Toroidal micelles formed in viscoelastic aqueous solutions of a double-tailed surfactant with two quaternary ammonium head groups

Innovation in surfactant structures is an effective way to prepare new soft materials with novel applications. In this study, we synthesized a double-tailed surfactant containing two quaternary ammonium head groups (Di-C12-N2). The Di-C12-N2 solution behavior was investigated by surface tension, fluorescence, rheology, and cryo-TEM methods. Although Di-C12-N2 contained a large double-tailed hydrophobic group, the solubility of Di-C12-N2 was ∼90 mmol L-1 at 25 °C with a Krafft temperature of ∼1 °C. The increase in Di-C12-N2 concentration in the solutions led to the formation of various aggregates, including spherical micelles, worm-like micelles, multi-layered vesicles, and a rare type of small toroidal micelles. The two quaternary ammonium head groups in Di-C12-N2 led to strong electrostatic interactions between molecules, which was critical for the formation of toroidal micelles. Moreover, with an added NaCl concentration of 40 mmol L-1, the viscosity of the 5 mmol L-1Di-C12-N2 solution increased by ∼1000 times compared to the pure 5 mmol L-1Di-C12-N2 solution, revealing the high sensitivity of the unique head groups to ionic strength. This study enriches the research on the self-assembly principles of surfactants and brings new potential applications for new soft materials.

The inactivation mechanism of chemical disinfection against SARS-CoV-2: from MD and DFT perspectives

Exploring effective disinfection methods and understanding their mechanisms on the new coronavirus is becoming more active due to the outbreak of novel coronavirus pneumonia (COVID-19) caused by severe acute respiratory coronavirus 2 (SARS-CoV-2). By combining molecular dynamics and first-principles calculations, we investigate the interaction mechanism of chemical agents with 3CL hydrolase of SARS-CoV-2. The radial distribution functions indicate that the biocidal ingredients are sensitive to the unsaturated oxygen atoms of 3CL hydrolase and their interactions remarkably depend on the concentration of the biocidal ingredients. Besides, we find that the adsorption performance of the active ingredients for the unsaturated oxygen atoms is superior to other styles of atoms. These computational results not only decipher the inactivation mechanism of chemical agents against SARS-CoV-2 from the molecule-level perspective, but also provide a theoretical basis for the development and application of new chemical methods with a high disinfection efficiency.

A CO2-responsive smart fluid based on supramolecular assembly structures varying reversibly from vesicles to wormlike micelles

CO2-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO2-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles. Firstly, oleic acid and 3-dimethylaminopropylamine reacted to form a single-chain weak cationic surfactant with a tertiary amine head group, N-[3-(dimethylamino)propyl]oleamide (NDPO). Then, 1,3-dibromopropane was used as the spacer to react with NDPO to form a gemini cationic surfactant, trimethylene α,ω-bis(oleate amide propyl dimethyl ammonium bromide) (GCS). By controlling the feed ratio of 1,3-dibromopropane and NDPO, we found that the mixtures of GCS and NDPO with the molar ratio of 7 : 3 approximately could form vesicles in aqueous solution by supramolecular self-assembly. After bubbling CO2, the tertiary amine of NDPO was protonated. The packing parameter of the mixed surfactants reduced accordingly, accompanied by the transition of aggregates from vesicles to wormlike micelles. As a result, the zero-shear viscosity of the solution increased by more than four orders in magnitude. When the solid content of GCS/NPDO mixtures was higher than 5 wt% in solution, the sample treated by CO2 behaved as a gel over a wide frequency range with shear-thinning and self-healing properties. In addition, the sol-gel transition could be repeatedly and reversibly switched by cyclically bubbling CO2 and N2. Our effort may provide a new strategy for the design of CO2-responsive smart fluids, fostering their use in a range of applications such as in enhanced oil recovery.

Conformational and solution dynamics of hemoglobin (Hb) in presence of a cleavable gemini surfactant: Insights from spectroscopy, atomic force microscopy, molecular docking and density functional theory

Herein, we have explored the conformational alterations of hemoglobin (Hb) in presence of a cleavable gemini surfactant (C16-C4O2-C16). The concerned surfactant was found to induce significant structural perturbations in Hb. UV-vis spectroscopy, steady-state/time-resolved fluorescence, and other utilized techniques have authenticated the complexation of Hb with the gemini surfactant. CD has demonstrated the alterations in secondary structural elements (α-helicity, β-sheet, β-turn, and random coil) of Hb upon C16-C4O2-C16 addition. Atomic force microscopy (AFM) has revealed the existence of unique star-shaped gemini surfactant microstructures aligned to Hb in a necklace pattern. The ¹H NMR peak broadening and lower delta values hint at the binding of the concerned gemini surfactant to Hb. Molecular docking and DFT calculations have further substantiated the Hb-gemini complex formation and the involvement of electrostatic/hydrophobic forces therein. In future, these results might pave-the-way to construct self-assembled, sustainable, and green surfactant-protein mixtures for their end-use in industrial, engineering, biomedical, drug delivery, gene transfection, and other relevant excipient formulations.