Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Includes bibliographical references. / by David Hales Bown. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Vita. / Includes bibliographical references. / A scalable and reproducible protocol has been developed for the preparation of (-)- neomenthyldiphenylphosphine ((-)-1) from inexpensive starting materials. This ligand was then utilized in the nickel-catalyzed reductive coupling of alkyne 3 and aldehyde 4 to afford allylic alcohol 5 in high yield and enantiomeric excess. Several important modifications were made to the initially communicated procedure in order to effectively translate this methodology from the millimole to decimole scale. Allylic alcohol 5 was then ozonolyzed to afford [beta]-hydroxy ketone 6 with complete preservation of enantiomeric purity. Chapter II. The endo-selective cyclization of alcohols onto epoxides provides a direct route for constructing the oxygen heterocycles found in ladder polyether natural products. Additionally strategies to transform multiple epoxides into multiple new rings have appealing parallels to the proposed biogenesis of these compounds. A continuing challenge is to overcome the inherent preference for the undesired smaller ring product over the larger ring product, processes termed exo and endo cyclization, respectively. Additionally, any method to address this problem should yield products that are themselves synthetically relevant intermediates. We discovered that a benzylidene acetal templated the cyclization of electronically unbiased epoxy alcohols, such as 75, affording products with significant synthetic utility. Critical for high endo-selectivity was the use of silicon-dioxide based promoters. / (cont.) Highlighting the template's utility, the newly formed product (76) was then transformed into a highly decorated THP template (84), corresponding to ring K of gymnocin A. In water, 84 underwent a waterpromoted cascade to construct three additional rings of gymnocin A. We have also achieved cascades of methylene acetal templates with electronically activated epoxides to construct the FG rings of gambierol. Use of these functionalized templates and the products derived from them sets the stage for the convergent total synthesis of ladder polyether natural products. / by Aaron R. Van Dyke. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2016. / 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 133-145). / Semiconductor nanocrystals, also known as quantum dots (QDs) have been used in solid state light emission applications ranging from fluorescent downconverters to LEDs and lasers, as well as energy generation devices such as solar photovoltaics and thermoelectrics. In order to realize these myriad applications, the fundamental physics of both electronic and vibrational energy transfer must be understood to engineer better device performance. This thesis begins with a general introduction to the physics and chemistry of QDs as well as an introduction to lattice vibrations, including a proposed model for understanding thermal conductivity in solid state QD-based devices. It continues with a discussion of the methods used to understand the photoluminescence and vibrational characteristics of QDs, including spectrally-resolved time-correlated single photon counting measurements to understand QD photoluminescence lifetime as a function of emission wavelength, and low-frequency Raman spectroscopy to measure acoustic phonons in nanocrystal solids. These two chapters serve as an introduction to the ideas and methods used throughout the thesis. In Chapter 3, Förster theory is used in conduction with spectrally- and temporally-resolved photoluminescence spectroscopy to understand the rates of excitonic energy transfer in CdSe/CdZnS core/shell QDs through a calculation of the effective dipole-dipole coupling distance known as the Förster radius. This work demonstrated energy transfer rates between donor and acceptor QDs between 10-100 times faster than the predictions based on standard applications of Förster theory, corresponding to an effective Förster radius of 8-9 nm in close packed QD films. Several possible effects, including an enhanced absorption cross section, ordered dipole orientations, or dipole-multipole coupling, can explain the observed difference between our measurements and the Förster theory predictions, demonstrating that several standard assumptions commonly used for calculating QD resonant energy transfer rates must be carefully considered when the QDs are in a thin-film geometry. Chapters 4-5 involve the use of low-frequency Raman spectroscopy to probe acoustic phonons in QDs. These low-frequency acoustic vibrations affect the electronic, optical, and thermal properties of semiconductor nanocrystals, and the ability to rationally tune these modes would offer a powerful strategy for controlling phonon-assisted processes. Chapter 4 demonstrates that surface chemistry can be used to manipulate the low-frequency acoustic vibrations of CdSe QDs, and shows in particular that surface-bound ligands modify the resonant vibrational frequencies of the core. This effect is more pronounced for smaller nanocrystals, where the surface ligands constitute a larger fraction of the overall mass. A continuum mechanics model that explicitly includes the ligand shell quantitatively reproduces most of our experimental results. This model can be extended to understand the effect of inorganic shells as well, and we demonstrate that by growing a CdS epitaxial shell we can achieve reduction in acoustic phonon frequencies by more than 70% compared to the CdSe core alone. In Chapter 5, these low frequency phonons are further measured as a function of temperature. Low-temperature measurements allow the unambiguous assignment of overtone modes in large CdSe/CdS nanocrystals to a higher order (n = 2) vibrational mode rather than a multiphonon mode. Additionally, the acoustic phonon frequency is shown to vary with temperature though the linewidth remains constant for a variety of sizes of QDs. This variation of frequency without a corresponding broadening suggests that the pure volume contribution to the temperature-dependent phonon energies dominates over phononphonon interactions through anharmonic coupling. / by Anna Jolene Mork. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1958. / Vita. / Includes bibliographical references (leaves 87-90). / by Alfred Danti. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004. / Vita. / Includes bibliographical references. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Coherent two-dimensional infrared (2D IR) spectroscopy is used as a tool for investigating the molecular structure and dynamics of coupled vibrations in solution on a picosecond timescale. The strongly coupled asymmetric and symmetric carbonyl stretches of Rh(CO)₂C₅H₇0₂ (RDC) dissolved in hexane serve as a convenient model system. Fourier transform 2D IR spectra are obtained from heterodyne-detected third-order nonlinear signals using a sequence of broad bandwidth femtosecond IR pulses. A 2D IR correlation spectrum with absorptive lineshapes results from the addition of 2D rephasing and non-rephasing spectra, which sample conjugate frequencies in the evolution time period. The 2D IR correlation spectrum contains peaks with different positions, signs, amplitudes and lineshapes. The positions of the peaks map the transition frequencies between the ground, singly, and doubly excited states of the system, and thus describe the anharmonic vibrational potential. Peak amplitudes reflect the relative magnitudes and orientations of the transition dipole moments in the molecular frame, the electrical anharmonicity of the system, and the vibrational relaxation dynamics. The 2D line shapes are sensitive to the complicated system-bath interactions in solution. 2D IR spectra taken with varying polarization conditions and as a function of a variable waiting time can be used to isolate and quantify these spectroscopic observables. The polarization-selective 2D IR spectra of RDC in hexane are analyzed in terms of two coupled local coordinates to obtain their mutual orientation and the magnitude of the coupling between them. Evidence of vibrational coherence transfer between close-lying transition frequencies is indicated by the presence of extra induced peaks in 2D IR / (cont.) rephasing spectra. The data is modeled by using Redfield theory to account for coherence transfer, vibrational dephasing and population relaxation in a multilevel vibrational system. Building on the studies of the RDC model system, 2D IR spectroscopy is used to study the thermal denaturation of RNase A by characterizing the temperature-dependent Amide I band. A nonlinear IR probe is used to study the early events in the laser temperature-jump initiated denaturation of RNase A. / by Munira Khalil. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Investigated herein is the reactivity of the terminal-nitrido, trisanilide tungsten complex, NW(N[i- Pr]Ar)3 (Ar = 3,5-Me 2C6H3, 1). Nitride 1 has been shown to undergo an "N for (O)C1 metathesis with a variety of acid chlorides to form oxochloride (Ar[i-Pr]N) 3W(O)C1 (2) and the corresponding nitriles. The reaction of 1 with acid chlorides has been shown to proceed through an acylimido chloride intermediate. Furthermore, oxochloride 2 has been converted to a terminal phosphido trisanilide tungsten complex, PW(N[i-Pr]Ar)3 (9) by treatment with the anionic niobium phosphide complex [Na(OEt2)][PNb(N[Np]Ar) 31. Nitride 1 and oxochloride 2 have been converted to pseudo-octahedral complexes through the use of electrophilic reagents such as oxalyl chloride and phosphorus pentachloride. (Ar[i- Pr]N)3W(OCN)(Cl) 2 (10) and (Ar[i-Pr]N)3W(N=PCl3)(Cl) 2 (11) are synthesized by treating compound 1 with oxalyl chloride and PCl5, respectively. Similarly, (Ar[i-Pr]N) 3W(Cl) 3 (12) is formed by treatment of oxochloride 2 with PC15 with concomitant loss of oxyphosphorus trichloride. Reaction studies of trichloride 12 undertaken in the attempt to generate a low-coordinate tungsten species are also presented. Also reported presently is a new procedure for synthesis of the terminal phosphoryl complex (Ar[t-Bu]N)3MoPO (17) by treating phosphide (Ar[t-Bu]N) 3MoP (16) with the potent oxygen atom transfer (OAT) reagent mesitylnitrile oxide (MesCNO). In conjunction with collaborators, the thermodynamic and kinetic aspects of MesCNO as an OAT reagent with phosphide 16 and phosphines have been investigated. Density Functional Theory calculations of OAT reactions of MesCNO are also shown. In an effort to further develop the coordination chemistry of the trianionic, tridentate ligand trimetaphosphate, studies are described whereupon trimetaphosphate is metallated with molybdenum. (MeCN)3Mo(CO) 3 reacts with [PPN] 3[P30 9] -H20 ([PPN] = [Ph3P=N-PPh3]') to form the trimetaphosphate salt [PPN]3[(P30 9)Mo(CO) 3] ([PPN] 3[18]) in high yield. Efforts to generate trimetaphosphate vanadium oxo ((P30 9)V--O, 19) are also revealed. Finally, the synthesis of a new bis-enamide ligand class is described by the double addition of ketenimines to dilithium arylphosphanides. Formation of [Li(thf)]2 {PhP[C(CPh2)NPh] 21 ([Li(thf)] 2[20]) and [Li(thf)]2{MesP[C(CPh2)NPh] 2} ([Li(thf)]2[21]) are presented. The synthesis of tantalum species utilizing these new bis-enamide ligands is also demonstrated. / by Christopher Robert Clough. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013. / Vita. Cataloged from PDF version of thesis. / Includes bibliographical references. / Chapter 1. Sensing Strategies for Detection of Mobile Zinc. Mobile zinc plays important physiological roles in areas such as the hippocampus, prostate, and pancreas. A better understanding of the distribution of intracellular mobile zinc could provide insight into the pathology of diseases including prostate cancer and Alzheimer's disease, both of which have been linked to abnormal mobile zinc levels. Accordingly, a palette of spatially-specific mobile zinc sensors is needed to investigate mobile zinc in important areas such as the mitochondria or zinc vesicles in neurons. Instead of repeating the de novo sensor design process for each target, a modular approach was developed to take advantage of the existing library of sensors and enable rapid creation of targeted probes. Chapter 2. Targeting Fluorescent Zinc Sensors to the Mitochondria Using Triphenylphosphonium Ions. Mitochondrial mobile zinc plays an important, although poorly understood, role in prostate cancer. To investigate the biology of zinc in the mitochondria, constructs incorporating fluorophores and the mitochondria-targeting triphenylphosphonium (TPP) moiety were tested and used to study sensor uptake and localization to the mitochondria. Chapter 3. Peptide-based Targeting of Fluorescent Zinc Sensors to the Plasma Membrane and Intracellular Targets in Live Cells. Peptide-sensor constructs were explored as a modular method of targeting sensors to specific locations. Taking advantage of the synthetic flexibility and targeting advantages of peptide-sensor constructs, mobile zinc sensors were directed to the exterior of the plasma membrane and to intracellular targets. A series of peptide-sensor constructs were created to further investigate fluorophore effects on sensor uptake and localization. Chapter 4. Improvement of Sensor Uptake, Localization, and Photophysics Through Acetylation of Fluorescein-based Sensors. A generalizable strategy for improving the uptake and photophysics of mobile zinc probes was explored. The ZPI-TPP sensor construct was modified by one-step acetylation of phenolic oxygen atoms. This modification dramatically improved photophysics and eliminated problems with membrane impermeability that would otherwise result in endosomal sequestration. The resulting DA-ZP1-TPP sensor was highly selective for zinc, resilient against cellular esterases, and, most importantly, was specifically targeted to the mitochondria. / by Wen Chyan. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1997. / Includes bibliographical references. / by Andrew J.E. Peat. / Ph.D.

Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 72-77). / This thesis is about the study and application of a stochastic optimization algorithm - Random Matrix Theory coupled with Neural Networks (RMT-RNN) to large static systems with relatively large disorder in mesoscopic systems. It is a new algorithm that can quickly decompose random matrices with real eigenvalues for further study of physical properties, such as transmission probability, conductivity and so on. As a major topic of Random Matrix Theory (RMT), free convolution has managed to approximate the distribution of eigenvalues in the Anderson Model. RMT has proven to work well when looking for the transport properties in slightly defect system. Systems with larger disorder require to take in account of the changes in eigenvectors as well. Hence, combined with parallelizable Neural Network (RNN), RMT-RNN turns out to be a great approach for eigenpair approximation for systems with large defects. / by Wanqin Xie. / Ph. D. in Physical Chemistry

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1988. / Includes bibliographical references. / by Mary Elizabeth Roth. / Ph.D.