Acta Chimica Sinica ›› 2019, Vol. 77 ›› Issue (12): 1279-1286.DOI: 10.6023/A19090331 Previous Articles     Next Articles

Special Issue: 分子探针、纳米生物学与生命分析化学



杨靖鸽, 李阳, 王小艾, 王栋, 孙亚伟, 王继乾, 徐海   

  1. 中国石油大学(华东)化学工程学院生物工程与技术中心 青岛 266580
  • 投稿日期:2019-09-07 发布日期:2019-10-21
  • 通讯作者: 王继乾, 徐海;
  • 基金资助:

Self-Assembly of Cyclic Dipeptides and Their Fluorescent Properties

Yang Jingge, Li Yang, Wang Xiaoai, Wang Dong, Sun Yawei, Wang Jiqian, Xu Hai   

  1. Center for Bioengineering & Biotechnology, College of Chemical Engineering, China University of Petroleum(East China), Qingdao 266580
  • Received:2019-09-07 Published:2019-10-21
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Nos. 21573287, 21673293, U1832108).

Cyclic dipeptide (CDP) is a kind of the smallest cyclic peptide with two amino acids cyclization through amide bonds. The two amide bonds with four hydrogen bonding sites give CDPs a high self-assembly propensity, mainly driven by the hydrogen bonding interactions. In this paper, we have designed four CDPs, c-SF, c-SY, c-SH and c-DF, and studied their self-assembly performance in aqueous solution with circular dichroism spectroscopy (CD) and atomic force microscopy (AFM), including the effects of pH and zinc ion coordination on self-assembly. The fluorescence properties of CDP self-assemblies have also been studied. CD results showed that c-SF, c-SY and c-DF adopted a β-sheet conformation, while c-SH was random coil secondary structure at the concentration of 2.0 mmol/L and pH 5.0. AFM results showed that c-SF, c-SY and c-DF could form nanofibers with different diameters ranged from 1.0 to 3.0 nm. In addition, c-SY self-assembled hierarchically over time. Not only the nanofiber diameter gradually increased, but also the nanofibers entangled into 3D networks. Although c-SH did not self-assemble at the concentration of 3.0 mmol/L and pH 7.0, it could form monolayers with the induction of zinc ion at pH 9.0. The self-assemblies of each CDP had different multiple fluorescent emission peaks with excitation of different wavelengths. Especially, c-SF emitted green fluorescent light under UV light of 365 nm. The fluorescent emission intensity of CDPs was much stronger than their corresponding linear dipeptides. It was assumed that the diketopiperazine structure contributed to the fluorescence enhancement. Moreover, the fluorescent emission intensity of CDP self-assemblies was much higher than that of their free molecules, which meant that the ordered aggregation made a significant contribution to the fluorescent properties. Both the coordination of zinc ions with the imidazole groups on histidine and the oxidation of phenolic hydroxyl groups in tyrosine could enhance the fluorescent emission intensity of CDPs. It was assumed that CDP molecules stacked one by one to form nanofibers during self-assembly. The diketopiperazine ring of CDPs and its self-assembly endowed CDPs with special fluorescent properties.

Key words: cyclic dipeptide, diketopiperazine, self-assembly, nanofiber, fluorescence