Nanjian Raaman

Synthesis, characterization, and antimicrobial activities of nickel(II) and copper(II) Schiff-base complexes

Ni(II) and Cu(II) metal complexes of simple unsymmetrical Schiff-base ligands derived from salicylaldehyde/5-methylsalicylaldehyde and ethylenediamine or diaminomaleonitrile (DMN) were synthesized. The ligands and their complexes were characterized by elemental analysis, 1H NMR, FT IR, and mass spectroscopy. The electronic spectra of the complexes show d–d transitions in the region at 450–600 nm. Electrochemical studies of the complexes reveal that all mononuclear complexes show a one-electron quasi-reversible reduction wave in the cathodic region. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts were also carried out. The in vitro antimicrobial activity of the investigated compounds was tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa and Escherichia coli. The antifungal activity was tested against Candida albicans. Generally, the metal complexes have higher antimicrobial activity than the free ligands.

Design, synthesis and gelation studies of 4,6-O-butylidene-α,β-unsaturated-β-C-glycosidic ketones: application to plant tissue culture

A series of α,β-unsaturated-β-C-glycosidic ketones was synthesized starting from D-glucose in three steps. 4,6-O-Butylidene-β-C-glycosidic ketones on aldol condensation with aromatic and heteroaromatic aldehydes in the presence of a suitable organocatalyst led to the stereoselective formation of the products in good yield. Hydrogen bonding and π–π stacking of these derivatives were established by single-crystal XRD. The soft material derived from this method had a diameter of 10–200 nm with a three-dimensional network, as determined by SEM and HR-TEM. In the present study, we discuss the mechanism of formation of these self-assembled nanostructures, the morphology of the soft material and its thermal stability. We also demonstrate the utility of these soft materials in the field of plant tissue culture.

New acyclic Schiff-base copper(II) complexes and their electrochemical, catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800 nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around −1.10 to −1.60 V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 1.72–1.76 BM, close to the spin-only value of 1.73 BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.

Synthesis and antioxidant activity of a novel class of 4,6-O-protected O-glycosides and their utility in disaccharide synthesis

BF(3).Et(2)O-catalysed O-glycosylation of 1,2,3-tri-O-acetyl-4,6-O-butylidene- and ethylidene-beta-d-glucopyranose with different aliphatic and aromatic alcohols proceeds for the most part with complete retention of anomeric configuration. Antioxidant activity of O-glycosides shows significant inhibition (IC(50) approximately 77%). 1,3-Dipolar cycloaddition of terminal alkyne derivatives of O-glycosides with glycosyl azide results in disaccharides.

Regioselective facile one-pot Friedländer synthesis of sugar-based heterocyclic biomolecules.

Regioselective facile one-pot synthesis of 16 different sugar-based quinoline, naphthyridine, and xanthone derivatives is reported. The compounds are characterized by NMR spectroscopy and elemental analysis. The beta-Anomeric form of the sugar moiety was identified from (1)H NMR studies. Antimicrobial studies of these sugar-heterocyclic derivatives, 3a, 3b, 3f, 5c, 7a, 7b, and 7c show excellent activity against different microbes.

N-benzoylated 1,4,8,11-tetraazacyclotetradecane and their copper(II) and nickel(II) complexes: spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies.

A series of N-benzoylated cyclam ligands incorporating three different benzoyl groups 1,4,8,11-tetra-(benzoyl)-1,4,8,11-tetraazacyclotetradecane (L(1)), 1,4,8,11-tetra-(2-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L(2)) and 1,4,8,11-tetra-(4-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L(3)) and their nickel(II) and copper(II) complexes are described. Crystal structure of L(1) is also reported. The ligands and complexes were characterized by elemental analysis, electronic, IR, (1)H NMR and (13)C NMR spectral studies. N-benzoylation causes red shift in the lambda(max) values of the complexes. The cyclic voltammogram of the complexes of ligand L(1) show one-electron, quasi-reversible reduction wave in the region -1.00 to -1.04 V, whereas that of L(2) and L(3) show two quasi-reversible reduction peaks. Nickel complexes show one-electron quasi-reversible oxidation wave at a positive potential in the range +1.05 to +1.15 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment values mu(eff) 1.70-1.73 BM which is close to the spin-only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. All the ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

Studies on the synthesis and the antimicrobial and antioxidant activities of a novel class of fluorescein-based glycosides.

Facile glycosylation of a fluorescein diol derivative with per-O-acetyl/benzoyl sugar derivatives using BF(3)·Et(2)O catalyst resulted in the formation of the expected glycosides in 54-66% yield. The biological screening of the glycosides against different microbes shows good inhibitory activity. The antioxidant activity of the fluorescein-based glycosides shows remarkable inhibition (IC(50) ∼80%).

Improving biological efficiency of Pleurotus strain through protoplast fusion between P. ostreatus var. florida and P. djamor var. roseus

Two hybrid strains were obtained through protoplasmic fusion between Pleurotus ostreatus var. florida and Pleurotus djamor var. roseus. The hybrid strains showed intermediate morphology (colony morphology, cultural characteristics, and fruiting body) to parents. The size and RFLP pattern of two recombinant hybrids were similar, and differed from the parental Pleurotus species. The internal transcribed spacer sequence data revealed that hybrids showed close clad with variety of Pleurotus spp. The hybrid strains showed maximum biological efficiency (138.97%) than the parental strains (110.48-119.19%). In addition, maximum proximate composition, energy values (268.28 kcal), vitamins (thiamine, riboflavin, pyridoxine, folic acid, and calcium pentothenate) and mineral contents (potassium, phosphorus, iron, calcium, and zinc) were recorded in hybrid strain. The hybrid Pleurotus sp. HS would be an important resource of food for mankind, utilize variety of agricultural waste, high amount of nutritional properties and essential food for human health.

Electrochemical, catalytic and antimicrobial activities of N-functionalized cyclam based unsymmetrical dicompartmental binuclear nickel(II) complexes

Five binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show red shift in the d-d transition. Electrochemical studies of the complexes show two irreversible one electron reduction processes in the range of 0 to -1.4V. The reduction potential of the complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves in the range 0.4-1.6V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 1.36x10(-2)-9.14x10(-2)min(-1). The rate constant values for the complexes containing aliphatic diimines are found to be higher than the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes show higher antimicrobial activity than the ligand and metal salt.

Synthesis, anti-microbial activity and molecular docking studies on triazolylcoumarin derivatives

AbstractA series of triazolylcoumarins was synthesized by the cycloaddition of acetylenic derivatives to azide in the presence of Cu(I) catalyst at room temperature. All the synthesized compounds were evaluated for their anti-microbial activity against Gram-positive (B. subtilis and S. aureus), Gram-negative bacteria (K. pneumonia and P. vulgaris) and human pathogenic fungi (C. tropicalis and C. krusei), with tetracycline and fluconazole as standards for anti-microbial and anti-fungal activity. Triazolylcoumarins exhibit anti-microbial activity against all the tested pathogens, which is further supported by molecular docking studies. Graphical AbstractA series of triazolylcoumarins was synthesized using click chemistry approach. All the triazolylcoumarin compounds were evaluated for their anti-microbial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi, with tetracycline and fluconazole as standards as supported by molecular docking studies.