Russell A. Bell

The biotic ligand model and a cellular approach to class B metal aquatic toxicity

The biotic ligand model (BLM) and a cellular molecular mechanism approach represent two approaches to the correlation of metal speciation with observed toxicity to aquatic organisms. The two approaches are examined in some detail with particular reference to class B, or soft metals. Kinetic arguments are presented to suggest situations that can arise where the BLM criterion of equilibrium between all metal species in the bulk solution and the biotic ligand may not be satisfied and what might the consequences be to BLM predictive capability. Molecular mechanisms of toxicity are discussed in terms of how a class B metal might enter a cell, how it is distributed in a cell, and how the cell might respond to the unwanted metal. Specific examples are given for copper as an organism trace essential metal, which is toxic in excess, and for silver, a non-essential metal. As class B metals all bind strongly to sulfur, regulation of these metals requires that all S(II-) species be accounted for in aquatic systems, even under oxic conditions.

Synthesis and characterization of cyclomaltoheptaose-based metal chelants as probes for intestinal permeability

Abstract The syntheses of two cyclomaltoheptaose-based metal chelants, cyclomaltoheptaose-ethylenediaminetetraacetate (CD-EDTA) and cyclomaltoheptaose-diamide-disulfur (CD-DADS), are described. The chelant moieties are attached to the 6-position of a single pyranose in the cyclomaltoheptaose via a short diamine spacer chain. Characterization of these novel chelants has been achieved using NMR and MS techniques. The peculiar fluxional properties of the CD-EDTA molecules is also discussed.

Evaluation of the protective effects of reactive sulfide on the acute toxicity of silver to rainbow trout (Oncorhynchus mykiss)

Acute 96-h toxicity tests were performed with juvenile rainbow trout (Oncorhynchus mykiss) exposed to AgNO3 in either the absence or the presence of 100 nM reactive sulfide to evaluate the protective effect of aqueous sulfides against ionic Ag toxicity. The sulfide was presented in the form of zinc sulfide (ZnS) clusters under oxic conditions. Silver was lost from the water column during the course of the experiment, so mean measured Ag concentrations were used to generate all median lethal concentration (LC50) data. The system was complicated in that Ag2S precipitated because of the need for large amounts of Ag to obtain lethal effects in the presence of ZnS. Some of the losses of Ag could be explained by complexation with ZnS and formation of solid Ag2S. Other losses were probably the result of partial adsorption to exposure-chamber walls or to complexation with ligands or functional groups within organic material produced by the fish. The LC50 (95% confidence interval) values generated using measured concentrations for total Ag were 139 (122-162) nM in the absence of sulfide and 377 (340-455) nM in the presence of 100 nM sulfide. The LC50 values generated using measured concentrations from filtered (pore size, 0.45 microm) water samples were 122 (105-145) nM in the absence of sulfide and 225 (192-239) nM in the presence of 100 nM sulfide. These results suggest a stoichiometric protection of sulfides up to a 2:1 ratio of Ag:sulfide. Greater accumulation of Ag at the gills was measured in fish exposed to AgNO3 in the presence of sulfide.

The synthesis, NMR and X-ray analysis of tris(1-ethyl-2-isopropylimidazol-5-yl)phosphine gold (I)-2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranoside, a bifunctional auranofin analogue

Abstract A derivative of auranofin, a drug used in the treatment of rheumatoid arthritis, was synthesised and examined by NMR spectroscopy and X-ray crystallography. The derivative, which contains a trisimidazole phosphine, was designed to complex hard metals in addition to binding to the gold(I) centre.

Silver Nanoparticle Toxicity and Biocides: Need for Chemical Speciation

Nanoparticles were first characterized in the 1970s.Analytical development, especially atomic force micro-scopy, allowed descriptions of nanotubes, nanorods, etc. Thisnew knowledge also resulted in a renewed interest in theuse of silver (Ag) as a biocidal agent. Increased use ofthis precious metal has likely elevated its concentration inthe environment. More recently, regulators and nongovern-mental organizations have expressed interest and concernabout the toxicological role of nanoparticles, and especiallythat of Ag. But what is the complete composition of theseAg nanoparticles, and are they toxic? Unfortunately therehas been incomplete and incorrect use, description, andanalysis of nano-Ag substances. Descriptions and discussionoften confuse discrete aquo Ag

Chromium tricarbonyl complexes of methyl O-methylpodocarpate: differentiation of diastereomers by high field NMR spectroscopy

Abstract The reaction of Cr(CO)6 with methyl O-methylpodocarpate yields diastereomeric complexes in which the Cr(CO)3 fragment binds to either the α- or the β-face of the aromatic C ring of the diterpenoid. These isomers are separable using reverse phase high pressure liquid chromatography and their 1H and 13C NMR spectra have been recorded at 500 and 125 MHz, respectively. By use of the 1H1H COSY and 1H13C shift-correlated two-dimensional spectra all the protons and carbons in the free ligand and in both complexes have been unambiguously assigned. The α- and β-Cr(CO)3 complexes can be clearly differentiated on the basis of their 500 MHz 1H NMR spectra. Protons proximal to the metal are markedly deshielded if they lie in the negative region of the cone of anisotropy of the carbonyl ligands. The changes in conformation of the diterpene skeleton are detectable by NMR and correlate very well with the X-ray crystallographic data. Analogies are drawn between the structures of the podocarpate complexes and those of related estrogenic steroids.

Synthesis and 1H NMR spectrum of N6′,N9-octamethylenepurine cyclophane

Abstract N6′,N9-Octamethylenepurine cyclophane, 1 , has been synthesized by intramolecular cyclization. Its pmr spectrum shows all 16 methylene protons to be resolved, their chemical shifts ranging from −0.6 to +4.8 ppm.

Dissolved fraction of standard laboratory cladoceran food alters toxicity of waterborne silver to Ceriodaphnia dubia

The biotic ligand model (BLM) for the acute toxicity of cationic metals to aquatic organisms incorporates the toxicity-modifying effects of dissolved organic matter (DOM), but the default parameterization (i.e., assuming 10% of DOM is humic acid) does not differentiate DOM from different sources. We exposed a cladoceran (Ceriodaphnia dubia) to Ag in the presence of DOM from filtered YCT (standard yeast–Cerophyll®–trout chow food recommended by the U.S. Environmental Protection Agency [EPA] for cladocerans), from the Suwannee River (GA, USA; relatively little anthropogenic input), and from the Desjardins Canal in Hamilton (ON, Canada; receives treated municipal wastewater effluent). In all three treatments, the dissolved organic carbon (DOC) concentration was 2 mg/L (the concentration following addition of YCT slurry at the U.S. EPA–recommended volume ratio). The average 48-h median effects concentration (EC50) ratios for dissolved Ag in the presence and absence of DOM [i.e., (EC50 with DOM)/(EC50 without DOM)] were as follows: Suwannee River, 1.6; Desjardins Canal, 2.2; and YCT filtrate, 26.8. Therefore, YCT filtrate provided much more protection against Ag toxicity than that provided by DOM from the surface waters. The major spectral characteristic that differentiated YCT filtrate from the other two types of DOM was a strong tryptophan peak in the excitation–emission matrix for YCT. These results have important implications for interpreting Ag toxicity tests in which organisms are fed YCT, and they suggest BLM-calculated toxicity predictions might be improved by incorporating specific chemical constituents or surrogate indices of DOM. Another component of the protective effect against Ag toxicity, however, might be that the dissolved fraction of YCT served as an energy and/or nutrient source for C. dubia.

Photolysis of 3,4-diamidophenyl azides: evidence for azirine intermediates

Photolysis of the monocyclic aryl azide 3-acetamido-4-trifluoroacetamidophenyl azide, 1a, furnished a long-lived, trapable azirine intermediate, 7, which was in equilibrium with the initially formed nitrene and subsequently rearranged to the didehydroazepine intermediate 5; the data presented demonstrate that mono- and bi-cyclic aryl azides follow the same chemistry, with the substituents controlling the observed product distributions.

Selectivity of the multiplet selection via the double-quantum coherence (DOUBTFUL) experiment

Recently, Kaptein et al. (I, 2) have described an elegant way of selecting particular multiplets (usually an AX spin system) out of a crowded ‘H NMR spectrum by using double-quantum coherence. This note offers an analysis of the selectivity of this experiment. The experiment, which they have called DOUBTFUL (I), works as follows. The standard 90°-~/2-1800-~/2-900 (where 7/2 = 1/4J) pulse sequence is used to create double-quantum coherence, as in the INADEQUATE experiment (3). The double-quantum coherence is allowed to evolve for some time t, and is then “read” with a final 90” pulse. The phases of the final pulse and the receiver are cycled so that only the signals that arrived via the double-quantum coherence are accumulated. The experiment is then repeated for a series of values of t,, the double-quantum evolution time, and all of the acquisitions for all of the t,‘s added together. In these types of experiments, the two members of each doublet appear in the spectrum 180” out of phase with each other. Since we will want to distinguish between positive and negative doublets, it is useful to add a spin echo at the end of the sequence to get the doublets in phase (4). The success of this experiment in selecting a multiplet out of a crowded spectrum is based on the double-quantum evolution time tI . Several theoretical analyses of this pulse sequence acting on an AX system have been published (5, 6) and from them it can be shown that the signal detected in this experiment is proportional to the product sin(2rJ(r/2)). cos(2mt,) where v is the double-quantum frequency relative to the carrier. If VA and vx are the Larmor frequencies of the A and X spins and v. is the rf carrier frequency then