| Thirteen gemini surfactants with different carbon chain lengths and spacers, 1,2-ethanediaminium, N, N’-didodecyl-N, N, N’, N’-tetramethyl-, dibromide (12-2-12), 1,3-propanediaminium, N, N’-didodecyl-N, N, N’, N’-tetramethyl-, dibromide (12-3-12),1,4-butanediaminium, N, N’-didodecyl-N, N, N’, N’-tetramethyl-, dibromid (12-4-12),1,5-pentanediaminium, N, N’-didodecyl- N, N, N’, N’-tetramethyl-, dibromid (12-5-12),1,6-hexanediaminium, N, N’-didodecyl-N, N, N’, N’-tetramethyl-, dibromid (12-6-12),1,8-octanediaminium, N, N’-didodecyl-N, N, N’, N’-tetramethyl-, dibromid (12-8-12),1,10-decanediaminium, N, N’-didodecyl-N, N, N’,N’-tetramethyl-, dibromid (12-10-12),1,12-dodecanediaminium, N, N’-didodecyl-N, N, N’,N’’-tetramethyl-, dibromid (12-12-12),1,3-propanediaminium, N, N, N’,N’-tetramethyl-N, N’-ditetradecyl-, dibromide (14-3-14), 1,4-butanediaminium, N, N, N’,N’-tetramethyl-N, N’-ditetradecyl-, dibromide (14-4-14),1,6-hexanediaminium, N, N, N’, N’-tetramethyl-N,N’-ditetradecyl-, dibromide(14-6-14),1,3-propanediaminium, N, N-dihexadecyl-N, N, N’, N’-tetramethyl-, dibromide (16-3-16), and 1,4-butanediaminium, N, N’-dihexadecyl-N, N, N’,N’-tetramethyl-, dibromide(16-4-16), have been synthesized and characterized by using NMR and elemental analysis. In this paper, the determinations of the micellizations, interfacial activities, antimicrobial effects, cell toxicities, and the interactions with human serum albumin (HSA) of the gemini quaternary ammonium surfactants are studied in detail. The results are expected to provide experimental and theoretical information for the applications of gemini surfactants in food, medicine and materials fields.The main contents and results are summarized as follows:The micellization of six gemini quaternary ammonium surfactant aqueous solutions has been investigated systematically from measurements on specific conductivity as a function of surfactant concentration at different temperatures from (298.15 to 323.15) K. The micellization parameters such as the critical micellar concentration (CMC) and the degree of counterion dissociation (β) are then obtained. It is shown that CMC values of the gemini quaternary ammonium surfactants become large with the increase of the temperature, while decrease with the increase of the alkyl chain length. The Gibbs free energy (ΔGmic), enthalpy (ΔHmic), and entropy (ΔSmic) of micellization are then calculated by using the mass action model. Among the thermodynamic functions, the value of AGmiC nearly keeps constant, while the values of ΔHmic and ΔSmic decrease with the increase of the temperature. The enthalpy-entropy compensation effect can be observed for the micellization of all surfactants studied. In addition, the interfacial tensions for the system of n-heptane/water/gemini quaternary ammonium surfactant are measured by using the spinning-drop method. The results show that with the increases of chain length, the minimum interfacial tension of the system decreases. Both the spacer group and hydrophobic carbon chain have significant influence on the interfacial activity of the gemini surfactant. Addition of NaCl can make the interfacial tension minima occur at lower surfactant concentrations. Moreover, addition of ethanol, propanoland n-butanol to the systerm reduce the minimum value of the interfacial tension. The effects are in the order:n-butanol> n-propanol> ethanol.Twelve gemini quaternary ammonium surfactants and two traditional single-chain surfactants (DTAB and CTAB) have been employed to evaluate the minimum inhibitory concentration (MIC) based on E. coli and S. aureus with the optical density (OD) method. The results show that the MIC values of all of the surfactants against both E. coli and S. aureus were smaller than the corresponding CMC values, and S. aureus is more susceptible to the surfactants than E. coli. The values of MIC for the gemini surfactants with the same spacer chain length approximately go along with the following trend:12-s-12> 14-s-14> 16-s-16. When the gemini surfactants possess the same alkyl chain like 12-s-12, values of ICso are found to decrease slightly with the spacer chain length changing from 2 to 8 and again to rise at higher spacer length (s=10 to 12). The morphology damages of bacteria in the presence of surfactants are observed by scanning electron microscopy (SEM). With the addition of the surfactant, the cytoplasm flow out of cells and then thus probably lifeless bacteria were observed. Isothermal titration calorimetry (ITC) was used to record the heat flow power-time curves of E. coli in the presence of different surfactants with various concentrations, which indicate that with the increase of surfactant concentration, the lag phase is delayed, logarithmic phase is shortened, and the maximum power output (Pmax) is also decreased.The cytotoxicity data of twelve gemini quaternary ammonium surfactants and two traditional single-chain surfactants (CTAB and SDS) on rat glioma cells (C6) and human embryonic kidney cells (HEK-293) are obtained by the MTT cell viability assay. The half inhibitory concentrations (IC50) are obtained by the corresponding survival curves and are compared with the CMC values of the surfactants in the DMED culture medium. The damages and the migration capacity of two cell lines in presence of surfactants are observed by Hematoxylin-Eosin (HE) staining and cell migration assay under the inverted fluorescence microscopy, respectively. Besides, the cell cycle arrests of C6 and HEK293 cells in presence of the surfactants are analyzed by the flow cytometry (FCM). The results show that the IC50 values of all of the surfactants against both C6 and HEK293 cells are smaller than the corresponding CMC values which were measured in DMEM, which indicate that it is the surfactant molecule rather than micelle has cytotoxic effect. The values of IC50 for the gemini surfactants with the same spacer chain length approximately go along with this trend: 12-s-12> 14-s-14> 16-s-16. When the gemini surfactants possess the same alkyl chain like 12-s-12, values of IC50 are found to decrease slightly with the spacer chain length changing from 2 to 8 and again to rise at higher spacer length (s= 10 to 12). In addition, the IC50 values of gemini quaternary ammonium surfactants on C6 and HEK293 cells are smaller than that of the CTAB and SDS. From the HE staining and cell migration experiments, cells revealed a slower migration rate, the morphologies of them are damaged, cytoplasm is significantly leaked and an amount of cell lysates can also be observed after they were treated with surfactants. Moreover, the FCM results indication that both C6 and HEK293 Cells treated with gemini surfactants exhibited a cell cycle arrest at the G2/M phase except for C6 cells treated with 12-3-12, which presented a high percentage of cells in the sub-G1 phase. In addition, the apoptosis is associated with the increases in the amounts of gemini surfactants.The interactions of human serum albumin (HSA) with four gemini surfactants and four single-chain surfactants have been explored from the measurements of fluorescence spectroscopy. The fluorescence enhancement mechanism at low surfactant concentration has been discussed by using the equation of Stern-Volmer. The fluorescence results show that the fluorescence intensity of HSA increases with the growth of surfactant concentration, coupled with the blue shift of maximum wavelength, indicating that surfactant can lead to the change of the HSA conformation. The absolute values of Ksv for gemini surfactants are larger than those for the corresponding single-chain surfactants. Furthermore, The absolute values of Ksv increase with the increasing of carbon chain length and hydrophilic group, indicating that the gemini surfactants have much stronger binding ability to HSA than the corresponding single-chain surfactants. It can be speculated from the experimental results of dynamic light scattering (DLS) and Zeta potential that the interactions between surfactant and HSA are mainly of electrostatic modulation at low surfactant concentrations. The electrostatic insertions of the surfactants make the particle sizes (RH) of the surfactant-HSA aggregates grow moderately, and the negative charge of HSA is neutralized by the positively charged head groups of surfactants. When the surfactant concentration is further increased, the surfactants bind to HSA molecules cooperatively through the hydrophobic interaction. Accordingly, the Ru and the Zeta potential of the aggregates are increased. The RH and Zeta potential are no longer increased when the concentration of surfactant increases to a certain degree. The conformational transformation of the secondary structures of HSA-surfactant aggregates have been confirmed through the quantitative analysis of the CD spectra. With the increase of the concentration of surfactants, the a-helical contents gradually convert into the β-sheet structures. To further analyze the processes of surfactants binding to HSA, studies on the interactions between single-chain surfactants and HSA are performed through isothermal titration calorimetry (ITC). The results show that the interaction enthalpies of HSA with C12HDAB and C12DHAB change with the increasing concentration of surfactant, two peaks can be observed before and after the critical micelle concentrations. The first endothermic peak should be mainly caused by the dehydration effects and the collapses of the secondary structure in HSA when the surfactant concentrations are less than CMC. After the concentrations becoming larger than the CMC values, the hydrophobic interactions between surfactants and HSA increase, resulting in the formation of second endothermic peaks. |
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