Ion implant-induced change in polyimide films monitored by variable energy positron annihilation spectroscopy

6FDA-pMDA polyimide membranes were implanted with 140 keV N⁺ ions to fluences between 2 × 10¹⁴ and 5 × 10¹⁵ cm⁻². Variable energy positron annihilation spectra were taken and spectral features compared to previously reported changes in gas permeability and permselectivity of these membranes as a function of ion fluence. Positron data corroborate the explanation of these changes in terms of molecular damage caused by the implant: for fluences up to about 1 × 10¹⁵ cm⁻², the concentration of irradiation-induced defects merely increases with implant fluence; while fluences exceeding this threshold value create a second type of positron annihilation site, thereby marking a distinct change in the structure of the polymer, which is responsible for the vast improvement of gas permselectivity data found at the same threshold fluence. PACS codes: 78.70.Bj—positron annihilation; 61.82.Pv—polymers, organic compounds; 61.72.Ww—doping and impurity implantation. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2413–2421, 1998     

Diffusion in gas separation membrane materials: A comparison and analysis of experimental characterization techniques

Typically, materials with high-performance transport properties such as zeolites, carbon molecular sieves, or hyper rigid polymers are inherently difficult or impossible to characterize by steady-state membrane permeation experiments used for conventional polymers. Diffusion coefficients determined by transient sorption, a measurement easily performed on brittle media, are analyzed here and compared to those determined by steady-state permeation/sorption and transient permeation for a glassy polymer and a carbon molecular sieve. Average and local diffusion coefficients are extrapolated to zero upstream partial pressure to eliminate effects caused by concentration dependence. Good agreement between the techniques was observed for the glassy polymer. On the other hand, carbon molecular sieves, possessing a more complex morphology, exhibit a greater difference in diffusion coefficients determined by the various techniques. Nevertheless, comparison of the analysis techniques is shown to provide potentially valuable insights into the morphological features of such carbon molecular sieves. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1747–1755, 1998     

膜/液界面浓度极化现象的介电解析

对由强、弱荷电膜和溶液构成的膜／液非均匀体系，在10－107Hz频率范围进行了介电测量，在直流偏压下，该体系显示了二个显著的介电弛豫．利用具有电导率分布相，即浓度极化相的介电理论对强行电的离子交换膜的结果进行了介电解析，从实验上测得的介电参数求出了反映膜／液界面浓度极化层构造的参数，讨论了该体系产生介电弛像的原因、说明了介电理论的合理性，并提出了膜／液界面体系产生介电弛豫现象的可能机理．     

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid) (PE-g-AA) and the olefin reversible coordinates with the PE-g-AA–Ag⁺ complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag⁺ ion. Also, the Ag⁺ ion in PE-g-AA-Ag⁺ membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag⁺ (olefin) complex was proposed. The coordination number of Ag⁺ ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag⁺ in the PE-g-AA–Ag⁺ complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA–Ag⁺ complex membranes were studied. The equilibrium, association, and dissociation constants were also presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 909–917, 1997     

在线液膜萃取富集流动注射荧光光度法测定水中痕量苯胺

设计并制造了用作苯胺在线富集的夹板式液膜(SSLM)萃取的流动注射分析装置。磷酸三丁酯用作流动载体,煤油为膜溶剂,试样中苯胺在SSLM萃取单元中得到分离和富集。SSLM萃取体系中pH 3盐酸溶液用作内相,pH 11氢氧化钠溶液用作外相。TBP溶液的适宜浓度为12%,富集时间为10 min,对经富集后pH 11碱性溶液中苯胺所产生荧光的强度进行测定。激发波长eλx为282 nm,发射波长eλm为345 nm,方法的检出限为0.2μg.L-1,苯胺浓度在1~150μg.L-1之间保持线性关系。将此方法用于测定河水中苯胺,根据分析结果算得RSD值均小于5%,回收率在97.6%至100.6%之间。     

Application of combined Monte Carlo and molecular dynamics method to simulation of dipalmitoyl phosphatidylcholine lipid bilayer

We describe a new equilibration procedure for the atomic level simulation of a hydrated lipid bilayer. The procedure consists of alternating molecular dynamics trajectory calculations in a constant surface tension and temperature ensemble with configurational bias Monte Carlo moves to different regions of the configuration space of the bilayer, in a constant volume and temperature ensemble. The procedure is described in detail and is applied to a bilayer of 100 molecules of dipalmitoyl phosphatidylcholine (DPPC) and 3205 water molecules. We find that the hybrid simulation procedure enhances the equilibration of the bilayer as measured by the convergence of the area per molecule and the segmental order parameters, as compared with a simulation using only molecular dynamics (MD). Progress toward equilibration is almost three times as fast in CPU time, compared with a purely MD simulation. Equilibration is complete, as judged by the lack of energy drift in three separate 200-ps runs of continuous MD started from different initial states. Results of the simulation are presented and compared with experimental data and with other recent simulations of DPPC. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1153–1164, 1999     

Simple Ion–Gas Mixtures as a Source of Key Molecules Relevant to Prebiotic Chemistry

Very simple chemistry can result in the rapid and high-yield production of key prebiotic inorganic molecules. The two reactions investigated here involve such simple systems, (a) carbon disulfide (CS₂) and acetate (CH₃COO¯) and (b) sulfur dioxide (SO₂) and formate (HCOO¯). They have been carried out under non-aqueous conditions, either in an organic solvent or with a powdered salt exposed to the requisite gas. Under such dry conditions the first reaction generated the thioacetate anion [CH₃COS]¯ while the second produced the radical [SO₂^·]¯anion. Anhydrous conditions are not rare and may have arisen on the early earth at sites where an interface between different phases (liquid/gas or solid/gas) could be generated. This is one way to rationalize the formation of molecules and ions (such as we have produced) necessary in the prebiotic world. Interpretation of our results provides insight into scenarios consistent with the more prominent theories of abiogenesis.     

Display of Potassium Channel–Blocking Tertiapin‐Q Peptides on Gold Nanoparticles Enhances Depolarization of Cellular Membrane Potential

The use of nanoparticle (NP) systems to control cellular physiology, including membrane potential, can facilitate furthered understanding of many disparate cellular processes ranging from cellular proliferation to tissue regeneration. A gold NP (AuNP) bioconjugate system based on the honeybee venom peptide, tertiapin‐Q (AuNP‐TPN‐Q), that depolarizes membrane potential by targeting inward rectifier potassium channels (Kir), is developed. The conjugate elicits, in a peptide concentration–dependent manner, a greater and more rapid depolarization response compared to the free peptide alone. The specificity of the interaction of the AuNP‐TPN‐Q conjugate with the Kir channel using immunocytochemistry and competition binding assays is confirmed. It is further shown that membrane depolarization is photothermally reversible via the laser‐induced plasmonic heating of the AuNP, providing a level of control over Kir channels not afforded by currently available drugs. The functional nanobioconjugate described herein provides a new research tool for understanding the intricacies of ion channel activity and the modulation of cellular membrane potential.     

Salt effect on bilayer phase transitions of dipalmitoylphosphatidylglycerol in saline water under high pressure

ABSTRACT

The phase transitions of dipalmitoylphosphatidylglycerol (DPPG) bilayer membrane at high NaCl concentrations under high pressure were investigated to construct the temperature–pressure phase diagram and to determine phase-transition properties. The constructed phase diagrams exhibited qualitative resemblance to that of the dipalmitoylphosphatidylcholine (DPPC) bilayer membrane: they showed the gel-phase polymorphism including the pressure-induced bilayer interdigitation. The phase-transition properties of the DPPG bilayer membrane changed in a salt concentration-dependent manner. We discussed the salt effect on the DPPG bilayer membrane from the variation in interactions between the polar head groups of the PG molecules.