The analytical chemistry approach : from bioorthogonal catalysis to soil organic carbon
Keywords: Chemistry.

Analytical chemistry is a metrological science that develops, optimizes and applies analytical measurements in order to solve complex problems and to facilitate educated and effective decision-making processes. Throughout the history of science, analytical chemists have expanded the field beyond routine characterization of the compositions samples into a much broader discipline through the development of new analytical methods for scientific advances, improvement upon established methods, and extension of existing methods to completely new sample types. In addition, many aspects of analytical chemistry have evolved through time, such as analytical instruments, reagents, detection limits, dimensions of analytical information, and the more recent introduction of mathematical models, computer science, and big data into chemical analyses. Regardless of these evolutions, the fundamental principle of analytical chemistry, that is, to use analytical measurements as universal vehicles to obtain information, persists throughout the history of analytical chemistry. This dissertation introduces a three-step "analytical chemistry approach" to solve scientific problems based on the fundamental principle of analytical chemistry. The three steps include: (1) frame a research question; (2) identify analytical method(s) that can acquire data to answer the research question; (3) use the analytical method(s) to obtain data and answer the research question. This dissertation demonstrated the remarkable versatility of the analytical chemistry approach by applying it to solve a wide spectrum of scientific problems, ranging from bioorthogonal catalysis with therapeutics and diagnostics applications to soil organic carbon characterization with fundamental impacts on the global carbon cycle, highlighting the paramount importance of analytical chemistry in solving problems and advancing science. Chapter 1 is an introduction to analytical chemistry, the evolution of the field, and the three-step analytical chemistry approach used throughout this dissertation. Chapter 2 showed how the analytical chemistry approach was used to develop a general method to evaluate metal-catalyzed reactions in living systems. In this chapter, a Ru-based bioorthogonal pre-catalyst was used to activates a caged aminoluciferin probe in cellular environments. Upon catalytic cleavage, the activated aminoluciferin is turned over by its target enzyme, luciferase, in cells to produce a bioluminescence readout. With the ability to amplify and/or target imaging readouts, this system opens up many new opportunities in research, imaging, diagnostics, and therapy. By using the three-step analytical chemistry approach, key factors that affect product distribution for the catalytic reaction was found, and the location of that the catalytic reaction was identified to be extracellular. Chapter 3 and Chapter 4 of this dissertation demonstrated the versatilely of the analytical chemistry approach by shifting focus from bioorthogonal catalysis to soil organic carbon. In Chapter 3, the analytical chemistry approach was applied to develop the SOC-fga method, which combines Fourier-transform infrared spectroscopy (FT-IR) and bulk carbon X-ray absorption spectroscopy (XAS) to quantitatively characterize the compositions of soil organic carbon (SOC) across a subalpine watershed in East River, CO, without going through traditional alkaline extractions and chemical treatments that alter SOC compositions. A large degree of variability in SOC functional group abundances was observed between sites at different elevations. The ability to identify the composition of organic carbon in soils quantitatively across biological and environmental gradients will greatly enhance our ability to resolve the underlying controls on SOC turnover and stabilization. Chapter 4 built on the findings of Chapter 3 to further evaluate the SOC-fga method with density fractionation and cross polarization/magic angle spinning (CP/MAS) 13C NMR spectroscopy. This chapter summarized the strengths and weaknesses of the SOC-fga method and 13C NMR and set up a platform to launch future work on SOC turnover mechanisms. Finally, Chapter 5 concluded this dissertation with summaries of findings, future directions, and ending remarks on analytical chemistry.