We have developed the synthesis of unsymmetrical metalloporphyrazines of the form M[pz(A:B 3 )], where A and B refer to two different types of peripheral functionality, and have used it to prepare new bi-and trimetallic solitaire-porphyrazines in which A represents a mono-or bimetallic moiety. The macrocyclic complexes described are based on the binucleating ligand, [M(norphthalocyanine-2,3-dithiolate)] 2-, [M(norpc)] 2-. This can be thought of as a metalloporphyrazine where B is a fused benzo ring; A represents two thiolates fused at the -pyrrole positions to form a dithiolene moiety that can bind a transition-metal ion in addition to one within the macrocyclic cavity. solitaire-Porphyrazines have been synthesized by chelation of [(L-L)M′] 2+ to the [M(norpc)] 2-ligand where M ) "2H", Ni, Cu, or Mn-Cl, L-L is a bis(diphosphino) or bis(diamino) group and M′ ) Ni, Pd, or Pt. Crystal structures have been obtained for 11b, where the [H 2 (norpc)] 2-ligand coordinates the diphosphinopalladium moiety, [Pd-(dppf)] 2+ , by the two thiolate sulfur atoms at its periphery, and for 11h, with the diaminoplatinum moiety, [Pt-(teeda)] 2+ , bound to the periphery of the [Ni(norpc)] 2-ligand.In crystals of 11b and 11h, the molecules appear as face-to-face dimers. However, the dimer of 11b and the two crystallographically independent dimers of 11h each shows a distinctly different degree of overlap. The electronic absorption spectra of a series of porphyrazines in which the two peripheral sulfur atoms form thioether moieties with a modified benzyl-protecting group (6-10) show that the peripheral asymmetry of the macrocyclic framework causes a strong splitting of the (π-π*) Q-band. In contrast, when the peripheral sulfurs bind a metal ion to form solitaire-porphyrazines 11a-h, the optical spectra closely resemble that of the symmetrical pc, with unsplit Q band. The EPR spectrum of solitaire 11d, where M ) Cu, L-L ) a bis(diphosphino) cap, M′ ) Pd, has features consistent with other square-planar copper(II) porphyrins and phthalocyanines. Cyclic voltammograms of compound 11b shows two reversible ring reductions at potentials similar to those of H 2 (pc) as well as a reversible oxidation associated with the ferrocene portion of the Pd(dppf) moiety.
Aflatoxins produced by Aspergillus flavus are commonly found in human and animal foods including grains, cereals, peanut products, sorghum, and soy seeds. Exposure to aflatoxins has been associated with carcinogenicity. This paper reports a simple, portable, and rapid fluorescence polarization (FP) assay for aflatoxin determination in grains. This immunoassay is field portable, homogeneous, and without any washing and cleaning steps. The assay is based upon the competition between free aflatoxin and an aflatoxin-fluorescein tracer for an aflatoxin-specific monoclonal antibody in solution. A series of naturally contaminated corn, sorghum, peanut butter, and peanut paste samples were analyzed by FP and compared with HPLC results. Similarly, spiked popcorn samples were analyzed by FP. FP results of naturally contaminated samples correlated well with HPLC (r (2) = 0.97). FP analysis of spiked popcorn samples (with a mixture of B(1)/B(2)/G(1)/G(2), 7/1/3/1, w/w) gave a good correlation with spiked values (r (2) = 0.99). However, FP consistently underestimated the aflatoxin contents. This was perhaps due to low cross-reactivity of the antibody used toward B(2), G(1), and G(2) aflatoxins. These results combined with the portability and simplicity of the assay suggest that the assay can be used for screening total aflatoxin in grains.
Fumonisins, mycotoxins produced by certain species of Fusaria, are commonly found worldwide as contaminants in maize. This paper reports the development of a rapid, portable fluorescence polarization-based assay for fumonisins in maize. The assay was based on the competition of unlabeled fumonisin, from a sample, with a fluorescently tagged fumonisin (FB(1)-FL) for a fumonisin-specific monoclonal antibody in solution. The fluorescence polarization (FP) of the tagged fumonisin was increased upon binding with the antibody. In the presence of free toxin, less of the FB(1)-FL was bound and the polarization signal was decreased. The assays were very simple to perform, requiring only mixing of an aqueous extract of maize with the tagged fumonisin and antibody, and required <2 min per sample, excluding extraction time. Two permutations of the assay were tested, one with each sample matrix serving as its own blank, and the other with all of the samples compared relative to a PBS blank with normalization of the data similar to an ELISA. The limit of detection, defined as the toxin content associated with a fluorescence polarization signal 5 standard deviations from that of a fumonisin-free control, was 0.5 microg of FB(1)/g in spiked maize. Recoveries from spiked maize over the range of 0.5-20 ppm averaged 94.3 +/- 13.8%. Forty-eight samples of field-contaminated maize were tested by the FP and an established HPLC method, with a good correlation between the two (r(2) = 0.85-0.88). For these samples, the two variations of the FP assay also compared well to one another (r(2) = 0.97), suggesting the assay principle is very robust. The results, combined with the speed and ease of use for the assay, suggest that this technology has substantial potential as a screening tool for mycotoxins in foods.
Successful use of fluorescence polarization assays (FPAs) in human clinical, infectious disease, and drug discovery fields has prompted us to extend its use to the grain mycotoxin field. An antibody specific to a mycotoxin and a mycotoxin-fluorophore conjugate are developed. Free toxin (extracted from the grains with a suitable solvent) competes with the toxin-fluorophore conjugate for the antibody and a change in FP relative to the quantity of free toxin occurs. This change is compared to a standard curve obtained by using known quantities of toxin. The use of FP and toxin-fluorophore conjugates for the quantification of fumonisins, deoxynivalenol and aflatoxins is described. These assays are field portable, simple to perform, rapid and require no washing steps.
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