Studies concerning two different copolymerization processes are detailed in this dissertation: propylene oxide/CO2 coupling to afford poly(propylene carbonate) and Nbutylaziridine/ CO coupling to afford poly-??-butylalanoid. The copolymerization of propylene oxide and CO2 to form the industrially useful poly(propylene carbonate) has been investigated employing chromium(salen)N3 complexes as catalysts. Unfortunately the reaction could not be studied in real time via in situ infrared spectroscopy, thereby obtaining detailed kinetic data, because of the copolymer-limited solubility in most solvents. Studies employing batch reactor runs concentrating on varying the cocatalyst, the equivalents of cocatalysts, and the steric and electronic structure of the catalyst through modification of the salen ligand were undertaken. It was discovered that the optimal catalyst for copolymer selectivity vs. the monomeric propylene carbonate was one that contained a salen ligand with an electron withdrawing phenylene backbone and electron donating tert-butyl groups in the phenolate rings. This catalyst was used to investigate the effect of altering the nature of the cocatalyst and its concentration. The coupling of carbon monoxide and aziridines has been shown to be selective for comonomer-alternating enchainment in the presence of PhCH2C(O)Co(CO)4 to afford poly-??-peptoids. The mechanistic aspects of the reaction of CO and Nbutylaziridine by means of in situ infrared spectroscopy employing CH3C(O)Co(CO)3L (L = PPh3 and P(o-tolyl)3) as precatalysts was investigated. It was found the PPh3 precatalyst exists in solution under catalytic conditions as an equilibrium mixture of CH3C(O)Co(CO)3PPh3 and CH3C(O)Co(CO)4, and affords both poly-??-butylalanoid and the corresponding lactam as a side-product. By way of contrast, the P(o-tolyl)3 precatalyst which possesses the sterically bulky and labile phosphine ligand, affords only the acyl cobalt tetracarbonyl species in solution during catalysis with the selective production of the copolymer. Kinetic studies conducted with CH3C(O)Co(CO)3P(otolyl) 3 showed the coupling reaction to have a first order dependence on catalyst, a first order dependence on N-butylaziridine, and only a slight dependence on the concentration of CO over the pressure range 17-69 bar. The working mechanistic model for the copolymerization reaction involves first aziridine insertion into the cobalt-acyl bond, rate determining ring opening by the cobaltate species, followed by the migratory CO insertion.

Berlin, Techn. Univ., Diss., 2000.

München, Techn. University, Diss., 2004.

Thèse--Sc. phys.--Paris 6, 1971. / Bibliogr. f. 62-66.

The objective of this research is to investigate synthetic and polypeptide block copolymers, the structures they form, their response to various stimuli in solution and their capabilities for use in biomimicry. The self-assembled structures of both polymers will be used as a basis for the templating of hydrogels materials, both in the interior and on the surface of the vesicles. The resulting particles will be designed to show the structural and mechanical properties of living cells. The synthetic block copolymers are a polyethylene glycol and polybutadiene (PEO-b-PBd) copolymer and the polypeptide block copolymers are Lysine and Glysine (K-b-G) copolymers. Investigation of the structures synthetic block copolymers will focus on whether the polymer can form vesicles, how small of a vesicle structure can be made, and the formation of internal polymer networks. Subsequent investigations will look at the needed steps for biomimicry, using the synthetic block copolymers as a starting point and transitioning to a polypeptide block copolymer. The Lysine-Glysine copolymers are a new system of materials that form fluid vesicle structures. Therefore, we must characterize its assembly behavior and investigate how it responds to solution conditions, before we investigate how to make a cellular mimic from it. The size and mechanical behavior of the K-G vesicles will be measured to compare and contrast with the synthetic systems. The goals for creating a biomimic include a hollow sphere structure with a fluid bilayer, a vesicle that has controllable mechanical properties, and a vesicle with controllable surface chemistry. Overall, these experiments were a success; we showed that we can effectively control the size of vesicles created, the material properties of the vesicles, as well as the surface chemistry of the vesicles. Investigations into a novel polypeptide block copolymer were conducted and the block copolymer showed the ability to create vesicles that are responsive to changing salt and pH concentrations.

No description available.

Ticks (Ixodes (Ceratixodes) uriae] were collected from two seabird colonies on the Isle of May in Scotland. Viruses were isolated from three tick pools, one from ticks collected during 1979 and two from ticks collected during 1981. The viruses replicated in suckling mouse brain, chick embryo fibroblasts, Vero and BHK-21 cells, but not in Xenopus cells. By virtue of their morphology in infected cells, physicochemical properties and reactions in complement fixation tests, they were identified as Kemerovo serogroup viruses belonging to the Great Island Complex (Orbivirus:Reoviridae). Ihe three isolates were distinguished from each other by plaque reduction neutralization tests. After three cycles of plaque purification, the replication of one isolate, Mill Door/79 virus, was examined in Vero and BHK-21 cells. The virus grew to maximum titres 8 to 9 hours post infection (p.i.); over 99% of the infectivity was cell-associated. Twelve virus-specified polypeptides, p141, p93, p69, p65, p53/51, p44, p37, p36, p30, p27, p21 and p20 were identified in infected Vero cell lysates by polyacrylamide gel electrophoresis (PAGE). Similar polypeptide profiles were observed in infected BHK-21 cell lysates. Attempts to purify the virus, by polyethylene glycol-6000 precipitation, resulted in the detection of p93, p69, p53/51, p37, p21 and p20 after PAGE, whereas only four, p93, p69, p53/51 and p37 were detected after attempts at purification using ether extractions. Results using pr~ase inhibitors and partial proteolysis indicated that three virus-specified polypeptides (p36, p30 and p27) may be cleavage products. All virus-specified polypeptides, with the exception of p30 and p20, were labelled in infected cell cultures with both [14c] mannose and [14c] glucosamine.

Objective. Albumin is an abundant and slowly-cleared plasma protein. Our laboratory previously incorporated albumin into recombinant fusion proteins to extend the plasma half-life of small proteins of potential therapeutic utility. We sought to determine if reiteration of albumin in a single polypeptide chain would further extend its half-life. Design. Hexahistidine-tagged rabbit serum albumin (RSA) with Cys 34 altered to Ala to prevent disulphide-bonded dimerization was produced in yeast (H₆-RSA-C34A), and compared to a reiterated forma of H₆-RSA-C34A containing two domains of amino acids 1-584 separated by a hexaglycine spacer. Clearance of these purified iodinated proteins was compared in rabbits. Materials and Methods. Site-directed mutagenesis employing PCR was used to alter the encoding plasmid. Proteins secreted from transformed Pichia pastoris yeast cell lines were purified using nickel-chelated affinity chromatography and radioiodinated by the Iodogen method. Labeled proteins were injected intravenously into rabbits and the residual acid-precipitable protein concentration in serial plasma samples was determined over time. Results. P. 𝘱𝘢𝘴𝘵𝘰𝘳𝘪𝘴 cells transformed with the expression plasmids secreted 140 kDa H₆-diRSA and 70 kDa H₆-RSA-C34A proteins, which were purified to apparent homogeneity. Mean terminal catabolic half-lives (±SD) were 4.9 (±0.7) and 3.0 (±0.3) days for H₆-RSA-C34A and H₆-diRSA, respectively. Then values were 9 for H₆-diRSA and 12 for H₆-RSA-C34A. conclusions. H₆-diRSA was cleared from the circulation more rapidly than H₆RSA-C34A. We hypothesized that increased catabolism of the reiterated molecule could be due to an increased rate of cellular uptake and endocytosis of H₆-diRSA due to increased avidity for cellular binding sites. Non-reiterated albumin therefore appears to be optimal as a carrier protein for small recombinant blood products. / Thesis / Master of Science (MSc)

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Structure-function relationships for an alanine-rich, α-helical antifreeze polypeptide (AFP) from winter flounder were studied with the goal of understanding how AFPs depress the freezing point of water. A 37-residue native AFP and 23 analogs with systematic variations in the polypeptide chain were synthesized, and the α-helix content, antifreeze activity, and effect on growth rates of ice crystals along the a and c axes were determined. The results indicate that both the regularly spaced threonine and asparagine (or aspartic acid) residues are critical for maximal activity, and that the asymmetric arrangement of these residues on the helix face causes asymmetric adsorption of AFPs on the ice surface. Charged-residues, except for C-terminal Arg, are not very critical for antifreeze activity. Studies of hydrophobic residue mutants showed that the overall hydrophobicity is not particularly important. However, the Ala residue in position 17 appears to be important, because replacement with a bulky group abolishes antifreeze activity, presumably by interfering with the favorable side-to-side hydrophobic A model for binding of the winter flounder AFP to ice is proposed, whereby the AFP inhibits the growth of ice crystals by hydrogen bonding of Thr, Asn and Asp side chains in a specific pattern to the { 20 21 } hexagonal bipyramidal planes of ice, unidirectionally along the vector <1102>. It is further proposed that ice crystal growth inhibition occurs by a two-step mechanism: first individual AFP molecules hydrogen bond to ice reversibly, allowing slow growth of ice crystal; then at sufficiently high AFP concentrations, the AFP molecules begin to pack together on the binding surface by cooperative, side-to-side, hydrophobic interpeptide interactions, resulting in essentially irreversible binding and arrested ice crystal growth. The D-enantiomer of the AFP was also synthesized. The D and L-enantiomers alone, as well as a 50:50 mixture of D and L, all show identical antifreeze activity. These results indicate that complete coverage of the ice surface is not necessary, and suggest a model whereby AFP molecules bind in patches on the ice surface. / 2999-01-01

No description available.