Biochemical evidence for the tyrosine involvement in cationic intermediate stabilization in mouse β-carotene 15, 15'-monooxygenase

Background  

β-carotene 15,15'-monooxygenase (BCMO1) catalyzes the crucial first step in vitamin A biosynthesis in animals. We wished to explore the possibility that a carbocation intermediate is formed during the cleavage reaction of BCMO1, as is seen for many isoprenoid biosynthesis enzymes, and to determine which residues in the substrate binding cleft are necessary for catalytic and substrate binding activity. To test this hypothesis, we replaced substrate cleft aromatic and acidic residues by site-directed mutagenesis. Enzymatic activity was measured in vitro using His-tag purified proteins and in vivo in a β-carotene-accumulating E. coli system.     

Probing interfacial interactions of nafion ionomer: Thermal expansion of nafion thin films on substrates of different hydrophilicity/hydrophobicity

Interfacial interactions of Nafion ionomer with superhydrophilic (Pt, Au), hydrophilic (SiO₂), and hydrophobic (graphene, octyltrichlorosilane [OTS]‐modified SiO₂) is investigated, using in situ thermal ellipsometry, by quantification of substrate‐ and thickness‐dependent thermal properties of the ultrathin Nafion films of nominal thickness ranging 25–135 nm. For sub‐50 nm thin Nafion films, the thermal expansion coefficient of films decreased in the order of most hydrophobic to most hydrophilic substrate: OTS > graphene > SiO₂ > Au > Pt, implying weaker interpolymer and polymer–substrate interactions for films on hydrophobic substrates. Expansion coefficient of films on SiO₂, graphene, and OTS‐modified SiO₂ decreased with thickness whereas that of films on Au and Pt substrates increased with thickness. Above ~100 nm of thickness, films on all substrates converged toward a common value representative of bulk Nafion. Thermal transition temperature was found to be higher for films on hydrophilic SiO₂ than that for films on hydrophobic graphene and OTS‐modified SiO₂ but was not discernible for films on Au and Pt substrates. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 343–352     

Enhancement of mechanical and barrier properties of LLDPE composite film via PET fiber incorporation for agricultural application

A study was conducted to determine the potential of linear low‐density polyethylene (LLDPE)‐PET fiber composite films to be used as an agricultural mulching film. Incorporation of 1 wt% PET fiber into the LLDPE matrix improved the tensile strength and percent elongation. The water vapor transmission rate was significantly lowered because of the presence of PET fibers. Also, the effect of continuous exposure of films to pesticide and UV light has been reported in terms of deterioration of mechanical and optical properties of the films. Differential scanning calorimetry shows that there is no effect of the presence of PET fibers on processing temperature of LLDPE at optimized loading; however, it was found that it lowers the latent heat of fusion and crystallization.     

Effect of the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions on barrier properties of mice skin for transdermal permeation of tetracaine hydrochloride: in vitro

Effect of composition of lecithin water-in-oil and oil-in-water microemulsion on in vitro transdermal permeation of tetracaine hydrochloride was studied on mice model. The results were compared with an aqueous solution of tetracaine hydrochloride (2.7 mg/ml). In vitro skin flux and permeability coefficients were obtained using the Franz diffusion cell. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to study the mechanism of action of the microemulsion. Micrographs of TEM and CLSM studies were analyzed by using Image Pro Plus image software. Skin flux of tetracaine hydrochloride was found to be dependent on the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions. At lower Km ratio (i.e. 0.5:1 and 0.8:1) of microemulsion, the rate of permeation of tetracaine hydrochloride was higher when compared to the microemulsion of higher Km ratio (1:1 and 1.5:1). Image analysis of TEM micrograph, 6h after application of lecithin microemulsion, showed 3.5+/-0.75-fold (p<0.001) increase in the intercellular space in the epidermis and 3.8+/-0.4-fold (p<0.001) enhancement in upper dermis. CLMS results show that sweat gland and hair follicles also provided path for permeation of the drug through the skin.     

Comparison of morphology and mechanical properties of surfactant aggregates at water-silica and water-graphite interfaces from molecular dynamics simulations

Cationic surfactants are important for a wide range of applications, including controlled drug delivery systems, emulsifiers, and chemical mechanical polishing. It is therefore important to better understand surfactant structure and properties at the solid-liquid interface. Here, classical molecular dynamics simulations with empirical potentials are used to compare the structures and mechanical properties of cationic surfactant micelles at hydrophobic (graphite) and hydrophilic (silica) surface-water interfaces. In particular, the morphology of monolayers and bilayers of C12TAB (n-dodecyltrimethylammoniumbromide) at these interfaces, and their responses to atomic force microscopy indentation, are examined. The simulations predict that surfactant monolayers and bilayers on silica evolve into a spherical micelle structure, in agreement with theoretical models of surfactant morphology. In contrast, surfactant monolayers on graphite evolve into a hemi-cylindrical structure, in agreement with experimental findings. In the simulated indentation of the micelle/silica system, the spherical micelle breaks apart and forms a surfactant monolayer. The indentation force curve has a maximum value of 2.25 nN. On the other hand, the simulated indentation of the micelle/graphite system causes the hemi-cylindrical micelle structure to break apart and the surfactant tails to wrap around the graphite indenter. The indentation force curve has a maximum value of 13 nN.     

Complementarity and clustering in a simple model mixed bilayer

A bilayer of uniform thickness containing a mixture of long and short lipids is simulated using a parallel hard-rod model to illustrate the effect of transbilayer repulsions between the tails of the long component. Monte Carlo simulations show considerable entropy-driven clustering within each layer. Demixing reaches a maximum at the highest packing fraction of the liquid state and decreases as the system orders. The formation of complementary clusters of long and short rods on opposite sides of the bilayer increases translational freedom within each cluster by reducing constraints imposed by the opposing leaflet, an effect that becomes less important as rods lock into facing hexagonally ordered arrays.     

Fabrication of catalyst-coated membrane by modified decal transfer technique

A decal transfer method based on colloidal ink was developed for the fabrication of membrane electrode assemblies (MEAs). The new method requires fewer steps and utilizes H⁺ form of membrane compared to conventional decal method based on solution ink utilizing Na⁺ form of membrane. The structural features of the electrodes made by the modified decal method were investigated by scanning electron microscopy (SEM). The performance of fabricated electrode was evaluated for oxygen reduction reaction in a proton exchange membrane fuel cell. The results indicate that the modified decal method has the potential to be a facile method of fabricating electrodes with high performance.     

Structural,morphological and photoluminescence characteristics of sol-gel derived nano phase CeO<Subscript>2</Subscript> films deposited using citric acid

Homogenous nano structured CeO₂ films have been prepared by a sol-gel process using different mole ratios of citric acid as additive. XPS studies clearly illustrate an increase in Ce³⁺ proportion upon the use of higher citric acid content for the deposition of films. The crystallite sizes in the films lie in the nanorange. Photoluminescence emission in the films is attributed to various defects resulting from crystallization. Lowest transparency, high Ce³⁺ content and optimum sized crystallites in CeO₂ (1:1.5) films have led to its highest PL characteristics. Ce³⁺ chemical state is the major contributor to the PL activity of these films. The SEM micrographs show a reduced level of CeO₂ agglomeration in the films deposited using higher citric acid contents. A comparison of different properties of CeO₂ films deposited using citric acid and CeO₂–TiO₂ films has also been made.