Keggin-type heteropoly-11-molybdo-1-vanadophosphoric acid supported montmorillonite K-10 clay-catalysed one-pot multi-component synthesis of chromeno[2,3-b]indoles

One-pot three-component synthesis of twelve different chromeno[2,3-b]indole derivatives were achieved by the condensation of β-naphthol, oxindole and various substituted aldehydes. Two more chromeno[2,3-b]indole derivatives were also synthesized through one-pot two-component condensation of salicylaldehyde with oxindole/chlorooxindole. Both the condensations were achieved by using Keggin-type heteropoly-11-molybdo-1-vanadophosphoric acid, H₄[PVMo₁₁O₄₀] supported on montmorillonite K-10 clay for about 10% as catalyst under environmentally benign solvent-free reaction condition. Shorter reaction time, excellent yield of product, sustainability of catalytic material and simple workup procedure under green experimental conditions are the advantages of this protocol.

     

Green Tea Versus Traditional Korean Teas: Antibacterial/Antifungal or Both?

The feasibility of utilizing the antimicrobial activity of naturally available teas was studied. Eleven teas including 2 green teas and 9 other traditional Korean mixed teas were tested for their antimicrobial properties. Antibacterial and antifungal properties were assessed. The results showed that green teas possessed significant antifungal and antibacterial properties, while most of the mixed teas showed some amount of antifungal activity and almost insignificant antibacterial properties. Confocal microscopic imaging revealed mycelial damage as well as attack on sporophores rather than spores/spore germination to be the reason behind the antifungal activity. EGCG was identified as the crucial catechin for antimicrobial activity. The study confirmed that green tea had a clear edge over the traditional mixed teas when it comes to antimicrobial activity.     

Spectral and electrochemical investigation of 1,8-diaminonaphthalene upon encapsulation of p-sulfonatocalix[4]arene

The ligand salt, Me₆[14]diene·2HClO₄ (L·2HClO₄) was prepared by condensation of acetone and ethylene diamine in the presence of perchloric acid. On reduction of this diene ligand salt, L·2HClO₄ with sodium borohydride, the two isomeric ligands, ‘tet-a’ and ‘tet-b’ were produced. The ligands, on reaction with ZnX₂ (X=Cl, ClO₄, NO₃ or CH₃COO) and ZnSO₄ produced the corresponding complexes. These complexes have been characterized on the basis of elemental analyses; IR, UV–Vis and ¹H-NMR spectroscopies; magnetic and conductance data. Based on these data, all of the complexes of the diene ligand L, as well as the perchlorate complexes of all of the ligands attained a square-pyramidal arrangement, whereas the complexes of ‘tet-a’ and ‘tet-b’, with X=NO₃, Cl or CH₃COO and with ZnSO₄ salt, were octahedral. Moreover, all complexes were monometallic except the nitrato complex, [(ZnL)₂(µ-NO₃)](ClO₄)₃ which is bimetallic. The structure of [(ZnL)₂(µ-NO₃)](ClO₄)₃ has been confirmed by X-ray crystallography. In this complex the zinc centres lie within a N₄O donor set, with the four nitrogen donors from L and one of the oxygen atom stemming from the bridging NO₃. The complexes show different electrolytic behavior in different solvents. The antibacterial activities of the ligands and complexes towards different phytopathogenic bacteria have been investigated.     

Effect of Solvents and pH on <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

The spectral characteristics of 2,4-dihydroxyazobenzene (DHAB, sudan orange G) and 4-hydroxyazobenzene (HAB) have been studied in various solvents, different hydrogen ion and β-cyclodextrin (β-CD) concentrations, and are compared with azobenzene (AB). The inclusion complexes of the above molecules with β-CD were analyzed by UV-vis spectrometry, flourometry, FT-IR, ¹H NMR, SEM and DFT methods. The solvent study shows that only the azo form is present in DHAB and HAB molecules. The unusually large red shift observed in acidic solutions indicates both molecules exhibit azo-hydrazo tautomerization. In the β-CD solutions, the increase in fluorescence intensity and large bathochromic shift in the S₁ state indicates that DHAB and HAB form 2:2 inclusion complexes, whereas AB forms a 1:1 inclusion complex.     

Ruthenium and enzyme-catalyzed dynamic kinetic resolution of alcohols

Ruthenium acts as a good catalyst for the racemization reaction of secondary alcohols and amines. Ruthenium-catalyzed racemization is coupled with enzymatic kinetic resolution to prepare chiral compounds in 100% theoretical yield. Ten ruthenium complexes (1–10) act as a good catalyst the for racemization reaction and are also compatible with DKR process. Two other ruthenium complexes [RuCl₂(PPh₃)₃] and [Cp^*RuCl(COD)] are active for racemization reaction but their successful compatibility with DKR has not yet been reported. Ru/γ-Al₂O₃ and Ru–HAP are the heterogeneous catalysts used for the racemization reaction. They have also not been employed for DKR process. Polymer supported ruthenium is employed as a reusable racemization catalyst for aerobic DKR of alcohols.     

Gold Decorated Graphene by Laser Ablation for Efficient Electrocatalytic Oxidation of Methanol and Ethanol

A well‐known limitation in the fabrication of metal‐graphene composite has been the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. We demonstrate here a novel one‐pot synthesis of gold nanoparticles by laser ablation of gold strip and in‐situ decoration on graphene substrate. Not only the impregnation of nanoparticles was linker free, but also the synthesis by itself was surfactant‐free. The composite materials were well characterized morphologically and functionally using electron microscopy, X‐ray and electron diffraction, Raman spectroscopy, Zeta potential, electrochemical measurements and UV‐Visible spectroscopic techniques. This linker‐free gold‐graphene based composite has been employed for catalytic applications pertaining to electrooxidation. We have explored the use of this composite as a binder‐free electrode in electrocatalytic oxidation of methanol and ethanol in alkaline medium. Additionally, the onset potential for ethanol oxidation was found to be more negative, ?100 mV, an indication of its promising application in direct ethanol fuel cells.     

Spectral Characteristics of Sulfa Drugs: Effect of Solvents,pH and <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin

The absorption and fluorescence spectra of sulfamethoxazole (SMO), sulfisoxazole (SFO), sulfathiazole (STO) and sulfanilamide (SAM) in different solvents, pH and β-cyclodextrin (β-CD) have been analyzed. The inclusion complexes of the above sulfa drugs with β-CD were investigated by UV-visible spectroscopy, fluorometry, DFT, SEM, FT-IR and ¹H NMR. The solvent study indicates that the position of the substituent (oxazole or thiazole group) in the SAM molecule (R–SO₂–NH-group) is not the key factor to change the absorption and emission behavior of these sulpha drug molecules. In aqueous solution, a single fluorescence band (340 nm) was observed whereas in solutions of β-CD dual emission (430 nm) was noticed in sulpha drug compounds. Formation of the inclusion complex in SMO, SFO and STO should result dual emission which is due to a Twisted Intramolecular Charge Transfer band (TICT). The β-CD study indicates that (i) sulpha drugs form 1:1 inclusion complexes with β-CD and (ii) the red shift and the presence of TICT in the β-CD medium confirms heterocyclic ring encapsulated in the β-CD cavity with the aniline ring present on the out side of the β-CD cavity.     

Growth, structure, and characterization of tris(thiourea)silver(I) nitrate

Single crystals of tris(thiourea)silver(I) nitrate have been grown by slow evaporation solution growth technique from an aqueous solution at 25 °C. The single crystal X-ray diffraction study reveals that the crystal belongs to tetragonal system and cell parameters are a = b = 14.2790(4) Å, c = 24.8900(7) Å, and V = 5074.8(2) Å³. The various functional groups present in the molecule are confirmed by Fourier transformed infrared spectroscopy (FT-IR). The structure and the crystallinity of the materials were further confirmed by powder X-ray diffraction analysis. Thermogravimetric and differential thermal analysis reveal the purity of the sample and no decomposition is observed up to the melting point. The crystal is further characterized by UV–Vis and Vickers microhardness analysis.