Effect of neem leaf inclusion rates on compost physico-chemical, thermal and spectroscopic stability.

Neem leaves possess antimicrobial, insecticidal and nitrification inhibitory biochemicals that may influence compost stability. However, if neem-based compost achieves stability, it can prove useful by providing fertilizer-cum-pesticide properties. Therefore, conventional (physico-chemical), thermogravimetric (TGA) and spectroscopic analyses (FTIR and 13C SS NMR) were used to evaluate the effects of neem leaf content on stability. Treatments included 0, 10, 20, 30, 40 and 50% neem leaves by volume combined with complimentary amounts of corn stover to form 50% of the substrate formulation (SF). Cow manure constituted the additional 50%. Despite all treatments reaching ambient temperature (32 °C ± 1 °C) by the 40th day, Solvita® results showed high CO2 respiration, thereby classifying the compost treatments as active, whereas decreased C:N ratio, NH4+: NO3- ratio and NH4+ values among treatments indicated stability. Furthermore, TGA, FTIR and 13C NMR revealed degradation of labile organic matter and showed that complex aromatic and lignin compounds were also degraded, particularly when neem leaves were added to the mixture, suggesting that aromatisation does not always indicate stability in compost. Spearman's rank correlation showed that physico-chemical methods were poorly correlated to respirometric, thermal and spectroscopic methods. It also suggests that these respirometric and advanced methods are important in understanding the mechanisms affecting neem compost stability.

Quantitative risk assessment of polychlorodibenzofurans (PCDFs) released in PCB fires: use of high-resolution gas chromatography.

The toxicity of polychlorodibenzofurans (PCDFs), produced during incineration and in accidental fires involving polychlorinated biphenyls (PCBs), is generally assessed in terms of total concentration or more recently in terms of the group concentrations of the tetra-, penta- and hexachloro-isomers. This approach fails to account for the great differences in potency of the relatively few toxic congeners and isomers present in the sample. A quantitative risk assessment of PCDF mixtures must not only be based on the concentrations of the toxic components but also account for the relative potency of each congener in a form which permits summation of the toxicities of the individual contributors. This paper outlines a method by which the concentration of each of the toxic components, determined by high-resolution congener-specific gas chromatographic analysis, may be converted to equivalent toxic concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Summation of the resulting values permits the overall toxicity of the sample to be expressed in terms of an equivalent toxic weight of TCDD per unit weight of sample (ng TCDD/g) in the case of fly ash or an equivalent toxic weight of TCDD per unit area (ng TCDD/m2) for soot deposit.

Structural variations in soluble iron complexes of models for ferritin: an x-ray absorption and Mössbauer spectroscopy comparison of horse spleen ferritin to Blutal (iron-chondroitin sulfate) and Imferon (iron-dextran).

Variations in the turnover of storage iron have been attributed to differences in apoferritin and in the cytoplasm but rarely to differences in the structure of the iron core (except size). To explore the idea that the iron environment in soluble iron complexes could vary, we compared horse spleen ferritin to pharmaceutically important model complexes of hydrous ferric oxide formed from FeCl3 and dextran (Imferon) or chondroitin sulfate (Blutal), using x-ray absorption (EXAFS) and Mössbauer spectroscopy. The results show that the iron in the chondroitin sulfate complex was more ordered than in either horse spleen ferritin or the dextran complex (EXAFS), with two magnetic environments (Mössbauer), one (80%-85%) like Fe2O3 X nH2O (ferritinlike) and one (15%-20%) like Fe2O3 (hematite); since sulfate promotes the formation of inorganic hematite, the sulfate in the chondroitin sulfate most likely nucleated Fe2O3 and hydroxyl/carboxyls, which are ligands common to chondroitin sulfate, ferritin and dextran most likely nucleated Fe2O3 X nH2O. Differences in the structure of the iron complexed with chondroitin sulfate or dextran coincide with altered rates of iron release in vivo and in vitro and provide the first example relating function to local iron structure. Differences might also occur among ferritins in vivo, depending on the apoferritin (variations in anion-binding sites) or the cytoplasm (anion concentration).

Conformational flexibility of poly (dG-m5dC) under very low salt conditions.

The methylated DNA polymer poly (dG-m5dC) which exhibits a B helical conformation in solutions containing 20 mM NaCl, undergoes a gradual and reversible transition to the Z conformation as the NaCl concentration is lowered. The midpoint of this transition occurs around 5-6 mM NaCl. The conformational flexibility of this polymer at such low NaCl concentrations opens up the possibility of studying the effects of other perturbants with negligible interference from salt concentration effects.

The effect of polychlorobiphenyls (Aroclor 1242) on bicarbonate-C14 uptake by Euglena gracilis.

Aroclor 1242 is inhibitory to long-term batch growth of Euglena gracilis at 10 ppm. Exposure to PCB's, subsequent to an initial drop of 50% in the first 30 minutes, does not appear to inhibit photosynthesis on a per cell basis over the time span of four hours. Consequently our experimental findings suggest that inhibition of population growth does not lie directly in the photosynthetic pathway despite the initial inhibition by Aroclor 1242 on Euglena gracilis in "light". "Dark" absorption of bicarbonate appears to decrease with increased PCB exposure. This decrease may be causally related to the population growth inhibition observed.

Temperature-induced perturbations in the circular dichroic spectrum of the synthetic polymer poly[d(G-C)].

The effect of increasing temperature on the double-helical synthetic DNA polymer poly[d(G-C)] with alternating base sequence, was studied by ultraviolet absorbance and circular dichroic techniques. While a cooperative hyperchromic effect was noticed in the ultraviolet absorbance spectrum above a temperature of 70 degrees C, an inversion of the circular dichroic spectrum was observed at a similar temperature range. On cooling to room temperature, the spectrum was reversed to the initial one. These observations, first reported here, are tentatively attributed to a conformational change of the polymer, from the right-handed double helix to the left-handed single strands, prior to complete denaturation.