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Nine metals (Fe, Cu, Mn, Ni, Cd, Pb, Hg, Cr, and Zn) were determined in soil and Digitaria eriantha plants within the vicinity of three coal power plants (Matla, Lethabo, and Rooiwal), using ICP-OES and GFAAS. The total metal concentration in soil ranged from 0.05 ± 0.02 to 1836 ± 70 μg g(-1), 0.08 ± 0.05 to 1744 ± 29 μg g(-1), and 0.07 ± 0.04 to 1735 ± 91 μg g(-1) in Matla, Lethabo, and Rooiwal, respectively. Total metal concentration in the plant (D. eriantha) ranged from 0.005 ± 0.003 to 535 ± 43 μg g(-1) in Matla, 0.002 ± 0.001 to 400 ± 269 μg g(-1) in Lethabo, and 0.002 ± 0.001 to 4277 ± 201 μg g(-1) in Rooiwal. Accumulation factors (A) of less than 1 (i.e., 0.003 to 0.37) at all power plants indicate a low transfer of metal from soil to plant (excluder). Enrichment factor values obtained (2.4-5.0) indicate that the soils are moderately enriched with the exception of Pb that had significant enrichment of 20. Geo-accumulation index (I-geo) values of metals indicate that the soils are moderately polluted (0.005-0.65), except for Pb that showed moderate to strong pollution (1.74-2.53).

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This review covers the phytochemical, biological properties, and synthesis of naturally occurring homoisoflavonoids. Homoisoflavonoids are a very important class of secondary metabolites whose numbers have grown from 20 in 1981 to 157 at the present time. They are found to occur in seven plant families. For the purpose of this review they are classified into five groups: 3-benzylchroman-4-ones, 3-benzylflavans, Δ3,9 and Δ2,3 3-benzylchroman-4-ones, benzocyclobutenes (scillascillins) and rearranged homoisoflavonoids (brazilin and related compounds). Biosynthetically, the 3-benzylchroman-4-ones and the 3-hydroxy-derivatives have been shown to arise from a chalcone precursor (sappanchalcone) and there is strong evidence that this isolable intermediate can be converted into the diverse structures such as the benzocyclobutenes (scillascillins) and the rearranged, brazilin-type compounds. Homoisoflavonoids possess a wide range of biological activities, including, antimicrobial, antimutagenic, anti-inflammatory, antidiabetic, etc, properties. The review also surveys the chemical synthesis of natural homoisoflavonoids. Analytical methods for the determination of these important metabolites are also reviewed. The last section is devoted to a brief review of the diagnostic NMR spectroscopic features of homoisoflavonoids. A comprehensive Table has also been compiled listing all known metabolites, their sources, melting points and optical rotation values (where available) and references.

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