Ab initio study on the thermolysis of β-hydroxyolefins in gas phase

Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G^* levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions.     

Stability of nonautonomous differential equations in Hilbert spaces

We introduce a large class of nonautonomous linear differential equations v^′=A(t)v in Hilbert spaces, for which the asymptotic stability of the zero solution, with all Lyapunov exponents of the linear equation negative, persists in v^′=A(t)v+f(t,v) under sufficiently small perturbations f. This class of equations, which we call Lyapunov regular, is introduced here inspired in the classical regularity theory of Lyapunov developed for finite-dimensional spaces, that is nowadays apparently overlooked in the theory of differential equations. Our study is based on a detailed analysis of the Lyapunov exponents. Essentially, the equation v^′=A(t)v is Lyapunov regular if for every k the limit of Γ(t)^1/t as t→∞ exists, where Γ(t) is any k-volume defined by solutions v₁(t),…,v_k(t). We note that the class of Lyapunov regular linear equations is much larger than the class of uniformly asymptotically stable equations.     

Rheo-NMR study of a non-flow-aligning side-chain liquid crystal polymer in nematic solution

The flow behavior of a highly concentrated solution of a nematic side-chain liquid crystal polymer in a low molecular mass nematic solvent is investigated by deuterium nuclear magnetic resonance with simultaneous measurement of the shear viscosity in a cone-and-plate NMR viscometer. The director orientation under shear in the magnetic field is determined from the quadrupole splitting of the NMR spectra. The orientation as a function of shear rate is analyzed in terms of the Ericksen-Leslie-Parodi theory, yielding the Leslie coefficients ₂ and ₃ and thus the flow alignment parameter . From the combined analysis of orientation and viscosity as a function of shear rate a total of four independent viscosity parameters is obtained for the nematic solution. The value determined for the flow-alignment parameter, 0.2, and the analysis of the data based on Brochard's theory show that the polymer is of the non-flow-aligning type and has a slightly prolate shape.     

Organocatalytic,Asymmetric Eliminative [4+2] Cycloaddition of Allylidene Malononitriles with Enals: Rapid Entry to Cyclohexadiene‐Embedding Linear and Angular Polycycles

A direct aminocatalytic synthesis has been developed for the chemo‐, regio‐, diastereo‐, and enantioselective construction of densely substituted polycyclic carbaldehydes containing fused cyclohexadiene rings. The chemistry utilizes, for the first time, remotely enolizable π‐extended allylidenemalononitriles as electron‐rich 1,3‐diene precursors in a direct eliminative [4+2] cycloaddition with both aromatic and aliphatic α,β‐unsaturated aldehydes. The generality of the process is demonstrated by approaching 6,6‐, 5,6‐, 7,6‐, 6,6,6‐, and 6,5,6‐fused ring systems, as well as biorelevant steroid‐like 6,6,6,6,5‐ and 6,6,6,5,6‐rings. A stepwise reaction mechanism for the key [4+2] addition is proposed as a domino bis‐vinylogous Michael/Michael/retro‐Michael reaction cascade. The utility of the malononitrile moiety as traceless activating group of the dicyano nucleophilic substrates is demonstrated.     

A PEGylated Photocleavable Auxiliary Mediates the Sequential Enzymatic Glycosylation and Native Chemical Ligation of Peptides

Research aimed at understanding the specific role of glycosylation patterns in protein function would greatly benefit from additional approaches allowing direct access to homogeneous glycoproteins. Herein the development and application of an efficient approach for the synthesis of complex homogenously glycosylated peptides based on a multifunctional photocleavable auxiliary is described. The presence of a PEG polymer within the auxiliary enables sequential enzymatic glycosylation and straightforward isolation in excellent yields. The auxiliary‐modified peptides can be directly used in native chemical ligations with peptide thioesters easily obtained by direct hydrazinolysis of the respective glycosylated peptidyl resins and subsequent oxidation. The ligated glycopeptides can be smoothly deprotected by UV irradiation. We apply this approach to the preparation of variants of the epithelial tumor marker MUC1 carrying one or more Tn, T, or sialyl‐T antigens.     

Electronic Olfactory Sensor Based on A. mellifera Odorant‐Binding Protein 14 on a Reduced Graphene Oxide Field‐Effect Transistor

An olfactory biosensor based on a reduced graphene oxide (rGO) field‐effect transistor (FET), functionalized by the odorant‐binding protein 14 (OBP14) from the honey bee (Apis mellifera) has been designed for the in situ and real‐time monitoring of a broad spectrum of odorants in aqueous solutions known to be attractants for bees. The electrical measurements of the binding of all tested odorants are shown to follow the Langmuir model for ligand–receptor interactions. The results demonstrate that OBP14 is able to bind odorants even after immobilization on rGO and can discriminate between ligands binding within a range of dissociation constants from K_d=4 μM to K_d=3.3 mM . The strongest ligands, such as homovanillic acid, eugenol, and methyl vanillate all contain a hydroxy group which is apparently important for the strong interaction with the protein.