Chivukula V Sastri

Indian Institute of Technology Guwahati | IIT Guwahati · Department of Chemistry

The first-coordination sphere of catalysts is known to play a crucial role in reaction mechanisms, but details of how equatorial ligands influence the reactivity remain unknown. Heteroatom ligated to the equatorial position of iron centers in nonheme iron metalloenzymes modulates structure and reactivity. To investigate the impact of equatorial het...

Chlorine oxyanions have various applications, such as bleaching and oxidizers in rocket fuels. However, their high solubility in water and long environmental lifetimes have led to ecological concerns, especially regarding drinking water quality. This study focuses on the conversion of chlorite to chlorine dioxide, which is of significant interest a...

High‐valent iron(IV)‐oxo intermediates are versatile oxidants in the biotransformation of various substrates by metalloenzymes and catalyze essential reactions for human health as well as in the biodegradation of toxic organic pollutants in the environment. Herein, we report a biomimetic system that efficiently reacts with halophenols through deflu...

Bisphenol A (BPA, 2,2-bis-(4-hydroxyphenyl)propane) is used as a precursor in the synthesis of polycarbonate and epoxy plastics; however, its availability in the environment is causing toxicity as an endocrine-disrupting chemical. Metabolism of BPA and their analogues (substitutes) is generally performed by liver cytochrome P450 enzymes and often l...

Due to its large natural abundance, iron is the metal that is often utilized by metalloenzymes in Nature. Their unique catalytic properties have triggered the interest of chemists and hence many studies have explored synthetic analogues, for instance, for C-H activation reactions. Herein, we show a number of examples where we describe how different...

In this Account, we review and summarize computational viewpoints on the high regio- and chemoselectivity of α-ketoglutarate-dependent non-heme iron dioxygenases and how external perturbations affect the catalysis. In particular, studies from our groups have shown that often a regioselectivity in enzymes can be accomplished by stabilization of the...

In recent years, a lot of effort has gone into developing metal organic frameworks (MOFs) based composites as anticancer drug delivery carriers. Among them, various nanoparticles (NPs) such as graphene oxide (GO), Iron oxide (Fe3O4 or Fe2O3), zinc oxide has been utilized to impart additional benefits in MOFS structure. In this study, CeO2 particles...

Mononuclear high-valent iron(IV)-oxo intermediates are excellent oxidants towards oxygenation reactions by heme and nonheme metalloenzymes and their model systems. One of the most important functions of these intermediates in nature is to detoxify various environmental pollutants. Organic substrates, such as halogenated phenols, are known to be wat...

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL-91(Al) was evaluated for permanent gases viz., CO2, CO, N2 , CH4, C2H6 and C3 H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type-1 adsorption isotherm was observed...

The cytochrome P450 enzymes are important enzymes in the liver that trigger drug metabolism reactions. In biotechnology and biomimetic chemistry, synthetic models of the active species of P450 have been developed and designed and often react differently. Here, we investigate a biomimetic P450 model complex with phthalocyanine equatorial ligand rath...

There are many examples in bioinorganic chemistry, where metalloenzymes produce different reaction products than analogous biomimetic model complexes despite them having the same transition metal and first-coordination sphere environment. As a result, a lot of research has been devoted to the understanding of the effect of the first- and second coo...

Aldehyde deformylation is an important reaction in biology, organic chemistry and inorganic chemistry and the process has been widely applied and utilized. For instance, in biology the aldehyde deformylation reaction has wide differences in biological function, whereby cyanobacteria convert aldehydes into alkanes or alkenes, which are used as natur...

Ligand framework in a metal complex has a pivotal role to play in orchestrating the spectroscopic and reactivity parameters. High‐valent non‐heme metal intermediates are known to be crucial species in the catalytic cycles of several metalloenzymes. Among the plethora of a variety of ligand frameworks employed in bioinorganic chemistry, the bispidin...

High-valent iron-nitrido intermediates have been postulated as reactive intermediates in various enzymes, including the nitrogenases and the cytochromes P450, but so far few have been trapped and characterized. As little is known on their oxidative and spectroscopic properties, we decided to create biomimetic models of iron(IV)-imido complexes and...

Transformation of renewable biomass into value-added chemicals and biofuels has evolved to be a vital field of research in recent years. Accurate estimation of reducing sugars post pretreatment of biomass has been very inconsistent. For a few decades, 3,5-dinitrosalicylic acid (DNS) assay has been widely employed for the estimation of reducing suga...

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL–91(Al) was evaluated for permanent gases viz., CO2, CO, N2, CH4, C2H6 and C3H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type–1 adsorption isotherm was observed....

A high‐valent diiron‐oxo species that can react with perfluoroarenes through an oxidative pathway is described. As far as the authors are aware, no enzymatic iron enzymes are able to complete this feat. Furthermore, it is shown that the aromatic hydroxylation of perfluoroarenes involves the activation of strong C−F bonds and operates through a diff...

The biodegradation of compounds with C−F bonds is challenging due to the fact that these bonds are stronger than the C−H bond in methane. In this work, results on the unprecedented reactivity of a biomimetic model complex that contains an N‐bridged diiron‐phthalocyanine are presented; this model complex is shown to react with perfluorinated arenes...

Mononuclear nonheme MnIII‐peroxo complexes are important intermediates in biology, and take part in oxygen activation by photosystem II. Herein, we present work on two isomeric biomimetic side‐on MnIII‐peroxo intermediates with bispidine ligand system and reactivity patterns with aldehydes. The complexes are characterized with UV/Vis and mass spect...

Mononuclear nonheme Mn(III)‐peroxo complexes are important intermediates in biology, and for instance take part in the oxygen activation by Photosystem II. Herein, we present work on two novel isomeric biomimetic side‐on Mn(III)‐peroxo intermediates with bispidine ligand system and reactivity patterns with aldehydes. The complexes are characterized...

Iron is an essential element in nonheme enzymes that plays a crucial role in many vital oxidative transformations and metabolic reactions in the human body. Many of those reactions are regio‐ and stereospecific and it is believed that the selectivity is guided by second‐coordination sphere effects in the protein. Here, results are shown of a few en...

Coordination and steric environment around a metal center plays an indispensable role in its reactivity. In this report we have synthesized two bispidine based Cu(II)-OOR (R = tBu) complexes [Cu(L1)(OOtBu)]⁺ and [Cu(L2)(OOtBu)]⁺ having different steric environment around the metal center and characterized by various spectroscopic techniques. These...

Nonheme iron dioxygenases are efficient enzymes with relevance for human health that regio- and stereospecifically transfer an oxygen atom to substrates. How they perform this task with this selectivity remains unknown, but may have to do with substrate binding, positioning and oxidant approach. To understand substrate approach on a catalytic react...

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL–91(Al) was evaluated for permanent gases viz., CO2, CO, N2, CH4, C2H6 and C3H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type–1 adsorption isotherm was observed....

Oxygen atom transfer by high-valent enzymatic intermediates remains an enigma in chemical catalysis. In particular, manganese is an important first-row metal involved in key biochemical processes including the biosynthesis of mo-lecular oxygen (through the photosystem II complex) and biodegradation of toxic superoxide to hydrogen peroxide by supero...

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL–91(Al) was evaluated for permanent gases viz., CO2, CO, N2, CH4, C2H6 and C3H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type–1 adsorption isotherm was observed....

Reaction bifurcation processes are often encountered in the oxidation of substrates by enzymes and generally lead to a mixture of products. One particular bifurcation process that is common in biology relates to electron transfer versus oxygen atom transfer by high-valent iron(IV)-oxo complexes, which nature uses for the oxidation of metabolites an...

Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(II...

Metal–peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)–peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(II...

In this work, the adsorption isotherms of small pore bisphosphonate MOF MIL–91(Al) was evaluated for permanent gases viz., CO2, CO, N2, CH4, C2H6 and C3H8. Gravimetric adsorption measurements were performed at three different temperatures 294, 318, 358 K and a wide range of pressures. For all measured gases type–1 adsorption isotherm was observed....

Heme and nonheme monoxygenases and dioxygenases catalyze important oxygen atom transfer reactions to substrates in the body. It is now well established that the cytochrome P450 enzymes react through the formation of a high-valent iron(IV)–oxo heme cation radical. Its precursor in the catalytic cycle, the iron(III)–hydroperoxo complex, was tested fo...

p>Intriguing Chemistry of Non-HemeHigh-ValentIron Intermediates</p

Mononuclear nonheme MnIVO complexes with two isomers of a bispidine ligand have been synthesized and characterized by various spectroscopies and density functional theory (DFT). The MnIVO complexes show reactivity in oxidation reactions (hydrogen-atom abstraction and sulfoxidation). Interestingly, one of the isomers (L1) is significantly more react...

Mononuclear nonheme MnIVO complexes with two isomers of a bispidine ligand have been synthesized and characterized by various spectroscopies and density functional theory (DFT). The MnIVO complexes show reactivity in oxidation reactions (hydrogen-atom abstraction and sulfoxidation). Interestingly, one of the isomers (L1) is significantly more react...

Nature often utilizes molecular oxygen for oxidation reactions through monoxygenases and dioxygenases. In many of these systems a high-valent iron(IV)-oxo active species is found. In recent years evidence has accumulated of possible iron(IV)-imido and iron(V)-nitrido intermediates in enzymatic catalysis, although little is known on their activity....

High-valent heme and nonheme iron(IV)–oxo complexes play key roles in biology as catalytic intermediates in enzymes, where they catalyze vital biotransformations for human health, including detoxification processes in the liver and also the biosynthesis of hormones. [1, 2] Mono-and dioxygenases bind and utilize molecular oxygen on an iron center an...

This work presents the first detailed study on mechanistic aspects of halide oxidation by non-heme iron complexes. We show that while iron(III)–hydroperoxo complexes oxidise halides via oxygen atom transfer, the corresponding iron(IV)–oxo complex reacts via electron transfer. A large variety of natural product biosynthesis reactions involve the hal...

Which is better? The first detailed comparison of the reactivity of nonheme iron(IV)-imido versus nonheme iron(IV)-oxo intermediates with substrates is presented. The iron(IV)-imido variant reacts with sulfides five times faster than iron(IV)-oxo, whereas the reverse trend is observed for hydrogen atom abstraction. These observed trends are analyze...

This work presents the first detailed study on mechanistic aspects of halide oxidation by non-heme iron complexes. We show that while iron(iii)-hydroperoxo complexes oxidise halides via oxygen atom transfer, the corresponding iron(iv)-oxo complex reacts via electron transfer.

Single step hydrothermal synthesis of CdS/Oxide (Oxide = ZnO, Al2O3) was demonstrated and examines their photocatalytic activity in presence of graphene oxide (GO). CdS/Al2O3/GO and CdS/ZnO/GO both exhibits enhanced photocatalytic activity for hydrogen generation with apparent quantum yields (AQY) of 14% and 30% respectively. Moreover, CdS/Oxide/GO...

This work presents the first combined experimental and computational study that gives evidence of the electrophilic reactivity of a nonheme iron(III)-hydroperoxo species. We show that in contrast to their heme counterparts the nonheme iron(III)-hydroperoxo complexes are catalytically much more active and even more so than nonheme iron(IV)-oxo speci...

Dibenzothiophene (DBT), a common component of crude oil, is a widespread environmental pollutant with known adverse effects. Oxidation of DBT to dibenzothiophene sulfone has been examined using in situ generated high-valent oxo-iron(IV) complexes. The reactivities and the corresponding thermodynamic parameters are evaluated and compared with those...

Dibenzothiophene (DBT), a common component of crude oil, is a widespread environmental pollutant with known adverse effects. Oxidation of DBT to dibenzothiophene sulfone has been examined using in situ generated high-valent oxoiron( IV) complexes. The reactivities and the corresponding thermodynamic parameters are evaluated and compared with those...

A series of complexes [FeIV(O)(TMC)(X)]+ (where X = OH−, CF3CO2−, N3−, NCS−, NCO−, and CN−) were obtained by treatment of the well-characterized nonheme oxoiron(IV) complex [FeIV(O)(TMC)(NCMe)]2+ (TMC = tetramethylcyclam) with the appropriate NR4X salts. Because of the topology of the TMC macrocycle, the [FeIV(O)(TMC)(X)]+ series represents an exte...

The reactivities of mononuclear nonheme iron(IV)–oxo complexes bearing different axial ligands, [FeIV(O)(TMC)(X)]ⁿ⁺ [where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is NCCH3 (1-NCCH3), CF3COO⁻ (1-OOCCF3), or N3⁻ (1-N3)], and [FeIV(O)(TMCS)]⁺ (1′-SR) (where TMCS is 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetr...

Umzug erledigt: Der Metall-Metall-Transfer eines Sauerstoffatoms von Nichthäm-Eisen(IV)-Oxo- auf Eisen(II)-Komplexe (siehe Beispiel; Fe violett, O rot, N blau, C grau) wurde eindeutig nachgewiesen – durch eine Kombination von spektrophotometrischen, massenspektrometrischen und elektrochemischen Methoden. Die Sauerstoffübertragung ist abhängig von d...

(Figure Presented) Completing the move: The intermetal transfer of an oxygen atom from nonheme iron(IV)-oxo to iron(II) complexes (see example, purple: Fe, red: O, blue: N, gray: C) has been unambiguously evidenced spectrophotometrically, mass spectrometrically, and electrochemically. The transfer of the oxygen atom was found to be dependent on the...

Axial ligand substitution of a mononuclear nonheme oxoiron(IV) complex, [FeIV(O)(TMC)(NCCH3)]2+ (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), leads to the formation of new FeIV=O species with relatively intense electronic absorption features in the near-UV region. The presence of these near-UV features allowed us to make the f...

We have used dioxygen, not artificial oxidants such as peracids, iodosylarenes, and hydroperoxides, in the generation of a mononuclear nonheme oxoiron(IV) complex, [Fe(IV)(TMC)(O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), from its corresponding Fe(II) complex, [Fe(TMC)(CF3SO3)2]. The formation of oxoiron(IV) species by acti...

A mononuclear nonheme oxoiron(IV) complex bearing a pentadentate N5 ligand was prepared in aqueous solution; the pH dependence of its stability and reactivities was reported along with the mechanistic details of sulfide oxidation by the oxoiron(IV) species.

The reactions of OH, O−, SO4−, N3 and eaq− with the ligands-1,10-phenanthroline (phen) and 6,7-dicyanodipyrido [2,2-d:2′,3′-f] quinoxaline (dicnq) and a series of their Ru(II) complexes ([Ru(phen)3]2+, [Ru(phen)2(dicnq)]2+, [Ru(phen)(dicnq)2]2+ and [Ru(dicnq)3]2+) have been studied by pulse radiolysis with optical detection. The OH and hydrated ele...

Resonance Raman (RR) spectroscopy was employed to study the metal to ligand charge transfer (MLCT) and intraligand transition (IL) state of the [Ru(phen)2qdppz]2+ complex, where phen = 1, 10-phenanthroline and qdppz = naphtho[2,3-a]dipyrido[3,2-h:2′,3′-f]phenazine-5,18-dione. The vibrational bands were assigned based on the data available for [Ru(p...

Four new mixed-ligand complexes, namely [Co(phen)(2)(qdppz)](3+), [Ni(phen)(2)(qdppz)](2+), [Co(phen)(2)(dicnq)](3+) and [Ni(phen)(2)(dicnq)](2+) (phen=1,10-phenanthroline, qdppz=naptho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine-5,18-dione and dicnq=dicyanodipyrido quinoxaline), were synthesized and characterized by FAB-MS, UV/Vis, IR, 1H NMR, cyclic v...

The hexafluorophosphate and chloride salts of two ruthenium(II) complexes, viz. [Ru(phen)(ptzo)2]2 and [Ru(ptzo)3]2+, where ptzo = 1,10-phenanthrolino[5,6-e]1,2,4-triazine-3-one (ptzo) — a new modified phenanthroline (phen) ligand, have been synthesised. These complexes have been characterised by infrared, UV-Vis, steady-state emission and1H NMR sp...