Synthesis and gas permeability of ABA‐type triblock copolymers derived from fluorine‐containing polyimide with polyhedral oligomeric silsesquioxane

ABA‐type triblock copolymers derived from 4,4'‐(hexafluoroisopropylidene)diphthalicanhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) and methacryl phenyl polyhedral oligomeric silsesquioxane (MPPOSS) were synthesized by atom transfer radical polymerization. The chemical structure of the synthesized ABA‐type triblock copolymer was confirmed by ¹H NMR, ¹³C NMR, ²⁹Si NMR and Fourier transform infrared analyses. The ratios of 6FDA‐TeMPD and MPPOSS determined by TGA were 94/6, 85/15, 77/23, 68/32, 57/43 and 31/69. The film density of the ABA‐type triblock copolymer films did not conform to the mixing rule because of polyimide (PI) chain aggregation. Based on contact angle and water uptake analyses, the hydrophobicity of the ABA‐type triblock copolymer film was determined to be higher than the theoretical value because of POSS cage effects and PI chain aggregation. The gas permeability coefficient of the ABA‐type triblock copolymer decreased compared with that of PI because of aggregation of PI chains and inhibition of solubility decreases by substitutes with high affinity. ABA‐type triblock copolymer CO₂/H₂ separation performance increased compared with that of PI. The ABA‐type triblock copolymer derived from PI and MPPOSS can be described as a polymer material with higher hydrophobicity and higher CO₂/H₂ selectivity than PI. © 2015 Society of Chemical Industry     

Formation of carbamates and cross-linking of microbial poly(ε-<Emphasis Type="SmallCaps">l</Emphasis>-lysine) studied by <Superscript>13</Superscript>C and <Superscript>15</Superscript>N solid-state NMR

Formation of carbamates by amino groups of poly(ε-l-lysine) (ε-PL) and cross-linking of ε-PL were studied by using ¹³C and ¹⁵N solid-state NMR. It is a characteristic found in ε-PL cast from basic aqueous solution exposed to the air or gaseous CO₂. It is not observed in ε-PL cast from acidic aqueous solution and ε-PL cast from degassed aqueous solution under CO₂ free environment. The carboxyl carbon and amide nitrogen appear at 164 ppm in ¹³C spectrum and 92 ppm in ¹⁵N spectrum, respectively, which arise when some amino groups of ε-PL react with gaseous CO₂ to make carbamates. In addition to these peaks a peak at 171 ppm appears. We assigned it to amide C=O carbons which can not make intermolecular hydrogen bondings since there exist bulky carbamates groups close to these C=O groups. Self-assembly of ionic pairs of ammonium groups and carbamate anions leads to cross-linking of ε-PL.     

Domain-Swapping Design by Polyproline Rod Insertion

During domain swapping, proteins mutually interconvert structural elements to form a di-/oligomer. Engineering this process by design is important for creating a higher order protein assembly with minimal modification. Herein, a simple design strategy is shown for domain-swapping formation by loop deletion and insertion of a polyproline rod. Crystal structures revealed the formation of the domain-swapped dimers and polyproline portion formed a polyproline II (PPII) structure. Small-angle X-ray scattering demonstrated that an extended orientation of domain-swapped dimer was retained in solution. It is found that a multiple of three of inserting proline residue is favored for domain swapping because of the helical nature of PPII. The rigid nature of the polyproline rod enables precise control of the interdomain distance and orientation.     

Synthesis and characterization of ABA‐type triblock copolymers derived from polyimide and poly(2‐methyl‐2‐adamantyl methacrylate)

ABA‐type triblock copolymers derived from 4,4‐(hexafluoroisopropylidene)diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine and 2‐methyl‐2‐adamantyl methacrylate (2‐MAdMA) were synthesized via atom transfer radical polymerization. The component ratios of polyimide (PI) and poly(2‐MAdMA) (PMAdMA) were about 8/2, 6/4 and 3/7, as determined using ¹H NMR spectroscopy and thermogravimetric analysis (TGA). The film structure of the triblock copolymers was dependent on the PI structure. Hydrophobicity increased as the component ratio of PMAdMA increased. Based on TGA, three‐step decomposition behaviors of all triblock copolymers derived from PI and PMAdMA in nitrogen and air atmosphere were observed. The gas permeability of the triblock copolymers was lower than that of PI. This finding can be attributed to the decrease in fractional free volume by the adamantane component and the decrease in permeability of the triblock copolymers compared with PI. The dielectric constant of the triblock copolymers was lower than that of PI. The dielectric constant was dependent on molar volume and molar porlarizability, and the dielectric constant derived from the symmetric structure of adamantane was reduced. The ABA‐type triblock copolymers derived from PI and PMAdMA can be considered as new polymer materials with high hydrophobicity, high H₂/CO₂ selectivity and low dielectric constant. © 2013 Society of Chemical Industry     

A new microcellular foam injection‐molding technology using non‐supercritical fluid physical blowing agents

A new foam injection‐molding technology was developed to produce microcellular foams without using supercritical fluid (SCF) pump units. In this technology, physical blowing agents (PBA), such as nitrogen (N₂) and carbon dioxide (CO₂), do not need to be brought to their SCF state. PBAs are delivered directly from their gas cylinders into the molten polymer through an injector valve, which can be controlled by a specially designed screw configuration and operation sequence. The excess PBA is discharged from the molten polymer through a venting vessel. Alternatively, additional PBA is introduced through the venting vessel when the polymer is not saturated with PBA. The amount of gas delivered into the molten polymer is controlled by the gas dosing time of the injector valve, the secondary reducing pressure of the gas cylinder and the outlet (back) pressure of the venting vessel. Microcellular polypropylene foams were prepared using the developed foam injection‐molding technology with 2–6 MPa CO₂ or 2–8 MPa N₂. High expansion foams with an average cell size of less than 25 μm were prepared. The developed technology dispels arguments for the necessity to pressurize N₂ or CO₂ to the SCF to prepare microcellular foams. POLYM. ENG. SCI., 57:105–113, 2017. © 2016 Society of Plastics Engineers     

(+)-cis-3,5-dimethyl-2-(3-pyridyl) thiazolidin-4-one hydrochloride (SM-12502) as a novel substrate for cytochrome P450 2A6 in human liver microsomes

(+)-cis-3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one hydrochloride (SM-12502) was oxidized by human liver microsomes to produce the S-oxide as a sole metabolite. Indirect evidence suggested that the S-oxidation was catalyzed by cytochrome P450 (CYP). Eadie-Hofstee plots showed biphasic pattern, suggesting that at least two enzymes were involved in the S-oxidation in human liver microsomes. Kinetic parameters of the S-oxidase with high-affinity showed Km and Vmax values of 20.9 +/- 4.4 microM and 0.111 +/- 0.051 nmol/min/mg microsomal protein, respectively. The S-oxidase activity was inhibited by coumarin and anti-CYP2A antibody. Among the contents of forms of CYP 20 samples of human liver microsomes, the content of CYP2A6 correlated with S-oxidase activity measured with 50 microM SM-12502 (r = .808, P < .0005). A close correlation (r = .908, P < .0001) was observed between activities of SM-12502 S-oxidase and coumarin 7-hydroxylase. Microsomes from genetically engineered human B-lymphoblastoid cells expressing CYP2A6 metabolized SM-12502 to the S-oxide efficiently. The results indicate that CYP2A6 isozyme is a major form of CYP responsible for the S-oxidation of SM-12502 in human liver microsomes. Thus, SM-12502 will be a useful tool in further research to analyze a human genetic polymorphism of CYP2A6.     

One Method for Selection of Circuit Parameters of a Self-Commutated Rectifier

A method of selecting the circuit parameters of a self-commutated rectifier circuit which aims at improving the power factor is proposed.     

Surface Engineering of Top7 to Facilitate Structure Determination

Top7 is a de novo designed protein whose amino acid sequence has no evolutional trace. Such a property makes Top7 a suitable scaffold for studying the pure nature of protein and protein engineering applications. To use Top7 as an engineering scaffold, we initially attempted structure determination and found that crystals of our construct, which lacked the terminal hexahistidine tag, showed weak diffraction in X-ray structure determination. Thus, we decided to introduce surface residue mutations to facilitate crystal structure determination. The resulting surface mutants, Top7sm1 and Top7sm2, crystallized easily and diffracted to the resolution around 1.7 Å. Despite the improved data, we could not finalize the structures due to high R values. Although we could not identify the origin of the high R values of the surface mutants, we found that all the structures shared common packing architecture with consecutive intermolecular β-sheet formation aligned in one direction. Thus, we mutated the intermolecular interface to disrupt the intermolecular β-sheet formation, expecting to form a new crystal packing. The resulting mutant, Top7sm2-I68R, formed new crystal packing interactions as intended and diffracted to the resolution of 1.4 Å. The surface mutations contributed to crystal packing and high resolution. We finalized the structure model with the R/R_free values of 0.20/0.24. Top7sm2-I68R can be a useful model protein due to its convenient structure determination.     

Tunable Seebeck Coefficient in Monolayer Graphene Under Periodic Potentials

The effect of the superlattice potential on the Seebeck coefficient tensor of graphene sheet is theoretically investigated. Strong anisotropy of the Seebeck coefficient tensor is observed. The origin of the anisotropy can be attributed to the modification of the dispersion relation in the vicinity of the Dirac point. Our finding shows that the magnitude of the Seebeck coefficient of graphene can be flexibly changed under a superlattice potential.     

Electrical Properties of (110)-Oriented Nondoped Mg2Si Films with p-Type Conduction Prepared by RF Magnetron Sputtering Method

Magnesium silicide (Mg₂Si) thick films with (110) orientation were fabricated on (001) sapphire substrate using radiofrequency magnetron sputtering. Stoichiometric Mg₂Si films with composition Si/(Mg + Si) = 0.33 were achieved over a range of vacuum from 10 mTorr to 140 mTorr and 300°C. On postannealing the film at 500°C, the out-of-plane lattice parameter shifted to lower values and the electrical conductivity increased by two orders of magnitude. A room-temperature Seebeck coefficient of 517 μV K^?1 was observed and found to decrease with increasing temperature; the Seebeck coefficient remained at a constant positive value of 212 μV K^?1 at 500°C. This can be related to the possibility of p-type conduction in this temperature range.