AbstractAn approach to access bioactive thioamides was developed based on elemental-sulfur-promoted C(sp3)−H activation of methyl heteroarenes. This transformation could successfully furnish a series of heterocyclic thioamides with excellent yields and it could be conducted on gram scale with good reaction efficiency. Mechanistic studies showed that methyl heteroarenes reacted with dimethylamine released from DMF to form the desired thioamide through elemental-sulfur-promoted C−H activation.

A new “turn-on” fluorescent probe based on 8-aminoquinoline for detection of Zn2+ was designed, synthesized and characterized. The sensor showed excellent selectivity and sensitivity with a fluorescence enhancement to Zn2+ over other cations in CH3OH–H2O solution. The detection limit for Zn2+ by HAQT reached 2.56 × 10−7 M. The binding ratio of the HAQT–Zn2+ complex was determined to be 1:1 according to the Job plot. The mechanism of HAQT for the recognition of Zn2+ has been investigated by FT-IR, 1H NMR and MS analyses. These advantages allowed for the application of HAQT to detect Zn2+ in real water samples.

•The interaction of helicid with HSA was investigated.•Helicid was located in the subdomain IIA of HSA.•Binding parameters are important for understanding toxicity of helicid.The interaction between human serum albumin and helicid was studied by steady-state fluorescence, ultraviolet–visible, circular dichroism, Fourier transform infrared techniques and molecular modeling. The binding site numbers, association constants, and corresponding thermodynamic parameters were used to investigate the quenching mechanism. The alternations of protein secondary structure in the presence of helicid were demonstrated using synchronous fluorescence, Fourier transform infrared, circular dichroism and three-dimensional fluorescence spectra. The molecular modeling results revealed that helicid could bind to hydrophobic pocket of HSA with hydrophobic and hydrogen bond force. The binding site of helicid in HSA was ascertained. Moreover, an apparent distance of 3.33 nm between the Trp214 and helicid was obtained via fluorescence resonance energy transfer method.Graphical abstractThe Scatchard plots for the fluorescence quenching of HSA in the presence of helicid and molecular docking analysis of HSA with helicid.

This paper was designed to investigate the interaction of ethyl maltol with human serum albumin (HSA) under physiological condition by fluorescence, synchronous fluorescence, three-dimensional fluorescence, Fourier transformation infrared spectra, and molecular docking method. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of HSA by ethyl maltol was static quenching mechanism. The binding constants of ethyl maltol–HSA complexes were observed to be 2.59, 1.88, 1.54, 1.13 × 104 M−1 at 289, 296, 303 and 310 K, respectively. The thermodynamic parameters, ΔH0 and ΔS0 were calculated to be −28.61 kJ mol−1 and −14.59 J mol−1 K−1. Energy transfer from tryptophan to ethyl maltol occurred by a FRET mechanism, and the donor–acceptor distance (3.04 nm) had been determined according to Förster’s theory. Molecular docking studies revealed that ethyl maltol situated within subdomain IIA (site I) of HSA. Fluorescence displacement experiments also proved the binding sites between ethyl maltol and HSA.Graphical abstractThe binding mode between ethyl maltol and HSA.Highlights► The binding properties of ethyl maltol and HSA was investigated in vitro by biophysical methods. ► Hydrogen bond and van der Waals force played a major role in the binding of ethyl maltol to HSA. ► The displacement experiments revealed that the binding of ethyl maltol to HSA mainly took place in subdomain IIA (site I).

A benzimidazole derivative, 1-(2-picolyl)-3-(2-picolyl) benzimidazole iodide (PPB), was synthesized. Fourier transform infrared spectroscopy (FT-IR), UV–visible, three-dimensional (3D) fluorescence, synchronous fluorescence (SF) and fluorescence spectroscopic methods were used to determine the PPB binding mode and the effects of PPB on protein stability and secondary structure. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of PPB to human serum albumin (HSA). The binding constants between PPB and HSA were obtained according to Scatchard equation. The number of binding sites, the binding constants and the thermodynamic parameters were measured. The results showed a spontaneous binding of PPB to HSA through hydrogen bonds and van der Waals forces. In addition, the distance between PPB and the Trp 214 was estimated via employing the Förster's non-radiative energy transfer theory, and was found to be 3.49 nm, which indicated that PPB can bind to HSA with high probability. Site marker competitive experiments indicated that the binding of PPB to HSA primarily took place in subdomain IIA.Graphical abstractHighlights► A novel benzimidazoles derivative, 1-(2-picolyl)-3-(2-picolyl) benzimidazole iodide (PPB), has been synthesized. ► Binding behavior of PPB with HSA was investigated under simulated physiologic conditions. ► The specific binding site of PPB on HSA was investigated by displacement experiments.

A new “turn-on” fluorescent probe based on 8-aminoquinoline for detection of Zn2+ was designed, synthesized and characterized. The sensor showed excellent selectivity and sensitivity with a fluorescence enhancement to Zn2+ over other cations in CH3OH–H2O solution. The detection limit for Zn2+ by HAQT reached 2.56 × 10−7 M. The binding ratio of the HAQT–Zn2+ complex was determined to be 1:1 according to the Job plot. The mechanism of HAQT for the recognition of Zn2+ has been investigated by FT-IR, 1H NMR and MS analyses. These advantages allowed for the application of HAQT to detect Zn2+ in real water samples.