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Chemistry - Master's degree

Mostrando recursos 1 - 20 de 124

  1. Studies on a catalytic cadogan cyclization by PI̳I̳I̳/PV̳=O redox cycling

    Harrison, Tyler S. (Tyler Steven)
    Organophosphorus reagents offer potential for developing catalytic protocols by inclusion of a reductant such as hydrosilanes to (re)generate the chemically active phosphine in situ. In our research, we have successfully adapted this concept to the Cadogan reductive cyclization by using a strained 4-membered phosphetane precatalyst, which proved to be more competent than acyclic and 5-membered analogs for P(III)/P(V)=O redox cycling. A variety of substrates were found to successfully undergo catalytic Cadogan indazole cyclization. The mechanism of the cyclization has been expanded. The resting state of phosphorus was determined to be the P" phosphetane, and this phosphetane proved to be 8...

  2. Flow-IEG enables programmable thermodynamic properties in sequence-defined unimolecular macromolecules

    Wicker, Amanda C. (Amanda Catherine)
    Flow-IEG has emerged as a powerful platform for the production of sequence-defined macromolecules and has demonstrated the utility of adapting continuous-flow methodologies to the production of materials for structure/function analysis. Our Flow-IEG system has been expanded to include both the ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC), as well as a more operationally simple version of the copper-catalyzed analogue (CuAAC). These advances have enabled the rapid synthesis of a library of oligomers with systematic variations in triazole connectivity, allowing us to probe the consequences of sequential connectivity on material properties. In our investigation, we found that the crystallinity of the synthesized materials increased...

  3. Synthesis of staphyloferrin B (SB)-cargo conjugates

    Gulati, Anmol
    The ability of the Gram-positive human pathogen Staphylococcus aureus to cause infection and develop antimicrobial resistance poses a significant threat to public health. One potential method to combat bacterial infections involves the use of siderophore-drug conjugates to selectively deliver antibiotics to bacteria. Siderophores are low-molecular-weight chelators with high affinity for iron(Ill) that are biosynthesized by bacteria to acquire iron from the environment. Several reports of siderophore-mediated delivery of antibiotics to Gram-negative bacteria have been published. However, only a few examples of applying this strategy to Gram-positive bacteria are reported. Here, the potential of staphyloferrin B (SB), a polycarboxylate siderophore and...

  4. A study of the reaction of hydrogen iodide with silicon

    Klein, Carolyn Horvey
    by Carolyn H. Klein.

  5. Regio- and size-selective catalysis : porous aromatic frameworks and C3-symmetric receptors

    Tanaset, Anont
    Porous aromatic frameworks (PAFs) have recently emerged as a new class of materials with impressive stability and high surface area, which led to their applications in gas storage and small molecule recognition. Herein, the synthesis and functionalization of PAFs were described, and their potential use as selective oligomerization for fuel upgrading was investigated. However, functionalized PAFs showed undesired reactivity possibly due to low rate of substrate and product diffusion in and out of the framework. On the other hand, a novel C3-symmetric hydrogen bonding receptor was synthesized and investigated for its use as size- and regioselective catalyst. It was demonstrated...

  6. Selective ethylene dimerization by a nickel-exchanged metal-organic framework catalyst

    Martin, Kathleen E. (Kathleen Ewing)
    Short linear [alpha]-olefins such as 1-butene are valuable commodity chemicals due to their use as comonomers in linear low-density polyethylene. Presently only homogeneous systems are used to catalyze ethylene dimerization in industry, causing many to suffer from quick deactivation and poor selectivity. The metal-organic framework (MOF) CPF-5 Mn₅(TBA)₃(HCOO)₃(OH)(H₂O₂)2]]₄·6DMF where TBA = 4-(l H-tetrazol-5-yl)benzoic acid provides an ideal structural template for the development of a heterogeneous catalyst for ethylene dimerization. Ni exchanged CPF-5 (Ni-CPF-5) treated with diethylaluminum chloride had a maximum turnover frequency of 23,000 mole ethylene per mole Ni per hour, and a maximum selectivity for 1-butene of 80% under...

  7. Metal metaphosphate complexes for redox flow batteries

    Avena, Laura
    In this thesis, possibility of using anionic metal complexes to limit crossover of active species in redox flow batteries was explored. A series of first row transition metal trimetaphosphate complexes as bis(triphenylphosphine)iminium (PPN) salts have been prepared. Their electrochemical properties have been studied to evaluate them for redox flow battery applications. [PPN]₃[Fe(P₃Og)₂] and [PPN]₂[VO(P₃O₉)(acac)] were identified as a suitable couple for a dual-active-species redox flow battery with an open cell potential of 1.5 V. [PPN]₃[V(P₃Og)₂] can be oxidized and reduced within the stability window of acetonitrile and it is therefor a promising candidate for single-active-species redox flow battery applications. The...

  8. Transparent-to-dark electrochromic behavior in naphthalene-diimide-based mesoporous MOF-74 analogs

    Al Kaabi, Khalid (Khalid Abdulaziz)
    The deliberate insertion of redox-active naphthalene diimide ligands in the versatile family of metal-organic frameworks known as MOF-74 (CPO-27) gives rise to a mesoporous electrochromic MOF that can be switched from transparent to dark, a desirable feature in electrochromic devices such as smart windows. Specifically, we report two new materials with the MOF-74 topology that display redox activity stemming from a naphthalene diimide salicylic acid (NDISA) ligand. We show that the new materials can be deposited as thin films on fluorinedoped tin oxide glass. The surprisingly different morphology of MOF films obtained from Mg²+ and Ni²+ ions is likely controlled...

  9. Advancements in polymer resins for solid-phase peptide synthesis

    Hewage, Gihan B. (Gihan Bhagye)
    The use of polymeric supports in solid-phase peptide synthesis has allowed for the facile, rapid synthesis of short peptides in a one bead/one sequence manner. This approach allows for screening peptide libraries for binding and catalytic activities. Once hits are found, the sequence of the active protein can be determined via mass spectrometry. However, problems arise when trying to create large libraries (on the order of 10⁹) of peptides. The resins large enough to provide sufficient amounts of peptide sample for sequencing would occupy too great a volume in order to create large quantities. Conversely, attempting to fold a protein...

  10. Mass transport in metal-organic frameworks as a limiting step in size-selective oligomerization

    Palmer, Ryan D. (Ryan Dee)
    Metal organic frameworks (MOFs) are a relatively new class of crystalline, porous materials at the interface of organic and inorganic chemistry that have been applied in gas absorption and storage systems, thin-film devices, and heterogeneous catalysts. While numerous examples of size-exclusive catalysis have been reported, to our knowledge no reports of size-selective oligomerization catalysis have been reported to date. Herein, chemically stable Zr based MOFs, namely UiO-67 and PCN-777, are investigated as possible candidates to promote size-selective oligomerization catalysis. Using acylated propylene-glycol methyl ethers as model substrates, the mass transport properties of these materials was investigated. Unfortunately, slow mass transport...

  11. Copper-catalyzed enantioselective stereodivergent synthesis of amino alcohols

    Wong, Zackary L. (Zackary Leland)
    Different stereoisomers of bioactive molecules can have distinct activities in biological systems. For this reason, it is routine procedure in the drug discovery and development process to prepare the full matrix of possible stereoisomers of drug candidates for biological evaluation and to determine the stereochemical purity of these molecules. Despite many recent advances in asymmetric synthesis, the development of general and practical strategies that are fully divergent and give rise to all stereoisomers of products bearing multiple contiguous stereocenters remains a significant challenge. Herein we report a stereodivergent copper-based approach for the expeditious construction of amino alcohols with high levels...

  12. Xenon difluoride etching and molecular oxygen oxidation of silicon by reactive scattering

    Rowlands, Daniel Walter
    While both molecular fluorine (F₂) and xenon difluoride (XeF₂) fluorinate Si(l00)2xI surfaces at coverages up to one monolayer, fluorine is unable to cleave Si-Si bonds that ultimately leads to etching silicon at coverages above one monolayer (reaction probability 9x 10-⁴) while XeF₂ does so readily (reaction probability 0.6). Previous studies have demonstrated that both fluorine and xenon difluoride react with silicon via atom-abstraction mechanisms at low coverages, and that the XeF radicals produced by atom abstraction from xenon difluoride dissociate in the gas phase, producing a source of F radicals that may contribute to Si-Si bond cleavage by formation of...

  13. Understanding colloidal quantum dot excitation with solution photon correlation fourier spectroscopy

    Heathcote, S. Leigh (Stephanie Leigh)
    Colloidal quantum dots (CQDs) have useful absorption and emission properties but exist in inhomogenous batches. Solution photon correlation fourier spectroscopy (S-PCFS) combines interferometry with fluorescence correlation spectroscopy (FCS) to measure the spectral correlation of the average single fluorophore in a solution. With S-PCFS, the intrinsic emission linewidth of CQDs can be assessed. This linewidth information is related to phonon coupling and gives insight into the separation of holes and electrons in excited CQDs. Experimental considerations and recommendations for troubleshooting a S-PCFS apparatus are also presented here.

  14. Advancements in branched bottlebrush polymers for responsive, targeted imaging

    Sowers, Molly A. (Molly Ann)
    Multi-modality and stimuli responsive nanoparticles are promising platform materials for medical imaging and diagnostics. Specifically magnetic resonance imaging (MRI) and nearinfrared (NIR) fluorescent probes can be used in combination to visualize biodistribution and in vivo clearance rates. We reasoned that through the use of a nitroxide radical MRI contrast agent along with a NIR fluorophore it would be possible to study these phenomena along with nitroxide reduction in vivo. Thus, we have developed branched bottlebrush copolymers that display compensatory fluorescence response to nitroxide reduction that enables correlation of MRI contrast, fluorescence intensity, and spin concentration in tissues. These polymers were...

  15. Free approximation of transport properties in organic system using Stochastic Random Matrix Theory

    Xie, Wanqin, Ph. D. Massachusetts Institute of Technology
    The proposed research is a study and application of Stochastic analysis- Random Matrix Theory(RMT) to fast calculate the transport properties of large static systems with relatively large disorder in mesoscopic size. As a major topic of Random Matrix Theory(RMT), free convolution managed to approximate the distribution of eigenvalues in an Anderson Model.So the next step is trying to expand RMT to approximate other quantities, such as transmission probability, conductivity and etc. Due to the eigenvectors' shifts, RMT works well only for small disorder. System with larger disorder requires to take in account of the changes in eigenvectors directly or through...

  16. New immobilized antimicrobial polyethylenimines : synthesis and properties

    Liu, Harris K. (Harris Ken-Ming)
    Surfaces modified with immobilized N-alkyl-polyethylenimines (N-alkyl-PEls) containing various alkyl groups were synthesized and tested against various pathogenic human influenza viruses to establish structure-to-virucidal activity relationships. Various physical-chemical properties of each surface were correlated with their virucidal activities to identify key antiviral surface properties. The accessibility of N-alkyl-PEI quaternary ammonium groups to influenza virus was subsequently identified as the key determinant of antiviral efficacy, as demonstrated by FITC-lysozyme surface titration. Previously used multistep syntheses to create antimicrobial surfaces by immobilizing Nalkyl- PEls were replaced with a novel aerosol-assisted plasma deposition procedure. N,N-hexyl,methyl-polyethylenimines were directly plasma-coated onto a glass surface. The resulting...

  17. Synthesis and mechanistic studies of novel antitumor transition metal complexes

    Yoo, Hyunsuk, S.M. Massachusetts Institute of Technology
    In order to overcome side effects and drug resistance associated with conventional Pt(II) drugs, our lab has developed novel platinum complexes. One of the new platinum complexes developed in our lab is the monofunctional platinum anti-cancer compound phenanthriplatin. We have found that by binding to sulfur complexes, phenanthriplatin undergoes changes in its kinetic and cytotoxic properties. Sulfur adducts of phenanthriplatin were synthesized to study the complex roles sulfur compounds serve in the cellular action of the monofunctional compound. In addition, we have examined how Pt(IV) chemistry can be successfully applied to increase the efficacy of Pt(II) compounds. We conjugated hydrophobic...

  18. Synthetic polypeptide-based hydrogel systems for biomaterials

    Martin, Mackenzie Marie
    Hydrogels formed from synthetic polypeptides generated by ring opening polymerization (ROP) of a-amino acid N-carboxyanhydrides (NCAs) present a robust material for modeling the interaction between extracellular matrix (ECM) properties and cellular phenomena. The unique properties of the polypeptide backbone allow it to fold into secondary structures and the ability to modify the side chain presents the opportunity to display chemical functionalities that dictate cellular signaling. The ability to induce cells to form tissue is a chemical and engineering challenge due to the fact that cells need physical support in the form of a 3D scaffold with both chemical and mechanical...

  19. Development of novel polymeric architectures for applications in drug delivery and studies towards the synthesis of perfect polymers by iterative exponential growth "Plus" (IEG+)

    Gao, Angela X. (Angela Xiaodi)
    Polymeric materials are ubiquitous in numerous facets of everyday life, and their applications will only become increasingly prevalent as the field of polymer science advances. The first chapter of this thesis describes the use of polymeric nanoparticles to overcome challenges in traditional drug delivery. Specifically, a series of novel acid-cleavable bisnorbornene crosslinkers were synthesized and evaluated as building blocks for the formation of acid-degradable brush-arm star polymers (BASPs) via the brush-first ring-opening metathesis polymerization (ROMP) method. A bis-norbornene acetal structure was identified that, when employed in conjunction with a poly(ethylene glycol) (PEG) macromonomer, provided highly controlled BASP formation reactions. Combination...

  20. Approaches towards development of novel fluorogenic biosensors for detection of small protein analytes

    Cheung, Stephanie, S.M. Massachusetts Institute of Technology
    One of the most remarkable ideas in modem biology is that organization of multicellular life is orchestrated by a relatively small repertoire of signaling molecules, which mediate communication between cells. Breakdown of these communication pathways can have profound consequences, leading to a multiplicity of developmental defects and disease states. In particular, the ErbB family of receptors and ligands regulate key cellular processes such as proliferation, differentiation, and apoptosis during embryonic development, cellular homeostasis, and tumorigenesis. The generality of the ErbB-network has made it one of the most well-studied cell signaling systems. However, traditional methods used to study cellular signaling either...

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