A novel sesquiterpenoid from Curcuma longa L / 药学学报

A new compound was isolated from the 95% ethanolic extract of the rhizomes of Curcuma longa L. using silica gel column chromatography, medium pressure liquid chromatography, and semi-preparative high performance liquid chromatography. The structure and absolute configuration of the compound was elucidated by HR-ESI-MS, NMR, and electronic circular dichroism (ECD) calculations. It is a novel sesquiterpenoid, which is named as isoturmeronol B (1). The carbon skeleton of compound 1 is similar to that of bisabolane-type sesquiterpenoid. The only difference is that the methyl group at C-4 in bisabolene-type sesquiterpenoid is migrated to C-5 in compound 1. Besides, the anti-inflammatory and antioxidant activities of the compound 1 were evaluated. The results showed that 1 has no anti-inflammatory and antioxidant activities.

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.