Activation of C-H bonds using an earth-abundant metal catalyst is one of the top challenges of ch... more Activation of C-H bonds using an earth-abundant metal catalyst is one of the top challenges of chemistry where high-valent Fe/Mn-O/OH biomimic species play an important role. There are several open questions related to the comparative oxidative abilities of these species, and a unifying concept that could accommodate various factors influencing the reactivity is lacking. To shed light on these open questions, here we have used a combination of the DFT (B3LYP-D3/def2-TZVP) and ab initio (DLPNO-CCSD(T); CASSCF/NEVPT2) calculations to study a series of high-valent metal-oxo/hydroxo species, [Mn+H3buea(X)] (M = Fe and Mn, n = II to V, X = O/OH; H3buea = tris[(N'-tert-butylureaylato)-N-ethylene)]aminato) towards the activation of dihydroanthracene (DHA). Detailed analysis unveils the following reactivity trend FeV=O > MnIII=O > MnIV=O > FeIII=O > MnV=O > FeII-OH > MnII-OH > MnIV-OH > FeIV-OH > FeIV=O > FeIII-OH > MnIII-OH and suggests that neither hig...
Synthetic non-heme iron-oxo and iron-halide complexes promote selective halogenation of the sp3-C... more Synthetic non-heme iron-oxo and iron-halide complexes promote selective halogenation of the sp3-C–H bonds via hydrogen atom abstraction and halide rebound phenomenon.
Guanine deaminases (GD) are essential enzymes that help in regulating the nucleobase pool. Since ... more Guanine deaminases (GD) are essential enzymes that help in regulating the nucleobase pool. Since the deamination reaction can result in the accumulation of mutagenic bases that can lead to genomic instability, these enzymes are tightly regulated and are nonpromiscuous. Here, we delineate the basis of their substrate fidelity via entailing the reaction mechanism of deamination by employing density functional theory (DFT) calculations on NE0047, a GD from Nitrosomonas europaea. The results show that, unlike pyrimidine deaminases, which require a single glutamic acid as a proton shuttle, GDs involve two amino acids, E79 and E143 (numbering in NE0047), which control its reactivity. The hybrid quantum mechanics/molecular mechanics (QM/MM) calculations have shown that the first Zn-bound proton transfer to the N3 atom of the substrate is mediated by the E79 residue, and the second proton is transferred to the amine nitrogen of substrate via E143. Moreover, cluster models reveal that the cr...
The concept of “OXO-WALL” was conceived about 60 years ago by Harry B. Gray, which is found to be... more The concept of “OXO-WALL” was conceived about 60 years ago by Harry B. Gray, which is found to be related to the non-existence of high-valent M-Oxo species in +IV oxidation...
Our calculations reveal strong multi-reference character for MnIVO species in OAT reactions util... more Our calculations reveal strong multi-reference character for MnIVO species in OAT reactions utilising several low-lying quartet states unravelling novel multi-state reactivity hitherto unestablished.
One of the main challenges in this area of Single Molecule Magnet is quenching quantum tunnelling... more One of the main challenges in this area of Single Molecule Magnet is quenching quantum tunnelling of magnetization (QTM), which often undercut the magnetization reversal barrier. Among several strategies employed,...
High-valent iron-oxo species are ubiquitous in nature and are present at the active site of sever... more High-valent iron-oxo species are ubiquitous in nature and are present at the active site of several metal-loenzymes which perform challenging organic transformations. Mimicking these metalloenzyme reactivities is one of the growing areas of research, and over the last two decades, tremendous progress has been made to mimic both the structure and function of various heme and non-heme metalloenzymes. Understanding the mechanism of catalytic reactions of these enzymes and their biomimetic models are extremely important to improvise the models further. However, due to the open-shell nature of the catalyst with often close-lying spin-states, the mechanistic aspects associated are highly complex. In this regard, computational tools have played a pivotal role in underpinning the mechanism and several important concepts such as two-state/multi-state reactivity, exchange-enhanced reactivity has emerged. While there are several reviews written already on the reactivity of the popular high-val...
Activation of C-H bonds using an earth-abundant metal catalyst is one of the top challenges of ch... more Activation of C-H bonds using an earth-abundant metal catalyst is one of the top challenges of chemistry where high-valent Fe/Mn-O/OH biomimic species play an important role. There are several open questions related to the comparative oxidative abilities of these species, and a unifying concept that could accommodate various factors influencing the reactivity is lacking. To shed light on these open questions, here we have used a combination of the DFT (B3LYP-D3/def2-TZVP) and ab initio (DLPNO-CCSD(T); CASSCF/NEVPT2) calculations to study a series of high-valent metal-oxo/hydroxo species, [Mn+H3buea(X)] (M = Fe and Mn, n = II to V, X = O/OH; H3buea = tris[(N'-tert-butylureaylato)-N-ethylene)]aminato) towards the activation of dihydroanthracene (DHA). Detailed analysis unveils the following reactivity trend FeV=O > MnIII=O > MnIV=O > FeIII=O > MnV=O > FeII-OH > MnII-OH > MnIV-OH > FeIV-OH > FeIV=O > FeIII-OH > MnIII-OH and suggests that neither hig...
Synthetic non-heme iron-oxo and iron-halide complexes promote selective halogenation of the sp3-C... more Synthetic non-heme iron-oxo and iron-halide complexes promote selective halogenation of the sp3-C–H bonds via hydrogen atom abstraction and halide rebound phenomenon.
Guanine deaminases (GD) are essential enzymes that help in regulating the nucleobase pool. Since ... more Guanine deaminases (GD) are essential enzymes that help in regulating the nucleobase pool. Since the deamination reaction can result in the accumulation of mutagenic bases that can lead to genomic instability, these enzymes are tightly regulated and are nonpromiscuous. Here, we delineate the basis of their substrate fidelity via entailing the reaction mechanism of deamination by employing density functional theory (DFT) calculations on NE0047, a GD from Nitrosomonas europaea. The results show that, unlike pyrimidine deaminases, which require a single glutamic acid as a proton shuttle, GDs involve two amino acids, E79 and E143 (numbering in NE0047), which control its reactivity. The hybrid quantum mechanics/molecular mechanics (QM/MM) calculations have shown that the first Zn-bound proton transfer to the N3 atom of the substrate is mediated by the E79 residue, and the second proton is transferred to the amine nitrogen of substrate via E143. Moreover, cluster models reveal that the cr...
The concept of “OXO-WALL” was conceived about 60 years ago by Harry B. Gray, which is found to be... more The concept of “OXO-WALL” was conceived about 60 years ago by Harry B. Gray, which is found to be related to the non-existence of high-valent M-Oxo species in +IV oxidation...
Our calculations reveal strong multi-reference character for MnIVO species in OAT reactions util... more Our calculations reveal strong multi-reference character for MnIVO species in OAT reactions utilising several low-lying quartet states unravelling novel multi-state reactivity hitherto unestablished.
One of the main challenges in this area of Single Molecule Magnet is quenching quantum tunnelling... more One of the main challenges in this area of Single Molecule Magnet is quenching quantum tunnelling of magnetization (QTM), which often undercut the magnetization reversal barrier. Among several strategies employed,...
High-valent iron-oxo species are ubiquitous in nature and are present at the active site of sever... more High-valent iron-oxo species are ubiquitous in nature and are present at the active site of several metal-loenzymes which perform challenging organic transformations. Mimicking these metalloenzyme reactivities is one of the growing areas of research, and over the last two decades, tremendous progress has been made to mimic both the structure and function of various heme and non-heme metalloenzymes. Understanding the mechanism of catalytic reactions of these enzymes and their biomimetic models are extremely important to improvise the models further. However, due to the open-shell nature of the catalyst with often close-lying spin-states, the mechanistic aspects associated are highly complex. In this regard, computational tools have played a pivotal role in underpinning the mechanism and several important concepts such as two-state/multi-state reactivity, exchange-enhanced reactivity has emerged. While there are several reviews written already on the reactivity of the popular high-val...
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