Studying On The Self-assembly Of Supermolecules Based On Diphenylalanine

Diphenylalanine (L-Phe-L-Phe, FF), the core motif of the Alzheimer’s disease-associated P-amyloid polypeptide, has the ability to self-assemble into some kind of structure. Many molecules based on it have been widely studied and developed. As a representative of a branch of the soft condensed matter (also known as "soft matter" for short), they have the common characteristics with the other soft matter.Thus, we introduce the concept and main features of soft matter in the first chapter. Shared the mesoscopic length scale-between atomic sizes and marcroscopic scales, almost all of them can easily be affected by the thermal fluctuations and Brownian motion, which will have great effects on the spontaneous self-assemble propensity of them. Different from the simple liquids or hard solids, interactions those function in soft matter are quite weak (act inter-molecules or inter-motifs), such as Van der Waals force, hydrophobic interaction, hydrogen bonds, etc. They are various and different between each other, and cooperate and/or compete in the self-assemble process. The driving force to assemble of soft matter is also quite different from the traditional hard matters. Entropy effect usually comes prior, and dominates in may process of soft matter, where the enthalpy who governs the hard matter reactions loses its first place.These distinct natures portray diphenylalanine and9-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) with colorful and plentiful features. They can show lots of self-assemble ways and morphology. The main inner driving force of these two molecules are hydrophobic interactions and they assemble hierarchically. For FF molecules, they could form the nanotubes or nanofibres in aqueous condition, and could turn to be micrometer-scale structures, depending on the concentration or the way they produced. In these structures, stacking of benzene rings is the core, which is also called as π-π stacking. The backbones of FF molecule in this structure face out to the solvent. So in the water, they can interact with the water molecules, and in turn, the water can change the fluorescence spectrum, the Raman spectrum and so on, which indeed the water molecules modify the structure. And as to Fmoc-FF molecules, they can gelate in water circumstance to hold the water molecules. The main driving force is also the hydrophobic interactions. However a homogeneous and reproducible Fmoc-FF hydrogel cannot be prepared easily. This is ascribed to the difference of prepare works, despite of the slightness. This drawback limits the use of it. The works those focuses on the prepare work and characteristics research are be collected in the second chapter.In the third chapter, we study on the effect that the urea did on the FF self-assembly. Urea is one of the most used protein denaturant. We so use fluorescence spectroscopy, circular dichroism, and attenuated total internal reflectance Fourier transform infrared spectroscopy techniques to try to know the FF structure changes urea makes. We discover that with the urea concentration increase, the amount of macroscopic structure reduces. Having more speculation on it, we take the opinion that the urea acts with the backbones and make the benzene ring stack loose.And in Chapter four, we succeed in developing two new approaches for Fmoc-FF gelation in the water:one is based on the nano-dispersed colloids to hydrogel transition and the other is based on the decomposition of potassium persulfate to mildly change the pH. The two new approaches have an apparent advantage over the tradition methods, which can be divided into two class:the pH-switch method and the solvent-switch method. The gels prepared by the new approaches turn to be more homogeneous and reproducible. This improvement helps understanding the assemble process at the same time.Depend on these studies, we will have more knowledge on the self-assembly of the molecules based on diphenylalanine and the denaturation urea induced. Meanwhile, they can help us to develop more kinds of homogeneous and reproducible hydrogel, and even other better materials.