Combining planar and central chirality in ferrocene thiophosphine-sulfoxides

Novel chiral ferrocenylthiophosphine–sulfoxide and phosphine–sulfoxide derivatives possessing planar chirality for the ferrocene moiety and central chirality at the sulfur atom have been synthesized. These ligands can be obtained as pure diastereoisomers in both racemic and enantiomerically pure forms. Complete characterization by XRD analysis has allowed the assignment of the absolute configuration in each case. Preliminary coordination studies of the phosphine–sulfoxide ligands on platinum are also reported. These show chelating complexation by the phosphorous and sulfur atoms.     

Organometallic mediated radical polymerization of vinyl acetate with Fe(acac)2

The radical polymerization of vinyl acetate (VAc) is moderated by iron(II) acetylacetonate (Fe(acac)₂) by the organometallic route (OMRP), as well as by degenerative transfer polymerization (DTP) when in the presence of excess radicals, through the formation of thermally labile organometallic Fe^III dormant species. The poly(vinyl acetate) (PVAc)‐Fe^III(acac)₂ dormant species has been isolated in the form of an oligomer and characterized by ¹H NMR, EPR, and IR methods, and then used as a single‐component initiator for the OMRP of VAc. The degree of polymerization of this isolated oligomeric species demonstrates the limited ability of Fe(acac)₂, relative to the Co(acac)₂ congener, to rapidly trap the growing PVAc radical chain. Control under OMRP conditions is improved by the presence of Lewis bases, especially PMe₂Ph. On the other hand, iron(II) phthalocyanine inhibits the radical polymerization of VAc completely. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3494–3504     

Fluid-like behavior of a one-dimensional granular gas

We study the properties of a one-dimensional (1D) granular gas consisting of N hard rods on a line of length L (with periodic boundary conditions). The particles collide inelastically and are fluidized by a heat bath at temperature Tb and viscosity gamma. The analysis is supported by molecular dynamics simulations. The average properties of the system are first discussed, focusing on the relations between granular temperature Tg=mv2, kinetic pressure, and density rho=N/L. Thereafter, we consider the fluctuations around the average behavior obtaining a slightly non-Gaussian behavior of the velocity distributions and a spatially correlated velocity field; the density field displays clustering: this is reflected in the structure factor which has a peak in the k approximately 0 region suggesting an analogy between inelastic hard core interactions and an effective attractive potential. Finally, we study the transport properties, showing the typical subdiffusive behavior of 1D stochastically driven systems, i.e., approximately Dt(1/2), where D for the inelastic fluid is larger than the elastic case. This is directly related to the peak of the structure factor at small wave vectors.     

Aggregation of perfluoroctanoate salts studied by 19F NMR and DFT calculations: counterion complexation, poly(ethylene glycol) addition, and conformational effects

The aggregation of perfluoroctanoate salts in H(2)O is studied by (19)F NMR on solutions of LiPFO, NaPFO, and CsPFO, without and with the addition of two poly(ethylene glycol) (PEG) oligomers of molecular weight 1500 and 3400 Da, respectively, and with the addition of suitable crown ethers. The (19)F chemical shift (cs) trends are monitored, at 25 °C, in a concentration range including the critical micellar concentration (cmc) or, in the presence of PEG, the critical aggregation concentration (cac). The cac values in the samples with PEG are lower than the cmc values of the corresponding samples without PEG; moreover, the (19)F cs trends above the cac and above the polymer saturation concentration reveal and help to explain some peculiarities of the aggregation process of PEG on PFO micelles, which, in the first step, seems to occur while the surfactant concentration in water is still increasing. Also in LiPFO/H(2)O or NaPFO/H(2)O solutions containing 12-crown-4 or 15-crown-5 ethers, suitable to complex Li(+) or Na(+) ions, respectively, the cmc decreases. On the other hand, the micellization process in the presence of crown ethers does not show other peculiarities. The prevailing conformations of the PFO chain are discussed on the basis of quantum-mechanical calculations. The theoretical chemical shifts were computed at the DFT level of theory, taking into account the effects of the environment by means of the IEF-PCM method. The helical structure is the most stable one, but anti conformations are easily accessible, in both the aqueous and fluorinated environment. The comparison between computed and experimental chemical shifts indicates that anti conformations are more important in the micelles than in water and in CsPFO micelles than in LiPFO or NaPFO ones.     

Assessment of the ageing of triterpenoid paint varnishes using fluorescence,Raman and FTIR spectroscopy

The assessment of the influence of natural and artificial ageing on the spectrofluorescence of triterpenoid varnishes dammar and mastic is the focus of this work. Both Fourier transform infrared (FTIR) microscopy using attenuated total reflectance and Raman spectroscopy have been employed for complementary molecular analysis of samples. Synchronous fluorescence spectroscopy, excitation emission spectroscopy, and statistical analysis of data have been used to monitor changes in the optical properties of varnish samples. Assessment of naturally and artificially aged samples using excitation emission spectroscopy suggests that extensive exposure to visible light does not lead to easily appreciable differences in the fluorescence of mastic and dammar; cluster analysis has been used to assess changes, which occur with artificial ageing under visible light, indicating that differences in the fluorescence spectra of aged triterpenoids may be insufficient for their discrimination. The results highlight significant differences between the initial fluorescence of films of dammar and mastic and the fluorescence, which develops with ageing and oxidation, and specific markers, which change with ageing in FTIR and Raman spectra, have been identified.     

Experimental and mechanistic investigation of an iodomalonic acid-based Briggs-Rauscher oscillator and its perturbations by resorcinol

Classic Briggs-Rauscher oscillators use malonic acid (MA) as a substrate. The first organic product is iodomalonic acid. Iodomalonic acid (IMA) can serve as a substrate also; thus, the first product in that case is diiodomalonic acid (I(2)MA). Nonoscillating iodination kinetics can be followed by absorbance at 462 nm in acidic KIO(3) so long as IMA is in substantial excess over [I(2)]. At 25 °C, simulations lead to the two most important rate laws, and related rate constant estimates are reported. I(2)MA eventually decomposes by unknown processes, but I(2), O(2), H(2)O(2), and Mn(2+) speed up that decomposition, liberating most of the iodine back to the solution. Resorcinol is an effective inhibitor of oscillations both in MA oscillators and in IMA oscillators. Response of an IMA oscillator to varying amounts of resorcinol is shown herein and is similar to that for MA-based oscillators. The inhibitory effect of resorcinol is diminished by addition of IMA to a MA-based oscillator. The iodination reaction between IMA and resorcinol is too slow (0.043 M(-1) s(-1)) to account for the decreased inhibitory effectiveness of resorcinol. Rather, the decomposition of I(2)MA is responsible for the inhibition decrease.     

Determination of haloalkane dehalogenase activity by capillary zone electrophoresis

A new sensitive method has been developed for the determination of haloalkane dehalogenase activity. The enzymatic reactions were carried out directly in thermostatted autosampler vials and the formation of product - bromide or chloride ions - was monitored by sequential capillary zone electrophoresis runs. The determinations were performed in a 75 microm fused-silica capillary using 5 mM chromate, 0.5 mM tetradecyltrimethylammonium bromide (pH 8.4) as a background electrolyte, separation voltage 15 kV (negative polarity) and indirect detection at sample wavelength 315 nm, reference wavelength 375 nm for brominated and chlorinated substrates, respectively 0.1 M beta-alanine-HCl (pH 3.50) as a background electrolyte, separation voltage 18 kV (negative polarity) and direct detection at 200 nm for brominated substrates. The temperature of capillary was in both cases 25 degrees C. The method is rapid, can be automated, and requires only small amount of enzyme preparation and substrate.     

Regiocontrolled synthesis of enantiopure 3,3'-thiosubstituted biphenyls

Sulfenylation of 6,6'-dimethoxy-2,2'-dihydroxybiphenyl, used as a racemic mixture and single enantiomers, by phthalimidesulfenyl chloride afforded the corresponding 3,3'-N,N'-dithiophthalimide with complete regioselectivity. Simple manipulations of the latter compound allowed access to the corresponding bis-thiol or o-thioquinone as useful intermediates for the synthesis of new sulfur-containing open-chain and macrocyclic C(2) enantiopure ligands. The application of this methodology to the preparation of a biphenyl bearing two cysteine units as potential HIV-1 protease inhibitor is also described.     

Synthesis,coordination to Rh(I), and hydroformylation catalysis of new beta-aminophosphines bearing a dangling nitrogen group: an unusual inversion of a Rh-coordinated P center

Variants of the beta-aminophosphine L(1) [Ph(2)PCH(2)CH(Ph)NHPh] containing additional nitrogen donor functions have been prepared. These functions are branched off the C atom adjacent to the P atom, or the P atom itself. Ligand [Ph(2)PCH(o-C(6)H(4)NMe(2))CH(Ph)NHPh] has been obtained as a mixture of two diastereomers L(3A) and L(3B) by lithiation of L(2) [Ph(2)PCH(2)(o-C(6)H(4)NMe(2))] with n-BuLi followed by PhCH=NPh addition and hydrolysis. The diastereomers have been separated by fractional crystallization from ethanol. Ligand Et(2)NCH(2)P(Ph)CH(2)CH(Ph)NHPh has been obtained as a mixture of two diastereomers L(5A) and L(5B)(starting with P-Ph reductive cleavage of L(1) by lithium and subsequent hydrolysis to give PhP(H)CH(2)CH(Ph)NHPh (mixture of two diastereomers L(4A) and L(4B)). The latter reacts with diethylamine and formaldehyde to afford the L(5) diastereomeric mixture. Complexes RhCl(CO)(L) (L = L(3A), 1(A); L(3B), 1(B); L(5A/B), 2(A/B)) were obtained by reaction of [RhCl(CO)(2)](2) and the appropriate ligand or ligand mixture. Complexes 1(A), 1(B), and 2(A) have been isolated in pure form and characterized by classical techniques and by single-crystal X-ray diffraction. All structures exhibit a bidentate kappa-P,kappa-N(NHPh) mode similar to the complex containing L(1). While complexes 1(A) or 1(B) are stable in CDCl(3) solution, complex 2(A) slowly converts to its diastereomer 2(B). This unexpected epimerization appears to take place by inversion at the Rh-coordinated P center, an apparently unprecedented phenomenon. A mechanism based on a reversible P-C bond oxidative addition is proposed. The influence of the pendant nitrogen function of the diaminophosphines L(3A) and L(5A/B) on the rhodium catalytic activity in styrene hydroformylation has been examined and compared to that of the aminophosphines L(1) or L(2). The observed trends are related to the basicity of the dangling amine function and to its proximity to the metal center.