Supramolecular Complexation of Azobenzene Dyes By Cucurbit[7]uril and Synthesis of Hypoxia-Responsive Near-Infrared Fluorescent Heptamethine Cyanine Probes

The beneficial role of molecular imaging in clinical decision-making has been clearly established in the past decade. Besides Superman with his X-ray vision, it is not possible to look at a sick person and instantly figure out the problem. In recent years, fluorescence imaging has attracted scientific interest due to high spatial and temporal resolution, enhanced sensitivity, specificity, low toxicity, adjustable emissions, and real-time measurement abilities. Fluorescent dyes absorbing and emitting in the near-infrared (NIR) region (700 - 2500 nm) are very attractive for biological imaging because there is maximal penetration of the light through dense biological samples including the skin and tissue of living subjects, and minimal scattering of the light, enhancing image contrast. Observer-driven pattern recognition is the standard for interpretation of medical images. A biomarker as recently defined by the NIH (National Institute of Health) is a biological molecule found in blood, other body fluids, or tissues acting as an indicator of either a regular biological process or a pathogenic process. Near-infrared fluorescence (NIRF) imaging of biomarkers exhibits the potential to detect change in disease early and less invasively, providing information about the diagnosis and prognosis of a patient. Despite the numerous advantages of near-infrared (NIR) fluorophores, they have certain shortcomings which need to be considered when utilizing them in various applications. Some limitations of NIR fluorophores are aggregation in polar environment, lower quantum yields relative to visible/UV light emitting fluorophores, chemical and photochemical degradation, photobleaching, dye stacking and off-target binding to non-specific biomolecules due to hydrophobicity rendered by extended conjugation, etc. This thesis is an amalgamation of strategies to overcome the limitations of NIR fluorophores with major focus on supramolecular strategies, and application of NIR fluorophores in optical imaging of tumor hypoxia through detection of certain overexpressed biomarkers. Chapter 1 provides an overall introduction to the area by discussing different strategies employed to overcome limitations of NIR fluorophores in detail. Chapter 2 describes the complexation of NIR fluorescent azobenzene-cyanine conjugates by a macrocyclic container Cucurbit[7]uril. Chapter 3 and Chapter 4 dive deeper into the binding modes between small molecule azobenzene dyes and Cucurbituril[7]. Chapter 5 focuses on the synthesis and study of novel bioresponsive NIR fluorescent probes for imaging tumor hypoxia. These probes are activated by rat-liver microsomes which are rich in clinically relevant hypoxia-associated enzymes, Cytochrome-P450 (Cy-P450) and Azoreductase (AzoR). The appendix consists of supporting information and a collection of interesting but peripheral results.