Fluorescence Dynamics of Dye Probes in Micelles

Maiti, Nakul C.; Krishna, M. Bala; Britto, P. J.; Periasamy, N.

doi:10.1021/jp9723123

Cited by 282 publications

(405 citation statements)

References 45 publications

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“…The time constants get faster upon increasing temperature which reflects the thermal effect on the microviscosity and consequently to the wobbling rate of the probe and also the increase of free water molecules at the interface. 34 The presence of offset even at 348 K confirms the location of the dye within the micellar interface at elevated temperatures. Thus, DCM is highly efficient to probe the dynamics of water located in the interfacial layer at all studied temperatures.…”

Section: Resultsmentioning

confidence: 84%

Temperature-Dependent Hydration at Micellar Surface: Activation Energy Barrier Crossing Model Revisited

2007

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In recent years, the validity of the activation energy barrier crossing model at the micellar surface brings notable controversy (Sen, P.; Mukherjee, S.; Halder, A.; Bhattacharyya, K. Chem. Phys. Lett. 2004, 385, 357-361. Kumbhakar, M.; Pal, H. J. Phys. Chem. B 2004, 108, 19246-19254.) in the literature. In order to check the validity of the model by time-resolved solvation of a probe fluorophore, a wider range of temperature must be considered. At the same time, spatial heterogeneity (solubilization) of the probe and structural perturbation of the host micelle should carefully be avoided, which was not strictly maintained in the earlier studies. We report here the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylamino-styryl) 4H-pyran (DCM) in the SDS micelle at 298, 323, and 348 K. The probe DCM is completely insoluble in bulk water in this wide range of temperature. The size of the micelle at different temperatures using the dynamic light scattering (DLS) technique is found to have insignificant change. The hydration number of the micelle, determined by sound velocity measurements, decreases with increasing temperature. Time-resolved fluorescence anisotropy reveals the retention of the probe in the micellar interface within the temperature range. The average solvation time decreases with increasing temperature. The result of the solvation study has been analyzed in the light of energetics of bound to free water conversion at a constant size and decreasing hydration number at the micellar surface. The solvation process at the micellar surface has been found to be the activation energy barrier crossing type, in which interfacially bound type water molecules get converted into free type molecules. We have calculated E a to be 3.5 kcal mol -1 , which is in good agreement with that obtained by molecular dynamics simulation studies.

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Section: Resultsmentioning

confidence: 84%

Temperature-Dependent Hydration at Micellar Surface: Activation Energy Barrier Crossing Model Revisited

2007

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“…[62] This suggests that finding more than one Acr molecule in an individual micelle would be very unlikely (Poisson Law). [63] However, the concentrations of the bases were varied over a wide range from hundreds of mm to a few orders of mm such that each micelle could have more than one quencher molecule.…”

Section: Methodsmentioning

confidence: 99%

Influence of 2′‐Deoxy Sugar Moiety on Excited‐State Protonation Equilibrium of Adenine and Adenosine with Acridine inside SDS Micelles: A Time‐Resolved Study with Quantum Chemical Calculations

2012

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The protonation dynamics of the DNA base adenine (Ade) and its nucleoside 2'-deoxyadenosine (d-Ade) are investigated by monitoring the deprotonation kinetics of an N-heterocyclic DNA intercalator, acridine (Acr), in the confined environment of sodium dodecyl sulfate (SDS) micelles. Protonation of acridine (AcrH(+)) occurs at the hydrophilic interface and this species remains in dynamic equilibrium with its deprotonated counterpart (Acr) inside the hydrophobic core of SDS micelles. Quenching of the fluorescence of AcrH(+)* at 478 nm is observed after addition of Ade and d-Ade with Stern-Volmer constant (K(SV)) 298 and 75 M(-1), respectively, with a concomitant increment in Acr* at 425 nm. Time-resolved fluorescence studies reveal quenching in the lifetime of AcrH(+)*. The relative amplitude of AcrH(+)* decreases from 0.97 to 0.51 and 0.97 to 0.89 with equimolar addition of Ade and d-Ade, respectively. These observations are explained by excited-state proton transfer (ESPT) from AcrH(+)* to the bases. The reduced K(SV) value and negligible change in the relative amplitudes of AcrH(+)* with d-Ade infer that ESPT is hindered substantially by the presence of a 2'-deoxy sugar unit. Transient time-resolved absorption spectra of Acr reflect that Ade reduces the absorbance of (3)AcrH(+)*; however, d-Ade keeps it unaltered for more than a time delay of 2 μs. The optimized geometries calculated by quantum chemical methods reflect deprotonation of AcrH(+)* with protonation at the N1 position of Ade, while it remains protonated with d-Ade. The hindered ESPT between AcrH(+)* and d-Ade singles out the significance of the 2'-deoxy sugar moiety in controlling the deprotonation kinetics.

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“…Furthermore, structural transitions can be induced in charged micelles at a given temperature by increasing the ionic strength of the medium or amphiphile concentration (Ikeda 1984;Porte and Appel 1984). The organization and dynamics of micellar environments, namely the core, the interface, and the immediate layers of water on the interface, have been investigated using experimental (Sarkar et al 1996;Maiti et al 1997;Rawat et al 1997;Rawat and Chattopadhyay 1999) and theoretical (MacKerell 1995) approaches. It is fairly well established now that practically all types of molecule have a surface-seeking tendency in micelles (due to very large surface area to volume ratio) and that the interfacial region is the preferred site for solubilization, even for hydrophobic molecules (Shobha et al 1989).…”

Section: Introductionmentioning

confidence: 99%

Effect of micellar charge on the conformation and dynamics of melittin

Raghuraman

Chattopadhyay

2004

Eur Biophys J

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Electrostatic interactions play a crucial role in modulating and stabilizing molecular interactions in membranes and membrane-mimetic systems such as micelles. We have monitored the change in the conformation and dynamics of the cationic hemolytic peptide melittin bound to micelles of various charge types, utilizing fluorescence and circular dichroism (CD) spectroscopy. The sole tryptophan of melittin displays a red-edge excitation shift (REES) of 3-6 nm when bound to anionic, nonionic, and zwitterionic micelles. This suggests that melittin is localized in a restricted environment, probably in the interfacial region of the micelles, and this region offers considerable restriction to the reorientational motion of the solvent dipoles around the excited state tryptophan in melittin. Further, the rotational mobility of melittin is considerably reduced in these micelles and is found to be dependent on the surface charge of micelles. Interestingly, our results show that melittin does not partition into cetyltrimethylammonium bromide (CTAB) micelles owing to electrostatic repulsion between melittin and CTAB micelles, both of which carry a positive charge. In addition, the fluorescence lifetime of melittin is modulated in micelles of different charge types. The lowest mean fluorescence lifetime is observed in the case of melittin bound to anionic sodium dodecyl sulfate (SDS) micelles. CD spectroscopy shows that micelles induce significant helicity to melittin, with maximum helicity being induced in the case of melittin bound to SDS micelles. Fluorescence quenching measurements using the neutral aqueous quencher acrylamide show differential accessibility of melittin in various types of micelles. Taken together, our results show that micellar surface charge can modulate the conformation and dynamics of melittin. These results could be relevant to understanding the role of the surface charge of membranes in the interaction of membrane-active, amphiphilic peptides with membranes.

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Fluorescence Dynamics of Dye Probes in Micelles

Cited by 282 publications

References 45 publications

Temperature-Dependent Hydration at Micellar Surface: Activation Energy Barrier Crossing Model Revisited

Temperature-Dependent Hydration at Micellar Surface: Activation Energy Barrier Crossing Model Revisited

Influence of 2′‐Deoxy Sugar Moiety on Excited‐State Protonation Equilibrium of Adenine and Adenosine with Acridine inside SDS Micelles: A Time‐Resolved Study with Quantum Chemical Calculations

Effect of micellar charge on the conformation and dynamics of melittin

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