• Volume 127, Issue 5

May 2015,   pages  770b-977

• Editorial Board

• Notes on the preparation of papers

• Macromolecular peroxo complexes of Vanadium(V) and Molybdenum(VI): Catalytic activities and biochemical relevance

Our recent achievements concerning the synthesis and characterization of water soluble peroxo complexes of V(V) and Mo(VI) in macroligand environment, as well as some key features of biological relevance of these compounds, such as their hydrolytic stability, activity with phosphohydrolase enzyme vis-à-vis free peroxovanadium (pV) or peroxomolybdenum (pMo) complexes, and their activity in biomimetic oxidative bromination are presented here. Immobilization of pMo species on insoluble polymer matrices viz., amino acid functionalized Merrifield resins and poly(acrylonitrile) on the other hand, afforded a set of heterogeneous catalysts highly effective in facile organic transformations such as selective oxidation of organic sulfides and oxidative bromination of aromatic substrates by H2O2, at ambient temperature. The methodologies are straightforward, high-yielding, halogen-free and the catalysts afford easy regeneration. Our findings illustrate the various features which make the procedures sustainable and synthetically useful.

• T3P as an efficient cyclodehydration reagent for the one-pot synthesis of 2-amino-1,3,4-oxadiazoles

A scalable and environmentally friendly one-pot method for the synthesis of 2-amino-1,3,4-oxadiazoles from acylhydrazides and isocyanates has been achieved with propane phosponic anhydride (T3P) acting as cyclodehydrating reagent.

• One-pot synthesis and UV-Visible absorption studies of novel tricyclic heterocycle tethered Xanthene-1,8-diones

A series of new tricyclic heterocyclic xanthene-1,8-diones tethered with chromophoric dibenzo [𝑏 , 𝑑]furan, dibenzo[𝑏 , 𝑑]thiophene and 9-methyl-9$H$-carbazoles were synthesized through one-pot condensation of dibenzo[𝑏 , 𝑑]furan-2-carbaldehyde, dibenzo[𝑏 , 𝑑] thiophene-2-carbaldehyde and 9-methyl-9𝐻-carbazole-3-carbaldehyde with cyclic 1,3-dicarbonyls in the presence of recyclable PPA-SiOM2 catalyst under solvent-free conditions. Further, UV-Visible absorption properties of all the synthesized compounds were investigated in CHCl3, THF and acetonitrile.

• Syntheses of fused tetrahydro-𝛽-carboline analogues through imide carbonyl activation using BBr3: Evidence for the involvement of fused cyclic 𝑁-acyliminium ion intermediate

The fused cyclic 𝑁-acyliminium ion generated during the imide carbonyl activation reaction of phenethylphthalimide was confirmed by single crystal X-ray diffraction. The Lewis acid assisted imide carbonyl activation methodology was successfully extended to synthesize fused tetrahydro-𝛽-carboline units from the corresponding 𝑁-indolylethylimides.

• (±)Methanodibenzodiazocine tethered [C-H]𝛿+ functional site: Study towards benzoin condensation and Baylis-Hillman reactions

New heterocyclic ring systems consisting of (±) methanodibenzodiazocine and imidazolium/benzimidazolium salts were synthesized in very good yield. Subsequently, these halide salts were subjected to the anion exchange reaction with KPF6 to yield the corresponding azolium salts in excellent yield. The possible applications of these newly prepared salts were investigated in homogeneous catalysis. Remarkable changes in the catalytic activity were observed by varying the bulkiness of N-substituent at imidazole. Catalytic activity of these newly prepared salts was tested for the benzoin condensation reaction. Exclusive formation of benzoin products were observed in good yield. Similarly, the dimerization of cyclohexen-1-one to Baylis-Hillman type product, 2-(3-oxocyclohexyl)-2-cyclohexen-1-one was studied.

• Liquid phase conversion of Glycerol to Propanediol over highly active Copper/Magnesia catalysts

In this work, a series of Cu/MgO catalysts with different copper metal loading were prepared by the precipitation-deposition method. Their catalytic behaviour was investigated for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO). The physico-chemical properties of the catalysts were characterized by various techniques such as BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), NH3-temperature programmed desorption (NH3-TPD) and scanning electron microscopy (SEM) methods. The characterization results showed that the copper metal was well-dispersed over MgO support and a new phase Cu-MgO was also identified from XRD results after calcination. The 25Cu/MgO (Cu:25 wt%) catalyst exhibited the highest glycerol conversion of 88.7% and 1,2-PDO selectivity of 91.7% at 210$^{\circ}$C, 4.5MPa of hydrogen pressure after 12 h. The high glycerol conversion was mainly due to the Cu dispersion on MgO support and high acidic strength. Further, the effects of temperature, hydrogen pressure, catalyst loading and glycerol concentration were studied over 25Cu/MgO catalyst for optimization of reaction parameters. Kinetic study over highly active 25Cu/MgO catalyst showed that the reaction followed the pseudo second order rate with respect to glycerol and the apparent activation energy was found to be 28.7 ± 0.8 kcal/mol.

• Para-amino benzoic acid–mediated synthesis of vaterite phase of calcium carbonate

Calcium carbonate polymorphs were precipitated at room temperature and 80$^{\circ}$C by varying the precipitation pH, carbonate source, effect of solvent in presence and absence of structure directing agent such as para-aminobenzoic acid. Calcite phase of calcium carbonate was obtained when sodium hydrogen carbonate and/or sodium carbonate (used as precipitating agents) were added to calcium chloride solution at different pHs in water and/or methanol as solvent in separate experiments. Vaterite phase of calcium carbonate (CaCO3) has been synthesized by mixing calcium chloride and sodium carbonate in presence of para-aminobenzoic acid when water–methanol binary mixture was used as solvent. Vaterite phase of calcium carbonate crystallizes in P63/mmc, while that of calcite phase in R-3mc, respectively. Calcite phase of calcium carbonate exhibits rhombohedral morphology, while vaterite phase has spherical morphology.

• Synthesis, crystal structure determination of two-dimensional supramolecular co-ordination polymer of silver(I) with 1,2-Bis(phenylthio)ethane and its Hirshfeld surface analysis

The 2-D polymeric complex (I) has the formula [Ag(phSE)(NO3)]n, which has been crystallized from methanol-acetonitrile mixture and characterized by elemental analysis and single-crystal X-ray diffraction analysis. In this polymer, each Ag(I) ion occupies distorted trigonal pyramidal geometry coordinating with two sulphur atoms from two different ligands and two oxygen atoms from two NO33 groups. Each NO3 acts as a bridging ligand coordinating through its two oxygen atoms to different Ag(I) ions. The Ag(I) ion and NO3 group are in plane with torsion angle 176.43$^{\circ}$. All the ligands adopt anti-conformation but the relative orientation of two -S-C-C-S units is perpendicular to one another such that two phenyl rings attached to the two sulphur atoms coordinating to a particular Ag ion lie on the same side. Each NO3 bridges two neighbouring Ag ions belonging to two different -S-Ag-S-C-C-S-Ag-S- tapes running along 𝑎-axis where two phenyl rings are not parallel to each other to reduce the steric hindrance and maximize packing. The adjacent chains are fused to form 2D sheet by bridging both through bidentate phSE ligand and NO3 anion stacking in 𝑎𝑏 plane. The structure consists of 4-c uninodal net where Point symbol for Ag (I) ion and net is (44.62) with sql type topology. X-ray diffraction analysis and Hirshfeld surface analysis give rise to comparable results but in Hirshfeld surface analysis, twothird times more close contacts are obtained. The fingerprint plots demonstrate that these weak non-bonding interactions are important for stabilizing the crystal packing.

• Supramolecular structures constructed from three novel rare earth metal complexes

Three rare earth metal supramolecular complexes,{[Tb(𝐿2)4](ClO4)3·2H2O(1), [Eu(𝐿2)2(H2O)5] (ClO4)3(2) and [Gd(NO3)3(𝐿2)2]·2CH3CH2OH(3) ( 𝐿2 = 3-Dimethylamino-1-pyridin-2-yl-propenone), have been synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction. The crystal structure analysis reveals that the coordination numbers of three complexes (1–3) are 8, 9 and 10, respectively. Three complexes assembled into 3D frameworks based on C-H⋯O, O-H⋯O hydrogen bond linkages.

• Syntheses, structures and luminescence behaviour of some zinc(II) complexes containing acetate and tetradentate Schiff bases

Two mononuclear compounds of the types pentacoordinated [Zn(L1)(OAc)]PF6·H2O (1) and hexacoordinated [Zn(L2)(OAc)]PF6 (2) [L1 = N,N′-(bis(pyridin-2-yl)formylidene)-1,3-propanediamine; L2 = N,N′-(bis(pyridin-2-yl)benzylidene)-1,4-butanediamine] have been synthesized using one-pot reactions of a 1:1:1 molar ratio of Zn(OAc)2.2H2O, L1/L2, ammonium hexafluorophosphate in MeOH at room temperature. Compounds 1 and 2 are characterized on the basis of microanalytical, spectroscopic, thermal and other physicochemical results. Single crystal X-ray structural study reveals that the zinc(II) centre in 1 is coordinated by four N atoms of the Schiff base L1 and one O atom of terminal acetate with a ZnN4O chromophore, whereas in 2, the zinc(II) centre is bound by four N atoms of the tailored Schiff base L2 and two O atoms of the chelated acetate. In the crystalline state, mononuclear units in 1 are engaged in weak cooperative intermolecular O-H⋯O and C-H⋯F hydrogen bonds affording a 1D chain. The individual units of 2 are packed by 𝜋 ⋯ 𝜋 and anion⋯ 𝜋 interactions to form a 2D sheet structure. The complexes show reasonable thermal stabilities and display intraligand 𝜋 $\to$ 𝜋 fluorescence in solid state at room temperature.

• A mixed Ni(II) ionic complex containing V-shaped water trimer: Synthesis, spectral, structural and thermal properties of {[Ni(2,2′-bpy)3][Ni(2-cpida)(2,2′ -bpy)]} (ClO4).3H2O

A mixed Ni(II) ionic complex of {[Ni(2,2′-bpy)3][Ni(2-cpida)(2,2′-bpy)]}(ClO4).3H2O (1) (2-H3cpida = N-(2-carboxyphenyl)iminodiacetic acid, 2,2′-bpy = 2,2′-bipyridyl) has been synthesized and characterized by infrared, ultraviolet and fluorescence spectroscopy, elemental and thermogravimetric analysis. The molecular structure of compound 1, as determined by single-crystal X-ray diffraction studies, showed all the three carboxylate groups are in monodendate mode. Compound 1 consists of a discrete mononuclear [Ni(2,2′-bpy)3]2+ cation, a [Ni(2-cpida)(2,2′-bpy)]$^−$ anion, a ClO$^−$4 anion and three lattice water molecules. The H-bonding interaction between three lattice water molecule forms a V-shaped trimer (H2O)3 which gives rise to a 1-D polymeric structure in the solid state.

• Application of quinoxaline based diimidazolium salt in palladium catalyzed cross-coupling reactions

The reaction of 2,3-bis(bromomethyl)quinoxaline with imidazole afforded the quinoxaline bridged diimidazolium salt (1) in good yield. Diimidazolium salt (1) in conjunction with Pd(OAc)2 was employed as a catalyst for C–C cross-coupling reactions. The diimidazolium salt was found to be efficient in catalyzing Suzuki-Miyaura cross-coupling reaction in ethanol under ambient conditions. Moderate to good selectivity of the trans product was observed in the Heck cross-coupling reaction. The molecular structure of 1 was confirmed by single crystal X-ray diffraction study.

• Nano-TiCl4/SiO2: An efficient heterogeneous solid acid catalyst for the one pot cascade five-component synthesis of densely functionalized tetrahydropyridines

Nano-TiCl4/SiO2 was found to be an inexpensive and efficient heterogeneous solid acid catalyst for the synthesis of one-pot cascade synthesis of highly functionalized asymmetric tetrahydropyridines from the five-component condensation reaction of the para-substituted anilines and aromatic aldehydes with ethyl acetoacetate under thermal conditions. Novel methodology, environmentally benign conditions, clean protocol, easy work-up and high yields are the important advantages of this protocol. The products were characterized using physical and spectroscopic data such as FT-IR, 1H-NMR and in some cases 13C-NMR and CHN analysis.

• Understanding the surface and structural characteristics of tungsten oxide supported on tin oxide catalysts for the conversion of glycerol

Catalysts with varying WO3 content on SnO2 were prepared and characterized by X-ray diffraction, in situ Raman spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption of NH3. In situ Raman analysis reveals the presence isolated monomers and polymeric species of WO3. These catalysts were evaluated for the conversion of glycerol into value added chemicals. Etherification of glycerol with tertiary butanol and preparation of glycerol carbonate from glycerol and urea are studied over these catalysts. The catalytic activity results suggest that the glycerol conversion and selectivity depends on the morphology of WO3 which in turn is related to its content in the catalyst. The catalysts with 5 wt.% of WO3 on SnO2 resulted in high dispersion with larger number of strong acidic sites. The selectivity in the glycerol etherification is related to the nature of the catalyst and reaction time. These catalysts also exhibited high activity for synthesis of glycerol carbonate. The effect of various reaction parameters was studied to optimize the reaction conditions. The catalysts also exhibited consistent activity upon reuse.

• Textural and morphological studies of transition metal doped SBA-15 by co-condensation method

The 3d transition metals were incorporated into SBA-15 matrix by co-condensation synthesis method. Very low concentrations of metals were introduced into silica framework by maintaining the metal to silica ratio in the synthesis gel at 0.01. The difference in hydrolysis rates of metal and silica precursors have led to textural modifications while demonstrating the structural integrity akin to pristine SBA-15. The physicochemical properties obtained offer some insights into the P123 micelle aggregation and mechanism of formation of silica network in the presence of metal salts under similar synthesis conditions of pure SBA-15. The metal doping into SBA-15 leads to increased pore diameters. Higher lattice constants (a0) observed in these samples are attributed to the increased pore wall thickness. The significant retention of the hexagonal mesostructure seen in LXRD indicates diminutive influence of metal salts at lower concentrations.Macroscopic morphologies studied by SEM show the formation of spheres along with conventional fibre-like rods.

• Effect of optimized structure and electronic properties of some benzimidazole derivatives on corrosion inhibition of mild steel in hydrochloric acid medium: Electrochemical and theoretical studies

The corrosion inhibitive action of a few benzimidazole derivatives namely 2-(benzamido) ethylbenzimidazole (BAEBI), 2-(𝛽-benzenesulphonamido) ethylbenzimidazole (BSAEBI), 2-(benzamido) methylbenzimidazole (BAMBI) and 2-(𝛽-benzenesulphonamido) methylbenzimidazole (BSAMBI), towards mild steel in hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) methods. The results show that these compounds get adsorbed on the mild steel surface following Temkin adsorption isotherm, and act as mixed-type inhibitors. The inhibition efficiencies are found to follow the order, BAEBI &gt; BSAEBI &gt; BAMBI &gt; BSAMBI. This observation is explained in terms of chain length, relative effects of amido and sulphonamido groups, possible structural factors, spatial orientations, energy gap between the frontier molecular orbitals, different intrinsic molecular parameters, like, global hardness and softness, and number of electrons transferred.

• DNA binding, anti-tumour activity and reactivity toward cell thiols of acridin-9-ylalkenoic derivatives

In this paper, we describe the synthesis, biochemical properties and biological activity of a series of new 9-substituted acridine derivatives with a reactive alkene moiety: 9-[(E)-2-phenylethenyl] acridine (1) and methyl (2E)-3-(acridin-9-yl)-prop-2-enoate (2). The interaction of derivatives 1 and 2 with calf thymus DNA was investigated using UV-Vis, fluorescence and circular dichroism spectroscopy. The binding constants K were estimated as being in the range of 1.9 to 7.1 $\times 10^5 M^{−1}$, and the percentage of hypochromism was found to be 40–57% (from spectral titration). UV-Vis, fluorescence, and CD measurements indicate that the compounds were effective DNA-intercalating agents. Electrophoretic separation proved that ligands 1 and 2 relaxed topoisomerase I at a concentration of 5 𝜇M. Ester 2 was shown to have a stronger cytostatic effect on leukemia cell line L1210 than alkene 1. The incubation of ligands 1 and 2 with the ovarian carcinoma cell line A2780 confirmed their extensive cytotoxic effects, an effect which was particularly pronounced in the case of ligand 2. Cytotoxicity tests against A2780 cells demonstrate that a conjugate of compound 2 with 𝐿-cysteine (3) is less cytotoxic than compound 2, especially at concentrations greater than 10 𝜇M.

• Introduction of an electron push-pull system yields a planar Red Kaede fluorescence protein chromophore analogue stabilized by a C = O…𝜋 interaction

Crystal structures of four red kaede fluorescence protein chromophore analogues are reported here. Molecules I-III adopt a non-planar geometry stabilized by 𝜋 …𝜋 stacking and hydrogen bonding. Introduction of an electron push-pull system induces molecule IV to be planar and a C = O…𝜋 supramolecular interaction is observed as well. Strong electron withdrawing and donating groups also ensure formation of a higher order two and three dimensional supramolecular architecture through hydrogen bonds in molecules I and IV. All the analogues exhibit good photoluminescence properties and emit in the red region with excellent quantum yields.

• Pt-Pd nanoelectrocatalyst of ultralow Pt content for the oxidation of formic acid: Towards tuning the reaction pathway

Synthesis of highly efficient functional electrocatalyst that favours the electrochemical oxidation of formic acid via CO-free dehydrogenation pathway is required for direct formic acid fuel cells. Traditional catalysts favour the dehydration pathway involving the generation of poisonous CO. Herein we demonstrate the superior electrocatalytic performance of Pt-Pd bimetallic nanoelectrocatalyst of ultralow Pt content and tuning the reaction pathway by controlling the Pt content. Bimetallic nanoparticles of Pt4Pd96, Pt7Pd93 and Pt47Pd53 compositions are synthesized by electrochemical co-deposition method in aqueous solution. The nanoparticles of ultralow Pt content, Pt4Pd96, favour the CO-free dehydrogenation pathway for formic acid oxidation with an onset potential of 0 V (SHE) whereas the Pt47Pd53 nanoparticles favour the dehydration pathway involving the formation of CO at high positive potential. The Pt content of the bimetallic nanoparticles actually controls the oxidation peak potential and catalytic activity. Significant negative shift (∼350 mV) in the oxidation peak potential and remarkable enhancement in the current density (2.6 times) are observed for Pt4Pd96 nanoparticles with respect to Pt47Pd53. The absence of three adjacent Pt and Pd atoms could be the reason for the suppression of CO pathway. The electrochemical impedance measurements indirectly support the CO-free pathway for the formic acid oxidation on Pt4Pd96 nanoparticles.

• Voltammetric determination of wedelolactone, an anti-HIV herbal drug, at boron-doped diamond electrode

Boron-doped diamond electrode has been utilized for the study of electrochemical behaviour of an anti-HIV herbal drug wedelolactone in Britton-Robinson buffer (pH-2.5) by square-wave and cyclic voltammetry techniques. The response characteristics of cyclic voltammetry and square wave voltammetry showed a remarkable increase in the anodic peak current and electrochemical impedance spectroscopy revealed a lowering in charge transfer resistance at the boron-doped diamond electrode as compared to the glassy carbon electrode that can be attributed to the higher sensitivity of boron-doped diamond sensor. Cyclic voltammetry at the boron-doped diamond surface revealed the oxidation of wedelolactone with two oxidation peaks (P1 and P2) with Ep1 = 0.4V and Ep2 =1.00 V with scan rate varying from 10 - 220 mV/s and exhibits diffusion-controlled process. Based on the electrochemical measurements, a probable oxidation mechanism has been deduced and the electrode dynamics parameters have been evaluated. The effect of concentration on the peak currents of wedelolactone was found to have a linear relationship within the concentration range of 50–700 ng/mL. The LOD and LOQ were found to be 43.87 and 132.93 ng/mL respectively. The applicability of the proposed method was further scrutinized by the successful determination of wedelolactone in real plant samples.

• Studies on 12 V substrate-integrated lead-carbon hybrid ultracapacitors

A cost-effective 12 V substrate-integrated lead-carbon hybrid ultracapacitor is developed and performance tested. These hybrid ultracapacitors employ flexible-graphite sheets as negative plate currentcollectors that are coated amperometrically with a thin layer of conducting polymer, namely poly-aniline to provide good adhesivity to activated-carbon layer. The positive plate of the hybrid ultracapacitors comprise conventional lead-sheet that is converted electrochemically into a substrate-integrated lead-dioxide electrode. 12 V substrate-integrated lead-carbon hybrid ultracapacitors both in absorbent-glass-mat and polymeric silicagel electrolyte configurations are fabricated and characterized. It is possible to realize 12 V configurations with capacitance values of ∼200 F and ∼300 F, energy densities of ∼1.9 Wh kg$^{−1}$ and ∼2.5 Wh kg$^{−1}$ and power densities of ∼2 kW kg$^{−1}$ and ∼0.8 kW kg$^{−1}$, respectively, having faradaic-efficiency values of ∼90 % with cycle-life in excess of 100,000 cycles. The effective cost of the mentioned hybrid ultracapacitors is estimated to be about ∼4 US$/Wh as compared to ∼20 US$/Wh for commercially available ultracapacitors.

• # Journal of Chemical Sciences

Current Issue
Volume 131 | Issue 10
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019