Sanjiv Arora

Synthesis of new pyrazolyl-2, 4-thiazolidinediones as antibacterial and antifungal agents

Background Thiazolidine-2, 4-diones (TZDs) have become a pharmacologically important class of heterocyclic compounds since their introduction in the form of glitazones into the clinical use for the treatment of type 2 diabetes. TZDs lower the plasma glucose levels by acting as ligands for gamma peroxisome proliferators-activated receptors. In addition, this class of heterocyclic compounds possesses various other biological activities such as antihyperglycemic, antimicrobial, anti-inflammatory, anticonvulsant, insecticidal, etc. TZDs are also known for lowering the blood pressure thereby reducing the chances of heart failure and micro-albuminuria in the patients with type 2 diabetes. Results We have described herein the synthesis of three series of compounds, namely, ethyl 2-((Z)-5-((3-aryl-1-phenyl-1H-pyrazol-4-yl)methylene)-2, 4-dioxothiazolidin-3-yl)acetates (4), methyl 2-((Z)-5-((3-aryl-1-phenyl-1H-pyrazol-4-yl)methylene)-2, 4-dioxothiazolidin-3-yl)acetates (5), and 2-((Z)-5-((3-aryl-1-phenyl-1H-pyrazol-4-yl)methylene)-2, 4-dioxothiazolidin-3-yl)acetic acids (6). The compounds 4 and 5 were synthesized by Knoevenagel condensation between 3-aryl-1-phenyl-1H-pyrazole-4-carbaldehydes (1) and ethyl/methyl 2-(2, 4-dioxothiazolidin-3-yl)acetates (3, 2) in alcohol using piperidine as a catalyst. The resultant compounds 4 and 5 having ester functionality were subjected to acidic hydrolysis to obtain 6. All the new compounds were tested for their in vitro antibacterial and antifungal activity. Conclusions Knoevenagel condensation approach has offered an easy access to new compounds 4-6. Antimicrobial evaluation of the compounds has shown that some of the compounds are associated with remarkable antifungal activity. In case of antibacterial activity, these were found to be effective against Gram-positive bacteria. However, none of the compounds were found to be effective against Gram-negative bacteria.

Synthesis and biological evaluation of dihydroindeno and indeno [1,2-e] [1,2,4]triazolo [3,4-b] [1,3,4]thiadiazines as antimicrobial agents

Two series of compounds namely, dihydroindeno and indeno [1,2-e] [1,2,4]triazolo [3,4-b] [1,3,4]thiadizines (9a-l & 11a-l) were synthesized by cyclocondensation between α-bromoindanones (7a-b) or/and α,α-dibromoindanones (8a-b) and various 3-alkyl/aryl-4-amino-5-mercapto-1,2,4-s-triazoles (3a-f) in methanol with an aim to explore their effect on in vitro growth of microorganism causing microbial infection. In vitro antibacterial activity was performed against four strains namely, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and antifungal activity against three fungal strains namely, Aspergillus niger, Aspergillus flavus, Penicillium species. Of all the compounds screened for activity some of the compounds were associated with considerably higher antibacterial and antifungal activity than commercial antibiotics.

Synthesis and antimicrobial activities of some new 5-((3-(aryl)-1-phenyl-1H-pyrazol-4-yl)methylene)-3-phenylthiazolidine-2,4-diones

A series of nine new compounds of 5-((3-(aryl)-1-phenyl-1H-pyrazol-4-yl)methylene)-3-phenylthiazolidine-2,4-diones was synthesized by Knoevenagel condensation of various 3-(aryl)-1-phenyl-1H-pyrazole-4-carbaldehydes with 3-phenylthiazolidine-2,4-dione in ethanol in the presence of piperidine as a catalyst. The reaction afforded the desired products in good yields. All the nine compounds were screened for their in vitro antibacterial (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli) and antifungal (Aspergillus niger and A. flavus) activity. Biological activities of these compounds were compared with those of commercially available antibiotics, ciprofloxacin and antifungal agent fluconazole. Two compounds 3e and 3i were found to be most effective against S. aureus and B. subtilis. Out of the nine compounds tested for antifungal activity, five, 3c–f and 3h showed more than 50% inhibition against the A. flavus, whereas the three compounds 3a, 3d and 3f showed more than 50% inhibition against A. niger.

Flammability and thermal degradation studies of PVA/rice husk composites

Biodegradable poly(vinyl alcohol)/rice husk (PVA/RH) unplasticized composites are prepared by blending 10 wt%, 20 wt%, and 30 wt% of RH with PVA via solvent-casting technique. Composites are also prepared using boric acid as cross-linking agent. Tensile properties of PVA improved, though slightly, on adding RH and boric acid. Flammability of composites is evaluated using limiting oxygen index (LOI) and Underwriters Laboratory test (UL 94), while thermal stability is determined by employing TG/DTA. Thermal stability of PVA increases on adding RH and boric acid. PVA/RH composite with only 10 wt% RH loading passes HB rating (UL 94) and LOI values increase from 20.5% to 23.5% for 30 wt% RH loading. Better flame retardancy of PVA/RH composites is explained on the basis of ‘heat shielding’ and ‘barrier’ theories. Besides, degradation activation energy calculated by model-free methods favors the flammability data. Silica present in RH is the core substance responsible for the improved flame retardancy of PVA.

Thermal degradation and flammability studies of wood coated with fly ash intumescent composites

In the present study, poplar (Populus) wood is coated with intumescent formulation (ammonium polyphosphate/melamine/pentaerythritol), using acrylic resin as binder. Samples have also been prepared by adding fly ash (FA) in intumescent formulation at different loading levels. Thermal stability of composites has been studied with thermogravimetry, derivative thermogravimetry and differential thermal analysis. Limiting oxygen index and Underwriter’s Laboratory (UL 94) studies point toward an appreciable increase in flame retardancy for intumescent coated sample and goes on increasing as loading of FA in intumescent formulation increases. Scanning Electron Microscopy is used to explain flame retardant mechanism of composites.

Preparation and thermal stability of poly(methyl methacrylate)/rice husk silica/triphenylphosphine nanocomposites: assessment of degradation mechanism using model-free kinetics

Nanostructured silica powder was prepared from rice husk (Oryza sativa), an outer covering of rice. Silica was characterized using Fourier transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The silica powder thus prepared was treated with stearic acid for the surface modification. The modified silica was utilized to prepare poly(methyl methacrylate)/modified silica composite films at 1, 5 and 10 wt% loadings by solution casting method, which promises the preparation of homogeneous composites. For comparative analyses, composite films were also made using unmodified silica. Distribution of silica particles in composite film was checked using scanning electron microscopy. Thermal analysis of the samples was carried out using thermogravimetric analyzer followed by model–free multiple–heating rate kinetics. The onset degradation temperature of poly(methyl methacrylate)/silica (modified) composites is found higher than both pure poly(methyl methacrylate) and corresponding poly(methyl methacrylate)/silica (unmodified) composites. This study also reveals the effect of a phosphorus flame retardant additive, triphenylphosphine, on the thermal degradation and flammability behavior of poly(methyl methacrylate) and poly(methyl methacrylate)/silica (modified).

Thermal and biological studies of Schiff bases of chitosan derived from heteroaryl aldehydes

The synthesis of Schiff bases of chitosan is performed by the reaction of chitosan with different heteroaryl aldehydes, i.e., furfuraldehyde, thiophene-2-carboxylaldehyde, pyrrole-2-carboxylaldehyde, pyridine-2-carboxylaldehyde, pyridine-3-carboxylaldehyde and pyridine-4-carboxylaldehyde. The structural characterizations of the biopolymeric Schiff bases are executed by 1H NMR spectroscopy, Fourier transform infrared spectroscopy and elemental analysis (C, H, N). The 1H NMR spectroscopy is also used to determine the degree of deacetylation of chitosan as well as the degree of substitution (DS) of Schiff bases and DS found to be varying from 58 to 74%. Thermogravimetry studies of chitosan and its Schiff base polymers show that they have nearly the same decomposition temperature and hence equally thermally stable. The model-free multiple heating rate method Kissinger–Akahira–Sunose has been employed for the thermal degradation kinetics of the most potent antimicrobial compound ChSB-6. The antimicrobial activities of chitosan and its Schiff bases are tested against different pathogenic bacteria: Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Aspergillus niger, and results shows that the activities of the Schiff bases of chitosan are found to be stronger than that of chitosan.

Electric Poling and Relaxation Studies of PMMA Thin Films Containing Diaminopyrazole Derivatives as Dipolar Chromophores

Vacuum-deposited thin films of polymethylmethacrylate (PMMA) doped by varying concentrations (2-10 % by weight of polymer) of some 3,5-diaminopyrazole derivatives as dipolar chromophores were prepared to study their relaxation behaviour . Poling of thin films was carried out using multi-point corona-poling technique to orient dipolar chromophores in proper aligned position. Poling and depoling behaviours of these thin films have been investigated by UV/Vis absorption spectra. For each chromophore, poling efficiency was found to increase with poling voltage as well as poling temperature up to a certain limit retaining the properties of thin films. Maximum value of concentration dependent order parameter was obtained at temperature slightly lower than glass transition temperatures of corresponding guest-host matrices. After 300 hrs. of poling under the conditions (5 kV, near T g , 30 min.), the decayed amounts of order parameters at room temperature were within the range 25-38 % of the initial value for various guest-host systems. Relaxation behaviour of poling-induced chromophore alignment has also been studied at elevated temperature.

ELECTRICAL AND OPTICAL NONLINEARITY IN VACUUM-DEPOSITED THIN FILMS OF POLY[N-(4-BENZOYLPHENYL)-2-METHYLACRYLAMIDE]

A new optically nonlinear material, poly[N-(4-benzoylphenyl)-2-methylacrylamide], for conversion of wavelength 1064 nm to 532 nm has been synthesized. The material possesses strong electrical and optical nonlinearity required for second harmonic generation (SHG). The thin films of poly[N-(4-benzoylphenyl)-2-methylacrylamide] were prepared by the vacuum-deposition technique. The optical UV-visible, IR, NMR studies, mass spectrometry, surface topography and nonlinear optical properties of the thin films were studied. The vacuum-deposited thin films of the polymer were subjected to optimized high potential multi-point corona poling at temperatures just below the glass transition temperature (Tg) to create directional orientation of the side chain groups. The optical UV-visible absorption indicates a complete transparency in the visible and IR regions with an absorption peak at ~350 nm. The energy band gap of the polymer was estimated to be ~2.9 eV, from the optical absorption spectra of the thin films. The electrical current–voltage (IV) and optical nonlinear characteristic indicate the strong potential of these polymeric thin films for nonlinear optical (NLO) applications.