Liu Jie, Wu Siwu, Tang Zhenghai, Lin Tengfei, Guo Baochun, Huang Guangsu
Department of Polymer Materials and Engineering, South China University of Technology, Guangzhou 510640, China.
Soft Matter. 2015 Mar 21;11(11):2290-9. doi: 10.1039/c4sm02521k.
Resolving the structure of natural rubber (NR) has been an important issue for a long time and essential progress has been made. It is well established that non-rubber components have significant effects on the performance of NR. A detailed discussion on the effects of proteins and phospholipids on the chain dynamics of NR will be crucial for the in-depth understanding of the role of proteins and phospholipids in NR. However, to date, there is still a lack of elaborate studies on the dielectric spectroscopy of NR. In the present study, we performed detailed dielectric relaxation analysis, together with rheological measurements, to reveal the effects of proteins and phospholipids on the chain dynamics of NR. Distinctly different from the widely accepted segmental mode (SM) and normal mode (NM), a new relaxation mode in deproteinized NR (DPNR) was identified for the first time, which cannot be found either in NR or in transesterified DPNR (TE-DPNR). Because this new mode relaxation process behaves as a thermally activated process and it is about four orders of magnitude slower than NM, it could be rationally attributed to the relaxation of the phospholipids core of DPNR, named branch mode (BM) relaxation. When further conversion of DPNR to TE-DPNR was conducted, the phospholipids were removed and BM disappeared. In addition, a new relaxation mode, which occurs at considerably lower temperature than that for SM, was revealed in TE-DPNR, and may be related to the relaxation of free mono- or di-phosphate groups at the α ends in TE-DPNR. Hence, the identification of the new relaxation modes in DPNR and TE-DPNR provide new evidence for the natural networking structure linked by protein-based ω ends and phospholipids-based α ends.
长期以来，解析天然橡胶（NR）的结构一直是一个重要问题，并且已经取得了重要进展。众所周知，非橡胶成分对NR的性能有显著影响。详细讨论蛋白质和磷脂对NR链动力学的影响对于深入理解蛋白质和磷脂在NR中的作用至关重要。然而，迄今为止，关于NR的介电谱仍缺乏详尽的研究。在本研究中，我们进行了详细的介电弛豫分析，并结合流变学测量，以揭示蛋白质和磷脂对NR链动力学的影响。与广泛接受的链段模式（SM）和正常模式（NM）明显不同，首次在脱蛋白天然橡胶（DPNR）中鉴定出一种新的弛豫模式，这种模式在天然橡胶（NR）或酯交换DPNR（TE-DPNR）中均未发现。由于这种新模式的弛豫过程表现为热激活过程，并且比NM慢约四个数量级，因此可以合理地归因于DPNR磷脂核心的弛豫，称为支链模式（BM）弛豫。当进一步将DPNR转化为TE-DPNR时，磷脂被去除，BM消失。此外，在TE-DPNR中还揭示了一种新的弛豫模式，其发生温度比SM低得多，可能与TE-DPNR中α端游离单磷酸或二磷酸基团的弛豫有关。因此，在DPNR和TE-DPNR中鉴定出新的弛豫模式为基于蛋白质的ω端和基于磷脂的α端连接的天然网络结构提供了新证据。
