A series of pH-sensitive lipids, la-h [(2,3-bis-alkylcarbamoyloxy-propyl)-trialkylammonium halide] and 2a-d (1-di-methylamino-2,3-bis-alkylcarbamoyloxy-propane), with carbamate linkages between the hydrocarbon chains and an ammonium or tertiary amine head, were synthesized for liposome-mediated gene delivery. The variable length of the carbon chains and the quaternary ammonium or neutral tertiary amine heads allowed us to identify the structure-function relationship showing how these factors would affect cationic lipids in gene delivery performance.

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In this work, the effect of layer charge density of Na-montmorillonite (Na-MT) and carbon chain length of alkyl ammonium on the structure and gel property of organo-montmorillonite (organo-MT) was studied by using X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric (TG) analysis, contact angle test, molecular dynamics (MD) simulation, and gel apparent viscosity determination experiment. The results of XRD show that Na-MT with lower layer charge density is easier to swell after intercalation of alkyl ammonium, and the basal spacing of organo-MT increases with the increase of carbon chain length. The results of FTIR show that the absorption bands at 2924 cm −1 and 2853 cm −1 shift towards low frequency region with the increase of carbon chain length, and the absorption bands at 515 cm −1 and 463 cm −1 move towards high frequency region when the layer charge density increases. The mass loss of organo-MT evidently increases with the increase of layer charge density of Na-MT or carbon chain length of alkyl ammonium. The contact angle test results are well in line with the TG data and reveal that alkyl ammonium with longer carbon chain can significantly improve the hydrophobicity of organo-MT. MD simulation indicates that, when the layer charge density is low, the distribution of alkyl ammonium gradually changes from parallel double layers to partially inclined distribution with the increase of carbon chain length, but when the layer charge density is high, the distribution of alkyl ammonium gradually changes from three layers into four layers. The test results of the apparent viscosity of the gel formed by organo-MT in xylene show that the apparent viscosity of organo-MT gel is negatively correlated with the layer charge density of Na-MT and positively correlated with the carbon chain length of alkyl ammonium. ability in aqueous solution, MT has attracted wide attention both in academia and in industry [3][4][5][6]. The occurrence of non-equivalent isomorphic substitution of Al 3+ for Si 4+ in the tetrahedral sheets and Mg 2+ for Al 3+ in the octahedral layers makes MT layers negatively charged [7]. To balance the negative layer charge density of MT, some hydrophilic exchangeable cations, such as Na + , K + , and Ca 2+ , are usually attracted into the interlayer domain, and due to the hydration of inorganic cation [8,9], confined basal spacing, and high surface energy, natural MT performs badly in organic phase environment [6,10].In order to expand the application of MT in industry, organo-MT is synthesized by intercalating surfactant into interlayer space of natural MT [11]. In this way, interlayer distance of MT obviously increase and new sorption sites can be formed [12], besides, inorganic cation can be exchanged by surfactant, which results in that the surface property of MT converts from hydrophilic to hydrophobic. As a result, the organo-MT can be applied in many fields, such as polymer MT nanocomposite [13,14], adsorbent for organic contaminant [15,16], oil-based drilling fluid [17], ...