The gas-phase pyrolysis of several aliphatic 1,3-diols. The kinetic and mechanism of 2,4-dimethyl-2,4-pentanediol

Satisfactory kinetic determinations of several aliphatic 1,3-diols were difficult to obtain. Moreover the product distributions from each of these substrates suggest complex parallel mechanisms. However, the elimination kinetic of 2,4-dimethyl-2,4-pentanediol has been measured over the temperature range of 419.7–459.9°C and pressure range of 47–115 torr. The reaction carried out by employing a static system, in seasoned vessel, and in the presence of the free-radical inhibitor propene, proved to be homogeneous, unimolecular, and follows a first-order rate law. The products are acetone, isobutene, and H₂O. The rate coefficient is expressed by the following Arrhenius equation: log k₁(s⁻¹)=(12.53±0.58)−(217.3±8.0) kJ mol⁻¹ (2.303RT)⁻¹. The pyrolytic elimination of this substrate is believed to proceed through a concerted six-membered cyclic transition-state type of mechanism. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 851–854, 1997     

Highly Enantioselective One-Pot Synthesis of Chiral Tri- and Tetrasubstituted Ferrocenes from 1,1′-Ferrocenedicarbaldehyde

Exclusively planar chirality is exhibited by the ferrocenes obtained in a highly enantioselective synthesis in which a chiral aminoamide acts as a temporary protecting/directing group. This method was used to obtain an enantiomerically pure tetrasubstituted ferrocene, which was transformed into the first C₂-symmetric disubstituted ferrocenophane [Eq. (1)].     

修正多重尺度法在圆薄板大挠度弯曲问题中的应用及其渐近性研究(Ⅰ)

本文应用修正多重尺度法研究圆板在铰链和简单支承条件下的大挠度弯曲。作出其级数解,分析其边界层效应和证明其渐近性。     

Nitrogen-Based Linkers with a Mesitylene Core: Synthesis and Characterization

Mesitylene was used as a core in seven new tritopic nitrogen containing linkers. Three of the linkers, each containing three nitrile groups, were obtained through Suzuki, Sonogashira and Heck-type coupling reactions. Next, these were converted to tetrazol-5-yl moieties by the cycloaddition of sodium azide to the nitrile functionalities. The last linker, containing three 1,2,3-triazol-4-yl moieties, was synthesized by the Huisgen cycloaddition of phenyl azide to the corresponding alkyne. The latter was obtained via a Corey–Fuchs reaction sequence from the previously reported formyl derivative. As the proof of concept for their potential in MOF design, one of the nitriles was used to build an Ag-based network.     

Adiabatic Perturbation Theory. Semiclassical Limit of the Reflection Coefficient on a Potential Barrier

Using methods of Adiabatic Perturbation Theory, the asymptotic behaviour in the semiclassical limit of the reflection coefficient for one dimensional collisions in quantum mechanics is studied rigorously. In this limit we give a recursive method for an exact calculation to all orders. In contrast to other methods (which fail), our method still works when the energy is near or equal to the top of the potential. First we derive the coefficient for a specific potential. Then we give the coefficient to first three orders for an arbitrary potential depending only on the potential's behaviour around its maximum. We point out that each term needs to be analysed to “all orders”.     

Polycaprolactone-b-Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL₄₄-b-PEO₁₁₄ biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL₄₄-b-PEO₁₁₄ polymer.     

Effect of graphene flake size on functionalisation: quantifying reaction extent and imaging locus with single Pt atom tags

Here, the locus of functionalisation on graphene-related materials and the progress of the reaction is shown to depend strongly on the starting feedstock. Five characteristically different graphite sources were exfoliated and functionalized using a non-destructive chemical reduction method. These archetypical examples were compared via a model reaction, grafting dodecyl addends, evaluated with TGA-MS, XPS and Raman data. A general increase in grafting ratio (ranging from 1.1 wt% up to 25 wt%) and an improvement in grafting stoichiometry (C/R) were observed as flake radius decreased. Raman spectrum imaging of the functionalised natural flake graphite identified that grafting is directed towards flake edges. This behaviour was further corroborated, at atomistic resolution, by functionalising the graphene layers with bipyridine groups able to complex single platinum atoms. The distribution of these groups was then directly imaged using aberration-corrected HAADF-STEM. Platinum atoms were found to be homogeneously distributed across smaller graphenes; in contrast, a more heterogeneous distribution, with a predominance of edge grafting was observed for larger graphites. These observations show that grafting is directed towards flake edges, but not necessary at edge sites; the mechanism is attributed to the relative inaccessibility of the inner basal plane to reactive moieties, resulting in kinetically driven grafting nearer flake edges. This phenomenology may be relevant to a wide range of reactions on graphenes and other 2d materials.

The flake size and morphology of the starting material strongly effect the degree and location of grafting when using reductive functionalisation.