Strong ion-exchange centrifugal partition chromatography as an efficient method for the large-scale purification of glucosinolates

The glucosinolates sinalbin and glucoraphanin were purified by strong ion-exchange displacement centrifugal partition chromatography (SIXCPC). The optimized conditions involved the biphasic solvent system ethyl acetate/n-butanol/water (3:2:5, v/v), the lipophilic anion-exchanger Aliquat 336 (trioctylmethylammonium chloride, 160 and 408 mM) and a sodium iodide solution (80 and 272 mM) as displacer. Amounts as high as 2.4 g of sinalbin and 2.6g of glucoraphanin were obtained in one step in 2.5 and 3.5h respectively, starting from 12 and 25 g of mustard and broccoli seed aqueous extracts, using a laboratory scale CPC column (200 mL inner volume).     

Catalytic Nitrene Transfer by an FeIV-Imido Complex Generated by a Comproportionation Process

Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from Fe^II and Fe^III precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an Fe^IV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the Fe^II precursor was expected by a two-electron oxidative addition, its formation from an Fe^III precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the Fe^III precursor, an Fe^III tosyliodinane adduct was formed and decomposed into an Fe^V tosylimido species which generated the catalytically active Fe^IV tosylimide through a comproportionation process with the Fe^III precursor.     

Snake Venom Components: Tools and Cures to Target Cardiovascular Diseases

Cardiovascular diseases (CVDs) are considered as a major cause of death worldwide. Therefore, identifying and developing therapeutic strategies to treat and reduce the prevalence of CVDs is a major medical challenge. Several drugs used for the treatment of CVDs, such as captopril, emerged from natural products, namely snake venoms. These venoms are complex mixtures of bioactive molecules, which, among other physiological networks, target the cardiovascular system, leading to them being considered in the development and design of new drugs. In this review, we describe some snake venom molecules targeting the cardiovascular system such as phospholipase A2 (PLA2), natriuretic peptides (NPs), bradykinin-potentiating peptides (BPPs), cysteine-rich secretory proteins (CRISPs), disintegrins, fibrinolytic enzymes, and three-finger toxins (3FTXs). In addition, their molecular targets, and mechanisms of action—vasorelaxation, inhibition of platelet aggregation, cardioprotective activities—are discussed. The dissection of their biological effects at the molecular scale give insights for the development of future snake venom-derived drugs.     

Spin State Tunes Oxygen Atom Transfer towards FeIVO Formation in FeII Complexes

Oxoiron(IV) complexes bearing tetradentate ligands have been extensively studied as models for the active oxidants in non-heme iron-dependent enzymes. These species are commonly generated by oxidation of their ferrous precursors. The mechanisms of these reactions have seldom been investigated. In this work, the reaction kinetics of complexes [Fe^II(CH₃CN)₂L](SbF₆)₂ ( [1](SbF₆)₂ and [2](SbF₆)₂ ) and [Fe^II(CF₃SO₃)₂L] ( [1](OTf)₂ and [2](OTf)₂ ( 1 , L=^Me,HPytacn; 2 , L=^nP,HPytacn; ^R,R′Pytacn=1-[(6-R′-2-pyridyl)methyl]-4,7- di-R-1,4,7-triazacyclononane) with Bu₄NIO₄ to form the corresponding [Fe^IV(O)(CH₃CN)L]²⁺ ( 3 , L=^Me,HPytacn; 4 , L=^nP,HPytacn) species was studied in acetonitrile/acetone at low temperatures. The reactions occur in a single kinetic step with activation parameters independent of the nature of the anion and similar to those obtained for the substitution reaction with Cl⁻ as entering ligand, which indicates that formation of [Fe^IV(O)(CH₃CN)L]²⁺ is kinetically controlled by substitution in the starting complex to form [Fe^II(IO₄)(CH₃CN)L]⁺ intermediates that are converted rapidly to oxo complexes 3 and 4 . The kinetics of the reaction is strongly dependent on the spin state of the starting complex. A detailed analysis of the magnetic susceptibility and kinetic data for the triflate complexes reveals that the experimental values of the activation parameters for both complexes are the result of partial compensation of the contributions from the thermodynamic parameters for the spin-crossover equilibrium and the activation parameters for substitution. The observation of these opposite and compensating effects by modifying the steric hindrance at the ligand illustrates so far unconsidered factors governing the mechanism of oxygen atom transfer leading to high-valent iron oxo species.     

Analysis of multiple pesticide residues in tobacco using pressurized liquid extraction, automated solid-phase extraction clean-up and gas chromatography-tandem mass spectrometry

A new method was developed for the analysis of pesticide residues in tobacco. The objective was to significantly increase the number of samples that can be processed by the laboratory and to enable the extension of the current coverage to additional pesticides. A new analytical approach was therefore defined based on two main axes, the automation of the sample preparation and the selectivity of the analyte detection using tandem mass spectrometry. This latter aspect reduces the stringency of the requirements placed on the clean-up of the extracts and on the chromatographic resolution when less selective detectors are used. The extraction of the analytes from the matrix is performed using the pressurized liquid extraction technique. Tobacco samples are extracted at elevated temperature and pressure (100 C and 100 atm; 1 atm = 101,325 Pa) using acetone as an extraction solvent. The resulting extract is then concentrated using a Vortex evaporator. Three different solid-phase extraction (SPE) procedures, adjusted to the chemical properties of the different active ingredients to be measured, are applied to the concentrated extract, thus leading to three extract fractions. The first fraction contains such main classes of active ingredients as organohalogenated and 2,6-dinitroaniline compounds while the second one collects the organophosphorus and acylalanines residues; these two fractions are analyzed by capillary gas chromatography coupled to tandem mass spectrometry using negative chemical ionization and electron impact ionization in the positive mode, respectively. The third extract fraction gathers the N-methylcarbamates residues which are analyzed by HPLC with post-column derivatization and fluorescence detection. The different sample preparation stages from extraction to SPE clean-up have been automated through the use of recent analytical technologies. In combination with the analysis by tandem mass spectrometry, this provided a potential for a high sample throughput.     

The pyridyl-tag strategy applied to the hydrocarbon/perfluorocarbon phase-switching of a porphyrin and a fullerene

A new hydrocarbon/perfluorocarbon phase-switching strategy based on coordination of pyridyl-tagged molecules to a highly fluorinated dicopper-carboxylate complex possessing two accessible axial coordination sites is described. When a chloroform solution of the tetrapyridyl-substituted porphyrin 3 (0.1 mM, 2 mL) is layered on a perfluorodecalin solution of 2 (3.25 mM, 1.5 mL), complete extraction of the porphyrin into the fluorous phase is observed after 30 min of stirring. Quantitative release of both the porphyrin and 2 is achieved simply by adding excess THF to the biphasic system, the THF acting as a pyridine competing ligand. The recovered perfluorocarbon solution containing 2 can be reused for another complexation with the same efficiency. The scope of this approach is emphasized by the phase-switching of a dipyridyl-substituted fullerene, another example of a molecule for which solubilization in perfluorocarbons is very challenging.     

Transition-metal-templated synthesis of rotaxanes and catenanes: From small molecules to polymers

This article provides an overview of the fundamental principles of the synthesis of metallocatenanes and metallorotaxanes. It also describes the synthesis and properties of electronic conducting polymers—polypyrrole and polythiophene—built around metallocatenanes and metallorotaxanes. The particular properties of this new class of polymers, including the possibility of transmetallation reactions being performed with them and the observation of electronic coupling between the metal centers and the conducting matrix, are discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3470–3477, 2003     

Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors

This paper is a review of the authors' publications concerning the development of biosensors based on enzyme field-effect transistors (ENFETs) for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and ion-selective field-effect transistors (ISFETs). Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools in medicine, biotechnology, environmental control, agriculture and the food industry.The biosensors based on ENFETs and direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, creatinine, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of the analytical characteristics of such biosensors may be achieved by using a differential mode of measurement, working solutions with different buffer concentrations and specific agents, negatively or positively charged additional membranes, or genetically modified enzymes. These approaches allow one to decrease the effect of the buffer capacity influence on the sensor response in an aim to increase the sensitivity of the biosensors and to extend their dynamic ranges.Biosensors for the determination of concentrations of different toxic substances (organophosphorous pesticides, heavy metal ions, hypochlorite, glycoalkaloids, etc.) were designed on the basis of reversible and/or irreversible enzyme inhibition effect(s). The conception of an enzymatic multibiosensor for the determination of different toxic substances based on the enzyme inhibition effect is also described.We will discuss the respective advantages and disadvantages of biosensors based on the ENFETs developed and also demonstrate their practical application.     

Face Selectivity of the Diels-Alder Additions of Sulfur-Substituted Dienes and Tetraenes Grafted onto 7-Oxabicyclo[2.2.1]heptanes

Stereoselective synthesis of 2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]-7-oxabicyclo[2.2.1]-heptane ( 16 ), 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethoxy-2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]anthracene ( 18 ), and 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethyoxy-2-methylidene-3-[(Z)-(phenylsulfenyl)-methylidene]anthracene ( 19 ) are presented. The Diels-Alder additions of these S-substituted dienes and those of 2,5-dimethylidene-3,6-bis{[(Z)-(2-nitrophenyl)sulfenyl]methylidene}-7-oxabicyclo[2.2.1]heptane ( 17 ) have been found to be face selective and ‘ortho’ regiospecific. The face selectivity depends on the nature of the dienophile. It is exo-face selective with bulky dienophiles such as ethylene-tetracarbonitrile (TCNE) and 2-nitro-1-butene and endo-face selective with methyl vinyl ketone, methyl acrylate, and 3-butyn-2-one. In the presence of a Lewis acid, the face selectivity of the Diels-Alder reaction can be reversed. The addition of the first equivalent of a dienophile to tetraene 17 is at least 100 times faster than the addition of the second equivalent of the same dienophile to the corresponding mono-adduct. The X-ray structure of the crystalline bis-adduct 43 , a 7-oxabicyclo[2.2.1]hepta-2,5-diene system annellated to two cyclohexene rings, resulting from the successive additions of methyl acrylate and methyl vinyl ketone to tetraene 17 is presented. Only one of the two endocyclic double bonds of the 7-oxabicyclo[2.2.1]hepta-2,5-diene deviates from planarity, the substituents bending towards the endo face by 5.7°.     

A Simple Procedure for the Preparation of Chiral ‘Tris(hydroxymethyl)methane’ Derivatives

The aldol adducts 1a – 13a of R,R-2(tertbutyl)-6-methyl-1,3-dioxan-4-one (from 3-hydroxybutanoic acid) to aldehydes, single diastereoisomers obtained as described previously, are acetylated or benzoylated to the corresponding esters 1b – 5b and 6c – 13c , respectively, which in turn are reduced with LiAlH₄ to the title compounds 14 – 24 . The enantiomerically pure triols thus available may be useful as chiral building blocks, as auxiliaries for enantioselective reactions, and as center pieces for chiral dendrimers.