Subensemble Investigations of Molecular Catalysts: Revealing Heterogeneity via Microscopy
- Author(s): Easter, Quinn T
- Advisor(s): Blum, Suzanne A
- et al.
The use of microscopy techniques to uncover the heterogeneity of molecular catalysts is herein reported. Prior to this work, molecular catalysts were detected and quantified through traditional ensemble analytical techniques, such as 1H NMR spectroscopy and mass spectrometry, but no information existed on molecular catalyst activity of single catalysts or small ensembles. Although appearing efficient on the bulk scale, microscopy techniques (Chapter 2) indicated that despite a uniform distribution of catalyst, the catalytic activity of molecular catalysts was poorly distributed. Surface intermediates were transformed by LiCl into soluble organozinc reagents (Chapter 3). Using fluorescence microscopy, spatiotemporal resolution of single active molecular polymerization catalysts was achieved (Chapter 4), which was the first single-turnover fluorescence microscopy imaging at any molecular catalyst. These molecular polymerization catalysts were found to exhibit time-variant chemical kinetics (Chapter 5), rather than continue to exhibit uniform polymerization activity at all time points, in contrast to their traditional textbook depictions. Finally, boundary conditions were established through fluorescence microscopy on when unique subensemble and single-turnover catalytic activity could be detected (Chapter 6). These studies redefine the concept of a “uniform” or “average” catalyst and suggest broad applicability to understanding the full picture of catalysis.