大環配位子DO2PA之熱力學研究與HEDTA鑭系金屬錯合物水解磷酸酯鍵之動力學研究

Abstract

鑭系金屬離子(Ln3+)與其金屬錯合物具有良好的路易士酸特性、高配位數與高電子密度與熱力學穩定度，且相關研究也已經證實其對於DNA、RNA與磷酸酯鍵的水解有效力，非常適合做為人造水解酶，因此合成設計一個能促進磷酸酯鍵水解的金屬錯合物，一直是我們實驗室很感興趣的領域。實驗室之前已成功的合成LnDO2A+、LnODO2A+、LnNO2A+、LnPhNO2A+、LnONO2A+，且經由實驗證實其具有極高水解BNPP的效力，同時也了解錯合物配位水數目、位向及其電性對於水解磷酸酯鍵的影響。 在此，我們合成了DO2PA(四氮十二元環二丙酸基)大環，並利用電位滴定法計算出其相關金屬錯合物的穩定常數，發現DO2PA的錯合效果不好，在取得足夠數據前就已經產生金屬氫氧化物沉澱。在HEDTA鑭系金屬錯合物水解磷酸酯鍵pH 6.96.-10.89的實驗中，我們發現反應速率大致隨著原子序的增加而減小，隨著pH值的增加而增加；另外，藉由改變LnHEDTA錯合物的濃度，同時將相關數據帶入簡單的飽和動力學反應機構，得到水解BNPP時的水解常數k(first order rate constant)及LnHEDTA-BNPP的鍵結常數K(LnHEDTA-BNPP binding constant)。

The cationic trivalent lanthanide (Ln3+) ions and complexes have good Lewis acids ability, high thermodynamics stability, low kinetics lability, high coordination numbers, and charge density. It has been demonstrated to be effective DNA, RNA, and phosphodiester compounds’ cleavage agents. So macrocyclic lanthanide complexes will be suitable as artificial nucleases. We have been interested in design and synthesis of macrocyclic lanthanide complexes which are capable of catalytically hydrolyzing phosphodiester bonds. Our lab had synthesized a few ligands LnDO2A+、 LnODO2A+、LnNO2A+、LnPhNO2A+、LnONO2A+ and verified they would promote effectively hydrolysis of BNPP by experiment. We also verified more coordinated water would make metal complexes more effectively in hydrolyzing phosphodiester bonds. And metal complexes carry positive charge would enhance its ability in hydrolyzing BNPP. In this thesis, we report the synthesis of DO2PA (1,7-dicarboxyethyl-1,4,7,10- tetraazacyclododecane) and their metals complex stability constant determined by potentiometric method. We oberserved that DO2PA is too weak a ligand for the pH titration method to be useful for the determination of the stability constants for most metal ions. Because the metal ions hydrolyze and form hydroxide precipitates before anymeasurable complexation takes place. In the BNPP hydrolysis by lanthanide complexes of HEDTA at pH 6.96.-10.89 experiment, the reaction rate increases as atomic number decreases and as pH increases. Further, in the [LnHEDTA] = 10 -50 mM experiment, we fit the data into simple-saturation kinetic mechanism and obtain the BNPP hydrolysis first order rate constant and the LnHEDTA-BNPP binding constant.