金屬有機骨架材料(Metal-organic frameworks；MOFs)是近年來迅速崛起的一種孔洞材料(porous material)之一，其藉由金屬離子(metal ion)或金屬團簇(metal cluster)與有機配位體(organic linker)所構成，不同的組成單元及官能基具有不同的物理或化學性質，同時具有多孔性與高比表面積，因此其應用性非常廣泛。其中一種具有新穎性與突破性的應用為本實驗室所發表，將ZIFs(為MOFs的一個分支)與蛋白質酵素結合(CAT@ZIF-90)，進行過氧化氫的催化反應，同時可以防止蛋白質水解酶的作用達到保護酵素的效果。並可藉由MOFs的結構提供一個研究生物分子行為的特殊的環境-如侷限性環境；因此這種酵素與骨架材料的結合的複合材料在生物催化上相當具有潛力，若能更進一步的拓展此領域，就可以探討更多的酵素行為。然而許多酵素的底物(substrates)都比過氧化氫大，無法進入ZIF-90孔洞被酵素催化；而且ZIF-90在酸性條件的結構穩定性不佳，無法應用到酸性環境中作用的生物分子。為此，我們選用相對穩定且孔徑較大的UiO-66，係因材料本身穩定性而有許多應用性，在近年來的研究更是如火如荼的展開，藉此期望能研究更多環境中的生物分子行為。然而，UiO-66一般都是在有機溶液下合成，縱使近年來已經有開發出利於蛋白酵素較溫和的水相合成條件，但還需加入會傷害酵素的乙酸當作添加劑，所以在水相尚待突破的同時，另一種只需少量溶劑的合成方法勢在必行。因此本研究主題為：利用機械力化學合成法的水輔助研磨反應得到金屬有機骨架材料UiO-66-F4，並以有機配位體與微量溶劑在球磨合成法中的溶解度效應切入，可於三分鐘的快速球磨反應後得到產物，並具有良好的水、熱穩定性及疏水性，且在實驗也發現反應六十分鐘後的產物具有較佳的孔洞性質。此種溫和且不需添加酸性有機溶劑的球磨合成環境，提供一個可應用於MOFs包覆酵素或奈米粒子的系統，兩種領域皆具有相當廣闊的前景。;Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of two main components: (i) clusters (or better multinuclear complexes) and (i) linker systems. In the past decade, they have been extensively studied because of their extraordinary porosity that makes them suitable for many applications. In particular, due to the variety of the choosing metallic clusters and organic linkers with different functional groups, MOFs have significantly physical and chemical properties. In these characters, a pretty interesting study reported by our lab about the combination of enzyme (Catalase) and MOF (ZIF-90) under a de novo approach. The ZIF-90 support provides an interesting size-sheltering function to catalase and protects catalase from the protein killer-proteinase-K. That study offers a novel tool to immobilize and impart new functions to biomolecules. In order to expand the routes for other enzymatic reactions, we choose UiO-66 (nominal composition: Zr6O4(OH)4(BDC)6; BDC = 1,4-benzene dicarboxylate) as our main material because UiO-66 with bigger aperture size at 6 Å comparing it in ZIF-90 at 3.5 Å. This property allows the bigger substrate to deliver into MOF structure for contacting embedded enzymes. Under harsh condition of the conventional way for the UiO-66 synthesis, normally, the catalytic activity of the biological component significantly is able to be deteriorated because of the chemically/thermally induced denaturation of protein. Therefore, a way of the milder condition to synthesize UiO-66 needs to be developed. In this regard, we provided a new approach, i.e., mechanochemistry, to synthesize MOF material in this study: a UiO-66 analog was synthesized in 180 s using water-assisted grinding. The linker solubility suggested that tetrafluorobenzene- 1,4-dicarboxylic acid was the best linker due to the lowest average pKa value. Zr-based Metal–organic framework nanocrystals displayed good topologies and hydrophobicities, and high water/thermal stabilities. The less amorphous complex led to higher porosities and pore volumes with a 60 min grinding time. Importantly, this mild approach for obtaining MOFs without hazardous solvents provides an additional avenue for converting biomolecules or metal nanoparticles into MOFs as composites for applications.
