Toward block copolymers from nonliving isospecific single‐site catalytic systems

Ethene/1‐olefin blocky copolymers were obtained through nonliving insertion copolymerizations promoted by an isospecific single site catalyst. Propene or 4‐methyl‐1‐pentene were copolymerized with ethene with metallocenes endowed with different stereospecificity in propene polymerization: (i) aspecific “constrained geometry” half‐sandwich complex, {η¹:η⁵‐([tert‐butyl‐amido)dimethylsilyl](2,3,4,5‐tetramethyl‐1‐cyclopentadienyl)}titanium dichloride [Me₂Si(Me₄Cp)(N‐^tBu)TiCl₂] ( CG ), (ii) moderately isospecific rac‐ethylenebis(indenyl)zirconium dichloride [rac‐(EBI)ZrCl₂] ( EBI ), (iii) slightly more isospecific hydrogenated homologue, rac‐ethylenebis(tetrahydroindenyl)zirconium dichloride [rac‐(EBTHI)ZrCl₂] ( EBTHI ), (iv) highly iso‐specific rac‐[methylenebis(3‐tert‐butyl‐1‐indenyl)]zirconium dichloride [rac‐H₂C‐(3‐^tBuInd)₂ZrCl₂] ( TBI ), (v) most isospecific rac‐[isopropylidene‐bis(3‐tert‐butyl‐cyclopentadienyl)]zirconium dichloride [rac‐Me₂C‐(3‐^tBuCp)₂ZrCl₂] ( TBC ). Copolymerizations were described by a 2^nd order Markovian copolymerization model and data are proposed to correlate the formation of 1‐olefin sequences with catalytic site isospecificity, made by the cooperation of organometallic complex and growing chain. Blocky copolymers were prepared over wide ranges of compositions: with any of the isospecific metallocenes when 4‐methyl‐1‐pentene was the 1‐olefin and only with the highly isospecific ones ( TBI , TBC ) when propene was the comonomer. A penultimate unit effect was observed with TBI as the metallocene, whereas a 1^st order Markov model described the ethene/propene copolymerization from TBC . A moderately isospecific metallocene, such as EBI , is shown to be able to prepare blocky ethene copolymers with 4‐methyl‐1‐pentene. These results pave the way for the synthesis of new ethene based materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2063–2075, 2010     

Monitoring oil displacement processes with k‐t accelerated spin echo SPI

Magnetic resonance imaging (MRI) is a robust tool to monitor oil displacement processes in porous media. Conventional MRI measurement times can be lengthy, which hinders monitoring time‐dependent displacements. Knowledge of the oil and water microscopic distribution is important because their pore scale behavior reflects the oil trapping mechanisms. The oil and water pore scale distribution is reflected in the magnetic resonance T₂ signal lifetime distribution. In this work, a pure phase‐encoding MRI technique, spin echo SPI (SE‐SPI), was employed to monitor oil displacement during water flooding and polymer flooding. A k‐t acceleration method, with low‐rank matrix completion, was employed to improve the temporal resolution of the SE‐SPI MRI measurements. Comparison to conventional SE‐SPI T₂ mapping measurements revealed that the k‐t accelerated measurement was more sensitive and provided higher‐quality results. It was demonstrated that the k‐t acceleration decreased the average measurement time from 66.7 to 20.3 min in this work. A perfluorinated oil, containing no ¹H, and H₂O brine were employed to distinguish oil and water phases in model flooding experiments. High‐quality 1D water saturation profiles were acquired from the k‐t accelerated SE‐SPI measurements. Spatially and temporally resolved T₂ distributions were extracted from the profile data. The shift in the ¹H T₂ distribution of water in the pore space to longer lifetimes during water flooding and polymer flooding is consistent with increased water content in the pore space. Copyright © 2015 John Wiley & Sons, Ltd.     

Insights into the Halogen Oxidative Addition Reaction to Dinuclear Gold(I) Di(NHC) Complexes

Gold(I) dicarbene complexes [Au₂(MeIm‐Y‐ImMe)₂](PF₆)₂ (Y=CH₂ ( 1 ), (CH₂)₂ ( 2 ), (CH₂)₄ ( 4 ), MeIm=1‐methylimidazol‐2‐ylidene) react with iodine to give the mixed‐valence complex [Au(MeIm‐CH₂‐ImMe)₂AuI₂](PF₆)₂ ( 1 a^I ) and the gold(III) complexes [Au₂I₄(MeIm‐Y‐ImMe)₂](PF₆)₂ ( 2 c^I and 4 c^I ). Reaction of complexes 1 and 2 with an excess of ICl allows the isolation of the tetrachloro gold(III) complexes [Au₂Cl₄(MeIm‐CH₂‐ImMe)₂](PF₆)₂ ( 1 c^Cl ) and [Au₂Cl₄(MeIm‐(CH₂)₂‐ImMe)₂](Cl)₂ ( 2 c^Cl‐Cl ) (as main product); remarkably in the case of complex 2 , the X‐ray molecular structure of the crystals also shows the presence of I‐Au‐Cl mixed‐sphere coordination. The same type of coordination has been observed in the main product of the reaction of complexes 3 or 4 with ICl. The study of the reactivity towards the oxidative addition of halogens to a large series of dinuclear bis(dicarbene) gold(I) complexes has been extended and reviewed. The complexes react with Cl₂, Br₂ and I₂ to give the successive formation of the mixed‐valence gold(I)/gold(III) n a^X and gold(III) n c^X (excluding compound 1 c^I ) complexes. However, complex 3 affords with Cl₂ and Br₂ the gold(II) complex 3 b^X [Au₂X₂(MeIm‐(CH₂)₃‐ImMe)₂](PF₆)₂ (X=Cl, Br), which is the predominant species over compound 3 c^X even in the presence of free halogen. The observed different relative stabilities of the oxidised complexes of compounds 1 and 3 have also been confirmed by DFT calculations.     

Direct Resolution of Aromatic Alcohols by Planar Chromatography on Tribenzoylcellulose as Chiral Stationary Phase

JPC – Journal of Planar Chromatography – Modern TLC -     

Efficient hydroxycarbonylation of aryl iodides using recoverable and reusable carbon aerogels doped with palladium nanoparticles as catalyst

Electron-rich and electron-poor aryl iodides are converted, in high to excellent yields, into the corresponding carboxylic acids through a hydroxycarboxylation reaction catalyzed by a recoverable and reusable phosphine free palladium-carbon aerogel catalyst using lithium formate and acetic anhydride as an internal condensed source of carbon monoxide. The catalyst system can be reused several times without any appreciable loss of activity.     

Fractal aspects of calcium binding protein structures

The structures of EF-hand calcium binding proteins may be classified into two distinct groups: extended and compact structures. In this paper we studied 20 different structures of calcium binding proteins using the fractal analysis. Nine structures show extended shapes, one is semi-compact and the other 10 have compact shapes. Our study reveals different fractal characteristics for protein backbones belonging to different structural classes and these observations may be correlated to the physicochemical forces governing the protein folding.     

Theoretical prediction of linear free energy relationships using proton nucleomers

Values of σ and σ⁺, for use in linear free energy relationships, are determined for para hydrogen atoms having nuclear charges other than 1 (nucleomers). Hammett ρ values for a variety of free energies of activation, reaction, and other extrathermodynamic properties (e.g., vibrational frequencies) are computed therefrom and compared to those computed using typical para functional groups. The nucleomer correlations show excellent qualitative agreement with standard correlations but the quantitative agreement is less good, typically underestimating the standard ρ‐value by 10–60%. Copyright © 2007 John Wiley & Sons, Ltd.