| 摘要: | 金屬有機骨架材料(Metal-organic frameworks, MOFs)是近年來興起的一項孔洞材料，由於其擁有高比表面積、良好的熱及化學穩定性等優點，因而被大量的研究與發表。其中類沸石咪唑骨架材料-8(Zeolitic imidazolate frameworks-8, ZIF-8)是MOFs材料中的一種，是以鋅離子和2-甲基咪唑(2-methylimidazole, HmIm)所構築而成的三維結構，然而由於其具有良好的氣體吸附力，故已被廣泛地報導與應用。
近期文獻指出，利用原位創新法(de novo)所合成CAT@ZIF-8複合材料，因ZIF-8材料本身為疏水性材料，會導致過氧化氫酶(Catalase, CAT)失去活性。且在經過文獻查找後發現，在pH大於12的強鹼性環境中，過氧化氫酶會變性失去原本之構形，然而我們推斷在原位創新法的合成過程中，2-甲基咪唑的溶液強鹼性可能會導致過氧化氫酶的失活，故本研究希望透過機械力化學法之少量溶劑特性來合成出CAT@ZIF-8，以提升此複合材料之酵素活性。
MOFs材料常見的合成方式有傳統加熱法(Convectional heating)、機械力化學法(Mechanochemistry)、超音波化學法(Sonochemistry)、微波輔助加熱法(Microwave-assisted heating)及電化學法(Electrochemistry)，而本研究使用原位創新法及機械力學法進行合成，同時對比機械力學法與原位創新法所合成複合材料的活性差異，探討CAT@ZIF-8中酵素失活的其他原因。
本研究首先以機械力化學合成法(Mechanochemistry)為重心，使用ZIF-8材料作為研究模板，來探討此材料以機械力學法合成之優化條件，試圖改善以機械力學法合成MOFs材料時，其外觀形貌的完整性與顆粒聚集之現象。
最後，本研究內容成功尋找了ZIF-8材料的合成優化條件，改良材料本身的外觀形貌與顆粒聚集，之後再以機械力學法合成CAT@ZIF-8，並相對於原位創新法合成之複合材料，成功地提升其活性，將活性係數kobs值自1.0×10-5 s-1提高至1.3×10-3 s-1，期望後續研究能繼續優化此複合材料活性，且將這樣的概念延伸至其他MOFs材料或酵素，拓展酵素固定化之應用。
;Metal-organic frameworks (MOFs) are porous material that have emerged in recent years. Because of its high surface area, superior thermal stability and chemical stability, it has been extensively researched and published. Zeolitic imidazolate frameworks-8 (ZIF-8) is a class of MOFs, which is a three-dimensional structure composed of zinc ions and 2-methylimidazole. Because of its high gas storage capacity, superior thermal and chemical stability, this material has been widely used and reported.
A recent literature indicates that the Catalase(CAT)@ZIF-8 biocomposite synthesized by de novo approach, water-based and mild condition, showed undetectable biological activity which majorly resulted from the hydrophobic surface of ZIF-8. Interestingly, one report addressed that the enzyme will be denatured and lost its bioactivity when it was incubated at pH 12 or higher. Thus, we develop a new concept that catalases with no bioactivity due to under strong basic synthetic condition which created by the 2-methylimidazole dissociation under water solvent. The proof-of-concept design is demonstrated by embedding catalase molecules into uniformly sized ZIF-8 crystals via a mechanochemical approach because of water unnecessary during this synthesis.
Several synthetic methods are for obtaining MOF material, such as convectional heating, mechanochemistry, sonochemistry, microwave-assisted heating and electrochemistry etc. Importantly, in this study, we focused on harvesting ZIF-8 particles with morphology and less aggregation phenomenon by use of optimal grinding conditions as well as compared the biological activity of enzyme biocomposites which are synthesized by mechanochemistry and de novo approach, respectively. In addition to the factor of basicity, we also investigated other factors, i.e., ligand effect, to deactivate enzymes.
Finally, the biocomposite of CAT@ZIF-8 with good morphology and less aggregation has been synthesized via mechanochemical method. It is worth noting here that CAT@ZIF-8 sample prepared by mechanochemical method shows an observed rate constant (kobs) of 1.3×10-3 s-1. The low activity (1.0×10-5 s-1) is observed for the sample prepared using de novo. The future studies will continue to optimize synthetic condition for preparing this catalase biocomposite with better bioactivity and then extend this concept to other MOFs materials or enzymes, expanding the applications for enzyme immobilization. |
