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To propose a sensory evaluation method suitable for Qingzhuan tea, a representative Qingzhuan tea produced in Hubei was soak or spray boiled in order to analyze the effects of different boiling conditions on the sensory quality and the leaching rate of major chemical components of Qingzhuan tea. The sensory quality and chemical components of the tea infusions were compared with those of tea infusion obtained by the brewing method specified in the Chinese national standard. The results showed that the sensory quality of the boiled tea infusion was significantly better than that of the brewed tea infusion; the leaching rates of major quality components such as water extract, tea polyphenols, amino acids, soluble sugars and tea pigments were much higher in the former than in the latter. From the perspectives of sensory quality and the leaching rate of major quality components, tea infusion prepared by boiling for 2 min with a tea/water ratio of 1:80 and then standing for 2–4 min tasted moderate and had good internal quality. Further correlation analysis showed high correlation coefficients between the leaching rates of soluble sugars, theabrownine and water extract and taste quality. The results of this study provide a reference for the objective evaluation of the sensory quality of Qingzhuan tea and other types of compressed tea.

In order to investigate the differences in the characteristic aroma of black teas from different regions, the volatile aroma compounds of Keemun black tea, Yichang black tea, Dianhong black tea and Yingde black tea were identified by solid phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC-MS) and were evaluated by gas chromatography-olfactory (GC-O). Odor activity value (OAV) calculation and correlation analysis between sensory aroma profile and key aroma-active compounds were performed to analyze the sensory attributes and chemical basis of the characteristic aroma of black tea. The results showed that the four black teas differed in the sensory attributes of seven aroma notes such as floral, sweet and herbal notes. Additionally, 24 differential key aroma compounds were identified (P 1). Geraniol contributed most to black tea aroma with the highest OAV in Keemun black tea (16 581.33), followed by Yichang black tea (7 463.65), Dianhong black tea (2 832.13) and Yingde black tea (467.96). Partial least squares (PLS) regression analysis and Pearson correlation analysis showed that β-ionone, geraniol and indole were responsible for the floral and sweet aroma of Keemun black tea, (Z)-3-hexenol and α-terpineol contributed to the fruity and woody aroma of Dianhong black tea, and 2-heptanol and (Z)-linalooloxide were responsible for the herbal aroma of Yingde black tea. In conclusion, this study has preliminarily clarified the characteristic aroma profiles of black tea from the four regions and their material basis at the molecular level.

The control of noncarbon stereogenic centers is of profound importance owing to their enormous interest in bioactive compounds and chiral catalyst or ligand design for enantioselective synthesis. Despite various elegant approaches have been achieved for construction of S‐, P‐, Si‐ and B‐stereocenters over the past decades, the catalyst‐controlled strategies to govern the formation of N‐stereogenic compounds have garnered less attention. Here, we disclose the first organocatalytic approach for efficient access to a wide range of nitrogen‐stereogenic compounds through a desymmetrization approach. Intriguingly, the pro‐chiral remote diols, which are previously not well addressed with enantiocontrol, are well differentiated by potent chiral carbene‐bound acyl azolium intermediates. Preliminary studies shed insights on the critical importance of the ionic hydrogen bond (IHB) formed between the dimer aggregate of diols to afford the chiral N‐oxide products that feature a tetrahedral nitrogen as the sole stereogenic element with good yields and excellent enantioselectivities. Notably, the chiral N‐oxide products could offer an attractive strategy for chiral ligand design and discovery of potential antibacterial agrochemicals. [ABSTRACT FROM AUTHOR]

Due to their eco‐friendly and functional attributes, the development of stain‐resistant poly(lactic acid) (PLA) fibers offers a multitude of benefits, including enhanced sustainability, ease of maintenance and expanded application fields. To investigate the feasibility of facile fabrication of stain‐resistant poly(lactic acid) (PLA) fibers, hydrophobic PLA fibers were produced using a scalable melt spinning technique employing silicone powder as the hydrophobic functional material. The influence of silicone powder content on the morphology and crystal structure of PLA fibers was investigated using different length scale characterization methods, including scanning electron microscopy and wide‐angle X‐ray diffraction. The relationships between the mechanical performance, hydrophobicity, and structure of the PLA fibers were established. The results showed that the synergistic effect of the micro/nanoconvex structure on the fiber surface created by silicon dioxide (SiO2) in silicone powder and the low surface energy of polydimethylsiloxane (PDMS) can considerably improve the hydrophobic functionality of the fibers. Compared with that of PLA fibers, the contact angle of hydrophobic PLA fibers increases from 67.3° to 87.6° with the addition of 3 wt% silicone powder. Furthermore, although silicone powder may accelerate PLA crystallization nucleation, it does not increase the crystallite size. When the silicone powder content is increased to 4 wt%, the mesophase fraction of the hydrophobic PLA fibers increases from 9.3% to 13.7%. This is the primary structural factor that allows the fiber to maintain its good tenacity. The tenacity of these hydrophobic PLA fibers is approximately 4.5 cN/dtex, which has excellent practical value. [ABSTRACT FROM AUTHOR]

Intermolecular pnictogen bonding (PnB) catalysis has received increased interest in non‐covalent organocatalysis. It has been demonstrated that organic electron‐deficient pnictogen atoms can act as prospective Lewis acids. Here, we present a catalytic approach for the asymmetric synthesis of chiral PIII compounds by combining intramolecular PnB interactions and carbene catalysis. Our design features a pre‐chiral phosphorus molecule bearing two electron‐withdrawing benzoyl groups, resulting in the formation of a σ‐hole at the P atom. X‐ray and non‐covalent interaction (NCI) analysis indicate that the model substrates exhibit intrinsic PnB interaction between the oxygen atom of the formyl group and the phosphorus atom. This induces a conformational locking effect, leading to the crystallization of the phosphorus substrate in a preferred conformation (P212121 chiral group). Under the catalysis of N–heterocyclic carbene, the aldehyde moiety activated by the pnictogen bond selectively reacts with an alcohol to yield the corresponding chiral monoester/phosphorus product with excellent enantioselectivity. This Lewis acidic phosphorus center, aroused by the non‐polarized intramolecular pnictogen bond interaction, assists in conformational and selective regulations, providing unique opportunities for catalysis and beyond. [ABSTRACT FROM AUTHOR]

Twisted a pair of stacked two-dimensional materials exhibit many exotic electronic and photonic properties, leading to the emergence of flat-band superconductivity, moiré engineering and topological polaritons. These remarkable discoveries make twistronics the focus point of tremendous interest, but mostly limited to the concept of electrons, phonons or photons. Here, we present twist piezoelectricity as a fascinating paradigm to modulate polarization and electromechanical coupling by twisting precisely the stacked lithium niobate slabs due to the interlayer coupling effect. Particularly, the inversed and twisted bilayer lithium niobate is constructed to overcome the intrinsic mutual limitation of single crystals and giant effective electromechanical coupling coefficient k t 2 is unveiled at magic angle of 11 1 ∘ , reaching 85.5%. Theoretical analysis based on mutual energy integrals shows well agreements with numerical and experimental results. Our work opens new venues to flexibly control multi-physics with magic angle, stimulating progress in wideband acoustic-electric, and acoustic-optic components, which has great potential in wireless communication, timing, sensing, and hybrid integrated photonics. Authors bond two layers of LiNbO3 as an acoustic resonator. With interlayer coupling of fields and modulation by twisted angle, a magic-angle effect is reported, as one mode exhibits huge electromechanical coupling while its twin-mode disappears. [ABSTRACT FROM AUTHOR]