Simultaneous detection of residues of 34 beta-lactam antibiotics in livestock and fish samples through liquid chromatography-tandem mass spectrometry.

ß-Lactam is one of the widely used veterinary drugs, but simultaneous analytical methods for ß-lactam on various animal foods have not been established. In this study, we aimed to detect 34 ß-lactam antibiotics simultaneously in livestock samples (beef, pork, chicken, egg, and milk) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Samples were extracted using phosphate buffer/acetonitrile or water/acetonitrile and then cleaned with 150 mg of C18 and 900 mg of MgSO4. The method showed acceptable recovery and repeatability of 66.1-119% and 1.5-26%, respectively. The method was employed to monitor 127 real samples from the domestic market to confirm its applicability, and no ß-lactam residues were detected. It was also applied to other matrices (eel, flat fish, and shrimp) and showed acceptable recovery (62.1-120%) and repeatability (1.0-28%). The method is expected to improve the efficiency of monitoring veterinary drug residues in domestic livestock products and fishery foods.

Ligand specificity and affinity in the sulforhodamine B binding RNA aptamer.

Binding affinity and selectivity are critical properties of aptamers that must be optimized for any application. The sulforhodamine B binding RNA aptamer (SRB-2) is a somewhat promiscuous aptamer that can bind ligands that vary markedly in shape, size and charge. Here we categorize potential ligands based on their binding mode and structural characteristics required for high affinity and selectivity. Several known and potential ligands of SRB-2 were screened for binding affinity using LSPR, ITC and NMR spectroscopy. The study shows that rhodamine B has the ideal structural and electrostatic properties for selective and high-affinity binding of the SRB-2 aptamer.

Trapping a Photoelectron behind a Repulsive Coulomb Barrier in Solution.

Multiply charged anions (MCAs) display unique photophysics and solvent-stabilizing effects. Well-known aqueous species such as SO42- and PO43- experience spontaneous electron detachment or charge-separation fragmentation in the gas phase owing to the strong Coulomb repulsion arising from the excess of negative charge. Thus, anions often present low photodetachment thresholds and the ability to quickly eject electrons into the solvent via charge-transfer-to-solvent (CTTS) states. Here, we report spectroscopic evidence for the existence of a repulsive Coulomb barrier (RCB) that blocks the ejection of "CTTS-like" electrons of the aqueous B12F122- dianion. Our spectroscopic experimental and theoretical studies indicate that despite the exerted Coulomb repulsion by the nascent radical monoanion B12F12-•aq, the photoexcited electron remains about the B12F12-• core. The RCB is an established feature of the potential energy landscape of MCAs in vacuo, which seems to extend to the liquid phase highlighting recent observations about the dielectric behavior of confined water.