Production of 3-desmethyl protostreptovaricin I from the genetically engineered Streptomyces spectabilis CCTCC M2017417.

A new streptovaricin analogue, namely 3-desmethyl protostreptovaricin I (1), was isolated from the culture of the genetically engineered strain ΔstvM2 derived from Streptomyces spectabilis CCTCC M2017417. Its structure was elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR tests, and high resolution mass spectrometry analysis. Compound 1 is the first example of 3-desmethyl streptovaricin analogues reported so far, however, it showed no antibacterial activities against Staphylococcus aureus ATCC 29213.

Mechanism of photocatalytic CO2 reduction to HCO2H by a robust multifunctional iridium complex.

The tetradentate PNNP-type IrIII complex Mes-IrPCY2 ([Cl-IrIII-H]+) is reported to be an efficient catalyst for the reduction of CO2 to formate with excellent selectivity under visible light irradiation. Density functional calculations have been carried out to elucidate the mechanism and the origin of selectivity in the present work. Calculations suggest that the double-reduced complex 1-H (1[IrI-H]0) demonstrates higher activity than the single-reduced complex 2-H (2[IrIII(L˙-)-H]+), possibly owing to the higher hydride donor ability of the former compared to the latter; thus 1-H functions as the active species in the overall CO2 reduction reaction. In the HCOO- formation pathway, the hydride of 1-H performs a nucleophilic attack on CO2via an outer-sphere fashion to generate species 1-OCHO (1[IrI-OCHO]0), which then releases HCOO- to produce an IrI intermediate. A subsequent protonation and chloride coordination of the Ir center leads to the regeneration of catalyst 1[Cl-IrIII-H]+. For the CO production, a nucleophilic attack on CO2 takes place by the Ir atom of 1-Hvia an inner-sphere manner to afford complex O2C-3-H (1[O2C-IrIII-H]0), followed by a two-proton-one-electron reduction to furnish the OC-2-H complex (2[OC-IrIII(L˙-)-H]+) after liberating a H2O. Ultimately, CO is released to form 2-H. The stronger nucleophilicity as well as smaller steric hindrance of the hydride than the Ir atom of the active species 1-H (1[IrI-H]0) is found to account for the favoring of formate formation over CO formation. Meanwhile, the CO2 reduction reaction is calculated to be preferred over the hydrogen evolution reaction, and this is consistent with the experimental product distributions.

Novel Dual-Emission Emitters Featuring Phenothiazine-S-Oxide and Phenothiazine-S,S-Dioxide Motifs.

In this study, we have successfully designed and synthesized two novel dual-emission emitters featuring phenothiazine-5-oxide and phenothiazine-5,5-dioxide motifs, characterized by highly lopsided and asymmetric conformational states. Through rigorous spectral examinations and DFT calculations, the compounds exhibit distinctive ICT phenomena, coupled with efficient emission in solid states and AIEE characteristics under high water fractions in DMF/H2O mixtures. These non-planar luminogens exhibit vibrant green and blue solid-state luminescence, with fluorescence quantum yields of 24.1 % and 15.21 %, respectively. Additionally, they both emit green fluorescence in THF solution, with notable emission quantum yields (QYs) 36.4 % and 30.4 %. Comprehensive theoretical investigations unveil well-defined electron cloud density separation between the energies of HOMO/LUMO levels within the two luminogens. Notably, the targeted molecule harboring the phenothiazine-S,S-dioxide motif also demonstrates remarkable reversible mechanofluorochromic properties. Moreover, we testify their potential in applications such as solid-state rewritable information storage and live-cell imaging in solution states. Through theoretical calculations and comparative studies, we have explored the intrinsic relationship between molecular structure and performance, effectively screening and identifying new fluorescent molecules exhibiting outstanding luminescent attributes. These discoveries establish a robust theoretical and technical foundation for the synthesis and application of efficient DSE-based MFC materials, opening new avenues in the realm of advanced luminescent materials.

Synthesis, structure and mechanofluorochromic properties of phenothiazine-S-oxide and phenothiazine-S,S-dioxide derivatives.

In this work, two novel luminescent molecules containing distorted phenothiazine-S-oxide and phenothiazine-S,S dioxide skeletons were synthesized by oxidation reactions using different oxidants (m-chloroperoxybenzoic acid, acetic acid /hydrogen peroxide). The target compounds were all confirmed by 1H NMR, 13C NMR and EI-MS. Combined with the results of UV-vis absorption spectra and fluorescence emission spectra, we found that the different oxidation states of S-atom, from sulfide (+2) to sulfoxide (+4) and sulfone (+6), led to the blue, yellow-green and yellowish fluorescence of these compounds in the solid states. Subsequent studies showed that the molecule containing the phenothiazine-S-oxide skeleton exhibited obvious solvatochromism, and the increase of solvent polarity induced a red-shift in the emission wavelength. Moreover, this molecule also exhibited a rare self-recovery mechanochromatic behavior. In addition, these properties were further confirmed by theoretical calculations and X-ray single-crystal diffraction analysis.

Entrepreneurial effect of rural return migrants: Evidence from China.

Entrepreneurship is an important means of economic development. Rural migrant workers returning home to start their own businesses can promote employment, alleviate poverty, and achieve rural development structural transformation of rural development. The entrepreneurial effect of rural return migrants is important for rural economic development. Using the data of the China Labor Force Dynamics Survey (CLDS thereafter) 2018 and China Household Finance Survey (CHFS thereafter) 2019, we analyze the entrepreneurial effects of return migrants upon their return to their hometowns. We construct a career choice model and build a mathematical model based on it to formulate the hypothesis. Then, we use the Probit regression model to test the hypothesis empirically. Results find that the rural return migrants can promote entrepreneurship among residents. Land circulation, human capital, and physical capital are stimulating factors in promoting the rural entrepreneurial activities of return migrants. We recommend that the government actively guide the rural return migrants to start businesses and provide security for entrepreneurial activities by upgrading various entrepreneurial elements.

Determination of melamine in milk powder based on the fluorescence enhancement of Au nanoparticles.

We have developed a new analytical method to detect melamine (MA) in milk powder based on the fluorescence enhancement of Au nanoparticles (AuNPs). AuNPs with the average diameter of ∼16 nm can emit stable fluorescence at 370 nm when the excitation wavelength was selected at 252 nm. The AuNPs could assemble with melamine to form larger aggregates (AuNPs-MA) through electrostatic interaction and coordinating interaction in acidic conditions, which led to the significant enhancement of the fluorescence intensity. Under the optimized conditions, the enhancement of the fluorescence intensity exhibited a good linear dependence on melamine concentration in the range from 8.0 × 10(-10) to 8.0 × 10(-8) M, and the detection limit is 6.1 × 10(-10) M (3σ). This proposed method showed high precision and accuracy when applied to the real sample analyses. In conclusion, a simple, rapid, accurate and sensitive method to detect melamine has been suggested.

3-(4-Fluoro-phen-yl)-2-(4-methoxy-phen-oxy)-4-oxo-5-phenyl-4,5-dihydro-3H-pyrrolo[3,2-d]pyrimidine-7-carbonitrile.

There are two crystallographically independent mol-ecules in the asymmetric unit of the title compound, C(26)H(17)FN(4)O(3), which differ in the dihedral angles between the aromatic rings (fluorophenyl, phenyl) and the pyrrolopyrimidine rings [0.6 (3)/76.3° and 73.7 (3)/64.6°, respectively]. The crystal structure is mainly stabilized by C-H⋯O and C-H⋯F inter-actions.

2-(Dibutyl-amino)-3-(4-fluoro-phen-yl)-5,6,7,8-tetra-hydro-7-methyl-6,8-di-phenyl-pyridine-[3',4':2,3]thieno[5,4-d]pyrimidin-4(3H)-one.

In the crystal structure of the title compound, C(36)H(39)FN(4)OS, the two fused rings of the thienopyrimidine system are coplanar. The 4-fluoro-phenyl ring is twisted with respect to the heterocyclic pyrimidinone ring by 67.21 (14)°. The piperidine ring shows a half-chair conformation. One of the n-butyl chains is disordered equally over two sites. The crystal packing is stabilized by C-H⋯O hydrogen bonds.

Ethyl 3-(4-fluoro-phen-yl)-6-methyl-4-oxo-2-(1-cyclohexylamino)-3,4-dihydro-furo[2,3-d]pyrimidine-5-carboxyl-ate.

In the crystal structure of the title compound, C(22)H(24)FN(3)O(4), the two fused rings of furo[2,3-d]pyrimidine form a dihedral angle of 0.88 (13)°. The attached benzene ring is twisted with respect to the heterocyclic pyrimidinone ring, making a dihedral angle of 75.07 (12)°. The cyclo-hexyl ring shows a distorted chair conformation. The mol-ecular structure is stabilized by intra-molecular C-H⋯O and C-H⋯N hydrogen-bonding inter-actions. The crystal packing is mainly stabilized by C-H⋯π hydrogen-bond inter-actions. Further stability is provided by C-F⋯π and C-O⋯π stacking inter-actions.

Tuning the luminescence of two 3d-4f metal-organic frameworks for the fast response and highly selective detection of aniline.

Two 3D solvent-stable zinc(ii)-lanthanide(iii) heterometallic metal-organic frameworks (MOFs) {[(CH3)2NH2]2[Zn2Ln2(FDA)6(DMF)2]·2DMF}n [Ln = Eu (Zn-Eu) and Tb (Zn-Tb); H2FDA = furan-2,5-dicarboxylic acid] based on Zn2Ln2(COO)10 tetrametallic clusters and furan-2,5-dicarboxylic acid have been successfully synthesized. These MOFs can serve as luminescent sensors for the fast response and highly selective detection of aniline via luminescence quenching. More importantly, a linear correlation is observed between their luminescence and the low concentration of aniline and the detection limits of aniline are 7.5 µmol L-1 for Zn-Eu and 5.2 µmol L-1 for Zn-Tb.

Magnetite Nanocrystals as Anode Electrode Materials for Rechargeable Li-Ion Batteries.

Monodispersed magnetite (Fe3O4) nanocrystals were synthesized and their electrochemical properties as anode electrode materials for rechargeable lithium ion batteries were measured. The magnetite anodes, in the form of monodispersed nanospheres with average diameters (< 10 nm), show particle size effects. Specifically, the first discharge curves show that the nanocrystals can hold much more Li+ per formula unit than their counterparts in bulk before the reduction begins. The electrolyte decomposition takes place before the reduction reaction is completed. The cycling performance of the Fe3O4 nanocrystals after being heated at 300 degrees C for different lengths of time show that heating can improve the integration of the nanocrystals and increase their capacity retention in consequence.

Magnetic microparticle-based multiplexed DNA detection with biobarcoded quantum dot probes.

We have developed a new analytical method to detect multiple DNA simultaneously based on the biobarcoded CdSe/ZnS quantum dot (QD) and magnetic microparticle (MMP). It was demonstrated by using oligonucleotide sequences of 64 bases associated with human papillomavirus 16 and 18 L1 genes (HPV-16 and HPV-18) as model systems. This analytical system involves three types of probes, a MMP probe and two streptavidin-modified QD probes. The MMPs are functionalized with HPV-16 and HPV-18 captures DNA to form MMP probes. The QDs are conjugated with HPV-16 or HPV-18 probe DNA along with FAM- or Rox-labeled random DNA to form HPV-16 and HPV-18 QD probes, respectively. A one-step hybridization reaction was performed by mixing the MMP probes, HPV-16 and HPV-18 target DNA (T-16 and T-18), HPV-16 and HPV-18 QD probes. Afterwards, the hybrid-conjugated microparticles were separated by a magnet and heated to remove the MMPs. Finally, the detections of T-16 and T-18 were done by measuring fluorescence signals of FAM and Rox, respectively. Under the optimum conditions, the fluorescence intensity exhibited a good linear dependence on target DNA concentration in the range from 8 × 10⁻¹¹ to 8 × 10⁻9 M. The detection limit of T-16 is up to 7 × 10⁻¹¹ M (3σ), and that of T-18 is 6 × 10⁻¹¹ M. Compared with other biobarcode assay methods, the proposed method that QDs were used as the solid support has some advantages including shorter preparation time of QD probes, faster binding kinetics and shorter analytical time. Besides, it is simple and accurate.

Visual detection of melamine in milk samples based on label-free and labeled gold nanoparticles.

Melamine that can cause serious damage to the organs of animal or human beings was found to bind to polythymine via hydrogen bonding. With this novel discovery, colorimetric detection of melamine based on label-free and labeled gold nanoparticles was developed, respectively. Both of the methods revealed good selectivity for melamine over other components that may exist in milk and good anti-influence ability. The raw milk samples were pretreated according to the National standard method combined with a solid phase extraction monolithic column. The accurate quantification of melamine as low as 41.7 nM and 46.5 nM was obtained, respectively. It also guarantees fast and reliable readout with naked eyes, making visual detection possible. Further comparison between label-free and labeled based methods was discussed in this paper.