Micellization-induced conformational change of a chiral proline surfactant |
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Authors: | Deng Manli Huang Xu Wu Rongliang Wang Yilin |
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Affiliation: | Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid and Interface Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. |
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Abstract: | A proline surfactant including two chiral carbons, sodium N-dodecanoyl-(4R)-hydroxy-L-prolinate (SDHP), has been synthesized, and its micellization behavior in aqueous solution has been investigated by 1H NMR spectroscopy. Two conformational isomers of SDHP, namely, Z and E, are discriminated in the NMR time scale, and critical micelle concentration is derived for each isomer separately. The transformation from E to Z is observed upon micellization, and the amount of Z isomer is approximately three times that of E isomer in the equilibrated system. Moreover, the variation in chemical shifts with the surfactant concentration reveals the shielding effect of the carboxyl group on the syn-side protons of the pyrrolidine ring, which implies that the pyrrolidine rings arrange in a side-to-side manner and lie parallel to the plane of the carboxyl bonds in the neighboring molecules. The difference in the directions of the carbonyl group between Z and E isomers essentially determines their different micellization abilities and molecular arrangements in the micellization process. |
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