Modulation of Tannic Acid on the Cholesteric Structure of Cellulose Nanocrystals.

The chiral nematic phase structure, formed by the self-assembly of cellulose nanocrystals (CNCs) in an aqueous suspension and maintained in a solid film, shows great potential for optical applications. To achieve complex structures in optical devices, it is crucial to subject CNCs to specific shearing processes, such as spinning and printing. Understanding the structural and property changes of the CNC liquid crystal phase in these processes is of utmost importance. In this study, we investigated the effect of adding tannic acid (TA) on the rheological properties and cholesteric phase structures of CNCs/TA mixed suspensions. By calculating the surface site interaction points, we observed that TA can adsorb onto the surface of CNC rods in suspensions through hydrogen bonding. Through characterization techniques, such as polarized optical microscopy, rheology, and synchrotron SAXS, we examined the effects of TA addition on the microstructure and rheological properties of the CNC liquid crystal phase and clarified the change relating to the system composition. Under the same CNC concentration, the volume fraction of the anisotropic phase, the pitch, and the rod spacing of the cholesteric phase were not significantly affected by the addition of TA. However, the system viscosity was significantly reduced with the appropriate amount of TA (2 wt %), in a wide range of CNC concentrations (up to 15 wt % CNCs). The flow indexes (n) in Region I and Region III of steady-state shear curves of CNCs/TA systems (11-15 wt % CNCs) were compared. Moreover, we introduced the well-established theoretical models for liquid crystal polymers to tentatively interpret Region I of the CNCs/TA cholesteric phase and realized that increased numbers of smaller cholesteric-phase domains in the CNCs/TA system and interfacial modification by TA may contribute to the fluidity change. The feature of the domain texture of CNCs/TA systems is verified by polarized optical microscopy observations.

Facile Synthesis of ZrO2-SiO2 Antireflective Films with Good Mechanical Performances for Perovskite Solar Cells.

Antireflective (AR) films are widely applied in solar cells to reduce the reflectivity toward sunlight, thus improving the photoelectric conversion efficiency (PCE) of solar cells. However, AR films are still suffering from poor mechanical properties and low transmittance in photovoltaic applications. Herein, a ZrO2-SiO2 composite film with enhanced mechanical properties was successfully synthesized by a facile sol-gel method, whose pencil hardness increased from less than 6B to B compared with the pure SiO2 film synthesized with the same alkali-catalyzed method. Moreover, the ZrO2-SiO2 film with a Zr/Si mole ratio (nZr/Si) of 0.06 exhibited a high transmittance gain (ΔT) of 3.0%, and an obvious increase (1.32%) in PCE was observed in a perovskite solar cell compared with the cell covered by a bare glass. Additionally, both the short-circuit current density (JSC) and PCE of perovskite solar cells have a non-linear increasing relationship with the average transmittance (Tavg) of the ZrO2-SiO2 composite film. In this sense, this work can provide a facile way to prepare AR films effectively improving performances of solar cells.

Formation and Transformation of Polystyrene-block-poly(2-vinylpyridine) Hexasomes in the Solvent Exchange.

The generation of inverse micellar nanostructures, especially those with open channels, using commercially available diblock copolymers (BCP), is vital for their wide applications in drug delivery and catalyst templating. However, the rigid requirements for forming inverse morphologies, such as the highly asymmetric molecular structures, the semicrystalline motifs, and concentrated solutions of diblock copolymers, represent obstacles to the development of successful strategies. In this study, the inverse polystyrene-block-poly(2-vinylpyridine) (PS30K-b-P2VP8.5K) micelles, i.e., the hexasomes with p6mm lattice, were generated through a modified solvent exchange via adding d-tartaric acid (d-TA) in the nonsolvent. Various intermediate morphologies have been identified with the change of d-TA concentration. Interestingly, in the high d-TA concentration (∼20 mg/mL), the hexasomes with close-packed hoops changed to mesoporous spheres with regularly packed perpendicular cylindrical channels (VD-TA: VBCP 6:100), and further to the mesoporous spheres with gyri-like open pores (VD-TA: VBCP > 15:100) with the increasing acidity in the mixed solvent. This study presents a simple and economical pathway for fabricating PS30K-b-P2VP8.5K hexasomes and first demonstrates these hexasomes can be modified to the morphology with open channels that will benefit their further applications.

A sustainable and efficient strategy for bioconverting naringin to L-rhamnose, 2R-naringenin, and kaempferol.

The development of a sustainable and efficient bioconversion strategy is crucial for the full-component utilization of naringin. In this study, an engineering Pichia pastoris co-culture system was developed to produce L-rhamnose and 2S/2R-naringenin. By optimizing transformation conditions, the co-culture system could completely convert naringin while fully consuming glucose. The production of 2S/2R-naringenin reached 59.5 mM with a molar conversion of 99.2%, and L-rhamnose reached 59.1 mM with a molar conversion of 98.5%. In addition, an engineering Escherichia coli co-culture system was developed to produce 2R-naringenin and kaempferol from 2S/2R-naringenin. Maximal kaempferol production reached 1050 mg/L with a corresponding molar conversion of 99.0%, and 996 mg/L 2R-naringenin was accumulated. Finally, a total of 17.4 g 2R-naringenin, 18.0 g kaempferol, and 26.1 g L-rhamnose were prepared from 100 g naringin. Thus, this study provides a novel strategy for the production of value-added compounds from naringin with an environmentally safe process.

Screening ß-glucosidase and α-rhamnosidase for biotransformation of naringin to naringenin by the one-pot enzymatic cascade.

Naringenin is a kind of flavonoid with many kinds of pharmacological activities, and is also a key intermediate metabolite in the flavonoid synthesis pathway. In this study, three α-rhamnosidases from Thermotoga petrophia DSM 13995 (TpeRha), Alternaria sp. L1 (AsRha), and Aspergillus mulundensis (AmRha), and three ß-glucosidases from T. thermarum DSM 5069 T (BGLI-Tt and BGLII-Tt), and A. niger NL-1 (BGL-NL) were cloned, expressed, and characterized. The Kcat/Km value of AmRha for naringin was 2.389 s-1mM-1 which was 796-fold and 26-fold of TpeRha and AsRha. The Kcat/Km value of BGL-NL for prunin was 0.946 s-1mM-1, which was about 4.4-fold and 4.6-fold of BGLI-Tt and BGLII-Tt. According to the catalytic efficiency, expression level, and reaction condition compatibility, AmRha was coupled with BGL-NL to construct a one-pot enzymatic cascade for preparing naringenin from naringin. The effects of the ratio and dosage of the enzyme, the naringin concentration, and reaction conditions on naringenin production were optimized. At a dosage of 200 U/L AmRha and 1000 U/L BGL-NL, a temperature of 50 °C and pH 5.0, 30 mM naringin was transformed into 29.3 mM naringenin for 24 h reaction with a corresponding molar conversion of 97.6%. Therefore, this study provides an efficient enzymatic cascade to meet the large-scale and low cost preparation of naringenin from naringin.

Exploring the Core Parameters of CNC-Based Chiral Nematic Structures for Enhancing the Dissymmetry Factor of Right-Handed Circularly Polarized Luminescence.

The chiral nematic nanostructure formed from cellulose nanocrystal (CNC) self-assembly has shown great potential as a matrix for generating circularly polarized luminescent (CPL) light with a high dissymmetry factor. Exploring the relationship between the device composition and structure and the light dissymmetry factor is crucial to a common strategy for a strongly dissymmetric CPL light. In this study, we have compared the single-layered and double-layered CNC-based CPL devices with different luminophores, such as rhodamine 6G (R6G), methylene blue (MB), crystal violet (CV), and silicon quantum dots (Si QDs). We demonstrated that forming a double-layered structure of CNCs nanocomposites is a simple but effective pathway for enhancing the CPL dissymmetry factor for CNC-based CPL materials containing different luminophores. The |glum| values of double-layered CNC devices (dye@CNC5||CNC5) versus that of single-layered devices (dye@CNC5) are 3.25 times for Si QDs, 3.7 times for R6G, 3.1 times for MB, and 2.78 times for CV series. The different enhancement degrees of these CNC layers with a similar thickness may be due to the different pitch numbers in the chiral nematic liquid crystal layers whose photonic band gap (PBG) has been modified to match the emission wavelengths of dyes. Furthermore, the assembled CNC nanostructure has great tolerance to the addition of nanoparticles. Gold nanorods coated with the SiO2 layer (Au NR@SiO2) were added for enhancing the dissymmetry factor of MB in CNC composites (named MAS devices). When the strong longitudinal plasmonic band of the Au NR@SiO2 matched the emission wavelength of MB and the PBG of assembled CNC structures simultaneously, the increase in the glum factor and quantum yield of MAS composites was obtained. The good compatibility of the assembled CNC nanostructures makes it a universal platform for developing strong CPL light sources with a high dissymmetry factor.

Cooperation of Zr(IV)-N and Zr(IV)-O coordinate bonds of Zr(IV)-amide ensures the transparent and tough polyacrylamide hydrogels.

Developing advanced soft machines and tissue engineering for load-bearing cartilage or tendons requires tough hydrogels. However, the construction of double or triple crosslinked networks for these tough hydrogels, i.e., a strong network crosslinked by covalent bonds and one or two sacrificial networks built by hydrogen bonds or coordinate bonds, generally asks for multiple steps. It remains a challenge to develop hydrogels with a combination of excellent toughness and a high content of water through the time-saving one-pot process. This study demonstrates that this puzzle could be solved through engineering zirconium(IV)-amide coordinate bonds. To be specific, the combination of strong Zr(IV)-O and moderate Zr(IV)-N coordinate bonds in Zr-polyacrylamide (Zr-PAAm) hydrogels has the advantage that they are usually generated through multiple cross-linked networks. Compared to chemical crosslinked PAAm hydrogels, the highly transparent Zr-PAAm hydrogels crosslinked by Zr(NO3)4 displayed a 26-times increase in fracture stress, 4-times in fracture strain, 6-times in elastic modulus, and over 250-times in toughness. Besides, the mechanical properties of Zr-PAAm hydrogels could be altered over a wide range via changing the anion species, showing a dependence on the Hofmeister effect. The co-existence of Zr(IV)-N and Zr(IV)-O has been confirmed through XPS and FTIR characterizations. In particular, the effect of Zr(IV)-N in Zr-PAAm hydrogels has been verified by comparing the property changes of Zr-PAAm hydrogels before and after swelling in water, in which the Zr(IV)-N in the as-prepared hydrogels was replaced by Zr(IV)-O in the swollen gels. With ultra-stretchability and high transparency, the colorless Zr-PAAm hydrogels displayed rich interference colors under stretching, which brought great potential in anti-counterfeiting materials.

The different composites of cellulose nanocrystals with d- or l-histidine.

Cellulose nanocrystals (CNCs) are inherently right-handed nanostructures that originate from nature, showing chirality in their fibrils, bundles, and self-assembled films. However, the enantio-specific interaction between CNCs and other chiral molecules has not been explored so far. In this study, we first demonstrated a chirality-related difference in the composite films of cellulose nanocrystals and histidine with a d- or l-configuration. The distinction is not only presented in the self-assembled nanostructures of CNCs, optical properties, and the thermal decomposition of composites but also in the crystallization of the amino acid. We suppose that it might have originated from the packing of amino acids on the twisted surface of CNCs. The knowledge about the enantio-specific interaction between the chiral amino acid and polysaccharide nanostructure is of significant importance for developing a new strategy for enantiomeric separation.

The treatment of mouse colorectal cancer by oral delivery tumor-targeting Salmonella.

Systemic administration of Salmonella to tumor-bearing mice leads to its preferential accumulation in tumor sites, the enhancement of host immunity, and the inhibition of tumor growth. However, the underlying mechanism for Salmonella-induced antitumor immune response via oral delivery remained uncertain. Herein, we used mouse colorectal cancer (CT26) as tumor model to study the therapeutic effects after oral delivery of Salmonella. When orally administered into tumor-bearing mice, Salmonella significantly accumulated in the tumor sites, inhibited tumor growth and extended the survival of mice. No obvious toxicity was observed during orally administered Salmonella by examining body weight and inflammatory cytokines. As indoleamine 2, 3-dioxygenase 1 (IDO) is a crucial mediator for tumor-mediated immune tolerance, we examined the expression of IDO. We demonstrated that Salmonella inhibited IDO expression in mouse cancer cells. Furthermore, immunohistochemical studies of the tumors revealed the infiltration of neutrophils and T cells in mice treated with Salmonella. In conclusion, our results indicate that Salmonella exerts its tumoricidal effects and stimulates T cell activities by inhibiting IDO expression. Oral delivery of Salmonella may, represent a potential strategy for the treatment of tumor.