Research Projects

Manganese can be found in a wide range of oxidation states, ranging from +2 to +7, with +2 being most common in biological systems. The Oxygen Evolving Complex (OEC) of PS II is the most significant among all Mn-based metalloenzymes since it facilitates the uphill water oxidation process at ambient temperature and pressure. The OEC consists of Mn4CaO5 cluster, where three manganese atoms are arranged in a cubane structure, and the other Mn(V)-oxo is linked with Lewis acid Ca2+. In addition, the key amino acids in the OEC are Histidine, glutamic acid, aspartic acid, and alanine which are crucial for its functional activity. Notably, Mn(V)-oxo is extremely important for the formation of O-O bonds during water oxidation reactions. Also, Mn(V)-Oxo also plays a significant role in synthetic oxidative transformations such as oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions. Inspired by Nature Design across the world scientists tried to understand the stability and reactivity of this Mn(V)-oxo intermediate. However, only a few Mn(V)-oxo are characterized so far. In the literature, Mn(V)-oxo intermediates are reported based on amide and salen-based ligand systems. So far, only Borovik and coworkers show the stabilization of Mn(V)-oxo core by supporting ligand[H₃buea]³⁻ ([H₃buea]³⁻ = tris[(N'-tert-butylureaylato)-N-ethylene]aminato) where it can be capable of having intramolecular hydrogen bonding from the secondary coordination sphere. Till then no such reports are available in the literature. In this Proposal inspired by the nature design where amino acids play a crucial role, we developed a ligand system i.e. DPAQ in which a tri-peptide sequence is incorporated in the ligand system which can anchored as hydrogen bonding interactions with oxo core. We will characterize the proposed Mn(V)-oxo via different spectroscopic techniques like UV/Vis, EPR, rRaman, XAS, and Electrochemistry. We believe that these secondary coordination-contained peptide scaffolds will help stabilize Mn(V)-oxo through hydrogen bonding interactions. Furthermore, Mn(V)-oxo tested its reactivity towards the water splitting reaction, OAT, hydroxylation, and epoxidation reactions. This introduction of peptide sequences can lower the activation energy barrier of the reaction which directly affects the reactivity pattern. Furthermore, the chiral nature of amino acids within peptides will give stereo-controlled product formation, while steric effects from peptides play a significant role in guiding substrate orientation and selectivity.