The resulting membrane topology transformations were monitored in phase contrast, while the DNA distribution was followed in fluorescence. DNA-induced endocytosis-like membrane morphology transformation due to the DNA/lipid membrane local interactions was observed. The DS, H and PA induced membrane topology transformations similar to those of the DNAs, while ATP did not cause any detectable ones. The endocytosis mechanism involves the formation of ordered domains in the GUV membrane where some surface and charge asymmetries between the two membrane monolayers were created. The sizes of created polyanionic/cationic membrane domains depend on the form, length and elasticity of the adsorbed highly charged molecules. Endosome-including capacities of polyanionic molecules depend heavily on the high linear negative charge at a certain length.An original method for direct studying of the DNA/membrane interactions in autoadaptable giant liposome system imitating biological membrane interactions was forwarded. The model observations could also help for understanding events associated with cationic liposome/DNA complex formation in gene transfer processes.     

Kinetic spectrophotometric method for the determination of urinary cobalt based on its catalytic effect on the oxidation of -adrenaline hydrochloride by hydrogen peroxide

A catalytic for determination of nanomolar concentrations of Co(II), i.e., oxidation of -adrenaline hydrochloride with H₂O² in alkaline medium, is proposed. The reaction gives a low limit of detection of 2.5 × 10 ⁻⁹ M Co(II) in the reaction mixture, good reproducibility with a relative standard deviation (R.S.D.) of 4−5% in the Co(II) concentration range 8.0 × 10⁻⁹−8.0 × 10⁻⁸M and good selectivity. On the basis of this indicator reaction, a catalytic-spectrophotometric method for the determination of cobalt in small urine samples (5.00 ml) was elaborated. The analysis of 17 urine samples, taken from healthy persons of different ages, gave cobalt concentrations in the range 0.20–1.50 μmol 1⁻¹. The R.S.D. for ten replicate analyses of a urine sample with an average cobalt content of 0.63 μmol 1⁻¹ was 5.6%. The reliability of the method was verified by a comparative photometric method (r = 0.9755) and by a determination based on known additions of cobalt (r = 0.9894).     

Crystallographic and IR spectral study ofcis-bis(creatinine-N)dinitro platinum(II)

Acis-Pt(creat)₂(NO₂)₂ complex was synthesized stereoselectively in a high yield (65%) and characterized by IR spectral and X-ray diffraction analysis. Crystal data: Pt(C₄H₇N₃O)₂(NO₂)₂,M _r=767.55, monoclinic, space groupP2₁/n,a=9.736(1),b=13.433(1),c=12.098(1) Å,=110.55(1)°,V _c=1482(1) ų,Z=2,D _x=3.441 g cm^–3,(MoK)=0.71073 Å,=97.0 cm^–1,F(000)=1504,T=292 K,R=0.026 andR _w=0.028 for 2061 observed reflections with I>2(I). The structure consists of Pt(creat)₂(NO₂)₂ molecules disposed in general positions and joined by N-HO and N-HN hydrogen bonds. The platinum atom has square-planar PtN₄ coordination of twocis disposed pairs of nitro [Pt-N_av 2.023(7) Å] and creatinine [Pt-N(endo)_av 1.991(8) Å] ligands. The creatinine moieties are planar and tilted to the equatorial plane by ~80°.     

Polyoxygenated ketopinic-acid-derived γ-amino alcohols in the enantioselective diethylzinc addition to benzaldehyde

Three N,N-dialkylated γ-amino alcohols, specifically 10-(dialkylamino)isoborneols, with different grades of oxygenation in the nitrogen’s alkyl groups (alkoxyalkyl groups), have been obtained from commercial (+)-ketopinic acid and tested as chiral ligands for the enantioselective addition of diethylzinc to benzaldehyde, in order to evaluate the effect of polyoxygenation on the ligand’s catalytic activity. An interesting effect of the oxygen atoms on the ligand activity is observed. The observation is in agreement with two unique previous results on amino-acid-derived polyoxygenated β-amino alcohols. A noticeable dependence of the observed effect with the conformational flexibility of the polyoxygenated chains is also demonstrated. The effect is explained by a pincer role of the polyoxygenated dialkylamino moiety, activating and directing a diethylzinc molecule.     

1:1 complexes of 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine with manganese(II) and copper(II) hexafluoroacetonylacetonate

Mn(hfac)2 and Cu(hfac)2 form 1:1 complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine that exhibit strong metal-nitroxide exchange; spin polarization models do not explain the antiferromagnetic exchange behavior between spin sites in these complexes.     

Phase-space transport of stochastic chaos in population dynamics of virus spread

A general way to classify stochastic chaos is presented and applied to population dynamics models. A stochastic dynamical theory is used to develop an algorithmic tool to measure the transport across basin boundaries and predict the most probable regions of transport created by noise. The results of this tool are illustrated on a model of virus spread in a large population, where transport regions reveal how noise completes the necessary manifold intersections for the creation of emerging stochastic chaos.