Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015. / 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 (pages 299-327). / Single-molecule spectroscopy has been a critical tool for the development and understanding of semiconductor nanocrystals because of their inherent heterogeneity size-dependent properties. In the past two decades, researchers have developed a diverse toolbox of single-nanocrystal techniques and analyses that is capable of elucidating the complex physics of nanocrystal fluorescence and characterizing many of the subtle but important optical properties of nanocrystal samples. This effort has been enabled by the flexible and modular structure of the single-molecule microscope, which offers a multitude of opportunities for shaping the information gained from single-nanocrystal experiments and provides a convenient and powerful framework for creativity in experimental design. In this thesis, we present two investigations that illustrate the full range and versatility of single-nanocrystal spectroscopy and, in particular, of photon correlation analysis. In Part I, we use single-nanocrystal spectroscopy as a tool for elucidating basic physics by investigating the rapid spectral diffusion of individual nanocrystals at low temperature. We develop a technique capable of measuring spectral dynamics over eight orders of magnitude in time ranging form microseconds to hundreds of seconds, and show that we can extract previously unavailable information about the spectral diffusion mechanism. In Part II, we use single-nanocrystal spectroscopy as a tool for characterizing optical properties by devising an experiment to measure the average biexciton quantum yield of nanocrystal samples. This experiment allows us to measure the biexcitonic properties of underdeveloped materials and can serve as a quick and reliable characterization technique to aid in synthetic optimization. Finally, in Part III, we look to the future by highlighting several modifications of existing experiments that could reveal new and exciting insight into nanocrystals. / by Andrew Paul Beyler. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Chemical modification of peptides and proteins is an enabling suite of tools for tailoring the properties of these biomolecules to specific applications. A number of bio-conjugation reactions allows fine-tuning of the biological activity, proteolytic stability, and immunogenicity of peptides and proteins, as well as equipping them with completely novel functions such as cell penetration, fluorescence, unique chemical reactivity, and much more. Described herein are a number of new methods for the synthesis of modified peptides and proteins, and an approach to the discovery of such methodologies. Applications of fast-flow solid phase peptide synthesis - a technique recently developed to accelerate and improve peptide synthesis- towards the synthesis of difficult sequences and the refinement of associated protocols is described. The utility of the system is demonstrated via rapid total synthesis of barnase, a model 110-residue RNase, in the L- and D-forms. Systematic characterization of the biochemical properties of the synthesized proteins revealed that barnase is able to hydrolyze substrates of various chiralities, and that D-barnase is fully proteolytically stable. Separately, a method for the preparation and utilization of unprotected peptide isocyanates in water was developed. It was shown that easily accessible C-terminal peptide isocyanates can be conjugated to a number of strong nucleophiles in the presence of unprotected amino acid side chains for peptides and proteins of various structures. Two-component macrocyclization of peptide isocyanates with bifunctional linkers was developed as an extension of the described chemistry. The resulting cyclic peptides were shown to be more proteolytically stable and more bioactive than their linear analogs. In pursuit of generalizing the C-terminal protein modification chemistry to fully proteogenic peptides and proteins, a number of library screening approaches was developed. Liquid chromatography coupled to tandem mass spectrometry was employed to screen and reliably decode synthetic peptide libraries in a high-throughput manner. These protocols were used to discover proteogenic sequence tags reactive towards substituted hydrazine derivatives in a transpeptidation reaction. The discovered C-terminal tripeptide tag His-Gly-Cys underwent transpeptidation with a number of structurally different nucleophiles in various sequence contexts. / by Alexander Alexandrovich Vinogradov. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2016. / Cataloged from PDF version of thesis. Page 171 blank. / Includes bibliographical references (pages [151]-170). / New methods are introduced for direct real-time observations of materials under dynamic loading. Traditionally, converging shock waves, which are of great interest for studying fundamental aspects of behavior of materials under extreme conditions, have been studied on the spatial scale ~1 m using facilities such as implosion chambers. In this work, direct real-time visualization of converging shock waves in a thin liquid layer was demonstrated at the micron scale in an all-optical experiment. Shock waves were generated in a 10 [mu]m-thick layer of water by sub-nanosecond laser pulses focused into a ring of 100 [mu]m radius. Time-resolved interferometry imaging with a femtosecond probe pulse was used to obtain full-field images at variable delays tracing the converging shock wave as it collapsed at the focal point leading to the formation of a cavitation bubble. Pressure values calculated from velocity measurements agreed with those obtained from quantitative analysis of interferometric images. Other samples were investigated using the same experimental setup. Focusing surface waves leading to material damage were observed on a glass substrate and conversion from highly-ordered pyrolytic graphite to nano-crystalline carbon was demonstrated under shock conditions. The developed technique will enable shock-induced chemical reactions to be investigated with direct access to the shocked reacting material for spectroscopic tools in a small-scale all-optical experiment. A novel approach for hypervelocity impact testing of materials using microprojectiles and a table-top laser system was also developed in this work. Microparticles were placed on a transparent substrate coated with a laser-absorbing polymer layer. Ablation of the polymer by a short laser pulse accelerated the particles to high velocities (~1 km/s). The impact events of high-speed particles with target material surfaces were monitored using an ultrafast multi-frame camera. In particular, the impact response of poly(urethane urea) (PUU) elastomers was investigated in order to further the understanding of the molecular influence on the dynamical behavior of PUUs. The results will provide an impetus for modeling microscale impact responses and high-strain rate deformation for a large spectrum of materials ranging from viscoelastic polymers and gels to elastic-plastic metals. / by David Veysset. / Ph. D.

Massachusetts Institute of Technology. Dept. of Chemistry. Thesis. 1974. Ph.D. / MICROFICHE COPY ALSO AVAILABLE IN SCIENCE LIBRARY. / Vita. / Includes bibliographical references. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1929. / Includes bibliographical references. / by Harold T. Gerry. / B.S.

Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Exposure of Au-Ni(111) surface alloys to molecular hydrogen results in the dissociative chemisorption of hydrogen to produce H atoms adsorbed on two distinct types of threefold hollow sites, as identified via thermal desorption spectroscopy (TDS), collision induced recombinative desorption (CIRD), and high resolution electron energy loss spectroscopy (HREELS). Hydrogen atoms bind relatively strongly to threefold hollow sites consisting only of Ni atoms, with a binding energy of 63 kcal/mol and characteristic vibrational frequencies of 970 and 1170 cm-¹. Hydrogen atoms bind relatively weakly to threefold hollow sites consisting of two Ni atoms and one Au atom, with a binding energy of 55 kcal/mol and characteristic vibrational frequencies of 820 and 1050 cm'. Alloying of Au into the Ni(l 11) surface reduces the amount of chemisorbed H upon molecular H2 exposure, but promotes the formation of bulk H upon atomic H exposure, compared to a Ni(111) surface. A robust algorithm for determining the Au coverage of Au-Ni(111) surface alloys using Auger electron spectroscopy is also developed. The observation of three vibrational features at 750, 1470, and 2220 cm-¹ in the HREEL spectra of purportedly clean Au-Ni(111) surface alloys is reported. These features are attributed to graphene, formed on the Au-Ni(111) surface alloys via segregation of very small amounts of residual carbon in the bulk. The alloyed Au atoms destabilize the carbide phase and promote the nucleation and growth of graphene. The features at 750 and 1470 cm-1 are assigned as the ZO and LO (TO) phonon modes of graphene, respectively. The feature at 2200 cm-¹ is tentatively assigned as a two-phonon (ZO + LO/TO) mode. An additional feature at 2990 cm-¹ is identified as the stretching mode of C-H bonds, formed through the interaction between water or hydrogen from the vacuum chamber background pressure and the dangling bonds of carbon atoms along the edges of graphene. The feature at 3670 cm-¹ is the O-H stretching mode of isolated water molecules or hydroxyl groups. The addition of Au weakens the interaction between the metal d band and graphene [pi] state, resulting in a stiffening of the ZO mode by 30 ~ 60 cm-', compared to graphene-Ni(111). The softening of the LO (TO) mode by 30 cm-¹ arises from the slightly larger unit cell of graphene adsorbed on Au-Ni(1 11) as compared to that on Ni(111). / by Qing Liu. / Ph. D. in Physical Chemistry

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1994. / Includes bibliographical references. / by Julie K. Thomas. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007. / Vita. / Includes bibliographical references (p. 193-212). / Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices (QD-LEDs), we set out to develop thin-film, layered photodetectors in which the active layer is a chemically annealed QD solid. This thesis reports initial steps in this development. Chapters 1 and 2 contain introductory material. In Chapter 3, we demonstrate a layered QD photodetector (QD-PD) in which the active layer is a 200-nm thick film of CdSe QDs annealed with n-butylamine. These "thick-slab" devices, active in the visible spectrum, represent a minimal transformation from the transverse channel test structures employed for more fundamental studies to a layered, sandwich geometry. The thick-slab design exhibits a number of desirable characteristics, including near-unity internal quantum efficiency and a 50-kHz bandwidth. More complex QD-PD designs, allowing the successful incorporation of much thinner QD solids, are discussed in Chapter 4, and these devices provide insight into the zero-bias operation of thick-slab QD-PDs. / (cont.) The final three chapters of the thesis focus on PbSe QDs, this group's initial material of choice for accessing the short-wavelength-IR spectral window. Initial study of PbSe QDs as a material for QD-PDs is described in Chapter 5. Chapter 6 discusses an 31P-based NMR investigation of the mechanism of PbSe monomer formation, allowing for rational "doping" of syntheses to increase chronically low yields. Finally, Chapter 7 discusses a brief assessment of the suitability of PbSe QDs for in vivo imaging. / by David C. Oertel. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. / Vita. / Includes bibliographical references. / I. Synthesis of Substituted Pyridine Derivatives via the Ruthenium-Catalyzed Cycloisomerization of 3-Azadienynes. The two-step conversion of various N-vinyl and N-aryl amides to the corresponding substituted pyridines and quinolines, respectively, is described. The process involves the direct conversion of amides, including sensitive N-vinyl amides, to the corresponding trimethylsilyl alkynyl imines followed by a ruthenium-catalyzed protodesilylation and cycloisomerization. A wide range of new alkynyl imines are prepared and readily converted to the corresponding azaheterocycles. II. Single-Step Synthesis of Pyrimidine Derivatives. The single-step conversion of various N-vinyl and N-aryl amides to the corresponding pyrimidine and quinazoline derivatives, respectively, is described. The process involves amide activation with 2-chloropyridine and trifluoromethanesulfonic anhydride followed by nitrile addition into the reactive intermediate and cycloisomerization. In situ nitrile generation from primary amides allows for their use as nitrile surrogates. The use of this chemistry with sensitive N-vinyl amides and epimerizable substrates in addition to a wide range of functional groups is noteworthy. III. Direct Synthesis of Pyridine Derivatives. The single-step conversion of various N-vinyl and N-aryl amides to the corresponding pyridine and quinoline derivatives, respectively, is described. The process involves amide activation with trifluoromethanesulfonic anhydride in the presence of 2-chloropyridine followed by t-nucleophile addition to the activated intermediate and annulation. Compatibility of this chemistry with sensitive N-vinyl amides, epimerizable substrates, and a variety of functional groups is noteworthy. / by Matthew D. Hill. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. / Vita. / Includes bibliographical references. / Chapter 1. Highly active and efficient catalyst systems derived from palladium precatalysts and monophosphine ligands for the Suzuki-Miyaura cross-coupling reaction of heteroaryl boronic acids and esters has been developed. This method allows for the preparation of a wide variety of heterobiaryls in good to excellent yields and displays a high level of activity for the coupling of heteroaryl chlorides as well as hindered aryl and heteroaryl halides. Specific factors that govern the efficacy of the transformation for certain heterocyclic motifs were also investigated. Chapter 2. A highly efficient method for the palladium-catalyzed Suzuki-Miyaura reaction of lithium triisopropyl 2-pyridylborates has been developed. Catalysts comprised of Pd2dba3 and either diaryl or dialkyl phosphine oxide supporting ligands were found to be ideal for the transformation. This report represents one of the most general systems for the cross-coupling of aryl and heteroaryl bromides and chlorides with 2-pyridyl-derived nucleophiles. Chapter 3. Catalysts comprised of Pd and dialkylmonophosphinobiaryl ligands provide highly active systems for the borylation of aryl and heteroaryl chlorides. The direct preparation of symmetrical and unsymmetrical biaryls from two aryl chlorides without the need to isolate the intermediate boronate esters is also described. Additionally, computational studies provide insight into the roles of the biaryl phosphine ligand as well as KOAc in the catalytic cycle. Chapter 4. A highly efficient method for the palladium-catalyzed borylation of aryl halides with an inexpensive and atom-economical boron source, pinacol borane, has been developed. / (cont.) This system allows for the conversion of aryl and heteroaryl iodides, bromides and several chlorides, containing a variety of functional groups, to the corresponding pinacol boronate esters. In addition to the increase in substrate scope, this is the first general method where relatively low quantities of catalyst and short reaction times can be employed. / by Kelvin L. Billingsley. / Ph.D.