Capture and dissociation in the complex-forming CH + H2 → CH2 + H, CH + H2 reactions

The rate coefficients for the capture process CH + H(2)→ CH(3) and the reactions CH + H(2)→ CH(2) + H (abstraction), CH + H(2) (exchange) have been calculated in the 200-800 K temperature range, using the quasiclassical trajectory (QCT) method and the most recent global potential energy surface. The reactions, which are of interest in combustion and in astrochemistry, proceed via the formation of long-lived CH(3) collision complexes, and the three H atoms become equivalent. QCT rate coefficients for capture are in quite good agreement with experiments. However, an important zero point energy (ZPE) leakage problem occurs in the QCT calculations for the abstraction, exchange and inelastic exit channels. To account for this issue, a pragmatic but accurate approach has been applied, leading to a good agreement with experimental abstraction rate coefficients. Exchange rate coefficients have also been calculated using this approach. Finally, calculations employing QCT capture/phase space theory (PST) models have been carried out, leading to similar values for the abstraction rate coefficients as the QCT and previous quantum mechanical capture/PST methods. This suggests that QCT capture/PST models are a good alternative to the QCT method for this and similar systems.     

A Solid‐Supported Organocatalyst for Highly Stereoselective,Batch, and Continuous‐Flow Mannich Reactions

The fast and highly stereoselective Mannich reaction of aldehydes and ketones with the N‐(p‐methoxyphenyl) ethyl glyoxylate imine catalyzed by polystyrene resins functionalized with (2S,4R)‐hydroxyproline is reported. The effect of the nature of the linker connecting proline with the polymeric backbone has been studied, and a 1,2,3‐triazole linker constructed from azidomethyl polystyrene and O‐propargyl hydroxyproline turns out to be optimal for catalytic activity and enantioselectivity. With aldehyde donors, fast reactions leading to complete conversion in 1–3 h are recorded in DMF. With ketone donors, the reactions tend to be slower, but can be efficiently accelerated (six‐membered ring cycloalkanones) by low‐power microwave irradiation. This approach, which greatly facilitates product isolation since the catalyst is removed by simple filtration, has allowed the implementation of the reactions of aldehyde substrates in a continuous‐flow, single‐pass system. In this manner, the continuous synthesis of the enantiomerically and diastereomerically pure adducts (syn/anti>97:3; ee>99 %) has been achieved at room temperature with residence times of 6.0 min. This methodology has allowed for the preparation of up to 7.8 mmol of the desired Mannich adduct through the use of 0.46 mmol of catalytic resin (5.9 mol %), in a greatly simplified experimental protocol that avoids purification steps.     

Improving adhesion of acrylic waterborne PSAs to low surface energy materials: Introduction of stearyl acrylate

The effect of incorporating stearyl acrylate (SA) in the polymer backbone of a pressure sensitive adhesive on its adhesion properties on low energy surfaces was investigated. The presence of SA did not affect the polymer microstructure (sol molecular weight, gel, and network density) but affected the compatibility with the low energy substrate and the elasticity of the adhesive. The combination of these effects resulted in an optimum SA content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A characterization of powerful p-groups

In [10] Benjamin Klopsch and Ilir Snopce recently posted the conjecture that for p ≥ 3 and G a torsion-free pro-p group, d(G) = dim(G) is a sufficient and necessary condition for the pro-p group G to be uniform. They pointed out that this follows from the more general question of whether for a finite p-group d(G) = log _p (|Ω₁(G)|) is a sufficient and necessary condition for the group G to be powerful. In this short note we will give a positive answer to this question for p ≥ 5.     

Toward an artificial aldolase

A new functional polymer where proline is bonded to polystyrene through a 1,2,3-triazole linker depicts characteristics targeted for an artificial aldolase. In spite of the hydrophobicity of the polymer backbone, the resin swells in water with building of an aqueous microenvironment. This property, arising from the formation of a hydrogen-bond network connecting the proline and 1,2,3-triazole fragments, is translated into a very high catalytic activity and enantioselectivity toward direct aldol reactions in water.     

Modeling the global potential energy surface of the N + N2 reaction from ab initio data

A new global potential energy surface for the N + N2 exchange reaction has been built from ab initio data. To overcome the difficulty of carrying out ab initio calculations for a large set of geometries the alternative strategy of fitting the minimum energy paths of the surface and their angular dependence using a modified LAGROBO functional form has been adopted. In this way we have been able to reproduce all the main features of the potential using a fairly small set of ab initio values.     

Synthesis and Characterization of Double Crystalline Cyclic Diblock Copolymers of Poly(ε‐caprolactone) and Poly(l(d)‐lactide) (c(PCL‐b‐ PL(D)LA))

The synthesis of symmetric cyclo poly(ε‐caprolactone)–block–poly(l (d )‐lactide) (c(PCL–b–PL(D)LA)) by combining ring‐opening polymerization of ε‐caprolactone and lactides and subsequent click chemistry reaction of the linear precursors containing antagonist functionalities is presented. The two blocks can sequentially crystallize and self‐assemble into double crystalline spherulitic superstructures. The cyclic chain topology significantly affects both the nucleation and the crystallization of each constituent, as gathered from a comparison of the behavior of linear precursors and cyclic block copolymers. The stereochemistry of the PLA block does not have a significant effect on the nonisothermal crystallization of both linear and cyclo PCL‐b‐PDLA and PCL‐b‐PLLA copolymers.

     

Capillary hydrodynamic fractionation of hydrophobic colloids：Errors in the estimated particle size distribution

Capillary hydrodynamic fractionation（CHDF） with turbidity detection at a single wavelength is an analytical technique that is often used for sizing the sub-micrometric particles of hydrophobic colloids.This article investigates three sources of errors that affect the particle size distribution（PSD） estimated by CHDF：diameter calibration errors,uncertainties in the particle refractive index（PRI）,and instrumental broadening（IB）.The study is based on simulated and experimental examples that involve unimodal and bimodal PSDs.Small errors in the diameter calibration curve can produce important deviations in the number average diameter due to systematic shifts suffered by the PSD modes.Moderate uncertainties in the PRI are unimportant in the analysis of unimodal PSDs,but in the specific case of bimodal PSDs,errors in the PRI can strongly affect the estimated number concentration of each mode.The typical IB correction（based on the IB function estimated from narrow standards） produces slightly erroneous average diameters but can lead to PSDs with underestimated widths and distorted shapes.In practice,the three investigated sources of errors can be present simultaneously,and uncertainties in the average diameters,the shape and width of the PSD,and the number concentration of the PSD modes are unavoidable.