Acceptor-Reactivity-Controlled Stereoconvergent Synthesis and Immunological Activity of a Unique Pentasaccharide from the Cell Wall Polysaccharide of Cutibacterium acnes C7.

Bacterial cell-surface polysaccharides are involved in various biological processes and have attracted widespread attention as potential targets for developing carbohydrate-based drugs. However, the accessibility to structurally well-defined polysaccharide or related active oligosaccharide domains remains challenging. Herein, we describe an efficiently stereocontrolled approach for the first total synthesis of a unique pentasaccharide repeating unit containing four difficult-to-construct 1,2-cis-glycosidic linkages from the cell wall polysaccharide of Cutibacterium acnes C7. The features of our approach include: 1) acceptor-reactivity-controlled glycosylation to stereoselectively construct two challenging rare 1,2-cis-ManA2,3(NAc)2 (ß-2,3-diacetamido-2,3-dideoxymannuronic acid) linkages, 2) combination use of 6-O-tert-butyldiphenylsilyl (6-O-TBDPS)-mediated steric shielding effect and ether solvent effect to stereoselectively install a 1,2-cis-glucosidic linkage, 3) bulky 4,6-di-O-tert-butylsilylene (DTBS)-directed glycosylation to stereospecifically construct a 1,2-cis-galactosidic linkage, 4) stereoconvergent [2+2+1] and one-pot chemoselective glycosylation to rapidly assemble the target pentasaccharide. Immunological activity tests suggest that the pentasaccharide can induce the production of proinflammatory cytokine TNF-α in a dose-dependent manner.

Simultaneous adsorption of fulvic acid and organic contaminants by KOH activated mesoporous biochar with large surface area.

Returning carbon materials from biomass to soil is a potential technology to retard organic contaminants or dissolved organic matter (DOM) in soil by adsorption, as well as to store carbon in soil for carbon sequestration. However, DOM was widely reported to inhibit adsorption of organic contaminants on carbon materials by competition and by enhancing contaminants' solubility. In this study, a KOH activated carbon material (KAC), pyrolyzed from bamboo chips, with high surface area (3108 m2/g), micropores volumes (0.964 cm3/g), mesopores volumes (1.284 cm3/g), was observed that it can adsorb fulvic acid (FA) and organic contaminants (e.g., nitrobenzene, phenols, and anilines) simultaneously with weak competition and high adsorption capacity. With 50 mg TOC/L FA, for example, the average competition suppressing rate (ΔKf/Kf-m) of organic contaminants on KAC was lower than 5%, the adsorption for organic contaminants and FA were higher than 1100 mg/g and 90 mg TOC/g, respectively. The weak competition on KAC could be attributed to the low micropore blockage (<35%) and the weak adsorption sites competition on mesopores of KAC, as well as the minimal solubility enhancement of organic contaminants by FA because most FA is adsorbed on KAC but is not dissolved in the solution. In addition, adsorption of organic contaminants with high hydrogen-bonding donor ability (αm) and adsorption affinity was less suppressed by FA because of the heterogeneous nature of hydrophilic sites on KAC's surface. Therefore, KAC could be a potential carbon material to be produced to implement to soil for carbon storage and simultaneous retarding organic contaminants and DOM.

Biochemical and Morphological Changes Triggered by Nitrogen Stress in the Oleaginous Microalga Chlorella vulgaris.

Oleaginous microalgae have been considered promising sources of biodiesel due to their high lipid content. Nitrogen limitation/starvation is one of the most prominent strategies to induce lipid accumulation in microalgae. Nonetheless, despite numerous studies, the mechanism underlying this approach is not well understood. The aim of this study was to investigate the effect of nitrogen limitation and starvation on biochemical and morphological changes in the microalga Chlorella vulgaris FACHB-1068, thereby obtaining the optimal nitrogen stress strategy for maximizing the lipid productivity of microalgal biomass. The results showed that nitrogen limitation (nitrate concentration < 21.66 mg/L) and starvation enhanced the lipid content but generally decreased the biomass productivity, pigment concentration, and protein content in algal cells. Comparatively, 3-day nitrogen starvation was found to be a more suitable strategy to produce lipid-rich biomass. It resulted in an increased biomass production and satisfactory lipid content of 266 mg/L and 31.33%, respectively. Besides, nitrogen starvation caused significant changes in cell morphology, with an increase in numbers and total size of lipid droplets and starch granules. Under nitrogen starvation, saturated fatty acids (C-16:0, C-20:0, and C-18:0) accounted for the majority of the total fatty acids (~80%), making C. vulgaris FACHB-1068 a potential feedstock for biodiesel production. Our work may contribute to a better understanding of the biochemical and morphological changes in microalgae under nitrogen stress. Besides, our work may provide valuable information on increasing the lipid productivity of oleaginous microalgae by regulating nitrogen supply.

Isotherm nonlinearity and nonlinear partitioning of organic compounds into resin XAD-7: Insight from displacement experiments.

Nonlinear sorption and isotherm nonlinearity of organic compounds by widely used porous resins such as XAD-7 are commonly interpreted as adsorption due to their large surface area. However, through displacement experiments using saturated 4-nitrophenol as the displacer, we observed that the nonlinear sorption and isotherm nonlinearity of selected organic compounds (i.e., naphthalene, nitrobenzenes, phenols and anilines) by XAD-7 was captured by a nonlinear partition mechanism rather than the adsorption mechanism. Nonlinear sorption of organic compounds by XAD-7 includes a nonlinear/displaced fraction and a linear/non-displaced fraction. A dual-mode (DM) model, including a nonlinear Dubinin-Ashtakhov (DA) model component and a linear model component, was developed to describe the nonlinear/displaced fraction and the linear/non-displaced fraction, respectively. The capacity of these two fractions are dependent on their solubility in water or octanol with positively linear relationships but not their molecular size, supporting the nonlinear partitioning mechanism. Besides van-der-waals force, hydrogen-bonding is primarily responsible for the nonlinear partitioning of phenols and anilines into XAD-7, while π-π interaction is responsible for the nonlinear partitioning of naphthalene and nitrobenzenes. The explored nonlinear partitioning mechanism for XAD-7 implies that the nonlinear sorption of organic compounds by porous resins should be recognized for their recovery and applications as sorbents.

Linear and nonlinear partition of nonionic organic compounds into resin ADS-21 from water.

The predominance of natural organic matter (NOM) in nonlinear sorption of nonionic organic compounds (NOCs) is a fundamental behavior that controlling the fate, transfer and bioavailability of NOCs in natural environment. There is a debate, i.e., whether the nonlinear sorption is captured by nonlinear partition mechanism or adsorption mechanism. The debate has been going on for decades because characteristics of nonlinear partition are still unknown due to the lack of an adsorbent that can partition NOCs nonlinearly. We find a resin ADS-21, with specific surface area undetectable (<0.5 m2 g-1) but high sorption capacity for NOCs (up to 1000 mg g-1 for phenol as an example), is an ideal adsorbent for examining characteristics of nonlinear partitioning. This resin has nonlinear isotherms for phenols and anilines but linear isotherms for polycyclic aromatic hydrocarbons and nitrobenzenes. The observed positively linear relationship of sorption capacities of NOCs with NOCs solubility in water or octanol, could be one of the characteristics of nonlinear partition. Moreover, competitive sorption and no desorption hysteresis could be observed for the nonlinear partition. Hydrogen-bonding of phenols and anilines with ADS-21 is responsible for nonlinear partition, competitive sorption and isotherm nonlinearity. These evidences would be supportive for understanding nonlinear partition and the nonlinear sorption of NOCs by NOM.