Solvation Dynamics in the Water Pool of an Aerosol-OT Microemulsion. Effect of Sodium Salicylate and Sodium Cholate

Dutta, Partha; Sen, Pratik; Mukherjee, Saptarshi; Halder, and Arnab; Bhattacharyya, Kankan

doi:10.1021/jp030083g

Cited by 56 publications

(61 citation statements)

References 78 publications

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“…6). 14 They also showed that the time constant of decay of G(t) of DCM is similar to that of C(t) and hence, in this case the slow solvation dynamics is attributed to self-diffusion of the probe (DCM). It should be noted that the time dependent change in spectral width observed is observed only in selected cases.…”

Section: Model 2: Self-diffusion Of the Probementioning

confidence: 90%

“…For instance, the same probe (DCM) which exhibits time dependent change in G in a reverse micelle does not show similar behavior when entrapped in a bile salt micelle. 14 In the latter, DCM is confined in a very long (5 nm) cylindrical water filled core. As a result, within its excited state lifetime the probe does not come out in bulk water and does not experience a large variation of local polarity.…”

Section: Model 2: Self-diffusion Of the Probementioning

confidence: 99%

“…As a result, within its excited state lifetime the probe does not come out in bulk water and does not experience a large variation of local polarity. 14 The diffusion coefficient (D || ) of fluorescent probe for translation parallel to the surface of an organized assemble may be obtained from the fluorescence anisotropy decays using the "wobbling-in-cone" model. 34 It is observed that D || is smaller than that in bulk water (~10 -5 cm 2 s -1 ) only by a factor of 2-5.…”

Section: Model 2: Self-diffusion Of the Probementioning

confidence: 99%

“…[1][2][3][4][5][6][7] However, in a biological or an organized assembly, the long component of solvation dynamics slows down quite dramatically. [8][9][10][11][12][13][14] At the surface of a protein, solvation dynamics displays a component which is slower by one to two orders of magnitude compared to bulk water and the ultraslow component ranges from a few tens to a few hundreds of picoseconds. [8][9][10] The ultraslow component in a cyclodextrin cavity is nearly 1000 times slower than that in bulk water.…”

Section: Introductionmentioning

confidence: 99%

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Solvation Dynamics in Biological Systems and Organized Assemblies

Sen¹,

Pal²,

Bhattacharyya³

et al. 2006

J Chinese Chemical Soc

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Solvation dynamics of a polar probe in many biological systems and organized assemblies displays a surprising ultraslow component. The origin of this anomalous ultraslow component is investigated using experiments, theory and computer simulations. We first summarize some recent experimental results on solvation dynamics, e.g., temperature dependence, site dependence at active site of an enzyme and red edge excitation shift (REES). Then we propose two new theoretical models to explain the ultraslow component. The first one involves the motion of the 'buried water' molecules (both translation and rotation) accompanied by cooperative relaxation ('local melting') of several surfactant chains. An estimate of the time is obtained by using an effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation invokes self-diffusion of the (di)polar probe (created by optical excitation) itself from a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic core, if the probe has a sizeable distribution inside the core prior to excitation. It may also involve escape of the probe to the bulk from the surface of the selfassembly. The second mechanism should result in the narrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the two mechanisms may give rise to an ultraslow time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe in such complex systems has been discussed. Finally, we give a brief overview of recent results on computer simulations on dynamics of water molecules around a protein and a micelle.

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Section: Model 2: Self-diffusion Of the Probementioning

confidence: 90%

Section: Model 2: Self-diffusion Of the Probementioning

confidence: 99%

Section: Model 2: Self-diffusion Of the Probementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solvation Dynamics in Biological Systems and Organized Assemblies

Sen¹,

Pal²,

Bhattacharyya³

et al. 2006

J Chinese Chemical Soc

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“…About 20 surfactant molecules of AOT form a reverse micelle having a diameter of 3.0 nm above the critical concentration of 1 mM in a hydrocarbon solvent such as n-heptane. 29 By adding water to the AOT solution, microemulsions of nanometer-sized water droplets surrounded by AOT molecules are formed, and the size of water nanopools confined in AOT reverse micelles increases as the concentration of water increases. In n-heptane, the diameters in nanometers of the waterpools have been reported to be about 0.3w 0 , in which w 0 is the molar ratio of water to AOT.…”

Section: -16mentioning

confidence: 99%

Anomalous Acid-Base Equilibria in Biologically Relevant Water Nanopools

Park

Yoo²,

Pyo³

et al. 2012

Bulletin of the Korean Chemical Society

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Water plays a crucial role in many principal biological phenomena such as enzymatic catalysis and proton pumping through a membrane protein channel.1-4 Moreover, in biological systems, water is usually contained in a small pocket of a membrane, 5-8 and such confined water, which is generally called a water nanopool, [8][9][10] shows peculiar properties differing considerably from the properties of bulk water. 8-16The confinement effect and the enclosing interfacial surfaces of waterpools are the main factors to determine the properties, such as polarity, viscosity, and H-bonding ability, of water nanopools.5-13 For example, the dielectric constant of a water nanopool has been reported to be much lower than that of bulk water (ε = 78.5)17 but similar to that of an alcohol (ε = 30-40).18,19 On the other hand, biological processes often take place based on proton relay along a hydrogen (H)-bonded chain, [1][2][3][4][20][21][22][23][24] and the dynamics of biological proton relay is determined by the size, the structure, and the motion of a water cluster which is the prime agent in most of biological systems. 3,[13][14][15][24][25][26] Thus, for better understanding of cellular dynamics, it is necessary to investigate the properties of a biologically relevant water nanopool as a biomimetic system of water confined in a cell membrane. In this regard, water nanopools confined in reverse micelles, which are formed by surfactant molecules having polar headgroups pointing inward and dispersed in hydrocarbon solvents, can be good model systems of biological water. 6,18,19,27 It is a unique feature of reverse micelles that they can make nonpolar media to solubilize a large amount of water by encapsulating water molecules in their inner polar cores; 28 reverse micelles are surrounded by a layer of surfactant molecules such as Aerosol-OT (sodium 1,4-bis-2-ethylhexylsulfosuccinate, AOT) and immersed in a nonpolar solvent, so that nanometer-sized droplets of a polar solvent such as water are formed inside. The polar headgroups of surfactant molecules point inward toward a polar solvent pool, and the alkyl chains of the surfactant molecules point outward toward a nonpolar solvent. About 20 surfactant molecules of AOT form a reverse micelle having a diameter of 3.0 nm above the critical concentration of 1 mM in a hydrocarbon solvent such as n-heptane.29 By adding water to the AOT solution, microemulsions of nanometer-sized water droplets surrounded by AOT molecules are formed, and the size of water nanopools confined in AOT reverse micelles increases as the concentration of water increases. In n-heptane, the diameters in nanometers of the waterpools have been reported to be about 0.3w 0 , in which w 0 is the molar ratio of water to AOT. 30The catalytic properties of water nanopools depend strongly on the hydration extent of reverse micelles and on the solvation structure of reactants relevant to the polarity of waterpools confined in reverse micelles. [5][6][7][8]17,18 The peculiar structure of waterpools contained in reverse mi...

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