Relationship between the Co-Continuous Morphology of Immiscible Polymer Blends and the Structure of an In Situ Formed Graft Copolymer.

In order to get stable co-continuous morphology in immiscible polymer blends, besides reducing the interfacial tension, the compatibilizer should not only promote the formation of flat interface between different phases, but also not hinder the coalescence of the dispersed phase. Herein, the relationship between the morphology of the compatibilized polystyrene/nylon 6/styrene-maleic anhydride (PS/PA6/SMA) immiscible polymer blends and the structures of the in-situ formed SMA-g-PA6 graft copolymers as well as the processing conditions are studied. Two kinds of SMA are used: SMA28 (28 wt.% MAH) and SMA11 (11 wt.% MAH). After melt blending with PA6, the in-situ formed copolymer SMA28-g-PA6 has on average of four PA6 side chains, while that of SMA11-g-PA6 has only one. Dissipative particle dynamics simulation results indicate that both SMA28-g-PA6 copolymer and PS/PA6/SMA28 blends tend to form co-continuous structure, while those related to SMA11 intend to form sea-island morphologies. These results are correct only at relatively low rotor speed (60 rpm). When the rotor speed is higher (105 rpm), sea-island morphologies are obtained in SMA28 systems, while that for SMA11 ones are co-continuous. This indicates that higher shear stress can elongate the minor phase domains to form flat interfaces, while the SMA28-g-PA6 copolymers can be pulled out from the interface.

Folate polyglutamylation eliminates dependence of activity on enzyme concentration in mitochondrial serine hydroxymethyltransferases from Arabidopsis thaliana.

The reversible reaction catalyzed by serine hydroxymethyltransferase (SHMT) is the major one-carbon unit source for essential metabolic processes. The Arabidopsis thaliana genome encodes seven SHMT isozymes localized in mitochondria, plastids, nuclei, and the cytosol. Knowledge of the biochemical properties of each isozyme is central to understanding and manipulating one-carbon metabolism in plants. We heterologously expressed and purified three recombinant SHMTs from A. thaliana (AtSHMTs) putatively localized in mitochondria (two) and the cytosol (one). Their biochemical properties were characterized with respect to the impact of folate polyglutamylation on substrate saturation kinetics. The two mitochondrial AtSHMTs, but not the cytosolic one, had increased turnover rates at higher (>0.4ng/µL) enzyme concentrations in the presence of monoglutamylated folate substrates, but not in the presence of pentaglutamylated folate substrates. We found no experimental support for a change in oligomerization state over the range of enzyme concentration studied. Modeling of the enzyme structures presented features that may explain the activity differences between the mitochondrial and cytosolic isozymes.

An FMN hydrolase of the haloacid dehalogenase superfamily is active in plant chloroplasts.

FMN hydrolases catalyze dephosphorylation of FMN to riboflavin. Although these enzymes have been described in many organisms, few had their corresponding genes cloned and their recombinant proteins biochemically characterized, and none had their physiological roles determined. We found previously that FMN hydrolase activity in pea chloroplasts is Mg(2+)-dependent, suggesting an enzyme of the haloacid dehalogenase (HAD) superfamily. In this study, a new FMN hydrolase was purified by multistep chromatography after ammonium sulfate precipitation. The molecular weight of the native protein was estimated at ∼59,400, a dimer of about twice the predicted molecular weight of most HAD superfamily phosphatases. After SDS-PAGE of the partially purified material, two separate protein bands within 25-30 kDa were extracted from the gel and analyzed by nanoLC-MS/MS. Peptide sequence matching to the protein samples suggested the presence of three HAD-like hydrolases. cDNAs for sequence homologs from Arabidopsis thaliana of these proteins were expressed in Escherichia coli. Activity screening of the encoded proteins showed that the At1g79790 gene encodes an FMN hydrolase (AtcpFHy1). Plastid localization of AtcpFHy1 was confirmed using fluorescence microscopy of A. thaliana protoplasts transiently expressing the N-terminal fusion of AtcpFHy1 to enhanced green fluorescent protein. Phosphatase activity of AtcpFHy1 is FMN-specific, as assayed with 19 potential substrates. Kinetic parameters and pH and temperature optima for AtcpFHy1 were determined. A phylogenetic analysis of putative phosphatases of the HAD superfamily suggested distinct evolutionary origins for the plastid AtcpFHy1 and the cytosolic FMN hydrolase characterized previously.

A narrative review on sacubitril/valsartan and ventricular arrhythmias.

Sacubitril/valsartan, the first angiotensin receptor neprilysin inhibitor approved by the Food and Drug Administration for marketing, has been shown to reduce the risk of cardiovascular death or heart failure hospitalization and improve symptoms in patients with chronic heart failure with a reduced ejection fraction. However, some researchers have also found that sacubitril/valsartan has an antiarrhythmic effect. The mechanism by which sacubitril/valsartan reduces the mortality associated with malignant ventricular arrhythmias is not precise. Many studies have concluded that ventricular arrhythmia is associated with a reduction in myocardial fibrosis. This article reviews the current understanding of the effects of sacubitril/valsartan on the reduction of ventricular arrhythmia and explains its possible mechanisms. The results of this study suggest that sacubitril/valsartan reduces the occurrence of appropriate implantable cardioverter-defibrillator shocks. Meanwhile, sacubitril/valsartan may reduce the occurrence of ventricular arrhythmias by affecting 3 pathways of B-type natriuretic peptide, Angiotensin II, and Bradykinin. The conclusion of this study is that sacubitril/valsartan reduces the number of implantable cardioverter-defibrillator shocks and ventricular arrhythmias in heart failure with reduced ejection fraction patients.

Synergistic Double Cross-Linked Dynamic Network of Epoxidized Natural Rubber/Glycinamide Modified Polyacrylic Acid for Silicon Anode in Lithium Ion Battery: High Peel Strength and Super Cycle Stability.

Silicon (Si), a high-capacity lithium-ion battery anode material, has aroused wide attention. Its further practical application has been limited by its huge volume change during the cycle. To reduce this defect, the double cross-linked product of glycinamide hydrochloride modified poly(acrylic acid) (PAG) and epoxidized natural rubber (ENR) was developed as a water-based binder to obtain sufficient elasticity and a sufficiently strong adhesive force. Due to the double cross-linked structures in the system, the binder was enabled to effectively disperse and transfer the stress generated by the volume expansion of the Si particles and keep the integrity of the electrode during the cycle, thus obtaining excellent cycle performance. When the current density was 1 A g-1, PE55 (PAG: ENR = 1:1 cross-linked polymer) electrode still achieved a specific capacity of 2322.2 mAh g-1 after 100 cycles of constant current charge and discharge, and PE55 binder exhibited excellent bonding properties (4.45 N) and mechanical properties (stress: 5.51 MPa, strain: 87.4%). The comparison of poly(acrylic acid) (PAA) electrodes suggests that the introduction of elastic polymer and the construction of double cross-linked structures can increase the stability of Si anodes.

A high-performance liquid chromatography-based fluorometric method for assaying serine hydroxymethyltransferase toward serine formation.

A high-performance liquid chromatography (HPLC)-based fluorometric method for measuring serine hydroxymethyltransferase (SHMT) activity toward formation of serine and (6S)-H(4)PteGlu(n) has been developed. In this method, serine formed by SHMT activity is reacted with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) to form the fluorescent adduct NBD-serine. The fluorescent assay components are then separated by reversed-phase chromatography, and NBD-serine is quantified by comparison with standards. This method was used to determine the K(m) and k(cat) values for 5,10-CH(2)-H(4)PteGlu(5) of an SHMT from Arabidopsis thaliana. These data represent the first determination of kinetic parameters for (6S)-5,10-CH(2)-H(4)PteGlu(5) for an SHMT from any organism.

The "criminal" artery of de Winter may be the left circumflex artery: A CARE-compliant case report.

RATIONALE: De Winter et al first described a new ST-segment elevation myocardial infarction (STEMI)-equivalent pattern associated with acute occlusion of the left anterior descending coronary artery (LAD). Studies show that this pattern has a positive predictive value of 95.2% to 100%. However, some cases of non-STEMI, caused by acute right coronary artery or LAD diagonal branch occlusion, have been reported, which exhibit electrocardiogram (ECG) changes similar to the de Winter pattern. Few cases of de Winter ECG pattern caused by left circumflex artery (LCX) stenosis have been reported. PATIENT CONCERNS: A 57-year-old man was admitted to the emergency department 12 hours after suffering from oppressive chest pain and diaphoresis. The patient had a history of diabetes and smoking. An initial ECG showed atrial fibrillation, upsloping ST-segment depression at the J point, followed by peaked, positive T waves in leads V2 to V6 and slight ST-segment elevation in lead aVR, with poor R-wave progression. Coronary angiography showed tubular stenosis (up to 95%) of the proximal portion of the LCX. DIAGNOSIS: LCX stenosis led to a diagnosis of non-STEMI. INTERVENTIONS: Left coronary artery stenosis was successfully treated with angioplasty and insertion of a drug-eluting stent. OUTCOMES: The patient's chest pain resolved completely after stent implantation. No myocardial infarction occurred during the 6-month follow-up period. LESSONS: De Winter ECG pattern cannot be presumed to be associated with LAD stenosis and 18-lead ECG is required to support the identification of the "criminal" artery and to rule out posterior myocardial infarction.

Density Functional Theory of Polymer Structure and Conformations.

We present a density functional approach to quantitatively evaluate the microscopic conformations of polymer chains with consideration of the effects of chain stiffness, polymer concentration, and short chain molecules. For polystyrene (PS), poly(ethylene oxide) (PEO), and poly(methyl methacrylate) (PMMA) melts with low-polymerization degree, as chain length increases, they display different stretching ratios and show non-universal scaling exponents due to their different chain stiffnesses. In good solvent, increase of PS concentration induces the decline of gyration radius. For PS blends containing short (m1 = 1 - 100) and long (m = 100) chains, the expansion of long chains becomes unobvious once m 1 is larger than 40, which is also different to the scaling properties of ideal chain blends.

Theoretical Insight into Dispersion of Silica Nanoparticles in Polymer Melts.

Silica nanoparticles dispersed in polystyrene, poly(methyl methacrylate), and poly(ethylene oxide) melts have been investigated using a density functional approach. The polymers are regarded as coarse-grained semiflexible chains, and the segment sizes are represented by their Kuhn lengths. The particle-particle and particle-polymer interactions are calculated with the Hamaker theory to reflect the relationship between particles and polymer melts. The effects of particle volume fraction and size on the particle dispersion have been quantitatively determined to evaluate their dispersion/aggregation behavior in these polymer melts. It is shown that theoretical predictions are generally in good agreement with the corresponding experimental results, providing the reasonable verification of particle dispersion/agglomeration and polymer depletion.

Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins.

Cytokinins are a major group of phytohormones regulating plant growth, development and stress responses. However, in contrast to the well-defined polar transport of auxins, the molecular basis of cytokinin transport is poorly understood. Here we show that an ATP-binding cassette transporter in Arabidopsis, AtABCG14, is essential for the acropetal (root to shoot) translocation of the root-synthesized cytokinins. AtABCG14 is expressed primarily in the pericycle and stelar cells of roots. Knocking out AtABCG14 strongly impairs the translocation of trans-zeatin (tZ)-type cytokinins from roots to shoots, thereby affecting the plant's growth and development. AtABCG14 localizes to the plasma membrane of transformed cells. In planta feeding of C(14) or C(13)-labelled tZ suggests that it acts as an efflux pump and its presence in the cells directly correlates with the transport of the fed cytokinin. Therefore, AtABCG14 is a transporter likely involved in the long-distance translocation of cytokinins in planta.