A small-angle neutron scattering study of biologically relevant mixed surfactant micelles comprising 1,2-diheptanoyl-sn-phosphatidylcholine and sodium dodecyl sulfate or dodecyltrimethylammonium bromide

Abstract

Small-angle neutron scattering (SANS) has been employed to characterize mixed micelles comprising the surfactants 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC)/sodium dodecyl sulfate (SDS) and 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC)/dodecyltrimethylammonium bromide (DTAB) using the classical model of a micelle consisting of a hydrocarbon core surrounded by a polar shell. Various constraints are applied to the data fitting, specifically the volume of the hydrocarbon core using the aggregation number determined from time-resolved fluorescence quenching (TRFQ) and the degree of micelle hydration as determined from an electron paramagnetic resonance (EPR) experiment. The morphologies of the DHPC/SDS and DHPC/DTAB mixed micelles are largely invariant with composition-as might be expected given the similarity in the tail volumes of the respective surfactants, and the observed behaviour of the aggregation number-with a radius comparable to the fully extended length of a dodecyl chain, i.e. the longer of the two hydrophobic moieties. The shell thickness is also largely invariant with composition, indicating that the phosphatidylcholine headgroup lies flat at the interface. For both cases, the degree of counter-ion dissociation extracted from the fitting of the SANS data increases significantly on addition of DHPC, in a manner very similar to that observed for related binary surfactant mixtures, provided there is only a small change in micelle aggregation number (micelle curvature). The coincidence of the degrees of counter-ion dissociation for these quite different systems suggests a common underlying behaviour in which the nonionic species merely dilutes the surface charge associated with the ionic headgroups.

Interfacial activity and micellar morphology of an imidazolium ring containing zwitterionic surfactants

“…Therefore, a core‐shell morphology has been adopted in which the intensity of scattered radiation, I ( Q ), as a function of the wave‐vector, Q , is given by (Griffiths et al, 2005). where n m is the number of micelles per unit volume, S ( Q ) is the structure factor, and B inc is the incoherent background.…”

“…Models describing morphologies based on solid spheres or solid ellipsoids did not give satisfactory fits in that features in the data were not reproduced in the fit. Therefore, a core-shell morphology has been adopted in which the intensity of scattered radiation, I(Q), as a function of the wave-vector, Q, is given by (Griffiths et al, 2005).…”

Adsorption of P103 Nanoaggregates on Graphene Oxide Nanosheets: Role of Electrostatic Forces in Improving Nanosheet Dispersion

“…As a result the number density of micelles increased up to five-fold. The numerical value of scattering length density highlights the contrast existing among core, shell and dispersion medium (heavy water) during data acquisition 28 . In nonionic assemblies, contraction of core and lowering in Nagg at fixed amphiphile concentration have been linked with increment in number density 29 .…”

“…As a result, the number density of micelles increased up to fivefold. The numerical value of scattering length density highlights the contrast existing among core, shell, and dispersion medium (heavy water) during data acquisition …”

Simple ApproximaTion for Aggregation Number Determination by Isothermal Titration Calorimetry: STAND-ITC

“…A large list of N agg values has been reported for the studied systems under different conditions (Table S1), ,− principally for C 12 TAB (Figure ). These values exhibit a significant discrepancy that is mainly due to the concentration where they have been measured.…”