Liyan Wang

A number of techniques, including conductivity, surface tension, dynamic light scattering, transmission electron microscopy, and ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FT-IR), and ¹H–¹H 2D nuclear Overhauser effect spectroscopy (¹H–¹H 2D NOESY), have been used to investigate the effect of amide bonds on the interfacial and assembly properties of a cationic surfactant, N-anilinoformylmethyl-N-cetyl-N,N-dimethyl ammonium chloride (AMC-C₁₆), in aqueous solutions. The adsorption of AMC-C₁₆ has been found to be much better than that of the conventional cationic surfactant, benzyl cetyldimethylammonium chloride (BAC-16) at the air/water interface and in solution. The surface tension measurements show the presence of two critical aggregation concentrations (CAC₁ and CAC₂) for AMC-C₁₆. The presence of a strong intermolecular hydrogen bond of AMC-C₁₆ was confirmed by ¹H NMR and FT-TR. The molecular interactions of AMC-C₁₆ were detected by ¹H–¹H 2D NOESY. The results show that the rigid group (phenyl) of AMC-C₁₆ was partially overlapped with its alkyl chain in aqueous solution, and the possible aggregation behavior for AMC-C₁₆ was proposed. The effects of an inorganic salt (NaCl) and an organic salt (C₆H₅COONa) to the aggregates of AMC-C₁₆ have been discussed.

The cationic surfactants containing aromatic rings and amide bonds, N,N‐dimethyl‐N‐dodecyl‐2‐pyrimidinylcarbamoylmethyl ammonium chloride (a), N,N‐dimethyl‐N‐dodecyl‐2‐thiazolylcarbamoylmethyl ammonium chloride (b), and N,N‐dimethyl‐N‐dodecyl‐phenylcarbamoylmethyl ammonium chloride (c), were synthesized and characterized. The surface tension and conductivity values were employed to investigate the absorption and micellization behavior of the three cationic surfactants. The results showed that the synthesized surfactants have shown a low critical micelle concentration (CMC) and a high adsorption efficiency (pC₂₀) compared with the traditional cationic surfactant of N,N‐dimethyl‐N‐dodecyl‐N‐benzyl ammonium chloride (BAC‐12). The aromatic rings of the a, b, and c molecular structures were analyzed using the ¹H NMR spectra for electrostatic repulsion effects between hydrophilic headgroups. The size distribution of the micelles was derived using dynamic light scattering (DLS) techniques. In addition, the foaming ability of a, b, c, and BAC‐12 was investigated and the antimicrobial activity of a, b, c, and BAC‐12 against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was examined. The effects of amide bonds and aromatic rings on the surface properties and antimicrobial activity of a, b, and c were analyzed and compared with BAC‐12 of the same alkyl chain length. The synthesized surfactants exhibited a high surface ability and better antibacterial activity compared with BAC‐12.

A series of novel gemini surfactants, namely, phenyl-1,4-bis[(carbamoylmethyl) N , N -(dimethylalkyl ammonium chloride)] ( a , b and c ), was synthesized systematically and characterized by FTIR, ¹ H NMR, ¹³ C NMR and MS.

A class of novel cationic Gemini imidazolium surfactants containing amide groups as the spacer were synthesized from ethylenediamine and 1‐bromoalkane(C₈, C₁₀, C₁₂, C₁₄, C₁₆) by N‐alkylation to get N,N′‐dialkyl ethylenediamine (1a–e), 1a–e was further reacted with chloroacetyl chloride by N‐acylation to get N,N′‐(ethane‐1,2‐diyl)bis(2‐chloro‐N‐alkylacetamide) (2a–e), which was further reacted respectively with 1‐methyl imidazole by quaternized to form the surfactant molecule, N,N′‐((ethane‐1,2‐diyl)bis(alkyl‐azanediyl)bis(2‐oxoethane‐2,1‐diyl)) bis(1‐methyl‐1H‐imidazol‐3‐ium) dichloride. The structures of intermediates (1a–e) and (2a–e) were characterized by IR and ¹H NMR. The structures of the surfactants (3a–e) were characterized by IR, ¹H‐NMR and ¹³C‐NMR and element analysis. The critical micelle concentrations (CMC) of 3a–e were determined by the conductivity method at 25 °C. The CMC values decreased with increasing the length of the hydrophobic chain. The surfactants (3a–e) showed good foaming stability, emulsion ability and wetting ability. The surfactants (3a–e) also have good antimicrobial activity against Staphylococcus aureus, Escherichia coli and Bacillus subtilis.

Three new taxoids (1–3), along with three known taxoids (4–6), were isolated from a EtOAc extract of Taxus cuspidata seed. The structures of 1–3 were determined by analyses of spectroscopic data.

A series of novel dissymmetric gemini cationics surfactants was synthesized by three‐step reactions. The dissymmetric gemini surfactants contain a dodecanoic acid dimethylethylamine ester as the constant cationic part on one side of the hydroxypropyl center and a similar other cationic part, but with a different acid length (from octanoic to palmitic), on the other side. The critical micelle concentration (CMC) and the effectiveness of surface tension reduction (γ_CMC) were determined. The surface tension measurements of dissymmetric gemini surfactants showed good water solubility, and low CMC had great efficiency in lowering the surface tension and a strong adsorption at the air/water interface. The CMC was observed to increase initially with the increase of the ester bond alkyl group. They also showed good foaming properties and wetting capabilites.