A Perturbed Hard-Sphere-Chain Equation of State for Polymer Solutions and Blends Based on the Square-Well Coordination Number Model

Based on the concept of a perturbed hard-sphere-chain (PHSC), where the square-well fluid is the reference system, a perturbation term is developed from the coordination number model for pure and mixture square-well fluids proposed by this group. Consequently, we derive a new PHSC type equation of state (EOS), which is of much simpler formulation and is even easier to use. The EOS has been extensively tested in terms of a large data bank, consisting of the properties of 37 normal fluids and solvents, 67 polymers. The correlation accuracy for the saturated properties is within the errors in common EOS approach. In particular, the grand average deviation for correlating the liquid densities for 67 polymers is 0.19%, which is of the same accuracy as that for commonly used lattice model EOSs. In all of the calculations, the EOS needs only three temperature- and composition-independent parameters. In addition, the new EOS is used for 40 sets of vapor−liquid equilibrium (VLE) calculations of polymer−solvent systems. Three typical liquid−liquid equilibrium (LLE) systems have been investigated by using the EOS, including both the upper critical solution temperature and the lower critical solution temperature polymer−solvent and polymer blend systems. The calculated binodal and spinodal curves are in good agreement with experimental data. All of the VLE and LLE calculations need conventional mixing rules and only a binary interaction parameter

Optimum placement of UAV as relays

IEEE Unmanned aerial vehicles (UAVs) as aerial base stations or relays are becoming increasingly important in communications. In this letter, the optimum placement of a relaying UAV for maximum reliability is studied. The total power loss, the overall outage and the overall bit error rate are derived as reliability measures. The optimum altitude is investigated for both static and mobile UAVs. Numerical results show that different reliability measures have slightly different optimum altitudes and that decode-and-forward is better than amplify-and-forward

Mechanism of Radical Initiation and Transfer in Class Id Ribonucleotide Reductase Based on Density Functional Theory

Class Id ribonucleotide reductase (RNR) is a newly discovered enzyme, which employs the dimanganese cofactor in the superoxidized state (MnIII/MnIV) as the radical initiator. The dimanganese cofactor of class Id RNR in the reduced state (inactive) is clearly based on the crystal structure of the Fj-β subunit. However, the state of the dimanganese cofactor of class Id RNR in the oxidized state (active) is not known. The X-band EPR spectra have shown that the activated Fj-β subunit exists in two distinct complexes, 1 and 2. In this work, quantum mechanical/molecular mechanical calculations were carried out to study class Id RNR. First, we have determined that complex 2 contains a MnIII-(μ-oxo)2-MnIV cluster, and complex 1 contains a MnIII-(μ-hydroxo/μ-oxo)-MnIV cluster. Then, based on the determined dimanganese cofactors, the mechanism of radical initiation and transfer in class Id RNR is revealed. The MnIII-(μ-oxo)2-MnIV cluster in complex 2 has not enough reduction potential to initiate radical transfer directly. Instead, it needs to be monoprotonated into MnIII-(μ-hydroxo/μ-oxo)-MnIV (complex 1) before the radical transfer. The protonation state of μ-oxo can be regulated by changing the protein microenvironment, which is induced by the protein aggregation and separation of β subunits with α subunits. The radical transfer between the cluster of MnIII-(μ-hydroxo/μ-oxo)-MnIV and Trp30 in the radical-transfer chain of the Fj-β subunit (MnIII/MnIV ↔ His100 ↔ Asp194 ↔ Trp30 ↔ Arg99) is a water-mediated tri-proton-coupled electron transfer, which transfers proton from the ε-amino group of Lys71 to the carboxyl group of Glu97 via the water molecule Wat551 and the bridging μ-hydroxo ligand through a three-step reaction. This newly discovered proton-coupled electron-transfer mechanism in class Id RNR is different from those reported in the known Ia–Ic RNRs. The ε-amino group of Lys71, which serves as a proton donor, plays an important role in the radical transfer

d‑Amino Acid Oxidase Immobilized on Pt Nanoparticle-Loaded Porous SiO₂ Nanospheres Coated with a Zirconium-Based Coordination Polymer for Catalytic Deamination of d‑Alanine

Porous SiO2 nanospheres are prepared and loaded with platinum (Pt) nanoparticles (Pt&SiO2). The Pt&SiO2 nanospheres are coated with a zirconium-based coordination polymer (Pt&SiO2&Zr-cp). Etching of the core SiO2 with NaOH produces hollow nanospheres Pt&h-SiO2&Zr-cp. d-Amino acid oxidase (DAAO) with hexahistidine tags was absorbed onto the hollow nanospheres strongly, by utilizing the coordinative interactions between Zr­(IV) and the hexahistidine tags. The conjugate DAAO&Pt&h-SiO2&Zr-cp possesses two-enzyme catalysis capability. The adsorbed DAAO catalyzes oxidative deamination of d-amino acids, and hydrogen peroxide (H2O2) is evolved as a byproduct. The loaded Pt nanoparticles possess peroxidase activity, decomposing H2O2 into H2O and O2. Thus, the byproduct inhibitory effect can be minimized. In addition, the generated dioxygen O2 can be used to oxidize the reduced cofactor FDA of the adsorbed DAAO. The hybrid DAAO&Pt&h-SiO2&Zr-cp was applied for catalytic deamination of d-alanine and exhibited a catalytic efficiency more than four times that of free DAAO

Effect of Chain Conformation on the Single-Molecule Melting Force in Polymer Single Crystals: Steered Molecular Dynamics Simulations Study

Understanding the relationship between polymer chain conformation as well as the chain composition within the single crystal and the mechanical properties of the corresponding single polymer chain will facilitate the rational design of high performance polymer materials. Here three model systems of polymer single crystals, namely poly­(ethylene oxide) (PEO), polyethylene (PE), and nylon-66 (PA66) have been chosen to study the effects of chain conformation, helical (PEO) versus planar zigzag conformation (PE, PA66), and chain composition (PE versus PA66) on the mechanical properties of a single polymer chain. To do that, steered molecular dynamics simulations were performed on those polymer single crystals by pulling individual polymer chains out of the crystals. Our results show that the patterns of force–extension curve as well as the chain moving mode are closely related to the conformation of the polymer chain in the single crystal. In addition, hydrogen bonds can enhance greatly the force required to stretch the polymer chain out of the single crystal. The dynamic breaking and reformation of multivalent hydrogen bonds have been observed for the first time in PA66 at the single molecule level

Low-Valent Titanium-Mediated Cyclopropanation of Vinylogous Esters

Inter- and intramolecular titanium-mediated cyclopropanation reactions of vinylogous esters are reported. Comparison between the Kulinkovich cyclopropanation of esters and vinylogous esters provides mechanistic insight regarding reaction variables such as reaction temperature, solvents, and a Lewis acid additive

Effect of Chain Conformation on the Single-Molecule Melting Force in Polymer Single Crystals: Steered Molecular Dynamics Simulations Study

Understanding the relationship between polymer chain conformation as well as the chain composition within the single crystal and the mechanical properties of the corresponding single polymer chain will facilitate the rational design of high performance polymer materials. Here three model systems of polymer single crystals, namely poly­(ethylene oxide) (PEO), polyethylene (PE), and nylon-66 (PA66) have been chosen to study the effects of chain conformation, helical (PEO) versus planar zigzag conformation (PE, PA66), and chain composition (PE versus PA66) on the mechanical properties of a single polymer chain. To do that, steered molecular dynamics simulations were performed on those polymer single crystals by pulling individual polymer chains out of the crystals. Our results show that the patterns of force–extension curve as well as the chain moving mode are closely related to the conformation of the polymer chain in the single crystal. In addition, hydrogen bonds can enhance greatly the force required to stretch the polymer chain out of the single crystal. The dynamic breaking and reformation of multivalent hydrogen bonds have been observed for the first time in PA66 at the single molecule level

Role of Surface Ligands in the Nanoparticle Assemblies: A Case Study of Regularly Shaped Colloidal Crystals Composed of Sodium Rare Earth Fluoride

Assembly of nanoparticles is a promising route to fabricate devices from nanomaterials. Colloidal crystals are well-defined three-dimensional assemblies of nanoparticles with long-range ordered structures and crystalline symmetries. Here, we use a solvent evaporation induced assembly method to obtain colloidal crystals composed of polyhedral sodium rare earth fluoride nanoparticles. The building blocks exhibit the same crystalline orientation in each colloidal crystal as indicated in electron diffraction patterns. The driving force of the oriented assembly is ascribed to the facet-selected capping of oleic acid molecules on {110} facets of the nanoparticles, and the favorable coordination behavior of OA molecules is explained by the steric hindrance determined adsorption based on the studies of the surface atomic structure of nanocrystals and molecular mechanics simulation of OA molecules. The capping ligands also provide hydrophobic interactions between nanoparticles and further direct the oriented assembly process to construct a face-centered cubic structure. These results not only provide a new type of building block for colloidal crystals, but also clarify the important role of surface ligands, which determine the packed structure and orientations of nanoparticles in the assemblies