The X-ray structure of a vinyl cation.
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Boron Compounds↗
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Theoretical study on the reactivities of stannylene and plumbylene and the origin of their activation barriers.
The potential energy surfaces corresponding to the reactions of heavy carbenes with various molecules were investigated by employing computations at the B3LYP and CCSD(T) levels of theory. To understand the origin of barrier heights and reactivities, the model system (CH3)2X+Y (X=C, Si, Ge, Sn, and Pb; Y=CH4, SiH4, GeH4, CH3OH, C2H6, C2H4, and C2H2) was chosen for the present study. All reactions involve initial formation of a precursor complex, followed by a high-energy transition state, and then a final product. My theoretical investigations suggest that the heavier the X center, the larger the activation barrier, and the less exothermic (or the more endothermic) the chemical reaction. In particular, the computational results show that (CH3)2Sn does not insert readily into C-H, Si-H, C-H, Ge-H, or C-C bonds. It is also unreactive towards C=C bonds, but is reactive towards C identical with C and O-H bonds. My theoretical findings are in good agreement with experimental observations. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. It is demonstrated that the singlet-triplet splitting of a heavy carbene (CH3)2X plays a decisive role in determining its chemical reactivity. The results obtained allow a number of predictions to be made.
Computer Simulation↗
Polystyrene-supported organotin dichloride as a recyclable catalyst in lactone ring-opening polymerization: assessment and catalysis monitoring by high-resolution magic-angle-spinning NMR spectroscopy.
Dialkyltin dichloride grafted to a cross-linked polystyrene, with the formula [P-H]((1-t))[P-(CH2)nSnBuCl2]t (P=[CH2CH(pC6H4)], t=the degree of functionalization, and n=6 or 11), is investigated as a recyclable catalyst in the ring-opening polymerization (ROP) of epsilon-caprolactone (CL). It is demonstrated that high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy is an invaluable tool to characterize completely the supported catalyst. The 2D 1H-13C HSQC HR-MAS spectrum, in particular, allowed extensive assignment of the 1H and 13C resonances, as well as accurate measurement of the (n)J((1)H-(117/119)Sn) and (n)J((13)C-(117/119)Sn) coupling constants. 1H and 119Sn HR-MAS NMR spectroscopy is presented as a monitoring tool for catalytic processes based on organotin compounds, particularly for the investigation of the extent to which polymerization residues are observable in situ in the material pores and for the assessment of the chemical integrity and recycling conditions of the grafted catalyst. From polymerization experiments with CL, initiated by n-propanol and with [P-H]((1-t))[P-(CH2)nSnBuCl2]t of various compositions as the supported catalyst, it appears that a partial 'burst' of the polystyrene support occurs when the length of the alkyl spacer is limited to n=6, as a result of polymer chains growing within the pores of the support. However, extension of the length of the aliphatic polymethylene spacer from 6 to 11 carbon atoms preserves the support integrity and allows the production of catalyst-deprived poly(epsilon-caprolactone) (PCL) oligomers. A preliminary attempt to recycle the heterogeneous catalyst has shown that very good reproducibility can be obtained, in terms of both catalyst activity and molecular-weight parameters of the as-recovered PCL polyester chains.
Journal Article↗
Synthesis of functionalized vinylgermanes through a new ruthenium-catalyzed coupling reaction.
Vinyl-substituted germanes react stereo- and regioselectively with olefins in the presence of complexes containing Ru-H and Ru-Ge bonds with the formation of functionalized vinylgermanes that cannot be synthesized by olefin cross-metathesis procedures. The reaction opens a new catalytic route for preparation of a class of organogermanes that are potent organometallic reagents for organic synthesis because they show very low toxicity and could replace organotin compounds. The mechanism of this new catalytic route was proven to involve an interesting insertion of the vinylgermane into the Ru-H bond and beta-Ge transfer to the metal with elimination of ethylene and generation of an Ru-Ge bond, followed by insertion of the alkene into the Ru-Ge bond and beta-H transfer to the metal to eliminate the substituted vinylgermane.
Journal Article↗
[Transformation reactions of special metals in organisms and in the environment. 2. Abiotic methylation reactions of mercury, especially by methyltin compounds and humic and fulvic acids].
Following a literature survey concerning abiological methylation reactions including transmethylation of mercury we present the results of transmethylation experiments. Model experiments in aqueous solution show an instantaneous methylation of mercuric chloride by mono-, di-, and trimethyltin chloride, the dimethyl compound having the highest rate of formation. The same is valid for similar experiments with soils, in which influences of the kind of soil also play a certain role. The methylation experiments of HgCl2 with humic and fulvic acids isolated from soil yielded positive results only in some few of the extracts and only with humic acid fractions.
Benzopyrans↗
Tributyltin is a potent inducer of the heat shock response in human diploid fibroblasts.
Submicromolar concentrations of tributyltin (TBT), a commercially used organotin compound, were found to induce the expression of several stress proteins, most notably HSP89 and HSP70, in IMR-90 human diploid fibroblasts in a time- and dose-dependent manner. This induction can be demonstrated by quantitation of 1) synthesis of the heat shock proteins (HSPs), 2) relative abundance of mRNA of hsp70, and 3) transient expression of a human hsp70 promoter driven reporter gene. TBT also increased the abundance of mRNA of heme oxygenase, whereas heat shock was without effect. Analysis of protein binding to a consensus heat shock element (HSE) by electrophoretic mobility shift assay suggests that the induction of the heat shock response by TBT was attributable to activation of the heat shock transcription factor (HSTF).
Base Sequence↗
Band composition analysis: a new procedure for deconvolution of the mass spectra of organometallic compounds.
A new chemometric procedure called band composition analysis (BCA) designed for the deconvolution of mass spectra of organometallics is proposed. BCA generates theoretical bands T(i), then combines them to obtain a model band M, which is finally compared with the experimental band E. All of these steps are realized with computer assistance. This modeling yields four parameters characterizing the experimental band: theoretical and model variances s(2) (theor) and s(2) (model), a fit factor alpha and a contribution x(i) from the theoretical band. If s(2) (theor) > 20 the band is deemed complex and needs modeling. The values alpha > 90 indicate that there is good agreement between the experimental and model bands. BCA is particularly effective for the modeling of complex isotopic bands often present in organometallics. Two illustrations of BCA for tetrabutyltin, C(16)H(36)Sn, and 1,1',2,2',3,3'-hexachloroferrocene, C(10)H(4)Cl(6)Fe, are shown.
Ferrous Compounds↗
New developments in insecticide resistance in the glasshouse whitefly (Trialeurodes vaporariorum) and the two-spotted spider mite (Tetranychus urticae) in the UK.
A recent survey of insecticide resistance in two of the most problematic pests in UK glasshouses revealed some new developments. At least some individuals in all UK samples of Trialeurodes vaporariorum that were tested resisted the insect growth regulator (IGR) buprofezin. The most strongly resistant strains were unaffected by the field application rate of this compound, and even samples from populations that had never been exposed to buprofezin contained individuals that survived the highest concentration applied (10,000 mg litre-1). The field rate of buprofezin was shown to select for resistance through vapour action alone. The benzophenylurea teflubenzuron, an unrelated IGR, was cross-resisted by buprofezin-resistant individuals. There was no evidence of resistance to imidacloprid, but all T vaporariorum strains tested, regardless of origin, exhibited a high innate tolerance to nicotine, when compared with another whitefly species, Bemisia tabaci. Marked resistance to fenbutatin oxide and tebufenpyrad was found in single glasshouse populations of Tetranychus urticae, but these compounds and abamectin appeared to remain highly effective against all other strains collected.
Acari↗
Cytotoxic effects of triphenylbismuth on rat thymocytes: comparisons with bismuth chloride and triphenyltin chloride.
The biomedical and industrial uses of organobismuth compounds have become widespread, although there is limited information concerning their cytotoxicity. Therefore, the actions of triphenylbismuth on rat thymocytes were examined using a flow cytometer with ethidium bromide, annexin V-FITC, fluo-3-AM, and 5-chloromethylfluorescein (5CMF) diacetate. Triphenylbismuth at 3-30 microM increased the population of cells stained with ethidium, indicating a decrease in cell viability. Organobismuth at 30 microM increased the population of cells positive to annexin V, suggesting an increase in the population of apoptotic cells. Triphenylbismuth at 3 microM or more decreased cellular glutathione content (5CMF fluorescence intensity) and increased intracellular Ca(2+) concentration ([Ca(2+)](i), fluo-3 fluorescence intensity) in a dose-dependent manner. Because an increase in [Ca(2+)](i) is linked to cell death or cell injury and a decrease in cellular glutathione content increases cell vulnerability to oxidative stress, the triphenylbismuth-induced changes in cellular parameters may be responsible for triphenylbismuth-induced cytotoxicity. Bismuth chloride at 10-30 microM did not significantly affect cell viability. These results suggest that triphenylbismuth at micromolar concentrations exerts cytotoxic action on rat thymocytes, possibly related to a health hazard. Although the cytotoxicity of triphenylbismuth was less than that of triphenyltin, one of the environmental pollutants, it is necessary to direct our attention to the use and disposal of organobismuth compounds.
Animals↗
Toxicity reduction of metal pyrithiones by near ultraviolet irradiation.
Zinc pyrithione (ZnPT) or copper pyrithione (CuPT) have been effectively used as ship-antifouling agents, as an alternative to organotin compounds. Because of their instability in light and a lack of suitable analytical procedures, there is little data on their residue levels in environmental matrices. It is possible to investigate the fate of such compounds by toxicity alteration with certain treatments. The purpose of this study was to evaluate the degradation of pyrithiones through toxicity reduction by near ultraviolet (UV-A) irradiation. Metal pyrithiones dissolved in acetonitrile were irradiated with a UV-A lamp for 0, 0.5, 1, and 2 h, and were subjected to UV spectral measurement and toxicity evaluation using both sea urchin and freshwater rotifer bioassays. For the bioassays, photolyzed samples were dissolved in dimethyl sulfoxide after evaporation of the acetonitrile. The changes in UV spectra of photolyzed ZnPT or CuPT showed a time-dependent degradation, and the UV spectra at 2 h irradiation suggested substantial decomposition. Toxicities of ZnPT and CuPT were 12 and 5 microg/L as 24 h LC50 to the survival of rotifers and 10(-6) ng/L and 2.3 ng/L as 27 h EC50 to normal pluteus formation, respectively. By evaporation of the acetonitrile, the EC50 of ZnPT was 2.2 ng/L, which was the same as that of CuPT. The EC50s of ZnPT or CuPT for both species increased with longer irradiation times. Photolyzed ZnPT or CuPT demonstrated substantial degradation in the UV spectra, but possessed marked toxicity, which is probably due to toxic degradation products. One reason why photolyzed CuPT was toxic to rotifers was explained by the high toxicity of copper ions formed by UV-A irradiation.
Animals↗
The role of calcium in pre- and postmitochondrial events in tributyltin-induced T-cell apoptosis.
Using a novel dual-channel FACS methodology, the organotin compound TBT (2 microM) was shown to induce rapid (maximal by 3 min) and sustained elevations in intracellular calcium levels [Ca(2+)](i) in Jurkat T cells. This was preceded by mitochondrial hyperpolarization (maximal at 1 min), with subsequent loss of membrane potential, (Deltapsi(m)) over the next 15 min and was associated with the release of mitochondrial cytochrome c and the activation of type II caspases. The activation of the caspases was blocked by calcium chelation with EGTA and/or BAPTA. Interestingly, changes in Deltapsi(m) caused by TBT were not affected by chelation of intra- and extracellular calcium or by performing the experiments in a Ca(2+)-free medium. TBT also caused rapid elevation of [Ca(2+)](i) in cells lacking glycolytic ATP production. Despite this, the loss of Deltapsi(m) and the activation of type II caspases were delayed (maximal by 2 h) in these cells. Further, there was a failure to activate type II caspases in cells treated with TBT in a Ca(2+)-free medium, despite rapid release of mitochondrial cytochrome c. Consequently, these cells evaded the induction of apoptosis and were diverted to delayed necrotic deletion. Taken together, these data strongly suggest that the rapid rise in [Ca(2+)](i) caused by TBT in Jurkat T cells is not directly coupled to the induction of mitochondrial permeability transition, which rather results from a direct interaction of TBT with mitochondrial component(s) controlling pore transition. However, the rise in [Ca(2+)](i) is a prerequisite for postmitochondrial events involved in caspase activation prior to the induction of apoptosis.
Apoptosis↗
Expression of EMAP-II by activated monocytes/microglial cells in different regions of the rat hippocampus after trimethyltin-induced brain damage.
Endothelial monocyte-activating polypeptide-II (EMAP-II), a novel cytokine with proinflammatory and antiangiogenic properties, has previously been shown to be expressed by activated monocytes/microglial cells in the rat brain and was therefore considered a useful marker to stage microglial activation in inflammatory lesions. The aim of the present immunohistochemical study was to investigate expression of EMAP-II in the rat hippocampus after intoxication with the organotin compound trimethyltin (TMT). Administration of this neurotoxicant is known to produce brain damage mainly affecting the hippocampal formation, with severe neuronal cell loss being observed predominantly in regions CA-1 and CA-3. The maximum severity of TMT-induced brain damage is observed 21 days after a single ip administration. In this well-characterized model of neurodegeneration, activated microglial cells have been described to occur mainly in the early stages of TMT-induced neurotoxicity. Following TMT intoxication, we observed a significant increase in EMAP-II(+) monocytes/microglial cells in the CA-1 and the CA-3 regions. The CA-2 region, however, was largely spared. While appearance of single EMAP-II(+) microglial cells was observed already after 5 days, EMAP-II immunoreactivity reached its maximum after 21 days and persisted in some of the rats up to 35 days. These findings show a close correlation to the temporal and spatial pattern of neuronal damage described in the rat hippocampus after TMT administration previously. Thus, upregulation of EMAP-II by activated monocytes/microglial cells may serve as a sensitive marker of neurotoxic lesions in the rat brain.
Animals↗
Glia increase degeneration of hippocampal neurons through release of tumor necrosis factor-alpha.
This study characterizes the role of glial cells in chemically induced neurodegeneration. We evaluated the effect of trimethyltin, a trisubstituted organotin compound that elicits distinct lesions in the central nervous system in vivo, on a sandwich co-culture of neurons and glia. Exposure of a 98% pure culture of rat hippocampal neurons to 0.1-1 microM trimethyltin for 24 h caused neural cell death and nuclear changes typical of apoptosis; at these doses glial cells viability was not affected but the cells released significant amounts of tumor necrosis factor-alpha (TNF-alpha). Neuronal apoptosis and TNF-alpha release from glial cells both increased when the two cell types were exposed together to trimethyltin, which indicates synergy. Treatment of a neuron-glia co-culture with TNF-alpha antibody prevented the increase in neuronal apoptosis, and TNF-alpha administration induced apoptosis in hippocampal cells. We conclude that glial cells and TNF-alpha both modulate trimethyltin-induced neurodegeneration.
Animals↗
A simple technique of testing for the influence of metal salts and other chemicals on macrophages and thymocytes in vito.
The spleen fragment test, originally used for estimation of factors of cell mediated immunity, was used to assess the relative toxicity of various metal salts and other chemicals on macrophages in vitro. The inhibition of macrophage migration from spleen fragments of guinea pigs was measured as a functional parameter for the toxic effects. Concentration response curves and the molar concentration that yielded a 50% inhibition of the macrophage migration (EC50) were determined. The EC50 values of the examined metal salts ranged from 1.7 X 10(-5) M for Na2SeO3 to 1.3 X 10(-2) M for MnCl2 and indicated that the relative toxicity was Na2SeO3 > K2Cr2O7 > CdCl2 > HgCl2 > NiCl2 > CrCl3 > MnCl2. Other investigations dealt with the interaction of Na2SeO3 and HgCl2 on macrophages in vitro. Corresponding to the spleen fragment test thymus fragments from mice and rats were used for the study of the influence of organotin compounds and prednisolone on the thymocyte migration in vitro.
Animals↗
Antitumor properties of organometallic metallocene complexes of tin and germanium.
The antitumor activity of the four metallocene compounds decaphenylstannocene [eta 5-(C6H5)5C5]2Sn(II), decabenzylstannocene [eta 5-(C6H5CH2)5C5]2Sn(II), decaphenylgermanocene [eta 5-(C6H5)5C5]2Ge(II), and decabenzylgermanocene [eta 5-(C6H5CH2)5C5]2Ge(II), containing the main group IV elements tin or germanium as the central metal atom and two pentasubstituted cyclopentadienyl ring ligands in sandwich arrangement, were tested against Ehrlich ascites tumor in female CF1 mice. The complexes caused cure rates of 40% to 90% of the animals treated over rather broad dose ranges. With both germanocene complexes, no strong dose-activity relationship was manifest. The toxicity of all four metallocenes was low, the LD10 values of both stannocenes being 460 and 500 mg/kg, and those of both germanocenes higher than 700 mg/kg. Regarding the isolated pentasubstituted cyclopentadiene ligands (C6H5)5C5H and (C6H5CH2)5C5H, these also exhibited antitumor activity which was less pronounced than that of the metal-containing sandwich complexes. Decasubstituted stannocene and germanocene compounds represent a new type of non-platinum group metal antitumor agents structurally differing from known inorganic and organometallic cytostatics.
Animals↗
Fenbutatin oxide and chlorfenvinphos effects on the entomophagous arthropod fauna of citrus.
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Animals↗
Bis(tri-n-butyltin)oxide induces programmed cell death (apoptosis) in immature rat thymocytes.
In order to characterise the mechanism of cytotoxicity of the immunotoxic organotin compound bis(tri-n-butyltin)oxide (TBTO) to lymphoid cells, isolated thymocytes from immature rats were exposed to TBTO (0.1-5 microM) for up to 6 h. At lower TBTO concentrations (0.1 and 1 microM) vital staining showed that only marginal loss of viability occurred, although morphological studies demonstrated increased numbers of cells with abnormal features indicative of programmed cell death (apoptosis). These changes included nuclear chromatin condensation (which was associated with increased DNA fragmentation), cytoplasmic contraction and formation of membrane bound apoptotic bodies. When visualised by agarose gel electrophoresis, genomic DNA appeared as a series of fragments with a repeat multiple of 180-200 base pairs. Comparable morphological changes and cleavage of DNA into oligonucleosomal fragments were evident in thymocytes incubated with 10 microM methyl prednisolone hemisuccinate (MPS); a glucocorticoid hormone known to induce programmed cell death in thymocytes. Marked cytotoxicity associated with degenerative changes indicative of necrosis was observed in thymocytes incubated with 5 microM TBTO. These findings indicate that, at levels which are not overtly cytotoxic, TBTO is capable of inducing programmed cell death in rat thymocytes. This suggests a possible mechanism for the T-cell immunodeficiency previously reported for TBTO in vivo.
Animals↗
Toxicity of tributyltin to willow trees.
BACKGROUND: Tributyltin is an organotin compound, used as an antifouling agent in ship paint, with heavy impact on the marine environment. Contaminated dredged harbor sludge is now dumped on land. The toxicity of tributyltin (TBT) to trees has not yet been quantified. Eventually, a vegetation cover on the dumped sludge could be established for the purpose of non-food cash crop production and phytoremediation. METHODS: The phytotoxicity of tributyltin chloride (TBTCl) and tributyltin hydride (TBTH) was measured at pH 4 and at pH 7 using the willow tree transpiration test. Different pH levels of the nutrient solutions were achieved by adding ammonium salt (low pH) or nitrate (high pH) as nitrogen source. RESULTS AND DISCUSSION: At low pH (pH 4), all trees showed symptoms of poor health. Transpiration decreased at concentrations above or equal to 0.1 mg TBTCl/l and 1 mg TBTH/L. The TBT toxicity was more pronounced at pH 7. The trees survived even the highest dose of 10 mg/l TBTCl or TBTH, although their growth and transpiration was strongly reduced. CONCLUSION: In contrast to other organisms, TBTCl and TBTH were less toxic to higher plants. RECOMMENDATIONS AND OUTLOOK: The toxicity of TBT is no hindrance for establishing vegetation on TBT-contaminated sludge. Phytoremediation and cash crop production could be possible with suitable plants.
Environmental Pollutants↗