Comparison of methods for the gas-chromatographic determination of PCB congeners and chlorinated pesticides in marine reference materials

Summary Three gas-chromatographic (GC) columns with different selectivity (DB-5, DB-1701, and C-18) and two different GC detectors (electron-capture and mass-spectrometric) were used to analyze three Standard Reference Materials (SRMs), which are available from the National Institute of Standards and Technology (NIST), and two Certified Reference Materials (CRMs), which are available from the Community Bureau of Reference (BCR), for polychlorinated biphenyl (PCB) congeners and chlorinated pesticides. The materials analyzed were: SRM 1588, Organics in Cod Liver Oil; SRM 1941, Organics in Marine Sediment; SRM 1974, Organics in Mussel Tissue (Mytilus edulis); CRM 349, Chlorobiphenyls in Cod Liver Oil; and CRM 350, Chlorobiphenyls in Mackerel Oil. Results from these different methods are compared, and concentrations for additional PCB congeners and chlorinated pesticides in these reference materials, which have not been measured previously, are reported.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

European intercomparison study for the determination of fumonisins in maize

Fumonisins are mycotoxins occurring largely in maize and maize products, which cause animal diseases, such as equine leukoencephalomalacia and porcine pulmonary edema, and may also induce liver cancer on experimental rats. The European Commission Standards, Measurements and Testing (SMT, formerly BCR) Programme, has sponsored a project to improve analytical methodologies for the determination of the two major fumonisins (fumonisin B1 and fumonisin B2) in maize materials. The project involved the following steps: i) the preparation of a blank and a maize material contaminated with fumonisins Bl and B2; ii) a preliminary study of the -irradiation conditions for sterilization; iii) homogeneity and stability studies of the maize materials; iv) an intercomparison study for fumonisins analysis in the above materials with the involvement of 24 European laboratories, most of which have national or international responsibilities for foodstuff and/or feedstuff quality control. Results of the intercomparison study are presented together with the homogeneity and stability data relevant to the maize materials.     

Gas-phase reactivity of rare earth cations with phenol: Competitive activation of C-O, O-H, and C-H bonds

The gas-phase reactions of Sc⁺, Y⁺, and Ln⁺ (Ln=La-Lu, except Pm) ions with phenol were studied by Fourier transform ion cyclotron resonance mass spectrometry. All the ions except Yb⁺ were observed to react with the organic substrate, activating O-H, C-O, and/or C-H bonds, with formation of MO⁺, MOH⁺, and/or MOC₆H ₄ ⁺ ions as primary products. The product distributions and the reaction efficiencies obtained showed the existence of important differences in the relative reactivity of the rare earth metal cations, which are discussed in terms of factors like the electron configurations of the metal ions, their oxophilicity, and the second ionization energies of the metals. The primary product ions participated in subsequent reactions, yielding species such as M(OH)(OC₆H₅)⁺, which lead mainly to M(OC₆H₅)₂(HOC₆H₅) _n ⁺ ions, where n=0–2. Formation of M(OC₆H₅)(HOC₆H₅) _n ⁺ species was also observed in the case of the metals that have high stabilities of the formal oxidation state 2+, Sm and Eu.     

Novel Trinor-eremophilanes (Dendryphiellin B,C, and D), Eremophilanes (Dendryphiellin E,F, and G), and Branched C9-Carboxylic Acids (Dendryphiellic Acid A and B) from the Marine Deuteromycete Dendryphiella salina (SUTHERLAND) PUGHet NICOT

Further investigation of global extracts from cultures of the marine deuteromycete Dendryphiella salina leads to the isolation of three novel trinor-eremophilanes esterified by branched C₉-carboxylic acids, dendryphiellin B (= (+)-(1R*,2S*,7R*,8aR*)-1,2,6,7,8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*, 2E, 4E)-6-hydroxy-6-methylocta-2,4-dienoate; (+)- 2 ), dendryphiellin C (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7,8,8a-hexa-hydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6S, 2E, 4E)-6-methylocta-2,4-dienoate; (+)- 3 )), and dendryphiellin D (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7(8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*,2E,4E)-6-(hydroxymethyl)octa-2,4-dienoate; (+)- 4 ). An intact eremophilane, dendryphiellin E ( 5 ), and its ethanolysis product dendryphiellin F whose absolute configuration is represented by structural formula (+)- 6 are also isolated from the above extracts. Dendryphiellin E exists as an open form 5a in equilibrium with a closed form 5b . A similar equilibrium exists between the open form 8a and the closed form 8b of a non-esterified eremophilane, dendryphiellin G ( 8 ), which is isolated too from the above extracts and proves structurally related to the cyclic portion of 5 . Finally, the free, branched C₉-carboxylic acids dendryphiellic acid A ((+)- 9 ) and B ((+)- 10 ) which correspond to side chains of the above esterified terpenes are also isolated from the above extracts.     

Determining pirimiphos-methyl in durum wheat samples using an acetylcholinesterase inhibition assay

An electrochemical assay used for detecting acetylcholinesterase (AChE) inhibitors has been optimised to detect pirimiphos-methyl in durum wheat. Pirimiphos-methyl is a phosphothionate insecticide and so it needs to be transformed into the corresponding oxo form to act as an effective AChE inhibitor. The inhibition assay was based on the electrochemical detection of the product of AChE, choline, via choline oxidase biosensors obtained with Prussian-Blue modified screen printed electrodes. The procedure for the oxidation of pirimiphos methyl via N-bromosuccinimide (NBS) and AChE inhibition was optimised for reagent concentrations and inhibition time in a buffer solution. A calibration of the pirimiphos-methyl (25–1,000 ng/ml) was obtained in the buffer. The intra-electrode CV ranged between 1.6 and 15.0, whereas the inter-electrode CV ranged between 4.6 and 16.0. The detection limit (LOD) was 38 ng/ml, and the I_50% was 360 ng/ml. The assay conditions were then re-optimised to work with durum wheat extracts, and the calibrations were obtained under different experimental conditions, such as sample pretreatment (milled or whole grains) and extract concentration. The calibrations were slightly affected by the sample matrix, resulting in an increased LOD (65–133 ng/ml) and I_50% (640–1,650 ng/ml). The LOD found for the sample, determined under optimal conditions, was 3 mg/kg. Spiked samples were prepared at the EU regulated level (5 mg/kg) and analysed with the optimised protocol, resulting in an average recovery of 70.3%.     

A recipe for the computation of the free energy barrier and the lowest free energy path of concerted reactions

The recently introduced hills method (Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 12562) is a powerful tool to compute the multidimensional free energy surface of intrinsically concerted reactions. We have extended this method by focusing our attention on localizing the lowest free energy path that connects the stable reactant and product states. This path represents the most probable reaction mechanism, similar to the zero temperature intrinsic reaction coordinate, but also includes finite temperature effects. The transformation of the multidimensional problem to a one-dimensional reaction coordinate allows for accurate convergence of the free energy profile along the lowest free energy path using standard free energy methods. Here we apply the hills method, our lowest free energy path search algorithm, and umbrella sampling to the prototype S(N)2 reaction. The hills method replaces the in many cases difficult problem of finding a good reaction coordinate with choosing relatively simple collective variables, such as the bond lengths of the broken and formed chemical bonds. The second part of the paper presents a guide to using the hills method, in which we test and fine-tune the method for optimal accuracy and efficiency using the umbrella sampling results as a reference.     

Charge and spin correlations of a one-dimensional electron gas on the continuum.

We present a variational Monte Carlo study of a model one-dimensional electron gas on the continuum, with long-range interaction (1/r decay). At low density, the reduced dimensionality brings about pseudonodes of the many-body wavefunction, yielding nonergodic behavior of naive Monte Carlo sampling, which affects the evaluation of pair correlations and the related structure factors. The problem is, however, easily solved, and we carefully analyzed the structure factors obtained from an optimal trial function, finding good agreement with the exact predictions for a Luttinger-like Hamiltonian with an interaction similar to the one used in the present study.     

The Active Centres of Agelastatin A,a Strongly Cytotoxic Alkaloid of the Coral Sea Axinellid Sponge Agelas dendromorpha,as Determined by Comparative Bioassays with Semisynthetic Derivatives

Agelastatin A ( 1 ), an unusual alkaloid of the axinellid sponge Agelas dendromorpha from the Coral Sea, can be selectively acetylated (→ 7 ) or methylated at OH? C(8a) (→ 4 ), peracetylated (→ 8 ) or permethylated at OH? C(8a), NH(5), and NH(6) (→ 5 ), or, finally, subjected to C(9)? C(8a) (→ 14 ) or C(5b)? C(8a) β-elimination (→ 11–13 ), in a regiospecific manner or not, depending on the reaction conditions. Under acidic conditions, compound 12 adds H₂O or MeOH, regioselectively though not endo/exo stereoselectively, giving transoid/cisoid mixtures 1/18 or 4/19 , respectively. Similarly 11 or 13 add MeOH to give mixtures (?)- 2/20 or 15/16 , respectively. Compound 13 also adds AcOH giving mixture 8/17 . The intermediate cisoid form obtained on treatment of 21 with H₃O⁺ undergoes N(5)? N(6) bridging affording pentacyclic 22 which constitutes a proof for the cisoid configuration. From conformational studies, rules are devised that allow assigning the configuration of these compounds from NMR data. In vitro comparative cytotoxicity assays of these compounds show that for high cytotoxic activity, such as of 1 in vivo, unsubstituted OH? C(8a), H? N(5), H? N(6) moieties are needed in the natural B/D transoid configuration.     

Intercomparison of suspended particles sampling methodologies

Sampling and sample preparation/processing are known to carry large, but typically unknown uncertainty contribution to the final analytical data and there is a lack of qualitative and quantitative data on the comparability of results achieved by the different sampling methods. To this end, an intercomparison programme was founded by the European Commission, in which different institutions participated using their own ”in-situ” methods (”ANPA”, ”EDF” and ”MIDIYA”) for collection of water and suspended material in freshwater bodies. The main criterion for this intercomparison was the agreement among the ¹³⁷Cs activity concentrations in the dissolved phase (Bq l^–1), those associated with the suspended particles (Bq g^–1) and the concentrations of total suspended material (TSM) in the water body (mg l^–1). The results show that the sampling systems provide TSM concentration results with low accuracy; on the contrary, they are recommended for the determination of ¹³⁷Cs activity concentration in the dissolved phase. Concerning the determination of radiocaesium activity concentration in the suspended particles, the ”EDF” system provides the more reliable results. Received: 10 December 2001 Accepted: 4 March 2002     

Caulerpenyne-Amine Reacting System as a Model for in vivo Interactions of Ecotoxicologically Relevant Sesquiterpenoids of the mediterranean-adapted tropical green seaweed caulerpa taxifolia

Caulerpenyne ( 1 ), the most abundant of the ecotoxicologically relevant sesquiterpenoids of the Mediterranean-adapted tropical green seaweed Caulerpa taxifolia, was found to react with Et₃N or pyridine in MeOH by initial deprotection of C(1)HO to give oxytoxin 1 ( 2a ), previously isolated from the sacoglossan mollusc Oxynoe olivacea. With BuNH₂, without any precaution to exclude light, 1 gave the series of racemic 3 and 4 , and achiral (4E,6E)- 5 , (4E,6Z)- 5 , (4Z,6E)- 5 , and (4Z,6Z)- 5 pyrrole compounds, corresponding to formal C(4) substitution, 4,5-β-elimination, and (E/Z)-isomerization at the C(4)?C(5) and C(6)?C(7) bonds. Changing to CDCl₃ as solvent in the dark, 1 gave cleanly, via 2a as an intermediate, 3 and (4E,6E)- 5 . The latter proved to be prone to (E/Z)-photoisomerization. Under standard acetylation conditions, 3 gave (4E,6E)- 5 via acetamide 7 as an intermediate. Particular notice is warranted by selective deprotection of 1 at C(1), mimicking enzyme reactions, and unprecedented formation of pyrrole compounds from freely-rotating, protected 1,4-dialdehyde systems.