Lipase-catalyzed ring-opening bulk polymerizations of ω-pentadecalactone (PDL) were investigated. Screening of selected commercial lipases as catalysts for PDL polymerization at 80 °C was carried out. The results of this work showed that polymerizations catalyzed by lipases PS-30, AK, Lipozyme-IM and Novozym-435 gave % PDL conversions ranging from 80 to 100% for 24 h reactions (M n = 15 000−34 400). Lipase PS-30 both physically immobilized onto Celite-521 (I-PS-30) and in the crude powder or nonimmobilized form (NI-PS-30) was selected for further study. Comparison of % conversion vs time for bulk PDL polymerizations at 70 °C catalyzed by NI- and I-PS-30 showed that for short reaction times, the immobilized catalyst gave % conversions that were more than 10 times greater. In fact, the % monomer conversion to poly(PDL) was nearly quantitative (>98%) for 8 h polymerizations catalyzed by I-PS-30. Furthermore, for reactions conducted at 70 °C with careful removal of water, substantially greater poly(PDL) molecular weights resulted by using I-PS-30 instead of NI-PS-30 as the catalyst. Increasing the % conversion above ∼40% for PDL polymerizations at 70 °C resulted in little or no change in PDL M n. This is consistent with chain polymerizations where the rate of propagation is much faster than initiation. The general trends observed by variation of the I-PS-30 catalyzed bulk PDL polymerization temperature were the following:  (i) increased % conversion and M n by increasing the reaction temperature from 60 to 70 °C and from 60 to 80 °C, respectively, (ii) similar polymerization rates between 70 and 90 °C, and (iii) a decrease in % monomer conversion and M n as the reaction temperature was increased from 90 to 110 °C. It was found that water was an important factor that controls not only the rate of monomer conversion but also the polymer molecular weight. From an increase in the water content in reactions, enhanced polymerization rates were achieved while the molecular weight of poly(PDL) decreased. At low reaction water levels (0.20% w/w water), the I-PS-30 catalyzed polymerization of PDL at 70 °C gave poly(PDL) with M n and M w/M n of 62 000 and 1.9, respectively. Thus far, this is the highest molecular weight polyester prepared by an enzyme-catalyzed polymerization reaction.

Studies were undertaken to gain mechanistic information on lactone ring-opening polymerization reactions using porcine pancreatic lipase (PPL) as the catalyst and ε-caprolactone (ε-CL) as the monomer. Polymerizations were carried out at low water levels (0.13 mmol) and supplemented with either butanol or butylamine. Rates of monomer conversion, product molecular weight, total chain number, and chain end structure were determined by 1H NMR. In the presence of water alone, a maximum M n of 7600 g/mol was obtained at 85% conversion, which decreased to 4200 g/mol as the reaction continued to 98% conversion. Reactions with butanol and butylamine at 100% conversion gave polymers with M n values of 1900 and 1200 g/mol, respectively. For these three polymerizations, the total number of polymer chains increased with conversion due to a simultaneous increase in carboxylic acid chain ends. Within 4 h (∼26% monomer conversion), butylamine was completely consumed but only 37% of butanol reacted. Reactions with butylamine occurred predominantly by an enzyme-mediated route to form N-butyl-6-hydroxyhexanamide. This step was rapid relative to subsequent chain growth. In addition, the living or immortal nature of the polymerizations was assessed from plots of log{[M]0/[M] t } versus time and M n versus conversion. These results indicate that termination and chain transfer did not occur, and we described the system as providing “controlled” polymerizations. Furthermore, an expression for the rate of propagation was derived from the experimental data which is consistent with that derived from the proposed enzyme-catalyzed polymerization mechanism. The absence of termination in conjunction with the relationship between molecular weight and the total concentration of multiple initiators suggests that ε-CL polymerization by PPL catalysis shares many features of immortal polymerizations.

This work was directed at extending the use of lipase-catalyzed ring-opening polymerizations to cyclic carbonate monomers. Of the seven lipases screened for bulk trimethylene carbonate (TMC) polymerization (70 °C, 120 h), Novozym-435 from Candida antarctica gave almost quantitative monomer conversion (97%) and poly(TMC) with a Mn ) 15 000 (Mw/Mn ) 2.2) with no apparent decarboxylation during propagation. The lipases from Pseudomonas species (AK and PS-30) and porcine pancreas (PPL) also exhibited high monomer conversions (>80%, 120 h) but gave lower molecular weight polymers with broad polydispersity. Analyses by 1 H-NMR spectroscopy suggested that poly(TMC) prepared by Novozym-435-catalyzed polymerization had terminal -CH2OH functionalities at both chain ends. A monotonic increase in monomer conversion with time and the rapid increase in Mn as a function of monomer conversion for Novozym-435-catalyzed TMC bulk polymerization at 70 °C suggest that the polymerization has chain-type propagation kinetics. An increase in conversion above 66% did not substantially change Mn. The percent conversion was larger when the reaction temperature was increased from 45 to 55 °C. Further increase in the reaction temperature from 55 to 85 °C did not give higher percent conversion values. The molecular weight decreased substantially as the reaction temperature was increased from 55 to 85 °C (Mn from 24 400 to 5 900). The highest poly(TMC) molecular weight (Mn ) 24 400) was obtained by conducting the polymerization at 55 °C. Monomer conversion and molecular weight as a function of the percent reaction water content (w/w) were investigated. Increasing the water content resulted in enhanced polymerization rates and decreased molecular weights. Separation of the oligomeric products from polymerizations of TMC in dried dioxane and toluene catalyzed by porcine pancreatic lipase led to the isolation of di-and triadducts of trimethylene carbonate. Based on the symmetrical structure of these products and the end-group structure of high molecular weight chains, a mechanism for chain initiation and propagation for lipase-catalyzed TMC polymerization was proposed.

Considerable advances in cancer-specific optical imaging have improved the precision of tumor resection. In comparison to traditional imaging modalities, this technology is unique in its ability to provide real-time feedback to the operating surgeon. Given the significant clinical implications of optical imaging, there is an urgent need to standardize surgical navigation tools and contrast agents to facilitate swift regulatory approval. Because fluorescence-enhanced surgery requires a combination of both device and drug, each may be developed in conjunction, or separately, which are important considerations in the approval process. This report is the result of a one-day meeting held on May 4, 2016 with officials from the National Cancer Institute, the FDA, members of the American Society of Image-Guided Surgery, and members of the World Molecular Imaging Society, which discussed consensus methods for FDA-directed human testing and approval of investigational optical imaging devices as well as contrast agents for surgical applications. The goal of this workshop was to discuss FDA approval requirements and the expectations for approval of these novel drugs and devices, packaged separately or in combination, within the context of optical surgical navigation. In addition, the workshop acted to provide clarity to the research community on data collection and trial design. Reported here are the specific discussion items and recommendations from this critical and timely meeting.

Volatile anesthetics and alcohols enhance transmission mediated by ␥-aminobutyric acid type A receptors (GABA A Rs) in the central nervous system, an effect that may underlie some of the behavioral actions of these agents. Substituting a critical serine residue within the GABA A R ␣ 1 subunit at position 270 with the larger residue histidine eliminated receptor modulation by isoflurane, but it also affected receptor gating (increased GABA sensitivity). To correct the shift in GABA sensitivity of this mutant, we mutated a second residue, leucine at position 277 to alanine. The double mutant ␣ 1 (S270H,L277A)␤ 2 ␥ 2S GABA A R was expressed in Xenopus laevis oocytes and human embryonic kidney (HEK)293 cells, and it had near-normal GABA sensitivity. However, rapid application of a brief GABA pulse to receptors expressed in HEK293 cells revealed that the deactivation was faster in double mutant than in wild-type receptors. In all heterologous systems, the enhancing effect of isoflurane and ethanol was greatly decreased in the double mutant receptor. Homozygous knockin mice harboring the double mutation were viable and presented no overt abnormality, except hyperactivity. This knockin mouse line should be useful in determining which behavioral actions of volatile anesthetics and ethanol are mediated by the GABA A Rs containing the ␣ 1 subunit.