gamma-Butyrolactone, unlike delta-valerolactone, does not polymerize despite a strain energy of approximately 8 kcal mol-1 which could be relieved by opening the s-cis lactone ester bond to an s-trans ester bond in the polymer. To explain this anomaly, we have applied quantum mechanical methods to study the thermochemistry involved in the ring-opening reactions of gamma-butyrolactone and delta-valerolactone, the conformational preferences of model molecules that mimic their corresponding homopolyesters, and the variation of enthalpy associated to the polymerizability of such two cyclic lactones. The overall results indicate that the lack of polymerizability of gamma-butyrolactone should be attributed to the low strain of the ring, which shows much less geometric distortion in the ester group than delta-valerolactone, and the notable stability of the coiled conformations found in model compounds of poly-4-hydroxybutyrate.

Polymerization of Cyclic Esters, TJrethans, Ureas and Imides 6409 became very viscous or solidified. The tube was then cooled and broken open and the polymer was washed thoroughly with warm water and acetone and dried. The polymerization results are summarized in Table I.Poly-Y-butyramide from 2-Pyrrolidinone.-In an experiment without cocatalyst, sodium hydride, 0.10 g., was dissolved in 10.0 g. of anhydrous 2-pyrrolidinone with evolution of hydrogen. The resulting solution slowly became turbid. After being kept at room temperature overnight, it gave an 8% yield of poly-Y-butyramide, ijinh 0.20 in m-cresol.The polymerization was accelerated strongly by the addition of cocatalysts (0.08-0.25 M) including N-acyl lactams, acyl halides, acid anhydrides, isocyanates, isothiocyanates, esters or dimethylcvanamide.12 Other effective substances were nitriles, aromatic nitro compounds (purple color), fluorene, dialkyl amides, and polyhalo aliphatics. Compounds without effect included aromatics, halo aromatics, various salts, amides, lactams, ketones, ethers, sulfones, sulfoxides and amines. Inhibitors at these concentrations included acidic materials like alcohols or phenols. At high concentrations, the "indifferent" materials inhibited polymerization.In a typical case of cocatalysis, acetic anhydride, 0.10 g., was added to a solution of 0.13 g. of NaH in 6.5 g. of pvrrolidinone. An exothermic reaction ensued, leading to the rapid formation of a hard white plug of polymer. This was broken into small pieces and extracted with water and acetone to give 5.7 g. of poly-y-butyramide, 0.88 in mcresol. Yields never exceeded 75-85% in such experiments, presumably because residual monomer became embedded in a matrix of polymer at these conversions.Trapping Anionic Intermediate with Methyl /'-Toluenesulfonate.-Sodium hydride, 0.75 g., was dissolved in 50 ml. of anhydrous pyrrolidone. With cooling, was added 5.0 g. of methyl p-toluenesulfonate, resulting in the precipitation of sodium p-toluenesulfonate. After 30 minutes, the mixture was distilled in a spinning band column. With a pot temperature of 150°, no distillation occurred, showing that no pyrrolidine or N-methylpyrrolidi'«e had formed. Vacuum distillation gave 2.21 g. (71.3%) of N-methylpyr-roYidone, ra27•5D 1.4679 (authentic material m27•5d 1.4676)'. This result is consistent with the view that the anion present is always that of pyrrolidone.Poly-e-caproamide from 2-Oxohexamethylenimine.-2-Oxohexamethylenimine, 25.0 g., and sodium hydride, 0.60 g., were placed in a polymer tube which was evacuated and filled with nitrogen several times. The lactam then was melted and the sodium hydride dissolved with evolution of hydrogen. N-Acetylcaprolactam, 0.33 g., was added. The tube was shaken thoroughly and placed in a 139°vapor bath. The contents solidified quickly. After 30 minutes, the tube was cooled, and opened. The polymer was ground up, extracted with hot water, and dried to give 18.9 g. (74.7%) of polymer, 7?rei 26.77 in formic acid. Other similar runs gave polymer in up to 80...

Black lipid membranes (BLMs) are widely used for recording the activity of incorporated ion channel proteins. However, BLMs are inherently unstable structures that typically rupture within a few hours after formation. Here, stabilized BLMs were formed using the polymerizable lipid bis-dienoyl phosphatidylcholine (bis-DenPC) on glass pipettes of ∼10 μm (I.D.). After polymerization, these BLMs maintained steady conductance values for several weeks, as compared to a few hours for unpolymerized membranes. The activity of an ion channel, α-hemolysin, incorporated into bis-DenPC BLMs prior to polymerization, was maintained for 1 week after BLM formation and polymerization. These lifetimes are a substantial improvement over those achievable with conventional BLM technologies. Polymerized BLMs containing functional ion channels may represent an enabling technology for development of robust biosensors and drug screening devices.

Suspended planar lipid membranes (or black lipid membranes (BLMs)) are widely used for studying reconstituted ion channels, although they lack the chemical and mechanical stability needed for incorporation into high-throughput biosensors and biochips. Lipid polymerization enhances BLM stability but is incompatible with ion channel function when membrane fluidity is required. Here we demonstrate the preparation of a highly stable BLM that retains significant fluidity by using a mixture of polymerizable and nonpolymerizable phospholipids. Alamethicin, a voltage-gated peptide channel for which membrane fluidity is required for activity, was reconstituted into mixed BLMs prepared using bis-dienoyl phosphatidylcholine (bis-DenPC) and diphytanoyl phosphatidylcholine (DPhPC)). Polymerization yielded BLMs that retain the fluidity required for alamethicin activity yet are stable for several days as compared to a few hours prior to polymerization. Thus these polymerized, binary composition BLMs feature both fluidity and long-term stability.