Crosslinking of a fibrous sample to a macro-oriented mesomorphic network

Preliminary results on the synthesis and characterization of anisotropic networks, oriented on a macroscopic scale, are reported. Fiber samples of segmented thermotropic liquid-crystalline polymers bearing the oxypentenyl lateral substituent have been crosslinked via thermally activated radical reaction. This was made possible by immersion of fiber samples in dichloromethane containing t-butylperoxybenzoate as activating agent, thus allowing its diffusion in the samples. Subsequent annealing at 145°C brings us to an anisotropic network with no loss of the original orientation. A mesophase is stabilized and no structural modification is observed by heating samples from room temperature up to 400°C, where thermal decomposition takes place. Crosslinked fibers exhibit good tensile properties, at both room temperature and at 150°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 433–438, 1998     

Covalent Reversible Inhibitors of Cysteine Proteases Containing the Nitrile Warhead: Recent Advancement in the Field of Viral and Parasitic Diseases

In the field of drug discovery, the nitrile group is well represented among drugs and biologically active compounds. It can form both non-covalent and covalent interactions with diverse biological targets, and it is amenable as an electrophilic warhead for covalent inhibition. The main advantage of the nitrile group as a warhead is mainly due to its milder electrophilic character relative to other more reactive groups (e.g., -CHO), reducing the possibility of unwanted reactions that would hinder the development of safe drugs, coupled to the ease of installation through different synthetic approaches. The covalent inhibition is a well-assessed design approach for serine, threonine, and cysteine protease inhibitors. The mechanism of hydrolysis of these enzymes involves the formation of a covalent acyl intermediate, and this mechanism can be exploited by introducing electrophilic warheads in order to mimic this covalent intermediate. Due to the relevant role played by the cysteine protease in the survival and replication of infective agents, spanning from viruses to protozoan parasites, we will review the most relevant and recent examples of protease inhibitors presenting a nitrile group that have been introduced to form or to facilitate the formation of a covalent bond with the catalytic cysteine active site residue.     

Copolymerization of Propene and Buta‐1,3‐diene in the Presence of Highly Hindered C2‐Symmetric Zirconocene‐Based Catalyst

Summary: Copolymerizations of propene and buta‐1,3‐diene performed in the presence of rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ and methylaluminoxane (MAO) have been investigated. Buta‐1,3‐diene gives prevailingly primary coordination to the metal, producing overall 1,2 units. Cyclopropane and cyclopentane rings, although in low amounts, are also obtained. The presence of butadiene would be responsible for some regioirregular 2,1‐inserted propene units, which at high temperatures give rearrangement to 3,1 units.

     

Synthesis and Pharmacological Characterization of New H2‐Antagonists Containing NO‐Donor Moieties,Endowed with Mixed Antisecretory and Gastroprotective Activities

Synthesis, structural characterization, and pharmacological profile of a series of H₂‐antagonists able to release nitric oxide (NO) are reported. These compounds were obtained by using appropriate spacers to join H₂‐antagonistic pharmacophoric groups related to lamtidine and tiotidine to different NO‐donor moieties such as esters of HNO₃, nitrosothio groups, and benzenesulfonyl‐substituted furoxans. All of the compounds were tested for their NO‐donor properties. Furthermore, the hybrid structures synthesized, together with some selected reference compounds, were tested for their H₂‐antagonistic properties, both in vitro and in vivo, and for their gastroprotective effects. Only the hybrid compounds were able both to antagonize histamine effects on guinea‐pig papillary muscle and to display in vivo antisecretory and gastroprotective action. The best results were obtained with the lamtidine/furoxan hybrid structure.     

Vortices in the Maxwell‐Chern‐Simons theory

Our aim is to prove rigorously that the Chern‐Simons model of Hong, Kim, and Pac [13] and Jackiw and Weinberg [14] (the CS model) and the Abelian Higgs model of Ginzburg and Landau (the AH model, see [15]) are unified by the Maxwell‐Chern‐Simons theory introduced by Lee, Lee, and Min in [16] (MCS model). In [16] the authors give a formal argument that shows how to recover both the CS and AH models out of their theory by taking special limits for the values of the physical parameters involved. To make this argument rigorous, we consider the existence and multiplicity of periodic vortex solutions for the MCS model and analyze their asymptotic behavior as the physical parameters approach these limiting values. We show that, indeed, the given vortices approach (in a strong sense) vortices for the CS and AH models, respectively. For this purpose, we are led to analyze a system of two elliptic PDEs with exponential nonlinearities on a flat torus. © 2000 John Wiley & Sons, Inc.