Photoisomerization of merocyanine 540 in polymer-surfactant aggregate

Photoisomerization of merocyanine 540 (MC540) in a polymer-surfactant aggregate is studied using picosecond time resolved emission spectroscopy. The aggregate consists of the polymer, poly(vinylpyrrolidone) (PVP) and the surfactant, sodium dodecyl sulphate (SDS). With increase in the concentration of SDS in an aqueous solution of MC540 containing PVP, the emission quantum yield and lifetime of MC540 increase markedly. This indicates marked retardation in the nonradiative photoisomerization process of MC540, when it binds to the polymer-surfactant aggregate. The critical association concentration of SDS for binding to PVP has been found to be 0.5 mM. This is about 16 times lower than the CMC of SDS in pure water (8 mM)

Isomerization and fluorescence depolarization of merocyanine 540 in polyacrylic acid. Effect of pH

Dynamics of isomerization and fluorescence depolarization of merocyanine 540 (MC540) in an aqueous solution of polyacrylic acid (PAA) have been studied using picosecond time resolved fluorescence spectroscopy. It is observed that the dynamics of isomerization and depolarization are sensitive enough to monitor the uncoiling of PAA at high pH (> 6). At low pH (< 3), when the polymer remains in a hypercoiled form, polymer bound MC540 experiences very high microscopic friction and, hence, the isomerization and depolarization processes are very slow. At high pH (> 6) a polyanion is formed and the polymer assumes an extended configuration due to electrostatic repulsion. At high pH(> 6), the anionic probe MC540 is expelled from the polyanion to bulk water and the dynamics of isomerization and fluorescence depolarization become faster by 12 and 5 times respectively, compared to those at low pH

Isomerization and fluorescence depolarization of merocyanine 540 in polyacrylic acid. Effect of pH

Abstract. Dynamics of isomerization and fluorescence depolarization of merocyanine 540 (MC540) in an aqueous solution of polyacrylic acid (PAA) have been studied using picosecond time resolved fluorescence spectroscopy. It is observed that the dynamics of isomerization and depolarization are sensitive enough to monitor the uncoiling of PAA at high pH (> 6). At low pH (< 3), when the polymer remains in a hypercoiled form, polymer bound MC540 experiences very high microscopic friction and, hence, the isomerization and depolarization processes are very slow. At high pH (> 6) a polyanion is formed and the polymer assumes an extended configuration due to electrostatic repulsion. At high pH (> 6), the anionic probe MC540 is expelled from the polyanion to bulk water and the dynamics of isomerization and fluorescence depolarization become faster by 12 and 5 times respectively, compared to those at low pH

Slow solvation dynamics of dimethylformamide in a nanocavity. 4-aminophthalimide in β -cyclodextrin

Solvation dynamics of a nonaqueous solvent, N,N-dimethylformamide (DMF) has been studied for the first time in a β -cyclodextrin (β -CD) cavity using picosecond time dependent fluorescence Stokes' shift and 4-aminophthalimide (4-AP) as a probe. Solvation dynamics of confined DMF molecules within the β -CD cavity is found to be described by a component of 400 ± 50 ps (25%) and a slow component of 8 ± 1 ns (75%). This is substantially slower than the solvation time (1 ps) in bulk DMF

Phenoxazinone synthase activity of two iron(III) complexes comprising the same Schiff base ligand: Biomimetic functional model and mechanistic investigation

A new 4,4′-bipyridine (4,4′-byp) mediated 1D- polymeric FeIII complex (complex 1) of Schiff base ligand H2L, a 1:2 condensation product of 1,2-diaminopropane and salicylaldehyde, has been synthesized. Complex 1 is structurally characterized by single crystal X-ray diffraction. A phenoxo bridged dinuclear FeIII complex (complex 2) of analogous ligand has been synthesized also. Dioxygen activation in terms of Phenoxazinone synthase activity using o-aminophenol (OAPH) as a model substrate catalyzed by both the complexes are thoroughly investigated here. ESI-MS spectral study reveals that polynuclear complex 1 dissociates into mononuclear units while dissolve in methanol during catalytic study. The kinetic study illustrates that both the complexes have well competence towards o-aminophenol oxidation where dinuclear FeIII species demonstrate higher activity than mononuclear intermediate species. Important finding from the mass spectral and electrochemical study provide significant information of the mechanistic pathway of the functioning phenoxazinone synthase like activity of synthesized iron complexes

Solvation dynamics of 4-aminophthalimide in a polymer (PVP)-surfactant (SDS) aggregate

Solvation dynamics of 4-aminophthalimide (4-AP) in a polymer-surfactant aggregate comprising poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS) is reported. In an aqueous solution even at a polymer concentration much higher than the cross over value (C∗), a significant portion (30%) of 4-AP molecules do not bind to PVP. In the presence of a surfactant, SDS, 4-AP binds to the PVP-SDS aggregate completely at a polymer concentration greater than C∗. The critical aggregation concentration (c.a.c.) of SDS for PVP is found to be 2 mM. The solvation dynamics of 4-AP in a PVP-SDS aggregate is observed to be slower compared to that in bulk water or in SDS micelles. The slow solvation dynamics is attributed to restrictions imposed on the water molecules squeezed between the polymer chain and micellar aggregates

Fluorescence anisotropy decay in polymer-surfactant aggregates

The fluorescence anisotropy decay of two dyes merocyanine 540 and oxazine 1 has been studied in a polymer-surfactant aggregate containing poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS). The results are analyzed in terms of the necklace model of the polymer-surfactant aggregate. The rotational motion of the probe is assumed to involve "wobbling-in-cone" along with translational motion along the micellar surface. It is observed that the presence of the polymer chains around the spherical SDS micelles causes significant retardation of both the wobbling motion as well as the translational motion of the two dyes. As a result, the wobbling and translational diffusion of the dyes in the PVP-SDS aggregate are slower than those in SDS micelle