Interaction Mechanism of Different Surfactants with Casein: A Perspective on Bulk and Interfacial Phase Behavior

Exogenous-Endogenous Surfactant Interaction Yields Heterogeneous Spreading in Complex Branching Networks

Experiments have shown that surfactant introduced to a liquid-filled maze can find the solution path. We reveal how the maze-solving dynamics arise from interactions between the added surfactant and endogenous surfactant present at the liquid surface. We simulate the dynamics using a nonlinear model solved with a discrete mimetic scheme on a graph. Endogenous surfactant transforms local spreading into a nonlocal problem with an omniscient view of the maze geometry, key to the maze-solving dynamics. Our results offer insight into surfactant-driven transport in complex networks such as lung airways.

Comparative interaction study of soy protein isolate and three flavonoids (Chrysin, Apigenin and Luteolin) and their potential as natural preservatives

In this work, the potential of soy protein isolate (SPI)-luteolin (Lut)/apigenin (Ap)/chrysin (Chr) complexes as natural preservatives for food and cosmetics was evaluated by comparing their interactional and functional properties with structure-activity relationship. The results of spectrometry and molecular docking indicated that the B-ring hydroxylation of flavonoids affected their binding constants with SPI, which were determined as Lut (1.45 × 10⁶ L/mol) > Ap (2.04 × 10⁵ L/mol) > Chr (3.81 × 10⁴ L/mol) at 298.15 K. It demonstrated that the hydrogen bonding force played an important role in binding flavonoids to SPI. Moreover, the anti-oxidation ability, antimicrobial effect, and foaming properties were positively correlated with increase in number of hydroxyl groups on the B-ring, but the amount and type of the preservative should be adjusted aimed at the nutrition components. This study provides a theoretical basis for the use of flavonoids and SPI-flavonoid complexes as natural preservatives for food and cosmetics.

Micellization Behavior of Conventional Cationic Surfactants within Glycerol-Based Deep Eutectic Solvent

The aggregation behavior of two cationic surfactants, i.e., cetyldimethylethanolammonium bromide (CDMEAB) and cetyltributylphosphonium bromide (CTBPB), within an aqueous deep eutectic solvent (DES) is studied. The synthesized DES is composed of 1:2 mole ratio of choline chloride and glycerol and is further characterized by Fourier transform infrared (FTIR) and 1H NMR spectroscopy techniques. The critical micellar concentration (CMC), micellar size, and intermolecular interaction in surfactants within Gly-based DES solutions are investigated by various techniques including surface tension, conductivity, fluorescence, dynamic light scattering (DLS), FTIR, 1H NMR, and two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY). The various interfacial properties and thermodynamic parameters are determined in the presence of 5 wt % glyceline (Gly)-based DES in an aqueous solution. The CMC, aggregation number (N agg), and Stern-Volmer constant (K sv) have also been determined by a steady-state fluorescence method. DLS is used to obtain information regarding the size of the aggregates formed by the cationic surfactants in DES solutions. FTIR spectroscopy is used to study the surfactant-DES interactions that tune the micellar structure of the surfactants within the Gly-based DES solution. The functional groups involved in the interactions (H-bonding and electrostatic) are the head groups (HO-CH2-CH2-N+ ion for CDMEAB and quaternary phosphonium (P+) ion for CTBPB) of the surfactants with the -OH-containing Gly DES. The hydrophobic moieties are involved in the hydrophobic interactions. The 1H NMR data show that differences in chemical shifts can provide significant information about the interactions taking place within the system. 1H NMR and NOESY techniques are further employed to strengthen our claim on the feasible structural arrangements within the aqueous surfactant-DES self-assembled structures. It is observed that both the cationic surfactants, i.e., CDMEAB and CTBPB, form self-assembled nanostructures in the Gly-based DES solutions. The present results are expected to be useful for colloidal solutions of DES and their mixtures with water.

Dynamic surface properties and dilational rheology of acidic and lactonic sophorolipids at the air-water interface

This study analyzes the equilibrium and dynamic surface tension curves of acidic and lactonic sophorolipids (SLs). It also investigates the dilational properties of the surface adsorptive film. Given their high hydrophobicity, lactonic SLs have lower surface tension and critical micelle concentration (CMC) than acidic SLs. As c_NaCl increases, the CMC values and the corresponding surface tension (γ_cmc) of acidic and lactonic SLs decrease gradually. For dynamic surface properties, lactonic SLs have a high diffusive rate from the bulk phase to the subsurface. At 0.05 CMC, the initial adsorption of acidic and lactonic SLs is diffusion-controlled. As c_surfactant increases, the values of diffusion coefficient (D) show a downward trend, and the mechanism is mixed kinetic diffusion. Adding NaCl increases the D values of acidic and lactonic SLs, and the influence degree for acidic SLs is more considerable than that for lactonic SLs. As frequency (ω) increases (0.005∼0.5 Hz), the dilational elasticity increases, and the phase angle decrease. The dilational elasticity of acidic and lactonic SLs shows a low-frequency dependence. Compared with acidic SLs, lactonic SLs have better dynamic surface properties, which decrease the gradient of interfacial tension because of the interface deformation. Consequently, the lactonic SLs exhibit a relatively small dilational elasticity. At 0.1 Hz, the dilational elasticity of acidic and lactonic SLs reaches the maximum values at 0.05CMC and 0.075CMC, respectively. When c_surfactant rises near CMC, the phase angle increases obviously, and the dilational elasticity further decreases. This result is attributed to the fast exchange of surfactant molecules between the interface and the micelles.