Modulating Local Charge Distribution of Carbon Nitride for Promoting Exciton Dissociation and Charge-Induced Reactions.

The sustainable light can generate reduction and oxidation centers in situ through the generation of photoexcited electrons and holes in the presence of photocatalyst. However, the photoexcited electrons and holes have huge Coulombic attraction and high exciton binding energy due to the weak screening effect and dielectric properties in many low-dimensional conjugated polymers, such as carbon nitride. Reducing the exciton binding energy of carbon nitride and promoting the conversion of excitons into free charge carriers are necessary for improving the activity of photocatalytic reactions but still very challenging. Here, by introducing amino-cyano functional groups into carbon nitride, it is demonstrated that excitons can be effectively dissociated into electrons and holes by finely controlling the charge distribution of heptazine ring. It is found that carbon nitride with heptazine rings of positive charge distribution can greatly reduce the exciton binding energy to 24 from 71 meV. Compared with heptazine ring having negative charge distribution, heptazine ring with positive charge distribution can increase photocatalytic hydrogen production of carbon nitride by up to ten times. This work provides an easy way to promote the dissociation of excitons in carbon nitride by regulating the charge distribution.

Synthesis of biscoumarin and dihydropyran derivatives as two novel classes of potential anti-bacterial derivatives.

A series of bisoumarin (1-4) and dihydropyran (5-8) derivatives were successfully synthesized as new antibacterial agents. The molecular structures of three representative compounds 1, 5 and 7 were confirmed by single crystal X-ray diffraction study. Among these compounds tested toward Staphylococcus aureus (S. aureus ATCC 29213), methicillin-resistant S. aureus (MRSA XJ 75302), vancomycin-intermediate S. aureus (Mu50 ATCC 700699), and USA 300 (Los Angeles County clone, LAC), compounds 1 and 2 displayed the most potent antibacterial activity. Additionally, the HB energy in biscoumarins 1-4 was calculated by density functional theory (DFT) [B3LYP/6-31G*] method.

Anion-dipole interactions make the homopolymers self-assemble into multiple nanostructures.

Anion-dipole interactions can make homopolymers self-assemble like an amphiphilic block copolymer. Generally, common homopolymers cannot self-assemble into multiple nanostructures. Here, it is reported that anion-dipole interactions can enable a number of homopolymers to achieve a variety of self-assembly behaviors in aqueous solution. Such interactions and self-assembly features have been exclusively reserved for amphiphilic (block) polymers until now.

Synthesis and pharmacological evaluations of 4-hydroxycoumarin derivatives as a new class of anti-Staphylococcus aureus agents.

OBJECTIVES: Due to the increasing prevalence of drug-resistant Staphylococcus aureus infection, we develop novel 4-hydroxycoumarin derivatives as antimicrobials. METHODS: The antibacterial activity of 4-hydroxycoumarin derivatives against drug-susceptive S. aureus (ATCC 29213) and methicillin-resistant S. aureus (MRSA) were evaluated using minimal inhibitory concentration (MIC) assay; the activity of favourable compound was further observed using bacterial growth curves assay and in the MRSA infection mice. KEY FINDINGS: Compared with dihydropyran derivatives, compound 1 as one of biscoumarins showed most potent activity with MIC values of 4-8 µg/ml and apparently inhibited the growth rate of S. aureus ATCC 29213 and USA300 strain in concentrations of both 16 and 32 mg/ml. In the mice infected with MRSA USA300, administration of 5 mg/kg compound 1 improved the animal survival rate to 66.7%, and improved the pathological change in lung tissue compared with the infection model animals. No significant cytotoxicity of compound 1 was observed on the umbilical vein endothelial cells (HUVECs) under the concentration of 800 µg/ml. CONCLUSION: Compared with the dihydropyran derivatives, biscoumarins exhibited more promising activity against both drug-sensitive and drug-resistant S. aureus, and it is efficacious in treating MRSA infections in mouse models with a favourable safety in human cells.

New biscoumarin derivatives: synthesis, crystal structure, theoretical study and antibacterial activity against Staphylococcus aureus.

Five novel biscoumarins 1-5 were synthesized and characterized. In these compounds, two classical asymmetrical intramolecular O-H···O hydrogen bonds were used to stabilize the whole structures and the HB energies were performed with the density functional theory (DFT) [B3LYP/6-31G*] method. The five compounds were evaluated for their in vitro antibacterial activities against Staphylococcus aureus (S. aureus ATCC 29213), methicillin-resistant S. aureus (MRSA XJ 75302), vancomycin-intermediate S. aureus (Mu50 ATCC 700699), and USA 300 (Los Angeles County clone, LAC) by the means of minimum inhibitory concentration and time-kill curves.

Synthesis, antibacterial activities, and theoretical studies of dicoumarols.

Four dicoumarols (DC, 2-PyDC, 3-PyDC and 4-PyDC) were synthesized and characterized via IR, (1)H NMR, HRMS, and single crystal X-ray crystallography. Two classical intramolecular O-H···O hydrogen bonds (HBs) stabilized their structures. The total HB energies in DC, 2-PyDC, 3-PyDC and 4-PyDC were calculated with the density functional theory (DFT) [B3LYP/6-31G*] method. The in vitro antibacterial activity of DC, 2-PyDC, 3-PyDC and 4-PyDC against Staphylococcus aureus (S. aureus ATCC 29213), methicillin-resistant S. aureus (MRSA XJ 75302), vancomycin-intermediate S. aureus (Mu50 ATCC 700699), and USA 300 (Los Angeles County clone, LAC) was evaluated by observing the minimum inhibitory concentration and time-kill curves. The results showed that among all the compounds, 2-PyDC exhibited the most potent antibacterial activity.