Ultrasonic relaxation studies on micelle formation in aqueous solutions of some bile salts

Ravichandran, G.; Gopinath, D.

doi:10.1016/j.molliq.2014.06.014

Cited by 7 publications

(13 citation statements)

References 32 publications

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“…40 Our results thus do not support the mechanism initially proposed by Small and Ekwall, 17,43 that larger micelles form primarily by fusion of smaller ones. In apparent contradiction with our observations and the ultrasonic relaxation measurements 58 we mentioned above, recent conductivity measurements 34 have been interpreted to support the twostage mechanism proposed by Small and Ekwall. 17,43 It is our opinion, however, that such a conclusion may not be reached from those measurements.…”

Section: Micelle Size Changes Occur Primarily Via Monomer Removal Andcontrasting

confidence: 99%

“…[36][37][38] Our results confirm that relaxation times in bile salt solutions at physiologically relevant concentrations may be interpreted using those models, as was recently successfully done by Ravichandran et al, 58 as discussed above. For improved quantitative agreement, however, fission and fusion of dimers and trimers should be included in the models at high concentrations, where these events become more frequent.…”

Section: Models Of Micellar Kinetics Developed For Head-tail Surfactasupporting

confidence: 89%

“…These results suggest that bile salts may leave bile micelles at much faster rates than those typically found for head-tail surfactants. These differences in free energy barriers are qualitatively consistent with differences in the monomer removal rate estimated from experiment: for sodium deoxycholate, 58 k À = O(10 7 s…”

supporting

confidence: 80%

“…31,[66][67][68] Our results indicate that the dominant mechanism of micelle size change in bile salt solutions is monomer addition or removal, even at concentrations 18 times higher than the critical micellar concentration, in agreement with recent ultrasonic studies of the kinetics of bile salt micelles. 58 The simulations do not support the popular assumption that bile micelles predominantly form in a two-stage process, by formation of oligomers and subsequent oligomer fusion to produce larger micelles. Addition of monomers to micelles is nearly barrierless, similarly to head-tail surfactants, and the free energy barrier to monomer removal is of order 2k B T, i.e., much lower than the 8k B T found for head-tail surfactants.…”

Section: Discussionmentioning

confidence: 66%

“…This observation is supported by recent ultrasonic relaxation measurements of micellar kinetics in bile salt solutions. 58 In that work, the experimental results were wellfitted by analytical models of micelle kinetics relying solely on monomer addition and removal, indicating that fission and fusion of larger micelles should play a secondary role. The observed importance of monomer addition and removal is in line with simulations of model coarse-grained ionic head-tail surfactants 42 and, more generally, with the expected behavior of ionic surfactants at concentrations near the CMC and for low to moderate counterion concentration.…”

Section: Micelle Size Changes Occur Primarily Via Monomer Removal Andmentioning

confidence: 82%

See 4 more Smart Citations

Kinetics of formation of bile salt micelles from coarse-grained Langevin dynamics simulations

Verde

Frenkel

2016

Soft Matter

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We examine the mechanism of formation of micelles of dihydroxy bile salts using a coarse-grained, implicit solvent model and Langevin dynamics simulations. We find that bile salt micelles primarily form via addition and removal of monomers, similarly to surfactants with typical head-tail molecular structures, and not via a two-stage mechanism -involving formation of oligomers and their subsequent aggregation to form larger micelles -originally proposed for bile salts. The free energy barrier to removal of single bile monomers from micelles is E2k B T, much less than what has been observed for head-tail surfactants. Such a low barrier may be biologically relevant: it allows for rapid release of bile monomers into the intestine, possibly enabling the coverage of fat droplets by bile salt monomers and subsequent release of micelles containing fats and bile salts -a mechanism that is not possible for ionic head-tail surfactants of similar critical micellar concentrations.

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Section: Micelle Size Changes Occur Primarily Via Monomer Removal Andcontrasting

confidence: 99%

Section: Models Of Micellar Kinetics Developed For Head-tail Surfactasupporting

confidence: 89%

supporting

confidence: 80%

Section: Discussionmentioning

confidence: 66%

Section: Micelle Size Changes Occur Primarily Via Monomer Removal Andmentioning

confidence: 82%

See 3 more Smart Citations

Kinetics of formation of bile salt micelles from coarse-grained Langevin dynamics simulations

Verde

Frenkel

2016

Soft Matter

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Bile salts and derivatives: Rigid unconventional amphiphiles as dispersants, carriers and superstructure building blocks

Galantini

Gregorio

Gubitosi

et al. 2015

Current Opinion in Colloid & Interface Science

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Gaussian Charge Distributions for Incorporation of Electrostatic Interactions in Dissipative Particle Dynamics: Application to Self-Assembly of Surfactants

Eslami

Khani

Müller‐Plathe

2019

J. Chem. Theory Comput.

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The point charges are distributed over the soft dissipative particle dynamics (DPD) beads using a Gaussian of tunable width. Screening the Gaussian smeared charge distributions, with wider Gaussians of opposite charge, splits the electrostatic interaction into the real-and the reciprocal-space contributions. This method is validated against model test systems in the literature. The method has also been employed to study self-assembly in solutions of sodium dodecyl sulfate (SDS) in water. The critical micelle concentration (CMC) and the equilibrium concentration of free surfactants, in solutions with SDS concentrations varying from CMC to ≈20 times larger than CMC, are in close agreement with experiment. The microscopic structure of the micelles and the distributions of its hydrophobic/hydrophilic groups and counterions at the water interface are in agreement with experiment. The dynamics of monomer exchange between micelles and solution is examined in terms of the intermittent and continuous correlation functions for the fluctuation of micelle size with time. Two discrete relaxation processes, whose relaxation times differ by 2 orders of magnitude are found. Using the natural DPD time unit, defined in terms of thermal velocity, the relaxation times are an order of magnitude shorter than experimental relaxation times for monomer exchange and establishment of equilibrium between surfactants in the solution and micelles through diffusion of surfactants. However, experimentally comparable relaxation times are obtained by defining the DPD time scale such that the calculated diffusion coefficient of water corresponds to its experimental value.

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Ultrasonic relaxation studies on micelle formation in aqueous solutions of some bile salts

Cited by 7 publications

References 32 publications

Kinetics of formation of bile salt micelles from coarse-grained Langevin dynamics simulations

Kinetics of formation of bile salt micelles from coarse-grained Langevin dynamics simulations

Bile salts and derivatives: Rigid unconventional amphiphiles as dispersants, carriers and superstructure building blocks

Gaussian Charge Distributions for Incorporation of Electrostatic Interactions in Dissipative Particle Dynamics: Application to Self-Assembly of Surfactants

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