Efficient improvement of surface activity of tea saponin through Gemini-like modification by straightforward esterification
Introduction
Tea saponin (TS) is traditionally referred to as a mixture of oleanane-type triterpenoid saponins isolated from the seeds of Camellia oleifera (distributed in the central and south China) after oil production (Liao et al., 2005, Sugimoto et al., 2009). Tea saponin has been used in China as soap, fish poison, and molluscicide for centuries. Recent studies have revealed that tea saponin is versatile in that it is not only a good nonionic surfactant with the emulsifying, foaming and wetting activities (Xia, Zhu, Tian, Liu, & Fan, 1990) but also has multiple bioactivities such as antimicrobial, antivirus, anti-inflammatory, antioxidant, anti-allergic activities (Hu et al., 2005, Kuo et al., 2010, Li et al., 2009, Sur et al., 2001). Because of its diversified physicochemical and biological activities, tea saponin has been widely used in food, medicines and materials.
Surfactants have taken central role in food science and technology. Recently concern about safety of synthetic surfactants is increasing specially in food. Hence development of new surfactants based on readily available natural products is highly desirable. As a traditional natural surfactant, tea saponin is an exceptional nonionic surfactant with ample natural supply. Modification of tea saponin would be an effective way to modulate its surface activity to fulfil various demands for green surfactants in food and other industries. However, owing to its structural complication studies on modification of tea saponin have not been carried out only until recently. Tao et al. reported a novel cationic-type tea saponin attached with silicone polymer quaternary ammonium salt which improved performance of the hair shampoo in both dry and wet states (Tao, Feng, Liang, & Cao, 2004). Yang et al. synthesized tea saponin monoethanolamide succinate single ester sodium sulphate which had lower critical micelle concentration and better foaming ability and stability (Yang & Fu, 2010). Song et al. prepared de-estered tea saponin through aminolysis that exhibited lower critical micelle concentration and enhanced foaming stability (Song, Shang, Song, & Li, 2011).
Inspired by these pioneering studies, we speculated a novel strategy of modification to efficiently improve surface activity of tea saponin. In our previous studies, we successfully developed a novel type of highly effective nonionic Gemini alkyl O-glucoside with one order of magnitude improvement of surface activity through Geminization strategy (Liu, Sang, Hong, Cai, & Wang, 2013). Therefore, we reasoned that esterification of tea saponin by acyl chlorides could readily introduce additional alkyl chains to tea saponin through the oligosaccharide portion and generate Gemini-like surfactants that would afford greatly enhanced surface activity (Fig. 1). To test this hypothesis, esterification of tea saponin with various acyl chlorides and their surface activity were carefully investigated in this study. Successful improvement of surface activity of tea saponin has been achieved. To the best of our knowledge, Gemini-like modification of tea saponin by acyl chlorides has not yet been reported in the literature.
Section snippets
Materials
Tea saponin (purity, ⩾98%) was purchased from Geneham Biomedical Technology Ltd. (Hunan, China). Octanoyl chloride, decanoyl chloride, dodecanoyl chloride, myristoyl chloride, palmitoyl chloride, stearoyl chloride, and potassium carbonate were purchased from Aladdin-Reagent (Shanghai, China). DMSO-d6 (Dimethyl sulfoxide-d6) was purchased from Sigma–Aldrich Inc. (St. Louis, MO, USA). The AB-8 macroporous resin was purchased from Nankai University Chemical Factory (Tianjin, China). All other
Preparation of TSEs
Intensive experimentation was carried out to optimize the condition of esterification of tea saponin. Poor solubility of highly polar tea saponin in conventional solvents such as ethyl acetate, diethyl ether and acetone prevented effective chemical transformation during esterification. Hence anhydrous N,N-dimethylformamide (DMF) that is a dipolar solvent and generally has good solubility for highly polar substance was applied to achieve completely dissolution of tea saponin. It was noted that
Conclusion
New nonionic surfactants were developed through esterification of tea saponin with acyl chlorides in this study. FI-IR, 1H NMR and ESI-MS analysis confirmed their structures. Tea saponin esterified with the chain length of C12 and C14 and the ratio of 1:4 to 1:6 produced significantly better surface activity compared with tea saponin. The strategy to improve the surface activity of tea saponin through simple esterification was proved effective. The new surfactants have great potential
Acknowledgement
This work was supported by Public Welfare Technology Research Program of Department of Scientific and Technology of Zhejiang Province (Grant no. 2011C22080), Foundation of Fuli Institute of Food Science, Zhejiang University.
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Tetraphenylethylene / tea saponin derivative nanocomposites for tribofilm visualization and efficient lubrication
2021, Composites Part B: EngineeringCitation Excerpt :The FTIR spectrum of TS exhibited the peak at 3401 cm−1 results from the stretching vibration of the –OH, the absorption band at 2932 cm−1 was ascribed to the C–H stretching vibrations, the peaks at 1715 cm−1 and 1610 cm−1 were designated to the C–O and CC stretching vibration, respectively [26,30]. The CO stretching vibration peaks at 1734 and 1703 cm−1 and the –CH2– stretching vibration and C–H rocking vibration peaks at 2849 cm−1 and 720 cm−1 represented the characteristic peaks of TSC14 [3,26], which further suggested the tetradecyl had been successfully grafted on the TS. The other significant evidence observed was 1H NMR spectrum of TSC14 corresponding to the –CH2– peak at δ1.24 ppm (Fig. S2) [3,26,31,32].
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