Dissipation of the plant growth regulator hexanoic acid 2-(diethylamino) ethyl ester in pakchoi and soil

A rapid and simple method for determining the plant growth regulator hexanoic acid 2-(diethylamino) ethyl ester (DA-6) in pakchoi and soil using gas chromatography-mass spectrometry (GC-MS) has been developed. For this purpose, a single step was used to extract DA-6 with dichloromethane from aqueous-acetone extracts of vegetables and soil. Average recoveries of DA-6 in pakchoi and soil were between 85% and 104% at both spiking levels 0.01 and 0.1 mg kg^?1. Relative standard deviations (RSD) were less than 11% for all of the recovery tests. The degradation of DA-6 in pakchoi and soil was studied. The results showed that DA-6 degradation in pakchoi and soil coincided with C = 3.9903 e^{?0.0516 t} , C = 0.3476 e^{?0.0224 t} , respectively; the half-lives were 13.43 h and 30.94 h in pakchoi and soil in Beijing, respectively.     

Insight into industrial PLA aging process by complementary use of rheology,HPLC, and MALDI

Nowadays, there is a growing availability of biodegradable industrial materials intended to food contact applications whose service life behavior needs to be further investigated. This article is focused on the degradation of two materials based on polylactic acid. The correlation between the rate of degradation and the amount of trapped degradation products was investigated applying three characterization techniques in parallel, namely rheology, high‐performance liquid chromatography (HPLC), and matrix‐assisted laser desorption/ionization (MALDI). The rate of degradation was studied through the evaluation of their rheological properties and calculation of the number of average molecular weights, and weight‐average molecular weights. Water‐soluble oligomers and lactic acid were quantified by HPLC‐ultraviolet. Changes in cyclic and linear oligomers were monitored by MALDI‐time‐of‐flight mass spectrometry. Specimens of 4‐mm thickness of each biopolymer were subjected to hydrolysis in deionized water up to 6 months at two temperatures, simulating service conditions of food packaging. The diminution in viscosity and consequently in molecular weight distribution (20–60%) showed the degradation of the molecular structure of both polylactic acids. The chain scission was followed through the increasing values of lactic acid and hydrolyzed oligomers (twofold to eightfold), and the predominant signal of the linear oligomers over the cyclic ones with aging. Rheology, HPLC, and MALDI showed to be complementary tools to better understand the changes in the molecular structure. The obtained results showed the necessity of adding suitable stabilizers for each particular food packaging application. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of multiwall carbon nanotubes on morphological and structural changes during UV irradiation of syndiotactic polypropylene films

The effect of UV irradiation on the morphology and structure of syndiotactic polypropylene (sPP) is investigated both for pure films and those filled with multiwall carbon nanotubes (MWCNTs). UV treatment causes a structural reorganization of pure sPP films. It seems that the incorporation of MWCNTs has a strong stabilizing effect, with nanotubes acting as a limiter of the UV‐induced chain breakage, especially when a good dispersion of carbon nanotubes in the polymer is achieved. The incorporation of MWCNTs introduces a high concentration of defects in the crystal structure of sPP, which limits the UV‐induced growth of crystallites, and prevents the development and propagation of cracks caused by UV irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Thermal and acid labile polyurethanes as a new class of responsive materials in polymeric nanoparticles and nanocapsules

A new class of polyurethanes has been designed, containing tertiary carbamate groups in the main chain of the polymer, which enable the resulting polymer to degrade completely under acid and thermal treatment. The decomposition temperatures of the polymers were determined by measuring the evolution of carbon dioxide and other decomposition products using TGA‐MS. Until decomposition of the polymer, no glass transition was found. The polymers exhibit excellent solubility in common organic solvents like chloroform and tetrahydrofuran, making them to suitable materials for film formation. From the obtained polymers, nanoparticles were synthesized by the solvent evaporation method combined with the miniemulsion technique. The resulting nanoparticles can be used as intelligent fillers in films and sensors, since they degrade at temperatures of above 180 °C, which can be detected by a color change reaction with ninhydrin. Polymeric nanocapsules were prepared by an interfacial polyaddition reaction from 2,4‐toluene diisocyanate and tertiary diols performed at the droplet's interface in inverse (water‐in‐oil) miniemulsions. These nanocapsules with an encapsulated photoacid generator can act as a release system, whereby an acidic release through irradiation with ultraviolet light can be triggered. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of Bovine Bone Content on In Vitro Degradation of Poly-L-lactic Acid and Bovine Bone Composite Materials

In vitro degradation experiments of poly-L-lactic acid (PLLA) and bovine bone (BB) composites were carried out in a phosphate-buffered solution (PBS) at 37°C with a pH of 7.4. The influence of BB content on pH value of PBS, water uptake, molecular weights, molecular weight distributions, weight losses, mechanical strengths, and morphologies of PLLA/BB was investigated with degradation times. The results indicated that the presence of the BB modified the degradation of the PLLA matrix. The degradation rate of PLLA in the PLLA/BB composite was slower than the degradation rate of the sole PLLA material. Furthermore, the degradation rate of the composites became slower with the increasing content of BB in PLLA/BB composites.     

Substituted Quinolinones. Part 19. New and Unexpected Results from Oxidation of 3-Acetyl-1-Alkyl- 4-Hydroxyquinolin-2(1H)-Ones Using Selenium Dioxide

Abstract

Oxidation of 3-acetyl-1-alkyl-4-hydroxyquinolin-2(1H)-ones using selenium dioxide under Riley conditions was described. The oxidation reaction produced a mixture of 2 unexpected α-keto acid and its dehydrated dimer derivatives. The oxidation reaction was studied under different reaction conditions in order to maximize the yields and optimize reaction conditions. Also, 1-alkyl-4-hydroxy-3-(2-nitroacetyl)quinolin-2(1H)-one and/or 3-acetyl-1-alkyl-4-diflouro-boryloxyquinolin-2(1H)-one derivatives were subjected to the same oxidation reaction giving rise improved reaction yields and selectivity in case of the boron-complex. Alkaline degradation of the dehydrated dimers led to formation of the 4-hydroxy-2-oxoquinoline-3-carboxylic acids while under the same conditions the α-keto acids underwent deoxalylation.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the following free supplemental files: Additional figures].     

Three-component diastereoselective cascade synthesis of thiohydantoins

A new three-component cascade reaction for the synthesis of thiohydantoins is reported. The reaction between α-amino esters, nitrostyrenes, and aromatic isothiocyanates is efficiently promoted by organic bases to afford highly substituted thiohydantoins in moderate to good yields and diastereoselectivities.     

MoO2@氮掺杂碳复合物的制备及其降解有机污染物

以多巴胺、钼酸铵、碳酸氢铵为原料，通过一步煅烧法合成一种 MoO₂@氮掺杂碳复合物(MoO₂@CN)，并利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、拉曼光谱(Raman)等对其进行表征。以卡马西平(CBZ)为目标污染物，以过一硫酸氢钾(PMS)为氧化剂，在温度为25 ℃、pH为6.5的条件下，MoO₂@CN/PMS在12 min内对CBZ的去除率达99.2%，与商用MoO₂相比，其表观速率常数k_obs(0.393 min^-1)是商用MoO₂(0.016 4 min^-1)的24.0倍，这主要是由于制备的MoO₂@CN比商用MoO₂具有更好的电子传输能力以及更大的比表面积。MoO₂@CN在 pH为 2.5~10.5时均能有效降解 CBZ，而且对大多数染料、酚类化合物、抗生素等多种污染物均具有良好的降解性能。此外，MoO₂@CN/PMS在60 min内对CBZ的总有机碳(TOC)去除率高达74.0%。电子顺磁共振波谱(EPR)和自由基猝灭实验显示MoO₂@CN/PMS体系中主要起作用是硫酸根自由基(SO₄^·-)和羟基自由基(·OH)。更有意思的是，在Fe²⁺/PMS体系加入MoO₂@CN后，其催化降解CBZ的性能显著增强，k_obs(1.25 min^-1)是单独Fe²⁺/PMS体系(0.079 7 min^-1)的15.7倍，这主要归因于MoO₂@CN的引入加快了Fe³⁺到Fe²⁺的转变，导致更多·OH的生成。     

Purification, cloning and expression of an Aspergillus niger lipase for degradation of poly(lactic acid) and poly(ε-caprolactone)

A lipase from Aspergillus niger MTCC 2594 was purified 53.8-fold to homogeneity by hydrophobic interaction chromatography using octyl sepharose and the enzyme showed two protein bands with apparent molecular mass of 35 and 37 kDa respectively. The lipase exhibited maximum activity at pH 7.0 and 37 °C and was stable between pH 4.0 and 10.0 and temperatures up to 50 °C. The values of K_m and V_max were 3.83 mM and 32.21 μmol/min/mg respectively, using olive oil as substrate. Lipase encoding gene, lipA, coded for 297 amino acid residues with conserved pentapeptide sequence, G-H-S-L-G, was cloned and expressed in Pichia pastoris. Although lipA showed high homology with the known Aspergillus lipases, it exhibited differences in putative lid domain. Both native and recombinant lipases have potential for degradation of poly(lactic acid) and poly(ε-caprolactone), and the present study will serve as a baseline of initial studies for its exploitation in polymer degradation.