Sensitive monitoring of penicillin antibiotics in milk and honey treated by stir bar sorptive extraction based on monolith and LC‐electrospray MS detection

In the present study, a convenient and sensitive method for determination of six penicillin antibiotics (amoxicillin, ampicillin, penicillin G, oxacillin, cloxacillin, and dicloxacillin) in milk and honey samples was developed. Milk and honey samples were diluted with water, then directly treated by stir bar sorptive extraction based on poly (vinylimidazole‐divinylbenzene) monolithic material as coating. The analytes were analyzed by LC/ESI‐ MS/MS. Several extraction parameters including extraction and desorption time, pH value, and ionic strength in sample matrix were investigated in detail. Under the optimized extraction conditions, the calculated detection limits for the target compounds were as low as 0.23–2.66 ng/kg in milk and 0.18–1.42 ng/kg in honey, respectively. Good linearity was obtained for analytes with the correlation coefficients (R²) above 0.997. Excellent method reproducibility was achieved in terms of intraday and interday precisions, indicated by the RSDs of <5.0 and <10.0%, respectively. Finally, the proposed method was successfully applied to the determination of penicillin antibiotics residues in different milk and honey samples.     

Single-drop microextraction technique for the determination of antibiotics in environmental water

Growing concerns related to antibiotic residues in environmental water have encouraged the development of rapid, sensitive, and accurate analytical methods. Single-drop microextraction has been recognized as an efficient approach for the isolation and preconcentration of several analytes from a complex sample matrix. Thus, single-drop microextraction techniques are cost-effective and less harmful to the environment, subscribing to green analytical chemistry principles. Herein, an overview and the current advances in single-drop microextraction for the determination of antibiotics in environmental water are presented were included. In particular, two main approaches used to perform single-drop microextraction (direct immersion-single-drop microextraction and headspace-single-drop microextraction) are reviewed. Furthermore, the impressive analytical features and future perspectives of single-drop microextraction are discussed in this review.     

Determination of 38 antibiotics in raw and treated wastewater from swine farms using liquid chromatography-mass spectrometry

The present study firstly aimed at developing a multi-residue method to identify and quantify 38 veterinary antibiotics (belonging to five different classes) not only for raw swine wastewater but also for wastewater differently treated by different units. The proposed method is based on a solid-phase extraction procedure and ultra high performance liquid chromatography with mass spectrometry. For sample preparation, the optimal loading sample volume was selected as 50 mL, the pH of which was adjusted to approximately 3.0 using formic acid. Then 0.1 g/L ethylenediaminetetraacetic acid disodium salt was added. The recovery rates for different types of wastewaters were in the range of 35.94–124.51% and the relative standard deviations were in the range of 0.36–14.62%. All the matrix standard curves exhibited high linearity (0.9956–0.9999). The matrix effects for the target antibiotics ranged from –61.73 to +148.75%. To ensure the practicality of the method, we performed the detection of the actually added concentration to determine method detection limits and quantitation limits. The quantitation limits of most of the target antibiotics were 0.04 μg/L, except for spiramycin (0.1 μg/L) and roxithromycin (0.2 μg/L). This optimized and validated method was applied to analyze antibiotic residues in swine water samples from four swine farms.     

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2-aminoethyl methacrylate unit in the 4,7-positions of the BD core. Concerted charge transfer in this electron donor-acceptor-donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron-rich carboxylate guests at the thiourea receptor leads to further analyte-induced red-shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1–5×10⁵ M⁻¹ in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP-coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.     

Optical Modulation of Antibiotic Resistance by Photoswitchable Cystobactamids

The rise of antibiotic resistance causes a serious health care problem, and its counterfeit demands novel, innovative concepts. The combination of photopharmacology, enabling a light-controlled reversible modulation of drug activity, with antibiotic drug design has led to first photoswitchable antibiotic compounds derived from established scaffolds. In this study, we converted cystobactamids, gyrase-inhibiting natural products with an oligoaryl scaffold and highly potent antibacterial activities, into photoswitchable agents by inserting azobenzene in the N-terminal part and/or an acylhydrazone moiety near the C-terminus, yielding twenty analogs that contain mono- as well as double-switches. Antibiotic and gyrase inhibition properties could be modulated 3.4-fold and 5-fold by light, respectively. Notably, the sensitivity of photoswitchable cystobactamids towards two known resistance factors, the peptidase AlbD and the scavenger protein AlbA, was light-dependent. While irradiation of an analog with an N-terminal azobenzene with 365 nm light led to less degradation by AlbD, the AlbA-mediated inactivation was induced. This provides a proof-of-principle that resistance towards photoswitchable antibiotics can be optically controlled.     

Late-Stage Modification of Aminoglycoside Antibiotics Overcomes Bacterial Resistance Mediated by APH(3’) Kinases

The continuous emergence of antimicrobial resistance is causing a threat to patients infected by multidrug-resistant pathogens. In particular, the clinical use of aminoglycoside antibiotics, broad-spectrum antibacterials of last resort, is limited due to rising bacterial resistance. One of the major resistance mechanisms in Gram-positive and Gram-negative bacteria is phosphorylation of these amino sugars at the 3’-position by O-phosphotransferases [APH(3’)s]. Structural alteration of these antibiotics at the 3’-position would be an obvious strategy to tackle this resistance mechanism. However, the access to such derivatives requires cumbersome multi-step synthesis, which is not appealing for pharma industry in this low-return-on-investment market. To overcome this obstacle and combat bacterial resistance mediated by APH(3’)s, we introduce a novel regioselective modification of aminoglycosides in the 3’-position via palladium-catalyzed oxidation. To underline the effectiveness of our method for structural modification of aminoglycosides, we have developed two novel antibiotic candidates overcoming APH(3’)s-mediated resistance employing only four synthetic steps.     

固相萃取–高效液相色谱法测定地表水中4种磺胺类抗生素

建立固相萃取–高效液相色谱法测定地表水中磺胺嘧啶、磺胺二甲嘧啶、磺胺氯哒嗪、醋磺胺甲恶唑4种磺胺类抗生素。样品采用HLB柱进行萃取富集,流动相为甲醇–水(体积比为20∶80),流量为0.5 m L/min,用SPD检测器检测,检测波长为270 nm;采用外标法定量。4种磺胺类抗生素质量浓度在4~160 ng/L范围内与色谱峰面积的线性关系良好,相关系数不低于0.998 2,方法检出限为1.0~1.7 ng/L,样品加标回收率为75.2%~97.4%,测定结果的相对标准偏差为2.8%~6.1%(n=7)。该方法操作简便,灵敏度高,可用于地表水中磺胺类抗生素的检测。     

Mannose‐Binding Geometry of Pradimicin A

Pradimicins (PRMs) and benanomicins are the only family of non‐peptidic natural products with lectin‐like properties, that is, they recognize D ‐mannopyranoside (Man) in the presence of Ca²⁺ ions. Coupled with their unique Man binding ability, they exhibit antifungal and anti‐HIV activities through binding to Man‐containing glycans of pathogens. Notwithstanding the great potential of PRMs as the lectin mimics and therapeutic leads, their molecular basis of Man recognition has yet to be established. Their aggregate‐forming propensity has impeded conventional interaction analysis in solution, and the analytical difficulty is exacerbated by the existence of two Man binding sites in PRMs. In this work, we investigated the geometry of the primary Man binding of PRM‐A, an original member of PRMs, by the recently developed analytical strategy using the solid aggregate composed of the 1:1 complex of PRM‐A and Man. Evaluation of intermolecular distances by solid‐state NMR spectroscopy revealed that the C2–C4 region of Man is in close contact with the primary binding site of PRM‐A, while the C1 and C6 positions of Man are relatively distant. The binding geometry was further validated by co‐precipitation experiments using deoxy‐Man derivatives, leading to the proposal that PRM‐A binds not only to terminal Man residues at the non‐reducing end of glycans, but also to internal 6‐substituted Man residues. The present study provides new insights into the molecular basis of Man recognition and glycan specificity of PRM‐A.