Thermodynamic and Structural Characterization of Zwitterionic Micelles of the Membrane Protein Solubilizing Amidosulfobetaine Surfactants ASB-14 and ASB-16

Abstract

Surface tension and isothermal titration calorimetry (ITC) were used to determine the critical micelle concentration (cmc) of the zwitterionic amidosulfobetaine surfactants ASB-14 and ASB-16 (linear-alkylamidopropyldimethylammoniopropanosulfonates) at 25 °C. The cmc and the heat of micellization were determined from 15 to 75 °C by ITC for both surfactants. The increase in temperature caused significant changes in the enthalpy and in the entropy of micellization, with small changes in the standard Gibbs energy (ΔG(mic)), which is consistent to an enthalpy−entropy compensation with a compensatory temperature of 311 K (ASB-14) and 314 K (ASB-16). In the studied temperature range, the heat capacity of micellization (ΔC(p)(mic)) was essentially constant. The experimental ΔC(p)(mic) was lower than that expected if only hydrophobic interactions were considered, suggesting that polar interactions at the head groups are of significant importance in the thermodynamics of micelle formation by these surfactants. Indeed, a NMR NOESY spectrum showed NOEs that are improbable to occur within the same monomer, resulting from interactions at the polar head groups involving more than one monomer. The ITC and NMR results indicate a tilt in the polar headgroup favoring the polar interactions. We have also observed COSY correlations typical of dipolar interactions that could be recovered with the partial alignment of the molecule in solution, which results in an anisotropic tumbling. The anisotropy suggested an ellipsoidal shape of the micelles, which results in a positive magnetic susceptibility, and ultimately in orientation induced by the magnetic field. Such an ellipsoidal shape was confirmed from results obtained by SAXS experiments that revealed aggregation numbers of 108 and 168 for ASB-14 and ASB-16 micelles, respectively. This study characterizes an interesting micelle system that can be used in the study of membrane proteins by solution NMR spectroscopy.

Micellization and Single-Particle Encapsulation with Dimethylammoniopropyl Sulfobetaines

“…The threshold values by DLS correlate well with the CMC values for lower MW surfactants (C12SB, C14SB), 26 although they are higher than those based on surface tension or isothermal calorimetry. 27,30 We also observed SB micellization to occur at lower concentrations in 1 M NaCl versus pure water, again in accord with an earlier work. 26 Although DLS is not a standard tool for measuring CMCs in absolute terms, 2 the instrument used in this study can detect signals from organic aggregates (1–100 kDa) at a limit close to 1 μg/mL.…”

Zwitterionic amphiphile coated magnetofluorescent nanoparticles – synthesis, characterization and tumor cell targeting

“…Literature has reported the following peaks due to the CB addition to polymer backbones: C(O)NH CH 2 at 2.75–3.48 ppm, C(O)NHCH 2 CH 2 at 1.55–2 ppm, CH 2 N + (CH 3 ) 2 at 2.75–3.48 ppm, N + ( CH 3 ) 2 at 2.9–3.3 ppm, CH 2 CH 2 COO − at 3.4–3.55 ppm, CH 2 COO − at 2.25–2.75 ppm; and the follow peaks due to the SB addition to polymer backbones: C(O)NH CH 2 at 3.2 ppm, C(O)NHCH 2 CH 2 at 1.9 ppm, CH 2 N + (CH 3 ) 2 at 3.3 ppm, N + ( CH 3 ) 2 at 3.05–3.1 ppm, CH 2 CH 2 CH 2 SO 3 − at 3.4 ppm, CH 2 CH 2 SO 3 − at 2.15 ppm, and CH 2 CH 2 SO 3 − at 2.89 ppm. 50–55 The peaks for PMAO-CB-SB match with what were reported.…”

Temperature‐Dependent Atomic Models of Detergent Micelles Refined against Small‐Angle X‐Ray Scattering Data

“…The formation of micelles involves a delicate balance of free‐energy contributions from enthalpy and both solute and solvent entropy . Consequently, many fundamental properties of micelles, such as the CMC, the aggregation number N , and their size and shape are temperature‐dependent …”