Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item LIGHT CONTROL OF CHEMICAL SYSTEMS: PHOTOCHEMICAL ELECTRON TRANSFER METHODS FOR RELEASING CALCIUM IONS AND THE PHOTOISOMERIZATION OF ALKENES TO MODULATE RHEOLOGICAL CHANGES.(2021) Heymann Loor, Romina R; Falvey, Daniel E; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our research combines organic photochemistry with the engineering principles of rheology through the study of photorheological fluids (PR). The two photochemical systems researched show changes in the rheological properties brought about by the addition of light. The investigated systems are the photoisomerization of cinnamic acid derivatives in the surfactant, Cetyltrimethylammonium bromide (CTAB), and calcium release through degradation ethylenediaminetetraacetic acid (EDTA) caused by an electron transfer mechanism. The CTAB system shows how a change in molecular conformation can cause significant changes in the bulk property of a solution. The calcium EDTA system employs targeted electron transfer to cause calcium release, which gels the biopolymer alginate with inexpensive, readily available materials. Chapter 2 details how the orientational binding, intermolecular interactions, and molecular geometry of cinnamic acid derivatives contribute to the rheological changes in CTAB. 1H NMR titration studies in CTAB identified binding patterns of the additives in CTAB. From those studies orientational binding models were developed for trans-ortho-methoxycinnamic acid (tOMCA), cis-ortho-methoxycinnamic acid (cOMCA), meta-methoxycinnamic acid (mMCA), para-methoxycinnamic (pMCA), ortho-hydroxycinnamic acid (oCoum), meta-hydroxycinnamic acid (mCoum), and para-hydroxycinnamic acid (pCoum). 1H-1H 2D NOESY spectra identified through space intermolecular interactions occurring within the micelle. Preliminary data into possible π-anion interaction between tOMCA molecules within the micelle is presented. Photolysis confirmed the creation of cis isomers for all additives but also identified coumarin by-products for oCoum. B3LYP calculations indicated out-of-plane geometry for all the cis isomers and possible intramolecular hydrogen bonding of oCoum. Finally, a model of binding interactions that lead to changes in the packing parameter of the surfactant and, therefore, a change into wormlike micelles for tOMCA versus cOMCA is introduced. In chapters three and four, we investigated calcium release using sensitizers that promote photoinduced electron transfer. Anthraquinones derivatives were shown in Chapter 3 to release calcium in stoichiometry amounts with UV light irradiation. In Chapter 4, flavins produced 1000-fold calcium release to sensitizer concentration in the visible light spectrum. In both chapters, there are detailed calcium release studies, degradation studies, and alginate experiments. We present calcium release studies at acidic and neutral pH, quantum yields, degradation of EDTA, sensitizer reoxidation studies, sensitizer degradation data, fluorescence, and transient spectra. While enough calcium was released to produce alginate gels, none were made in vitro at neutral and acidic pH.Item RAPID Lithography: Photopolymerization Characterization and Initiation Kinetics(2012) Stocker, Michael Paul; Fourkas, John T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In order to improve upon the resolution of photolithography, a technique that is used to produce features for today's micro and nanodevices, techniques must move beyond e-beam and deep-UV sources. Multiphoton absorption polymerization (MAP) uses near-infrared light for the creation of complex, three-dimensional features on the sub-100 nm scale. The resolution of MAP can be enhanced further using a two-beam technique called resolution augmentation through photo-induced deactivation (RAPID) to the reach feature sizes as small as 40 nm. The mechanism and kinetics of photo-induced deactivation are not well understood. To better understand these processes, studies of different photoinitiators have been performed. We find that some photoinitiators are so efficient at deactivation that they are capable of undergoing self-deactivation by addition of another photon from the excitation source. This phenomenon is manifested in a polymerization trend in which feature size has a proportional velocity (PROVE) dependence, the opposite of the conventional velocity dependence. We also demonstrate that the velocity dependence can also be tuned between PROVE and conventional dependences. Kinetic models have been formulated to account for the observed deactivation. By reconciling experimental data for some sample photoinitiators with the kinetic model through the use of simulations, kinetic rate constants are determined. The self-deactivation efficiency of each photoinitiator was determined. The lifetimes of intermediates in the radical photopolymerization process were also determined. The kinetic rate constants associated with photoinitiators should allow for the customization of photoinitiators for specific applications and make RAPID a more efficient process capable of reaching resolution on the level of 30 nm and below.