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標題: 低分子量有機酸影響金屬離子氧化還原反應之密度泛函理論計算
Redox reactions of metal ions affected by low molecular weight organic acids - A DFT study.
作者: 王雅真
Wang, Ya-Jen
關鍵字: Density function theory;密度泛函理論;formation constant;錯合常數
出版社: 土壤環境科學系
低分子量的有機酸(LMWOAs)是來自於自然界中植物根的分泌物、微生物的代謝產物和有機質降解後的物質,土壤中的重金屬容易和這些有機酸形成鍵結,進而影響金屬離子在環境當中的溶解度、生物可利用性、錯合、沉澱和氧化還原作用。本研究是採用密度泛涵理論(Density functional theory, DFT)的計算,探討有機酸和金屬離子錯合後,錯合物在溶液當中的氧化還原特性之研究。
結果顯示,四種有機酸(草酸、胡蘿蔔酸、琥珀酸和水楊酸)和第一列過渡金屬離子的錯合常數,可以錯合反應前後的總能量變化對實驗的錯合常數值作線性迴歸,其R2分別為0.95、0.95、0.94及0.92。對於同一金屬離子和不同有機酸的錯合常數,其大小依序是水楊酸(pht) >草酸(ox) >胡蘿蔔酸(mal) > 琥珀酸(suc)。主要影響的因素有配位基的酸度、硬度和立體遮敝效應(steric hindrance)。而影響金屬離子和有機酸錯合能力的強弱,主要和金屬離子本身內層水合水的鍵強及金屬離子的LUMO軌域能階有關。

Low-molecular weight organic acids ((LMWOAs) are produced from root exudates, microbial processes and decomposition of organic material in soil environmental. These organic acids have a high complex ability with heavy metals in soil and can affect the metal ions solubility, bio-ability, complex, precipitation and redox reaction. The density functional theory was used to investigate the character of the redox reactions that organic acids complex with the first row metal ions.
In the results, calculated total energy change is in linear correlation with the complex formation constant, the R square of organic acids (oxalic, malonic, succinic and salicylic) is 0.95, 0.92, 0.94 and 0.91 respectively. The order of complex formation constant of the first row metal ions complex with four organic ligands is salicylic > oxalic > malonic > succinic. The most important chemical property affecting complex ability in organic ligands are acid, hardness and steric hindrance and the main factors affect metal ions complex with one ligand are bond order between first hydration shells and the Lowest Unoccupied Molecular Orbital (LUMO) of center metal ions.
Metal ions complex with these four organic ligands and shift redox potential to more negative value. This decreased the ability to accept electorn on trivalent metal-organic ligand and for the divalent metal-organic ligands complexes that is a much stronger one-electron oxidant than aqueous divalent metal ions. Use solvent effect system via quantum chemistry calculation can calculate outer sphere electron transfer rates of hydration metal ions accurately. In an oxalic acid complex system, the self-exchange electron transfer rate increase with increasing the ligand number.
Appears in Collections:土壤環境科學系

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