Structural Features of Micelles of Zwitterionic Dodecyl-phosphocholine (C₁₂PC) Surfactants Studied by Small-Angle Neutron Scattering

Abstract

Small-angle neutron scattering (SANS) was used to investigate the size and shape of zwitterionic dodecyl phosphocholine (C12PC) micelles formed at various concentrations above its critical micelle concentration (CMC = 0.91 mM). The predominant spherical shape of micelles is revealed by SANS while the average micellar size was found to be broadly consistent with the hydrodynamic diameters determined by dynamic light scattering (DLS). Cryogenic tunneling electron microscopy (cryo-TEM) shows a uniform distribution of structures, proposing micelle monodispersity ( Supporting Information ). H/D substitution was utilized to selectively label the chain, head, or entire surfactant so that structural distributions within the micellar assembly could be investigated using fully protonated, head-deuterated, and tail-deuterated PC surfactants in D2O and fully deuterated surfactants in H2O. Using the analysis software we have developed, the four C12PC contrasts at a given concentration were simultaneously analyzed using various core-shell models consisting of a hydrophobic core and a shell representing hydrated polar headgroups. Results show that at 10 mM, C12PC micelles can be well represented by a spherical core-shell model with a core radius and shell thicknesses of 16.9 ± 0.5 and 10.2 ± 2.0 Å (total radius 27.1 ± 2.0 Å), respectively, with a surfactant aggregation number of 57 ± 5. As the concentration was increased, the SANS data revealed an increase in core-shell mixing, characterized by the emergence of an intermediate mixing region at the spherical core-shell interface. C12PC micelles at 100 mM were found to have a core radius and shell thicknesses of 19.6 ± 0.5 and 7.8 ± 2.0 Å, with an intermediate mixing region of 3.0 ± 0.5 Å. Further reduction in the shell thickness with concentration was also observed, coupled with an increased mixing of the core and shell regions and a reduction in miceller hydration, suggesting that concentration has a significant influence on surfactant packing and aggregation within micelles.

Novel features in the structure of P-glycoprotein (ABCB1) in the post-hydrolytic state as determined at 7.9Å resolution

“…This has been observed in several cryo-EM studies of membrane protein/detergent micelle complexes, and presumably results from some local organization of the detergent polar head-groups due to the high curvature of the micelle. It is likely that water molecules intercalate into this region of the micelle and account for the lower density areas in the lattice (18).…”

Structural and Dynamic Insights of the Interaction between Tritrpticin and Micelles: An NMR Study

“…Micelle-forming detergents provide amphipathic environments similar to those found in lipid bilayers and biomembranes. Micelles have different shapes and sizes determined by the chemical nature of their headgroups and the length of their hydrophobic tails (23,24). Physicochemical conditions such as temperature, solutes, and concentration can also affect micellar structure and eventually influence the conformation of bound proteins or peptides, especially the latter.…”

“…Our study focuses on TRP3 accommodation at the hydrophilic/ hydrophobic interface of micelles and subsequent events. The structure and dynamics of TRP3 were examined in the presence of micelles of different chemical nature: zwitterionic (lysolauroylphosphatidylcholine 1-lauroyl-2-hydroxy-sn-glycero-3-phosphocholine (LLPC), n-dodecylphosphocholine (DPC), and N-dodecyl-N,N-(dimethylammonio) butyrate (DDMAB), anionic 1-myristoyl-2-hydroxy-sn-glycero-3-phospho-(1 0 -rac-glycerol) (LMPG), and nonionic (octylglucoside (OG)) (23,24,(31)(32)(33)(34)(35). The conformational ensemble was evaluated during detergent titration and it was found that the peptide interacts via conformational selection.…”

pH‐Dependent Chloride Transport by Pseudopeptidic Cages for the Selective Killing of Cancer Cells in Acidic Microenvironments

“…[f ]The numerical values must be considered with caution since the ISE traces showed an initial efflux that was not maintained during the experimenttime (see Figures S58-60 in the SupportingInformation). DPC micelles, [16] and much larger than the r H of the cage when DOSY NMR spectroscopy was performed with 1c in [D 6 ]DMSO (0.66 nm alone and 0.76 nm with protonated 1c and TBACl). Theobserved changes in the NMR spectra of 1c within the micelles upon variations in the composition of the external aqueous solution were also very illustrative.T he proton NMR spectrum of the sample at pH 7.1 showed the presence of two sets of signals for some of the protons,which were especially important for those of the aromatic side chains (Figure 3).…”