Search

Picosecond time resolved and steady state emission spectroscopy were employed to study the dual emission phenomenon of 2-(2′-hydroxyphenyl)-benzimidazole (HPBI) in aerosol OT (AOT) reverse micelle in n -heptane. It is observed that the microenvironment inside the water pool markedly affects the dual emission (normal and tautomer) of HPBI. While the normal emission is negligible in n -heptane, on addition of AOT and water its intensity increases gradually and reaches a moderate value ( φ f =0.04) at a water-to-surfactant ratio, w 0 ≈40. The decay of the normal emission becomes faster with addition of water. The intensity and lifetime of the tautomer emission increase on addition of AOT. The increase in the intensity of the normal emission with w 0 is ascribed to the formation of the polyhydrates in which excited state intramolecular proton transfer is blocked. The increase in the intensity of the tautomer emission in reverse micelles, compared with n -heptane, is attributed to the reduction in the non-radiative rates. The polarity of the water pool inferred from both the emission parameters of the normal, and the tautomer emission is less than that of ordinary bulk water.

Picosecond time-resolved emission of 4-aminophthalimide (4-AP) in neat water and D2O and in the water pool of aerosol OT reverse micelles in n-heptane is reported. It is proposed that in protic solvents 4-AP undergoes ultrafast solvent-mediated proton transfer and the emission originates from the proton-transferred species. The abrupt decrease in the emission quantum yield and lifetime of 4-AP in protic solvents is attributed to the reduction in the S1−S0 energy gap in the proton-transferred species. Nearly 4-fold increase in the emission quantum yield (φf) and lifetime (τf) of 4-AP is observed in neat D2O compared to water. This is ascribed to the retardation of the nonradiative S1 → S0 internal conversion processes on deuteration of the imide proton. In neat water or D2O the solvation dynamics is too fast to be detected using our picosecond setup. However, in the water pool of reverse micelles the relaxation of the water (or D2O) slows down appreciably. The initial component of the solvation dynamics in...

Conducting polymer polypyrrole is reported to have a poor adhesion to substrate which limits its applicability asthin films. In this article, we report synthesis of well-formed and continuous film of polypyrrole through treatment of hydropho-bic substrates. However, in place of the widely used organosilanes, the substrates were simply treated with surfactant cetyl trime-thylammonium bromide (CTAB) prior to vapor phase polymerization under controlled environment. Polypyrrole films formedon CTAB pretreated substrates were found to have improved adhesion and continuity compared to the films formed onuntreated substrates. The improved adhesion results in better electronic properties as seen during Electron field emission studies.Based on contact angle analysis, we propose that CTAB molecules act as anchoring agents for the oxidant layer on the substrateand hence assist in the deposition of a more continuous polypyrrole film. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000:000–000, 2013

Highly-luminescent nanophosphors have a decisive role in solid-state lighting (SSL) as well as in field emission display (FED) applications due to their potential use in fabrication of nanophosphor based FED and solid state display devices. Herein, the red emitting highly-luminescent Eu(3+)-Li(+) co-doped magnesium aluminate (MgAl2O4) nanophosphors were synthesized by a customized sol-gel route with an average particle size of 18 nm, which can be easily scaled up in a large quantity. The resulting nanophosphor exhibits hypersensitive red emission, peaking at 615 nm upon 394 nm excitation. Furthermore, comparative photoluminescence (PL) studies have been carried out for Eu(3+) doped and Eu(3+) doped-Li(+) co-doped magnesium aluminate (Li(+) co-doped MgAl2O4:Eu(3+)) nanophosphors, which indicated that Li(+) co-doping significantly improves luminescence intensity along with good crystallinity. Moreover, the charge compensation by addition of Li(+) co-activator in MgAl2O4:Eu(3+) lattice led to the two fold enhancement of PL intensity. The obtained results suggest that this nanophosphor could be an ultimate choice for next generation advanced luminescent nanomaterials for solid state lighting and portable FED devices.

Cupric oxide mesospheres composed of its nanoparticles have been synthesized by a simple template free chemical route at different temperatures. Thermal aging followed by higher temperature (350 degrees C, 6 hours) annealing on these architects transformed them into hollow mesospheres consisting of sharp needle like structures with high aspect ratio (- 10(3)). A detailed analysis of field emission scanning electron microscopy confirmed a uniform registry of the prepared nanostructures. High resolution transmission electron microscopy showed that the as-grown mesospheres have hollow inner cavity with a thin outer shell. X-ray photoelectron spectroscopic analysis showed no obvious changes in the chemical composition of the nanostructures after annealing, confirming that the elements in the final products were in the proper oxidation states. Electron emission under electric field was investigated from these interesting structures. It was found that both of these nanostructures showed electron emission, but emission performance of the hollow mesospheres consisting of nanoneedles exhibited excellent performance with turn-on field as low as 2.8 V/microm and high enhancement factor (beta) - 5537.

The dynamics of solvation of coumarin 480 guest molecule in supercages of a faujasite zeolite 13X is studied using picosecond time-resolved emission spectroscopy. The guest molecule exhibits a time-resolved Stokes shift in zeolite 13X. The decay of the response function, C(t), is nonexponential with the major components on a nanosecond timescale. The average solvation time is observed to be 8.13 ns. The nanosecond solvation is attributed to the self-motion of the probe solute and the motion of the sodium ions present in the zeolite host.

The picosecond time-resolved Stokes shift of the laser dye, coumarin 480 (I) is studied in neutral (Triton X-100, TX), cationic (cetyltrimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles. Above critical micellar concentration (cmc) for all three micelles I exhibits wavelength dependent fluorescence decays and a distinct growth at the long wavelengths. The time dependent Stokes shift studies indicate that the water molecules in the Stern layer of the micelles relax on the time scale 180−550 ps, which is slower than the subpicosecond relaxation dynamics observed in ordinary bulk water.

The picosecond time-resolved Stokes shift of the laser dye coumarin 480 (I) is studied in Aerosol OT-heptane reverse micelles at various concentrations of water. On addition of water to a n-heptane solution of I containing 0.09 M AOT, the emission spectrum of I exhibits a prominent shoulder at 480 nm which is ascribed to the dye molecules in the water pool of the reverse micelles. In n-heptane, the fluorescence decays of I at short and long wavelengths are identical, which rules out any time-resolved Stokes shift. On addition of water to the AOT/heptane system, the decay at long wavelengths exhibit a distinct growth on the nanosecond time scale. This and the time-dependent Stokes shift indicate that the water molecules in the water pool of the AOT reverse micelles undergo slow relaxation on the nanosecond time scale.

Excited-state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) has been studied using steady-state and time-resolved emission spectroscopy in neutral (Triton X-100), anionic (sodium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) micelles. It is found that the tautomer intensity and the lifetime of the tautomer emission are sensitive monitors to estimate the critical micellar concentration (cmc) for all three micelles. Above the cmc the intensity of the normal emission band decreases while there is a large enhancement of the intensity of the tautomer emission along with a red shift of the emission maxima by about 20 nm. The decay of the normal emission of HPBI remains similar below and above the cmc for all three micelles. However, the lifetime of tautomer emission of HPBI increases sharply above the cmc. The enhanced tautomer emission is ascribed to the HPBI molecules residing in the less polar and aprotic interior of the micelles.

The effect of the linear oligosaccharides dextrin (α-1a,4e-D-glucopyranose) and dextran (α-1,6-D-glucopyranose) on the emission properties of 2-(p-toluidino)-6-naphthalenesulfonate (TNS) has been studied in aqueous solution. TNS exhibits a 30-fold fluorescence enhancement on binding to dextrin, while with dextran there is only a marginal increase in the emission intensity. The polarity values of the binding sites are estimated by comparing the nonradiative rates of TNS with those in aqueous dioxane-water mixtures. The results indicate that the binding surface of dextrin is markedly less polar than that of dextran. This difference is attributed to the differing stereochemical constraints imposed on the two chains. The binding constants of TNS with the two polysaccharides in pure water have been determined in the presence and absence of several salting-in denaturants and salting-out reagents. Salting-in agents cause a decrease in the number of TNS molecules bound to the dextrin surface and an increase in the local polarity, while the salting-out agent LiCl increases the number of TNS molecules bound to dextrin. The interaction of TNS with dextran, however, is found to be very weak even in the presence of LiCl. Energy minimization studies reveal a hydrophobic surface for dextrin while no such amphiphilicity is observed in dextran.

A total synthesis of (±)-isolongifolene (1) has been accomplished using intramolecular anionic cyclisation of the bromophenol 2 as the key step. Aryl participated intramolecular cyclisation of the diamethyl ketones 17 and 23 provided the dienediones 18 and 24 which were stereoselectively converted into the diketones 19 and 25 respectively.

Stereocontrolled synthesis in racemic form of the title diterpene ethers is described. Friedel-Crafts acylation of the naphthalene derivative 15 afforded the methyl ketone 16 in high yield. The compounds 5 and 16 were converted into the hydrophenanthrenones 6 and 7 respectively. Reductive methylation of 6 and 7 in anhydrous ammonia furnished the β, γ -unsaturated ketones 8 and 9 which were stereoselectively transformed into the trans -fused ketones 10 and 11. Huang-Minlon reduction of 10 and 11 afforded the octahydrophenanthrene 27 and (±)-totaryl methyl ether (2) respectively. Friedel-Crafts acylation of 27 provided the methyl ketone 28 which was converted into (±)-semperviryl methyl ether (4).

Pleural involvement in nocardiosis is rarely reported from India. A case of hydropneumothorax due to Nocardia asteroides in a patient with diabetes mellitus is reported. Tube thoracostomy drainage and therapy with trimethoprim-sulphamethoxazole for seven months prevented reaccumulation of pleural fluid and improved the general condition but failed to expand the lung. Bronchoscopy may be useful if multiple sputum examinations are negative in diagnosing pulmonary nocardiosis.

Sharp knife edged copper oxide (CuO) nano architectures were directly grown on the surface of flexible carbon fabric by a facile chemical route with the assistance of nonionic surfactant PEG-6000. The carbon fabric substrate preserves its high flexibility even after the growth of the entire nanostructure. Moreover, it can be rolled-up and twisted to a large degree without affecting the electrical characteristics. The phase purity and degree of crystallinity of the developed nanostructures were systemically supported by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. A proposed growth mechanism has been offered by thoroughly analyzing the field emission scanning electron microscopic images of the nanostructures grown at different concentrations of PEG. Among the as grown nanostructures, copper oxide nanoknives have exhibited remarkable field emission properties and high stability with a lower turn-on field of 0.9 V μm−1 (10 μA cm−2) at room temperature, which is sufficient for electron emission based devices like field emission displays and vacuum nano-electronic devices.

Fluorescence properties of p-toluidinonaphthalene sulfonate (TNS) are studied in the presence of tetra-n-butylammonium bromide (TBBr) in different solvents. In the presence of TBBr, in solvents of low polarity (tetrahydrofuran, THF), the fluorescence decay of TNS at the blue end (395 nm) is distinctly faster than that at the red end (500 nm). This is attributed to the formation of ionic aggregates involving negatively charged TNS and positively charged tetrabutylammonium ions. From the difference in the lifetimes at the red and blue ends, the ionic relaxation rates are obtained. In solvents of moderately high polarity (dimethylformamide, DMF) no such aggregates are detected and the decay at the red end is very similar to that at the blue end. In highly polar aqueous media, however, micellar aggregates of TBBr are formed, but there is no difference in the decay at the red and blue ends. The micellar aggregates in aqueous media remain unaffected in the presence of 3 mol dm–3 urea.

The effect of lithium perchlorate (LiClO4), guanidinium hydrochloride (GdmCl) and lithium chloride (LiCl) on the resonance surface second harmonic generation (SSHG) of p-nitrophenol (PNP) at the air/water interface is reported. On addition of GdmCl and LiClO4 the intensity of the SSH signal decreases appreciably, which is attributed to the decrease in surface population of PNP. Addition of LiCl causes an increase in the intensity of SSHG due to increase in surface population. The orientation of the PNP molecules remains unchanged on addition of all the salts. The free energy of adsorption (ΔadG) of PNP increases upon addition of the salting-in agents, but decreases for the salting-out agent. The results indicate that the factors which increase solubility of organic solutes in the bulk decrease the surface population of organic molecules at the surface and vice versa.

The effect of salting-in denaturant, urea and a water-soluble surfactant, cetyltrimethylammonium bromide (CTAB), on the resonance surface second-harmonic generation (SSHG) of p-nitrophenol (PNP) is reported. On addition of urea to an aqueous PNP solution the intensity of the SSH signal decreases markedly. CTAB on the other hand produces a 10-fold increase in the SSH signal of PNP at a concentration one-quarter of the critical micellar concentration. Addition of urea reduces the intensity of the SSH signal in the presence of CTAB also. The orientation of the PNP molecule at the surface remains unchanged in both cases. The free energy of adsorption (ΔadG) of PNP does not change on addition of CTAB. However, the urea-induced decrease both in the absence and in the presence of CTAB is accompanied by an increase in ΔadG.

The tricyclic ketones 13 and 14, prepared from naphthalene and 2-methoxynaphthalene respectively, were subjected to reductive methylation in anhydrous ammonia to provide the β, γ -unsaturated ketones 16 and 17 in high yield which were stereoselectively converted into the A/B trans-fused compounds 3 and 4 respectively.

Mangiferin, a naturally occurring glucosylxanthone, was assessed for its immunomodulatory potential. The phytochemical induced extensive in vitro proliferation of murine splenocytes and thymocytes at the doses of 5–40 μg ml −1 . Suppression of the proliferative response of the cells was observed with higher doses of mangiferin. Mangiferin also activated the splenocytes of tumor hosts at early and late stages of tumor growth. The Phytohemagglutinin (PHA) and Con A unresponsive splenocytes of advanced tumor bearer proliferated extensively in response to mangiferin. Mangiferin when used with Con A produced additive stimulatory effect and induced heightened DNA synthesis of normal and advanced tumor bearers' splenocytes.

Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta.-32 Manuscript received 16 November 1972; revised 27 June 1973; accepted 7 November 1973 Conversion-time data were obtained for the polymerization of acrylamide in water initiated by hydrogen peroxide hydroxylamine redox pair. The polymerization was carried out under nitrogen at 30°; the yield was obtained gravimetrically, using an excess of methanol-acetone mixture as precipitant. The effect of initiator concentration, monomer concentration and temperature have been studied. The overall activation energybetween 30°-50° is about 6.5 Kcal/mole, It appears from the dependence of the rate of polymerization on the initiator concentration and end group analysis that a free radical mechanism is operative here.