Preparation and characterization of curdlan with unique single-helical conformation and its assembly with Congo Red

Structural characterization and immune-enhancing effects of a novel polysaccharide extracted from Sargassum fusiforme

To alleviate the adverse effects of chemotherapy and bolster immune function, a novel polysaccharide derived from Sargassum fusiforme named as SFP-αII. The structural composition of SFP-αII predominantly consisted of guluronic and mannuronic acids in a molar ratio of 33.8:66.2, with an average molecular weight of 16.5 kDa. Its structure was primarily characterized by →4)-α-GulA-(1 → and →4)-β-ManA-(1 → linkages confirmed by FT-IR, methylation, and NMR analyses. The absence of a triple-helix structure was in SFP-αII was confirmed using circular dichroism and Congo red dye assays. The dimensions varied with lengths ranging from 20 nm up to 3 μm revealed by atomic force microscopy (AFM). SFP-αII has been found to enhance immunomodulatory activity in cyclophosphamide (CTX)-induced immunosuppressed mice. This was evidenced by improvements in immune organ indices, cytokine levels, and the release of nitric oxide (NO). Specifically, SFP-αII mitigated immunosuppression by upregulating the secretion of IL-1β (167.3 %) and TNF-α (227.1 %) at a dose of 400 mg/kg, compared with the CTX group in macrophages. Ultimately, SFP-αII may serve as a mechanism for immune enhancement through modulation of TLR4-mediated NF-κB and MAPK signaling pathways. This integration of traditional Chinese and Western medicine, leveraging SFP-αII as a potential functional food could be pivotal in alleviating immunosuppressive side effects in CTX treatment.

Preparation of Single-Helical Curdlan Hydrogel and Its Activation with Coagulation Factor G

β-1,3-glucans are a kind of natural polysaccharide with immunomodulatory, antitumor, and anti-inflammatory properties. Curdlan, as the simplest linear β-1,3-glucan, possesses a variety of biological activities and thermogelation properties. However, due to the complexity and variability of the conformations of curdlan, the exact structure-activity relationship remains unclear. We prepare a chemically crosslinked curdlan hydrogel with the unique single-helical skeleton (named S gel) in 0.4 wt% NaOH at 40 °C, confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). X-ray diffractometry (XRD) data show that S gel maintains the single-helical crystal structure, and the degree of crystallinity of the S gel is ~24%, which is slightly lower than that of the raw powder (~31%). Scanning electron microscopy (SEM) reveals that S gel has a continuous network structure, with large pores measuring 50-200 μm, which is consistent with its high swelling property. Using the 13C high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) method, we determine that most of the single-helical skeleton carbon signals in the swollen S gel are visible, suggesting that the single-helical skeleton of S gel exhibits fascinating mobility at room temperature. Finally, we reveal that the binding of S gel to coagulation Factor G from tachypleus amebocyte lysate increases and saturates at 20 μL tachypleus amebocyte lysate per mg of S gel. Our prepared S gel can avoid the transformation of curdlan conformations and retain the bioactivity of binding to coagulation Factor G, making it a valuable material for use in the food industry and the pharmaceutical field. This work deepens the understanding of the relationship between the single-helical structure and the activity of curdlan, promoting the development and application of β-1,3-glucans.

Structure and Properties of Exopolysaccharide Produced by Gluconobacter frateurii and Its Potential Applications

An exopolysaccharide (EPS)-producing bacterium was isolated from apricot fermentation broth and identified as Gluconobacter frateurii HDC-08 (accession number: OK036475.1). HDC-08 EPS is a linear homopolysaccharide mainly composed of glucose linked by α-(1,6) glucoside bonds. It contains C, H, N and S elements, with a molecular weight of 4.774 × 106 Da. Microscopically, it has a smooth, glossy and compact sheet structure. It is an amorphous noncrystalline substance with irregular coils. Moreover, the EPS showed surface hydrophobicity and high thermal stability with a degradation temperature of 250.76 °C. In addition, it had strong antioxidant properties against DPPH radicals, ABPS radicals, hydroxyl radicals and H2O2. The EPS exhibited high metal-chelating activity and strong emulsifying ability for soybean oil, petroleum ether and diesel oil. The milk solidification test indicated that the EPS had good potential in fermented dairy products. In general, all the results demonstrate that HDC-08 EPS has promise for commercial applications as a food additive and antioxidant.

Self-Assembling Gelatin-Curdlan Fibril Hydrogels for Oriented Neural Cell Growth

The ex vivo replication of the highly helical and fibril structures of load-bearing soft tissue is a challenging goal for the study of hydrogels. Inspired by nature, we prepared tissue-like physical gels based on curdlan and gelatin by self-assembly. The hybrid gels have a flexible fibril-matrix architecture, and the fibril orientation is highly tunable. The tensile strength of the gels can be tuned from ∼1.1 to ∼16.5 MPa. The coil-helix transition and nanofibril formation process in the self-assembly system was thoroughly investigated. These helical gels exhibit excellent cell compatibility, which supports adhesion and oriented growth of neural cells. Furthermore, the oriented nanofibrils in the gel are found to be associated with an upregulated expression of regeneration-related genes like N-cadherin (Cdh2) and neural growth factor (NGF). Owing to the strength and biomimetic structure, these gels have great potential in tissue engineering applications.

(3,3)-Connected Triazine-Based Covalent Organic Frameworks for Efficient CO2 Separation over N2 and Dye Adsorption

Covalent organic frameworks (COFs) are a promising class of adsorption and separation materials that can meet the needs of ecological sustainability, such as the removal of carbon dioxide and organic dyes. The two synthesized (3,3)-connected triazine-based COFs demonstrate high specific surface area and good thermal and chemical stability. COFZ1 shows good CO2 adsorption selectivities for different CO2 and N2 volume percentage systems at 273 K and 1 bar, with an ideal adsorbed solution theory (IAST) CO2 selectivity (i.e., separation factor) of 35.09 for the simulated flue gas component and a CO2 adsorption capacity of 24.21 cm3 g-1. In the aqueous dye solutions, both COFs present good adsorption performance for the selected dyes, and the maximum adsorption capacities of COFZ1 for methylene blue (MB) and gentian violet (GV) reach 510 and 564 mg g-1, respectively. Each of the two COFs shows a high anti-interference performance and excellent recyclability. The adsorption capacities of two COFs for RhB (Rhodamine B), MB, and GV hardly vary with pH values and salt concentrations. The adsorption behaviors of the two COFs for dyes follow Langmuir isothermal adsorption and quasi-secondary kinetic adsorption, approaching monolayer adsorption and chemisorption.

Influence of physicochemical changes and aggregation behavior induced by ultrasound irradiation on the antioxidant effect of highland barley β-glucan

The effect of ultrasonic treatment on the structure, morphology and antioxidant activity of highland barley β-glucan (HBG) was investigated. Ultrasonic treatment for 30 min was demonstrated to improve the aqueous solubility of HBG, leading to a decrease in turbidity. Meanwhile, moderate ultrasound was found to obviously reduce the particle size distribution of HBG, and transform the entangled HBG molecules into flexible and extended chains, which reaggregated to form larger aggregates under long-time ultrasonication. The in vitro antioxidant capacity of HBG treated by ultrasonic first increased and then decreased compared to native HBG. Congo red complexation analysis indicated the existence of helix structure in HBG, which was untwisted after ultrasonic treatment. Furthermore, ultrasound treatment influenced the glucopyranose on HBG, which weakened the intramolecular hydrogen bond of HBG. The microscopic morphology showed that the spherical aggregates in native HBG solution were disaggregated and the untangled HBG chains reaggregated with excessive ultrasonication.

Laminarin acetyl esters: Synthesis, conformational analysis and anti-viral effects

Chemical modification of polysaccharides is important for expanding their applications and gaining new insights into their structure-property relationships. Here we reported the synthesis, characterization, and anti-viral activities of laminarin acetyl derivatives. The chemical structure and chain conformation of acetylated laminarin were characterized by FT-IR, H¹ NMR, AFM, UV-vis spectrum, and induced circular dichroism based on a modified Congo Red assay (ICD-CR assay). The inhibition effect of laminarin and its acetyl derivatives on HSV-1 was evaluated by viral plaque assay and virus-associated DNA/protein change. Acetylation modification was found to trigger the conformation transition of laminarin from triple helix to single helix, and the extent of transition can be tuned by the degree of substitution. The single helical acetylated laminarins were found to be stable in neutral aqueous solution and exhibited no cytotoxicity. However, the acetylated laminarin exhibited declined antiviral activity after modification.

The effect of carboxymethylation on the macromolecular conformation of the (1 → 3)-β -D-glucan of curdlan in water

The chain conformational change in curdlan during carboxymethylation was investigated using nuclear magnetic resonance (NMR), circular dichroism (CD) spectroscopy, and atomic force microscopy (AFM). The distributions of carboxymethyl substituents within anhydroglucose unit (AGU) of CMCD were found to follow the order of OH (6) > OH (4) > OH (2) for CMCD with a low DS and OH (6) > OH (2) > OH (4) for CMCD with relatively high DS. The increased carboxymethylation level induced the chain conformation transition of curdlan from triple helix to random coil in water. The DS of 0.25 was the critical value of chain conformation transition, below which CMCD chains were triple helices. For DS larger than 0.25, CMCD existed in the state of random coils. The intermolecular hydrogen bonding between C2 hydroxyls in AGU sustained the triple helical conformation and stiffness of the polymer chain, which weakened with the increase in DS.