Theoretical Approach Towards the Understanding of Asymmetric Additions of Dialkylzinc to Enals and Iminals Catalysed by [2.2]Paracyclophane‐Based N,O‐Ligands

The 1,2‐ and 1,4‐asymmetric additions of dialkylzinc reagents (ZnMe₂ and ZnEt₂) to cinnamaldehyde and N‐formylbenzylimine catalysed by [2.2]paracyclophane‐based N,O‐ligands were studied with quantum chemical methods. High level LPNO‐CEPA/1 (local pair natural orbital coupled electron pair approximation 1) calculations were performed to obtain reliable reaction barriers and binding energies. The calculations supported the experimentally observed selectivities. In the reaction, the alkyl transfer takes place on a binuclear zinc complex. Regioselectivity can be traced back to changes in π‐conjugation. Because the less conjugated N‐formylbenzylimine is more flexible, it is better suited for 1,4‐additions. Moreover, bulky ligands were shown to be important for stereoselectivity. The reason is that the tricyclic motif present in the transition states is sterically less hindered in the anti conformation. Based on the LPNO‐CEPA/1 data, a set of popular theoretical methods are validated. Although it was possible to set up a procedure to obtain the stereoselectivities with computationally less demanding methods, this was not possible for the regioselectivity of the reactions.     

One‐pot inimer promoted ROCP synthesis of branched copolyesters using α‐hydroxy‐γ‐butyrolactone as the branching reagent

An array of branched poly(?‐caprolactone)s was successfully synthesized using an one‐pot inimer promoted ring‐opening multibranching copolymerization (ROCP) reaction. The biorenewable, commercially available yet unexploited comonomer and initiator 2‐hydroxy‐γ‐butyrolactone was chosen as the inimer to extend the use of 5‐membered lactones to branched structures and simultaneously avoiding the typical tedious work involved in the inimer preparation. Reactions were carried out both in bulk and in solution using stannous octoate (Sn(Oct)₂) as the catalyst. Polymerizations with inimer equivalents varying from 0.01 to 0.2 were conducted which resulted in polymers with a degree of branching ranging from 0.049 to 0.124. Detailed ROCP kinetics of different inimer systems were compared to illustrate the branch formation mechanism. The resulting polymer structures were confirmed by ¹H, ¹³C, and ₁H‐₁₃C HSQC NMR and SEC (RI detector and triple detectors). The thermal properties of polymers with different degree of branching were investigated by DSC, confirming the branch formation. Through this work, we have extended the current use of the non‐homopolymerizable γ‐butyrolactone to the branched polymers and thoroughly examined its behaviors in ROCP. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1908–1918     

Different Synthesis Protocols for Co3O4–CeO2 Catalysts—Part 1: Influence on the Morphology on the Nanoscale

Co₃O₄‐modified CeO₂ (Co/Ce 1:4) was prepared by a combination of sol–gel processing and solvothermal treatment. The distribution of Co was controlled by means of the synthesis protocol to yield three different morphologies, namely, Co₃O₄ nanoparticles located on the surface of CeO₂ particles, coexistent Co₃O₄ and CeO₂ nanoparticles, or Co oxide structures homogeneously distributed within CeO₂. The effect of the different morphologies on the properties of Co₃O₄–CeO₂ was investigated with regard to the crystallite phase(s), particle size, surface area, and catalytic activity for CO oxidation. The material with Co₃O₄ nanoparticles finely dispersed on the surface of CeO₂ particles had the highest catalytic activity.     

Reversible Hydrogenation of Graphene on Ni(111)—Synthesis of “Graphone”

Understanding the adsorption and reaction between hydrogen and graphene is of fundamental importance for developing graphene‐based concepts for hydrogen storage and for the chemical functionalization of graphene by hydrogenation. Recently, theoretical studies of single‐sided hydrogenated graphene, so called graphone, predicted it to be a promising semiconductor for applications in graphene‐based electronics. Here, we report on the synthesis of graphone bound to a Ni(111) surface. We investigate the formation process by X‐ray photoelectron spectroscopy (XPS), temperature‐programmed desorption (TPD), and density‐functional theory calculations, showing that the hydrogenation of graphene with atomic hydrogen indeed leads to graphone, that is, a hydrogen coverage of 1 ML (4.2 wt %). The dehydrogenation of graphone reveals complex desorption processes that are attributed to coverage‐dependent changes in the activation energies for the associative desorption of hydrogen as molecular H₂.     

Proton Transverse Relaxation as a Sensitive Probe for Structure Determination in Solid Proteins

Solid‐state nuclear magnetic resonance (NMR) spectroscopy has been successfully applied to elucidate the atomic‐resolution structures of insoluble proteins. The major bottleneck is the difficulty to obtain valuable long‐distance structural information. Here, we propose the use of distance restraints as long as 32 Å, obtained from the quantification of transverse proton relaxation induced by a methanethiosulfonate spin label (MTSL). Combined with dipolar proton–proton distance restraints, this method allows us to obtain protein structures with excellent precision from single spin‐labeled 1 mg protein samples using fast magic angle spinning.     

Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor‐π‐acceptor system

Two symmetrically substituted phenylenevinylene D‐A‐D′‐A‐D type siblings, (2Z,2′Z)‐2,2′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(3‐(4‐(dimethylamino)phenyl)acrylonitrile) (↑‐dscn) and (2Z,2′Z)‐3,3′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(2‐(4‐(dimethylamino)phenyl)acrylonitrile) (↓‐dscn), are prepared. We investigate the effect of different but symmetrical location of these cyano groups in vinylene bridges on the 1‐photon and 2‐photon absorption behaviors. We report that the closeness of CN group on the vinyl group to the central phenyl ring in ↑‐dscn induces an intramolecular geometric distortion between the central phenyl ring and vinylene group, preventing the effective π‐conjugation length in ground and excited states. Thus, the transition energy that is observed in 1‐photon absorption and fluorescence is larger in ↑‐dscn than in ↓‐dscn. This leads to a different intramolecular charge distribution, as a result of which the linear and nonlinear optical properties strongly depend on the position of acceptors. These results are theoretically unraveled in terms of charge transfer pathways, charge distribution, and charge distribution differences on transition.     

Hydroxylated oxanes as xyloside analogs for determination of the minimal binding requirements of β4GalT7

β-1,4-Galactosyltransferase 7 (β4GalT7) is a key enzyme in the biosynthesis of glycosaminoglycan (GAG) chains. Natural and synthetic xylosides can be used to both inhibit and prime GAG synthesis by acting as inhibitors or substrates for β4GalT7. In this report, we exploit hydroxylated oxanes as deoxygenated xyloside analogs to clarify the minimum protein-ligand interactions required for galactosylation and/or inhibition. Enantiomerically pure substances were synthesized using a chiral pool approach whereas the corresponding racemates were obtained from simple starting materials. The results of a β4GalT7 assay show that a single hydroxyl group on an oxane ring is insufficient to induce galactosylation or inhibition, which implies that at least two substituents, one of which being 3-OH, needs to be present.