Dipak Kumar Dutta

Adsorption of Cr(VI) in layered double hydroxides

Abstract Adsorption of Cr(VI) by various uncalcined and calcined layered double hydroxides (LDH) of Mg–Al, Ni–Al and Zn–Cr types was investigated. Adsorption of Cr 2 O 7 2− through ion exchange in uncalcined LDH is slower in rate and smaller in amount than in calcined one where the adsorption occurs via rehydration. The nature and content of bi- and trivalent metal ions in LDH influence the adsorption. Calcined Mg–Al LDH with higher Al 3+ content in the precursor structure shows higher adsorption capacity. Adsorption is higher in the Mg–Al LDH than in Ni–Al and Zn–Cr LDH. A two-step first-order rate kinetics was observed for the adsorption process which follows the Freundlich-type adsorption isotherm. The explanation of adsorption phenomenon has been supported by X-ray diffraction patterns. The pH of initial Cr 2 O 7 2− solution has no affect on adsorption by calcined LDH. Release of Cr 2 O 7 2− from the adsorbed product depends upon the type of anion in the aqueous phase and CO 3 2− being the most effective ion. Calcination of the Cr 2 O 7 2− adsorbed product up to 1250°C has not resulted in the formation of Cr-immobilized phases.

In situ generation of metal clusters in interlamellar spacing of montmorillonite clay and their thermal behaviour

Intercalated Ni–Ni(CH3COO)2–montmorillonite (I), Ni 0 –montmorillonite (II), Zn–Zn(CH3COO)2–montmorillonite (III) and Zn 0 –montmorillonite (IV) composites have been synthesised and their thermal behaviour is studied by TG, DTG and DTA substantiated by XRD and TEM. The endothermic DTA peaks of the composites I–IV due to dehydration and dehydroxylation, in general, occur at lower temperature compared to those of untreated Na–montmorillonite. The phase change of the clay matrix for the composites I and II takes place at slightly higher temperature compared to Na–montmorillonite, while for the composites III and IV it occurs at lower temperature. XRD data show that the basal spacing (d 001 value 13.7 A u ) of the intercalated metal cluster composite II is higher than that of the composite IV (d 001 value 12.8 A u ) at about 300 8C revealing intercalated metal cluster of size 4.1 and 3.2 A u , respectively. TEM study shows that the particle size of the metals for the composite II is in the range of about 0–80 nm while for the composite IV, the size range is about 0–30 nm. Therefore, bigger sized metal nanoparticles (>0.41 nm) are not present in the interlamellar spacing of the clay. # 2002 Elsevier Science B.V. All rights reserved.

Thermal and spectroscopic studies on the decomposition of [Ni{di(2-aminoethyl)amine}2]- and [Ni(2,2′:6′,2′′-terpyridine)2]-Montmorillonite intercalated composites

Abstract Intercalated [Ni{di(2-aminoethyl)amine}2]-Montmorillonite (I) and [Ni(2,2′:6′,2′′-terpyridine)2]-Montmorillonite (II) composites have been synthesized and their thermal behavior studied by TG, DTG and DTA substantiated by XRD and IR spectroscopy. Thermal stabilities of the composites I and II were about 50 and 150°C higher, respectively, compared to their respective free metal complex salts. These results indicate that the metal complex with aromatic backboned ligands had higher thermal stability than that of the aliphatic one upon intercalation into layered clay. XRD data showed that on heating, the basal spacing (d001) of the I composite decreased gradually from 14.5xa0A at 50°C to about 13.5xa0A at 250°C which may correspond with the transformation to a distorted octahedral metal complex in the interlamellar spacing of the clay. On the other hand, the II composite showed a basal spacing (d001) of about 19.4xa0A at 50°C, which decreased slightly to 19.0xa0A at about 350°C indicating the presence of intercalated octahedral metal complex and thus corroborates the thermal analyses. IR spectra show characteristic bands of I and II composites up to about 250 and 350°C, respectively, which also support the data of thermal as well as XRD analyses. Such metal–complex–clay composites may be utilized for developing microporous layered materials exhibiting comparatively higher thermal stability.

Catalytic activity of dicarbonylrhodium complexes of aminobenzoic acid ligands on carbonylation of alcohol

Abstract Rhodium(I) complexes of the type, [Rh(CO) 2 ClL] ( 1 ), where L=2-aminobenzoic acid ( a ), 3-aminobenzoic acid ( b ) and 4-aminobenzoic acid ( c ), have been synthesised. Oxidative addition (OA) of complexes 1 with electrophiles like RI (R=CH 3 , C 2 H 5 ) produce Rh(III) complexes of the type [Rh(CO)(COCH 3 )IClL] ( 2 ) and [Rh(CO)(COC 2 H 5 )IClL] ( 3 ). The OA reactions of complexes 1 with RI follow a two stage kinetics and the observed rate constants are in the order 1 b > 1 c > 1 a irrespective of stages. The complexes 1 show higher catalytic activity for carbonylation of methanol and ethanol than that of the well known species [Rh(CO) 2 I 2 ] − .

Properties of HflX, an Enigmatic Protein from Escherichia coli

The Escherichia coli gene hflX was first identified as part of the hflA operon, mutations in which led to an increased frequency of lysogenization upon infection of the bacterium by the temperate coliphage lambda. Independent mutational studies have also indicated that the HflX protein has a role in transposition. Based on the sequence of its gene, HflX is predicted to be a GTP-binding protein, very likely a GTPase. We report here purification and characterization of the HflX protein. We also specifically examined its suggested functional roles mentioned above. Our results show that HflX is a monomeric protein with a high (30% to 40%) content of helices. It exhibits GTPase as well as ATPase activities, but it has no role in lambda lysogeny or in transposition.

Rhodium nitrone complexes: efficient catalyst for carbonylation of methanol

Abstract Newly synthesized rhodium(I) carbonyl complexes of the type [Rh(CO)2ClL] (1), where L=α,N-diphenylnitrone (a), α-styryl-N-phenylnitrone (b), N,N′-diphenyldinitrone (c) and α-(2-furyl)-N-phenylnitrone (d), act as efficient catalyst precursors (maximum turn over number (TON) 1200–1400 per 90xa0min) for carbonylation of methanol to produce acetic acid and its ester at temperature 150±10xa0°C and pressure 20xa0bar.

Crystal structure of Mycobacterium tuberculosis CarD, an essential RNA polymerase binding protein, reveals a quasidomain‐swapped dimeric structural architecture

Mycobacterium tuberculosis (Mtb) CarD is an essential transcriptional regulator that binds RNA polymerase and plays an important role in reprogramming transcription machinery under diverse stress conditions. Here, we report the crystal structure of CarD at 2.3 Å resolution, that represents the first structural description of CarD/CdnL‐Like family of proteins. CarD adopts an overall bi‐lobed structural architecture where N‐terminal domain resembles ‘tudor‐like’ domain and C‐terminal domain adopts a novel five helical fold that lacks the predicted leucine zipper structural motif. The structure reveals dimeric state of CarD resulting from β‐strand swapping between the N‐terminal domains of each individual subunits. The structure provides crucial insights into the possible mode(s) of CarD/RNAP interactions. Proteins 2014; 82:879–884.

Carbonyl complexes of ruthenium(II) with unsymmetrical phosphine–phosphinesulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n=1–4

Reaction of [Ru(CO) 2Cl 2] n with ligands Ph 2P(CH 2)nP(S)Ph 2 (n0/1(a), 2(b), 3(c), 4(d)) in 1:1 molar ratio produces complex cis[Ru(CO) n2Cl 2(PS/S)](1a)(PS/S0/h 2-(P, S) coordinated) and cis-[Ru(CO)2Cl2(Pue001/S)](1bue001/d)(Pue001/S0/h 1-(P) coordinated), while 1:2 nmolar ratio yields complex of the type cis-[Ru(CO) 2Cl 2(Pue001/S) 2](2aue001/d). The complex 2a undergoes partial decarbonylation reaction ninCH 2Cl 2ue001/hexanesolutiontogiveanewchelatedcomplex[Ru(CO)Cl(PS/S) 2]Cl(2a?).AbstractionofhalidewithAgClO 4fromthe nnon-chelated complexes 1bue001/d and 2aue001/d afford corresponding chelated complexes [Ru(CO) 2Cl(PS/S)](ClO 4)(3bue001/d) and n[Ru(CO) 2(PS/S) 2](ClO 4)2(4aue001/d). The molecular structure of the complex 2a? has been determined by single crystal X-ray ndiffraction. The ruthenium atom is at the centre of slightly distorted octahedral structure having the two phosphorus atoms of the ntwochelatedP,Scoordinatedligandsattrans toeachother,oneCOgroupandClatomcompletingthecoordinationsphere.Other ncomplexes have been characterized by elemental analysis, IR, 1H and 31P {H} NMR spectroscopy.

Novel MntR-Independent Mechanism of Manganese Homeostasis in Escherichia coli by the Ribosome-Associated Protein HflX

Manganese is a micronutrient required for activities of several important enzymes under conditions of oxidative stress and iron starvation. In Escherichia coli, the manganese homeostasis network primarily constitutes a manganese importer (MntH) and an exporter (MntP), which are regulated by the MntR dual regulator. In this study, we find that deletion of E. coli hflX, which encodes a ribosome-associated GTPase with unknown function, renders extreme manganese sensitivity characterized by arrested cell growth, filamentation, lower rate of replication, and DNA damage. We demonstrate that perturbation by manganese induces unprecedented influx of manganese in ΔhflX cells compared to that in the wild-type E. coli strain. Interestingly, our study indicates that the imbalance in manganese homeostasis in the ΔhflX strain is independent of the MntR regulon. Moreover, the influx of manganese leads to a simultaneous influx of zinc and inhibition of iron import in ΔhflX cells. In order to review a possible link of HflX with the λ phage life cycle, we performed a lysis-lysogeny assay to show that the Mn-perturbed ΔhflX strain reduces the frequency of lysogenization of the phage. This observation raises the possibility that the induced zinc influx in the manganese-perturbed ΔhflX strain stimulates the activity of the zinc-metalloprotease HflB, the key determinant of the lysis-lysogeny switch. Finally, we propose that manganese-mediated autophosphorylation of HflX plays a central role in manganese, zinc, and iron homeostasis in E. coli cells.

Novel synthesis of active metal oxide surface from a self-organising system of inorganic solids

Abstract Self-organising aqueous suspension of layers of cationic montmorillonite and anionic mixed metal layered hydroxides (MMLH) after thermal treatment at about 500°C gives active and well-dispersed layers of metal oxides over montmorillonite matrix exhibiting enhanced reactivity with gaseous reactants. Increased absorption of H 2 S by ZnO supported on montmorillonite matrix is given as an example.