Application of matrix solid-phase dispersion to the determination of a new generation of fungicides in fruits and vegetables

A method based on matrix solid-phase dispersion (MSPD) and gas chromatography to determine eight fungicides in fruits and vegetables is described. Fungicide residues were identified and quantified using nitrogen-phosphorus detection and electron-capture detection connected in parallel and confirmed by mass spectrometric detection. The method required 0.5 g of sample, C18 bonded silica as dispersant sorbent, silica as clean-up sorbent and ethyl acetate as eluting solvent. Recoveries from spiked orange, apple, tomato, artichoke, carrot and courgette samples ranged from 62 to 102% and relative standard deviations were less than 15% in the concentration range 0.05-10 mg kg(-1). Detection and quantitation limits ranged 3-30 microg kg(-1) and 10-100 microg kg(-1), respectively, with linear calibration curves up to 10 mg kg(-1). The analytical characteristics of MSPD compared very favourably with the results of a classical multiresidue method, which uses ethyl acetate and anhydrous sodium sulphate for the extraction.     

Heteronuclear Nickel‐Iron Complexes and the Crystal Structure of [Fe2(CO)6(μ3‐S)2{Ni(dppe)}]

A series of heteronuclear nickel‐iron complexes [Fe₂(CO)₆(μ‐SH)(μ₃‐S){NiCl(PPh₃)₂}] ( 1 ), [Fe₂(CO)₆(μ‐SH)(μ₃‐S){NiCl(dppe)}] ( 2 ), [Fe₂(CO)₆(μ₃‐S)₂{Ni(PPh₃)₂}] ( 3 ), [Fe₂(CO)₆(μ₃‐S)₂{Ni(dppe)}] ( 4 ) and [Fe₂(CO)₆(μ‐SPh)(μ₃‐S){NiCl(dppe)}] ( 5 ) have been prepared. The structure of 4 has been determined by X‐ray crystallography. The central metal‐sulfur core of 4 has a trigonal bipyramidal shape with a NiFe₂ base plane with two axial sulfur atoms. Each iron atom is 5‐coordinate forming a distorted square pyramid; the nickel is square planar coordinated by two sulfur atoms and two phosphorus atoms.     

Réactions de germylènes avec divers oxirannes et le thiiranne. Mise en évidence de germanones et germathiones intermédiaires. Communication préliminaire

Complexed dialkylgermylenes R₂GeNR₃ or R₂GePy react with oxiranes or thiirane and lead to dialkylgermanone and germathione via germaoxetanes or germathiacyclobutane. The formation of germadioxolanes or germadithiolane finally observed arises from condensation of dialkylgermanone (or germathione) on oxiranes (or thiirane).     

An unprecedented highly efficient solvent-free oxidation of alkynes to α,β-acetylenic ketones with tert-butyl hydroperoxide catalyzed by water-soluble copper complex

The catalytic system composed of CuCl₂ and 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC) was found to be highly efficient for the selective α-oxidation of internal alkynes to the corresponding α,β-acetylenic ketones, with aqueous tert-butyl hydroperoxide under mild conditions. For the first time, full conversions of alkynes were reached with excellent selectivities, and propargylic tert-butylperoxy ethers were observed and suggested as the reaction intermediates. In the case of terminal alkynes, the oxidations are sluggish and low yields ranging from 32% to 40% were obtained.     

Tailoring the cavities of hydrogen-bonded amphidynamic crystals using weak contacts: towards faster molecular machines

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. The crystal structures of these rotors, determined by synchrotron radiation experiments at different temperatures, show the presence of such C–H⋯F–C contacts between extended carbazole stators featuring fluorinated phenyl rings and the 1,4-diazabicyclo[2.2.2]octane (DABCO) rotator. According to the ²H NMR results, using deuterated samples, and periodic density functional theory computations, the rotators experience fast angular displacements (preferentially 120° jumps) due to their low rotational activation energies (E_a = 0.8–2.0 kcal mol⁻¹). The higher rotational barrier for 1 (2.0 kcal mol⁻¹) is associated with a larger number of weak C–H⋯F–C contacts generated by the stators. This strategy offers the possibility to explore the correlation among weak intermolecular forces, cavity shape, and internal dynamics, which has strong implications in the design of future fine-tuned amphidynamic crystals.

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I.     

Short synthesis of the CDEF ring system of lactonamycin

[reaction: see text]. A synthesis of the CDEF fragment of lactonamycin is achieved in eight steps (six pots) from the known and readily available anhydride 4 via a Diels-Alder reaction between tricycle 13 and 2,3-dimethylbenzoquinone.     

MP2 study of substituent effects of 2-substituted alkyl ethyl methylcarbamates in homogeneous, unimolecular gas phase elimination reaction

Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a C_β–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log k_rel is plotted against the theoretical log k_rel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism.     

Bis(2,4,6-trifluorophenyl) derivatives of palladium(II)

Summary The organopalladium(II) complexes: Pd(2,4,6-C₆F₃H₂)₂L₂ [L=triphenylphosphine(PPh₃), methyldiphenylphosphine(PPh₂Me), dimethylphenylphosphine-(PPhMe₂) or pyridine(py); L₂=1,2-bis(diphenylphosphino)ethane(dpe), 2,2-bipyridine(bipy), 1, 10-phenanthroline(phen) or ethylenediamine(en)] have been prepared by addition of the appropriate compound to the THF-dioxane solution resulting from the arylation of potassium tetrachloropalladate(II) with (2,4,6-C₆F₃H₂)MgBr. The i.r. data suggest that the py and PPhMe₂ compounds are thecis-isomers, whereas the PPh₃ and PPh₂Me compounds have thetrans configuration.¹H- and¹⁹F-n.m.r. data for the compounds are reported.     

Thermal decomposition of some imidazole and N-methyl substituted imidazole complexes of palladium(II)

We describe in this paper the thermal decomposition in air of several complexes of palladium(II) chloride with imidazole and N-methylimidazole. Although the final process of the decomposition gives (PdCl₂)_n which then decomposes to pa ladium which oxidizes to PdO, there are interesting differences in the initial decomposition path. The reasons for these differences appear to be related to the trans-effect and to the presence in the imidazole complexes of hydrogen bonds which break down at temperatures of around 220.

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Zusammenfassung In diesem Beitrag wird die thermische Zersetzung verschiedener Komplexe des Palladium(II)chlorids mit Imidazol und N-Methylimidazol in Luft beschrieben. Obwohl der Endvorgang der Zersetzung (PdCl₂)_n ergibt, welches dann zu Palladium zersetzt und zu PdO oxidiert wird, bestehen interessante Unterschiede im Anfangsschritt der Zersetzung. Die Ursachen dieser Unterschiede scheinen mit dem Trans-Effekt und der Anwesenheit von Wasserstoffbindungen in den Imidazolkomplexen verbunden zu sein, welche bei Temperaturen um 220 zerstört werden.

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Résumé La décomposition thermique dans l'air de plusieurs complexes du chlorure de palladium(II) avec l'imidazole et le méthyl-4-imidazole est décrite. Bien que l'étape finale de la décomposition donne (PdCl₂)_n qui se décompose ensuite en palladium qui s'oxyde en PdO, des différences intéressantes apparaissent dans les étapes initiales de la décomposition. Les causes de ces différences sont en rapport avec l'effet trans et la présence, dans les complexes avec l'imidazole, de liaisons hydrogÊne qui se rompent vers 220.

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(II) -. (PdCl₂)_n, , PdO, . , - , 220.

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One of us (M.C. Navarro Ranninger) would like to thank the D.G.E.S.I. for a grant that allowed her to work on this research.     

Theoretical analysis of the porphyrin-porphyrin exciton interaction in circular dichroism spectra of dimeric tetraarylporphyrins

Chiral bis-porphyrins are currently the subject of intense interest as chiral receptors and as probes in the determination of structure and stereochemistry. To provide an improved framework for interpreting the circular dichroism (CD) spectra of bis-porphyrins, we have calculated the CD spectra of chiral bis-porphyrins from three classes: I, where porphyrins can adopt a relatively wide range of orientations relative to each other; II, porphyrins have a fixed relative orientation; III, porphyrins undergo pi-stacking. The calculations primarily utilized the classical polarizability theory of DeVoe, but were supplemented by the quantum mechanical matrix method. Class I was represented by three isomers of the diester of 5alpha-cholestane-3,17-diol with 5-(4'-carboxyphenyl)-10,15,20-triphenylporphin (2-alphabeta, 2-betaalpha, 2-betabeta). Careful analysis of the torsional degrees of freedom led to two to four minimum-energy conformers for each isomer, in each of which the phenyl-porphyrin bonds had torsional angles near 90 degrees. Libration about these bonds is relatively unrestricted over a range of +/-45 degrees. CD spectra in the Soret region were calculated as Boltzmann-weighted averages over the low-energy conformers for each isomer. Three models were used: the effective transition moment model, in which only one of the degenerate Soret components is considered, along the 5-15 direction; the circular oscillator model, in which both Soret components are given equal weight; and the hybrid model, in which the 10-20 oscillator is given half the weight of the 5-15 oscillator, to mimic the effect of extensive librational averaging about the 5-15 direction. All three models predict Soret exciton couplets with signs in agreement with experiment. Quantitatively, the best results are given by the hybrid and circular oscillator models. These results validate the widely used effective transition moment model for qualitative assignments of bis-porphyrin chirality and thus permit application of the exciton chirality model. However, for quantitative studies, the circular oscillator or hybrid models should be used. The simplified effective transition moment and hybrid models are justified by the librational averaging in the class I bis-porphyrins and should only be used with such systems. Two class II bis-porphyrins were also studied by DeVoe method calculations in the circular oscillator model, which yielded good agreement with experiment. Class III bis-porphyrins were represented by 2-alphaalpha, for which the calculations gave qualitative agreement. However, limitations in the conformational analysis with the close contacts and dynamic effects in these pi-stacked systems preclude quantitative results.