Electrochemistry of phosphaferrocenes: II. Electrochemical behavior of 3,3′,4,4′-tetramethyl-1,1′- diphosphaferrocene bonded to M(CO)5 (M = Cr,Mo, W) fragments forming heterometallic complexes with multiple redox centers

The redox behaviour of a series of heterometallic phosphaferrocenes (hereafter refered to as I, II and III) has been studied in propylene carbonate containing 0.1 M (C₂H₅)₄N⁺ ClO₄^? both mercury and platinum electrodes.Complex I (DPF) undergoes a reversible one-electron reduction. Complexes II and III exhibit the same reversible reduction step and one (species II) or two (species III) additional irreversible reduction step(s) generating [M(CO)₅]^? anions (M = Cr, Mo, W).Oxidation of the complexes II and III indicates that fragment I is involved in the first, easiest, oxidation step, whereas further step(s) involve the M(CO)₅ moieties. The redox characteristics of the complexes I, II, III, clearly indicate the absence of cooperation between metallic centers in II and III and the very effective barrier provided by the central iron in moiety I towards mutual effects of both phospholyl rings.     

Electrochemical behaviour and chemical oxidation study of the thio- and phosphido-bridge binuclear iron complexes

The electrochemical behaviour of thio and phosphido complexes of iron(I): Fe₂XY(CO)_6nL_n (X = Y = SR, PR₂ and X = SR, Y = PR₂, L = PR₃) has been studied on platinum and mercury electrodes, in organic solvent. These complexes are reduced in a two-electron irreversible process. A large difference is observed between their oxidation potentials on mercury and platinum electrodes; this is ascribed to the formation of a mercury complex in which mercury is inserted into the metalmetal bond. In oxidation on platinum electrodes, two mono-electronic waves are observed. The influece of the ligand basicity on the cathodic E_{$\text{1}\text{2}$} values is discussed. A parallel shift is observed between the E_{$\text{1}\text{2}$} and the IR ν(CO) of the totally symmetrical mode. Chemical oxidation of the complexes shows that the dications cannot be isolated, and leads to isolation of the following species: [FeP(CH₃)₂(CO)₃]₂AgNO₃, [FeSCH₃(CO)₂P(CH₃)₃]₂(NO₃)₂, {[FeSCH₃(CO)₂P(CH₃)₃]₂F} PF₆, where NO₃^? and F^? act as ligands.     

HETEROCYCLIC SULFUR COMPOUNDS LXXXIV: 3-Alkoxy-1,2-dithio-isocoumarins and 3-Alkylthio-1,2-dithio-isocoumarins

Abstract

Reaction of phosphorus pentasulfide with alkyl hydrogen homophthalates or dialkyl homophthalates gives a mixture of 3-alkoxy-1,2-dithio-isocoumarins and of 3-alkylthio-1,2-dithio-isocoumarins; some of these compounds resulting from a migration of an alkoxy or of an alkylthio group.

Oxidation of these dithio-isocoumarins into 2-thio-isocoumarins has been performed either by potassium permanganate or by benzonitrile N-oxide.     

Electrochemistry of platinum(II) coordination compounds II. Electroreduction of trimetallic dimetalliobis(isocyanide)platinum(II) complexes

Linear trimetallic MPPt^IIL₂M complexes (M = Cr(CO)₃(η-C₅H₅), Mo(CO)₃- (η-C₅H₅), W(CO)3(η-C₅-H₅), Mn(CO)₅, Fe(CO)₃NO, Co(CO)₄; L = t-BuNC, cyclo- C₀H₁₁ NC) are reduced on platinum and gold electrodes in non-aqueous medium. All these complexes undergo irreversible one electron reductions, which result in the rupture of one Ptmetal bond and the liberation of one M^? ion per mole reduced. Coupled ESR spectroscopy and coulometry show that a radical is generated during the reduction of the trimetallic complexes. The several ESR signals obtained for these paramagnetic Pt¹ species exhibit no hyperfine structure.The electrochemical behaviour of MPtL₂M complexes is compared with that of the following linear trimetallic complexes: MHgM and (MAuM)^?.     

Novel N-(4-Piperidinyl)benzamide antimalarials with mammalian protein farnesyltransferase inhibitory activity

Protein farnesyltransferase of Plasmodium falciparum is a potential target in the treatment of malaria for which increased drug resistance is observed. The design, synthesis and evaluation of a series of N-(4-piperidinyl)benzamides is reported. The most potent compounds showed in vitro activity against the parasite at submicromolar concentrations.     

Hopping conduction in epitaxial n-GaAs layers

The conductivity results of the phonon-assisted hopping process in n-type GaAs at low temperatures are presented. The conductivity variation with T, N_D and H are analyzed in terms of the percolation theory results.     

Stereochemical elucidation and total synthesis of dihydropacidamycin D, a semisynthetic pacidamycin.

Hydrogenation of the C(4') exocyclic olefin of the pacidamycins has been shown to produce a series of semisynthetic compounds, the dihydropacidamycins, with antimicrobial activity similar to that of the natural products. Elucidation of stereochemistry in the pacidamycins has been completed through a campaign of natural product degradation experiments in combination with the total synthesis of the lowest-molecular weight dihydropacidamycin, dihydropacidamycin D. The stereochemical identities of the tryptophan and two alanine residues contained in pacidamycin D have been shown to be of the natural (S) configuration, and the unique 3-methylamino-2-aminobutyric acid contained in this series of antibiotics has been shown to be of the (2S,3S) configuration. Finally, the stereochemistry obtained by hydrogenation of the C(4')-C(5') exocyclic olefin has been shown to be (R) at the C(4') nucleoside site.     

Evaporating and combusting droplet temperature measurements using two-color laser-induced fluorescence

 The paper presents a new technique based on laser-induced fluorescence, allowing droplet temperature measurement of evaporating and combusting droplets to be performed. The liquid spray is seeded with a low concentration of rhodamine B. The fluorescence, induced by the green line of an argon laser, is measured on two separated color bands. It is demonstrated that two color bands can be selected for their strong difference in the temperature sensitivity of the fluorescence quantum yield. The determination of the fluorescence ratio between the fluorescence intensity corresponding to each color band allows the tracer concentration and the droplet size dependences to be eliminated. The technique was applied on a monodisperse spray: the effect of a thermal impulse on the distribution of the droplet temperature is studied and, the temperature of combusting droplets is investigated. Received: 16 June 2000/Accepted: 10 November 2000     

Investigation of the metabolic biotransformation of substance P in liver microsomes by liquid chromatography quadrupole ion trap mass spectrometry

Substance P (SP) belongs to the tachykinin family and plays an essential role in pain transmission and in neurogenic inflammation. It can be detected in the central and peripheral nervous systems. The objectives of this study were to establish SP metabolic stability in liver microsomes in three species (rat, mouse and human), and identify and characterize SP metabolites by LC‐MS/MS. Endogenous peptide metabolism is not well documented and this is particularly true for neuropeptides participating in neurogenic inflammation. In vitro, T_1/2 results in pooled liver microsomes were 9.2, 5.6 and 18.6 min for rat, mouse and human liver microsomes, respectively. Five major SP metabolites were identified and quantified, including C‐terminal SP fragments SP_3–11, SP_5–11, SP_6–11, SP_8–11 as well as N‐terminal fragment SP_1–7. The results suggest significant differences between species in SP metabolite concentrations. Consequently, the metabolic profile of each species is distinctive and may have a significant impact on biomolecular mechanisms involved in specific pathophysiological changes. Copyright © 2012 John Wiley & Sons, Ltd.