Search

Transition metal–catalyzed C─H bond activation and borylation is a powerful synthetic method that offers versatile synthetic transformation from organoboron compounds to virtually all other functional groups. Compared to the ortho-borylation, remote borylation remains more challenging owing to the inaccessibility of these C─H bonds. Enforcing the metal catalyst toward the remote C─H bonds needs well-judged catalyst design through proper ligand development. This review article aims to summarize the recent discoveries for the remote C─H borylation by the employment of new catalyst/ligand design with the help of steric of the ligand, noncovalent interactions. It has been found that C─H borylation now takes part in the total synthesis of natural products in a shorter route. Whereas, Ir-catalyzed C─H borylation is predominant, cobalt catalyst has also started to affect this field for sustainable and cost-effective development.

Iridium-catalyzed C–H activation and borylation reactions operate under mild conditions that enable easy and atom-economical installation of the versatile boronate ester group in (het)arenes and alkanes. The standard catalytic system for iridium-catalyzed borylation uses [Ir(cod)(OMe)]2 as a precatalyst, a bipyridine type ligand, and B2pin2 or HBpin as the borylating agent. Initially, a bipyridine-ligated trisboryl–iridium complex is generated that enables the borylation reaction and the regioselectivity is mainly governed by the sterics of substituents present on the ring. As a result, monosubstituted and 1,2-disubstituted arenes give mixtures of isomers. Significant efforts by several research groups have overcome the selectivity issue for directed proximal C–H borylation by introducing a directing group and newly developed ligands. This short review aims to summarize recent elegant discoveries in directed C(sp2)–H and C(sp3)–H borylation by using heterobidentate ligand (P/N–Si, N–B, and N–C) coordinated iridium catalysts.1 Introduction2 Iridium-Catalyzed Directed C–H Borylation of C(sp2)–H Bonds3 Iridium-Catalyzed Directed C–H Borylation of C(sp3)–H Bonds4 Conclusions

The constitutional challenge of an electrostatically directed meta borylation of sterically biased and unbiased substrates is summarized in the present work. The borylation follows an electrostatic interaction between the partially positive and negative charges of the ligand and substrate, respectively. Using our developed strategy, it has been demonstrated that a wide range of challenging substrates, especially 4-substituted substrates can be borylated at the meta position with excellent selectivity. Moreover, unsubstituted substrates are also displayed excellent meta selectivity. The reaction employs bench-stable ligand, proceeds at moderate reaction temperature (40–80 °C), precluding the need to synthesize bulky and sophisticated ligand/template.

Transition metal-catalysed direct borylation of hydrocarbons via C–H bond activation has received a remarkable level of attention as a popular reaction in the synthesis of organoboron compounds owing to their synthetic versatility.

A catalytic system for intramolecular C(sp2)–H and C(sp3)–H amination of substituted tetrazolopyridines has been successfully developed.

ConspectusThe pursuit for the discovery of new and powerful synthetic methods to access high-value N-heterocycles has been at the forefront of organic chemistry research for more than a century. Considering the importance of N-scaffolds in modern science, over the past few decades, great research efforts have been made to develop efficient synthetic methods for the construction of nitrogen-rich molecules. Among many efforts, transition metal catalyzed denitrogenative annulation reaction has emerged as a cornerstone due to its innate versatility and wider scope of application.The denitrogenative annulation approach offers clear advantages over many existing methods, as it enables effective, single-step interconversion of easily available feedstocks into a variety of other important N-containing heterocyclic frameworks. Recently, transition metal catalyzed denitrogenative annulation reaction of the 1,2,3-triazole via a metal carbene intermediate sparked significant interest in the application of various important heterocycle syntheses. Denitrogenative annulation reaction of 1,2,3-triazoles proceeds via an ionic mechanism. Recently, we demonstrated a new concept for the denitrogenative reaction of triazoles with alkenes and alkynes via in situ generated 2-(diazomethyl)pyridines. The method takes advantage of the inherent properties of a Co(III)-carbene radical intermediate and is the first report of the denitrogenative annulation/cyclopropanation by a radical-activation mechanism.On the other hand, in contrast to the denitrogenative annulation of 1,2,3-triazole, annulation reaction of 1,2,3,4-tetrazole (a surrogate of azide having an important pyridyl unit) via metal nitrene remains a big challenge. Previously, flash vacuum pyrolysis studies had been used for nitrene-nitrene rearrangement of 1,2,3,4-tetrazole at high temperature. This Account summarizes our recent efforts in developing transition metal catalyzed denitrogenative annulation of 1,2,3-triazoles via a radical mechanism and 1,2,3,4-tetrazoles via metal nitrene to access important nitrogen-rich molecules. We demonstrated that the 1,2,3,4-tetrazole under Ir-catalyzed reaction conditions can produce a productive Ir-nitrene intermediate that can successfully be employed for the construction of a wide number of α-carbolines and 7-azaindoles. Moreover, we developed an iron-based unique strategy for the intermolecular denitrogenative annulation reaction between tetrazoles and alkynes. The reaction overcomes the traditional click reaction and proceeds via an unprecedented metalloradical activation mechanism. Furthermore, we used our understanding of tetrazole reactivity to design an iron-catalyzed intramolecular denitrogenative C(sp3)-H amination reaction of primary, secondary, and tertiary centers by using a metalloradical activation concept. At the same time, we also developed a general catalytic method to enable two distinct reactions (1,3-cycloaddition and denitrogenative annulation) using Mn(TPP)Cl that afforded two different classes of nitrogen heterocycles. Mechanistic studies showed that although the click reaction likely proceeds through an ionic mechanism and the denitrogenative annulation reaction likely proceeds via an electrophilic metallonitrene intermediate rather than a metallonitrene radical intermediate. Finally, we report an iron-catalyzed rearrangement reaction (ring expansion/migration) that proceeded with an unprecedented level of selectivity, reactivity, and functional group tolerance offering rapid access to numerous complex N-heterocycles. We believe that our continuous efforts in this field would be beneficial for pharmaceutical industries, drug discovery, and other fields of medicinal chemistry.

Over the past few years, the development of efficient methods to construct high-valued N-heterocyclic molecules have received massive attention owing to their extensive application in the areas of medicinal chemistry, drug discovery, natural product synthesis and so on. To access those high-valued N-heterocycles, many methods have been developed. In this context, transition-metal-catalyzed denitrogenative annulation of 1,2,3-triazoles and 1,2,3,4-tetrazoles has appeared as a powerful synthetic tool because it offers a step- and atom-economical route for the preparation of the nitrogen-rich molecules. Compared with the denitrogenative annulation of various 1,2,3-triazole frameworks, annulation of 1,2,3,4-tetrazole remains more challenging due to the inertness of the tetrazole moiety. This Review summarizes the significant achievements made in the field of denitrogenative annulation of various 1,2,3-triazoles and 1,2,3,4-tetrazoles including some pioneering examples in this area of research. We anticipate that this denitrogenative annulation reaction will find broad applications in the pharmaceutical industry, drug discovery and other fields of medicinal chemistry.

Remote meta selective C–H functionalization , , of aromatic compounds remains a challenging problem in chemical synthesis. Here, we report an iridium catalyst bearing a bidentate pyridine-pyridone (PY-PYRI) ligand framework that efficiently catalyzes this meta selective borylation reaction. We demonstrate that the developed concept can be employed to introduce a boron functionality at the remote meta position of phenols, phenol containing bioactive and drug molecules, which was an extraordinary challenge. Moreover, we have demonstrated that the method can also be applied for the remote C6 borylation of indole derivatives including tryptophan that was the key synthetic precursor for the total synthesis of Verruculogen and Fumitremorgin A alkaloids. The origin of the remote meta selectivity was described as a secondary silicon oxygen interaction that was never used in C–H functionalization chemistry.

We report a convenient method for the highly site-selective borylation of 8-arylquinoline. The reaction proceeds smoothly in the presence of a catalytic amount of [Ir(OMe)(cod)]2 and 2-phenylpyridine derived ligand using bis(pinacolato)diborane as the borylating agent. The reactions occur with high selectivity with many functional groups, providing a series of borylated 8-aryl quinolines with good to excellent yield and excellent selectivity. The borylated compounds formed in this method can be transformed into various important synthons by using known transformations.

Here we describe the discovery of a new class of C-H borylation catalysts and their use for regioselective C-H borylation of aromatic, heteroaromatic, and aliphatic systems. The new catalysts have Ir-C(thienyl) or Ir-C(furyl) anionic ligands instead of the diamine-type neutral chelating ligands used in the standard C-H borylation conditions. It is reported that the employment of these newly discovered catalysts show excellent reactivity and ortho-selectivity for diverse classes of aromatic substrates with high isolated yields. Moreover, the catalysts proved to be efficient for a wide number of aliphatic substrates for selective C(sp3)-H bond borylations. Heterocyclic molecules are selectively borylated using the inherently elevated reactivity of the C-H bonds. A number of late-stage C-H functionalization have been described using the same catalysts. Furthermore, we show that one of the catalysts could be used even in open air for the C(sp2)-H and C(sp3)-H borylations enabling the method more general. Preliminary mechanistic studies suggest that the active catalytic intermediate is the Ir(bis)boryl complex, and the attached ligand acts as bidentate ligand. Collectively, this study underlines the discovery of new class of C-H borylation catalysts that should find wide application in the context of C-H functionalization chemistry.

An iron-catalyzed denitrogenative rearrangement of 1,2,3,4-tetrazole is developed over the competitive C(sp3 )-H amination. This catalytic rearrangement reaction follows an unprecedented metalloradical activation mechanism. Employing the developed method, a wide number of complex-N-heterocyclic product classes have been accessed. The synthetic utility of this radical activation method is showcased with the short synthesis of a bioactive molecule. Collectively, this discovery underlines the progress of radical activation strategy that should find wide application in the perspective of medicinal chemistry, drug discovery and natural product synthesis research.

A concept for intramolecular denitrogenative C(sp3)–H amination of 1,2,3,4-tetrazoles bearing unactivated primary, secondary, and tertiary C–H bonds is discovered. This catalytic amination follows ...

Over the past two decades, the C-H bond activation and functionalization reaction has been known as a prevailing method for the construction of carbon-carbon and carbon-heteroatom bonds using various transition metal catalysts. In this context, the iridium-catalyzed C-H bond activation and borylation reaction is one of the most valued methods. However, the major challenge in these borylation reactions is how to control the proximal (ortho) and distal (meta and para) selectivity. Interestingly, while so many approaches are now available for the proximal ortho selective borylation of arenes, borylation at the distal meta and or para position of arenes remains still challenging. Only a few approaches have been reported so far in the literature employing iridium catalysis. In this feature article, we have demonstrated some of the recent discoveries from our laboratories for the proximal (ortho) and distal (meta and para) selective borylation reactions. Moreover, some of the recent catalyst engineering discoveries for the selective proximal ortho borylation reactions for a diverse class of substrates have also been discussed. The discussion part of several other pioneering reports is limited due to the lack of scope of this feature article.

The pursuit for the discovery of new and powerful synthetic methods to access high-value

By modifying ligand steric and electronic profiles it is possible to C–H borylate ortho or meta to substituents in aromatic and heteroaromatic compounds, where steric differences between accessible C–H sites are small. Dramatic effects on selectivities between reactions using B(2)pin(2) or 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin) are described for the first time. Judicious ligand and borane combinations give highly regioselective C–H borylations on substrates where typical borylation protocols afford poor selectivities.

A double-fold ortho and remote C-H borylation of BINOL is described. The proposed mechanisms involved electrostatically and sterically directed ortho and remote C-H activation processes, respectively. While B2eg2 (eg = ethylene glycolate) directs the C-H activation at ortho positions, a combination of HBpin and B2pin2 activates remote C-H bonds. The strategy was combined with Suzuki arylation as a one-pot protocol for the rapid synthesis of BINOL derivatives with retention of chirality.

An electrostatically directed meta borylation of sterically biased and unbiased substrates is described. The borylation follows an electrostatic interaction between the partially positive and negative charges between the ligand and substrate. With this strategy, it has been demonstrated that a wide number of challenging substrates, especially 4-substituted substrates, can selectively be borylated at the meta position. Moreover, unsubstituted substrates also displayed excellent meta selectivity. The reaction employs a bench-stable ligand and proceeds at a milder temperature, precluding the need to synthesize a bulky and sophisticated ligand/template.

Here we describe the discovery of a new class of C-H borylation catalysts and their use for regioselective C-H borylation of aromatic, heteroaromatic, and aliphatic systems. The new catalysts have Ir-C(thienyl) or Ir-C(furyl) anionic ligands instead of the diamine-type neutral chelating ligands used in the standard C-H borylation conditions. It is reported that the employment of these newly discovered catalysts show excellent reactivity and

A concept for intramolecular denitrogenative C(sp

A general catalytic method using a Mn-porphyrin-based catalytic system is reported that enables two different reactions (click reaction and denitrogenative annulation) and affords two different classes of nitrogen heterocycles, 1,5-disubstituted 1,2,3-triazoles (with a pyridyl motif) and 1,2,4-triazolo-pyridines. Mechanistic investigations suggest that although the click reaction likely proceeds through an ionic mechanism, which is different from the traditional click reaction, the denitrogenative annulation reaction likely proceeds via an electrophilic metallonitrene intermediate rather than a metalloradical intermediate. Collectively, this method is highly efficient and offers several advantages over other methods. For example, this method excludes a multi-step synthesis of the N-heterocyclic molecules described and produces only environmentally benign N2 gas a by-product.

A new concept for the meta-selective borylation of aromatic amides is described. It has been demonstrated that while esters gave para borylations, amides lead to meta borylations. For achieving high meta selectivity, an L-shaped bifunctional ligand has been employed and engages in an O⋅⋅⋅K noncovalent interaction with the oxygen atom of the moderately distorted amide carbonyl group. This interaction provides exceptional control for meta C-H activation/borylation.

An efficient strategy for the intramolecular denitrogenative transannulation/C(sp2)–H amination of 1,2,3,4-tetrazoles bearing C8-substituted arenes, heteroarenes, and alkenes is described. The process involves the generation of the metal–nitrene intermediate from tetrazole by the combination of [Cp*IrCl2]2 and AgSbF6. It has been shown that the reaction proceeds via an unprecedented electrocyclization process. The method has been successfully applied for the synthesis of a diverse array of α-carbolines and 7-azaindoles.

High ortho selectivity for Ir-catalyzed C–H borylations (CHBs) of anilines results when B2eg2 (eg = ethylene glycolate) is used as the borylating reagent in lieu of B2pin2, which is known to give isomeric mixtures with anilines lacking a blocking group at the 4-position. With this modification, high selectivities and good yields are now possible for various anilines, including those with groups at the 2- and 3-positions. Experiments indicate that ArylN(H)Beg species are generated prior to CHB and support the improved ortho selectivity relative to B2pin2 reactions arising from smaller Beg ligands on the Ir catalyst. The lowest-energy transition states (TSs) from density functional theory computational analyses have N–H···O hydrogen-bonding interactions between PhN(H)Beg and O atoms in Beg ligands. Ir-catalyzed CHB of PhN(H)Me with B2eg2 is also highly ortho-selective. 1H NMR experiments show that N-borylation fully generates PhN(Me)Beg prior to CHB. The TS with the lowest Gibbs energy was the ortho TS, in which the Beg unit is oriented anti to the bipyridine ligand.

Noncovalent interactions play a fundamental role in molecular biology, crystal engineering, supramolecular chemistry, drug design, sensing applications, and many other research fields in the chemical sciences. Because of this importance, thorough research efforts have been focused on the interpreting and quantifying these interactions, which include H-bonding, electrostatic effects, π π interaction, cation-π interaction, hydrophobic-hydrophobic interaction, van der Waals forces, and other such type of interactions. However, on the synthetic standpoint, use of these noncovalent interactions are rare, although might be beneficial for the site-selective C H bond activation and functionalization by transition metal catalysis. In this context, iridium-catalyzed C H borylation has gained immense popularity due to the versatility conferred to the C B bonds. Very recently, researchers have started employing these interactions as a governing factor for attaining regioselectivity in arene C H borylation. In this perspective, we will focus on the advancements made so far by the use of various noncovalent interactions in Ir-catalyzed borylations.

A new catalytic method for the denitrogenative transannulation/cyclopropanation of in-situ-generated 2-(diazomethyl)pyridines is described using a cobalt-catalyzed radical-activation mechanism. The method takes advantage of the inherent properties of a CoIII -carbene radical intermediate and is the first report of denitrogenative transannulation/cyclopropanation by a radical-activation mechanism, which is supported by various control experiments. The synthetic benefits of the metalloradical approach are showcased with a short total synthesis of (±)-monomorine.

An efficient strategy for the para-selective borylation of aromatic esters is described. For achieving high para-selectivity, a new catalytic system has been developed modifying the core structure of the bipyridine. It has been proposed that the L-shaped ligand is essential to recognize the functionality of the oxygen atom of the ester carbonyl group via noncovalent interaction, which provides an unprecedented controlling factor for para-selective C-H activation/borylation.

Wetland is the largest sink of C among entire terrestrial C pool, however, species specific efficiency of wetland macrophytes for sequestering C is not studied well. This study reports seasonal variations of the C sequestration efficiency of twelve abundantly grown wetland macrophytes in East Kolkata Wetland ecosystem (EKW) of India. The total amount of dry biomass and in sequel with the C content were higher in monsoon than postmonsoon and premonsoon periods. Considering all plants the C content of the leaf was the highest followed by the stem and root. Among the twelve plants studied, the C in total dry biomass of Phragmites karka was recorded as the highest followed by Eichhornia crassipes, Typha angustifolia. It was estimated that 1.17 kg C m−2 yr.−1 was captured by marginal aquatic plants, while 0.74 kg C m−2 yr.−1 was captured by the three floating macrophytes in EKW areas. To execute sustainable EKW conservation plans this study would provide an opportunity to refine our understanding about the role of macrophytes in C sequestration and gives a way to claim carbon credit from this service.

A ligand-controlled discovery of ortho and meta C–H boryl­ation of aromatic aldehydes is described. In both cases, an amine is used and it was proposed that ortho borylation could be realized using tert-butylamine as the traceless protecting/directing group and meta boryl­ation undergoes via an electrostatic interaction and a secondary interaction between the ligand of the iridium catalyst and the substrate. Remarkably, these electrostatic interactions and secondary B–N interactions offer a unique and unprecedented guiding factor for the meta-selective C–H activation/borylation of benzaldehydes. This is the first example for the C–H activation and functionalization where the ortho and meta position of a substrate has selectively been functionalized, which open a new chapter in electrophilic aromatic substitution chemistry. 1 Introduction 2 C–H Activation and ortho Borylation of Benzaldehydes 3 C–H Activation and meta Borylation of Benzaldehydes 4 Conclusion

Pisciculture by using composite effluent of Kolkata city is a common indigenous practice in East Calcutta Wetlands (ECW), a Ramsar site in India. Apprehension over the consequences of heavy metal pollution through this practice led to the present study to examine metal accumulation related histological changes in gill and liver tissues of Tilapia ( Oreochromis niloticus ) cultivated in the wastewater fed fishponds of ECW if any. Further, induction of metallothionein, in liver tissues of the same fish was also studied. Concentration of metals (chromium(Cr), manganese(Mn), Iron(Fe), Copper(Cu), Zinc(Zn) and lead(Pb)) were evaluated and found higher in both water and bottom sediment of the wastewater fed fishponds. In fish, liver was the major site for accumulation of metals with a metal profile of Fe > Cu > Zn > Mn > Cr > Pb. Microscopic studies including optical, scanning electron microscopic (SEM), transmission electron microscopic (TEM) and atomic force microscopic (AFM) studies showed considerable changes. Higher expression of metallothionein was found in the liver of contaminated fish hepatocytes through flow cytometry, immunohistochemistry (IHC) and immuno-gold labelling (IEM). It is assumed that chronic exposure of different metal complexes lead to tissue-specific changes in organisms which may also reflect their potential to adapt survival strategies.

The ligand-enabled development of ortho and meta C-H borylation of aromatic aldehydes is reported. It was envisaged that while ortho borylation could be achieved using tert-butylamine as the traceless protecting/directing group, meta borylation proceeds via an electrostatic interaction and a secondary interaction between the ligand of the catalyst and the substrate. These ligand-substrate electrostatic interactions and secondary B-N interactions provide an unprecedented controlling factor for meta-selective C-H activation/borylation.

The present study focus the variation of carbon concentrations within three trophic level i.e., primary producer (phytoplankton), primary consumers (zooplankton) and secondary consumers (fish) in three selected ponds at East Kolkata Wetland area. Depending on the amount and frequency of wastewater input, physico-chemical characteristics of pond, species richness, predator-prey interactions and pond wise different piscicultural practices, the amount of carbon sequestration varied spatially. Significant temporal variations were also observed in each trophic level of these three selected East Kolkata Wetland pond ecosystems. On average primary producers were sequestered 2038.6 ± 244.8mg C m-3 d-1 whereas 307 ± 19.3 mg C m-3 and 11531.4 ± 318.2mg C m-3 was sequestered by primary and secondary consumers, respectively. In Kolkata and its nearby districts over 90% of the production was marked from the East Kolkata Wetland area. Consequently, a significant amount of sequestered carbon was exported from the East Kolkata Wetland ecosystem in the form of fish and this continuous system might increase the carbon sequestration efficiency of the aquatic ecosystem.

The present investigation was made to characterize spatial and temporal variations in soil properties and to evaluate possible differences that could be dependent on the tannery effluent discharges, municipal sewage discharges, vegetation cover, soil settlement rate, crop rotation, etc. Soil total organic matter (TOM), cations like, Sodium (Na), Ammonium (NH4), Potassium (K), Calcium (Ca) and Magnesium (Mg) contents in the bank soils and bottom sediments were recorded from seven different characteristic sites in East Kolkata wetland ecosystem, a Ramsar site (Ramsar site No. 1208). The profile maps were constructed by geostatistical methods to describe the spatial distribution as well as temporal variations of all the factors to identify the influences of composite wastewaters. The work was initiated to identify causes and consequences of the waste dumping in the concerned region for the past hundred years and thereby to suggest necessary precautionary measures to prevent further loss of soil quality.

The municipal sewage of Calcutta city together with industrial effluents traversed the East Calcutta Wetlands (ECW) (Ramsar Site No. 1208) for nearly a century. The composite wastewater at the ECW, was used for pisciculture and agriculture after natural stabilization. Such uses have always been thought to be a source of contamination to biota and humans. Some water-borne pollutants generate reactive oxygen species including superoxide radical anion (O2−.), hydrogen peroxide (H2O2), and hydroxyl radical (.OH), which are highly reactive and potentially deleterious to biological systems. The present study was initiated to examine the antioxidant activities against oxidative stress during different seasons in body fluids of two zooplankters, Moina micrura and Mesocyclops leuckarti thriving in wastewater-fed ponds of ECW. Results showed significantly higher electrical conductivity, chloride and metal (Cr, Cu, and Pb) concentrations in contaminated wastewater-fed pond (CP) at ECW compared to the uncontaminated ...

Calcutta Leather Complex (CLC) near Bantala, Calcutta was constructed in the late 1990s. The ostensible purpose was to bring together the widely dispersed and haphazardly located tanning industry of Calcutta in a single location and to facilitate hazardous waste management by establishing a Common Effluent Treatment Plant. Unfortunately, for a number of reasons, the CLC is not yet fully operational. Further, the continued operation of illegal tanneries outside CLC has worsened matters. This study was undertaken to assess the physicochemical conditions of wastewater carrying canals within the East Calcutta Wetland (ECW) ecosystem (a Ramsar site) with special reference to the relocation of tanneries. Results revealed a great change in the values for physicochemical conditions; most changes were statistically significant (p

East Calcutta Wetland ecosystem is a Ramsar Site in India covering almost 51 km2 and is one of the largest of its type. This wetland receives a massive load of almost untreated industrial and domestic effluents every day, throughout the year, that has been effectively utilized in pisciculture for having a better yield (2.85 metric tons of fish per 0.01 km2 of water body per annum). The present investigation was carried out to study the toxicity of the untreated effluents discharged from tanneries located at the fringe of East Calcutta wetlands. Guppy (Poecilia reticulata) was chosen as a model fish and was exposed to three different sublethal concentrations (3%, 6% and 9%) of composite tannery effluents (TE) for different time periods (4 days, 7 days and 15 days). Exposed fish livers were analyzed for metallothionein (MT, a ubiquitous metal binding protein), cytochrome P4501A1+1A2 (CYP, a major family of xenobiotic metabolizing enzyme in fish biosystem) and nonspecific cytotoxic cells (NCCs, a major group of innate immune system in fish) expressions applying indirect enzyme-linked immunosorbent assay (ELISA) procedure. Results showed that expression of all the three chosen biomarkers were significantly dose and time dependent upon tannery effluent exposure. Major significances drawn from the present study was that fish species cultivated in east Calcutta wetland ecosystem are under potential threat of contamination and stress induced by composite tannery effluents that could lead to adverse physiological conditions. Moreover, these findings could be important in terms of designing biomarkers for early environmental warning system and also for monitoring fish health.

Composite tannery effluent (TE) contaminated with a load of metals, especially chromium, is used in East Calcutta Wetland Ecosystem (ECW; a Ramsar site of West Bengal; No 1208) after natural stabilization for pisciculture and agriculture. Quantity and synergistic and antagonistic activities of both essential and nonessential metals in the effluents can induce a variety of complex changes in animal physiology. High fish yield and no apparent adverse influence on the fish biosystems thriving under pollutant stress at ECW allowed the practice to thrive sustainably over the last nearly 100 years. Thus, the present study was conducted to investigate the role of metallothionein (MT) as a potential biomarker in a fish biosystem following acute and chronic exposure to sublethal concentrations of tannery wastewater. MT localization in the liver tissue of guppy fish (Poecilia reticulata) was studied by the immuno gold-labeled electron microscopic technique. The data demonstrated increased metal content in fish body upon exposure to TE. Electron micrographs showed significant induction of hepatic MT in exposed P. reticulata over control specimens. Liver, being the detoxification site of an organism, plays a crucial role in the synthesis of MT and arrest of excess metal. The method employed in the present study for demonstrating the induction and localization of MT is innovative and could be used as a biomarker in fish exposed to metal stress. Our study also indicated that the metalloprotein complexes in fish tissue sequestered excess load of metals and thereby arrested unwanted interferences of excess metal loads in metabolic processes.

The ligand-enabled development of ortho and meta C–H borylation of aromatic aldehydes is reported. It was envisaged that while ortho borylation could be achieved using tert-butylamine as the traceless protecting/directing group, meta borylation proceeds via an electrostatic interaction and a secondary interaction between the ligand of the catalyst and the substrate. These ligand–substrate electrostatic interactions and secondary B–N interactions provide an unprecedented controlling factor for meta-selective C–H activation/borylation.

Determination of different environmental factors and their spatio-temporal variations is sparingly important theme in ecological science because the productivity of an ecosystem is regulated by these factors. Here in East Kolkata Wetland (EKW) through a web of canal the composite tannery effluent is discharged and these are productively used in the piscicultural and agricultural farming of this area. So, in concern of agro-piscicultural productivity it is very essential to know the present soil profile of EKW. Soil organic carbon (SOC) and some essential anions/nutrients like F, Cl, NO3, PO4 and SO4 in the agricultural/bank surface soils and bottom sediments are recorded from the seven different characteristic regions in EKW area. To describe precisely the variations of all these factors in spatio-temporal scale, the profile maps are constructed by using geostatistics. 1.03–2.25 % SOC in marginal bank soil and 1.26–2.42 % SOC in bottom soil are present in EKW area. Except NO3 all other measured anions are present higher concentration than normal level in EKW area and these have both positive and negative impact especially on the SOC concentration i.e. in carbon sequestration, anion-cation balance, ecotoxicity, nutrient availability of that area. Results of this study indicate that under proper management strategies of site specific use of tannery effluent will reduce the fertilizer/manure cost of farmers. These will surely increase the contribution of leather industry in ecologically and ecological productivity of EKW Ecosystem.

The NHBoc group affords ortho selective C-H borylations in arenes and alkenes. Experimental and computational studies support an outer sphere mechanism where the N-H proton hydrogen bonds to a boryl ligand oxygen. The regioselectivities are unique and complement those of directed ortho metalations.

This is the first report on the use of waste chrome-tanned Indian leather buffing dust for plasticizing atactic polystyrene (PS). There is no effective re-use of waste leather buffing dust reported till today. This waste material, after preliminary characterization, has been dispersed in solvated polystyrene. Resultant composites prepared therefrom via solution cast method exhibit a drastic drop in surface hardness up to certain modifier concentration, beyond which it increases. Addition of surfactants during dispersion of the buffing dust at the optimum level further reduces surface hardness. Para-toluene sulphonic acid (PTSA) has been found to be a better compatibilizer than more conventional sodium lauryl sulphate (LS) in this system. The compatibilized composites show substantial “yield behaviour” when stretched and the breaking strain has been improved drastically from 0.2% in pure polystyrene to 25% in PTSA compatibilized system without any loss in strength. Accordingly, the breaking energy has been increased to much greater than that of the virgin polymer. Effective plasticization of the composites has lowered the glass transition temperature (Tg); PTSA containing composite has shown the minimum value, possibly due to generation of more free volume around the rigid polystyrene molecules on account of its effective adsorption over finer dust particles. Accelerated thermal degradation study shows greater thermal stability of the composites as compared to virgin polymer and this possibly resulted due to the presence of chromium content in the waste, which acts as heat sinks.