Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2001. / Includes bibliographical references (p. 190-201). / The triplet electronic states of acetylene and the intersystem crossing process that populates these states were studied using a second-generation, supersonic jet molecular beam machine with a multispectral capability. Surface Electron Ejection (SEELEM), Ultraviolet Laser Induced Fluorescence (UV-LIF), and Infrared Laser Induced Fluorescence (IR-LIF) spectra were acquired simultaneously following excitation in the vicinity of the A1Au [upsilon]3 = 3 [left arrow]X1[sum of]+g [upsilon] = 0 transition of acetylene. The A1Au [upsilon]3 = 3 level of acetylene is known to be coupled strongly to a background of near-degenerate triplet states. Simultaneous analysis of the complementary SEELEM and UV-LIF data using a set of recently developed analytical tools, yielded mechanistic insights into the non-radiative relaxation (i.e. intersystem crossing) process that distributes the optically accessible bright state over the background of dark states. The potential of the IR-LIF signal as an indirect probe of the triplet states of acetylene has also been demonstrated. Mechanistic insights into the SEELEM detection process itself were gained through a comparison of SEELEM data obtained separately in the first-generation and second-generation molecular beam machines. The two versions of the apparatus differed in their respective operating pressures. The operating background pressure has been found to be an important external factor in the SEELEM process. The much higher sensitivity (a factor of 103) of low-work function SEELEM surfaces such as Cs ([Phi]=2.1 eV) compared to that of other metals such as Au ([Phi]=5.1 eV) is observed only under low operating background pressures (4x 10-7 Torr). / by Selen Altunata. / Ph.D.

Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018. / Cataloged from PDF version of thesis. Vita. / Includes bibliographical references. / I. Total Synthesis of (-)-Hodgkinsine, (-)-Calycosidine, (-)-Hodgkinsine B, (-)-Quadrigemine C and (-)-Psycholeine The enantioselective total synthesis of (-)-hodgkinsine, (-)-calycosidine, (-)-hodgkinsine B, (-)- quadrigemine C, and (-)-psycholeine through a diazene-directed assembly of cyclotryptamine fragments is described. Our synthetic strategy enables multiple and directed assembly of intact cyclotryptamine subunits for convergent synthesis of highly complex bis- and tris-diazene intermediates. Photoextrusion of dinitrogen from these intermediates enables completely stereoselective formation of all C3a-C3a' and C3a-C7' carbon-carbon bonds and all the associated quaternary stereogenic centers. The synthesis of these complex diazenes was made possible through a new methodology for synthesis of aryl-alkyl diazenes using electronically attenuated hydrazine-nucleophiles in a silver-promoted addition to C3a-bromocyclotryptamines. The application of Rh- and Ir-catalyzed C-H amination reactions in complex settings were used to gain rapid access to C3a- and C7-functionalized cyclotryptamine monomers, respectively, used for diazene synthesis. II. Total Synthesis of (-)-Naseseazine C and Identification of its Biosynthetic Pathway The biogenesis of unsymmetrical dimeric diketopiperazines is investigated, in collaboration with the Sherman group at the University of Michigan. Sequencing and mining the genome of Streptomyces sp. CB MQ-030, known to produce unsymmetrical diketopiperazine dimers, allowed the identification of NasB, a cytochrome P450 responsible for catalyzing late-stage oxidative dimerization of brevianamide F into (-)-naseseazine C. The relative and absolute stereochemical assignment was confirmed via its total synthesis using highly convergent late-stage fragment union of complex diketopiperazines. / by Petra Lindovská. / Ph. D. in Organic Chemistry

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references. / by Jon H. Come. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1999. / Includes bibliographical references. / by Frederick A. Hicks. / Ph.D.

Thesis (Ph.D.) Massachusetts Institute of Technology. Dept. of Chemistry, 1951. / Vita. / by Elias James Corey, Jr. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references (leaves 276-314). / by Marshall Lee Morningstar. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references (leaves 104-118). / by Scott Charles Berk. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2011. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Asparagine-linked protein glycosylation entails the stepwise assembly of an oligosaccharide onto a polyisoprenyl diphosphate carrier, followed by the en bloc transfer of the glycan onto acceptor proteins by oligosaccharyl transferase (OTase). It is now clear that this N-linked protein modification catalyzed by OTases is conserved in all three kingdoms of life. In contrast to eukaryotic OTases, which are multimeric complexes made up of several membrane-spanning proteins, bacterial and archaeal OTases instead appear to be composed of just a single membrane-bound subunit, offering a more tractable system for detailed biochemical characterization. Although significant progress has been made with the bacterial OTase PglB from Campylobacterjejuni, problems with low protein expression yields and poor stability have complicated in depth study. In order to identify a more suitable OTase candidate, a selection of archaeal OTases was screened for heterologous expression levels in Escherichia coli, and it was determined that the homolog from the methanogen Methanococcus voltae possessed the best protein expression profile, indicating a 100-fold improvement over PglB. In an effort to generate a substrate to probe the function of the M voltae OTase, we required a robust synthesis of the highly modified UDP-GlcNAc(3NAc)A and thus turned to the Wbp pathway from the opportunistic pathogen Pseudomonas aeruginosa. Early genetic studies suggested that P. aeruginosa produces UDP-GlcNAc(3NAc)A as a precursor to ManNAc(3NAc)A, a carbohydrate found in the O-antigen of the lipopolysaccharide of the organism. Using a combination of protein biochemistry and NMR spectroscopy, three enzymes (WbpB, WbpE, and WbpD) were confirmed to be responsible for the biosynthesis of UDPGlcNAc( 3NAc)A. It is shown that WbpB and WbpE are a dehydrogenase/aminotransferase pair that converts UDP-GlcNAcA to UDP-GIcNAc(3NH 2)A in a coupled reaction via a unique NAD* recycling pathway. In addition, the X-ray crystal structure of WbpE was solved in complex with its PLP cofactor and UDP-GlcNAc(3NH 2)A product as the external aldimine. With UDP-GlcNAc(3NAc)A in hand, preliminary steps towards completion of the desired dolichyl-linked substrate for the study of the M. voltae OTase are described. Finally, biochemical studies were undertaken in an attempt to inhibit the C. jejuni OTase, PglB. To this end, a panel of isosteric peptides was synthesized to identify possible PglB inhibitors. In addition, treatment of PglB with residue-specific alkylating agents coupled with site-directed mutagenesis revealed a key histidine residue that may play an important role in enzyme catalysis. Taken together, these studies offer insight into long-standing questions about the mechanism of oligosaccharide transfer. / by Angelyn Larkin. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / In Chapter 1, we synthesize dithienobenzotropone-based conjugated alternating copolymers by direct arylation polycondensation. Post-polymerization hydride reduction furnishes cross-conjugated copolymeric hydrogels that undergo phosphorylation and subsequent ionization upon exposure to chemical warfare agent (CWA) mimics. The resulting conjugated, cationic copolymer is intensely colored and facilitates spectroscopic and colorimetric detection of CWA mimics in solution and as a thin film. Similarly, we report the incorporation of CWA-responsive units into random copolymers prepared by ringopening metathesis polymerization (ROMP) to create highly modular, chromogenic thin films. In Chapter 2, we explore homoconjugated polynorbornadienes possessing various electron-withdrawing groups as polymeric precursors to electron-accepting poly(cyclopentadienylene vinylene) derivatives. Tungsten oxo alkylidene catalysts were utilized to polymerize a variety of 7-isopropylidene- and 7-oxa-2,3-disubstituted norbornadienes in a cis-highly tactic fashion by ROMP. We further demonstrate the excellent scope of tungsten oxo complexes by polymerizing norbornadienes that are unreactive with traditional molybdenum-, tungsten-, and ruthenium-based catalysts. In Chapter 3, we employ atomic force microscopy (AFM) and scanning tunneling microscopy (STM) to examine graphene oxide (GO) samples with gradations of (de)oxygenation. We analyze the roughness of the apparent height in STM topographic measurements - i.e. the "apparent roughness" - and report a correlation between increasing deoxygenation and decreasing surface roughness. The "apparent roughness" therefore serves as a supplemental technique for analyzing samples of GO. Furthermore, we report the first example of using an STM tip to locally reduce GO without local destruction of the graphene sample. In Chapter 4, we exploit the extraordinary self-recognition properties of deoxyribonucleic acid (DNA) to assemble single-walled carbon nanotubes (SWCNTs) in a controllable manner. Networks of SWCNTs with three-way junctions could be constructed in solution or sequentially on a surface. We envision that more complex nanoscale architectures and circuits can be prepared in this bottom-up manner. In Chapter 5, we introduce halogen bonding in SWCNT-based chemiresistive gas sensors. These chemiresistors were prepared by ball milling of SWCNTs and selectors, compression into a pellet, and mechanical abrasion between gold electrodes on paper. We demonstrate that sensing responses reflect halogen bonding trends, with some exceptions. The predominant signal transduction mechanism is likely attributed to swelling of the insulating haloarene matrix. / by Jonathan G. Weis. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1996. / Includes bibliographical references. / by Kevin L. Ward. / M.S.