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PubMed1983

Inactivation of yeast hexokinase B by triethyltin bromide.

Triethyltin bromide was found to demonstrate temperature-dependent inactivation of yeast hexokinase B. At temperatures of 20 degrees C or lower, little or no inactivation of the enzyme was detected after 2 h of reaction with 50-300 microM concentrations of the reagent. However, incubation at 25 degrees C or higher resulted in an increased rate and extent of loss of the enzyme activity with increasing incubation temperatures. The Arrhenius plot for the inactivation process showed a sharp break at approximately 30 degrees C, with a heat of activation (delta H*) above this temperature of 55.2 kcal, indicating that a triethyltin-induced conformational change occurred at the elevated temperatures. Sugar substrates provided protection against the inactivating effect by reducing the binding of triethyltin to the enzyme. In the absence of glucose, two sites of different affinity for triethyltin exist in the hexokinase monomer. Binding of triethyltin to the enzyme shifted its monomer-dimer equilibrium toward the monomeric form in an early stage of the interaction. Inactivation of the enzyme was associated with a slower subsequent event. Comparative effects of various organotin compounds on the activity of the enzyme indicated that inhibitory potency was associated with increasing hydrophobicity of the alkyl groups attached to the tin.

Adenosine Triphosphatases↗
PubMedDate not supplied

Copolymerizations of epsilon-caprolactone and glycolide-a comparison of tin(II)octanoate and bismuth(III)subsalicylate as initiators.

Copolymerizations of epsilon-caprolactone (epsilonCL) and glycolide (GL) were conducted in bulk at 120 degrees C with variation of the reaction time. Either Sn(II) 2-ethylhexanoate (SnOct(2)) or bismuth(III)subsalicylate (BiSS) were used as initiators combined with tetra(ethylene glycol) as co-initiator. The resulting copolyesters were analyzed by (1)H and (13)C NMR spectroscopy with regard to the total molar composition and to the sequence of the comonomers. Furthermore, two series of copolymerizations (either Sn- or Bi-initiated) were performed at constant time with variation of the temperature. It was found that BiSS favors alternating sequences more than SnOct(2). Time-conversion curves and MALDI-TOF mass spectrometry of homopolymerization suggest that SnOct(2) is the more efficient transesterification catalyst. A hypothetical reaction mechanism is discussed.

Bismuth↗
PubMed2001

Effect of solid surface composition on the migration of tributyltin in groundwater.

Tributyltin (TBT) is the most important organotin compound that has been introduced into aquatic ecosystems. A better understanding of its interactions with solid surfaces is essential to estimate the possibilities of TBT migration through subsurface environments. For this purpose, TBT sorption onto a porous matrix of natural origin, a quartz sand as an aquifer material, was studied at low concentration levels with a monodirectional model of column type allowing sequential investigation of sorption and desorption processes. Different treatments of the solid phase were performed by injecting alkaline solutions, NaOH at pH 10.8 or NaClO-NaCl at pH 11.5, by decreasing the ionic strength or by adding kaolinite to change the surface composition and properties. The removal of iron and aluminum (hydr)oxides from the sand surface did not affect so much the sorption (decrease in 14% as compared to sorption on the raw sand). The original use of X-ray photoelectron spectroscopy to control treatment efficiency and to characterize sand surface modifications permitted to relate TBT sorption onto the aquifer material to quartz, the main component of the sand, and clay minerals (mainly kaolinite) present at trace levels at the sand surface. A first attempt of transport modeling with these two surface sites showed the consistency of our assumption. Moreover, estimation of Langmuir-type constants showed that TBT sorption affinity for the quartz surface (KL = 26.7 L micromol(-1)) was much greater than for kaolinite (KL = 6.3 L micromol(-1)).

Adsorption↗
PubMed2006

TBT causes regime shift in shallow lakes.

Tributyltin (TBT) is an organotin compound used since the early 1960s as a biocide in boat antifouling paints. Its use has been linked to a host of negative effects in marine ecosystems including malformations and imposex in Mollusca and acute toxicity in many other aquatic animals. Yet, the consequences of TBT use in freshwaters are largely unknown. Here, for the first time we reveal that TBT may have caused hitherto unsuspected damage to freshwater ecosystems. Through an analysis of dated sediment cores collected from a system of recreationally boated, shallow lakes, we show that first evidence of TBT is associated with a dramatic loss of submerged vegetation and associated diverse animal communities. Cause and effect are difficult to unravel in our study. However, we hypothesize that TBT, through reducing populations of grazing organisms in lakes already affected by eutrophication, promoted the replacement of macrophytes by phytoplankton, ultimately leading to a regime shift in the ecosystem. Our findings may have parallels in freshwater ecosystems all over the world.

Trialkyltin Compounds↗
PubMed2004

Reversal of enantioselectivity in the hydroformylation of styrene with [2S,4S-BDPP]Pt(SnCl3)Cl at high temperature arises from a change in the enantioselective-determining step.

Deuterioformylation of styrene catalyzed by [(2S,4S)-BDPP]Pt(SnCl(3))Cl at 39 degrees C gave 3-phenylpropanal (3) and 2-phenylpropanal (2) (n:i = 1.8, 71% ee (S)-2) with deuterium only beta to the aldehyde carbonyl and in the formyl group. Small amounts of deuterium were also found in the internal (2.8%), cis terminal (1.4%), and trans terminal (1.3%) vinyl positions of the recovered styrene. Deuterioformylation of styrene at 98 degrees C gave 3- (3) and 2-phenylpropanal (2) (n:i = 2.3, 10% ee (R)-2) with deuterium both alpha and beta to the aldehyde carbonyl and in the formyl group. Deuterium was also found in the internal (20%), cis terminal (12%), and trans terminal (12%) vinyl positions of the recovered styrene. These deuterioformylation results establish that platinum hydride addition to styrene is largely irreversible at 39 degrees C but reversible at 98 degrees C. Hydroformylation of (E)- and (Z)-beta-deuteriostyrene at 40 degrees C, followed by oxidation of the aldehydes to acids, and subsequent derivitization to the (S)-mandelate esters confirmed that 84% of 2-phenylpropanal (2) arises from platinum hydride addition to the si-face of styrene, while 73% of 3-phenylpropanal (3) arises from platinum hydride addition to the re-face of styrene. At 100 degrees C, the effect of variable H(2) and CO pressure on n:i, % ee, and TOF of hydroformylation of styrene was investigated. The results are consistent with enantioselectivity not being fully determined until the final hydrogenolysis of a platinum acyl intermediate.

Aldehydes↗
PubMed2004

Catalytic homologation of vinyltributylstannane to allyltributylstannane by Mo(IV) complexes in the presence of ethylene.

We have found that CH2=CHSnBu3 is converted into CH2=CHCH2SnBu3 catalytically in the presence of Mo(IV) olefin complexes such as Mo(NAr)(CH2CH2)[biphen] (where Ar = 2,6-i-Pr2C6H3 and [biphen]2- = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The proposed mechanism involves formation of a metalacyclopentane (MC4) complex from ethylene and CH2=CHSnBu3, "contraction" of this MC4 complex to a metalacyclobutane (MC3) complex, and finally metathesis of the MC3 complex to give CH2=CHCH2SnBu3 and Mo(NAr)(CH2)[biphen]. These new findings suggest (inter alia) that contraction of an MC4 ring to an MC3 ring may be a much more common mode of decomposition of metalacyclopentane rings in d0 complexes than previously believed.

Catalysis↗
PubMed2003

Use of highly active palladium-phosphinous acid catalysts in Stille, Heck, amination, and thiation reactions of chloroquinolines.

An efficient synthetic route toward a variety of 2,4-disubstituted quinolines has been developed. Alkylation and arylation of 4-chloroquinoline using organolithium reagents proceed with high regioselectivity in position 2 under cryogenic conditions. The intermediate 1,2-dihydro-4-chloroquinoline derivatives are unstable to air and are easily oxidized to the corresponding 2-substituted 4-chloroquinolines in high yields. Highly active palladium-phosphinous acid catalysts POPd, POPd1, and POPd2 have been employed in Stille cross-couplings of quinaldine with arylstannanes and in Heck additions of various 2-substituted 4-chloroquinolines to tert-butyl acrylate. In particular, POPd combines high catalytic activity for cross-coupling reactions with simplicity of use due to its stability to air. Utilizing CsF in POPd-catalyzed Stille couplings further increased the reactivity of arylstannanes, which was attributed to the fluorophilicity of organotin compounds. Basic additives were found to exhibit a significant effect on the yields of the POPd-promoted Heck reactions. In general, dicyclohexylmethylamine affords superior results than NaOAc, Cs(2)CO(3), or t-BuOK. POPd was also found to tolerate amine and thiol substrates and proved to promote carbon-heteroatom bond formation of chloroquinoline derivatives with aliphatic and aromatic amines and thiols, respectively.

Journal Article↗
PubMed2005

Efficient Stille cross-coupling reaction catalyzed by the Pd(OAc)2/Dabco catalytic system.

[reaction: see text] An efficient Pd(OAc)2/Dabco-catalyzed Stille cross-coupling reaction procedure has been developed. In the presence of Pd(OAc)2 and Dabco (triethylenediamine), various aryl halides including aryl iodides, aryl bromides, and activated aryl chlorides were coupled efficiently with organotin compounds to afford the corresponding biaryls, alkene, and alkynes in good to excellent yields. Furthermore, high TONs [turnover numbers, up to 980,000 TONs for the coupling reaction of 1-bromo-4-nitrobenzene and furan-2-yltributyltin] for the Stille cross-coupling reaction were observed.

Journal Article↗
PubMed2000

Synthesis and reactivity of conformationally locked alpha-aminoorganostannanes and alpha-aminoorganolithiums. Discovery of a surprising configurational requirement for transmetalation.

[equation--see text] 2-Tributylstannyl-N-methylpiperidines that are conformationally locked by a 4-tert-butyl substituent were evaluated in transmetalations (Sn-Li exchange) and reactions with electrophiles. When the tin is equatorial, transmetalation occurs smoothly as does reaction with carbonyl electrophiles. Alkyl halides seem to undergo single electron transfer reactions, affording nonselective alkylation products, along with products of radical disproportionation. In a surprise, an axially oriented tin failed to transmetalate, suggesting that a synclinal relationship between the nitrogen lone pair and the carbon-tin bond is a requirement for transmetalation.

Lithium↗
PubMed2004

Pd2(dba)3/P(i-BuNCH2CH2)3N-catalyzed Stille cross-coupling of aryl chlorides.

[reaction: see text] The Pd(2)(dba)(3)/P(i-BuNCH(2)CH(2))(3)N (1d) catalyst system is highly effective for the Stille cross-coupling of aryl chlorides with organotin compounds. This method represents only the second general method for the coupling of aryl chlorides. Other proazaphosphatranes possessing benzyl substituents also generate very active catalysts for Stille reactions. Noteworthy features of the method are: (a) commercial availability of ligand 1d, (b) the wide array of aryl chlorides that can be coupled, and (c) applicability to aryl, vinyl, and allyl tin reagents.

Journal Article↗
PubMed1999

Catalytic asymmetric allylation reactions using BITIP catalysis and 2-substituted allylstannanes as surrogates for beta-keto ester dianions.

[formula: see text] Catalytic asymmetric allylation (CAA) reactions using the indicated allylstannane and the BITIP catalysts previously described by us give high yields and enantioselectivities in additions to aldehydes. The products are convertible to beta-keto esters by oxidative cleavage of the olefin. These reactions thus provide a useful catalytic enantioselective method for chain extension with introduction of a versatile four-carbon unit.

Allyl Compounds↗
PubMed2002

Mixture toxicity of priority pollutants at no observed effect concentrations (NOECs).

Environmental exposure situations are often characterised by a multitude of heterogeneous chemicals with ambiguous or unknown modes of action present at low concentrations. While multiple exposure is widely acknowledged, arguments are raised that adverse combined effects might not be evoked by mixtures of substances with dissimilar modes of action and being present at only low concentrations. In this study the combined effect of a multiple mixture composed of structurally dissimilar priority pollutants with mostly unknown modes of action has been investigated using an algal biotest. The concentrations of the components in the mixture equalled statistically estimated, individual no observed effect concentrations (NOECs). The observed mixture toxicity was not only clearly higher than expected for any single substance alone, but also well predictable using the concept of independent action.

Atrazine↗
PubMed2002

Characterization of resistance to clofentezine in populations of European red mite from orchards in Ontario.

Resistance to clofentezine was identified in four populations of the European red mite, Panonychus ulmi (Koch), from apple orchards in Ontario after ca. 5 years use. Resistance was expressed at high levels (> 2000-fold at the LC 50) to clofentezine in a population selected in the laboratory. This population was resistant to hexythiazox and to the organotin compounds cyhexatin and fenbutatin-oxide. However, a population selected with fenbutatin-oxide did not show cross resistance to clofentezine. The clofentezine-resistant population was not resistant to pyridaben, propargite or dicofol. The synergists, piperonyl butoxide and DEF, were ineffective in overcoming the resistance. Resistance to clofentezine declined rapidly in a mixed population (most resistance was lost in fewer than three generations). There were several fitness factors (fewer eggs/female, longer egg stage, longer development time for males) associated with the resistant population which may have contributed to the loss of resistant phenotypes. However, in a second test in which selection was removed from a resistant population, resistance persisted for at least 10 generations. Observations on field populations indicated that resistance persisted for at least two seasons.

Animals↗
PubMed2005

Blockade of glutamatergic and GABAergic receptor channels by trimethyltin chloride.

1. Organotin compounds such as trimethyltin chloride (TMT) are among the most toxic of the organometallics. As their main target for toxicity is the central nervous system, the aim of the present study was to investigate the effects of TMT on receptor channels involved in various processes of synaptic transmission. 2. The Xenopus oocyte expression system was chosen for direct assessment of TMT effects on voltage-operated potassium channels and glutamatergic and GABAergic receptors, and hippocampal slices from rat brain for analyzing TMT effects on identified synaptic sites. 3. TMT was found to be ineffective, at 100 micromol l(-1), against several potassium- and sodium-operated ion channel functions as well as the metabotropic glutamate receptor. 4. The functions of the ionotropic glutamate and the GABA(A) receptor channels were inhibited by TMT in micromolar concentrations. Thus, at a maximum concentration of 100 micromol l(-1), around 20-30% of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and GABA(A) receptor-mediated ion currents and 35% of the N-methyl-D-aspartate receptor-mediated ion currents were blocked. 5. In the hippocampal slice model, the inhibitory effects of TMT were much stronger than expected from the results on the ion channels. Bath application of TMT significantly reduced the amplitudes of evoked excitatory postsynaptic field potentials in a concentration-dependent and nonreversible manner. 6. Induction of long-term potentiation, recorded from the CA1 dendritic region, was inhibited by TMT and failed completely at a concentration of 10 micromol l(-1). 7. In general, TMT affects the excitatory and inhibitory synaptic processes in a receptor specific manner and is able to disturb the activity within a neuronal network.

Animals↗
PubMed2001

Organic contaminants and trace metals in flounder liver and sediment from the Amsterdam and Rotterdam harbours and off the Dutch coast.

Organic contaminants [polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenylethers (PBDEs), nonylphenols], organotin compounds and trace metals (cadmium, chromium, mercury and zinc) were determined in flounder (Platichthys flesus) liver and sediment from the Amsterdam harbour (North Sea Canal) and Rotterdam harbour (Euromonding) and off the Dutch coast between the Amsterdam and Rotterdam harbour mouths in order to assess the level of contamination in these harbours and to study contamination gradients.

Animals↗
PubMed2005

Enantioselective allylation of aldehydes catalyzed by chiral indium(III) complexes immobilized in ionic liquids.

In the presence of chiral catalytic complexes prepared from In(OTf)3 and chiral PYBOX ligands, allytributylstannane reacted with aldehydes in ionic liquids to afford the corresponding homoallylic alcohols in high enantioselectivities (86-94% ee) and good yields (68-89%); the chiral catalysts immobilized in ionic liquids could be reused with comparable enantioselectivities and yields.

Alcohols↗