Membrane receptor probes: solid-phase synthesis of biotin-Asp-PEG-arvanil derivatives

[structure: see text] A modular, flexible solid-phase synthetic route for the preparation of biotinylated cross-linking probes of membrane receptors is described. The route utilizes an orthogonal protection strategy employing a Pd[0] cleavable allyl linker attached to the probe via an aspartate residue. The versatility of the method is illustrated through the synthesis of a number of arvanil-derived cannabinoid receptor ligands displaying either a photoaffinity or a chemical cross-linking group.     

Thermal behavior of some aromatic copolyethers containing a propylenic spacer

The main objective of this paper is to study the thermal stability of some aromatic copolyethers containing a propylenic spacer. Some of the investigated copolyethers displayed a liquid crystalline (LC) behavior, with the presence of the mesogenic groups in the main chain, inducing high values of the thermal transition temperatures. As a consequence, a thermal stability study was necessary to establish the maximum temperature value for the LC behavior characterization. A thermal degradation mechanism is proposed, taking into consideration the azobenzenic unit as the weakest link in the polymer chain and thus, the starting point of the thermal degradation process. The degradation mechanisms were correlated with the chemical structure and the polarity and conformation of the chains. Conformational analysis was performed using molecular simulations. Freeman-Caroll and Coats-Redfern methods were used to calculate some kinetic characteristics.     

The methoxycarbonylation of aryl chlorides catalysed by palladium complexes of bis(di-tert-butylphosphinomethyl)benzene

A catalyst system based on palladium-1,2-bis-(di-tert-butylphosphinomethyl)benzene (BDTBPMB) shows good activity for the methoxycarbonylation of strongly activated aryl chlorides, like 4-chloromethylbenzoate or 4-chlorocyanobenzene. Surprisingly, the use of less activated aryl chlorides, like 4-chloroacetophenone, leads to the formation of dimethyl terephthalate amongst other products arising from organic reactions of methoxide ion and/or CO. Less nucleophilic alcohols such as 2,2,2-trifluoroethanol promote the formation of carbonylation products even from 4-chloroacetophenone and chlorobenzene. Labelling studies involving CD3OH, CD3OD or 13CO give information on the origin of many of the products.     

Constructive techniques for approximating collocation linear systems

A high order discretization by spectral collocation methods of the elliptic problem $$\begin{gathered} \left\{ \begin{gathered} A_{A,b} u \equiv - \nabla [A(x)\nabla u(x)] + b(x)u(x) = c(x){\text{ on}}\;\Omega \; = ( - 1,1)^2 \hfill \\ u\left| {\partial \Omega \equiv 0,} \right. \hfill \\ \end{gathered} \right. \hfill \\ \hfill \\ \end{gathered} $$ is considered where A(x)=a(x)I ₂, x=(x ^[1],x ^[2]) and I ₂ denotes the 2×2 identity matrix, giving rise to a sequence of dense linear systems that are optimally preconditioned by using the sparse Finite Difference (FD) matrix-sequence {A _n } _n over the nonuniform grid sequence defined via the collocation points [11]. Here we propose a preconditioning strategy for {A _n } _n based on the “approximate factorization” idea. More specifically, the preconditioning sequence {P _n } _n is constructed by using two basic structures: a FD discretization of (1) with A(x)=I ₂ over the collocation points, which is interpreted as a FD discretization over an equidistant grid of a suitable separable problem, and a diagonal matrix which adds the informative content expressed by the weight function a(x). The main result is the proof that the sequence {P _n ^?1 A _n } _n is spectrally clustered at unity so that the solution of the nonseparable problem (1) is reduced to the solution of a separable one, this being computationally more attractive [2,3]. Several numerical experiments confirm the goodness of the discussed proposal.     

Synthesis and electrochemical characterization of dipyrroles separated by diphenyleneoxide and diphenylenesulfide spacers via the Trofimov reaction

4,4′-Bis[2-(1-vinylpyrrolyl)]diphenyloxide, 4,4′-bis(2-pyrrolyl)diphenylsulfide, 4-(2-pyrrolyl)-4′-[2-(1-vinylpyrrolyl)]diphenylsulfide and 4,4′-bis[2-(1-vinylpyrrolyl)]diphenylsulfide have been synthesized in a one-pot procedure from oximes of corresponding diacetylphenylenoxide and -sulfide through their reaction with acetylene in the MOH-DMSO systems (M=Li, K) at 80-130 °C under pressure of 10-15 atm, thus illustrating applicability and general character of the reaction of synthesis of diverse dipyrrole-phenylene assemblies and their N-vinyl derivatives. Two of the pipyrroles are promising for creating new conducting polymers with sulfur and oxygen atoms in the conjugation chain and for the study of the influence of the diphenyleneheteroatom moiety on conductivity of final polymer products. For the dipyrroles with the diphenyleneheteroatom moieties and 1,4-phenylene spacer the luminescence characteristics were determined.     

Asymptotic and Lyapunov stability of constrained and Poisson equilibria

This paper includes results centered around three topics, all of them related with the nonlinear stability of equilibria in constrained dynamical systems. First, we prove an energy-Casimir type sufficient condition for stability that uses functions that are not necessarily conserved by the flow and that takes into account the asymptotically stable behavior that may occur in certain constrained systems, such as Poisson and Leibniz dynamical systems. Second, this method is specifically adapted to Poisson systems obtained via a reduction procedure and we show in examples that the kind of stability that we propose is appropriate when dealing with the stability of the equilibria of some constrained mechanical systems. Finally, we discuss two situations in which the use of continuous Casimir functions in stability studies is equivalent to the topological stability methods introduced by Patrick et al. (Arch. Rational Mech. Anal., 2004, preprint arXiv:math.DS/0201239v1, to appear).