Sequential cropping

An obvious place for intensive work on allelopathy is in the weed science area. Here, plant interference is either our problem or our opportunity. We should be clever enough to exploit allelopathy as a weed-suppression strategy. This could be accomplished with crops that release allelochemicals through exudation or by crop residues placed into sequential cropping systems. My research team and others have already developed some promising leads in this area. 

The process was further improved by replacing diphenylethylene with thiophene in the end-capping process [109], The advantage of this modification was related to the quantitative functionahzation of Hving PIB with thiophene, and the possibility of metallation of the thiophene end groups with n-BuLi. This is an important improvement for industrial processes, as lithiation by -BuIi is much more convenient than metallation with a Na/K alloy. Another example of this strategy is the one-pot synthesis of a novel polyoxetane-b-poly(e-caprolactone) by sequential CROP and AROP, using triflate complexes of bulky titanium bispheno-lates [110]. 

Hydroxycortisone BMD) (48) A solution of 4 g of 17a,20 20,21-bis-methylenedioxypregn-4-ene-3,l 1-dione (cortisone BMD) (46) dissolved in 300 ml of t-butanol and 5 ml of water is treated with 34 ml of 35 % hydrogen peroxide and 0.45 g of osmium tetroxide predissolved in 36 ml of /-butanol. The resulting mixture is allowed to stand at room temperature for 2 days. Diol (47) which crystallizes during the reaction is collected by filtration and washed with /-butanol and water. The filtrate is diluted with ethyl acetate and washed sequentially with aqueous sodium chloride, aqueous 10% sodium bisulfite, aqueous 10% sodium bicarbonate and finally with water to neutrality. The solvent is evaporated and a second crop of the diol (47) is collected, providing a total of about 3.8 g. 

Chlorinated anilines are produced by the reduction of PCNB that is used as a fungicide against a variety of commercial crops. The transformation of PCNB has been examined with a methanogenic enrichment culture from contaminated sediment, although this contained neither PCNB nor its reduction product pentachloroaniline (PCNA). The culture not only reduced the initial PCNB, but also carried out sequential dechlorination to tetra-, tri-, dichloroanilines, and ultimately to 3- and 4-chloroaniline (Tas and Pavlostathis 2005). 

Wheat samples are extracted with dilute ammonia on the ASE200. The extracts are amended with isotopically labeled internal standards. The extracts are purified by sequential octadecyl reversed-phase solid-phase extraction (Cig SPE) and ethylenediamine-iV-propyl anion exchange (PSA) SPE. The samples are analyzed by LC/MS/MS. This method determines crop residues of flucarbazone-sodium and A-desmethyl flucarbazone with a limit of quantitation (LOQ) of 0.01 mgkg for each analyte. 

The effect of amending soil with other types of organic-rich material has also been investigated by sequential extraction. These materials include chicken manure and cowpea leaves (Li et al, 1997) spent mushroom compost, commercial humic acid and poultry litter (Shuman, 1998) and cow manure, pig manure and peat soil (Narwal and Singh, 1998). The mechanisms by which inorganic additives (zeolite, apatite and iron oxide) reduce uptake of Cd and Pb by crops have also been studied (Chlopecka and Adriano, 1997). 

Fig. 17 Detection of B. anthracis from murine blood, (a) Detector responses during all three stages of sample processing and analysis are portrayed in terms of total analysis time. The SPE trace (green) was taken from off-line DNA extraction of the same murine sample and is representative of the total DNA concentration observed in a typical extraction. The temperature (blue) and fluorescence intensity (black) represent on-line data, with a total analysis time <24 min. Three sequential injections and separations were carried out to ensure the presence of amplified product, (b) Fluorescence data from an integrated analysis of a blank sample (no DNA) control with marker peaks labeled. The inset represents valve actuation during co-injection, with the PR and MR pumping inlets indicated by the arrows, (c) Zoomed view of the first separation shown in (a), with the product peak marked. The second and third runs are overlaid with the time axis cropped. Inset shows the sizing curve of inverse migration time vs. logfbase pairs) with both the sizing standard peaks (open diamonds) and product (square) plotted for all three runs shown in (a). From these data, the product was 211 2 bp. Reproduced from [10] with permission...

Solomon, D. and Lehmann, J. (2000) Loss of phosphorus from soil in semi-arid northern Tanzania as a result of cropping evidence from sequential extraction and P NMR spectroscopy. European Journal of Soil Science 51, 699-708. 

Finally, the living CROP of 2-oxazolines provides direct access to well-defined diblock copolymers by sequential monomer addition, that is, addition of a second monomer after full conversion of the first monomer [193, 194]. Further monomer addition after the second and third monomer has been demonstrated to result in defined triblock [195, 196] and tetrablock copoly(2-oxazoline)s [197]. 

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