Modulating Reactivity of Bioinspired Non-heme Complexes Through Secondary Confinement in Aqueous Medium

De, Puja (2025) Modulating Reactivity of Bioinspired Non-heme Complexes Through Secondary Confinement in Aqueous Medium. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Puja De (19RS052)) 19RS052.pdf - Submitted Version Restricted to Repository staff only Download (30MB)

Abstract

The secondary coordination sphere, largely shaped by protein scaffolds and bound water molecules, plays a crucial role in metalloenzymatic catalysis by fine-tuning the primary coordination sphere, stabilizing the high-valent intermediates, and enabling selective smallmolecule (O₂, NO) activation. Inspired by this natural design, my thesis explores supramolecular confinement and aqueous environments as strategies to stabilize elusive highvalent reactive intermediates in bioinspired oxidation catalysis using earth-abundant metals (Fe, Mn). A water-soluble octahedral Pd₆L₄¹²⁺ nanocage was employed to encapsulate FebTAML complex, enabling reversible O2 binding and the first room-temperature stabilization of elusive Fe(IV) superoxo and high spin, {FeNO}⁶ species in water, mimicking oxygenase and nitric oxide dioxygenase pathways. These confined complexes exhibited selective reactivity, including O₂- and NO-mediated nitrate formation, thereby replicating both direct and indirect NOD enzymatic routes. Beyond supramolecular stabilization, newly developed biomimetic iron and manganese complexes with sterically bulky (Ph,Me-bTAML) ligand framework, were shown to access high-valent oxoiron(V) and Mn(V) oxo intermediates in pure water, achieving efficient C H bond oxygenation reactions with excellent regio- and stereoselectivity. Remarkably, Mn(V) oxo displayed a 20,000-fold rate enhancement in water relative to organic solvent, CH3CN, solely through solvent-induced transition-state stabilization. Furthermore, a light-driven Mn(V) oxo platform enabled selective hydroxylation of strong C H bonds via short-lived LMCT photoexcited states, demonstrating new opportunities in photochemical oxidation. Together, these studies underscore the cooperative role of water and supramolecular confinement in stabilizing reactive species and promoting enzyme-like reactivity. This work advances the design of robust aqueous oxidation catalysts, bridging enzymatic precision with synthetic versatility, and opens pathways toward sustainable and selective bioinspired catalysis.

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