Manmohan Chhibber

Chemoselective Oxidation of Benzylic Alcohols with Solid Supported CrO3/TBHP under Microwave Irradiation.

Abstract The efficient use of microwave energy coupled with dry media technique for the oxidation of benzylic alcohols using catalytic CrO3 and TBHP has been effectively projected

Diphenylether based derivatives as Fe(III) chemosensors: spectrofluorimetry, electrochemical and theoretical studies

4-(2,4-Dinitrophenoxy)-3-methoxybenzaldehyde (DPE-I) and (4-(2,4-dinitrophenoxy)-3-methoxyphenyl)methanol (DPE-II) were synthesized with high yield and characterized by spectroscopic techniques. The complexation behaviours of DPE-I and DPE-II for various cationic species (Na+, K+, Mg2+, Cu2+, Ba2+, Cr3+, Fe3+, Co2+, Ni2+, Zn2+, Cd2+, and Pb2+) in HEPES buffered CH3CN : H2O system were investigated and compared by spectroscopic and voltammetric techniques. Both receptors showed high degree of selectivity for Fe3+ over other cations. Receptors showed 1 : 1 complexation with Fe3+. DPE-I showed fluorescence quenching on complexation with Fe3+ ion at 350 nm due to PET (photon induced transfer) mechanism between Fe3+ and the large π electron conjugate system of ligand, while DPE-II displayed emission band at 314 nm which underwent fluorescence quenching selectively on gradual addition of Fe3+ at 314 nm and simultaneously a new band at 424 nm emerged with isosbestic point at 355 nm which increases with increase in Fe3+ conc. Electrochemically, DPE-I due to presence of electron withdrawing (aldehydic group) facilitates reduction of nitro group on benzene ring of the molecule so, peak potentials of the two curves obtained for DPE-I appear at −1.16 V (Epc1) and −1.39 V (Epc2) respectively, while in DPE-II (methanolic group) due to its electron donating character makes the reduction of nitro group a little difficult due to which peak potentials occur at higher potential as compared to DPE-I i.e. at −1.30 V (Epc1) and −1.43 V (Epc2) respectively.

Whole cell catalyzed esterification of fatty acids to biodiesel using Aspergillus sp.

Abstract Powdered biomass of Aspergillus sp. (RBD01) was used to carry out esterification of long chain fatty acids for biodiesel production. Dry biomass of Aspergillus sp. at 20% (w/w) with respect to the fatty acid was able to completely esterify oleic acid to ethyl ester at 35°C, in 36 h, with step wise addition of alcohol. Similar conditions also resulted in yield of 64.5% and 58% of ethyl ester from stearic acid and palmitic acid, respectively. However, the presence of methanol resulted in 87.5%, 71% and 41% of methyl ester from oleic, palmitic and stearic acid. Furthermore, it was found that the efficiency of biomass decreased by only 10% with its repeated use up to four cycles.

A new ionophore for chemical sensing of F−, CN− and Co2+ using voltammetric, colorimetric and spectrofluorimetric techniques

The TPEI molecule with ether-imine functional groups was synthesized and characterized by spectroscopic techniques. The TPEI receptor was analyzed for its interaction with different cations and anions. TPEI showed instant visual color change on addition of fluoride, cyanide and cobalt ions, which led to a study of the interaction of TPEI with Co2+, F− and CN−. An obvious color change of TPEI from light yellow to colorless was observed for CN− through a nucleophilic addition mechanism, while F− was detected through a H-bonding mechanism with a distinct color change from light yellow to dark yellow. Co2+ was detected by pseudocavity formation of TPEI in the vicinity of cobalt ions causing a color change from yellow to blue. Paper strips of the TPEI receptor were also prepared, which can be used to detect the presence of Co2+, F− and CN−.

Synthesis and Anti-Staphylococcal Activity of 2,4-Disubstituted Diphenylamines

Infections caused by Staphylococcus aureus are ubiquitous and life threatening. Evolution of resistant strains has necessitated the need to continuously discover new drugs to combat such organisms. Diphenyl ethers, such as triclosan, have recently shown potential as antibacterial agents. In this study, a series of diphenyl amines were synthesized and evaluated for in vitro antibacterial activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida) bacteria. Preliminary results showed that six of the twelve synthesized molecules were active against Staphylococcus aureus. Most notable amongst them were compounds 2(2,4-dinitrophenylamino)phenol and 2(2-dinitrophenylamino)phenol having minimum inhibitory concentration (MIC) in the range of 7.8-15.6 µg mL-1 and 7.8-62.5 µg mL-1respectively for all the eight selected organisms. Five active compounds from the preliminary results were further screened against resistant S. aureus cultures where compounds 2(2,4-dinitrophenylamino)phenol, 2(2-dinitrophenylamino)phenol and 2-chloro-N-(2-(2,4-dichlorophenylamino)phenyl)acetamide gave encouraging results having MIC in the range 3.9-7.8 µg mL-1for most of the organisms. Results obtained above for the selected organisms and the resistant S. aureus strains conclude that hydroxyl group at 2-position of ring B potentiates the antibacterial activity and overcomes the antibiotic resistance.

Fibrillogenesis in ADan peptides is inhibited by biphenyl ethers

In this study, biphenyl ethers of diverse functionality were used to assess their effect on fibrillogenesis of both the oxidized and reduced ADan peptides, in vitro. It was noted that these compounds not only stalled fibrillogenesis but were also able to disrupt pre-formed fibers. The EC(50) values for the inhibition of this process lie in the nanomolar range for 50 microM of peptide concentration, indicating the high potency of these compounds as inhibitors. It was found that these compounds impart to the peptides, an alpha-helical conformation which does not allow them to aggregate and form fibrils. These studies also point out that the transition of peptides through alpha-helical conformation may be a prelude to the onset of fibrillogenesis for oxADan peptides.