Salt Effects on Solute Exchange and Micelle Fission in Sodium Dodecyl Sulfate Micelles below the Micelle-to-Rod Transition

Abstract

This paper describes micelle exchange kinetics of hydrophobic pyrene derivatives between SDS micelles in the presence of moderate concentrations of sodium counterions ([Na + ] < 150 mM). The kinetics were followed by fluorescence time-scan measurements in which the disappearance of excimer over time was monitored. The exchange rate constant k obs is highly sensitive to the counterion concentration and increases as a power law against [Na + ] with an exponent of 4, from a value of almost 0 in the absence of salt to 10 -2 s -1 for [Na + ] )100 mM. The exchange rate is not very sensitive to the concentration of SDS micelles, except as the SDS concentration affects the ionic strength, which indicates that the kinetics are dominated by a first-order process. This process is attributed to a fission-growth mechanism in which the fission rate is rate-limiting. Although fission can yield any size micelles, the use of hydrophobic probes restricts the observation to the events yielding two micelles large enough to bear the probe molecules. We propose that the barrier to fission is the creation of surface instabilities, which are enhanced in the proximity of the micelle-to-rod transition. Over the range of counterion concentrations investigated here, micelle fusion is inhibited by electrostatic repulsion.

Exchange dynamics between amphiphilic block copolymers and lipidic membranes through hydrophobic pyrene probe transfer

“…1-octylpyrene PyC 8 , 1-dodecylpyrene PyC 12 and PyC 18 , were tested and caused an increase on the rst-order process rate with the decrease of the size of the probe, directly related with the decrease on the hydrophobicity of the molecule. 59,63 So one would also expect an interesting variation of, mainly, the rst order mechanism as a function of pyrene derivative chain-length in our study system. Finally, the results allow proposing an interaction mechanism between P104 triblock copolymer micelles and liposomes suspensions dominated by collective dynamics that could involve the following steps: collision of a micelle and a liposome, adhesion of micelles on the lipidic membrane, transfer of solute inside the lipidic membrane of the liposome followed by a possible separation (Fig.…”

Chlorophyll-Inspired Red-Region Fluorophores: Building Block Synthesis and Studies in Aqueous Media

“…The distributions of tetrapyrroles in micelles should not be regarded as static, given that hydrophobic solutes typically undergo extensive exchange among micelles; for example, substrates such as dodecylpyrene undergo extensive exchange in minutes–hours among SDS micelles [ 60 ]. The exchange of solutes between micelles [ 55 , 61 , 62 , 63 , 64 , 65 ] can entail exchange through the aqueous solution, fusion–fission of micelles, and/or micellar fission. The prevalence of a given mechanism depends on the micellar surface charge, aqueous ionic strength, and solute polarity.…”

Paley's watchmaker analogy and prebiotic synthetic chemistry in surfactant assemblies. Formaldehyde scavenging by pyrroles leading to porphyrins as a case study

“…4 for 0.39 mM micelles (for 0.20 and 0.58 mM, see Fig. 21,[38][39][40][41] Three distinct mechanisms include (1) exit-re-entry of the solute (i.e., exchange via water mechanism); (2) micellar collisionexchange-separation (i.e., fusion-fission); and (3) micellar fission-growth. Porphyrin formation requires four pyrroles to create the macrocycle, thus we are interested in the fraction of micelles that contain 4 pyrroles.…”