Preparation and properties of biodegradable foams from starch acetate and poly(tetramethylene adipate-co-terephthalate)

Biodegradable composite foams were prepared by extruding starch acetate, with degree of substitution (DS) 1.78, with poly(tetramethylene adipate-co-terephthalate) (EBC). The foams' chemical structures, thermal behaviors, and microstructures were investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). By measuring these properties, it was found that low EBC contents in the blends favored the miscibility of the two polymers, as characterized by (1) disappearance of EBC carbonyl peak and appearance of hydrogen-bonded EBC carbonyl groups in FTIR spectra; (2) an increase in T_g of starch acetate and the decreases in T_m values of starch acetate and EBC in DSC thermograms; and (3) formation of a homogeneous morphology in SEM. However, large amounts of EBC decreased the miscibility of these two polymers, as reflected by the foams' physical and mechanical properties. With a small amount of EBC, the foams had high radial expansion ratios (RER) and spring indices (SI) and low unit densities and compressibilities. Biodegradation rates of the composite foams decreased with the addition of EBC to starch acetate.     

纳米二氧化硅复合寒冷对A549细胞毒性及其炎性因子分泌的影响*

目的: 本研究旨在探讨纳米二氧化硅(Nano-SiO₂)颗粒和寒冷复合对人肺腺癌上皮细胞A549细胞毒性及炎性因子分泌的影响。方法: 本研究以A549细胞为实验对象,分别用10, 50, 100, 200 μg/ml Nano-SiO₂颗粒对A549细胞染毒,以及分别在35℃,33℃,31℃条件下对A549细胞进行低温暴露,培养48 h后,观察细胞形态及测定细胞相对存活率。根据单因素分析结果,选出对A549细胞相对存活率有显著降低作用的Nano-SiO₂剂量和温度的基础上,按照2×2析因设计实验,分为4组:①37℃对照组;②Nano-SiO₂染毒组;③低温暴露组;④Nano-SiO₂和低温复合组,不同条件下暴露48 h后,收集细胞上清液采用比色法检测LDH活性,以及ELISA法测定细胞因子白介素-6(IL-6)和白介素-8(IL-8)的水平,采用qRT-PCR法检测细胞IL-6和IL-8的基因表达水平。结果: 100 μg/ml Nano-SiO₂组和31℃低温组能够显著降低A549细胞活性(P＜0.01),在复合条件作用下对A549细胞活性抑制最为显著,且炎性因子IL-6和IL-8及mRNA的表达水平均显著升高(P＜0.01)。结论: 100 μg/ml Nano-SiO₂与31℃低温复合暴露可协同降低A549细胞的相对存活率,增加炎性因子IL-6和IL-8表达水平。     

Immobilization of horseradish peroxidase with a regenerated silk fibroin membrane and its application to a tetrathiafulvalene-mediating H2O2 sensor

Horseradish peroxidase (HRP) was immobilized onto a membrane of the regenerated silk fibroin (RSF) from waste milk. The structure of the blend membrane of RSF and HRP was characterized by the use of IR spectra. A second generation of H₂O₂ sensor on the basis of the immobilized HRP was fabricated, in which tetrathiafulvalene acts as mediating electron transfer between the immobilized enzyme and a glassy carbon electrode. Dependencies of pH and temperature on the H₂O₂ biosensor were checked by utilizing cyclic voltammetry. The sensor exhibits high sensitivity, good reproducibility and storage stability.     

Total luminescence intensity as a tool to classify degradable polyethylene films by early degradation detection and changes in activation energy

Total luminescence intensity (TLI) was shown to be a valuable tool to monitor early degradation and thereby classify degradable polyethylene. The photo oxidation and thermal oxidation of polyethylene films containing different prooxidant systems were monitored. The chemiluminescence results were compared with results from FTIR, DSC, and SEC measurements. TLI gave an earlier detection of degradation and offered complementary information regarding changes in activation energies during the course of the degradation. TLI measurements were more sensitive to relative differences in degradation between the materials than the carbonyl index and crystallinity measurements, especially in the case of the UV-aged samples.     

The new enneanuclear nickel carbonyl anion [Ni9(CO)16] and its relationships with the [Ni12(CO)21] and [Ni6Rh3(CO)17] clusters

The reaction of [N(PPh₃)₂]₂[Ni₆(CO)₁₂] with Cu(PPh₃)_xCl (x=1, 2), as well as the degradation of [N(PPh₃)₂]₂[H₂Ni₁₂(CO)₂₁] with PPh₃, affords the new and unstable dark orange–brown [N(PPh₃)₂]₂[Ni₉(CO)₁₆].THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni₉(CO)₁₆]²⁻ dianion is directly related to that of the bimetallic [Ni₆Rh₃(CO)₁₇]³⁻ trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni₁₂(CO)₂₁]⁴⁻ by the substitution of one of the two outer [Ni₃(CO)₃(μ−CO)₃]²⁻ layers with a face-bridging carbonyl group.     

Alkaline N-deacetylation of chitin enhanced by flash treatments. Reaction kinetics and structure modifications

A new method for N-deacetylation of chitin is proposed in which a polymer almost free of N-acetyl groups is obtained by flash treatment. The reaction is carried out in 40% NaOH solution for 30–270 s at 140–190°C, using saturated steam.

Flash treatment was found to proceed faster and with a higher activation energy for the deacetylation reaction (E_a = 36 kcal mol⁻¹) compared with the traditional treatment (E_a = 11 kcal mol⁻¹). X-Ray diffractometry, CP-MAS ¹³C-NMR and FTIR spectroscopy show that the flash treatment induces structure modifications; in particular, higher crystallinity indexes and specific area values are observed together with changes in the local and chain conformation.     

Topotactic crystallization of isolated poly(β-hydroxybutyrate) granules from Alcaligenes eutrophus

Abstract Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray powder diffractometry (WAXD) and Fourier transform infrared spectroscopy (FTIR) were used to investigate the crystallization behavior of PHB granules from Alcaligenes eutrophus isolated by enzymatic purification. TEM examination of freeze dried granules after mortar and pestle grinding at liquid nitrogen temperature revealed that the dry granules have a non-crystalline core/crystalline shell morphology. TEM micrographs sections of PHB granules showed that upon annealing, the non-crystalline molecules in the core transform into stacks of lamellar crystals with a thickness of ∼ 100 Å. The FTIR results revealed the presence of bound water in a sample of freeze dried granules and WAXD of the same sample showed an increase in crystallinity after removal of this water by vacuum drying. The WAXD diffractograms showed an increase in crystallinity of PHB granules when going from the in vivo to the dry state. In spite of the possibility of deforming them at very low temperatures (liquid nitrogen temperature) the glass transition temperature ( T _g ) of nascent PHB granules, as revealed by the DSC thermograms, was in the range −0.5−4°C. These results suggest that water is responsible for keeping the core of nascent PHB granules in a non-crystalline state. A model for biosynthesis where emerging PHB chains in an extended conformation are simultaneously hydrogen bonded to water molecules is proposed.     

Preparation and properties of banana fiber-reinforced composites based on high density polyethylene (HDPE)/Nylon-6 blends

Banana fiber (BaF)-filled composites based on high density polyethylene (HDPE)/Nylon-6 blends were prepared via a two-step extrusion method. Maleic anhydride grafted styrene/ethylene–butylene/styrene triblock polymer (SEBS-g-MA) and maleic anhydride grafted polyethylene (PE-g-MA) were used to enhance impact performance and interfacial bonding between BaF and the resins. Mechanical, crystallization/melting, thermal stability, water absorption, and morphological properties of the composites were investigated. In the presence of SEBS-g-MA, better strengths and moduli were found for HDPE/Nylon-6 based composites compared with corresponding HDPE based composites. At a fixed weight ratio of PE-g-MA to BaF, an increase of BaF loading up to 48.2 wt.% led to a continuous improvement in moduli and flexural strength of final composites, while impact toughness was lowered gradually. Predicted tensile modulus by the Hones–Paul model for three-dimensional random fiber orientation agreed well with experimental data at the BaF loading of 29.3 wt.%. However, the randomly-oriented fiber models underestimated experimental data at higher fiber levels. It was found that the presence of SEBS-g-MA had a positive influence on reinforcing effect of the Nylon-6 component in the composites. Thermal analysis results showed that fractionated crystallization of the Nylon-6 component in the composites was induced by the addition of both SEBS-g-MA and PE-g-MA. Thermal stability of both composite systems differed slightly, except an additional decomposition peak related to the minor Nylon-6 for the composites from the HDPE/Nylon-6 blends. In the presence of SEBS-g-MA, the addition of Nylon-6 and increased BaF loading level led to an increase in the water absorption value of the composites.     

The synthesis, fluctionality and structural characterization of ReMo3H4(CO)12

The reaction of ReH₉²⁻ with Mo(diglyme)(CO)₃ leads to the formation of the mixed metal cluster trianion, ReMo₃H₄(CO)₁₂³⁻. This species has been characterized analytically, spectroscopically and through X-ray diffraction analysis. A pseudo-tetrahedral arrangement of M(CO)₃ fragments is adopted, such that each set of three carbonyl ligands eclipses the adjacent three tetrahedral edges, an apparent result of the location of the hydride ligands on the tetrahedral faces. Variable temperature NMR studies revealed a fluctional process for some of the carbonyl ligands, but not for the hydrides. Crystal data for [Me₄N]₃[ReMo₃H₄(CO)₁₂]·THF; space group P2₁/n, a = 12.157(2), B = 21.480(4), C = 15.964(3) Å, β = 98.26(1)°, Z = 4, R = 0.067 and R_w = 0.076.     

Construction of stably maintained non-mobilizable derivatives of RSF1010 lacking all known elements essential for mobilization

Background  

RSF1010 is a well-studied broad-host-range plasmid able to be mobilized to different bacteria and plants. RSF1010-derived plasmid vectors are widely used in both basic research and industrial applications. In the latter case, exploiting of mobilizable plasmids or even the plasmids possessing negligible mobilization frequency, but containing DNA fragments that could promote conjugal transfer, is undesirable because of biosafety considerations. Previously, several mutations significantly decreasing efficiency of RSF1010 mobilization have been selected. Nevertheless, construction of the RSF1010 derivative lacking all known loci involved in the conjugal transfer has not been reported yet.     

Characterization of citric acid/glycerol co-plasticized thermoplastic starch prepared by melt blending

A novel citric acid (CA)–glycerol co-plasticized thermoplastic starch (CGTPS) was prepared by melt blending. The CA content varies from 10% to 40 wt%. Result from Fourier Transform Infrared spectroscopy (FTIR) show that partial esterification occurred during blending. The degrees of substitution and esterification increased as the CA content increased. Results from intrinsic viscosity measurement, laser light scattering (LLS), and FTIR demonstrate the molecular weight of starch decreased as the CA percentage increased. The weight average molecular weight (M_w) of CGTPS with 20 wt% CA was only one-tenth of that without CA under the same processing conditions. Crystal type and crystallinity changes as a function of CA were recorded by X-ray diffraction (XRD). Thermal stability and the glass transition temperature (T_g) were detected by thermogravimetric (TG) and differential scanning calorimeter (DSC). Compared to the traditional GTPS, the novel CGTPS exhibits the special characters of partial esterification, low molecular weight and stronger interaction between starch and plasticizers. These new properties can be expected to prevent retrogradation, promote compatibility with polyesters, improve the processing ability, and adjust the degradation properties.     

The RSF1 Histone-Remodelling Factor Facilitates DNA Double-Strand Break Repair by Recruiting Centromeric and Fanconi Anaemia Proteins

ATM is a central regulator of the cellular responses to DNA double-strand breaks (DSBs). Here we identify a biochemical interaction between ATM and RSF1 and we characterise the role of RSF1 in this response. The ATM–RSF1 interaction is dependent upon both DSBs and ATM kinase activity. Together with SNF2H/SMARCA5, RSF1 forms the RSF chromatin-remodelling complex. Although RSF1 is specific to the RSF complex, SNF2H/SMARCA5 is a catalytic subunit of several other chromatin-remodelling complexes. Although not required for checkpoint signalling, RSF1 is required for efficient repair of DSBs via both end-joining and homology-directed repair. Specifically, the ATM-dependent recruitment to sites of DSBs of the histone fold proteins CENPS/MHF1 and CENPX/MHF2, previously identified at centromeres, is RSF1-dependent. In turn these proteins recruit and regulate the mono-ubiquitination of the Fanconi Anaemia proteins FANCD2 and FANCI. We propose that by depositing CENPS/MHF1 and CENPX/MHF2, the RSF complex either directly or indirectly contributes to the reorganisation of chromatin around DSBs that is required for efficient DNA repair.     

Active establishment of centromeric CENP-A chromatin by RSF complex

Centromeres are chromosomal structures required for equal DNA segregation to daughter cells, comprising specialized nucleosomes containing centromere protein A (CENP-A) histone, which provide the basis for centromeric chromatin assembly. Discovery of centromere protein components is progressing, but knowledge related to their establishment and maintenance remains limited. Previously, using anti-CENP-A native chromatin immunoprecipitation, we isolated the interphase–centromere complex (ICEN). Among ICEN components, subunits of the remodeling and spacing factor (RSF) complex, Rsf-1 and SNF2h proteins, were found. This paper describes the relationship of the RSF complex to centromere structure and function, demonstrating its requirement for maintenance of CENP-A at the centromeric core chromatin in HeLa cells. The RSF complex interacted with CENP-A chromatin in mid-G1. Rsf-1 depletion induced loss of centromeric CENP-A, and purified RSF complex reconstituted and spaced CENP-A nucleosomes in vitro. From these data, we propose the RSF complex as a new factor actively supporting the assembly of CENP-A chromatin.     

Intermolecular Re---H·H---X hydrogen bonding (X = N, C) involving ReH5(PPh3)3

Ab initio (B3LYP) calculations show that PD·H---ReH₄(PH₃)₃ (PD = Proton donor) interactions follow the order PD = pyrrole > NH₃ > HCCH > C₂H₄ > CH₃---H 0 and decrease with the pK_a of the PD. For equivalent pK_a's, NH interacts more strongly than CH. However, intermolecular hydrogen-bonding of the M---H·H---C type is too weak to be detected experimentally in FTIR or UV-vis studies between ReH₅(PPh₃)₃ and PhCCH, C₆F₅H or PhCHCl₂.     

HNO3/H3PO4–NANO2 mediated oxidation of cellulose — preparation and characterization of bioabsorbable oxidized celluloses in high yields and with different levels of oxidation

The reaction of cellulose with a mixture of HNO₃/H₃PO₄–NaNO₂ (2:1:1.4, v/v/%w) at room temperature for different time intervals has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed an increase in carboxyl content of OC with increasing reaction time, corresponding to about 8.0, 13.4, 17.4 and 18.4% carboxyl content after 12, 24, 36, and 48 h, respectively. The yield of OC ranged between 75 and 81%. The use of different ratios of HNO₃ and H₃PO₄, (11:1, 4:1, 2:1, 1:1, 1:2, and 1:4; v/v), in the reaction had no significant effect on the carboxyl content and yield of the OC products. All products, as produced, were low crystallinity (27–35%) fibrous materials. The length of fibers decreased with increasing reaction time. After ball milling for 24 h, the length of fibers further decreased and products converted into a fine powder consisting of small fibers and aggregated non-fibrous particles. The degrees of polymerization (DP) of the OC products produced after 12, 24, and 48 h of reaction duration were 81, 63, and 53, respectively. After ball milling for 24 h, the corresponding values changed to 57, 51 and 46. However, no significant change in the crystallinity of the products was noted after ball milling. The TGA results showed the OC products to be less thermally stable than cellulose. The degradation temperature appears to decrease with increasing carboxyl content. In conclusion, the results show that the low crystallinity OC products can be successfully prepared in high yields and with different levels of carboxyl content from cellulose by treatment with a mixture of HNO₃/H₃PO₄–NaNO₂.     

The effect of water concentration on the activity and stability of CLECs in supercritical CO2 in continuous operation

In this study the effect of the water concentration on a crystallized enzyme of Candida antarctica lipase B (ChiroCLEC™-CAB) in supercritical carbon dioxide (scCO₂) is studied. The model reaction used is the enantioselective esterification of racemic 1-phenyl ethanol with vinyl acetate; the reaction is performed in scCO₂ at 40 °C and 90 bar in batch and in continuous operation. Kinetic parameters have been derived from continuous experiments, leading to a catalytic turnover number of 0.95 s⁻¹. The optimum activity is reached at low water concentrations (0.05 g L⁻¹). At lower concentrations, CO₂ is stripping water from the enzyme leading to deactivation. However, adding a small amount of water to the substrates can reverse this deactivation and the enzyme activity is restored.     

Plasmids related to RSF1010 from Bordetella bronchiseptica

Six out of 14 Bordetella bronchiseptica isolates from U.K. pigs each contained one plasmid, of 8.7-44 kb. All plasmid-containing isolates were sulfonamide resistant, and this property was shown to be plasmid-encoded. Five of the plasmids were related; two were indistinguishable from the broad-host-range plasmid, RSF1010. The other three, two of which appeared to be identical, were shown to have regions of homology with RSF1010. One of these regions encompassed the sulfonamide resistance determinant while the other contained oriV, which also determines plasmid incompatibility. None of the plasmids could be associated with virulence or phase variation, and it appears likely that they have been acquired in response to antibiotic pressure.     

Comparative biodegradation of HDPE and LDPE using an indigenously developed microbial consortium

A variety of bacterial strains were isolated from waste disposal sites of Uttaranchal, India, and some from artificially developed soil beds containing maleic anhydride, glucose, and small pieces of polyethylene. Primary screening of isolates was done based on their ability to utilize high- and low-density polyethylenes (HDPE/LDPE) as a primary carbon source. Thereafter, a consortium was developed using potential strains. Furthermore, a biodegradation assay was carried out in 500-ml flasks containing minimal broth (250 ml) and HDPE/ LDPE at 5 mg/ml concentration. After incubation for two weeks, degraded samples were recovered through filtration and subsequent evaporation. Fourier transform infrared spectroscopy (FTIR) and simultaneous thermogravimetric-differential thermogravimetry-differential thermal analysis TG-DTG-DTA) were used to analyze these samples. Results showed that consortium-treated HDPE (considered to be more inert relative to LDPE) was degraded to a greater extent 22.41% weight loss) in comparison with LDPE (21.70% weight loss), whereas, in the case of untreated samples, weight loss was more for LDPE than HDPE (4.5% and 2.5%, respectively) at 400 degrees . Therefore, this study suggests that polyethylene could be degraded by utilizing microbial consortia in an eco-friendly manner.     

Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire

1 In a glasshouse experiment we studied the effect of raised CO₂ concentration (720 p.p.m.) on CH₄ emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH₄ production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH ₄ from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO₂ treatment doubled the potential CH₄ production but had no effect on the potential CH₄ oxidation. A raised concentration of CO₂ increased CH₄ efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO₂ concentrations, and would thus retard any consequent increase in CH₄ emission.     

RSF governs silent chromatin formation via histone H2Av replacement

Human remodeling and spacing factor (RSF) consists of a heterodimer of Rsf-1 and hSNF2H, a counterpart of Drosophila ISWI. RSF possesses not only chromatin remodeling activity but also chromatin assembly activity in vitro. While no other single factor can execute the same activities as RSF, the biological significance of RSF remained unknown. To investigate the in vivo function of RSF, we generated a mutant allele of Drosophila Rsf-1 (dRsf-1). The dRsf-1 mutant behaved as a dominant suppressor of position effect variegation. In dRsf-1 mutant, the levels of histone H3K9 dimethylation and histone H2A variant H2Av were significantly reduced in an euchromatic region juxtaposed with heterochromatin. Furthermore, using both genetic and biochemical approaches, we demonstrate that dRsf-1 interacts with H2Av and the H2Av-exchanging machinery Tip60 complex. These results suggest that RSF contributes to histone H2Av replacement in the pathway of silent chromatin formation.