http://hdl.handle.net/1721.1/7594 Sat, 08 Jun 2013 13:59:12 GMT 2013-06-08T13:59:12Z http://hdl.handle.net/1721.1/79039 Development of glucose valves for metabolic engineering applications in E. coli Solomon, Kevin Val-Murvin Microbial production platforms have extraordinary potential to help meet the energy, material and health needs of tomorrow. Through the reactions of cellular metabolism, microbes are an attractive option for the sustainable production of commodity and enantiopure specialty chemicals. One outstanding challenge, however, is the engineering of these systems for economic viability. As a solution to this issue, a metabolite valve is proposed: a biochemical device which may be used to dynamically redirect metabolite flux away from endogenous processes into production pathways. In this work, we develop and characterize a glucose valve. First, a novel E. coli strain was engineered to allow the redirection of glucose flux from central metabolism via glucokinase. Using a promoter library, glucokinase expression was varied with an attendant change in specific growth rate and carbon flux. A model pathway was then constructed to utilize the redirected carbon demonstrating that the efficiency of such pathways may be controlled through glucokinase expression. Next, inducible antisense RNA and inverting genetic circuits were developed to dynamically control glucokinase expression. With dynamic control, carbon was redirected from endogenous processes only once sufficient cellular resources had accumulated, further improving performance. In this manner, yields and titers of the model pathway were increased with a concomitant decrease in acetate waste. Finally, elements of this system were modeled to gain mechanistic insight and to establish a control envelope of viable expression and production regimes. This thesis represents one of the first reports of glucose redirection in E. coli and is an example of the ongoing development of a relatively new paradigm in metabolic engineering: dynamic flux control. With a glucose valve, the needs of cellular health and demands of heterologous production may be balanced, enabling the development of efficient processes with glucose as a sole carbon source for both cell growth and biochemical production. This ability to use a single carbon source simplifies process design, lowering capital and operating costs. Furthermore, a glucose valve has potential applications in the optimization of existing processes where carbon is underutilized and wasted as fermentation products such as acetate. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 104-120). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/79039 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/79026 Theoretical and simulations-based modeling of micellization in linear and branched surfactant systems Mendenhall, Jonathan David Surfactants are chemically-heterogeneous molecules possessing hydrophilic (head) and hydrophobic (tail) moieties. This dual nature of surfactants leads to interesting phase behavior in aqueous solution as a function of surfactant concentration, including: (i) formation of surfactant monolayers at surfaces and interfaces, and (ii) self-assembly into finite aggregates (micelles) in the bulk solution beyond the critical micelle concentration (cmc). This concentration-dependent phase behavior induces changes in solution properties. For example, the surface activity of surfactants can decrease the surface tension, and self-assembly in bulk solution can lead to changes in viscosity, equivalent conductivity, solubilization capacity, and other bulk properties. These effects make surfactants quite attractive and unique for use in product formulations, where they are utilized as detergents, dispersants, emulsifiers, solubilizers, surface and interfacial tension modifiers, and in other contexts. The specific chemical structure of the surfactant head and tail is essential in determining the overall performance properties of a surfactant in aqueous media. The surfactant tail drives the self-assembly process through the hydrophobic effect, while the surfactant head imparts a certain extent of solubility to the surfactant in aqueous solution through preferential interactions with the hydrogen-bonding network of water. The interplay between these two effects gives rise to the particular phase diagram of a surfactant, including the specific cmc at which micelles begin to form. In addition to serving as a quantitative indicator of micelle formation, the cmc represents a limit to surface monolayer formation, and hence to surface and interfacial tension reduction, because surfactant adsorption at interfaces remains approximately constant beyond the cmc. In addition, the cmc represents the onset of changes in bulk solution properties. This Thesis is concerned with the prediction of cmc's and other micellization properties for a variety of linear and branched surfactant chemical architectures which are commonly encountered in practice. Single-component surfactant solutions are investigated, in order to clarify the specific contributions of the surfactant head and tail to the free energy of micellization, a quantity which determines the cmc and all other aspects of micellization. First, a molecular-thermodynamic (MT) theory is presented which makes use of bulk-phase thermodynamics and a phenomenological thought process to describe the energetics related to the formation of a micelle from its constituent surfactant monomers. Second, a combined computer-simulation/molecular-thermodynamic (CSMT) framework is discussed which provides a more detailed quantification of the hydrophobic effect using molecular dynamics simulations. A novel computational strategy to identify surfactant head and tail using an iterative dividing surface approach, along with simulated micelle results, is proposed. Force-field development for novel surfactant structures is also discussed. Third, a statistical-thermodynamic, single-chain, mean-field theory for linear and branched tail packing is formulated, which enables quantification of the specific energetic penalties related to confinement and constraint of surfactant tails within micelles. Finally, these theoretical and simulations-based strategies are used to predict the micellization behavior of 55 linear surfactants and 28 branched surfactants. Critical micelle concentration and optimal micelle properties are reported and compared with experiment, demonstrating good agreement across a range of surfactant head and tail types. In particular, the CSMT framework is found to provide improved agreement with experimental cmc's for the branched surfactants considered. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 446-471). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/79026 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77762 Studies in the revulcanization of reclaim rubber Roboff, Stanley B Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1943.; MIT copy bound with: The use of scrap leather for artificial leather soles / Alfred B. Babcock, Jr. and William R. Kittredge. 1943.; Includes bibliographical references (leaves 20-21). Fri, 01 Jan 1943 00:00:00 GMT http://hdl.handle.net/1721.1/77762 1943-01-01T00:00:00Z http://hdl.handle.net/1721.1/77761 Absorption coefficients in light oil scrubbers Forbes, Edward Colin; Kao, John Yü-Ling Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1941.; Includes bibliographical references (leaf 91). Wed, 01 Jan 1941 00:00:00 GMT http://hdl.handle.net/1721.1/77761 1941-01-01T00:00:00Z