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Title: | 二氧化錳對頭孢子類抗生素降解機制之研究 Oxidative Transformation of Cephalosporin Antibiotics by Manganese Dioxides |
Authors: | Hua-Lin Wu 吳華琳 |
Advisor: | 林郁真(Angela Yu-Chen Lin) |
Keyword: | 頭孢子類抗生素,二氧化錳,氧化作用,副產物鑑定, Cephalosporin,Manganese oxides,Oxidative degradation, |
Publication Year : | 2012 |
Degree: | 碩士 |
Abstract: | 民眾錯誤的用藥觀念及藥物丟棄的習慣,導致藥物進入環境水體中造成生態衝擊。近年來,隨著檢測技術進步偵測極限降低,許多藥物於環境水體中檢測出微量濃度(ng-μg/L習慣,使得自然水體中經常檢測出抗生素。本研究的目的分三部分,首先探討五種頭孢子類抗生素 (cefotaxime (CEFO), cephapirin (CFP), cephradine (CPD), cephalexin (CPN), and cefazolin (CFZ)) 於不同環境因子下 (二氧化錳濃度、目標污染物初始濃度、pH、水中陽離子),經由合成的二氧化錳 (δ-MnO2) 之化學氧化反應及轉換作用的宿命研究;其次,五個頭孢子類抗生素具有共同的主結構 (β-lactam ring),接上不同的官能基後具有不同的反應速度,本研究為探討官能基的活性對降解速度的影響;最後,鑑定最終氧化反應的副產物結構。
批次實驗結果顯示,CFZ (100 μg/L) 於合成水樣中不會被δ-MnO2氧化降解,反之CEFO、CFP、CPD及CPN (100 μg/L) 於酸性環境 (pH = 5) 中,經過48小時後分別被4 mg/L δ-MnO2氧化降解95.5%、58.4%、86.1%及28.5%,中性環境 (pH = 7) 下則無任何的降解情況 (≤5%);鹼性環境 (pH = 9) 下,CFP有明顯的水解現象。此外,水中二氧化錳濃度與抗生素濃度比例上升會加速反應速率。再者,水體中存在二價 (Mn2+, Ca2+, Mg2+),三價 (Fe3+) 陽離子,其陽離子抑制能力的權重為Mn2+ > Fe3+> Ca2+ > Mg2+,伴隨二、三價陽離子,其氧化反應抑制的情形也會隨之上升。 頭孢子類抗生素的氧化作用導因於主結構 (beta-lactam ring) 的破壞,藉此針對副產物進行定性及半定量分析。官能基的活性會影響主結構 (beta-lactam ring) 的反應性,當加入4 mg/L δ-MnO2, 99 % CEFO的官能基 (methoxyimino) 在48小時內被降解,表示該官能基在CEFO的降解過程中結構會被破壞;反觀CFP的官能基,在反應時間內不會被降解,推斷CFP在氧化過程中,該官能基結構不會被破壞。因CPD具有不穩定的dienyl官能基,在氧化反應中大部分會快速轉換成苯環(即CPN的官能基),而後被氧化降解成其他小分子,可證實CPN為CPD的中間產物。 Incorrect practices of disposing residual medicine cause potential risk for ecosystem and human health. Antibiotics, in particular, are of significant concern. Cephalosporin, which is a class of β-lactam antibiotics, is relatively resistant to enzymes and acid. With impending concern, the average occurring concentrations of cephalosporin in contamination sources are in the range of 12-6221 ng/L in Taiwan. Manganese dioxides are abundant in soils and sediment as colloidal particle. Because of strong adsorption capacity and oxidation rate, manganese dioxide (MnO2) has been reported to oxidize a wide range of organic contaminants. This study used batch experiments to investigate the oxidative transformation of five cephalosporin antibiotics (cefotaxime (CEFO), cephapirin (CFP), cephradine (CPD), cephalexin (CPN), and cefazolin (CFZ)) by MnO2 in aquatic environments and to study the effect of different environmental factors such as MnO2 loading, initial cephalosporin concentration, pH, humic acid (HA) and cations on the transformation rates. Also, the relationship between the oxidation rate and the reactivity of each substructure for CEFO and CFP are studied. Final, we will try to identify the structures of the oxidative products for each cephalosporin. In the synthetic water experiments, CFZ (100 μg/L) cannot be degraded by MnO2 while CEFO, CFP, CPD and CPN (100 μg/L) can be degraded by 4 mg/L MnO2 to 95.5%, 58.4%, 86.1% and 28.5% respectively after 48 hours reaction at pH 5. Higher MnO2 concentration increased the reaction rate of CFX and CFP. The reaction rate increases with decreasing pH from 9 to 4. The presence of dissolved cations and HA could cause inhibitive effects, and the inhibitive capacity is Mn2+ > Fe3+ > Ca2+ > Mg2+. These results demonstrated MnO2 may facilitate transformation of cephalosporin antibiotics in the natural environment. The MnO2 oxidation resulted in the opening of the beta-lactam ring and the resulting byproducts were identified and semi-quantified. The reactivity of substructures is found to affect the oxidation rate of CEFO and CFP. The substructure (methoxyimino) for CEFO has similar degradation rates at pH 5 by 4 mg/L MnO2 within 96 hrs of reaction time. We assumed that the substructure (methoxyimino) of CEFO may be the reactive site to be degraded. For the substructure (pyridinylthio) of CFP, it remained stable at pH 5 by 4 mg/L MnO2 within 48 hrs. It indicated that the pyridinylthio of CFP was probably not oxidized in the reaction of CFP oxidation. For the byproduct of CPD, due to the unstable nature of dienyl ring, most of it will be quickly transformed into phenyl ring and be decomposed into smaller fragment. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/65616 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 環境工程學研究所 |
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