LIGHT CONTROL OF CHEMICAL SYSTEMS: PHOTOCHEMICAL ELECTRON TRANSFER METHODS FOR RELEASING CALCIUM IONS AND THE PHOTOISOMERIZATION OF ALKENES TO MODULATE RHEOLOGICAL CHANGES.
Heymann Loor, Romina R
Falvey, Daniel E
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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.