Increasing Order (increasing + order)

Distribution by Scientific Domains

Selected Abstracts

Factors influencing the partitioning and toxicity of nanotubes in the aquatic environment,,

Alan J. Kennedy
Abstract Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to nanomaterials with a lower aspect ratio. Whereas the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration regarding how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups and coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and settling experiments indicated that raw, multiwalled NTs (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. The presence of functional groups, however, slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. Aqueous exposures to raw MWNTs decreased Ceriodaphnia dubia viability, but such effects were not observed during exposure to functionalized MWNTs (>80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (median lethal concentration [LC50], 50 to >264 g/kg) than carbon black (LC50, 18,40 g/kg) and activated carbon (LC50, 12,29 g/kg). Our findings stress that it may be inappropriate to classify all NTs into one category in terms of their environmental regulation. [source]

Tetrakis-phthalocyanines bearing electron-withdrawing fluoro functionality: Synthesis, spectroscopy, and electrochemistry

Ahmet T. BilgiÁli
In this study, 2,9,16,23-tetrakis-4,-(2,3,5,6-tetrafluoro)-phenoxy-phthalocyaninatometalfree and metal(II) complexes, (H2PcBzF16, ZnPcOBzF16, CuPcOBzF16, and CoPcOBzF16) (Bz: Benzene) (2H, Zn, Cu, and Co), have been prepared directly from the corresponding 4,-(2,3,5,6-fluorophenylthio)-phthalonitrile compounds in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in high boiling quinoline solvent. Tetrafluoro atoms on 2,3,5,6-position of benzene at the peripheral sites of phthalocyanines (Pcs) give rise interesting solubility to tetrakismetallophthalocyanines. Although all complexes were soluble in DCM, CHCl3, THF, DMF, and DMSO with increasing order, complexes synthesized, particularly H2PcBzF16, CuPcOBzF16, have very limited solubility in DMF and DMSO. The complexes have been characterized by elemental analysis, FTIR, 1H NMR, UV,vis, and MALDI,TOF mass spectral data. The cyclic voltammetry and differential pulsed voltammetry of the complexes show that while H2PcBzF16, CuPcOBzF16, and ZnPcOBzF16 give ligand-based reduction and oxidation processes, CoPcOBzF16 gives both ligand and metal-based redox processes, in harmony with the common metallophthalocyanine complexes. Redox processes due to both aggregated and disaggregated species were simultaneously observed during the first reduction process. The nature of the metal-based redox processes was confirmed using spectroelectrochemical measurements. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:262,271, 2009; Published online in Wiley InterScience ( DOI 10.1002/hc.20545 [source]

Effects of azadirachtin and of simpler epoxy-alcohols on survival and behaviour of Galleria mellonella (Lepidoptera)

C. Charbonneau
Abstract:, Investigations into the toxicity of three simpler molecules based on the epoxy-alcohol fragment of azadirachtin have revealed insecticidal activity on the greater wax moth Galleria mellonella L. larvae. The simpler epoxy-alcohols doses giving 50% mortalities (LD50) for G. mellonella larvae were in the increasing order from glycidol (0.022 mg/g), 4,5-epoxy-2-pentanol (0.068 mg/g) and finally, glycerol diglycidyl ether (0.147 mg/g). The three epoxy-alcohols exhibited higher insecticidal activity when compared with the commercial neem product for which the dose giving 50% mortalities was 10.6 mg/g and to azadirachtin that killed the larvae only by injection (dose of 0.20 mg/g of larvae body weight). Our results confirm the importance of the epoxy-alcohol junction between the two parts of the azadirachtin molecule for the biological activity. Other effects of the epoxy-alcohols tested were blackening of larvae and morphological deformities of some adults hatching. In future, the molecules should be complexified (degree of ramification, length of chain and presence of bulky ramified substituent) to obtain an insecticide as toxic for insects only and environmentally safe as azadirachtin but more stable, and their physiological activities on insect's tissues and cells should be studied. [source]

Thermal stability and ablation properties of silicone rubber composites

Eung Soo Kim
Abstract Effects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy-acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS4: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS4 layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS4 composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy-acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF , HTV/MMTS4 < HTV/CF/MMTS4 , HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS4 compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS4 specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]