Tf2O-Mediated Direct Synthesis of 4-Sulfenylated Oxazoles from ß-Keto Sulfoxides and Nitriles.

A general and efficient method for the synthesis of 4-sulfenylated oxazoles is described. Trisubstituted oxazoles are obtained in good to excellent yields from ß-keto sulfoxides and nitriles. The mechanistic study suggests that the reaction proceeds via the nucleophilic addition of nitriles to the in situ formed α-carbonyl cation followed by intramolecular cyclization.

Decomposing and analyzing contact resonance frequency in contact mode voltage modulated scanning probe microscopies.

Contact mode voltage modulated scanning probe microscopy (SPM) techniques, such as switching spectroscopy piezoresponse force microscopy (SS-PFM), are powerful tools for detecting local electromechanical behaviors. However, interpreting their signals, especially the contact resonance frequency (f0), is difficult due to the complexity of the tip-sample contact and the signal tracking system. In a previous study, an interesting phenomenon on the variation of f0 was observed, showing distinctions between ferroelectric and non-ferroelectric materials. Therefore, it is believed that f0 conveys important information about the tip-sample contact which is real-timely affected by charge accumulation or polarization switching. In this study, principal component analysis (PCA) and correlation analysis are applied to decompose the signal of f0. The first and second principal components successfully restore most information of the original data, and they describe different features which are related to the surface morphology and electromechanical behavior, respectively. In addition, a customized method based on the PCA and correlation analysis of f0 can well distinguish the responses from different materials of which the amplitude and phase signals show "ferroelectric like" phenomena during the SS-PFM measurements.

Infection by and genotype characteristics of Enterocytozoon bieneusi in HIV/AIDS patients from Guangxi Zhuang autonomous region, China.

BACKGROUND: Enterocytozoon bieneusi has been increasingly reported to infect humans and various mammals. Microsporidia cause diarrhea in HIV-infected patients worldwide. PCR amplification and sequencing based on the internal transcribed spacer region have been used to describe the genotypes of E. bieneusi and transmission of microsporidiosis. METHODS: In this study, we examined E. bieneusi infection and genotypes in HIV-positive patients in Guangxi, China. Stool specimens were collected from 285 HIV-positive patients and 303 HIV-negative individuals. E. bieneusi genotypes were characterized using nested PCR and sequencing. RESULTS: Thirty-three (11.58%) HIV-positive patients were infected with microsporidia, and no infection was found in the 303 healthy controls. Three new genotypes were identified and named as GX25, GX456, and GX458; four known genotypes, PigEBITS7, Type IV/K, D, and Ebpc, were also identified. Our data showed that the positive rate for microsporidia was significantly higher in the rural patients than in the other occupation groups. In addition, the positive rate for microsporidia was significantly higher in the patients who drink unboiled water than in those with other drinking water sources. CONCLUSIONS: Our results will provide baseline data for preventing and controlling E. bieneusi infection in HIV/AIDS patients. Further studies are required to clarify the epidemiology and potential sources of microsporidia. Our study showed that microsporidium infection occurs in the HIV/AIDS patients in Guangxi, China.

High-Speed Piezoresponse Force Microscopy and Machine Learning Approaches for Dynamic Domain Growth in Ferroelectric Materials.

Domain dynamics has been one of the hottest research topics for ferroelectric materials in order to understand the ferroelectric mechanisms and to develop the related applications. By using high-speed piezoresponse force microscopy (HSPFM), it is possible to observe the dynamic domain evolution in an ultrashort time increment. This paper combines the HSPFM experiments and machine learning to study the domain growth under a weak AC field in ferroelectric materials. Here, the Bayesian optimized support vector machine is employed to classify the switching domain and stable domain. The results indicate that the machine learning classifier is capable of discerning the switching area. In addition, the domain associated characteristics, such as domain pinning and domain wall pinning, can also be observed and analyzed by combining experiments and machine learning. The machine learning approach can fast and deeply extract the complicated features related to free energy from the multidimensional signals obtained by HSPFM.

Optimizing the Thermoelectric Performance of Poly(3-hexylthiophene) through Molecular-Weight Engineering.

Poly(3-hexylthiophene) (P3HT) films with various molecular weights (MWs) were successfully prepared, and both their molecular structures and thermoelectric (TE) properties were investigated. It was found that the molecular weight of P3HT had an important effect on the carrier-transport properties by affecting the molecular structure and, as a result, also had an effect on the TE performance. The electrical conductivity of the P3HT films first increased upon increasing the molecular weight and then decreased at high molecular weights, whereas the Seebeck coefficient remained at the same level. As a result, the P3HT-M50k (MW≈50 000 g mol-1 ) film reached an electrical conductivity of (103.8±1.2) S cm, which is more than 20 times higher than the electrical conductivity of P3HT-M10k (MW≈10 000 g mol-1 ) and almost 30 % higher than the electrical conductivity of P3HT-M100k (MW≈100 000 g mol-1 ). Consequently, the maximum TE power factor of P3HT-M50k at room temperature was as high as (22.6±0.6) µW mK-2 , which is much higher than that of either P3HT-M10k or P3HT-M100k . Microstructure analysis combined with C-AFM suggested that carrier transport between most of the ordered and amorphous regions was unconnected in films with low molecular weights, and this resulted in a high migration barrier and poor carrier mobility. Upon increasing the molecular weight, the long molecular chain provided enough connectivity for the charge to move through the ordered regions, which decreased the carrier barrier and increased carrier mobility. Therefore, both the conductivity and Seebeck coefficient were significantly improved. However, a too-high molecular weight could cause more folding of the polymer chain, which would deteriorate the electrical-transport properties. The experimental results not only reveal the intrinsic effect of molecular weight on the electric transporting properties of conducting polymers but also suggest that molecular-weight engineering is an effective way to design and screen high-performance polymer TE materials.