Effects of Chain End Structures on Pyrolysis of Poly(L-lactic acid) Containing Tin Atoms

Thermal degradation of high molecular weight PLLA containing residual tin atoms was investigated as a means of controlling the reaction for feedstock recycling to L,L-lactide. To clarify the pyrolysis mechanism of the PLLA, three samples with different chain end structures were prepared, namely, as-polymerized PLLA-ap, precipitated-with-methanol PLLA-pr, and purified PLLA-H. From pyrolyzate and kinetic analyses, typical degradation mechanisms of Sn-containing PLLA were clarified. In other words, it was assumed that the pyrolysis of PLLA-ap proceeds through a zero-order weight loss process with the apparent Ea = 80-90 kJ mol-1, and with the occurrence of backbiting and transesterification reactions caused by Sn-alkoxide chain ends. The pyrolysis of PLLA-pr was also assumed to proceed via a zero-order weight loss process with apparent Ea = 120-130 kJ mol-1, with the proposed mechanism being Sn-catalyzed selective lactide elimination caused by Sn-carboxylate chain ends. Both pyrolysis of PLLA-ap and PLLA-pr produced L,L-lactide selectively. These degradation mechanisms and products are in contrast to those of PLLA-H, in which a large amount of diastereoisomers and cyclic oligomers were formed by random degradation. From this study, the complicated PLLA pyrolysis behavior as reported previously could be explained properly

Thermal degradation of poly(L-lactide): effect of alkali earth metal oxides for selective L,L-lactide formation

To achieve the feed stock recycling of poly(L-lactide) (PLLA) to L,L-lactide, PLLA composites including alkali earth metal oxides, such as calcium oxide (CaO) and magnesium oxide (MgO), were prepared and the effect of such metal oxides on the thermal degradation was investigated from the viewpoint of selective L,L-lactide formation. Metal oxides both lowered the degradation temperature range of PLLA and completely suppressed the production of oligomers other than lactides. CaO markedly lowered the degradation temperature, but caused some racemization of lactide, especially in a temperature range lower than 250 °C. Interestingly, with MgO racemization was avoided even in the lower temperature range. It is considered that the effect of MgO on the racemization is due to the lower basicity of Mg compared to Ca. At temperatures lower than 270 °C, the pyrolysis of PLLA/MgO (5 wt%) composite occurred smoothly causing unzipping depolymerization, resulting in selective L,L-lactide production. A degradation mechanism was discussed based on the results of kinetic analysis. A practical approach for the selective production of L,L-lactide from PLLA is proposed by using the PLLA/MgO composite

Femtosecond laser quenching of the ε phase of iron

The quenching of the ε phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. The crystalline structure in a recovered iron sample was determined using an electron backscatter diffraction pattern system. The femtosecond laser driven shock may have the potential to quench high-pressure phases of other materials.Sano T., Mori H., Ohmura E., et al., Appl. Phys. Lett. 83(17), 3498-3500 (2003) https://doi.org/10.1063/1.162393

Effect of Sn Atom on Poly(Ｌ-lactic acid) Pyrolysis

Tin 2-ethylhexanoate is an indispensable component of commercially available poly(L-lactic acid) (PLLA). However, the thermal degradation kinetics of PLLA containing Sn have not yet clearly been established; in particular, whether the degradation mechanism is a 1st-order or a random reaction. To clarify the effects of residual Sn on PLLA pyrolysis, PLLA samples with different Sn contents from 20 to 607 ppm were prepared and subjected to pyrolysis analysed with pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) and thermogravimetry (TG). The pyrolysis of PLLA Sn-607 (Sn content: 607 ppm) with Py-GC/MS in the temperature range of 40–400 °C selectively produced lactides. In contrast, the pyrolysis of PLLA Sn-20 (Sn content: 20 ppm) was accompanied by the production of cyclic oligomers. The dynamic pyrolysis of PLLA-Sn samples by TG clearly indicated that with an increase in Sn content there was a shift to a lower degradation temperature range and a decrease in activation energy Ea. The kinetic analysis of the dynamic pyrolysis data indicates that the Sn-catalyzed pyrolysis starts through a random degradation behaviour and then shifts to a zero-order weight loss as the main process. Three reactions were put forward as being possible mechanisms of the zero-order weight loss; one being an unzipping reaction accompanying a random transesterification, the other two being the Sn-catalyzed pseudo-selective and selective lactide elimination reactions from random positions on a polymer chain. The kinetic parameter values obtained could be adequately explained for each degradation process

Construction of novel metabolic pathways with artificial enzymes

Non-fossil raw materials can be utilized for the production of useful compounds by way of microbial fermentation . Sugars are obtained from carbon fixations of plants or photosynthetic microorganisms, and are used as a carbon source for the biosynthesis of useful target compounds by genetically modified microorganisms. In order for a microorganism to produce enough target compound, techniques for optimal metabolic design must include balance of energy production/consumption, redox pathways, and intracellular carbon flow. With recent innovations in genome analysis technology and information processing technology, computational design tools that can describe more than 1000 genome-scale metabolic reactions to efficiently produce target compounds have been developed worldwide. However, the established tools are not designed to search and create biosynthetic pathways for production of non-natural compounds from fossil resources. We developed BioProV and M-path, new simulation tools that enable metabolic design for the biosynthesis of unnatural compounds. By combining these tools with enzyme engineering technology, we succeeded in expanding the scope of bioproduction targets. The first example is construction of an artificial metabolic pathway to biosynthesize isoprene. Isoprene the raw material for production of synthetic rubber that can be used in automobile tires. Currently, isoprene is industrially produced as a by-product of naphtha pyrolysis. Therefore, by establishing green isoprene production technology, dependence upon petroleum can be reduced. Isoprene is a substance that can exist within cells of many organisms as a monomer of polyisoprene rubber, and also as a structural unit of secondary metabolites. It is difficult to optimize its synthentic pathway due to shortages of intracellular ATP supply, and challenges in the introduction of improved biosynthetic pathways. In nature, isoprene is produced from mevalonic acid through a five-step reaction, but the newly constructed artificial metabolic pathway consists of just two steps from mevalonic acid to isoprene. This results in a three-fold reduction in cellular energy consumption. Furthermore, we succeeded in constructing a highly active enzyme that exhibits 10,000-fold higher isoprene-producing activity relative to natural enzymes. By introducing these artificial metabolic reactions into Escherichia coli, efficient artificial isoprene production was achieved. In addition, we have developed a microbial production system for 1,3-butadiene, another alternative source for synthetic rubber. Moreover, rationally engineered enzymes from insects and plants enzymes have resulted in the construction of an artificial pathway to benzylisoquinoline alkaloids and downstream opioid analgesics

Feedstock Recycling of Flame-Resisting Poly(lactic acid)/Aluminum Hydroxide Composite to L,L-lactide

To achieve the chemical recycling of flame-resisting materials consisting of poly(L-lactic acid) (PLLA), a safer flame-resisting material, PLLA/aluminum hydroxide {Al(OH)3} composite, was investigated the capability of the feedstock recyclability to optically active monomer L,L-lactide. The thermal stabilization of the composite was improved compared to those of as-polymerized PLLA and Al(OH)3 themselves, which makes the melt processing of the composite easier. Nevertheless, at temperatures lower than 300°C the effective depolymerization of PLLA proceeded, without any racemization reaction, to selectively convert into L,L-lactide, with Al(OH)3 acting as a catalyst for the depolymerization. This means that the PLLA/Al(OH)3 composite is capable of reconciling flame resistance with feedstock recycling of PLLA to cyclic monomer

Rapid Elimination of the Persistent Synergid through a Cell Fusion Mechanism

SummaryIn flowering plants, fertilization-dependent degeneration of the persistent synergid cell ensures one-on-one pairings of male and female gametes. Here, we report that the fusion of the persistent synergid cell and the endosperm selectively inactivates the persistent synergid cell in Arabidopsis thaliana. The synergid-endosperm fusion causes rapid dilution of pre-secreted pollen tube attractant in the persistent synergid cell and selective disorganization of the synergid nucleus during the endosperm proliferation, preventing attractions of excess number of pollen tubes (polytubey). The synergid-endosperm fusion is induced by fertilization of the central cell, while the egg cell fertilization predominantly activates ethylene signaling, an inducer of the synergid nuclear disorganization. Therefore, two female gametes (the egg and the central cell) control independent pathways yet coordinately accomplish the elimination of the persistent synergid cell by double fertilization

ADAR1 is a promising risk stratification biomarker of remnant liver recurrence after hepatic metastasectomy for colorectal cancer

Adenosine-to-inosine RNA editing is a process mediated by adenosine deaminases that act on the RNA (ADAR) gene family. It has been discovered recently as an epigenetic modification dysregulated in human cancers. However, the clinical significance of RNA editing in patients with liver metastasis from colorectal cancer (CRC) remains unclear. The current study aimed to systematically and comprehensively investigate the significance of adenosine deaminase acting on RNA 1 (ADAR1) expression status in 83 liver metastatic tissue samples collected from 36 patients with CRC. The ADAR1 expression level was significantly elevated in liver metastatic tissue samples obtained from patients with right-sided, synchronous, or RAS mutant-type CRC. ADAR1-high liver metastasis was significantly correlated with remnant liver recurrence after hepatic metastasectomy. A high ADAR1 expression was a predictive factor of remnant liver recurrence (area under the curve = 0.72). Results showed that the ADAR1 expression level could be a clinically relevant predictive indicator of remnant liver recurrence. Patients with liver metastases who have a high ADAR1 expression requires adjuvant chemotherapy after hepatic metastasectomy

Prolyl Isomerase Pin1 Regulates Mouse Embryonic Fibroblast Differentiation into Adipose Cells

isomerase, Pin1, regulates insulin signal transduction. Pin1 reduces responses to insulin stimulation by binding CRTC2 (CREB-regulated transcriptional co-activator 2) and PPARγ (peroxisome prolifereator- activated receptor γ), but conversely enhances insulin signaling by binding IRS-1 (insulin receptor substrate-1), Akt kinase, and Smad3. Therefore, it is still unclear whether Pin1 inhibits or enhances adipose cell differentiation. mice was restored by increasing expression of Pin1. We found that Pin1 binds to phosphoThr172- and phosphoSer271-Pro sites in CREB suppress the activity in COS-7 cells.Pin1 enhanced the uptake of triglycerides and the differentiation of MEF cells into adipose cells in response to insulin stimulation. Results of this study suggest that Pin1 down-regulation could be a potential approach in obesity-related dysfunctions, such as high blood pressure, diabetes, non-alcoholic steatohepatitis