Adsorption of C₁–C₄ Alcohols in Zeolitic Imidazolate Framework-8: Effects of Force Fields, Atomic Charges, and Framework Flexibility

A molecular simulation study is reported for the adsorption of normal alcohols (methanol, ethanol, propanol, and butanol) in zeolitic imidazolate framework-8 (ZIF-8). The effects of force fields, atomic charges, and framework flexibility are systematically examined and compared with experimental data. Among three force fields (UFF, AMBER, and DREIDING), DREIDING has the best agreement with experiment. The atomic charges and framework flexibility are found to have negligible effects. The four alcohols exhibit S-shaped isotherms without hysteresis loop, as attributed to adsorption at different preferential sites. At a low pressure, cluster formation is observed near the organic linker (2-methylimidazolate) in ZIF-8; with increasing pressure, cage-filling occurs in the large sodalite cage. The interaction between alcohol and ZIF-8 framework is enhanced as the chain length of alcohol increases; thus, the isosteric heat of adsorption rises with chain length. The simulation study provides microscopic insight into alcohol adsorption in ZIF-8, which is useful for quantitative understanding of adsorption mechanism in other ZIFs and nanoporous materials

Water Desalination through Zeolitic Imidazolate Framework Membranes: Significant Role of Functional Groups

A molecular simulation study is reported for water desalination through five zeolitic imidazolate framework (ZIF) membranes, namely ZIF-25, -71, -93, -96, and -97. The five ZIFs possess identical rho-topology but differ in functional groups. The rejection of salt (NaCl) is found to be around 97% in ZIF-25, and 100% in the other four ZIFs. The permeance ranges from 27 to 710 kg/(m²·h·bar), about one∼two orders of magnitude higher compared with commercial reverse osmosis membranes. Due to a larger aperture size <i>d</i>_a, ZIF-25, -71, and -96 exhibit a much higher water flux than ZIF-93 and -97; however, the flux in ZIF-25, -71, and -96 is governed by the polarity of functional group rather than <i>d</i>_a. With the hydrophobic CH₃ group, ZIF-25 has the highest flux despite the smallest <i>d</i>_a among ZIF-25, -71, and -96. The lifetime of hydrogen bonding in ZIF-25 is shorter than that in ZIF-71 and -96. Furthermore, water molecules undergo a fast flushing motion in ZIF-25, but frequent jumping in ZIF-96 and particularly in ZIF-97. An Arrhenius-type relationship is found between water flux in ZIF-25 and temperature, and the activation energy is predicted to be 6.5 kJ/mol. This simulation study provides a microscopic insight into water desalination in a series of ZIFs, reveals the key factors (aperture size and polarity of functional group) governing water flux, and suggests that ZIF-25 might be an interesting reverse osmosis membrane for high-performance water desalination

Rapid review biochemistry.

Publisher’s licensing agreement prohibits multiple on-line access.Includes index.Rev. ed. of: Biochemistry. 2nd ed. c2007.Book fair 2012xi, 186 p.

Covalently Functionalized Metallic Single-Walled Carbon Nanotubes Studied Using Electrostatic Force Microscopy and Dielectric Force Microscopy

Contactless electrostatic force microscopy (EFM) and dielectric force microscopy (DFM) are demonstrated to be very powerful tools of characterizing the electronic properties of individual single-walled carbon nanotubes (SWCNTs). Taking the advantages of the tools, we confirm that the metallicity of metallic SWCNTs can be largely preserved upon dichlorocarbene functionalization ([2 + 1] cycloaddition) in comparison with the SWCNTs subject to the Prato reaction ([2 + 3] cycloaddition). This work demonstrates the distinct difference between sp² rehybridized and sp³ rehybridized covalent configurations on their influences to electronic properties of metallic SWCNTs and supports the hypothesis that [2 + 1] cycloaddition could recover the sp² hybridization on the sidewall of metallic SWCNTs and preserve the intrinsic electronic properties of SWCNTs

Efficient Removal of Pb²⁺ from Aqueous Solution by an Ionic Covalent–Organic Framework: Molecular Simulation Study

An ionic covalent–organic framework (ICOF-1 containing sp³ hybridized boron anionic centers formed by spiroborate linkage and dimethylammonium ions) is explored as an ion exchanger for the removal of lead (Pb²⁺) ions from aqueous solution. From molecular simulations, the Pb²⁺ ions are observed to exchange with the nonframework DMA⁺ ions in the ICOF-1. At a concentration of 600 ppm, the Pb²⁺ ions are completely exchanged and reside in the ICOF-1, while the DMA⁺ ions are in a dynamic equilibrium with the solution. It is revealed that the exchange between Pb²⁺ and DMA⁺ is governed by the stronger attraction of Pb²⁺ with the negatively charged ICOF-1 framework. The radial distribution functions and mean-squared displacements further show that the exchanged Pb²⁺ ions are in a closer proximity to the ICOF-1 framework with a smaller mobility than DMA⁺ ions. The simulation study provides microscopic insight into the ion-exchange process between Pb²⁺ and DMA⁺, and it suggests that the ICOF-1 might be an intriguing candidate for water purification

Differential deposition of H2A.Z in rice seedling tissue during the day-night cycle

<p>Chromatin structure has an important role in modulating gene expression. The incorporation of histone variants into the nucleosome leads to important changes in the chromatin structure. The histone variant H2A.Z is highly conserved between different species of fungi, animals, and plants. However, dynamic changes to H2A.Z in rice have not been reported during the day-night cycle. In this study, we generated genome wide maps of H2A.Z for day and night time in harvested seedling tissues by combining chromatin immunoprecipitation and high-throughput sequencing. The analysis results for the H2A.Z data sets detected 7099 genes with higher depositions of H2A.Z in seedling tissues harvested at night compared with seedling tissues harvested during the day, whereas 4597 genes had higher H2A.Z depositions in seedlings harvested during the day. The gene expression profiles data suggested that H2A.Z probably negatively regulated gene expression during the day-night cycle and was involved in many important biologic processes. In general, our results indicated that H2A.Z may play an important role in plant responses to the diurnal oscillation process.</p

Seawater Pervaporation through Zeolitic Imidazolate Framework Membranes: Atomistic Simulation Study

An atomistic simulation study is reported for seawater pervaporation through five zeolitic imidazolate framework (ZIF) membranes including ZIF-8, -93, -95, -97, and -100. Salt rejection in the five ZIFs is predicted to be 100%. With the largest aperture, ZIF-100 possesses the highest water permeability of 5 × 10^–4 kg m/(m² h bar), which is substantially higher compared to commercial reverse osmosis membranes, as well as zeolite and graphene oxide pervaporation membranes. In ZIF-8, -93, -95, and -97 with similar aperture size, water flux is governed by framework hydrophobicity/hydrophilicity; in hydrophobic ZIF-8 and -95, water flux is higher than in hydrophilic ZIF-93 and -97. Furthermore, water molecules in ZIF-93 move slowly and remain in the membrane for a long time but undergo to-and-fro motion in ZIF-100. The lifetime of hydrogen bonds in ZIF-93 is found to be longer than in ZIF-100. This simulation study quantitatively elucidates the dynamic and structural properties of water in ZIF membranes, identifies the key governing factors (aperture size and framework hydrophobicity/hydrophilicity), and suggests that ZIF-100 is an intriguing membrane for seawater pervaporation

Seawater Pervaporation through Zeolitic Imidazolate Framework Membranes: Atomistic Simulation Study

An atomistic simulation study is reported for seawater pervaporation through five zeolitic imidazolate framework (ZIF) membranes including ZIF-8, -93, -95, -97, and -100. Salt rejection in the five ZIFs is predicted to be 100%. With the largest aperture, ZIF-100 possesses the highest water permeability of 5 × 10^–4 kg m/(m² h bar), which is substantially higher compared to commercial reverse osmosis membranes, as well as zeolite and graphene oxide pervaporation membranes. In ZIF-8, -93, -95, and -97 with similar aperture size, water flux is governed by framework hydrophobicity/hydrophilicity; in hydrophobic ZIF-8 and -95, water flux is higher than in hydrophilic ZIF-93 and -97. Furthermore, water molecules in ZIF-93 move slowly and remain in the membrane for a long time but undergo to-and-fro motion in ZIF-100. The lifetime of hydrogen bonds in ZIF-93 is found to be longer than in ZIF-100. This simulation study quantitatively elucidates the dynamic and structural properties of water in ZIF membranes, identifies the key governing factors (aperture size and framework hydrophobicity/hydrophilicity), and suggests that ZIF-100 is an intriguing membrane for seawater pervaporation

MOESM1 of High-level extracellular protein production in Bacillus subtilis using an optimized dual-promoter expression system

Additional file 1. Additional Figures and Tables