Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment

Characterization Techniques of Polymer Aging: From Beginning to End

Polymers have been widely applied in various fields in the daily routines and the manufacturing. Despite the awareness of the aggressive and inevitable aging for the polymers, it still remains a challenge to choose an appropriate characterization strategy for evaluating the aging behaviors. The difficulties lie in the fact that the polymer features from the different aging stages require different characterization methods. In this review, we present an overview of the characterization strategies preferable for the initial, accelerated, and late stages during polymer aging. The optimum strategies have been discussed to characterize the generation of radicals, variation of functional groups, substantial chain scission, formation of low-molecular products, and deterioration in the polymers' macro-performances. In view of the advantages and the limitations of these characterization techniques, their utilization in a strategic approach is considered. In addition, we highlight the structure-property relationship for the aged polymers and provide available guidance for lifetime prediction. This review could allow the readers to be knowledgeable of the features for the polymers in the different aging stages and provide access to choose the optimum characterization techniques. We believe that this review will attract the communities dedicated to materials science and chemistry.

Isothiazolone-Nitroxide Hybrids with Activity against Antibiotic-Resistant Staphylococcus aureus Biofilms

Isothiazolones are widely used as biocides in industrial processing systems and personal care products, but their use to treat infections in humans has been hampered by their inherent cytotoxicity. Herein, we report a strategy to alleviate isothiazolone toxicity and improve antibacterial and antibiofilm potency by functionalization with a nitroxide moiety. Isothiazolone-nitroxide hybrids 6 and 22 were prepared over three steps in moderate yields (58 and 36%, respectively) from (Z)-3-(benzylsulfanyl)-propenoic acid. Hybrid 22 displayed better activity (minimum inhibitory concentration (MIC) = 35 μM) than the widely used methylisothiazolinone (MIT 1, MIC = 280 μM) against methicillin-susceptible Staphylococcus aureus (MSSA). Hybrid 22 was even more active against drug-resistant strains, such as vancomycin-resistant Staphylococcus aureus (VRSA, MIC = 8.75 μM) over MIT 1 (MIC = 280 μM). The enhanced antibacterial activity of hybrid 22 over MIT 1 was retained against established MSSA and VRSA biofilms, with minimum biofilm eradication concentration (MBEC) values of 35 and 70 μM, respectively, for 22 (the MBEC value for MIT 1 against both strains was ≥280 μM). No toxicity was observed in human epithelial T24 cells treated with hybrid 22 in concentrations up to 560 μM using a lactate dehydrogenase assay.

Perylene diimides: will they flourish as reaction-based probes?

Perylene diimides (PDI) are a well-studied class of functional organic dyes, and in recent years, they have been accepted as promising scaffolds for the design of small molecule/polymer-based chromogenic and fluorogenic reaction-based-probes because of their strong absorption combined with high fluorescence quantum yield in organic solvents, low reduction potential, good electron-acceptor properties, and broad color range properties. Undoubtedly, the intrinsically poor solubility of PDI-based derivatives in water greatly hampers their exploitation as reaction-based probes; however, a vast array of functionalizations now offer design strategies that have resulted in >50% solubility of PDI derivatives in water. A chemodosimeter, wherein chemical transformation is achieved by specific reactions, affords naked-eye visibility, fast response time, sensitivity, ratiometric response, and low cost. The present review focuses on the progress of PDI-based chemodosimeters achieved so far since the inception of this member in the rylene diimide family. This comprehensive review may facilitate the development of more powerful chemodosimeters based on PDI for broad and exciting applications in the future.

Profluorescent Fluoroquinolone-Nitroxides for Investigating Antibiotic⁻Bacterial Interactions

Fluorescent probes are widely used for imaging and measuring dynamic processes in living cells. Fluorescent antibiotics are valuable tools for examining antibiotic⁻bacterial interactions, antimicrobial resistance and elucidating antibiotic modes of action. Profluorescent nitroxides are 'switch on' fluorescent probes used to visualize and monitor intracellular free radical and redox processes in biological systems. Here, we have combined the inherent fluorescent and antimicrobial properties of the fluoroquinolone core structure with the fluorescence suppression capabilities of a nitroxide to produce the first example of a profluorescent fluoroquinolone-nitroxide probe. Fluoroquinolone-nitroxide (FN) 14 exhibited significant suppression of fluorescence (>36-fold), which could be restored via radical trapping (fluoroquinolone-methoxyamine 17) or reduction to the corresponding hydroxylamine 20. Importantly, FN 14 was able to enter both Gram-positive and Gram-negative bacterial cells, emitted a measurable fluorescence signal upon cell entry (switch on), and retained antibacterial activity. In conclusion, profluorescent nitroxide antibiotics offer a new powerful tool for visualizing antibiotic⁻bacterial interactions and researching intracellular chemical processes.

Biological Relevance of Free Radicals and Nitroxides

Nitroxides are stable, kinetically-persistent free radicals which have been successfully used in the study and intervention of oxidative stress, a critical issue pertaining to cellular health which results from an imbalance in the levels of damaging free radicals and redox-active species in the cellular environment. This review gives an overview of some of the biological processes that produce radicals and other reactive oxygen species with relevance to oxidative stress, and then discusses interactions of nitroxides with these species in terms of the use of nitroxides as redox-sensitive probes and redox-active therapeutic agents.

New reagents for detecting free radicals and oxidative stress

Free radicals and oxidative stress play important roles in the deterioration of materials, and free radicals are important intermediates in many biological processes. The ability to detect these reactive species is a key step on the road to their understanding and ultimate control. This short review highlights recent progress in the development of reagents for the detection of free radicals and reactive oxygen species with broad application to materials science as well as biology.