Key Laboratory of Western China's Environmental Systems (Ministry of Education), Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
Key Laboratory of Western China's Environmental Systems (Ministry of Education), Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
Environ Pollut. 2019 May;248:815-822. doi: 10.1016/j.envpol.2019.02.077. Epub 2019 Feb 28.
Fluoroquinolone antibiotics (FQs) are considered to be emerging environmental contaminants that have been detected extensively in aquatic environment. It is of quite importance to explore FQs interacting with dissolved organic matter (DOM). The interactions of FQs with DOM were examined by nuclear magnetic resonance (NMR) spectroscopy, fluorescence quenching, UV-vis, Fourier transform infrared (FT-IR) spectroscopic techniques. The bindings of FQs to DOM had one single binding site and their quenching mechanisms were static, which were evaluated by the Stern-Volmer and Site-binding equations. Addition of DOM could result in micro-environmental changes of fluorophores groups in FQs. The location adjacent oxygen right of Ofloxacin (OFL) and the aromatic ring (the adjacency replaced by two nitrogen-containing groups) of Ciprofloxacin (CIP), Enrofloxacin (ENR), Norfloxacin (NOR) might be highly affected by DOM molecule. The negative enthalpy change (ΔH), negative entropy change (ΔS) and the positive Gibbs' energy change (ΔG) figured out that the binding processes were exothermic but not thermodynamic favorable, the formation of HA-FQs complexes would be powered chiefly by the ΔS. H-bonding, electrostatic effect, van der Waals force were the acting force in the binding reactions and the π-π stacking effect was the major binding force under alkaline conditions. Moreover, the protonated, deprotonated, or partially protonated state of FQs were found to have different binding capacity to DOM, and the binding reactions for FQs-HA system were suppressed as the ionic strength increased. Meanwhile, alterations of FQs conformation in the presence of DOM were evaluated by FT-IR and UV-vis spectra.
氟喹诺酮类抗生素（FQs）被认为是新兴的环境污染物，已在水生环境中广泛检出。因此，研究 FQs 与溶解有机质（DOM）的相互作用具有重要意义。本研究采用核磁共振（NMR）光谱、荧光猝灭、紫外-可见光谱（UV-vis）、傅里叶变换红外（FT-IR）光谱技术考察了 FQs 与 DOM 的相互作用。结果表明，FQs 与 DOM 之间存在单一结合位点，猝灭机制为静态猝灭，通过 Stern-Volmer 和 Site-binding 方程对其进行了评估。DOM 的添加会导致 FQs 荧光团基团的微环境发生变化。Ofloxacin（OFL）中邻位氧原子和 Ciprofloxacin（CIP）、Enrofloxacin（ENR）、Norfloxacin（NOR）中被两个含氮基团取代的芳环的位置可能会受到 DOM 分子的强烈影响。负的焓变（ΔH）、负的熵变（ΔS）和正的吉布斯自由能变（ΔG）表明，结合过程是放热的，但不是热力学有利的，HA-FQs 配合物的形成主要由ΔS 驱动。氢键、静电作用、范德华力是结合反应的作用力，在碱性条件下，π-π 堆积作用是主要的结合力。此外，发现 FQs 的质子化、去质子化或部分质子化状态对 DOM 具有不同的结合能力，随着离子强度的增加，FQs-HA 体系的结合反应受到抑制。同时，通过 FT-IR 和 UV-vis 光谱评估了 DOM 存在下 FQs 构象的变化。
