Influence of Cations on the Fluorescence Quenching of an Ionic, Sterically Congested Pyrenyl Moiety by Iodide in Water

Horizontal comparison of "red or blue shift" and binding energy of six fluoroquinolones: Fluorescence quenching mechanism, theoretical calculation and molecular modeling method

In this article, the interaction between six fluoroquinolones (FQs) and bovine serum albumin (BSA) was initially studied at 298 K, 303 K and 310 K respectively under simulated physiological conditions by fluorescence spectroscopy. At the same time, the sub-structural domains on BSA that may bind to FQs were investigated by molecular docking simulation technique. A combination of quantitative and qualitative approaches was used in the analysis of the binding constants, binding sites and corresponding thermodynamic parameters in the interaction system, it was found that FQs forms a complex with BSA and undergoes static quenching, which is the main cause of fluorescence quenching. The results indicated that hydrogen bonds, Van der Waals force and electrostatic interaction were the main binding forces between the complexes, it also showed that these six fluoroquinolones mainly bound to the IIA and IIIA structural domains of BSA, while DANO and SARA may be more toxic than other antibiotics. Based on Foster's non-radiative energy transfer theory, the binding distance between FQs and BSA was calculated to be less than 7 nm, indicating the existence of energy transfer between small molecule drugs and proteins. Synchronous fluorescence and UV-Vis absorption spectroscopy further confirmed that FQs can alter the secondary conformational change of BSA. Lomefloxacin has a different effect from the other five fluoroquinolone antibiotics because it causes a decrease in polarity and an increase in hydrophobicity around tryptophan residues, while the other five FQs have the opposite effect. Together, the study of FQs-BSA is of great significance to elucidate the pharmacokinetics and pharmacodynamics of FQs.

Aggregation-Induced Emission Boosting the Study of Polymer Science

The past one hundred years witness the great development of polymer science. The advancement of polymer science is closely related with the developing of characterization techniques and methods, from viscometry in molecular weight determination to advanced techniques including differential scanning calorimetry, nuclear magnetic resonance and scanning electron microscopy. However, these techniques are normally constrained to tedious sample preparation, high cost, harsh experimental condition, or ex-situ characterization. Fluorescence technology has the merits of high sensitivity and direct visualization. Contrary to conventional aggregation-causing quenching fluorophores, those dyes with aggregation-induced emission characteristic show high emission efficiency in aggregate states. Based on the restriction of intramolecular motions for AIE properties, the AIE materials are very sensitive to the surrounding microenvironments owing to the twisted propeller-like structures and therefore reveal great potentials in polymer's study. The AIE concept has been successfully used in polymer's study and provides us a deeper understanding on polymer structure and properties. In this review, the applications of AIEgens in polymer science for visualizing polymerization, glass transition, dissolution, crystallization, gelation, self-assembly, phase separation, cracking and self-healing were exemplified and summarized. Lastly, the challenges and perspectives in the study of polymer science using AIEgens are addressed. This article is protected by copyright. All rights reserved.

In Situ Monitoring of RAFT Polymerization by Tetraphenylethylene-Containing Agents with Aggregation-Induced Emission Characteristics

A facile and efficient approach is demonstrated to visualize the polymerization in situ. A group of tetraphenylethylene (TPE)-containing dithiocarbamates were synthesized and screened as agents for reversible addition fragmentation chain transfer (RAFT) polymerizations. The spatial-temporal control characteristics of photochemistry enabled the RAFT polymerizations to be ON and OFF on demand under alternating visible light irradiation. The emission of TPE is sensitive to the local viscosity change owing to its aggregation-induced emission characteristic. Quantitative information could be easily acquired by the naked eye without destroying the reaction system. Furthermore, the versatility of such a technique was well demonstrated by 12 different polymerization systems. The present approach thus demonstrated a powerful platform for understanding the controlled living radical polymerization process.