Synthesis of Site‐Specifically Phosphate‐Caged siRNAs and Evaluation of Their RNAi Activity and Stability

A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site‐specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate‐caged siRNA and the single‐stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg²⁺. Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate‐caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate‐caged siRNA or single‐stranded caged RNA prefers to form π–π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications.     

Synthesis and Characterization of Ag8(Ge1−x,Snx)(S6−y,Sey) Colloidal Nanocrystals

A facile colloidal approach to synthesize Ag₈(Ge_1?x,Sn_x)(S_6?y,Se_y) nanocrystals (NCs) in a highly controlled way across the entire compositional ranges (0≤x≤1, 0≤y≤6) has been developed. The NCs exhibit a uniform size distribution, highly crystalline structure, over 1 g scalable synthesis, and tunable band gaps in the range of 0.88–1.45 eV by varying their chemical compositions. The Ag₈GeS₆ NCs with a band gap of approximately 1.45 eV were employed as a model light harvester to assess their applicability in solar cells by a full solution‐processing device, yielding an efficiency of 0.28 % under AM1.5 illumination, demonstrating their application potential in solar energy utilization.     

Crystallization behavior,tensile behavior and hydrophilicity of poly(vinylidene fluoride)/poly(vinyl pyrrolidone) blends

Binary polymer blends of hydrophobic poly(vinylidene fluoride) (PVDF) and hydrophilic poly(vinylpyrrolidone) (PVP) were prepared by melt blending. The crystallization behavior, mechanical properties and hydrophilicity of the binary blends were investigated using Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffractometry (WAXD), differential scanning calorimeter (DSC) scanning, non-isothermal crystallization kinetics, successive self-nucleation and annealing (SSA) fractionation, tensile tests and contact angle tests. The analysis of FTIR, WAXD, DSC scanning, non-isothermal crystallization kinetics and SSA fractionation showed that the addition of PVP greatly influenced the crystallization behavior of the sample. As the PVP content increased, the crystallization temperature, crystallization rate, degree of crystallinity, and the amount of thick lamellaes decreased gradually. Meanwhile, PVP favored the formation of β-phase of PVDF. The results of tensile test revealed that the addition of PVP increased the elongation at break of the sample, and lowered the yield stress. Besides, the result of contact angle test indicated that the hydrophilicity of PVDF was remarkably improved in the presence PVP. The relationship between crystallization behavior and the tensile behavior, hydrophilicity were discussed.     

Study on the interaction between urea and cellulose by combining solid-state 13C CP/MAS NMR and extended Hückel charges

In this article, solid-state ¹³C CP/MAS NMR combined with extended Hückel charges was applied to investigate the interaction between urea and cellulose in the NaOH/urea aqueous solvent system. Direct experimental evidence was provided to support the interaction between urea and cellulose. The solid-state ¹³C CP/MAS NMR results revealed that complicated complexes are formed by urea, NaOH and cellulose in the solution. Excess urea exists in a free state, which explains why 7 wt% NaOH/12 wt% urea/81 wt% H₂O is the optimal ratio selection to dissolve cellulose. Based on the correlation in which the computed extended Hückel charge on carbon of urea is approximately inversely proportional to its ¹³C chemical shift, a possible interaction model of cellulose, NaOH and urea was proposed. Interactions exist between any two of urea, NaOH and cellulose, which results in the cellulose chain being surrounded by NaOH and urea molecules. NaOH and urea may be in the same surface layer of cellulose chains.     

A Protic Ionic Liquid Catalyzes CO2 Conversion at Atmospheric Pressure and Room Temperature: Synthesis of Quinazoline‐2,4(1H,3H)‐diones

The chemical fixation of CO₂ under mild reaction conditions is of significance from a sustainable chemistry viewpoint. Herein a CO₂‐reactive protic ionic liquid (PIL), [HDBU⁺][TFE^?], was designed by neutralization of the superbase 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) with a weak proton donor trifluoroethanol (TFE). As a bifunctional catalyst for simultaneously activating CO₂ and the substrate, this PIL displayed excellent performance in catalyzing the reactions of CO₂ with 2‐aminobenzonitriles at atmospheric pressure and room temperature, thus producing a series of quinazoline‐2,4(1H,3H)‐diones in excellent yields.     

Skeleton Decoration of NHCs by Amino Groups and its Sequential Booster Effect on the Palladium‐Catalyzed Buchwald–Hartwig Amination

A challenging synthetic modification of PEPPSI‐type palladium pre‐catalysts consisting of a stepwise incorporation of one and two amino groups onto the NHC skeleton was seen to exert a sequential enhancement of the electronic donor properties. This appears to be positively correlated with the catalytic performances of the corresponding complexes in the Buchwald–Hartwig amination. This is illustrated, for example, by the quantitative amination of 4‐chloroanisole by morpholine within 2 h at 25 °C with a 2 mol % catalyst/substrate ratio or by a significant reduction of catalytic loading (down to 0.005 mol %) for the coupling of aryl chlorides with anilines (max TON: 19 600).     

Concerted Asynchronous Hula‐Twist Photoisomerization in the S65T/H148D Mutant of Green Fluorescent Protein

Fluorescence emission of wild‐type green fluorescent protein (GFP) is lost in the S65T mutant, but partly recovered in the S65T/H148D double mutant. These experimental findings are rationalized by a combined quantum mechanics/molecular mechanics (QM/MM) study at the QM(CASPT2//CASSCF)/AMBER level. A barrierless excited‐state proton transfer, which is exclusively driven by the Asp148 residue introduced in the double mutant, is responsible for the ultrafast formation of the anionic fluorescent state, which can be deactivated through a concerted asynchronous hula‐twist photoisomerization. This causes the lower fluorescence quantum yield in S65T/H148D compared to wild‐type GFP. Hydrogen out‐of‐plane motion plays an important role in the deactivation of the S65T/H148D fluorescent state.     

Diastereoselective Synthesis of Functionalized Tetrahydropyrimidin‐2‐thiones via ZnCl2 Promoted One‐pot Reactions

In the presence of zinc chloride, the in situ generated β‐enamino ester from the reaction of morpholine, piperidine and pyrrolidine with methyl propiolate reacted, with aromatic aldehydes and thiourea in ethanol resulting in the functionalized tetrahydropyrimidin‐2‐thiones in satisfactory yields and with good diastereoselectivity. When aromatic aldehydes bearing electron‐withdrawing group were used in the reaction, the 4‐hydroxytetrahydropyrimidin‐2‐thione derivatives were obtained as the main product.     

Turn-on fluorescence sensing of cyanide ions in aqueous solution简

A sensitive fluorescent probe, 2,2＇-bisbenzimidazole （L）, for CN has been developed. This structurally simple receptor displays great selectivity for the cyanide anion over other common inorganic anions in an aqueous environment. In addition, further study demonstrates the lower detection of the fluorescence response of the sensor to CN is in 10 9 mol/L range. Thus, the present probe should be applicable as a practical system for the monitoring of cyanide concentrations in aqueous samples.     

A novel method for the synthesis of sulfur substituted-cyclopyrophosphate of cADPR analogs

A facile and efficient protocol for the synthesis of sulfur substituted-cyclopyrophosphate of cIDPRE(P_S~1-cIDPRE) was developed.The key step was the cyclization process which was completed by the sulfur substituted cyclization precursor 1b via the one-pot phosphoramidite strategy.