ABSTRACT
The antifouling effects of a toothbrush-shaped photo-responsive polyzwitterionic membrane were studied via dissipative particle dynamics simulations in this work. The results reveal that the membrane modified by spiropyran methacrylate brushes displays photo-switchable and antifouling capability due to the photo-induced ring-opening reaction. Namely, surface morphology and hydrophilicity change in response to visible or UV light irradiation, which can be observed visually by protein adsorption and desorption. Further study indicates that: (1) brush-modification density can influence the structure and properties of the membrane. With low modification density, systems cannot establish an intact selective layer, which hinders the antifouling ability; as the modification density increases, the intact selective layer can be formed, which is conducive to the expression of photo-responsiveness and antifouling capability. (2) Factors of toothbrush-hair length and grafting ratio can influence the establishment of a light-responsive surface: as the grafting ratio and toothbrush-hair length increase, the light-responsive surface is gradually formed, meanwhile, the antifouling ability can be continuously reinforced under UV light irradiation. (3) As the brushes switch into a zwitterionic merocyanine state under UV exposure, the selective layer swelling becomes stronger than that with a hydrophobic spiropyran state under visible exposure. This is owing to the enhanced interaction between zwitterionic brushes and water, which is the root of the antifouling effect. The present work is expected to provide some guidelines for the design and development of novel antifouling membrane surfaces.
ABSTRACT
The self-assembly and stimuli-responsive properties of nanogel poly(n-isopropylacrylamide) (p(NIPAm)) and zwitterion-modified nanogel poly(n-isopropylacrylamide-co-sulfobetainemethacrylate) (p(NIPAm-co-SBMA)) were explored by dissipative particle dynamics simulations. Simulation results reveal that for both types of nanogel, it is beneficial to form spherical nanogels at polymer concentrations of 5-10%. When the chain length (L) elongates from 10 to 40, the sizes of the nanogels enlarge. As for the p(NIPAm) nanogel, it shows thermoresponsiveness; when it switches to the hydrophilic state, the nanogel swells, and vice versa. The zwitterion-modified nanogel p(NIPAm-co-SBMA) possesses thermoresponsiveness and ionic strength responsiveness concurrently. At 293 K, both hydrophilic p(NIPAm) and superhydrophilic polysulfobetaine methacrylate (pSBMA) could appear on the outer surface of the nanogel; however, at 318 K, superhydrophilic pSBMA is on the outer surface to cover the hydrophobic p(NIPAm) core. As the temperature rises, the nanogel shrinks and remains antifouling all through. The salt-responsive property can be reflected by the nanogel size; the volumes of the nanogels in saline systems are larger than those in salt-free systems as the ionic condition inhibits the shrinkage of the zwitterionic pSBMA. This work exhibits the temperature-responsive and salt-responsive behavior of zwitterion-modified-pNIPAm nanogels at the molecular level and provides guidance in antifouling nanogel design.
ABSTRACT
In this work, dissipative particle dynamics simulation was carried out to investigate the intelligent switching effect of nanopores grafted by the zwitterionic polymer brushes poly(carboxybetaine) with excellent antifouling properties. The result shows that with different grafting densities and grafting lengths, zwitterionic polymer brushes show typical pH- and salt-responsiveness features. When the grafting density is greater than 0.2 accompanying a grafting length of 40, pH has a significant effect on the structure and pore size of the nanopores, that is, the pore remains open under neutral condition and exhibits a switching effect under acidic condition. Similarly, the size of the nanopore can be tuned by altering the grafting density and polymer chain length under salt-concentration-responsive conditions. Differently, compared with the pH effect, the salt concentration has an obvious impact on the switching effect, i.e., responsiveness emerges with a lower grafting density and length. This work provides molecular level mechanism and theoretical guidance for the design of smart nanopores modified by zwitterionic polymer brushes, as well as plays an important role in the construction of nanopores with antifouling and pH/salt-responsive properties.
Subject(s)
Nanopores , Computer Simulation , Hydrogen-Ion Concentration , Polymers/chemistryABSTRACT
Unimolecular micelles have attracted wide attention in the field of drug delivery because of their thermodynamic stability and uniform size distribution. However, their drug loading/release mechanisms at the molecular level have been poorly understood. In this work, the stability and drug loading/release behaviors of unimolecular micelles formed using generation-5 polyamidoamine-graft-poly(carboxybetaine methacrylate) (PAMAM(G5)-PCBMA) were studied by dissipative particle dynamics simulations. In addition, the unimolecular micelles formed using generation-5 polyamidoamine-graft-poly(ethyleneglycol methacrylate) (PAMAM(G5)-PEGMA) were used as a comparison. The simulation results showed that PAMAM(G5)-PCBMA can spontaneously form core-shell unimolecular micelles. The PAMAM(G5) dendrimer constitutes a hydrophobic core to load the doxorubicin (DOX), while the zwitterionic PCBMA serves as a protective shell to improve the stability of the unimolecular micelle. The DOX can be encapsulated into the cavity of PAMAM(G5) at the physiological pH 7.4. The drug loading efficiency and drug loading content showed some regularities with the increase in the drug concentration. At the acidic pH 5.0, the loaded DOX can be released gradually from the hydrophobic core. The comparison of DOX-loaded morphologies between the PAMAM(G5)-PCBMA system and PAMAM(G5)-PEGMA system showed that the former has better monodisperse stability. This work could offer theoretical guidance for the design and development of promising unimolecular micelles for drug delivery.
Subject(s)
Dendrimers , Micelles , Computer Simulation , Doxorubicin , Drug Carriers , Drug Delivery Systems , Hydrogen-Ion Concentration , PolyaminesABSTRACT
Two new caesium borates, CsB7O10(OH)2 and CsBaB7O12, were synthesized in a high-temperature vacuum system and high-temperature open system, respectively. They all crystallize in the monoclinic space groups, C2/c (no. 15) and P21/c (no. 14), respectively. Their structures show different dimensional anionic architectures. CsB7O10(OH)2 has two-dimensional (2D) ∞[B7O10(OH)2] anionic layers with the [B7O12(OH)2] fundamental building block (FBB) which displays a novel connection mode. CsBaB7O12 possesses a three-dimensional (3D) ∞[B7O12] anionic open-framework with the [B7O15] FBB. The characterization of their properties combined with experimental and theoretical methods reveals that the two hepta-borates show differences in their optical properties due to their different optical anisotropies which are influenced by their anionic structures. The former compound CsB7O10(OH)2 presents a wide band gap of 6.6 eV and the latter compound CsBaB7O12 presents a band gap of 5.6 eV, which is smaller than that of CsB7O10(OH)2. The first-principles calculation results suggest that the birefringences are 0.08 and 0.05 at 1064 nm for CsB7O10(OH)2 and CsBaB7O12, respectively. Furthermore, the detailed summaries and structural comparisons have been provided for all available disorder-free mixed alkali- and alkaline-earth metal caesium borates.
ABSTRACT
A new borosilicate, NaCa5BO3(SiO4)2, has been synthesized by a high-temperature solution method, which crystallizes in the centrosymmetric monoclinic space group P21/ c (No. 14), having a tangled three-dimensional (3D) network including isolated [BO3] triangles, isolated [SiO4] tetrahedra, and [CaO n] ( n = 7-9) and [NaO7] polyhedra. According to our surveys, it is the first compound containing both isolated [BO3] triangles and isolated [SiO4] tetrahedra in alkali- and alkaline-earth-metal borosilicates, which enriches the structure chemistry of borosilicates. The UV-vis-NIR diffuse reflectance spectrum shows that NaCa5BO3(SiO4)2 exhibits a wide transparent region which covers the near-IR, visible, and UV windows and displays a short UV cutoff edge at about 240 nm. Additionally, the thermal behavior (TG and DSC) and IR spectrum were also analyzed. For a deeper understanding of the relationships between the structure and properties, an analysis of theoretical calculations by density functional theory was also performed.
