Specific effects of monovalent counterions on the structural and interfacial properties of dodecyl sulfate monolayers

Abstract

A series of molecular dynamics simulations have been conducted in order to study the structural and interfacial properties of dodecyl sulfate (DS − ) monolayers with Li + , Na + , Cs + and NHcations. Varying the counterion has no significant effect on the structural properties of the surfactant molecules within the different monolayers. However, the different counterions have a significant effect on the interfacial properties of the monolayer. The NH + 4 ions are the most strongly bound to the headgroup, the least hydrated at the interface, directly compete with the hydrating water molecules for hydrogen bonds with the headgroup and more frequently interact with more than one headgroup. The Cs + ions are strongly bound to the headgroup and weakly hydrated, such that they would prefer to displace water in the DS − hydration shell to interact with headgroup. Also, the Cs + ions frequently interact with more than one headgroup. In the case of the Li + ions, they interact almost as strongly with the DS − headgroups as the Na + ions, but are generally less hydrated than the Na + ions and therefore they bring less water to the monolayer interface than the Na + ions. Therefore, by changing the counterion, one can modify the interfacial properties of the aggregates, and therefore effect their ability to encapsulate drug molecules, which we discuss in further greater detail.

Interaction of testosterone-based compounds with dodecyl sulphate monolayers at the air–water interface

“…The TIP3P water model 57 , modified for the CHARMM forcefield 58 , was used to describe interactions involving water. This combination of forcefields has previously been shown to give a good description of SDS micelles and DS − monolayers 1,26,59,60 .…”

“…There are a number of different ways to construct the intrinsic surface for liquid interfaces reported in the literature. For computational efficiency, the algorithm proposed by Berkowitz et al 64 was employed in this manuscript to determine the intrinsic surface of the DS − monolayers, as it was employed previously to investigate the interaction of various counterions with DS − surfactants 26 . In essence, this method is performed by projecting the location of a particle of interest and the anchor points used to define the interface onto the x-y plane.…”

“…As a re-sult there have been used in several investigations of the solubilisation of small molecules in surfactant micelles 1,[18][19][20][21][21][22][23][24][25] . Meanwhile, there has been a wealth of scientific research using MD simulations to gain a similar understanding of the molecularscale interactions that govern the interfacial properties of the surfactants and the self-assembled structures that they form at the air/water interface [26][27][28][29][30][31][32][33][34][35][36][37][38] . However, very little has been done with simulations investigating the interactions of drug molecules with surfactant monolayers, and the research that has been done primarily focusses on the interaction of drug molecules with lipid monolayers [39][40][41][42][43] .…”

Structure and Dynamics of Nanoconfined Water Between Surfactant Monolayers

“…This shows that water molecules are able to permeate past the monolayer headgroups, as has been previously observed for SDS monolayers. [55][56][57]59 This behavior is not seen at the air-water interface, where the water intrinsic density decays monotonically, 2 as shown in SI Figure 5 interface, which suggests that water molecules are unlikely to interact strongly with a neutral substrate, as in the experiments of Dhopatkar and co-workers. 9 We note that in a symmetric system, shown in Figure 2(a), the two intrinsic densities are identical.…”

3-dimensional electrode structure for enhanced electrochemical performance of in-plane microsupercapacitors

“…Therefore, there is surely a dependency of capacitance retention performance on the combination of PPy dopants and electrolytes.The capacitance retention figures are reflected in a scatter plot of capacitance retention performance against the ratio of dopant anion size and electrolyte anion size (Figure4-3). Note that the sizes of Cl -, NO3 -, PO4 3and DSions are 184 pm, 179 pm, 238 pm and 1070 pm respectively[310][311][312]. A sharp drop in capacitance retention was observed when the ratio was lesser than 1 (the dopant size was smaller than electrolyte anion size).…”