合成酵素固定或化學酸官能化磁性中孔洞氧化矽奈米粒子做為可回收式固體催化劑應用於纖維素-葡萄糖-果糖-5-羥甲基糠醛序列式生質轉換

Abstract

本研究主要致力於合成有磁性的中孔洞氧化矽奈米粒子(MSN)，利用它來固定兩種酵素(纖維素水解酶、葡萄醣異構酶)做成可方便回收的催化劑，並使用架接法接上磺酸官能基(SO3H)作為酸性催化劑。此三種催化劑應用於木質纖維素至化學精緻品序列式轉換反應，以達到在水相和兩相(水相和有機相)中纖維素轉換成5-羥甲基糠醛的目的。 首先，我們合成了鑲嵌入氧化鐵的中孔洞氧化矽奈米粒子(Fe3O4-MSN)固定化兩種酵素，也就是纖維素水解酶和葡萄醣異構酶，由於酵素昂貴，所以我們選擇把它們固定化在基材上就可以利用磁鐵進行回收然後再次使用；此外，我們合成了中孔洞氧化矽奈米粒子(MSN)，由於它表面上有很多的羥基(-OH)，可以利用縮合反應和矽烷類形成化學鍵結使矽烷類被牢牢地固定在基材上，我們選擇的矽烷尾端有硫氫酸根(-SH)，之後藉由氧化作用把官能基氧化成磺酸根(SO3H)，就會形成酸度很高的固體催化劑，我們利用固態核磁共振儀定性且定量出有多少磺酸根接上去；最後利用三種催化劑來做生質轉換，纖維素寡聚物為起始物，加入已固定在基材上的纖維素水解酶，可以催化纖維素寡聚物水解成葡萄醣；回收酵素調整pH值後，再加入固定在基材上葡萄醣異構酶催化葡萄醣異構化成果醣，回收催化劑之後再加入有機溶劑二甲基亞碸(DMSO)使其形成兩相溶液，再加入有修飾磺酸根的中孔洞氧化矽奈米粒子，催化果醣脫水成最終產物5-羥甲基糠醛(HMF)，此步驟為序列式反應。序列式反應的優點是可以藉由最佳化每個小步驟的反應條件，使每個小步驟產物的產率達到最高，而上個步驟的產物是下個步驟的反應物，如此下去可以讓最後的產物產率達到最大，而且藉由分開每個步驟也可以使反應簡單化減少副產物的產生。在三種催化劑的催化下，可從果醣、葡萄醣和纖維素寡聚物的轉化分別得到產率最高的HMF產率分別為81.3%、46.1%及45.6%。這是第一次有研究報告利用序列式反應做纖維素的生質轉換。

This study focuses on the synthesis of magnetic mesoporous silica nanoparticles (MSN). We obtained two recyclable catalysts by utilizing magnetic mesoporous silica nanoparticles to immobilize two types of enzymes (cellulase and isomerase). Furthermore, we functionalized mesoporous silica nanoparticles with sulfonic groups by a grafting method. By utilizing these three kinds of solid recyclable catalysts, we successfully converted cellulose to 5-hydroxymethylfurfural (HMF) in a bi-phase system via a sequential reaction. First, because of the expensive price of enzymes, we tried to immobilize cellulase or isomerase on Fe3O4@MSN and recycle these catalysts using magnetic force. Second, we utilized mesoporous silica nanoparticles with many hydroxyl groups to functionalize them with sulfonic groups. We chose silane with thiol functional groups, and after performing a condensation reaction between the materials and silane, we oxidized the thiol groups to sulfonic groups. We could obtain acidic solid catalysts. Then we characterized functionalized the MSN by solid-state NMR to quantify how many sulfonic functional groups had been connected onto the solid materials. Finally, we utilized these three types of recyclable solid catalysts to conduct cellulosic bioconversion. We used pretreated cellulose as the reactant and immobilized cellulase on Fe3O4@MSN as the catalyst to hydrolyze cellulose to glucose. Then after recycling the solid catalysts using magnetic force and changing the buffer pH value, we added immobilized isomerase on Fe3O4@MSN as a catalyst to isomerize glucose to fructose. Finally, after recycling the recycle solid catalysts using magnetic force and adding an organic phase (DMSO), we added functionalized MSN (with sulfonic groups) as a catalyst to dehydrate fructose to HMF. This step-by-step reaction was called a sequential reaction. The advantage of this sequential reaction is that we can optimize the reaction conditions of each step, obtain high product yields, and lower the production of by-products. By utilizing this sequential reaction, we were able to obtain a high yield of the final product. The HPLC results showed that the highest yield of HMF converted from fructose, glucose and pretreated cellulose were 81.3%, 46.1%, and 45.6%, respectively in the presence of the three solid catalysts. This is the first report on the generation of HMF from fructose, glucose, and pretreated cellulose via a sequential reaction with immobilized enzymes on magnetic mesoporous silica nanoparticles that are grafted with sulfonic groups.