多環芳香烴（polyaromatic hydrocarbons, PAHs）是一類結合多個苯環而成的芳香族化合物，因為這類化合物具有多個共軛pi電子系統和強分子間作用力，使其產生獨特的光學活性和電子特性。透過分子設計，這一類分子可以進行堆疊，自組裝成一維至三維的結構，而在生物醫學領域中，PAHs可以與胜肽結合，創造出具有生物相容性和生物活性的自組裝材料，例如：做成三維的水凝膠可以用於細胞支架，以及PAHs-胜肽與其他化合物混合的共聚物可以用作藥物載體。然而，PAHs-胜肽中的PAHs分子結構對自組裝的影響尚未有充分的研究。
本篇研究探討不同大小和平面性的疏水性PAHs，與親水性的胜肽結合後對自組裝行為的影響。我們選用的PAHs中，包含了較大的環且平面的六苯駢蒄（hexabenzocoronene, HBC）和非平面的六苯基苯（hexaphenylbenzene, HPB）；而較小的環則包含了平面的dibenzo[g,p]chrysene, DBC和非平面的四苯基乙烯（tetraphenylethylene, TPE），並藉此合成了四種PAHs-胜肽（HBC-ahx-K6、HPB-ahx-K6、DBC-ahx-K6、TPE-ahx-K6），研究其自組裝的特性以及光學活性。
從光譜測量結果中，我們得知這些胜肽皆具有獨特的吸收以及螢光的特性，而在自組裝的過程中，也發現TPE-ahx-K6以及HBC-ahx-K6具有聚集誘導發光（aggregation-induced emission, AIE）的現象，而HPB-ahx-K6以及DBC-ahx-K6具有的聚集誘導猝滅（aggregation-caused quenching, ACQ）的現象。
從電子穿透顯微鏡（transmission electron microscopy, TEM）的圖像觀察下，在中性水溶液中，大環PAHs-胜肽可以形成特定結構。如HPB-ahx-K6在pH 7的磷酸鹽緩衝液（phosphate-buffered saline, PBS）和水（pH 7）中，可以形成纖維狀結構，而HBC-ahx-K6則在水中形成奈米片狀（nanosheets）結構；相比之下，小環的PAHs-胜肽需要在高濃度下培養才能自組裝形成特定結構。例如，DBC-ahx-K6可以在PBS（pH 7）中形成扭曲狀纖維結構，而TPE-ahx-K6只能自組裝成無定型的聚集體。在未來，我們將與物理所合作，利用選區電子衍射（selected area electron diffraction, SAED）觀察特定結構的晶體性質與取向。
另外，本論文研究還探討了PAHs-胜肽在複合凝聚層（complex coacervates）中與四種帶負電化合物混合的自組裝特性，其分別為聚尿苷酸（polyuridylic acid, polyU）、lysophosphatidylglycerol (LysoPG)、十二烷基硫酸鈉（sodium dodecyl sulfate, SDS）和二肉豆蔻醯基磷脂醯甘油（dimyristoylphosphatidylglycerol, DMPG）。從光學顯微鏡影像顯示，所有PAHs-胜肽可以與polyU形成複合凝聚層。然而，PAHs-胜肽當與LysoPG或SDS等帶負電的兩親分子混合時，只有非平面PAHs的PAHs-胜肽（如HPB-ahx-K6和TPE-ahx-K6）傾向於形成複合凝聚物。最後，使用具有兩個長碳鏈的DMPG混合後，所有的PAHs-胜肽皆形成了聚集體。接下來，我們進一步挑選了HPB-ahx-K6並研究其與polyU及LysoPG形成的複合凝聚層的化學特性。結果顯示，在高鹽環境下，LysoPG複合物仍保持其球形形態，而polyU複合物則轉變為無定型的聚集體。根據此結果，我們計劃在未來測試其LysoPG複合物的細胞活性和生理環境穩定性，以評估其作為藥物載體的潛力。
這些發現提供了有關PAHs在接到胜肽上後，PAHs結構可能如何影響其自組裝形態，其中包含了PAHs-胜肽纖維化以及共聚物形成過程。這些知識有助於我們研究這類分子形成自組裝結構的性質和堆疊取向之外，也有助於我們設計用於醫學的功能性生物材料。

Polyaromatic hydrocarbons (PAHs) are class of aromatic compounds with fused benzene rings, characterized by unique optical and electronic properties stemming from their conjugated π-electron systems and strong intermolecular interactions. Through molecule design, these molecules could self-assemble into 1D to 3D structures with distinctive stacking. In the field of biomedicine, PAHs can be conjugated with peptides to create self-assembling materials with biocompatibility or bioactivity. For example, hydrogels can be used for cell scaffolding and coacervates can be used as drug carriers. However, the relationship between the molecular structure of PAHs and the resulting self-assembled structures has not been well-studied.
In this study, we investigated the self-assembly of hydrophobic PAHs with different sizes and planarities [i.e., The large planar hexabenzocoronene (HBC) and non-planar hexaphenylbenzene (HPB), along with the small planar dibenzo[g,p]chrysene (DBC) and non-planar tetraphenylethylene (TPE)] conjugated with hydrophilic peptide sequence (ahx-K6). These PAHs-peptide conjugates (HBC-ahx-K6, HPB-ahx-K6, DBC-ahx-K6, and TPE-ahx-K6) were synthesized in our laboratory and their self-assembly behaviors and optical properties were studied.
We observed that PAHs-peptides exhibit unique absorption and fluorescence properties from their absorption and fluorescence spectra. Additionally, during the self-assembly process, TPE-ahx-K6 and HBC-ahx-K6 demonstrated AIE phenomena, while HPB-ahx-K6 and DBC-ahx-K6 showed ACQ phenomena.
Transmission electron microscopy (TEM) revealed that larger PAHs-peptides formed ordered structures under neutral conditions. For instance, HPB-ahx-K6 formed fibrous structures in phosphate-buffered saline (PBS) at pH 7 and water. In contrast, HBC-ahx-K6 formed nanosheets in water (pH 7). Additionally, peptides conjugated with smaller PAHs require higher concentrations to form specific structures. For example, DBC-ahx-K6 can form twisted fibrous structures in PBS at pH 7, whereas TPE-ahx-K6 only form amorphous aggregates in all concentrations. In the future, we will collaborate with the Institute of Physics and apply selected area electron diffraction (SAED) to observe the crystal properties and orientations of specific structures.
The self-assembly properties of the PAHs-peptides were also investigated by mixing them with four negatively charged compounds, including polyuridylic acid (polyU), lysophosphatidylglycerol (LysoPG), sodium dodecyl sulfate (SDS) and dimyristoylphosphatidylglycerol (DMPG). We found that all four PAHs-peptides formed complex coacervates with polyU in the optical microscopy. However, when mixed with negatively charged amphiphiles such as LysoPG or SDS, only PAHs-peptides with non-planar PAHs (i.e., HPB-ahx-K6 and TPE-ahx-K6) tended to form complex coacervates. Finally, PAHs-peptides mixed with DMPG only tended to form aggregates. The chemical properties of the complex coacervates formed by HPB-ahx-K6 with polyU and LysoPG were further investigated. The results showed that the LysoPG complexes retained their spherical morphology even under high salinity, while the polyU complexes eventually turned into amorphous aggregates. We will test the additional stability and cellular activity of LysoPG to evaluate its potential as a drug carrier in the future.
These findings offer insights into how PAHs structures influence the self-assembly morphologies, no matter in PAHs-peptide fibrillization or coacervation. This knowledge can aid not only in studying the properties and stacking orientations of self-assembled structures formed by such molecules but also in designing functional biomaterials for medicine.

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