碳酸氫根離子對於TiO2光催化降解抗癌藥物之影響−機制、反應性及毒性變化探討

The role of bicarbonate anions in antineoplastic agents degradation via TiO2 photocatalytic process: mechanisms, reactivity and change in toxicity

賴威博(Webber Wei-Po Lai)

指導教授 ： 林郁真

國立臺灣大學/工學院/環境工程學研究所/博士(2016年)

https://doi.org/10.6342/NTU201700961

摘要

近十幾年來，水體中藥物殘留已成為熱烈關切之環境議題，其中尤以抗癌藥物特別受關注。抗癌藥物無法經由傳統污水處理設施有效去除，亦因其對生態環境及人類健康具有潛在衝擊，故本研究探討用紫外光結合二氧化鈦光觸媒之光催化處理程序以降解三種最為廣泛使用之抗癌藥物：異環磷酰胺、環磷酰胺及氨甲喋呤。此外，由於碳酸氫根離子為污水及自然水體中主要成分之一，故本研究亦探討碳酸氫根離子於二氧化鈦光催化降解抗癌藥物過程所扮演之角色及其對光催化程序之影響：針對反應機制、降解中間產物及降解途徑、反應性及毒性變化(使用Microtox®生物急毒性分析儀)進行深入探討。
在最佳光催化操作條件下(目標抗癌藥物為100 μg/L、二氧化鈦為100 mg/L、溶液pH值為5.5)，異環磷酰胺能於10分鐘內被完全去除(擬一階反應速率常數為0.433 min−1)。而碳酸氫根離子存在之光催化系統(UV/TiO2/HCO3–)對於三種目標抗癌藥物之降解速率呈現相反結果之影響：異環磷酰胺及環磷酰胺之降解速率減緩(異環磷酰胺：半衰期由1.2 min延緩至3.5 min；環磷酰胺：半衰期由1.1 min延緩至6.9 min)；相反地，碳酸氫根離子之存在使得氨甲喋呤降解加速(半衰期由13.8 min縮短至1.8 min)，此結果指出碳酸根自由基參與光催化反應。氨甲喋呤對於碳酸根自由基及氫氧自由基之二階反應速率常數經估算分別為1.4 × 107 M–1 s–1及 8.7 × 109 M–1 s–1。抑制劑實驗(添加t-BuOH、i-PrOH及KI於光催化系統)結果顯示，價帶電洞及氫氧自由基皆會造成碳酸根自由基之產生。
抗癌藥物經降解後，不完全的礦化結果顯示目標藥物轉變為中間產物存在於溶液中。本研究針對異環磷酰胺、環磷酰胺及氨甲喋呤之降解中間產物進行鑑定，並提出此三種抗癌藥物之降解途徑。異環磷酰胺及環磷酰胺遵循非常類似之降解及斷鍵途徑，包含酮化、斷碳氯鍵、斷磷氮鍵及斷碳氮鍵(脫氯乙基)；氯離子釋放非常可能為首步、亦為主要降解途徑。而氨甲喋呤遵循氧原子加成、羥化、脫胺基、斷碳碳鍵及斷碳氮鍵之降解途徑；斷苯胺結構上的碳氮鍵為主要降解途徑，進而產生氨基喋呤(產率為43%)。然而，碳酸氫根離子之存在使得光催化降解途徑及毒性生成產生改變。對於異環磷酰胺及環磷酰胺而言，於UV/TiO2/HCO3–系統中偵測出兩種新副產物N1 (分子量為197)及N2 (分子量為101)；毒性試驗結果亦指出於六小時反應時間內有毒性產生，而相較於UV/TiO2系統，UV/TiO2/HCO3–將產生更高的毒性。對於氨甲喋呤而言，UV/TiO2/HCO3–系統所產生之碳酸根自由基將優先與氨甲喋呤所具有之4-氨基苯甲酰胺(ABZ)官能基反應，進而於較後期反應階段產生有毒副產物(於UV/TiO2系統並未發現此毒性生成現象)。三種氨甲喋呤子結構反應性如下：ABZ>>DHP>>LG~0 (UV/TiO2/HCO3–系統)；ABZ~DHP>LG (UV/TiO2系統) (DHP：二氨基蝶啶；LG：L-谷氨酸)，再次證實碳酸根自由基具有選擇性及專一性。本研究結果顯示，當應用光催化程序進行水處理時，碳酸氫根離子之影響不容忽視。由於廢水中可能包含各種具ABZ官能基結構之藥物，由碳酸氫根離子所導致毒性上升現象亦可能會發生於其他同以氫氧自由基為主要反應物種之高級氧化處理程序中。

關鍵字

抗癌藥物 ； 二氧化鈦光觸媒 ； 碳酸氫根離子 ； 碳酸根自由基 ； 降解中間產物 ； 毒性

並列摘要

The issues involved with the presence of pharmaceutical residues in aqueous environments have gained increasing environmental attention over the past decade. Antineoplastic agents are of special concern because of their incomplete removal through conventional wastewater treatment and their potential effects on ecosystems and human health. The aim of this study was to investigate the UV/TiO2 photocatalytic process to decompose ifosfamide, cyclophosphamide and methotrexate, which are three commonly prescribed antineoplastic agents. Additionally, because bicarbonate anions (HCO3−) are a major constituent in wastewater and natural water matrices, the role and effect of HCO3− in the degradation of antineoplastic agents via UV/TiO2 were also investigated. The reaction mechanism, byproduct formation and pathways, reactivity and change in toxicity (by Microtox® acute toxicity test) during the photocatalytic process were comprehensively explored.
Ifosfamide was completely removed within 10 min in the UV/TiO2 system (the pseudo-first-order rate constant k = 0.433 min−1) under the following optimal conditions: ifosfamide = 100 μg/L, TiO2 = 100 mg/L, and solution pH = 5.5. In the presence of HCO3− (UV/TiO2/HCO3− system), the degradation rates of ifosfamide, cyclophosphamide and methotrexate exhibited contrasting outcomes: the rates of ifosfamide and cyclophosphamide were retarded (t1/2 was prolonged from 1.2 to 3.5 min and from 1.1 to 6.9 min, respectively). However, the addition of HCO3− enhanced methotrexate degradation (t1/2 was shortened from 13.8 to 1.8 min). The results indicate the involvement of •CO3− in the photocatalytic reaction. The estimated second-order rate constants of methotrexate with •CO3− and •OH were 1.4 × 107 M–1 s–1 and 8.7 × 109 M–1 s–1, respectively. The scavenger experiment (by addition of t-BuOH, i-PrOH and KI) results indicate that both valence hole (hvb+) and •OH result in the generation of •CO3−.
The results show antineoplastic agent degradation with incomplete mineralization, which indicates that the parent compounds were transformed into byproducts. Photocatalytic byproducts of ifosfamide, cyclophosphamide and methotrexate were identified, and degradation pathways were proposed. Ifosfamide and cyclophosphamide follow notably similar pathways and bond-breaking processes, such as ketonization and breaking of the C–Cl, P–N and C–N bonds (N-dechloroethylation). Chloride (Cl−) release is likely the first and primary step in the decomposition process. Methotrexate proceeds transformation pathways including the addition of atomic oxygen, hydroxylation, deamination, C–C and C–N cleavage; C–N cleavage at the aniline moiety is the primary decomposition pathway, which causes an aminopterin yield of 43%. However, the presence of HCO3− results in a change in photocatalytic degradation pathways and toxicity. For ifosfamide and cyclophosphamide, two new byproducts N1 (M.W. = 197) and N2 (M.W. = 101) were detected in the UV/TiO2/HCO3− system; the toxicity tests showed that higher toxicity occurred in the presence of HCO3− during the UV/TiO2 treatment and within 6 h of reaction time. On the other hand, for methotrexate, the •CO3− that was generated in the UV/TiO2/HCO3− system preferentially reacted with the 4-aminobenzamide (ABZ) moiety and generated toxic byproducts during the later stages of decomposition, which was not observed in the UV/TiO2 system. The reactivity of the three methotrexate substructures decreased in the following order in the presence of HCO3−: ABZ>>DHP>>LG~0. However, without HCO3−, the following order was observed: ABZ~DHP>LG (DHP: diamino-pteridine; LG: L-glutamic acid), which reconfirms the selectivity and specificity of •CO3−. The results of this work suggest that the effects of HCO3− should not be ignored when the photocatalytic treatment is applied to treat actual wastewater. The increase in toxicity induced by the presence of HCO3− likely occurs in many other •OH-based advanced oxidation processes in wastewater that contains pharmaceutical cocktails with ABZ moieties.

並列關鍵字

Antineoplastic agents ； TiO2 photocatalysis ； Bicarbonate ； Carbonate radical ； Degradation byproducts ； Toxicity

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