Swati Das

Solvation dynamics in organized assemblies, 4-aminophthalimide in micelles

Solvation dynamics of 4-aminophthalimide (4-AP) has been studied in neutral (triton X-100, TX), cationic (cetyl trimethyl ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) micelles using picosecond time resolved Stokes shift. Above critical micellar concentration (CMC), for all the three micelles, 4-AP exhibits wavelength dependent fluorescence decays with a fast decay at the blue end and a slow decay accompanied by a distinct growth at the red end of the emission spectra. The time dependent Stokes shift indicates that the water molecules in the Stern layer of the micelles relax in ≈100 ps time scale which is markedly slower than the subpicosecond relaxation dynamics observed in ordinary bulk water.

Synthesis of silver nanoparticle inside the nonaqueous ethylene glycol reverse micelle and a comparative study to show the effect of the nanoparticle on the reverse micellar aggregates through solvation dynamics and rotational relaxation measurements.

In this work, we have reported the application of less familiar ethylene glycol-AOT reverse micelle for the synthesis of silver nanoparticle using glucose as mild reducing agent and isooctane as the continuous media. We have also studied the pure ethylene glycol-AOT reverse micelle and the perturbed reverse micelle (containing silver nanoparticle in its womb) through solvation dynamics measurement using steady-state and time-resolved fluorescence spectroscopy. Finally, we compared both of the results to get the valuable information about the perturbed reverse micellar system containing silver nanoparticle. Through the work, we found that in the pure reverse micellar system, with increasing ethylene glycol loading, solvation time was decreasing and anisotropy value became slower. In the perturbed reverse micellar system (containing silver nanoparticle) having the same environmental state, that is, at the same ethylene glycol content, solvent and rotational relaxation became slower and faster, respectively.

Interaction of Triton X-100 with cyclodextrins. A fluorescence study

The interaction of Triton X-100 (TX) with α- and β-cyclodextrins (CD) has been studied, using 2,6-p-toluidinonaphthalene sulfonate (TNS) as a fluorescent probe, by steady-state and time-resolved emission spectroscopy. The critical micellar concentration (c.m.c.) is indicated by the point of abrupt increase of emission intensity and lifetime of TNS. The apparent c.m.c. increases significantly in the presence of β-CD by as much as 28±1 times at 10 mM β-CD but remains more or less unaffected in the presence of α-CD at similar concentrations. This is attributed to the very strong binding of TX with the large β-CD cavity and negligible binding to the small α-CD. At concentrations below the c.m.c., on addition of TX to aqueous TNS solution containing β-CD the emission intensity decreases. This is ascribed to the competitive binding of TNS and TX with β-CD. This causes displacement of TNS from the CD cavity by the TX surfactant molecules. The binding constant of TX with β-CD is found to be ca. 9400±1300 L mol-1.

Solvation dynamics in a solid host. Coumarin 480 in zeolite 13X

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.

Dual emission of 2-(2'-hydroxyphenyl) -benzimidazole in reverse micelle

Abstract 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.

Aryl participated cyclisations involving indane derivatives a total synthesis of (±)-isolongifolene

Abstract 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.

SALT EFFECT ON P-NITROPHENOL AT THE WATER SURFACE : A SURFACE SECOND HARMONIC GENERATION STUDY

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.

Effect of urea and surfactant on p-nitrophenol at the water surface: a surface second-harmonic generation study

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.

Effect of salt and solvents on the ionic solvation of p-toluidinonaphthalene sulfonate

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.

Stereocontrolled total synthesis of (±)-totaryl methyl ether and (±)-semperviryl methyl ether

Abstract 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).