Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / by Lisa Dhar. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006. / Includes bibliographical references. / Oxygen is observed to adsorb molecularly on 0.13 - 0.27 ML Au/Ni(1 111) surface alloys at 77 K, in stark contrast to dissociative adsorption on Ni and no adsorption on Au surfaces. Molecular 02 adsorbates on the Au/Ni(111) surface alloy are identified by their 0=0 vibrational modes at 790, 850 and 950 cm-', measured by electron energy loss spectroscopy. Possible Ni adsorption sites for the three types of molecularly adsorbed 02 are proposed. The dramatic change in Ni reactivity occurs within a narrow Au coverage range around 0.13 ML Au and arises from poorer overlap between the Ni d-band and the 02 LUMO as the Ni d-band shifts to lower energy with increasing Au content of the Au/Ni surface alloy. The amount of molecular adsorption as a function of Au coverage cannot be described by an analytical or simulated model based on Au atom proximity to Ni sites, suggesting the role of cooperative effects in 02 stabilization. Adsorbed molecular 02 dissociates between 110 to 150 K. No oxygen desorbs. At Au coverages greater than 0.27 ML, the energy of the Ni d-band is shifted sufficiently low to destabilize oxygen adsorption. / (cont.) Carbon monoxide is catalytically oxidized on the Au/Ni(111) surface alloy at 70 and 77 K via a Langmuir-Hinshelwood mechanism. Molecularly adsorbed 02 is identified as the reactant with adsorbed CO. The reaction probability at 77 K is 0.4. Atomically adsorbed O and CO do not react at 77 or 300 K. Between 108 and 125 K, CO reacts with either atomic O adsorbed on Au atoms or with molecularly adsorbed 02. Between 125-150 K, CO2 production coincides with 02 dissociation, suggesting a "hot atom" mechanism. The reactive potential energy surfaces likely have a late transition state. This work demonstrates that the nanoscale size of Au clusters and its associated quantum size effect are not the necessary feature that enables Au-catalyzed low temperature CO oxidation. Rather, this work strongly suggests that an adsorbed 02 species similarly stabilized at the perimeter of Au nanoparticles is the critical reactant in supported oxide systems. / by David Louis Lahr. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Organic polymers can be used as the active component of sensors, smart materials, chemical-delivery systems and the active layer of solar cells. The rational design and modification of the chemical structure of polymers has enabled control over their properties and morphology, leading to the advancement of nanotechnology. A deeper understanding of structure-property relationships, as described in this thesis, affords control over the nanostructure of devices made from these macromolecular materials, which is crucial to the optimization of their performance. In Chapter 1, a new sensor for ionizing radiation based on composites of electron beam lithography resists, poly (olefin sulfone)s (POSs), and multiwalled carbon nanotubes is presented. The polymeric active component is radiation labile and its degradation after a sensing event leads to morphological and electrical changes in the composite at the nanoscale. As a result, a signal can be detected. Systematic sensitivity improvements can be accomplished by rational modifications of the chemical structure of the polymer side-chains. Orthogonal postpolymerization modifications performed using "click" chemistry, incorporate functional groups capable of increasing either the homogeneity of the composite, or its opacity towards radiation. In Chapter 2, a smart hybrid polymer composed of a POS and a silicone linked by "click" chemistry is described. By tuning the chemical structure of these two components and varying their ratio, composites with different mechanical properties and hardness can be achieved. This elastomeric smart material exhibits switchable mechanical properties: exposure to mild bases triggers disassembly into its monomers and individual constituents. In Chapter 3, the design, synthesis and properties of new polymer surfactant additives for photovoltaic devices is shown. The AB alternating regioregular polythiophene copolymer additives are obtained via a combinatorial approach, and contain functional groups in every other repeat unit. In Chapter 4 incorporation of small amounts of these polymer additives (0.25 weight %) is shown to result in large increases of up to 30% in the power conversion efficiency of organic solar cells consisting primarily of the benchmark system of poly (3-hexylthiophene) and Phenyl-C6 1-butyric acid methyl ester (PCBM) as the active layer. This effect is mainly due to the presence of dipoles at the interface of the bulk heterojunction introduced by the additives, which prevent charge recombination and lead to increases in the photocurrent collected across the polymer-fullerene interface. In Chapter 5, the synthesis of liquid crystalline polymer brushes is described, and their supramolecular and self-assembly properties are studied. The solid-state ordering and alignment properties of these highly substituted polymers can be affected by chemically tuning their mesogenic oligomeric side-chains, the length of the polymer backbone and the degree of crosslinking. The morphologies obtained with these macromolecules are interesting from the point of view of future photovoltaic applications. / by Jose Miguel Lobez Comeras. / Ph.D.

Thesis (Ph. D. in Inorganic Chemistry)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / Multi-electron reaction chemistry, from both ground- and excited-state species, is at the heart of many topics in renewable energy and catalysis. In this thesis, two classes of reactions central to the themes of energy conversion and multi-electron chemistry are studied on mono- and bimetallic late transition-metal platforms. In the early chapters, studies of photochemical halogen elimination, the key energy-storing step in photocatalytic hydrogen production from HX (X = Cl, Br), are described. In the latter sections of the thesis, the oxygen-activation and reduction chemistries of rhodium and iridium hydride complexes are highlighted. In Chapters 1 and 2, photochemical halogen elimination from a variety of late transition-metal complexes is described. Studies of phosphine-terminated gold(III) halide complexes demonstrated that efficient halogen photoelimination can be promoted by ligand-to-metal charge-transfer (LMCT) excitation, in complexes devoid of a formal metal-metal interaction. In addition, gold was partnered with rhodium and iridium in a series of heterobimetallic complexes, and these complexes were also shown to cleanly eliminate halogen when illuminated, with additional electronic structural insights and reactivity trends emerging from this latter suite of compounds. In Chapters 3-6, small-molecule reactivity studies of rhodium and iridium complexes, with a particular slant towards oxygen reduction, are disclosed. A new class of two-electron mixedvalent dirhodium and diiridium complexes is described. Featuring a coordinatively unsaturated M0 center, these complexes display an expansive reactivity with numerous small-molecule substrates. A dirhodium hydride complex, prepared by HCl addition to the mixed-valent precursor, mediates the reduction of oxygen to water. Studies on iridium model complexes, coupled with detailed kinetic studies, produced a clear mechanistic understanding of this chemistry. In particular, the preparation and reactivity of a diiridium hydroperoxo complex gave many key insights into the activation of O2 and the subsequent release of water. Analogous oxygen-reduction chemistry was also demonstrated to occur on a monorhodium platform, which will facilitate detailed mechanistic studies enabled by systematic ligand alteration. / by Thomas S. Teets. / Ph.D.in Inorganic Chemistry

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1998. / Includes bibliographical references. / by Sheree Lynell Stokes. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Chemistry, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 34-36). / An apparatus that utilizes buffer gas cooling to produce slow atomic (Ba, Ca) and molecular (BaF, CaF) beams is constructed. In-cell temperatures of 20 ± 0.25K are achieved with chamber cooldown times of under two hours. Laser Induced Fluorescence (LIF) spectra of BaF and CaF confirmed thermalization of the molecular beam to the temperature of the buffer gas and additional hydrodynamic cooling to rotational and translational temperatures under 10K. Laser fluence effects on the intensity of barium and calcium ablation were studied and used to optimize laser parameters for maximum ablation of the desired species. A chirped pulse millimeter wave (CPmmW) setup was combined with the buffer gas cooling apparatus for combined laser and millimeter wave spectroscopy experiments of Rydberg states. LabVIEW programming is used for an internal temperature feedback system, raster scanning of the ablation target, as well as millimeter wave FID signal digital acquisition. Use of the apparatus for chirped pulse microwave spectroscopy of buffer gas cooled beams have led to orders of magnitude improvement in both the resolution and the reduction of time required to record molecular Rydberg spectra. / by Ethan Avram Klein. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2001. / Includes bibliographical references (leaves 161-175). / A series of alkenyl (-C[Ad]Ar) and thioalkenyl (-SC[Ad]Ar, Ad=2-adamantylidene, Ar=3,5-Me2C6H3, 4-tBuC6H4, 3,5-(C6H5)2C6H3, 3,5-(4-tBu-C6H4)2 C6H3) ligands have been prepared. The alkenyl ligands are synthesized by bromination and dehydrohalogenation of an adamantyl olefin to yield an alkenyl bromide. The Grignard reagent, derived from the bromide, is used either as a transmetallation reagent, or reacted with elemental sulfur to form a magnesium thiolate, (THF)2Mg(SC[Ad]Ar)2. The magnesium thiolate can be protonated to give a free thiol, oxidized to afford a disulfide or reacted with ClTi(O'Pr)3 to give the titanium reagent, Ti(SC[Ad]Ar)(O'Pr)3. Treatment of CrC13 with an alkenyl Grignard reagent forms the Cr(III) complex, (THF)Cr(C[Ad]ArMe)3. While this compound reacts with pyridine to give (py)-Cr(C[Ad]ArMe)3, it fails to react with THT or PEt3. (THF)Cr(C[Ad]ArMe)3 can be oxidized with I2 or PhSSPh, however, the oxidation products are thermally unstable and disproportionate back to (THF)Cr(C[Ad]ArMe)3. Reactivity with nitric oxide is also discussed. Molybdenum nitrides of the form N-Mo(SC[Ad]Ar)3 have been prepared by re-action of Ti(SC[Ad]Ar)(O'Pr)3 with N-Mo(OtBu)3. The nitride reacts with Mo(N-[R]ArMe)3 to give (IL-N)[Mo(SC[Ad]Ar)3]2. Reaction of (THF)2Mg(SC[Ad]Ar)3 with MoCl3(THF)3 in diethyl ether leads to the formation of a molybdenum-molybdenum triply bonded compound, Mo2(SC[Ad]Ar)6, while performing the same reaction in THF followed by addition of pyridine leads to the isolation of (py)Mo(SC[Ad]Ar)3. / (cont.) A series of tungsten nitrides with amide ligands, NW(NMe2)3, N-W(N[iPr]-ArMe)2(NMe2), and NW(N['Pr]ArMe)3 have been synthesized by the reaction of a titanium or zirconium amide reagent with N-W(OtBu)3. Nitride N-W(N['Pr]-ArMe)3 has been compared to the molybdenum analogue N-Mo(N['Pr]ArMe)3 on the basis of crystal structure data and Density Functional Theory calculations. Treatment of N-W(NMe2)3 with Mo(H)(172-Me2C=NArMe)(N[iPr]ArMe)2 leads to formation of (Me2N)3W(/u-N)Mo(N[iPr]ArMe)3. Reaction of (Me2N)3W(tL-N)Mo(N[iPr]-ArMe)3 with other small molecules leads to the transfer of the nitride atom from tungsten to molybdenum. However, in the case of the larger nitride, NW(N['Pr]-ArMe)3, the bridging nitride formed with Mo(H)(r72-Me2C=NArMe)(N['Pr]ArMe)2 is present in solution in equilibrium with the starting materials. The rate of proton transfer self exchange of [C-Mo(N[R]ArMe)3]- with HCMo-(N[R]ArMe)3 has been measured by line shape kinetics in the 13C NMR and found to be 7 x 106 M-1 s-1. This very fast proton transfer rate has been used, in conjunction with solution and solid state NMR studies and DFT calculations, to develop a bonding picture for the carbide anion in which the lone pair on the carbon is localized in a nonbonding s orbital. / by Jane Brock Greco. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references. / APEX is an engineered peroxidase that catalyzes the oxidation of a wide range of substrates, facilitating its use in a variety of applications, from subcellular staining for electron microscopy to proximity biotinylation for spatially restricted proteomics and transcriptomics. While this strategy has provided access to many cellular regions and organelles, there are still many compartments and structures that cannot be accessed; this strategy is limited by the specificity of genetic targeting; there are cellular regions that cannot be exclusively targeted by a single genetic tag (Chapter 1). To further advance the capabilities of APEX and address the need for an interaction-dependent proximity labeling tool, this thesis describes the development of a split APEX2 system. Short enzymatic reconstitution times are also desired, to further ensures both organelles' morphological integrity. Thus, it is critical that split APEX2 reconstitute peroxidase activity both rapidly and robustly. We first performed two subsequent rounds of structure-guided screening to determine the most optimal cut site (Chapter 2). We then used directed evolution on the top candidate pair to engineer a split APEX tool (sAPEX). Selections were performed via FACS on yeast-displayed fragment libraries, and 20 rounds of evolution produced a 200-amino acid Nterminal fragment (with 9 mutations relative to APEX2) called "AP" and a 50-amino acid Cterminal fragment called "EX". AP and EX fragments were each inactive on their own, but reconstituted to give peroxidase activity when driven together by a molecular interaction (Chapter 3). Our resulting split APEX2 fragment pair has significantly diverged from its parental sequence and shows interaction-dependent reconstitution in multiple contexts in living mammalian cells (Chapter 4). Our split APEX tool adds to the proximity labeling toolkit (Chapter 5 and 6), and in the future, should extend the utility of APEX-based approaches to new areas of biology at higher spatiotemporal resolution. / by Yisu Han. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references. / by Andrew Robert Cook. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Steven Michael Peseckis. / Ph.D.