Copper reagents: a new and efficient solution for the selective addition of metallated propargylic amines to aldehydes

[reaction: see text] Anti alpha-amino-homopropargylic alcohols are prepared by addition of metallated propargylic amines to aldehydes. Among the four organometallic (LI, Zn, Ti, Cu) derivatives used, the most effective are the copper reagents.     

Nonadiabatic alignment of asymmetric top molecules: rotational revivals

The rotational revival structure of asymmetric top molecules, following irradiation by an intense picosecond laser pulse, is explored theoretically and experimentally. Numerically we solve nonperturbatively for the rotational dynamics of a general asymmetric top subject to a linearly polarized intense pulse, and analyze the dependence of the dynamical alignment on the field and system parameters. Experimentally we use time-resolved photofragment imaging to measure the alignment of two molecules with different asymmetry, iodobenzene, and iodopentafluorobenzene. Our numerical results explain the experimental observations and generalize them to other molecules. The rotational revival structure of asymmetric tops differs qualitatively from the intensively studied linear top case. Potentially it provides valuable structural information about molecules.     

Investigating the interaction of crystal violet probe molecules on sodium dodecyl sulfate micelles with hyper-Rayleigh scattering

We report the use of the nonlinear optical technique of hyper-Rayleigh scattering to investigate the interaction of the cationic probe molecule crystal violet with micelles of sodium dodecyl sulfate. An absolute value of (847 +/- 80) x 10(-30) esu is measured at the fundamental wavelength of 870 nm for the molecular hyperpolarizability of crystal violet free in pure aqueous solutions. In aqueous solutions of sodium dodecyl sulfate, above and below the critical micelle concentration, the measured hyperpolarizability of crystal violet is weaker than in the solution free of sodium dodecyl sulfate. From the comparison with linear optical photoabsorption spectroscopy data, this difference is attributed to electrostatic interactions between the cationic crystal violet molecules and the negatively charged sodium dodecyl sulfate surfactant molecules present in excess. Polarization resolved hyper-Rayleigh scattering measurements are then performed to show that, below and above the critical micelle concentration, crystal violet molecules also undergo symmetry changes upon interaction with sodium dodecyl sulfate. Above the critical micelle concentration, the minimum fraction of micelles interacting with at least one CV molecule is estimated. For instance, for a crystal violet aqueous concentration of 150 microM, this fraction is larger than 7%.     

Proton-coupled electron transfer of flavodoxin immobilized on nanostructured tin dioxide electrodes: thermodynamics versus kinetics control of protein redox function

In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transfer in flavodoxin D. vulgaris Hildenborough (Fld). Poly-L-lysine is used to promote the binding of Fld to the nanocrystalline, mesoporous SnO(2) electrodes. Two reversible redox couples of the immobilized Fld are observed electrochemically and are assigned by spectroelectrochemistry to the quinone/semiquinone and semiquinone/hydroquinone couples of the protein's flavin mononucleotide (FMN) redox cofactor. Comparison with control data for free FMN indicates no contamination of the Fld data by dissociated FMN. The quinone/semiquinone and semiquinone/hydroquinone midpoint potentials (E(q/sq) and E(sq/hq)) at pH 7 were determined to be -340 and -585 mV vs Ag/AgCl, in good agreement with the literature. E(q/sq) exhibited a pH dependence of 51 mV/pH. The kinetics of these redox couples were studied using cyclic voltammetry, cyclic voltabsorptometry, and chronoabsorptometry. The semiquinone/quinone reoxidation is found to exhibit slow, potential-independent but pH-sensitive kinetics with a reoxidation rate constant varying from 1.56 s(-)(1) at pH 10 to 0.0074 s(-)(1) at pH 5. The slow kinetics are discussed in terms of a simple kinetics model and are assigned to the reoxidation process being rate limited by semiquinone deprotonation. It is proposed that this slow deprotonation step has the physiological benefit of preventing the undesirable loss of reducing equivalents which results from semiquinone oxidation to quinone.     

Comparative study of copper(II) interactions with monomeric ligands and synthetic or natural organic materials from potentiometric data

Potentiometric measurements were used to characterize the complexing properties of (a) a mixture of five monomeric ligands, (b) a synthetic humic-like substance and (c) fulvic acids extracted from soils, with copper (II). In order to compare the binding strengths involved, the same mathematical treatments of the data were used for all measurements. Calculations of the total ligand concentration with the Gran function give underestimated values for the multiligand mixture because of the known presence in the mixture of functional groups with pK^H ; 11 which > cannot be titrated and are revealed only by complexation phenomena. The acid-base properties of the humic substances are better described with a continuous model than with the descrete Henderson-Hasselbach model, because of the inability to distinguish properly between equivalent and independent types of functional groups. In the presence of copper (II), the formation functions show that a mixture of different kinds of complexes with different stability constants is probably formed. Extra protons released during the titration of the various copper (II) systems with alkali are attributed to untitrated functional groups with extremely low protonation constants in the case of the multiligand mixture, but ambiguity remains with the humic substances because their chemical structure is not known. Comparison of binding strengths can be made in terms of global conditional stability constants, by taking into account the three parameters, pH, concentrations of metal and of ligand. It is shown that the mechanisms of complexation are different for monomers and for polymers.     

Synthesis of (-)-ilimaquinone via a radical decarboxylation and quinone addition reaction

[reaction: see text] A stereoselective synthesis of (-)-ilimaquinone (4) is presented. The synthetic strategy is based on a novel radical decarboxylation and quinone addition methodology that produces quinone 7 from reaction of thiohydroxamic acid derivative 8 with benzoquinone (9). Final functionalization of 7 to ilimaquinone (4) is achieved by exploring the electronic effects of the residual thiopyridyl group.     

New fluorinated polysiloxanes containing an ester function in the spacer. I. Synthesis and characterization

Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH₂?CH? (CH₂)₈? COO? CH₂? CH₂? R_F (with R_F?C₆F₁₃, 2a and R_F?C₈F₁₇, 2b ) and C₈F₁₇? (CH₂)₁₀? COO? CH₂? CH?CH₂, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by ¹H- and ¹³C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc.     

“In situ” ESR and UV-visible spectroscopic studies of iron phthalocyanine films deposited on gold electrodes

The electrochemical behaviour of iron phthalocyanine (Fe^IIPc) films, supported on gold substrates, was studied in 3.5 M NaOH solution, using cyclic voltammetry and coupled “in situ” ESR and UV-visible spectroscopic techniques. Two types of electron transfer were observed in the potential range from −0.45 to −1.0 V vs. Hg/HgO. According to the “in situ” spectroscopy investigations, these two processes were assigned respectively to electron transfers involving first the ligand ring, and then the centre iron ion.