• Volume 118, Issue 6

      November 2006,   pages  441-643

    • Modern Trends in inorganic chemistry - Foreword

      Ajai Kumar Singh Ashok Kumar Ganguli

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    • Photocleavage of DNA by copper(II) complexes

      Akhil R Chakravarty

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      The chemistry of ternary and binary copper(II) complexes showing efficient visible light-induced DNA cleavage activity is summarized in this article. The role of the metal in photo-induced DNA cleavage reactions is explored by designing complex molecules having a variety of ligands. Ternary copper(II) complexes with amino acid like L-methionone or L-lysine and phenanthroline base are efficient photocleavers of DNA. Complexes of formulation [Cu(Ln)(phen)](C1O4) with NSO-donor Schiff base (HLn) and NN-donor heterocyclic base 1,10-phenanthroline (phen) show significant cleavage of super-coiled (SC) DNA on exposure to red light at ≈ 700 nm. Thed-d and CT electronic bands of the copper(II) complexes play important roles in DNA cleavage reactions. The mechanistic pathways are found to be dependent on the types of ligands present in the copper(II) complexes and the photo-excitation energy. While UV exposure generally proceeds via a type-II process forming singlet oxygen as the reactive species, red-light exposure leads to DNA cleavage following different mechanistic pathways, viz. type-I, type-II and photo-redox pathways. Ternary copper(II) complexes with phen as DNA binder and Schiff base with a thiomethyl group as photosensitizer, cleave SC DNA to its nicked circular (NC) form in a type-II process in red-light. The binary complex [Cu(dpq)2(H20)](C104)2 (dpq, dipyridoquinoxaline) cleaves DNA by photo-redox pathway at 694 nm. The binuclear complex [CuII2(RSSR)2], where H2RSSR is a Schiff base derived from 2-(thioethyl)salicylaldimine, cleaves SC DNA at 632.8 nm (CW He-Ne laser) and 694 nm (ruby laser) involving sulphide (type-I process) and hydroxyl radicals (photo-redox pathway) as the reactive species.

    • Stannoxanes and phosphonates: New approaches in organometallic and transition metal assemblies

      Vadapalli Chandrasekhar Kandasamy Gopal Loganathan Nagarajan Palani Sasikumar Pakkirisamy Thilagar

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      Phosphonate ligands, [RPO3]2-, are extremely versatile in the assembly of multi-tin and multi-copper architectures. We have used organostannoxane cores for supporting multi-ferrocene and multi-porphyrin peripheries. The copper-metalated multi-porphyrin compound is an excellent reagent for facile cleavage of DNA, even in the absence of a co-oxidant. Reaction oft-BuPO3H2 with Cu(C104)2. 6H2O in the presence of 2-pyridylpyrazole (2-Pypz) leads to the synthesis of a decanuclear copper (II) assembly.

    • Dioxygen reactivity ofmeso-hydroxylated hemes: Intermediates in heme degradation process catalyzed by heme oxygenase

      Sankar Prasad Rath

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      Heme oxygenase (HO) is the only enzyme in mammals known to catalyse the physiological degradation of unwanted heme into biliverdin, Fe ion and CO. The process involves introduction of the hydroxyl group at one of itsmeso-positions as the first fundamental step of the heme cleavage process. It was also found thatmeso-amino heme undergoes similar ring-cleavage process while reacting with dioxygen in presence of pyridine as an axial ligand. The present paper briefly reviews the reactions of modelmeso-hydroxylated heme and its analogues with dioxygen, and their relevance in the heme degradation process.

    • Utilization of LVO2 species (L2− is a tridentate ONS donor) as an inorganic analogue of carboxylate group: A journey to a new domain of coordination chemistry

      Satyabrata Samanta Subodh Kanti Dutta Muktimoy Chaudhury

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      The anionic cis-dioxovanadium (V) complex species LVO2- of tridentate biprotic dithiocarbazate-based ligands H2L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocabazate, R = H, L = L1; and R = Br, L = L2) can bind alkali metal ions. The products [LVO2M(H2O)n] (M = Na+, L = L1,1; L = L2, 2 and M = K+, L = L1,3) have extended chain structures in the solid state, stabilized by strong hydrogen bonding and Coulombic interactions as revealed from X-ray crystallography. The LVO2- moieties here behave like analogues of carboxylate groups and display interesting variations in their binding patterns. It appears thatl is a single stranded helicate with LVO2- units forming the strands which surround the labile sodium ions occupying positions on the axis. The compounds are stable in water and methanol as solvents, while in aprotic solvents of higher donor strengths, viz. CH3CN, DMF and DMSO, they undergo photo-induced reduction when exposed to visible light, yielding green solutions from their initial yellow colour. The putative product is a mixed-oxidation (μ-oxo)divanadium (IV/V) species as revealed from EPR, electronic spectroscopy, dynamic1H NMR, and redox studies.

    • Structural, thermal and spectroscopic properties of supramolecular coordination solids

      Birinchi Kumar Das Sanchay Jyoti Bora Monideepa Chakrabortty Laksheswar Kalita Rajesh Chakrabarty Ramakanta Barman

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      Molecules in metal isonicotinate tetrahydrates, M(NC5H4-p-CO2)2.4H2O with M = Mn, Fe, Co, Ni, Cu, Zn, consisting of the hexacoordinate complexestrans-[M(NC5H4-p-CO2)(OH2)4], participate in exhaustive hydrogen-bond formation among themselves to lead to a robust 3D supramolecular network in the solid state. Solid-state diffuse reflectance UV-Vis-NIR spectra of the complexes have been assigned to ligand field and charge transfer transitions. Sharp weight loss due to dehydration, as shown by TGA of Cu(NC5H4-p-CO2)2.4H2O, suggests the suitability of this complex for the gravimetric estimation of copper.

    • Unusual products in the reactions of phosphorus(III) compounds with N=N, C≡C or conjugated double-bonded systems

      K C Kumara Swamy E Balaraman M Phani Pavan N N Bhuvan Kumar K Praveen Kumar N Satish Kumar

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      The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.

    • Structural models of vanadate-dependent haloperoxidases and their reactivity

      Mannar R Maurya

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      Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)2] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO2(ONO)]- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]+ and to peroxo complexes [VO(O2)(ONO)]-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H2cat) and benzohydroxamic acid (H2bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO2(ONN)] as observed by51V NMR and electronic absorption spectroscopic studies.

    • Reverse micellar synthesis and properties of nanocrystalline GMR materials (LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3): Ramifications of size considerations

      Tokeer Ahmad Kandalam V Ramanujachary Samuel E Lofland Ashok K Ganguli

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      Nanoparticles of complex manganites (viz. LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca{0.33}MnO3) have been synthesized using the reverse micellar route. These manganites are prepared at 800‡C and the monophasic nature of all the oxides has been established by powder X-ray diffraction studies. TEM studies show an average grain size of 68, 80 and 50 nm for LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca{0.33}MnO3respectively. Ferromagnetic ordering is observed at around 250 K for LaMnO3, 350 K for La0.67Sr0.33MnO3 and 200 K for La0.67Ca{0.33}MnO3. These Curie temperatures correspond well with those reported for bulk materials with similar composition.

    • Low-molecular-weight poly-carboxylate as crystal growth modifier in biomineralization

      Ballav Moni Borah Bhaskar Jyoti Bhuyan Gopal Das

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      Construction of modified inorganic mineral with controlled mineralization analogues of those produced by nature is now of current interest for understanding the mechanism of thein vivo biomineralization processes, as well as looking for fresh industrial and technological applications. Low-molecular-weight chiral poly-carboxylate ligands derived from naturally occurring L-α-amino acids have been used as model systems to study the effect of molecular properties on crystal growth modification.

    • The use of hydrothermal methods in the synthesis of novel open-framework materials

      Srinivasan Natarajan Sukhendu Manual Partha Mahata Vandavasi Koteswara Rao Padmini Ramaswamy Abhishek Banerjee Avijit Kumar Paul K V Ramya

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      The preparation of inorganic compounds, exhibiting open-framework structures, by hydrothermal methods has been presented. To illustrate the efficacy of this approach, few select examples encompassing a wide variety and diversity in the structures have been provided. In all the cases, good quality single crystals were obtained, which were used for the elucidation of the structure. In the first example, simple inorganic network compounds based on phosphite and arsenate are described. In the second example, inorganic-organic hybrid compounds involving phosphite/arsenate along with oxalate units are presented. In the third example, new coordination polymers with interesting structures are given. The examples presented are representative of the type and variety of compounds one can prepare by careful choice of the reaction conditions.

    • Tuning intermetallic electronic coupling in polyruthenium systems via molecular architecture

      Sandeep Ghumaan Goutam Kumar Lahiri

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      A large number of polynuclear ruthenium complexes encompassing selective combinations of spacer (bridging ligand,BL) and ancillary (AL) functionalities have been designed. The extent of intermetallic electronic communication in mixed-valent states and the efficacy of the ligand frameworks towards the tuning of coupling processes have been scrutinised via structural, spectroelectrochemical, EPR, magnetic and theoretical investigations. Moreover, the sensitive oxidation state features in the complexes of non-innocent quinonoid bridging moieties have also been addressed.

    • Synthesis and characterization of single-source molecular precursors for the preparation of metal chalcogenides

      Vimal K Jain

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      Metal chalcogenides constitute an important family of functional materials. Subtle changes in shape, size and phase of these materials result in variations in physical properties (e.g. electronic and optical), which can be exploited for various technological applications. Several strategies have evolved recently for controlling shape, size and phase of these materials. This work discusses design and synthesis of single-source molecular precursors for the preparation of metal chalcogenides both in bulk and nano-size regime. Precursors for palladium chalcogenides, indium sulphides andII–VI materials are presented. Synthesis of a variety of palladium(II)/platinum(II) complexes with internally functionalised chalcogenolate ligands, selenocarboxylates; gallium and indium dithiolate complexes and zinc/cadmium/ mercury complexes with N,N′-dimethylaminoalkylselenolate ligands and their characterization by NMR and X-ray crystallography are also discussed. Data on thermal behaviour of a few representative complexes, [Pd(SeCOAr)2(PR3)2], [PdCl(E∩N)(PR3)], [InMe2(S∩S)], [In(S∩S)3] and [M(E(CH2)nNMe2)2] (M = Zn, Cd, Hg;n = 2 or 3) are presented.

    • Activation of peroxyl and molecular oxygen usingbis-benzimidazole diamide copper (II) compounds

      Pavan Mathur

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      New tetradentatebis-benzimidazole ligands have been synthesized and utilized to prepare copper (II) complexes. Some of these copper (II) complexes have been characterized structurally. The copper (II) in these complexes is found to possess varying geometries. A distorted octahedral geometry is found with a highly unsymmetrical bidentate nitrate group. An unusual polymeric one-dimensional structure is observed where copper (II) is in a distorted square pyramidal geometry with a monodentate nitrate ion, having long Cu-O bond, while a distorted triagonal bipyramidal geometry is found with two carbonyl O atoms and a Cl atom in the equatorial plane, and two benzimidazole imine N atoms occupy the axial position. These compounds are found to activate the cumylperoxyl group, and this has been utilized in the facile oxidation of aromatic alcohols to aldehydes, where they act as catalysts with large turnovers. The yields of the respective products vary from 32 to 65%. The role of molecular oxygen has been studied and an attempt has been made to identify the “active copper species”. Activation of molecular oxygen has also been observed and has been used for oxidative dealkylation of a hindered phenol, producing di-butyl quinones with yields of 20–25% and 10–12 fold catalytic turnover. Dihydroxybenzenes and substituted catechols are also readily oxidized to the corresponding quinones, in oxygen-saturated solvents. Yields of 84% have been observed with 34-fold catalyst turnover, with di-t-butylcatechol. The activity of these copper (II) —bis-benzmidazolediamide compounds is reminiscent of the functioning of copper centres in galactose oxidase, tyrosinase and catechol oxidase.

    • On the key role of water in the allylic activation catalysed by Pd (II)bisphosphinite complexes

      Rakesh Kumar Sharma Ashoka G Samuelson

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      Palladium and platinum complexes of bisphosphinites and bisphosphines derived from mandelic acid have been prepared and characterized. Their ability to catalyze allylation of imines with allyltributylstannane has been studied. Bisphophinite complexes of Pd (II) are shown to be ideal and they work best in the presence of one equivalent of water. The near neutral conditions employed make the catalysts suitable for a wide variety of substrates.

    • Theoretical study of aromaticity in inorganic tetramer clusters

      Sandeep Nigam Chiranjib Majumder S K Kulshreshtha

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      Ground state geometry and electronic structure of M42- cluster (M = B, Al, Ga) have been investigated to evaluate their aromatic properties. The calculations are performed by employing the Density Functional Theory (DFT) method. It is found that all these three clusters adopt square planar configuration. Results reveal that square planar M42- dianion exhibits characteristics of multifold aromaticity with two delocalised π-electrons. In spite of the unstable nature of these dianionic clusters in the gas phase, their interaction with the sodium atoms forms very stable dipyramidal M4Na2 complexes while maintaining their square planar structure and aromaticity.

    • Snapshots of the “breaking” of the H-H bond in the oxidative addition of H2 to a metal centre

      Saikat Dutta Balaji R Jagirdar

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      Three new monocationic molecular hydrogen complexes of ruthenium of the typetrans-[RuCl(η2-H2)(PP)2][BF4] (PP = bis-l,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, benzyl,p-methyl-benzyl) have been prepared by protonating the precursor hydride complexes trans-[RuCl(H)(PP)2] using HBF4.Et20. These three dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times(T1, ms) and the observation of substantial H, D couplings in the HD isotopomers. The H-H bond distances(dHH, å) increase from 0.97 to 1.01 å as the electron donor ability of the diphosphine ligand increases from the p-fluorobenzyl to the benzyl to the p-methylbenzyl moiety. These dihydrogen complexes constitute the initial stages of elongation of the H-H bond enroute to its cleavage along the reaction coordinate for the oxidative addition of H2 to a metal centre.

    • Metal-catalysed organic transformations in water: From bromination to polymerisation

      Manish Bhattacharjee Braja N Patra

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      Reaction ofα,Β-unsaturated aromatic carboxylic acids with KBr and H2O2 in the presence of Na2MoO4·2H2O in aqueous medium affordsΒ-bromo alkenes in high yields. Metallocene dichlorides, Cp2MCl2 (M = Ti, Zr, or V) catalyse polymerisation of olefins in aqueous medium to afford high molecular weight polymers with low molecular weight distribution.

    • Nanostructured metal particlemodified electrodes for electrocatalytic and sensor applications

      Ramasamy Ramaraj

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      Nanotechnology has become one of the most exciting frontier fields in analytical chemistry. The huge interest in nanomaterials, for example in chemical sensors and catalysis, is driven by their many desirable properties. Although metal is a poor catalyst in bulk form, nanometre-sized particles can exhibit excellent catalytic activity due to their relative high surface area-to-volume ratio and their interface-dominated properties, which significantly differ from those of the bulk material. The integration of metal nanoparticles into thin film of permselective membrane is particularly important for various applications, for example in biological sensing and in electrocatalysis. We have already established different techniques to design permselective membrane-coated chemically modified electrodes with incorporated redox molecules for electrocatalytic, electrochromic and sensor applications. Recently, we have prepared nanostructured platinum and copper (represented Mnano, M = Pt and Cu) modified GC/Nafion electrodes (GC/Nf/Mnano) and characterized by using AFM, XPS, XRD and electrochemical techniques. The nanostructured Mnano modified electrodes were utilized for efficient electrocatalytic selective oxidation of neurotransmitter molecules in the presence of interfering species such as ascorbic acid (AA) and uric acid (UA). It has been also shown that the modified electrodes could be used as sensors for the detection of submicromolar concentrations of biomolecules with practical applications to real samples such as blood plasma and dopamine hydrochloride injection solution. The GC/Cunano electrode has been used for catalytic reduction of oxygen.

    • Iron(III) complexes of certain tetradentate phenolate ligands as functional models for catechol dioxygenases

      Mallayan Palaniandavar Marappan Velusamy Ramasamy Mayilmurugan

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      Catechol 1,2-dioxygenase (CTD) and protocatechuate 3,4-dioxygenase (PCD) are bacterial non-heme iron enzymes, which catalyse the oxidative cleavage of catechols tocis, cis-muconic acids with the incorporation of molecular oxygen via a mechanism involving a high-spin ferric centre. The iron(III) complexes of tripodal phenolate ligands containing N3O and N2O2 donor sets represent the metal binding region of the iron proteins. In our laboratory iron(III) complexes of mono- and bisphenolate ligands have been studied successfully as structural and functional models for the intradiol-cleaving catechol dioxygenase enzymes. The single crystal X-ray crystal structures of four of the complexes have been determined. One of thebis-phenolato complexes contains a FeN2O2Cl chromophore with a novel trigonal bipyramidal coordination geometry. The Fe-O-C bond angle of 136.1‡ observed for one of the iron(III) complex of a monophenolate ligand is very similar to that in the enzymes. The importance of the nearby sterically demanding coordinated -NMe2 group has been established and implies similar stereochemical constraints from the other ligated amino acid moieties in the 3,4-PCD enzymes, the enzyme activity of which is traced to the difference in the equatorial and axial Fe-O(tyrosinate) bonds (Fe-O-C, 133, 148‡). The nature of heterocyclic rings of the ligands and the methyl substituents on them regulate the electronic spectral features, FeIII/FeII redox potentials and catechol cleavage activity of the complexes. Upon interacting with catecholate anions, two catecholate to iron(III) charge transfer bands appear and the low energy band is similar to that of catechol dioxygenase-substrate complex. Four of the complexes catalyze the oxidative cleavage of H2DBC by molecular oxygen to yield intradiol cleavage products. Remarkably, the more basic N-methylimidazole ring in one of the complexes facilitates the rate-determining productreleasing phase of the catalytic reaction. The present study provides support to the novel substrate activation mechanism proposed for the intradiol-cleavage enzymes.

    • One-pot synthesis of an Mn(III)-Cu(II)-Mn(III) trinuclear heterometallic compound formed by Mn…S-Cu-S…Mn supramolecular interactions: Crystal structure of [MnIII(salph)(H2O)2CuII(mnt)2].4DMF

      Vedichi Madhu Samar K Das

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      A one-pot synthesis, that includes CuCl2.2H2O, Na2mnt, H2salph and Mn(CH3COO)3.H2O, leads to the isolation of a trinuclear heterometallic compound [MnIII(salph)(H2O)2CuII(mnt)2].4DMF (1) formed by Mn…S-Cu-S…Mn supramolecular interactions. Compound1 crystallizes in the monoclinic space groupP21/c witha = 13.433(4),b = 16.283(5),c = 15.072(4) å, Β= 107.785(4)‡, Z = 2. In the crystal structure, the complex anion [CuII(mnt)2]2- bridges two [MnIII(salph)(H2O)]1+ cations through Mn…S contacts. The non-covalent hydrogen bonding and π-π interactions among the trinuclear [MnIII (salph)(H2O)2CuII(mnt)2)] complexes lead to an extended chain-like arrangement of [MnIII(salph) (H2O)]1+ cations with [CuII(mnt)2]2- anions embedded in between these chains.

    • Thyroid hormone synthesis and anti-thyroid drugs: A bioinorganic chemistry approach

      Gouriprasanna Roy G Mugesh

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      Hydrogen peroxide, generated by thyroid oxidase enzymes, is a crucial substrate for the thyroid peroxidase (TPO)-catalysed biosynthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3) in the thyroid gland. It is believed that the H2O2 generation is a limiting step in thyroid hormone synthesis. Therefore, the control of hydrogen peroxide concentration is one of the possible mechanisms for the inhibition of thyroid hormone biosynthesis. The inhibition of thyroid hormone synthesis is required for the treatment of hyperthyroidism and this can be achieved by one or more anti-thyroid drugs. The most widely used anti-thyroid drug methimazole (MMI) inhibits the production of thyroid hormones by irreversibly inactivating the enzyme TPO. Our studies show that the replacement of sulphur in MMI by selenium leads to a selone, which exists predominantly in its zwitterionic form. In contrast to the sulphur drug, the selenium analogue (MSeI) reversibly inhibits the peroxidase-catalysed oxidation and iodination reactions. Theoretical studies on MSeI reveal that the selenium atom in this compound carries a large negative charge. The carbon-selenium bond length in MSeI is found to be close to single-bond length. As the selenium atom exhibits a large nucleophilic character, the selenium analogue of MMI may scavenge the hydrogen peroxide present in the thyroid cells, which may lead to a reversible inhibition of thyroid hormone biosynthesis.

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