Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Administrative Home Department

Department of Chemistry

Advisor 1

Haiying Liu

Committee Member 1

Tarun K. Dam

Committee Member 2

Loredana Valenzano

Committee Member 3

Qinghui Chen

Abstract

Varied intracellular pH levels are critical for various physiological processes such as enzymatic activity, cell proliferation and apoptosis, ion transport, and muscle contraction. Cellular compartments, like lysosomes, must retain an acidic environment (pH ~ 4.5) to activate hydrolytic enzymes necessary for the breakdown of large biomolecules. Another cellular organelle, the mitochondria, provides the cell with energy and must retain an alkalis environment (pH ~ 8.0) for proper function. Substantial lysosomal and mitochondrial pH deviation is associated with cellular dysfunction and disease. Therefore, the precise detection of lysosomal and mitochondrial pH is essential to provide a better understanding of cellular physiological and pathological processes. Due to their superior features, such as cheap and simple operation, high spatial and temporal resolution, and noninvasive fluorescence imaging, fluorescent probes are the ideal methodology to visualize and monitor lysosomal and mitochondrial pH variation.

We have developed three morpholine-functionalized BODIPY-based fluorescent probes that can be used to monitor lysosomal pH. The fluorescent probes are highly fluorescent under basic conditions, but when exposed to an acidic environment the fluorescence is quenched via an electron donor photoinduced energy transfer. Moreover, we have developed and synthesized a series of sterically hindered fluorescent probes based on spirolactam ring modifications. These modifications were developed by introducing 2-aminophenylboronic acid pinacol ester to rhodamine B, a near-infrared rhodamine dye, and a near-infrared hemicyanine dye. The probes display high fluorescence under acidic conditions but exhibit weak fluorescence under basic conditions due to the significant steric hindrance in the spirolactam ring. Since the probes were functional in an acidic environment, they were successfully applied for the sensing of lysosomal pH variations in living cells.

We have also developed a NIR fluorescent probe to determine mitochondrial pH variations by incorporating an oxazolidine switch onto a near-infrared hemicyanine. The probe has the ability to rapidly switch from an oxazolidine moiety to a hemicyanine group when the pH level decreases from 10.0 to 5.0. This response to pH changes is reversible and has been successfully used to determine pH levels in mitochondria.

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