多氢键型超分子聚合物的理论设计与模拟

Hydrogen-bonded supramolecular polymers have tremendous potential in many areas, such as photoelectric materials, molecular recognition and biomedical engineering. As we all know, water is the major component of the organisms, whereas the available hydrogen-bonded supramolecular polymers are not stable enough in the water environment, which builds up the largest barrier preventing their extensive application in biomedical engineering. Therefore, design and synthesis of the multiple hydrogen-bonded supramolecular polymers that can present stably in water, is considered as one of the most significant and challenging research issues. However, it is difficult to reveal the systemic relationships between the structures and stability of supramolecular polymers only by the experimental means. Computational chemistry tools can compensate for the lack of experimental research efficiently and economically by explaining and predicting the contributions of multiple hydrogen-bonded motifs and polymer chains to stability of the polymers accurately...This project is firstly to investigate the structural and environmental factors favoring hydrogen bonding of the reported multiple hydrogen-bonded dimers using quantum chemistry methods. Then, more multiple hydrogen-bonded dimers will be designed based on our discovered principles to further strengthen hydrogen bonding. Next, the corresponding preferable multiple-point hydrogen-bonding motifs will be modified by adding various chemical chains to build up the supramolecular polymers. Molecular dynamics methods will be used to explore their dynamic behavior in water, in order to evaluate their dynamic stability in water environment. Finally, a series of potential supramolecular polymers which are stable in the organisms will be designed and confirmed theoretically. The prospective achievements will provide effective direction for the related experimental research and will further promote the applications of hydrogen-bonded supramolecular polymers in the field of biomedical engineering.

多氢键型超分子聚合物在很多领域，如光电材料、分子识别、生物医学等都具有潜在的应用前景。由于生物体主要成分是水，已报道的此类聚合物在水中较差的稳定性是其在生物医学方面广泛应用亟需解决的重要科学问题。然而，仅通过实验研究难以对聚合物结构与其稳定性之间的关系得到系统的认识，理论化学研究是弥补实验手段不足的高效方法，能合理地解释和预测氢键结合单元和端基聚合链的结构等对增强聚合物稳定性的作用。本项目以实验报道的四氢键二聚物为基础，采用量子化学计算方法，揭示能够增强二聚体氢键能的结构和环境因素。在此基础上，设计更多的多氢键二聚物，以进一步提高其氢键结合能力。基于上述研究，选取氢键结合能力较强的单体，在其末端引入不同的化学结构，通过分子动力学的研究，观测其在水中的动力学平衡过程，最终得到在水中能够稳定存在的超分子聚合物。研究成果将有效地指导该领域的实验研究，推动超分子聚合物在生物医学方面的广泛应用。

多氢键型聚合物广泛应用于构筑超分子材料领域，设计并合成出具有高聚合强度和稳定性的多氢键型聚合物已成为化学家们的研究热点和长期目标。本项目主要研究氢键结合单元和端基聚合链对聚合过程的影响。. (一)首次对氢键阵列中二级静电作用进行了定量计算。相邻给受体之间的吸引作用有利于形成稳定的二聚体，使结合能增强2.44—2.70kcal/mol(氯仿)和2.41—2.67kcal/mol(乙腈)，对自由能最大可降低5.28kcal/mol(氯仿) 和3.14kcal/mol(乙腈)。这些结果可以为实验上设计新的氢键结合单元或者调解氢键阵列的结合能给出理论依据。(二)研究了不同取代基的DeAP及其异构体形成的二聚体。二聚体bb最稳定，拓扑分析证实了分子间与分子内氢键共存，所有氢键的伸缩振动频率都表现出明显的红移。给电子取代基使二聚体自由能降低，弱极性溶剂对二聚作用更有利。单体和二聚体的最大吸收波长差异显著，因此在实验上对于鉴别分子间氢键和计算DeAP平衡体系的结合常数方面具有潜在应用。(三)从理论上阐释了实验中DAN能够与UPy，DeAP及DeUG形成稳定二聚体等结果。二聚自由能不随溶剂极性的增加而单调递减，DAN-8在水中具有较大的自由能，对DAN二聚体系在极性溶剂中的稳定形成具有指导意义。C-H键替换N-H键，二聚物结合能降低25.3%到35.8%，说明N-H键对二聚体稳定性贡献很大。紫外可见吸收光谱可用于DAN•DeUG二聚平衡体系的鉴定。(四)研究了一种新颖的DDDD-AAAA型氢键二聚体。二聚过程形成了较强的分子内和分子间氢键，各种环境中二聚体[5.4]的稳定性都优于[5.6]和[5.7]。氢键阵列中氮原子替换为碳后，聚合物稳定性明显降低。溶剂极性对聚合过程有很大影响，随着溶剂极性的增加，结合能与自由能减小，二聚过程不易发生。(五)脲基末端PPG或PEG数目对UPy二聚体的氢键能有增强作用，并使二聚过程自由能降低，有利于形成更稳定的二聚体。随着聚合链结构单元数量增加，末端PPG与UPy的相互作用可能更加复杂。虽然比二聚体的氢键能小，但仍会对二聚作用产生竞争，从而阻碍了二聚体的产生。我们预测网状或树枝状的结构可能对多氢键的保护作用更强，更容易在极性溶剂中形成稳定的聚合物。. 项目组共发表SCI论文7篇，培养硕士研究生两名，发表会议论文3篇。3篇正在准备中。