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离子液体应用的潜在隐患不容忽视

发布时间:2014-05-03 17:31:54        阅读次数:

关于离子液体的应用前景,《科学时报》2010年08月04日曾经有专门报道——“离子液体应用孕育新突破 规模化应用前景光明”。离子液体作为一种全新的功能化介质和材料,已在材料、化工、生物质、电化学等诸多领域展现了良好的应用前景,其应用领域也从化学制备扩展到了环境科学、材料科学和工程技术等领域。化学工业是国民经济的支柱产业,但传统化学工业存在能耗高、物耗高、污染严重等问题。实践证明,新型介质的出现往往能够产生工艺过程的重大革新,从而大幅度降低能耗、物耗和污染。离子液体作为一种新型介质,为节能减排及实现物质温和转化提供了新的途径。离子液体已引起国内外的广泛关注,目前(2010年前后)相关研究论文接近每年3000篇,离子液体产品的专利近千篇,已逐渐成为国际化学化工领域的研究前沿和热点。离子液体之所以在众多领域得到越来越广泛的应用,源于其具有独特的物理化学性质,例如液态温度范围宽、几乎可忽略的挥发性、电化学窗口宽,尤其是其性质可调。对其微观结构与物理化学性质之间定量关系的全面掌握、调控及建立相关性质的计算模型,是离子液体筛选、设计以及获得工业化应用的前提。离子液体或作为“绿色”介质,或作为催化材料,或二者兼而有之。离子液体向工业化推进的速度以及所展现的巨大潜力仍令人鼓舞。在生物质能源利用方面,研究表明离子液体对于纤维素的溶解处理具有良好的效果,开发新型、低毒、价廉且高效溶解纤维素的离子液体成为该领域的重要研究内容。在能源及环境方面,采用离子液体可以对二氧化碳进行高效、高选择性、环境友好的捕集或固定。离子液体还可作为新型材料、润滑剂等,它的研究与开发对国家能源及国防安全具有重要意义。

有分析认为,未来10年(2010-2020)全球离子液体需求将大幅增长,2020年的销售额将从当前(2010年)的约3亿美元强劲增长至34亿美元。目前,离子液体已在聚合反应、选择性烷基化和胺化反应、酰基化反应、酯化反应、催化加氢反应、烯烃的环氧化反应、电化学合成、支链脂肪酸的制备等方面显示出应用成效和优势,如反应速度快、转化率和选择性高、催化剂可循环重复利用等优点。将来,离子液体可能实现大规模应用或引领高新技术发展的方向还有溶剂萃取、物质的分离和纯化、废旧高分子化合物的回收、燃料电池和太阳能电池、工业废气中二氧化碳的提取、核燃料和核废料的分离与处理等。就在离子液体应用研究如火如荼之时,我们万万不可忘记,任何事物都是具有两面性,利与弊是孪生体。我们在利用利之时,不要忘记其可能存在的弊端。

天津大学的毛大庆和南开大学的罗义等人的研究结果,就对我们开展离子液体应用给出了一个令人吃惊的提醒。

罗义(南开大学环境科学与工程学院教授)

据美国化学会《化学与工程新闻》(C&EN)周刊网站2014年4月30日报道,我国南开大学环境科学与工程学院教授罗义(Yi Luo音译)博士和天津大学环境科学与工程学院毛大庆(Daqing Mao音译)等人的研究结果表明,离子液体作为绿色化学的环境友好型溶剂,可以替代传统的溶剂特别是挥发性有机溶剂。但是它的使用也有令人担忧的一面,增加细菌细胞膜的渗透性,有助于抗性基因在微生物之间的转移或传播。图1是提升抗性的离子液体的结构式其化学名称为1-butyl-3-methylimidazolium hexafluorophosphate 翻译成中文为1-丁基-3-甲基六氟磷酸盐咪唑鎓或者1-丁基-3-甲基咪唑六氟磷酸盐,通过该离子液体可以提升抗生素抗性基因在细菌之间的转移。

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FIG. 1 Raising Resistance

The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, enhances the transfer of antibiotic resistance genes among bacteria.

Credit: grhowes/Wikipedia

绿色和可持续发展化学领域的一些研究者已经提出在工业反应中使用离子液体溶剂来取代挥发性有机溶剂。这些有机盐的绝大多数并不挥发,所以它们被吹捧为是替代传统溶剂的一种安全而环境友好型溶剂。但罗义等人的一项新的研究表明,当它们被释放到环境中时,可能会产生其自身的一些问题。罗义等人的研究报告指出,一种离子液体有助于细菌共享一种抗生素抗性基因,导致该基因在微生物之间繁殖,相关研究结果已经在《环境科技快报》(Environ. Sci. Tech. Lett., DOI: 10.1021/ez500103v)——Yi Luo, Qing Wang, Qian Lu, Quanhua Mu, and Daqing Mao. An Ionic Liquid Facilitates the Proliferation of Antibiotic Resistance Genes Mediated by Class I Integrons(可以免费下载). Environ. Sci. Tech. Lett., DOI: 10.1021/ez500103v, Publication Date (Web): April 17, 2014.

对于离子液体人们提出的环境优势之一就是其大多数并不排放有害的挥发性有机化合物(简称VOCs)。然而,环境科学家近期已经开始研究,离子液体被处理后究竟会如何影响生态系统。天津大学(Tianjin University )的环境工程师毛大庆和他的同事,最近研究了离子液体对细菌的毒性。当他们将离子液体溶剂添加到微生物体系中时,他们意外发现抗生素抗性基因的水平明显飙升。

通常情况下,科学家指出抗生素的广泛使用,在细菌之间会成为增加细菌对抗生素抗性基因的主要途径,这可能导致危险,酿成无法治愈的感染。但某些化学物质(包括清洁剂和杀虫剂)可以增强这种细胞繁殖而导致扩散。所以毛大庆的团队想看看离子液体是否也有同样的效果。为此目的,该团队用从天津的城市公园收集的水装满玻璃瓶,并添加一种常用的离子液体即1-丁基-3-甲基六氟磷酸盐咪唑鎓(1-butyl-3-methylimidazolium hexafluorophosphate),使其浓度达到2.5 g/L。然后研究人员对其在为期两周之内进行取样,从样品中提取DNA,使用定量聚合酶链反应(quantitative polymerase chain reaction)对其进行分析。分析结果表明,同样是天津城市公园的水样,加入离子液体的和没有加入离子液体的水样进行比较,加入离子液体的水样中抗生素磺酰胺(antibiotic sulfonamide)的抗性基因是尚未加入离子液体水样的500倍。而且加入离子液体的水样中,一种基因编码整合子(a gene encoding an integron)的浓度更高,这种整合子是一种在细菌之间可以移动的遗传单位,它可以促进细菌之间的水平基因转移。当科学家们在对添加了离子液体的水样中分离的菌株进行DNA测序时,他们发现这种整合子携带抗性基因(resistance gene),而且有助于其在细菌之间跳跃。

为了确定离子液体对整合子调节基因转移会产生多么强烈的影响,研究人员将从天津城市公园收集的细菌,即没有携带整合子基因的细菌与其接触,包括含有离子液体的培养液和不含离子液体的培养液,研究结果显示在含有离子液体的培养液中,抗生素抗性基因转移(antibiotic resistance gene transfer)比不含离子液体培养液中的相应转移高88倍。毛大庆的研究团队认为,离子液体可能增强基因转移,使细菌细胞膜更容易渗透所致。为了检验他们的假设,他们对该细菌添加了一种染料,来表明细胞膜的渗透性和使用流式细胞术(flow cytometry)来检测它们。用离子液体处理过的细菌的细胞膜渗透性要比未经处理的细菌的细胞膜渗透性高得多,超过230%。

美国弗吉尼亚理工大学(Virginia Tech)环境工程师艾米·普鲁登(Amy Pruden)对此谈到:她从来没有猜想到离子液体会刺激抗生素耐药性。称之为化学品环境友好能够暗示将其从下水道排放就可以万事大吉,安然无事吗?看来实际情况并非那么简单,任何事物都有利与弊的两面性,环境友好型化学品同样也不例外,对其利的一面过分看重的同时,也不可以忽视存在弊的一面,目前对于离子液体的认识,对于弊的一面可能有所忽视,毛大庆等人的研究结果已经证明,离子液体仍然存在一定的环境风险,尤其是在废水处理厂会产生一些问题,控制抗生素抗性基因的传播成为关键。艾米·普鲁登说:“我们在开始广泛使用离子液体之前,看看这些问题才是最理想的。”不要等到问题成了堆才来找解决问题的办法,未雨绸缪总是比亡羊补牢更胜一筹。更多信息请浏览原文——An Ionic Liquid Facilitates the Proliferation of Antibiotic Resistance Genes Mediated by Class I Integrons。或者浏览下文:

 

Latest News
Web Date: April 30, 2014
 

ionic liquids Could Enhance Spread Of Antibiotic Resistance Genes

Green Chemistry: One of the alternative solvents increases the permeability of bacteria cell membranes, helping resistance genes to jump from microbe to microbe
 
Department: Science & Technology | Collection: Green Chemistry, Life Sciences 
News Channels: Environmental SCENE, Biological SCENE
Keywords: antibiotic resistance, volatile organic solvents, industrial chemistry, ionic liquids
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[URL]a14082eac015c2da38d67624ddd7ed34.jpg

 
Raising Resistance
The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, enhances the transfer of antibiotic resistance genes among bacteria.
Credit: grhowes/Wikipedia
Some researchers in the field of green and sustainable chemistry have proposed replacing volatile organic solvents in industrial reactions with a class of solvents called ionic liquids. Most of these organic salts are not volatile, so they have been touted as a safe, environmentally friendly alternative to conventional solvents. But a new study shows that they could create problems of their own when released into the environment. Chinese researchers report that one ionic liquid helps bacteria share an antibiotic resistance gene, causing the gene to proliferate among the microbes (Environ. Sci. Tech. Lett., DOI: 10.1021/ez500103v).
One proposed environmental advantage for ionic liquids is that most don’t emit harmful volatile organic compounds (VOCs). However, environmental scientists have only recently begun to study how these solvents might affect ecosystems after they’re disposed of. Daqing Mao, an environmental engineer at Tianjin University in China, and his colleagues recently investigated the toxicity of the solvents in bacteria. When they added the solvent to the microbes, they noticed that the levels of antibiotic resistance genes spiked unexpectedly.
Normally, scientists point to widespread usage of antibiotics as the main pathway for the increase in antibiotic resistance genes among bacteria, which can lead to dangerous, untreatable infections. But some chemicals, including detergents and pesticides, can enhance this proliferation. So Mao’s team wanted to see if the ionic liquids had the same effect.
To do this, the team filled flasks with water collected from an urban park in Tianjin, and added a commonly used ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, to some of the flasks at levels up to 2.5 g/L. Then they sampled the flasks over a period two weeks, extracting the DNA from the samples and analyzing it using quantitative polymerase chain reaction.
A resistance gene to the antibiotic sulfonamide was up to 500 times more abundant in flasks treated with the ionic liquid than in flasks with just the park water. The treated flasks also had much higher concentrations of a gene encoding an integron, a mobile genetic unit that facilitates horizontal gene transfer among bacteria. When the scientists sequenced the DNA in bacterial strains isolated from the treated samples, they found that the integron carried the resistance gene, helping it hop between bacteria.
To determine just how strong an effect the ionic liquid had on integron-mediated gene transfer, the team exposed bacteria collected from the park that did not carry the integron gene to bacteria that did. Cultures that included the ionic liquid showed 88-fold higher antibiotic resistance gene transfer than cultures without the solvent.
Mao’s team thought the ionic liquid might enhance gene transfer by making the bacteria’s cell membranes more permeable. To test their hypothesis, they added a dye to the bacteria that indicates the permeability of cell membranes and examined them using flow cytometry. The membranes of ionic-liquid-treated bacteria were 230% more permeable than untreated ones.
“I would never have guessed that ionic liquids stimulate antibiotic resistance,” says Amy Pruden, an environmental engineer atVirginia Tech. Calling chemicals environmentally friendly can imply that it is fine to dump them down the drain, she says. But the study suggests that ionic liquids could create problems in wastewater treatment plants, which are critical points for controlling the spread of antibiotic resistance genes. “It’s ideal to look at these issues before we start using ionic liquids widely,” she says.
 
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