Mesomorphic-like character of long-chain amine salts formed by template neutralization on polyacids

Several examples of monomeric and polymerized surfactants exhibiting liquid-crystalline behaviour have recently been reported. In the present investigation a novel process for the formation of liquid crystals is introduced, according to which certain functionalized polymers induce mesomorphism when they react with appropriate amines. For instance, neutralization of polyacrylic or polymaleic acid with long-chain amines forms alkylammonium salt surfactants which exhibit mesomorphic-like character. In this type of experiment, however, the known lamellar structure of alkylammonium salts was modified by this so-called template neutralization. The carboxylate groups, due to their location on the polymeric chain, appear to exert a topochemical effect on alkylammonium moieties which in turn affect the mesomorphic behaviour compared with that of common surfactants. The mesomorphic behaviour of these materials was established by optical microscopy and differential scanning calorimetry.     

Nitrene insertion reactions. 1. Dimethyl N-carbethoxyazepines and their cycloaddition reaction products

Dimethyl-N-carbethoxyazepines, isolated from the reaction between ethyl azidoformate and o-, m- and p-xylenes, react with tetracyanoethylene to give [4 + 2] Diels-Alder adducts. Nitroso-benzene is inert toward 2-methylazepines, but reacts with 3,6-dimethyl-N-carbethoxyazepine to give a [6 + 2] cycloadduct. The effect of two methyl substituents on the course of the cycloaddition reactions is discussed.     

Ge quantum dot molecules and crystals: Preparation and properties

Templated self-organization has been used to prepare two-dimensional arrays as well as three-dimensional quantum dot crystals (QDC) containing Ge dots in a Si host crystal. Si(1 0 0) substrates have been patterned with two-dimensional hole gratings using extreme ultra-violet interference lithography (EUV-IL) and reactive ion etching. The EUV-IL was realized by multiple beam diffraction using Cr gratings on SiN_x membranes fabricated by e-beam lithography. Si/Ge overgrowth was performed by molecular beam epitaxy. The impact of the microscopic shape and size of the prepattern using the mask design and the EUV-IL exposure dose as parameters on the Ge dot nucleation has been studied with atomic force microscopy, transmission electron microscopy and photoluminescence measurements. Adjusting the growth parameters in multiple layer deposition the initial two-dimensional configuration was transferred into three-dimensional QDC.     

A boundedness result for toric log Del Pezzo surfaces

In this paper we give an upper bound for the Picard number of the rational surfaces which resolve minimally the singularities of toric log Del Pezzo surfaces of given index ℓ. This upper bound turns out to be a quadratic polynomial in the variable ℓ. Received: 18 June 2008     

Simultaneous determination of phenolic compounds and triterpenic acids in oregano growing wild in Greece by 31P NMR spectroscopy

³¹P nuclear magnetic resonance (NMR) spectroscopy was used to detect and quantify simultaneously a large number of phenolic compounds and the two triterpenic acids, ursolic acid and oleanolic acid, extracted from two oregano species Origanum onites and Origanum vulgare ssp. Hirtum using two different organic solvents ethanol and ethyl acetate. This analytical method is based on the derivatization of the hydroxyl and carboxyl groups of these compounds with the phosphorous reagent 2‐chloro‐4,4,5,5‐tetramethyl‐1,3,2‐dioxa phospholane and the identification of the phosphitylated compounds on the basis of the ³¹P chemical shifts. Unambiguous assignment of the ³¹P NMR chemical shifts of the dihydroxy‐ and polyhydroxy‐phenols in oregano species as well as those of the triterpenic acids was achieved upon comparison with the chemical shifts of model compounds assigned by using two‐dimensional NMR techniques. Furthermore, the integration of the appropriate signals of the hydroxyl derivatives in the corresponding ³¹P NMR spectra and the use of the phosphitylated cyclohexanol as an internal standard allowed the quantification of these compounds. The validity of this technique for quantitative measurements was thoroughly examined. Copyright © 2012 John Wiley & Sons, Ltd.     

Polymerization of oriented monomers. IX. Further studies on the polymerization and vesicular properties of allyl and diallyl based monomeric and polymerized quaternary ammonium salts

The polymerization of the previously reported allyl and diallyl quaternary ammonium salts, which from vesicles in water, to their polymerized analogs was further investigated. The structure of the polymer derived from the diallyl derivative, for which some controversy existed, was elucidated by ¹³C-NMR spectroscopy. Mixed vesicles, based on the monoallyl monomer and incorporating certain vesicle forming quaternary ammonium salts, cholesterol, or cholesteryl acrylate were also formed. These mixed vesicles were characterized primarily as far as their stability is concerned. It was found that the incorporation of the additives does not enhance the stability of the mixed vesicles compared to that exhibited by monoallyl simple vesicles. In addition, polymerization of mixed monoallyl-cholesteryl acrylate vesicles results in the destruction of their structure. On the contrary, simple polymerized vesicles, resulting from the diallyl monomer, showed excellent long-term stability. Specifically, samples prepared two years ago are still dispersed and, very possibly, they will remain so for a longer period since they are not showing signs of precipitation.     

Mesomorphic-like character of long-chain amine salts formed by template neutralization on polyacids

Several examples of monomeric and polymerized surfactants exhibiting liquid-crystalline behaviour have recently been reported. In the present investigation a novel process for the formation of liquid crystals is introduced, according to which certain functionalized polymers induce mesomorphism when they react with appropriate amines. For instance, neutralization of polyacrylic or polymaleic acid with long-chain amines forms alkylammonium salt surfactants which exhibit mesomorphic-like character. In this type of experiment, however, the known lamellar structure of alkylammonium salts was modified by this so-called template neutralization. The carboxylate groups, due to their location on the polymeric chain, appear to exert a topochemical effect on alkylammonium moieties which in turn affect the mesomorphic behaviour compared with that of common surfactants. The mesomorphic behaviour of these materials was established by optical microscopy and differential scanning calorimetry.