不同pH溶液中四环素类抗生素与金属离子配合前后的光化学性质及毒性差异

Alteration of photochemical properties and toxicity of tetracycline antibiotics complexed with metal ions in solutions with different pH values

水环境特别是金属复合污染水体中,可酸碱解离抗生素-金属配合物是普遍存在的新污染物,但其配合形态的光化学性质和毒性却少有报道.本文考察了四环素(TC)、土霉素(OTC)两种四环素类抗生素(TCs)与金属离子Fe(Ⅲ)、Cu(Ⅱ)、Al(Ⅲ)在不同pH条件下配合前后的典型光谱学性质变化,并通过发光细菌(Vibrio fischeri)评估了配合前后体系的毒性变化.结果表明,两种TCs均能在不同解离形态下与3种金属离子发生配合,配位位点为酮基基团上的碳氧双键.TCs在碱性条件下比中性和酸性条件下更易配合,并且对3种金属离子的配合能力大小依次为Fe(Ⅲ)>Cu(Ⅱ)>Al(Ⅲ).在pH=7.0时,TCs与金属离子的配合会导致紫外吸收峰减弱甚至消失,在多数情况下使得紫外吸收光谱出现不同程度红移.这种配合反应的发生也使得抗生素在短波长处的荧光强度增大,这是因为配位作用形成了氧桥型杂多核配合物,增加了平面的刚性结构.毒性实验表明,TC与Fe(Ⅲ)、Cu(Ⅱ)配合后对Vibrio fischeri的毒性增强,与Al(Ⅲ)配合后毒性减弱,而OTC与3种金属离子配合后毒性均表现为增强.以上结果揭示了不同pH溶液中TCs与金属离子配合前后的光化学性质及毒性具有差异,这对于准确评价金属复合污染的水环境中抗生素类新污染物的光化学行为和风险具有重要意义.

The prevalence of acid-base dissociable antibiotic-metal complexes as emerging contaminants in the aquatic environment,especially in metal complex polluted waters,is well recognized.However,little information is available on the photochemical properties and toxicity of these complex forms.This study investigated the spectral properties of tetracycline(TC)and oxytetracycline(OTC)with and without metal ions Fe(Ⅲ),Cu(Ⅱ),and Al(Ⅲ)in solutions under different pH conditions.The changes in toxicity due to the complex with these metal ions were also evaluated using luminescent bacteria(Vibrio fischeri).Both TCs can form complexes with the three metal ions in different dissociation states,with the coordination site located at the carbonyl group's carbon-oxygen double bond.TCs show a higher tendency to coordinate under alkaline conditions compared to neutral and acidic conditions,and the coordination ability with the three metal ions follows the order of Fe(Ⅲ)>Cu(Ⅱ)>Al(Ⅲ).At pH=7.0,the coordination of TCs with metal ions leads to a weakening or disappearance of the ultraviolet absorption peak.This process usually results in a redshift in the ultraviolet absorption spectrum to varying degrees.This coordination reaction also increases the fluorescence intensity of antibiotics at shorter wavelengths due to the formation of oxygen-bridged hetero-polynuclear complexes by coordination,enhancing the plane's structural rigidity.Enhanced toxicity of TC upon coordination with Fe(Ⅲ)and Cu(Ⅱ)was observed,while reduced toxicity was obtained for coordination with Al(Ⅲ).OTC,on the other hand,exhibits increased toxicity upon coordination with all three metal ions.These results reveal differences in the photochemical properties and toxicity of TCs before and after coordination with metal ions in different pH solutions.This is important for accurately evaluating the photochemical behavior and risk of these antibiotics in aquatic environments contaminated with metals.