Hexafluoroethane Research Articles

Anesthetic and non-anesthetic effects on interfacial lipids around an ion channel

All atom molecular dynamics simulations were used to investigate the anesthetic and non-anesthetic effects on the dynamics of bulk and the interfacial dimyristoylphosphatidylcholine lipids surrounding a gramicidin-A (gA) channel. Two pairs of simulations in the presence and absence of halothane and of hexafluoroethane (HFE) were carried out for 2.2 and 8 ns, respectively. The order parameters, determined from the asymptotes of the autocorrelations of the vector between the nitrogen and the immediate methylene carbon of the choline head group and the Ci−1–Ci+1 vectors for the ith carbon (Ci) in the lipid chains, show that the head groups are less ordered in the interfacial lipids than in the bulk lipids, and that neither halothane nor HFE at 5 mol% concentration has significant effects on the ordering of the interfacial or bulk lipid chains. Because halothane and HFE produce distinctly different effects on the global dynamics of gA channel, it is unlikely that anesthetic effects on gA are indirectly mediated through the lipids.

Molecular Dynamics Simulations of C2F6 Effects on Gramicidin A: Implications of the Mechanisms of General Anesthesia

It was recently postulated that the effects of general anesthetics on protein global dynamics might underlie a unitary molecular mechanism of general anesthesia. To verify that the specific dynamics effects caused by general anesthetics were not shared by nonanesthetic molecules, two parallel 8-ns all-atom molecular dynamics simulations were performed on a gramicidin A (gA) channel in a fully hydrated dimyristoylphosphatidylcholine membrane in the presence and absence of hexafluoroethane (HFE), which structurally resembles the potent anesthetic molecule halothane but produces no anesthesia. Similar to halothane, HFE had no measurable effects on the gA channel structure. In contrast to halothane, HFE produced no significant changes in the gA channel dynamics. The difference between halothane and HFE on channel dynamics can be attributed to their distinctly different distributions within the lipid bilayer and consequently to the different interactions of the anesthetic and the nonanesthetic molecules with the channel-anchoring tryptophan residues. The study further supports the notion that anesthetic-induced changes in protein global dynamics may play an important role in mediating anesthetic actions on proteins.

Influence of Anesthetic and Nonimmobilizer Molecules on the Physical Properties of a Polyunsaturated Lipid Bilayer

We use molecular dynamics simulations to investigate the effects of halothane, a volatile anesthetic, and hexafluoroethane (HFE), its nonimmobilizer analogue, on the physical properties of a fully hydrated polyunsaturated (1-stearoyl- 2-docosahexaenoyl-sn-glycero-3-phosphocholine) lipid bilayer in the liquid crystalline fluid lamellar phase, L R. In addition, we discuss the results obtained comparing them to previous studies on saturated lipid bilayers with the same solutes. At the analyzed concentration (25% mole fraction), the halothane molecules are located preferentially near the upper part of the lipid acyl chains, while the HFE molecules prefer the hydrocarbon chains and methyl trough region. In the case of halothane in the polyunsaturated lipid bilayer, there is an additional density maximum at the membrane center not observed in saturated lipids. The subtle effect of the solutes on the structural properties of the highly unsaturated lipid bilayer and the properties of the membrane interior is somewhat different from that observed for saturated lipids. Here, these differences are interpreted in terms of the unique properties of the polyunsaturated lipid bilayers. The effect of anesthetic molecules on the electrostatic properties of the membrane interface is similar for saturated and polyunsaturated lipid bilayers and is characterized by a change in the most probable orientation of the lipid headgroup dipoles, which point toward the membrane interior for halothane and are basically unchanged for HFE, i.e., point toward the water phase. The different distributions of anesthetic and nonimmobilizer molecules within the lipid bilayer systems seem to be a generic feature in simple models of biological membranes and are similar to those observed in systems with saturated lipids. Since polyunsaturated and other unsaturated lipids are ubiquitous in cell membranes, it is plausible to generalize these features to the more complex biological membranes.

Capillary condensation of hexafluoroethane in an ordered mesoporous silica

A total of 43 adsorption isotherms are reported for hexafluoroethane (HFE) on an ordered mesoporous silica (MCM-41) at 2 K intervals for temperatures from 196 K to 280 K. All isotherms are reversible and, at lower temperatures, exhibit the abrupt step characteristic of capillary condensation in such adsorbents, but at higher temperatures both the extent and slope of the step decrease. The step is absent at temperatures greater than 255 K, here interpreted as the capillary critical temperature for first-order capillary condensation. Equations describing the capillary coexistence boundary and the rectilinear diameter are presented. Pore radii and pore volumes calculated from the isotherms are consistent with the assumption that capillary condensed HFE has essentially the same surface tension and density as bulk liquid over the entire temperature range. We conclude that capillary condensation at T > 255 K occurs by a second-order process.

Adhesion of the plasma polymer of trimethylsilane to aluminum alloys

AbstractThe adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrates depends on the cleanliness of the substrate surface and the state of oxides on the aluminum alloy surface. Both factors are dependent on what type of alloy is used, and consequently, the best preparation of the substrate surface differs on the type of aluminum alloy. Oxygen plasma treatment is effective for the elimination of organic surface contamination, but plasma treatment, such as that of mixed argon and hydrogen, cannot be used to modify the surface state of oxides on these alloys. This is because oxides of aluminum are stable and thus resist plasma modification, and prolonged plasma treatment has been observed to change concentrations of alloy components at the surface due to the heating of the alloy. Chemical cleaning of the surface is necessary before the application of the plasma polymer used for corrosion protection enhancement. Once the surface was properly prepared, a plasma polymer of trimethylsilane (TMS), prepared by cathodic polymerization, adhered well to aluminum alloys investigated in this study. Major adhesive failure, however, occurred as a consequence of reactor contamination when hexafluoroethane (HFE) plasma treatment of initially formed TMS plasma polymers was employed. Plasma pretreatment of the substrate with O2 or postplasma treatment of the plasma polymer of TMS with Ar (instead of HFE) was effective in eliminating the surface‐contamination effect on the adhesion. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1387–1398, 2002

Effects of wall contamination on consecutive plasma processes

Plasma processes often go beyond the primary objectives focused on the substrate, or targeted materials. For instance, sputtered materials deposit on surfaces other than the substrate, and plasma deposition extends to the walls of the reactor. In the process of plasma polymerization, or plasma chemical vapor deposition (PCVD), every surface (not just the substrate surface) participates in the overall plasma deposition process. Consequently the chemical and physical natures of all surfaces within a reactor are very important factors that determine the fate of the PCVD process. The materials deposited on the wall surface (wall contaminants) are created in the previous run in a batch operation of PCVD. In a sequential plasma process, where plasma polymerization of trimethylsilane (TMS) was followed by plasma polymerization of hexafluoroethane (HFE), F-containing oligomers (low molecular weight compounds), created during the plasma polymerization of HFE in the previous run, remain on surfaces in the reactor. The wall contaminants were found to migrate to the new substrate (aluminum alloy) surface in the subsequent run upon the evacuation of the reactor. If an O2 plasma treatment is applied, F-containing organic compounds chemisorbed on the new substrate surface are converted to F-containing inorganic compounds, which decreases the plasma-ablatable F on the surface. If no O2 plasma treatment is applied, the F-containing organic compounds are exposed to the environment of the TMS plasma. From the viewpoint of the sequence of plasma processes, a new HFE/TMS sequence is created without the O2 plasma treatment. The HFE/TMS system (reversed order to the normal cycle) causes adhesion failure at the interface between the plasma polymers and the aluminum alloys, whereas the TMS/HFE system yields good adhesion of plasma deposited layers to the substrate and provides superior adhesion of a primer applied on the plasma polymer coating. This difference was created by the difference in handling of the wall contaminants.

ESR Study of Trimethylsilane Plasma Polymer Part II; Effect of Consecutive Treatments and Mixed Gases

An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethylsilane (TMS) monomer gas has the ability to modify the characteristics of the primary plasma polymer significantly in a favorable manner for many applications. The effect of the second plasma polymerization on the primary plasma polymer of TMS depends on the nature of the second monomer. Plasma of F-containing monomer, hexafluoroethane (HFE) and perfluoromethane (CF4), decreases the ESR signal of TMS and no detectable signal due to F-containing monomer was found. The decay rate of the signal decreased significantly. In contrast to this situation, CH4 plasma treatment yields an ESR signal that is a composite of that observed from TMS and CH4 films individually. The overall signal increased in this instance, but didn't show appreciable decay in 24 hr period. A second treatment by nonpolymer forming plasmas also decreased the ESR signal of TMS, and decreased the decay rate, indicating that the second gas plasma treatment yields a somewhat similar effect found with the HFE plasma treatment. Plasma polymerization of mixtures of TMS and nonpolymer-forming gases increased the ESR signal but decreased the decay rate, except in the case of oxygen. A mixture of (TMS + O2) behaved as a completely different monomer. No ESR signal was found in this system. The ESR analysis was supported by XPS data and an insight into the mechanisms occurring in these thin films are discussed.

Model Study Investigating the Role of Interfacial Factors in Electrochemical Impedance Spectroscopy Measurements

Abstract To observe the effect of interfacial factors on electrochemical impedance spectroscopy (EIS), model systems consisting of Parylene C (PC) film coated on Alclad 7075-T6 (UNS A97075) sheets and freestanding PC films were investigated. To modify the top surface of PC coating, the coating on Al alloy panels were treated with two plasmas: trimethylsilane (TMS) and a mixture of TMS + O2. Plasma polymerization of TMS followed by hexafluoroethane (HFE) also was applied to the substrate surface prior to the deposition of PC film to improve the adhesion of the film to the surface. Coating performance was evaluated using EIS, and interfacial factors produced by plasma treatments were studied by applying suitable equivalent circuit models, which take into account all the interfacial parameters and bulk coating. Simulations performed with circuit models proposed in this work indicated that top surface modification with plasma treatment influenced the salt intrusion property of the top layer as well as of the ...

Selective adsorption of fluorocarbons and its effects on the adhesion of plasma polymer protective coatings

Cathodic DC plasma deposited films have shown promise as intermediate adhesion and barrier layers for use in the interface engineering of corrosion protection systems on various materials. The surface treatment of plasma deposited trimethylsilane (TMS) films with various post-deposition plasma treatments can improve the adhesion of various paints to these films, which are usually strongly adhered to underlying substrates. Research into the application of these systems for corrosion protection of aluminum alloys included post-deposition treatments of the TMS films with hexafluoroethane (HFE) plasmas, which was seen to significantly improve the adhesion of primers. Oxygen plasma cleaning of the alloy surfaces, prior to deposition of the TMS film, is normally employed to remove organic contaminants. During testing of sample aluminum panels, one batch was processed without the oxygen plasma treatment and exhibited extensive adhesion failures. The investigation of these results shows that low levels of fluorocarbon contaminants readily react with the alloy surface and deposit a fluorine containing carbonaceous layer, which dramatically interferes with the adhesion of the plasma polymer to the alloys, but the adhesion with primer coatings remains tenacious. X-ray photoelectron spectroscopy (XPS) studies also show that the presence of even low levels of these contaminants in the chamber, during the oxygen cleaning process, is sufficient to induce the conversion of the surface from oxide to a mixture of oxide and fluoride. This conversion is considered detrimental to the corrosion resistance of these systems.

Surface and Corrosion Characteristics of a-C:H/Fluorocarbon Films

Fluorocarbon films were deposited on type 301 stainless steel substrates from mixtures of hexafluoroethane (HFE) or hexafluoroacetone (HFA) and acetylene and argon in a radio-frequency (13.56 MHz) plasma discharge. A 10 nm thick polysilicon interlayer was deposited prior to fluorocarbon film deposition to obtain good adhesion. To prevent film failure. a-C:H layer was deposited on the polysilicon layer prior to fluorocarbon film deposition, resulting in a-C:H/fluorocarbon composite film structures. The influence of the feed gas composition on the properties of the layered structure was investigated. Surface energies of the films were calculated from the film contact angle values obtained with water and diiodomethane. The composition of the surface layer of these films was characterized using X-ray photoelectron spectroscopy (XPS). The resistance offered by these a-C:H/fluorocarbon film structures to anodic breakdown in an electrolyte containing 0.1 M NaCl and 0.1 M Na2SO4 was studied using a potentiostatic technique. The anodic current density for the coated type 301 stainless steel samples was at least 3 orders of magnitude smaller than that for the bare sample and more than an order of magnitude smaller than that observed with samples coated with only the (equally thick) a-C:H layer. The resistance offered by the layered coatings to solution penetration increased with increasing fluorine content in the films.

Surface and bulk compositional characterization of plasma-polymerized fluorocarbons prepared from hexafluoroethane and acetylene or butadiene reactant gases

The surface tension and surface and bulk composition of plasma-polymerized fluorocarbon films (PPFCs) prepared from hexafluoroethane (HFE) and either acetylene or butadiene reactant gases were determined. Increasing the HFE reactant gas content from 0 to 100% gave an increase in the amount of fluorine incorporated in the films and a shift to incorporation of more highly fluorinated species at the film surface, according to X-ray photoelectron spectroscopy (XPS) data. Hydrogen levels in the films were determined by forward recoil spectrometry (FRS) and were shown to be inversely dependent on HFE concentration in the reactant gas feed and dependent on hydrocarbon co-reactant type. The compositional changes were mirrored by changes in the surface tension from 52 to 20 mN/m. XPS and surface tension results demonstrated that fluorine incorporation at the surface of the PPFCs is significantly reduced when butadiene, rather than acetylene, is used as a co-reactant gas with HFE. The differences are attributed to higher concentrations of hydrogen, which acts as a scavenger for reactive fluorine atoms and as an inhibitor in the CFx → CFx+1 reaction, and of carbon, decreasing the F/C ratio, when butadiene is used as the hydrocarbon source. Furthermore, potential changes in surface composition due to energetic ion bombardment are discussed. Three factors were suggested as strongly influencing the composition and the properties of the PPFCs: 1) the energy input into the plasma polymerization reaction, 2) the amount and type of fluorine scavenging reagent introduced with the HFE, and 3) the elemental composition of the reactant gases. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 409–421, 1997