In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel

Based on chelation effect between iron ions and amino groups of chitosan, in situ mineralization of magnetite nanoparticles in chitosan hydrogel under ambient conditions was proposed. The chelation effect between iron ions and amino groups in CS–Fe complex, which led to that chitosan hydrogel exerted a crucial control on the magnetite mineralization, was proved by X-ray photoelectron spectrum. The composition, morphology and size of the mineralized magnetite nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and thermal gravity. The mineralized nanoparticles were nonstoichiometric magnetite with a unit formula of Fe2.85O4and coated by a thin layer of chitosan. The mineralized magnetite nanoparticles with mean diameter of 13 nm dispersed in chitosan hydrogel uniformly. Magnetization measurement indicated that superparamagnetism behavior was exhibited. These magnetite nanoparticles mineralized in chitosan hydrogel have potential applications in the field of biotechnology. Moreover, this method can also be used to synthesize other kinds of inorganic nanoparticles, such as ZnO, Fe2O3and hydroxyapatite

The magnetocaloric effect and critical behavior in amorphous Gd 60Co 40-xMn x alloys.

The amorphous alloys Gd60Co40−xMnx (x = 0, 5, 10, 15) were prepared by melt spinning. The Curie temperature,T c, increases monotonously with Mn addition, ranging from 198 K for x = 0 to 205 K for x = 15, while the maximum values of −ΔSM under the applied field change from 0 to 5 T are 7.7, 7.1, 6.2 and 5.4 J·kg−1·K−1 for x = 0, 5, 10, and 15, respectively. All samples undergo a second order ferri-paramagnetic phase transition. The critical behavior around the transitiontemperature is investigated in detail, using both the standard Kouvel-Fisher procedure as well as the study of the field dependence of the magnetocaloric effect. Results indicate that the obtained critical exponents are reliable, and that the present alloys exhibit local magnetic interaction

Strand-specific PCR of UV radiation-damaged genomic DNA revealed an essential role of DNA-PKcs in the transcription-coupled repair

<p>Abstract</p> <p>Background</p> <p>In eukaryotic cells, there are two sub-pathways of nucleotide excision repair (NER), the global genome (gg) NER and the transcription-coupled repair (TCR). TCR can preferentially remove the bulky DNA lesions located at the transcribed strand of a transcriptional active gene more rapidly than those at the untranscribed strand or overall genomic DNA. This strand-specific repair in a suitable restriction fragment is usually determined by alkaline gel electrophoresis followed by Southern blotting transfer and hybridization with an indirect end-labeled single-stranded probe. Here we describe a new method of TCR assay based on strand-specific-PCR (SS-PCR). Using this method, we have investigated the role of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a member of the phosphatidylinositol 3-kinase-related protein kinases (PIKK) family, in the TCR pathway of UV-induced DNA damage.</p> <p>Results</p> <p>Although depletion of DNA-PKcs sensitized HeLa cells to UV radiation, it did not affect the ggNER efficiency of UV-induced cyclobutane pyrimidine dimers (CPD) damage. We postulated that DNA-PKcs may involve in the TCR process. To test this hypothesis, we have firstly developed a novel method of TCR assay based on the strand-specific PCR technology with a set of smart primers, which allows the strand-specific amplification of a restricted gene fragment of UV radiation-damaged genomic DNA in mammalian cells. Using this new method, we confirmed that siRNA-mediated downregulation of Cockayne syndrome B resulted in a deficiency of TCR of the UV-damaged dihydrofolate reductase (<it>DHFR</it>) gene. In addition, DMSO-induced silencing of the c-myc gene led to a decreased TCR efficiency of UV radiation-damaged c-myc gene in HL60 cells. On the basis of the above methodology verification, we found that the depletion of DNA-PKcs mediated by siRNA significantly decreased the TCR capacity of repairing the UV-induced CPDs damage in <it>DHFR </it>gene in HeLa cells, indicating that DNA-PKcs may also be involved in the TCR pathway of DNA damage repair. By means of immunoprecipitation and MALDI-TOF-Mass spectrometric analysis, we have revealed the interaction of DNA-PKcs and cyclin T2, which is a subunit of the human transcription elongation factor (P-TEFb). While the P-TEFb complex can phosphorylate the serine 2 of the carboxyl-terminal domain (CTD) of RNA polymerase II and promote transcription elongation.</p> <p>Conclusion</p> <p>A new method of TCR assay was developed based the strand-specific-PCR (SS-PCR). Our data suggest that DNA-PKcs plays a role in the TCR pathway of UV-damaged DNA. One possible mechanistic hypothesis is that DNA-PKcs may function through associating with CyclinT2/CDK9 (P-TEFb) to modulate the activity of RNA Pol II, which has already been identified as a key molecule recognizing and initializing TCR.</p

Novel Csf/SiBCN composites prepared by densifying Csf/MA-SiBCN with the PIP process: Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber (Csf)-reinforced mechanically alloyed SiBCN (MA-SiBCN) (Csf/MA-SiBCN) composites, dense amorphous Csf/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN (PDCs-SiBCN) were prepared by repeated polymer infiltration and pyrolysis (PIP) of layered Csf/MA-SiBCN composites at 1100 °C, and the oxidation behavior and damage mechanism of the as-prepared Csf/SiBCN at 1300–1600 °C were compared and discussed with those of Csf/MA-SiBCN. The Csf/MA-SiBCN composites resist oxidation attack up to 1400 °C but fail at 1500 °C due to the collapse of the porous framework, while the PIP-densified Csf/SiBCN composites are resistant to static air up to 1600 °C. During oxidation, oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon (PyC) to the interior of the matrix. Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices, a relatively continuous and dense oxide layer is formed on the sample surface, and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix, which is primarily responsible for improving the oxidation resistance

Composition-dependent structural characteristics and mechanical properties of amorphous SiBCN ceramics by ab-initio calculations

The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si–BN–C phase diagram are investigated employing ab-initio calculations. Both chemical bonds and local structures within the amorphous network relate to the elemental composition. The distribution of nine types of chemical bonds is composition-dependent, where the B–C, Si–N, Si–C, and B–N bonds hold a large proportion for all compositions. Si prefers to be tetrahedrally coordinated, while B and N prefer sp2-like trigonal coordination. In the case of C, the tetrahedral coordination is predominant at relatively low C contents, while the trigonal coordination is found to be the main feature with the increasing C content. Such local structural characteristics greatly influence the mechanical properties of SiBCN ceramics. Among the studied amorphous ceramics, SiB2C3N2 and SiB3C2N3 with low Si contents and moderate C and/or BN contents have high elastic moduli, high tensile/shear strengths, and good debonding capability. The increment of Si, C, and BN contents on this basis results in the decrease of mechanical properties. The increasing Si content leads to the increment of Si-contained bonds that reduce the bond strength of SiBCN ceramics, while the latter two cases are attributed to the raise of sp2-like trigonal configuration of C and BN. These discoveries are expected to guide the composition-tailored optimization of SiBCN ceramics

Enhanced mechanical properties and thermal shock resistance of Si2BC3N ceramics with SiC coated MWCNTs

Abstract Bulk Si2BC3N ceramics were reinforced with SiC coated multi-walled carbon nanotubes (MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si2BC3N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength (532.1 MPa) and fracture toughness (6.66 MPa·m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si2BC3N ceramics maintains much higher residual strength (193.0 MPa) after thermal shock test at 1000 °C. The enhanced properties should be attributed to: (1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation; (2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the “pull out” of MWCNTs

Mitochondrial genome diversity in Beta vulgaris L. ssp. vulgaris (Leaf and Garden Beet Groups) and its implications concerning the dissemination of the crop

Four mitochondrial minisatellites were used to study cytoplasmic diversity in leaf and garden beet germplasm resources. Eleven multi-locus haplotypes were identified, of which one (named mitochondrial minisatellite haplotype 4, hereafter min04) was associated with male-sterile Owen cytoplasm and two others (min09 and min18), with a normal fertile cytoplasm. European leaf beet germplasm exhibited the greatest haplotype diversity, with min09 and min18 predominating. In North African leaf beet accessions, only these two haplotypes were observed, making it likely that North African accessions were descended from European genotypes. The prevalence of min18 was also noted in leaf beet from the Middle East and western Asia. Such a pattern contrasts with that found in east Asian leaf beet where the two haplotypes were extremely rare. The geographical structure of the mitochondrial haplotypes allowed us to infer possible dissemination pathways of leaf beet. Additionally, we showed that mitochondrial genome diversity was low in garden beet germplasm, with min18 being highly predominant. An explanation of this limited diversity may lie in the geographically restricted origin of as well as relatively short cultivation histories of garden beet