Effect of Counterions on the Shape, Hydration, and Degree of Order at the Interface of Cationic Micelles: The Triflate Case

Lima, Filipe da Silva; Cuccovia, Iolanda M.; Horinek, Dominik; Amáral, L. Q.; Riske, Karin A.; Schreier, Shirley; Salinas, Roberto Köpke; Bastos, E. L.; Pires, Paulo Augusto Rodrigues; Bozelli, José Carlos; Favaro, Denize C.; Rodrigues, Ana Clara B.; Dias, Luís Gustavo; Seoud, Omar A. El; Chaimovich, Hernán

doi:10.1021/la304658e

Cited by 33 publications

(80 citation statements)

References 86 publications

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“…2 Additionally, the hydration behavior of the counterions has drastic effects on micelle size and shape. 3…”

Section: Introductionmentioning

confidence: 99%

“…The micellization of surfactants is regarded as a useful model process for their investigation. To understand these effects on a molecular level, recent studies attempted to explore the complete atomistic structure of a micelle and its surroundings in solution. − It was found that the hydrophobic core of a micelle is surrounded by a highly corrugated surface containing hydrated nonpolar cavities, whose depth increases with increasing surfactant chain length . Additionally, the hydration behavior of the counterions has drastic effects on micelle size and shape …”

Section: Introductionmentioning

confidence: 99%

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Insight into the Hydration of Cationic Surfactants: A Thermodynamic and Dielectric Study of Functionalized Quaternary Ammonium Chlorides

et al. 2019

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Hydrophobic interactions are one of the main thermodynamic driving forces in self-assembly, folding, and association processes. To understand the dehydration-driven solvent exposure of hydrophobic surfaces, the micellization of functionalized decyldimethylammonium chlorides, XC 10 Me 2 N + Cl – , with a polar functional group, X = C 2 OH, C 2 OMe, C 2 OC 2 OMe, C 2 OOEt, together with the “reference” compound decyltrimethylammonium chloride, C 10 Me 3 N + Cl – , was investigated in aqueous solution by density measurements, isothermal titration calorimetry (ITC), and dielectric relaxation spectroscopy (DRS). From the density data, the apparent molar volumes of monomers and micelles were estimated, whereas the ITC data were analyzed with the help of a model equation, yielding the thermodynamic parameters and aggregation number. From the DRS spectra, effective hydration numbers of the free monomers and micelles were deduced. The comprehensive analysis of the obtained results shows that the thermodynamics of micellization are strongly affected by the nature of the functional group. Surprisingly, the hydration of micelles formed by surfactant cations with a single alkyl chain on quaternary ammonium is approximately the same, regardless of the alkyl chain length or functionalization of the headgroup. However, notable differences were found for the free monomers where increasing polarity lowers the effective hydration number.

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“…2 Additionally, the hydration behavior of the counterions has drastic effects on micelle size and shape. 3…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insight into the Hydration of Cationic Surfactants: A Thermodynamic and Dielectric Study of Functionalized Quaternary Ammonium Chlorides

et al. 2019

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“…The properties of the interface of cationic amphiphiles, which contain a quaternary ammonium head group, can be significantly modified by changing the counterion (Lima et al 2013). Anions containing a more hydrophobic group, like triflates, alkyl carboxylates, aromatic carboxylic acids and aromatic sulfonic acids, can lead to viscoelastic solutions with different aggregates structures, such as rodlike, threadlike, wormlike or polymer-like micelles.…”

Section: Shape Changes and Interface Compositionmentioning

confidence: 99%

Counting ions and other nucleophiles at surfaces by chemical trapping

2017

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The interfaces of membranes and other aggregates are determined by the polarity, electrical charge, molecular volume, degrees of motional freedom and packing density of the head groups of the amphiphiles. These properties also determine the type of bound ion (ion selectivity) and its local density, i.e. concentration defined by choosing an appropriate volume element at the aggregate interface. Bulk and local ion concentrations can differ by orders of magnitude. The relationships between ion (or other compound) concentrations in the bulk solvent and in the interface are complex but, in some cases, well established. As the local ion concentration, rather than that in the bulk, controls a variety of properties of membranes, micelles, vesicles and other objects of theoretical and applied interests, measurement of local (interfacial, bound) ion concentrations is of relevance for understanding and characterizing such aggregates. Many experimental methods for estimating ion distributions between the bulk solution and the interface provide indirect estimates because they are based on concentration-dependent properties, rather than concentration measurements. Dediazoniation, i.e. the loss of N, of a substituted diazophenyl derivative provides a tool for determining the number of nucleophiles (including neutral or negatively charged ions) surrounding the diazophenyl derivative prior to the dediazoniation event. This reaction, defined as chemical trapping, and the appropriate reference points obtained in bulk solution allow direct measurements of local concentrations of a variety of nucleophiles at the surface of membranes and other aggregates. Here we review our contributions of our research group to the use, and understanding, of this method and applications of chemical trapping to the description of local concentrations of ions and other nucleophiles in micelles, reverse micelles, vesicles and solvent mixtures. Among other results, we have shown that interfacial water determines micellar shape, zwitterionic vesicle-forming amphiphiles display ion selectivity and urea does not accumulate at micellar interfaces. We have also shown that reaction products can be predicted from the composition of the initial state, even in non-ideal solvent mixtures, supporting the usefulness of chemical trapping as a method to determine local concentrations. In addition, we have analysed the mechanism of dediazoniation, both on theoretical and experimental basis, and concluded that the formation of a free phenyl cation is not a necessary part of the reaction pathway.

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“…The micelle properties can be affected by surfactant concentration, salt, counterions, and temperature [62][63][64]. For the nonionic surfactant, Triton X-100, the aggregation number and radius of its micelles increase with increasing ionic strength, with the micelles becoming larger and more diffuse in structure [64].…”

Section: Hydration Of Collector Aggregatesmentioning

confidence: 99%