Adsorption and Micellization of Gemini Surfactants with Diethylammonium Headgroups: Effect of the Spacer Rigidity

Self-Aggregation, Antimicrobial Activity and Cytotoxicity of Ester-Bonded Gemini Quaternary Ammonium Salts: The Role of the Spacer

Five ester-bonded gemini quaternary ammonium surfactants C₁₂-E_n-C₁₂ (n = 2, 4, 6), with a flexible spacer group, and C₁₂-B_m-C₁₂ (m = 1, 2), with rigid benzene spacers, were synthesized via a two-step reaction and analyzed. Furthermore, the effects of the spacer structure, spacer length and polymerization degree on the self-aggregation, antimicrobial activity and cytotoxicity of C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ and their corresponding monomer N-dodecyl-N,N,N-trimethyl ammonium chloride DTAC were investigated. The results showed that C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ had markedly lower critical micellar concentration (CMC) values and lower surface tension than DTAC. Moreover, the CMC values of C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ decreased with increasing spacer length. In the case of equivalent chain length, the rigidity and steric hindrance of phenylene and 1,4-benzenediyl resulted in larger CMC values for C₁₂-B_m-C₁₂ than for C₁₂-E_n-C₁₂. The antibacterial ability of C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ was assessed using Escherichia coli (E. coli) and Staphylococcus albus (S. aureus) based on minimum inhibitory concentrations (MICs). Furthermore, C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ exhibited higher antimicrobial activity than DTAC and had stronger function toward S. aureus than E. coli. The antimicrobial activity was enhanced by increasing the spacer chain length and decreased with the increased rigidity of the spacers. The cytotoxic effects of C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ in cultured Hela cells were evaluated by the standard CCK8 method based on half-maximal inhibitory concentration (IC₅₀). The cytotoxicity of C₁₂-E_n-C₁₂ and C₁₂-B_m-C₁₂ was significantly lower than alkanediyl-α,ω-bis(dimethyldodecylammonium) bromide surfactants and DTAC. The spacer structure and the spacer length could induce significant cytotoxic effects on Hela cells. These findings indicate that the five ester-bonded GQASs have stronger antibacterial activity and lower toxicity profile, and thus can be used in the pharmaceutical industry.

Oligomeric cationic Gemini surfactants: synthesis, surface activities and rheological properties as thickener

In this study, three oligomeric cationic Gemini surfactants (Ⅲ1, Ⅲ2, and Ⅲ3) were prepared from different major raw materials, including long-chain alkyl amine (dodecyl amine, tetradecyl amine or cetyl amine), formic acid, formaldehyde, diethyl amine hydrochloride and epichlorohydrin. The synthesis conditions for one of the three surfactants, bis-[2-hydroxy-3-(N,N-dimethyl-N-dodecyl)propyl]dipropylammonium chloride (Ⅲ1), were optimised by orthogonal experiments. The optimum synthesis conditions were: molar ratio of intermediate Ⅱ to intermediate Ⅰ1 = 1.0:2.2, reaction temperature = 85 °C and reaction time = 16 h. The structures of the three prepared compounds were characterised by FTIR and 1H NMR. Their thermal properties were evaluated by thermal gravimetric analysis (TGA). The Geminisurfactants prepared exhibited better surface active properties than conventional single chain cationic surfactants. With increasing carbon chain length from C12 to C16, both CMC and surface tension γ CMC decreased, while the viscosity of the thickening solution prepared with the synthesised oligomeric cationic Gemini surfactants as the main component increased. The optimum thickening formula was: 2.0 wt% Ⅲ3 + 0.8 wt% sodium salicylate (NaSal) + 0.6 wt% KCl. The viscosity of the optimum thickening formulation was 190.4 mPa s. Gemini oligomeric cationic surfactants could be used as thickeners in the production of fracturing fluids, flooding agents and drilling fluids for oil and gas production in oil fields.

Effect of Spacer Structures on the Interfacial Adsorption and Micelle Properties of Quaternary Ammonium Salt-Based Gemini Surfactants

In this study, we synthesized quaternary ammonium salt-based gemini surfactants, 2C₁₂(Spacer), with different spacer structures using ethylenediamine derivatives, and investigated their adsorption and aggregation properties by measuring their electrical conductivity, surface tension, fluorescence, and viscosity in conjunction with dynamic light scattering and small-angle X-ray scattering studies to investigate the effect of spacer structures on the properties of the gemini surfactants. The gemini surfactants with spacers containing nitrogen and oxygen atoms were highly soluble in water, whereas those with rigid spacers containing diethylene and triethylene chains exhibited low water solubility. The adsorption and orientation of the gemini surfactants at the air/water interface were significantly affected by the spacer length. Among the synthesized gemini surfactants, the one with the N,N'-dimethylpiperazine spacer showed the highest surface activity. In contrast, the gemini surfactant with the 1-methyl-4-[2-(N,N-dimethylammonio)ethyl]piperazin-1-ium spacer containing an ethylene chain attached to the amino group in the N,N'-dimethylpiperazine spacer (2C₁₂(2/2-N-2)) adsorbed efficiently. However, due to the increased spacer length, this surfactant was unable to orient efficiently at the air/water interface.

Controlled Synthesis of Carbon Nanospheres via the Modulation of the Hydrophilic Length of the Assembled Surfactant Micelles

A co-polymerization-carbonization method was employed to synthesize porous carbon nanospheres (PCNSs) using pyrrole-aniline polymers as a carbon source and alkyl phenol non-ionic surfactants as templates. The effect of the hydrophilic length on the carbon nanosphere size was systematically investigated. The so-prepared PCNSs were characterized via high-magnification scanning electron microscopy, dynamic light scattering (DLS) analysis, and N₂ adsorption and desorption analysis. The results indicate that the obtained nanosphere diameter can be tuned by changing the length of the hydrophilic groups. The length of the hydrophilic groups mainly affects the size of the vesicles or micelles formed by the assembly of the surfactant in solution, as was verified by the DLS results. After activation by KOH, the typical sample EO(30)-PCNS has a high specific surface area of 2137 m²/g and a large pore volume of 1.76 cm³/g. Electrochemical tests in 6 M KOH demonstrated that the assembled EO(30)-PCNS supercapacitor electrode displays good capacitive properties, such as a high specific capacitance of 221 F/g at 1.0 A/g and a good rate capacity of 68% retention at 10.0 A/g. This finding suggests that the uniform particle shape and high specific surface area are beneficial for the ion transportation, leading to good electrochemical performances. Our work provides a novel synthetic strategy for the fabrication of carbon nanospheres or other nanosphere materials for the construction of high-performance supercapacitors by optimizing few parameters, such as the length of the hydrophilic or hydrophobic groups of the surfactants.

The adsorption and aggregation properties of dendritic cationic tetrameric surfactants

A series of dendritic cationic tetrameric surfactants (4C_ntetraQ, n = 12, 14, 16) were synthesized with raw materials that are commercially available.