A time-dependent density functional theory study of a fluorescent probe to detect hydroxyl radicals: Inhibiting the twisted intramolecular charge-transfer process.

Due to the relevance to excited-state processes, sensing mechanisms of fluorescent probes were difficult to study directly by experimental methods. This work investigated theoretically the sensing mechanism of a reported bifunctional fluorescent probe to detect intracellular hydroxyl radicals and their environmental viscosity (J. Am. Chem. Soc. 2019, 141, 18301). Calculations were performed at the B3P86/TZVP/SMD level using density functional theory and time-dependent density functional theory. The transition from the ground-state (S0) to the first singlet excited state (S1) was calculated to have the largest oscillation strength for the probe. The wavelength that corresponded to the S0-S1 vertical excitation energy (427 nm) agreed well with the maximum absorption band at 400 nm in the ultraviolet-visible spectra. Theoretical results showed that the probe had two distinct geometries in the S0 and S1 states, respectively. This difference was caused by the different distributions of frontier molecular orbitals that were involved in the S0-S1 transition and corresponds to a twisted intramolecular charge transfer. The S1-state potential energy curve of the probe molecule confirmed that the twisted intramolecular charge transfer could proceed spontaneously with a potential barrier of only 12.20 kJ/mol. This result provided an irradiative approach for the probe molecule to dissipate the S1-state energy, which explained its fluorescence quenching. In contrast, the hydroxyl oxidation reaction changed frontier molecular orbitals of the probe molecule, which made its S1 state a local S1 state with a strong fluorescence emission. Precisely due to the mechanism, the hydroxyl radicals could be detected by changes in the fluorescence signal of the probe molecule.

Research progress of new antibacterial drugs that target bacterial quorum sensing systems / 药学学报

In recent years, antibiotic resistance of bacteria has become a global health crisis. Especially, the new class of "superbug" was found in South Asia, which is resistant to almost known antibiotics and causes worldwide alarm. Through the underlying mechanisms of bacterial pathogenecity, the expression of many pathogen virulence factors is regulated by the process of quorum sensing. Screening efficient quorum sensing inhibitors is an especially compelling approach to the future treatment of bacterial infections and antibiotic resistance. This article focuses on bacterial quorum sensing system, quorum sensing screening model for in vitro and evaluation of animal models in vivo, recent research of quorum sensing inhibitors and so on.

Isolation and Identification of Marine Actinomycetes with Quorum Sensing Inhibitory Activity / 微生物学通报

Quorum sensing systems of pathogens are central regulators for the expression of virulence factors. Increasing evidence implies that targeting the quorum sensing system of many pathogenic bacteria is a promising therapeutic approach to control infections. In this work,we isolated 47 strains of actinomycetes from the mud sample of Jiaozhou Bay. Quorum sensing inhibitory activity was monitored by Chromobacterium violaceum CV026. As a result,the culture broth extract of actinomycetes WA-7 was found to have significant quorum sensing inhibitory activity. This strain was assigned to the genus Streptomyces based on its 16S rDNA sequence. Further investigation revealed that the extract could inhibit the quorum sensing-controlled violacein and proteases production of C. violaceum in a concentration-dependent manner.