Efficient adsorption of selenium (Se(IV) and Se(VI)) from water using Acacia senegal polysaccharide with multiple amine groups: Synthesis and application.

In this study, an amine-rich gel (ARAS) was prepared by chemically altering Acacia senegal (AS). ARAS acts as an adsorbent for selenium. Owing to the introduction of amino functional groups and a remarkable specific surface area (91.89 g/m2), ARAS shows maximum adsorption capacities at 75 and 130 mg g-1 for Se(IV) and Se(VI), respectively. The removal efficiency of ARAS is higher (ωSeIV = 98.2 % and ωSeVI = 98.6 %) at lower concentrations (CSeIV = 100 ppm and CSeVI = 95 ppm) and the adsorption equilibrium is achieved within 60 min. The adsorption process of Se (IV) and Se (VI) via ARAS is elucidated using the Quasi-Second-Order kinetic and Langmuir models. The enhanced adsorption capacity of the adsorbent could be attributed to the synergistic effects of electrostatic attraction, hydrogen bonding, and specific physicochemical properties. Thermodynamic studies reveal that the surface adsorption process is spontaneous and exothermic. Notably, ARAS maintains remarkable adsorption stability under a variety of solution conditions, including variable pH (4-11), NaCl concentrations (0-1 M), and the presence of organic solvents. It retains approximately 60 % of its initial adsorption capacity for Se(IV) and Se(VI) after three adsorption cycles. Therefore, ARAS with its cost-effectiveness and exceptional performance shows considerable potential for applications in water treatment.

Solvent effects on the motion of a crown ether/amino rotaxane.

Solvents have been recognized as a significant factor for modulating the shuttle of rotaxanes and regulating their functions regarding molecular machines by a lot of published studies. The mechanism of the effects of solvents on the motion of crown ether/amino rotaxanes, however, remains unclear. In this work, a rotaxane, formed by dibenzo-24-crown-8 (C[8]) and a dumbbell-shaped axle with two positively charged amino groups, was investigated at the atom level. Two-dimensional free-energy landscapes characterizing the conformational change of C[8] and the shuttling motions in chloroform and water were mapped. The results indicated that the barriers in water were evidently lower than those in chloroform. By analyzing the trajectories, there was no obvious steric effect during shuttling. Instead, the main driving force of shuttling was verified from electrostatic interactions, especially strong hydrogen bonding interactions between the axle and water, which resulted in the fast shuttling rate of the rotaxane. All in all, the polarity and hydrogen bond-forming ability of solvents are the main factors in affecting the shuttling rate of a crown ether/amino rotaxane. In addition, C[8] would adopt S-shaped conformations during shuttling except for situating in the amino sites with C-shaped ones adopted due to π-π stacking interactions. The results of this research improve the comprehension of the solvent modulation ability for shuttling in crown ether-based rotaxanes and illustrate the effects of structural modifications on motions. These new insights are expected to serve the efficient design and construction of molecular machines.

Protective Mechanism of a Layer-by-Layer-Assembled Artificial Cell Wall on Probiotics.

Constructing an artificial cell wall (AFCW) based on the layer-by-layer assembly of polymer films to protect probiotics in harsh conditions is highly desirable. Early findings showed that encapsulating yeast cells by an AFCW improved the cell viability by 50% in antibiotic solution. However, the detailed molecular interaction mechanism remains unclear by experiments. Herein, two ciprofloxacin (CPFX) permeation models, including models 1 and 2 that were, respectively, composed of just the yeast cell membrane and the AFCW coating cell membrane, were investigated by molecular dynamics simulations. The free energy profiles delineating the permeation process of CPFX reveal that the permeation of CPFX through the cell membrane of model 2 is more difficult than through that of model 1. The analysis results show that the AFCW leads to two sharp increases in free energy barriers, amounting to 8.9 and 6.2 kcal/mol, thereby reducing the penetrating rate of CPFX into the cell membrane. Moreover, decomposition of the potentials of mean force into free energy components suggested that the electrostatic interactions of CPFX with the AFCW predominantly contributed to the high free energy barriers. The current results provide a good understanding of the protective mechanism of the self-assembled cell walls against CPFX and help to design other AFCWs.

Selenium-Functionalized Corn Starch as a Biodegradable GPx Mimic with High Catalytic Performance.

Selenium-functionalized starch (Se-starch80) is one of the main functional foods used for selenium supplementation. In traditional agriculture, Se-starch has some deficiencies such as long growth cycle and unstable selenium content that prevent its antioxidant performance. In this study, Se-starch was prepared by the nucleophilic addition between NaSeH and carbon-carbon double bond of octenyl succinic anhydride waxy corn starch ester (OSA starch). Some techniques such as 1HNMR, XPS, SEM-EDS, XRD and FT-IR were used to characterize the relevant samples and the results showed that the modification did not destroy the starch framework significantly and the catalytic center (negative divalent selenium) was anchored on the starch framework. The intensive distribution of catalytic center on the starch surface and the hydrophobic microenvironments derived from the OSA chains furnished the Se-starch80 with a high GPx-like catalytic activity (initial reaction rate = 3.64 µM/min). This value was about 1.5 × 105 times higher than that of a typical small-molecule GPx mimic (PhSeSePh). In addition, the Se-starch80, without any cytotoxicity, showed a saturated kinetic catalytic behavior that is similar to a typical enzyme. This work exemplifies a biodegradable selenium-functionalized polymer platform for the high-performing GPx mimic.

One-pot synthesis of biomimetic glutathione peroxidase with temperature responsive catalytic behaviors.

Excessive reactive oxygen free radicals (ROS) are the main cause of various oxidative diseases. It is of great significance to develop antioxidant drugs that can intelligently regulate free radical concentrations. The biomimetic simulation of glutathione peroxidase (GPx) can provide an important theoretical basis for the development of antioxidant drugs. In order to explore a simple and efficient strategy for constructing biomimetic GPx, a microgel biomimetic GPx (PNTegel) with temperature responsive catalytic activity was prepared by a one-pot synthesis method. The PNTegel, with typical enzymatic catalytic characteristics, exhibited a maximum catalytic activity at 37 °C (υ 0 = 11.51 mM min-1). The investigation of the catalytic mechanism of PNTegel suggested that the binding of different hydrophobic substrates to PNTegel was altered by the change of hydrophobicity of poly(N-isopropylacrylamide) (PNIPAM) in the microgel scaffold of PNTegel during the temperature response process. The change of hydrophobicity was the main factor for regulating the catalytic activity of PNTegel, which resulted in a temperature responsive catalytic behavior of PNTegel. This new strategy for the simple and efficient construction of biomimetic GPx by a one-pot method provides important theoretical support for exploring the preparation of highly effective antioxidant drugs.

Construction of a smart microgel glutathione peroxidase mimic based on supramolecular self-assembly.

In an effort to construct smart artificial glutathione peroxidase (GPx) featuring high catalytic activity in an efficient preparation process, an artificial microgel GPx (PPAM-ADA-Te) has been prepared using a supramolecular host-guest self-assembly technique. Herein, 6,6'-telluro-bis(6-deoxy-ß-cyclodextrin) (CD-Te-CD) was selected as a tellurium-containing host molecule, which also served as the crosslinker for the scaffold of the supramolecular microgel. And an adamantane-containing block copolymer (PPAM-ADA) was designed and synthesized as a guest building block copolymer. Subsequently, PPAM-ADA-Te was constructed through the self-assembly of CD-Te-CD and PPAM-ADA. The formation of this self-assembled construct was confirmed by dynamic light scattering, NMR, SEM and TEM. Notably, PPAM-ADA-Te not only exhibits a significant temperature responsive catalytic activity, but also features the characteristic saturation kinetics behaviour similar to that of a natural enzyme catalyst. We demonstrate in this paper that both the hydrophobic microenvironment and the crosslinker in this supramolecular microgel network played significant roles in enhancing and altering the temperature responsive catalytic behaviour. The successful construction of PPAM-ADA-Te not only provides a novel method for the preparation of microgel artificial GPx with high catalytic activity but also provides properties suitable for the future development of intelligent antioxidant drugs.

Construction of a artificial glutathione peroxidase with temperature-dependent activity based on a supramolecular graft copolymer.

A supramolecular artificial glutathione peroxidase (PNIPAM-CD-g-Te) was prepared based on a supramolecular graft copolymer. PNIPAM-CD-g-Te was constructed by supramolecular host-guest self-assembly. Significantly, PNIPAM-CD-g-Te displayed noticeable temperature-dependent catalytic activity and typical saturation kinetics behavior. It was also proved that the change in the self-assembled structure of PNIPAM-CD-g-Te during the temperature-dependent process played a significant role in the temperature-dependent catalytic behavior. The construction of PNIPAM-CD-g-Te based on supramolecular graft copolymer endows artificial GPx with temperature-dependent catalytic ability, enriched catalytic centers, and homogeneously distributed catalytic centers. This work bodes well for the development of other biologically related host-guest supramolecular biomaterials.

A supramolecular microgel glutathione peroxidase mimic with temperature responsive activity.

Glutathione peroxidase (GPx) protects cells from oxidative damage by scavenging surplus reactive oxygen species (ROS). Commonly, an appropriate amount of ROS acts as a signal molecule in the metabolism. A smart artificial GPx exhibits adjustable catalytic activity, which can potentially reduce the amount of ROS to an appropriate degree and maintain its important physiological functions in metabolism. To construct an optimum and excellent smart artificial GPx, a novel supramolecular microgel artificial GPx (SM-Te) was prepared based on the supramolecular host-guest interaction employing the tellurium-containing guest molecule (ADA-Te-ADA) and the cyclodextrin-containing host block copolymer (poly(N-isopropylacrylamide)-b-[polyacrylamides-co-poly(6-o-(triethylene glycol monoacrylate ether)-ß-cyclodextrin)], PPAM-CD) as building blocks. Subsequently, based on these building blocks, SM-Te was constructed and the formation of its self-assembled structure was confirmed by dynamic light scattering, NMR, SEM, TEM, etc. Typically, benefitting from the temperature responsive properties of the PNIPAM scaffold, SM-Te also exhibited similar temperature responsive behaviour. Importantly, the GPx catalytic rates of SM-Te displayed a noticeable temperature responsive characteristic. Moreover, SM-Te exhibited the typical saturation kinetics behaviour of a real enzyme catalyst. It was proved that the changes of the hydrophobic microenvironment and the pore size in the supramolecular microgel network of SM-Te played significant roles in altering the temperature responsive catalytic behaviour. The successful construction of SM-Te not only overcomes the insurmountable disadvantages existing in previous covalent bond crosslinked microgel artificial GPx but also bodes well for the development of novel intelligent antioxidant drugs.

Construction of a novel guest biomimetic glutathione peroxidase with solvent-dependent catalytic behavior by incorporating the active center into adamantyl molecule.

A novel guest biomimetic glutathione peroxidase (3,3'-tellurobis(propane-3,1-diyl) diadamantanecarboxylate, denoted as ADA-Te-ADA) was synthesized. ADA-Te-ADA functioned to overcome the disadvantages in the construction of building block for giant supramolecular biomimetic enzyme. To reveal the catalytic property of hydrophobic ADA-Te-ADA, the catalytic mechanism was investigated using PBS (phosphate buffer (pH 7.0. 50 mM))/methanol solvent mixture as assay solution. Itindicated that ADA-Te-ADA exhibited typical enzyme catalytic behavior by saturation kinetics measurement. Importantly, ADA-Te-ADA exhibited the typical solvent-dependent catalytic behavior. And the highest catalytic rate 4.29 µM x min-1 was obtained when the volume ratio of PBs: methanol was 5 : 5. Especially, the catalytic rates obtained based on various substrates proved that ADA-Te-ADA slightly displayed special substrate selectivity, which was the ideal catalytic characterization of building block for giant supramolecular biomimetic enzyme. The successfully synthesis of ADA-Te-ADA might highlight for the understanding of the catalytic mechanism of hydrophobic guest biomimetic glutathione peroxidase. And it also might provide the basement for the construction of giant supramolecular biomimetic enzyme.