目的：过渡金属配合物有望成为先进的结构材料，由于金属配位键，与典型的共价键不同，可以在破裂后再生，允许动态，可调，和可逆的机械特性。很少报道泡沫材料中金属配位交联的整合。
方法：我们开发了水解大米蛋白（HRP）作为两亲性过渡金属配位络合物的结构单元，可用于制造具有高屈服应力的长寿命泡沫。使用平衡和动态张力计测定发泡溶液的表面性质。通过小角度X射线散射（SAXS）和Cryo-Tem检测发泡溶液中聚集体的结构信息。通过反射光学干涉技术研究了界面液膜中液体流动的可视化。液体泡沫的流变响应通过具有振幅扫描和频率扫描模式的流变仪来表征。
结果：在过渡金属离子的存在下，HRP形成机械强度高的刚性膜。在不存在过渡金属离子或添加烷基多糖苷（APG）的情况下，将HRP解吸以产生具有洗涤剂状态的可移动膜。基于本体溶液组成(金属离子或烷基糖苷或螯合剂)的容易变化,可以主动切换两种界面状态。两种状态之间的转换导致了具有高屈服应力的极其稳定的泡沫的形成或屈服极限显著降低的泡沫的塌陷。吸附在液膜表面的过渡金属配位络合物可以使液体泡沫的弹性模量提高一个数量级以上，而不会增加发泡溶液的粘度。我们进一步揭示了泡沫稳定性/不稳定性的起源，并使用其他特征明确的蛋白质来制备过渡金属配位络合物以制造长寿命泡沫。这项工作中描述的案例说明了该战略的普遍性，原则上可以扩展到许多类型的蛋白质。
OBJECTIVE: Transition-metal coordination complexes are hopeful to make advanced structural materials, since the metal-coordination bonds, unlike typical covalent bonds, can regenerate after rupture, allowing for dynamic, tunable, and reversible mechanical characteristics. Integration of metal-coordinate crosslinking in foam material has rarely been reported.
METHODS: We developed the hydrolyzed rice proteins (HRP) as the building block for amphiphilic transition-metal coordination complexes that could be used to make long-lived foams with high yield stress. Surface properties of the foaming solution were determined using equilibrium and dynamic tensiometers. Structural information of aggregates in the foaming solution was detected by small-angle X-ray scattering (SAXS) and Cryo-Tem. Visualization of liquid flow in the interfacial liquid film was studied by the reflective optical interference technique. Rheological response of liquid foam was characterized by a rheometer with amplitude-sweep and frequency-sweep modes.
RESULTS: In the presence of transition metal ions, HRP formed a mechanically strong rigid film. In the absence of transition metal ions or the addition of alkyl polyglycoside (APG), HRP was desorbed to produce a mobile film with a detergent state. The two interfacial states could be actively switched based on facile changes in bulk solution composition (metal ions or alkyl glycoside or chelating agent), and the switching between the two states led to the formation of extremely stable foam with high yield stress or the collapse of foam with a significant decrease in yield limit. The transition-metal coordination complexes adsorbed on the surface of the liquid film could increase the elastic modulus of liquid foam by more than an order of magnitude without increasing the viscosity of the foaming solution. We further revealed the origin of foam stability/instability and used other well-characterized proteins to prepare transition-metal coordination complexes to make long-lived foams. The cases described in this work illustrate the universal nature of the strategy, which in principle can be extended to many types of protein.
